The ability of the electric system to supply the aggregate electrical demand and energy requirements of the end-use customers at all times, taking into account scheduled and reasonably expected unscheduled outages of system elements.
Of, relating to, or being a reversible thermodynamic process that occurs without gain or loss of heat and without a change in entropy.
Adverse reliability impact
The impact of an event that results in frequency-related instability; unplanned tripping of load or generation; or uncontrolled separation or cascading outages that affects a widespread area of the Interconnection.
Alberta Electric System OperatorAcronym(s): AESO
Agency responsible for the safe, reliable and economic planning and operation of the Alberta Interconnected Electric System (AIES). Provides 1. open and non-discriminatory access to Alberta’s interconnected power grid for generation and distribution companies and large industrial consumers of electricity, 2. contracts with transmission facility owners to acquire transmission services and 3. with other parties; provide fair and timely access to the system, 4. develop and administer transmission tariffs, 5. procure ancillary services to ensure system reliability and 6. manage settlement of the hourly wholesale market and transmission system services.
Allowance for funds used during constructionAcronym(s): AFUDC
AFUDC is an accounting practice whereby the costs of debt and equity funds used to finance plant construction are credited on the statement of income and charged to construction in progress on the balance sheet.Source: ESA Technical Working Group
Alternating currentAcronym(s): AC
Flow of electricity whose polarity/voltage changes (alternates) between positive and negative. The majority of power produced by electric utilities in the U.S. the form of current that alternates at a rate of 60 cycles per second (Hz), also known as the fundamental frequency. In Europe and elsewhere the fundamental frequency is 50 Hz.Source: ESA Technical Working Group
American National Standards InstituteAcronym(s): ANSI
The organization responsible for approving U.S. standards in many areas, including computers and communications. Standards approved by this organization are often called ANSI standards.
Amp hoursSee: Ampere hoursSource: ESA Technical Working Group
Ampere hoursSee: Current
A unit of measurement of the amount of current that can or does flow over a given amount of time. See also current.Source: ESA Technical Working Group
Those services that are necessary to support the transmission of capacity and energy from resources to loads while maintaining reliable operation of the Transmission Service Provider’s transmission system in accordance with good utility practice. (From FERC order 888-A.)
ANSISee: American National Standards Institute
Area control errorAcronym(s): ACE
The instantaneous difference between a Balancing Authority
The extent to which an asset is used relative to the maximum amount of use that is possible. For example, an asset that could be used throughout he entire year and that is only used during half of the year has an asset utilization of 50%. Another relevant metric for electric utility assets is kWh generated, transmitted or delivered per kW of (asset) rated capacity.Source: ESA Technical Working Group
Automatic generation controlAcronym(s): AGC
Equipment that automatically adjusts generation in a Balancing Authority Area from a central location to maintain the Balancing Authority
Available transfer capabilityAcronym(s): ATC
1. A measure of the transfer capability remaining in the physical transmission network for further commercial activity over and above already committed uses. It is defined as Total Transfer Capability less existing transmission commitments (including retail customer service), less a Capacity Benefit Margin, less a Transmission Reliability Margin. 2. The amount of additional [transmission] capability available in the transmission network to accommodate additional requests for transmission services.
The revenue requirement of a utility divided by the utility.
Backup Power (Reliability)
This electric service reliability application focuses on the need for back-up power systems at Commercial and Industrial facilities. Usually, the facilities use a combination of batteries for ride-through of momentary outages and then have a diesel generator for longer duration outages.Source: ESA Technical Working Group
Balancing authorityAcronym(s): BA
The responsible entity that integrates resource plans ahead of time, maintains load-interchange-generation balance within a balancing authority area (BAA), and supports Interconnection frequency in real time.
Balancing authority areaAcronym(s): BAA
The collection of generation, transmission, and loads within the metered boundaries of the Balancing Authority. The Balancing Authority maintains load- resource balance within this area.
The minimum amount of electric power delivered or required over a given period at a constant rate.
Electricity generation designed/intended to operate constantly almost all of the time.Source: ESA Technical Working Group
1. Two or more electric cells connected together electrically. In common usage, the term “battery” is also applied to a single cell, such as a household battery. 2. A system comprised of identical electrochemical cells.Source: ESA Technical Working Group and AA Portable Power Corp.
Battery electric vehicleAcronym(s): BEV
A battery electric vehicle (BEV) is a type of electric vehicle (EV) that uses chemical energy stored in rechargeable battery packs. BEVs useelectric motors and motor controllers instead of internal combustion engines (ICEs) for propulsion.Source: ESA Technical Working Group
Battery electricity storageAcronym(s): BES
Large scale battery systems connected to the electrical grid for both power and energy StorageSource: ESA Technical Working Group
A transaction between two willing parties who negotiate an agreement. For example, the sale of electricity from an Independent Power Producer (IPP) to utility customers and other large customers is often the result of a bi-lateral transaction.
Black start service is the ability of a generating unit to start without an outside electrical supply, or is the demonstrated ability of a generating unit with a high operating factor to automatically remain operating at reduced levels when disconnected from the grid. Black start service is necessary to help ensure the reliable restoration of the grid following a blackout.Source: PJM Interconnection LLC (PJM)
Black start capability plan
A documented procedure for a generating unit or station to go from a shutdown condition to an operating condition delivering electric power without assistance from the electric system. This procedure is only a portion of an overall system restoration plan.
Bulk electric system
As defined by the Regional Reliability Organization, the electrical generation resources, transmission lines, interconnections with neighboring systems, and associated equipment, generally operated at voltages of 100 kV or higher. Radial transmission facilities serving only load with one transmission source are generally not included in this definition.
Operation of the Bulk Electric System that violates or is expected to violate a System Operating Limit or Interconnection Reliability Operating Limit in the Interconnection, or that violates any other North American Electric Reliability Corporation (NERC), Regional Reliability Organization, or local operating reliability standards or criteria.
1. A charge rate that, under ideal conditions, is equal to the energy storage capacity of an electricity storage device divided by 1 hour. For example, a storage device that can store 5 kiloWatt-hours of electric energy has a C rate of five kiloWatts, also known as a C rate of 1. And, a C rate of 5 means energy storage divided by 12 minutes. 2. 1 C is the charge rate necessary to charge a battery in one hour. 10 C charges in 6 minutes and 0.1 C charges in 10 hours. 3. C rate is the charge rate a) for a specific storage device/system or type, b) under ideal conditions, c) that is equal to the energy storage capacity of the device divided by 1 hour. For example, a storage device that can store 5 kiloWatt-hours of electric energy has a C rate of five kiloWatts, also known as a C rate of 1. A C rate of 5 for the same system means energy storage capacity of five kilowatt-hours divided by 12 minutes whereas a C Rate of 1/5 would indicate discharge of a 5 kiloWatt-hour storage device divided by five hours.Source: ESA Technical Working Group
California Public Utilities CommissionAcronym(s): CPUC
CPUC regulates investor-owned utility companies (IOUs) and sets the rates customers pay for electricity.
The rate at which equipment can either generate, convert or transfer energy.Source: ESA Technical Working Group
A capacity emergency exists when a Balancing Authority Area
A value indicating the average percentage of full capacity used over a given period of time. For example, a generating facility which operates at an average of 70% of its normal full capacity over a measured period has a capacity factor of 0.7 for that period.Source: ESA Technical Working Group
Use of storage to provide energy to fill-in when variable generation (i.e. solar and wind) output is below the generator’s rated power output; done to provide constant power output.Source: ESA Technical Working Group
Capital expendituresAcronym(s): CAPEX
All costs associated with design, purchase, installation/construction and financing of investments in/purchase of capital equipment.Source: ESA Technical Working Group
The uncontrolled successive loss of system elements triggered by an incident at any location. Cascading results in widespread electric service interruption that cannot be restrained from sequentially spreading beyond an area predetermined by studies.
The uncontrolled successive loss of bulk electric system facilities triggered by an incident (or condition) at any location resulting in the interruption of electric service that cannot be restrained from spreading beyond a pre- determined area.
The inherent voltage at which the storage system operates. For electrochemical batteries; the inherent voltage of individual cells, which is driven by the underlying chemical reaction(s) within the cell.Source: ESA Technical Working Group
The process of injecting energy to be stored into the storage system.Source: ESA Technical Working Group
The rate at which storage can be charged.Source: ESA Technical Working Group
Circuit recloserSee: RecloserSource: ESA Technical Working Group
Coalition to Advance Renewable Energy through Bulk StorageAcronym(s): CAREBS
CAREBS promotes energy storage and provides a policy voice for the energy storage community.
Generation of useful electric and heat energy using the same conversion system (e.g. internal combustion engine, combustion turbine or fuel cell).Source: ESA Technical Working Group
Combined cooling, heating and powerSee: CogenerationAcronym(s): CCHPSource: ESA Technical Working Group
Combined cycle gas turbineAcronym(s): CCGT
Combined cycle gas turbine plants utilize more than one cycle to generate electricity with waste heat used to make steam, generating additional electricity through a steam turbine.
Combined heat and powerSee: CogenerationAcronym(s): CHPSource: ESA Technical Working Group
Competitive power supplier
An entity that owns and/or operates one or more independent power facilities that are not regulated under the traditional terms. These suppliers are regulated and monitored by the Federal Energy Regulatory Commission (FERC).
Conservation voltageSee: Conservation voltage reduction
Conservation voltage reductionAcronym(s): CVR
Operation of T&D equipment at the minimum allowable voltage to improve energy efficiency and/or to reduce peak demand. Most CVR schemes contain two fundamental components: reactive power compensation and voltage optimization. Reactive power compensation is achieved through the operation of shunt capacitors in order to maintain the power factor at the substation transformer within a prescribed band. Voltage optimization is achieved through the operation of substation voltage regulators in order to regulate the voltage at specific end of line points within a prescribed range.
1. For batteries; a charging process during which the electric current into the battery is constant. 2. For batteries; a charging process during which the electric current into the battery is constant. Charging is stopped when the battery is fully charged and constant-voltage charging is used.Source: ESA Technical Working Group
For batteries; a charging process during which the voltage applied to a battery’s terminals is constant.Source: ESA Technical Working Group
A transmission facility (line, transformer, breaker, etc.) that is approaching, is at, or is beyond its System Operating Limit or Interconnection Reliability Operating Limit.
The unexpected failure or outage of a system component, such as a generator, transmission line, circuit breaker, switch or other electrical element.
1. The provision of capacity deployed by the balancing authority to meet the disturbance control standard (DCS) and other North American Electric Reliability Corporation (NERC) and regional reliability organizations’ contingency requirements. 2. Reserves set aside to support the transmission system in the case of the worst foreseeable contingency event (often referred to as N-1)
An agreed upon electrical path for the continuous flow of electrical power between the parties of an Interchange Transaction.
Control performance standardAcronym(s): CPS
The reliability standard that sets the limits of a Balancing Authority
The total cost incurred by the utility to generate, transmit and deliver electricity and to provide customer service.Source: ESA Technical Working Group
Facilities, systems, and equipment which, if destroyed, degraded, or otherwise rendered unavailable, would affect the reliability or operability of the Bulk Electric System.
Critical peak pricingAcronym(s): CPP
A program involving “high” or “very high” prices (relative to normal prices) that are assessed during “critical peak” periods (when demand is at or near supply).Source: ESA Technical Working Group
CurrentSee: Electric currentSource: ESA Technical Working Group
The amount of current per unit area such as the amount of current flowing through a wired per unit of cross sectional area of the wire that is perpendicular to flow of current. Current density is a vector quantity whose direction is the same as the direction of current flow.Source: ESA Technical Working Group
1. A reduction in the scheduled capacity or energy delivery of an Interchange Transaction. 2. A temporary reduction in customer load that occurs or that is imposed because demand exceeds the capacity.
Customer facility charge
An charge that is part of an end-use customer’s electricity bill that may be used to cover—among other utility costs— cost to maintain utility facilities and infrastructure needed to provide electric service to the respective customer. Charges may include, for example, T&D equipment, accounting, meter reading and site-specific services. Facility charges may also be a way to combine several small fixed-cost charges associated with maintaining a customer’s energy account.Source: ESA Technical Working Group
Cutoff voltageSee: End-point voltage
Voltage at the end of useful discharge.
CycleSee: Cycle life
One sequence of storage charging and discharging. Also known as charge-discharge cycle.Source: ESA Technical Working Group
The number of charge-discharge cycles after which storage becomes inoperable or unusable for a given application. In practice, storage may be inoperable or unusable when it can still deliver a portion of its initial rated energy and/or power rating.Source: ESA Technical Working Group
Any effect that tends to reduce the amplitude (magnitude) of oscillations in a system.Source: ESA Technical Working Group
Day ahead scheduling reserveAcronym(s): DASR
Supplemental reserves procured and scheduled the day before they will be used.Source: ESA Technical Working Group
A forward market for electric energy, capacity or ancillary services that will be provided or purchased during the next day.Source: ESA Technical Working Group
Day-ahead priceSee: Day-ahead market
Price for electricity in an day-ahead market.Source: ESA Technical Working Group
Declining block rate
An energy price structure for high-volume end-users involving prices for energy that decline as the customer’s energy use increases. Typically; the end-user purchases an initial amount of energy for an initial price and additional energy is purchased at prices whose decline is commensurate with increasing energy use. The opposite of inverted block rate.Source: ESA Technical Working Group
Delayed fault clearing
Fault clearing consistent with correct operation of a breaker failure protection system and its associated breakers, or of a backup protection system with an intentional time delay.
1. The rate at which electric energy is delivered to or by a system or part of a system, generally expressed in kilowatts or megawatts, at a given instant or averaged over any designated interval of time. 2. The rate at which energy is being used by the customer.
The price paid by a retail electricity user for each unit of power draw on the electric grid. (That power draw drives the amount of electricity generation and T&D infrastructure needed by the utility to serve all load.) Typically demand charges are applied to the maximum demand during a given month, hence units are $/kW-month.Source: ESA Technical Working Group
A period of time in which system, group, or customer demand is measured. This term is most commonly used to refer to periods of measured or expected energy use ranging from 15 minutes to one hour.
Demand responseAcronym(s): DR
Reduction of retail electricity end-users’ electric load (power draw) in response to control or price signals. DR resources are deployed and used in lieu of installing/operating peaking generation capacity.Source: ESA Technical Working Group
Demand side managementAcronym(s): DSM
1. Measures or programs undertaken by a utility designed to influence the level or timing of customer demands for energy in order to optimize the use of available supply resources, in turn allowing suppliers to defer the purchase of additional generating capacity. 2. The term for all activities or programs undertaken by Load-Serving Entity or its customers to influence the amount or timing of electricity they use.
1. Of or related to end-user electric demand, often said to be “on the customer side of the meter.” 2. Of or pertaining to electricity demand, sometimes referred to as “customer side of the meter.”Source: ESA Technical Working Group
Depth of dischargeAcronym(s): DOD
The portion of energy discharged from a storage system relative to the amount extractable stored energy.Source: ESA Technical Working Group
(Physics) involving a transfer of heat.
A substance that does not conduct electricity.Source: ESA Technical Working Group
1. Affording generators, marketers and large users of electricity the ability to receive transmission services to serve load directly without exercising the traditional method of going through the utility. 2. A retail utility end-user that can purchase electricity from the wholesale market, thus bypassing the default electric service provider (e.g. the retail electric utility). Typically direct access is available or feasible for large-scale or relatively large-scale end-users, in part because the end-user must also arrange for transmission and delivery of the energy.
Direct control load managementAcronym(s): DCLM
Demand-Side Management that is under the direct control of the system operator. DCLM may control the electric supply to individual appliances or equipment on customer premises. DCLM as defined here does not include Interruptible Demand.
Direct load controlSee: Direct control load managementAcronym(s): DLCSource: ESA Technical Working Group
The process of extracting stored energy from the storage system.Source: ESA Technical Working Group
The amount of time that a storage device can be discharged at the nominal power rating.Source: ESA Technical Working Group
The process of varying the output from generation on a moment-to-moment basis to meet changing supply requirements.Source: ESA Technical Working Group
Distributed energy resourceAcronym(s): DER
Relatively small and modular electrotechnologies that are deployed at the subtransmission or distribution level.Source: ESA Technical Working Group
Distributed generationAcronym(s): DG
Small, modular electric generation that is interconnected with the electricity grid at the subtransmission or distribution level.Source: ESA Technical Working Group
The practice of and infrastructure for distribution of electricity to end-users by utilities. Typical voltages range from 12 to 138 kiloVolts (kV)Source: ESA Technical Working Group
Distribution cooperativeAcronym(s): D co-op
A not-for-profit, customer/member owned electric company that purchases electric power at wholesale and distributes it to its customers.Source: ESA Technical Working Group
Distribution providerAcronym(s): DP
Provides and operates the “wires” between the transmission system and the end use customer. For those end-use customers who are served at transmission voltages, the Transmission Owner also serves as the Distribution Provider. Thus, the Distribution Provider is not defined by a specific voltage, but rather as performing the Distribution function at any voltage.
1. An unplanned event that produces an abnormal system condition. 2. Any perturbation to the electric system. 3. The unexpected change in ACE that is caused by the sudden failure of generation or interruption of load.
Disturbance control standardAcronym(s): DCS
The reliability standard that sets the time limit following a Disturbance within which a Balancing Authority must return its Area Control Error to within a specified range.
Disturbance monitoring equipmentAcronym(s): DME
Devices capable of monitoring and recording system data pertaining to a Disturbance. Such devices include the following categories of recorders (e.g. PMUs): 1. Sequence of event recorders which record equipment response to the event 2. Fault recorders, which record actual waveform data replicating the system primary voltages and currents. This may include protective relays. 3. Dynamic Disturbance Recorders (DDRs), which record incidents that portray power system behavior during dynamic events such as low- frequency (0.1 Hz
Disturbance recovery period
The maximum amount of time allowed for the responsible entity (balancing authority or reserve sharing group) to meet North American Electric Reliability Corporation (NERC)‘s disturbance recovery criteria for all “reportable disturbances.” The disturbance recovery criteria are: 1. A balancing authority shall return its area control error (ACE) to zero if its ACE just prior to the reportable disturbance was positive or equal to zero. For negative initial ACE values just prior to the disturbance, the balancing authority shall return ACE to its pre-disturbance value. 2. The default disturbance recovery period is 15 minutes after the start of a reportable disturbance. This period may be adjusted to better suit the needs of an Interconnection based on analysis approved by the North American Electric Reliability Corporation (NERC) Operating Committee.Source: ESA Technical Working Group
A primary cell in which the electrolyte is absorbed in a porous medium, or is otherwise restrained from flowing.
Dynamic interchange schedule or dynamic schedule
A telemetered reading or value that is updated in real time and used as a schedule in the AGC/ACE equation and the integrated value of which is treated as a schedule for interchange accounting purposes. Commonly used for scheduling jointly owned generation to or from another Balancing Authority Area.
The provision of the real-time monitoring, telemetering, computer software, hardware, communications, engineering, energy accounting (including inadvertent interchange), and administration required to electronically move all or a portion of the real energy services associated with a generator or load out of one Balancing Authority Area into another.
The allocation of demand to individual generating units on line to effect the most economical production of electricity.
Edison Electric InstituteAcronym(s): EEI
An association of investor-owned electric utility companies created in 1933 “to exchange information on industry developments and to act as an advocate for utilities on subjects of national interest.” The EEI acts as an information exchange for its members and a public relations voice for the electric energy industry as a whole.Source: ESA Technical Working Group
Elastic potential energy
A form of potential energy that is stored in “elastic” materials (i.e. materials that can be stretched or compressed). So, elastic potential energy can be stored, for example, in springs, rubber bands and compressed air.Source: ESA Technical Working Group
An adjective meaning “needing electricity to operate” such as electric motor or wire. IEEE: Containing, producing , arising from, actuated by or carrying electricity.Source: ESA Technical Working Group
Electric cooperativeAcronym(s): co-op
A not-for-profit electric utility that is owned by the members it serves. A co-op exist solely to provide high-quality service at the lowest possible price for its customer-owners. A co-op’s profits are retained by the co-op to offset future costs and/or profit is returned to the customer-owner. Many co-ops are own T&D needed to serve member-owners though many own limited or no generation.Source: ESA Technical Working Group
Flow of electrons. The common metric is ampere or amp.Source: ESA Technical Working Group
Electric distribution information systemAcronym(s): EDIS
A computerized mapping system which tracks resources within a distribution network.
Electric energy time-shift
Storage of energy during times when cost or price is low, for use or sale when the energy’s value is high.Source: ESA Technical Working Group
Electric gridSee: Electrical utility grid
A common term used to refer to the electric utility grid.Source: ESA Technical Working Group
Electric Reliability Council of TexasAcronym(s): ERCOT
The independent system operator in Texas.Source: ESA Technical Working Group
A source of electric energy and/or capacity, possibly including generation facilities and purchases.Source: ESA Technical Working Group
Electric supply resource
A source of electricity and/or demand reduction that is included in a utility’s electric supply portfolio.Source: ESA Technical Working Group
Electric supply resources
All generation, power purchases and load management resources that can be called upon to provide electricity to the grid.Source: ESA Technical Working Group
1. An adjective meaning “pertaining to electricity”. Electrical Engineer. 2. Related to, pertaining to or associated with electricity but not having its properties or characteristics.Source: ESA Technical Working Group
The generation or use of electric power by a device over a period of time, expressed in kiloWatt-hours (kWh), MegaWatt-hours (MWh), or GigaWatt-hours (GWh).
A portion of (i.e., electrical “island” within) a larger electric system that operates autonomously when the larger electric power system is not available or not operational. Traditionally electric utilities have discouraged islanded operation due to safety concerns related to exposing work persons to danger if equipment is energized during repair or maintenance.Source: ESA Technical Working Group
Electrical utility grid
The network of generators, transformers, wires, capacitors and other equipment that comprise the physical utility electric power supply, transmission and distribution systems. Also referred to as the electric grid or just the grid.Source: ESA Technical Working Group
Electrochemical batterySee: BatterySource: ESA Technical Working Group
Devices in which oxidation-reduction (redox) reactions occur. Two types of electrochemical cells: 1. spontaneous reactions occur in galvanic (voltaic) cells and 2. nonspontaneous reactions occur in electrolytic cells. Both types contain electrodes where the oxidation and reduction reactions occur. Oxidation occurs at the electrode termed the anode and reduction occurs at the electrode called the cathode. The anode is positive (cathode is negative), because the anode attracts anions from the solution. However, the anode of a galvanic cell is negatively charged, since the spontaneous oxidation at the anode is the source of the cell’s electrons or negative charge. The cathode of a galvanic cell is its positive terminal. In both galvanic and electrolytic cells, oxidation takes place at the anode and electrons flow from the anode to the cathode.Source: About.com (chemistry)
The system of active materials within a cell that provides electrical energy storage through an electrochemical reaction.Source: GreenBatteries.com
An electrical conductor through which an electric current enters or leaves a conducting medium, whether it be an electrolytic solution, solid, molten mass, gas, or vacuum. For electrolytic solutions, many solids, and molten masses, an electrode is an electrical conductor at the surface of which a change occurs from conduction by electrons to conduction by ions. For gases and vacuum, the electrodes merely serve to conduct electricity to and from the medium.
For electrochemical batteries; A chemical compound which, when fused or dissolved in certain solvents, usually water, will conduct an electric current. All electrolytes in the fused state or in solution give rise to ions which conduct the electric current.
Emergency or BES emergency
Any abnormal system condition that requires automatic or immediate manual action to prevent or limit the failure of transmission facilities or generation supply that could adversely affect the reliability of the bulk electric system.
The rating as defined by the equipment owner that specifies the level of electrical loading or output, usually expressed in megawatts (MW) or Mar or other appropriate units, that a system, facility, or element can support, produce, or withstand for a finite period. The rating assumes acceptable loss of equipment life or other physical or safety limitations for the equipment involved.
The person or entity that uses energy, as distinct from, for example, entities that engage in wholesale energy transactions or purchases made by a landlord or other “distributor.”Source: ESA Technical Working Group
For electrochemical batteries; the voltage of the battery that has been fully discharged.Source: ESA Technical Working Group
Cell/battery voltage below which the connected equipment will not operate or below which operation is not recommended.Source: GreenBatteries.com
1. Energy is the potential of a physical system to perform work. (A common unit of work is foot-pound—the amount of energy needed to lift one pound up a distance of one foot.) Energy exists in several forms such as electromagnetic radiation (light and heat), kinetic or mechanical energy, potential energy, electric, chemical and others. Note that power is the rate at which energy is generated, transferred or used. So energy generated, transferred or used is a function of power and time. For example, power generation, transfer or use of 1 kilowatt (kW) for one hour indicates energy use of one kilowatt-hour (kWh). See also kinetic energy and potential energy. 2. The ability a physical system has to do work on other physical systems, typically measured in kWh in the electric utility context. Measured in kWh kilowatt hours as well as other units. 3. Ability to do work, force through a distance.Source: ESA Technical Working Group
Periodic balancing of energy supply and demand between two or more entities. For example, during one 15 minute period entity 1 needs more energy than its scheduled resources can provide. So entity 1 receives the necessary energy from entity 2. During the next 15 minute period entity 1 supplies an amount of energy to entity 2 equal to the extra energy used (from entity 2) during the previous 15 minute period.Source: ESA Technical Working Group
The amount of energy that a storage system can store per unit volume occupied by the system.Source: ESA Technical Working Group
A condition when a Load-Serving Entity has exhausted all other options and can no longer provide its customers
Energy imbalance service
An ancillary service provided via a wholesale market which operates under a tariff approved by the FERC and consistent with the mandate of FERC Order No. 2000, which requires real-time EIS and market monitoring functions. One of six ancillary services specified by the FERC under Order 888.Source: ESA Technical Working Group
The maximum and minimum voltage, current, frequency, real and reactive power flows on individual equipment under steady state, short-circuit and transient conditions, as permitted or assigned by the equipment owner.
Exempt wholesale generatorAcronym(s): EWG
A generator of electric energy for sale exclusively to competing wholesale customers, and who is exempt from some requirements of the Public Utilities Holding Company Act of 1935. An exempt wholesale generator may sell to publicly-owned municipal utilities, but their exemption allows them to sell - or not sell - energy to whomever they choose at whatever rate they choose. The exemption applies federally, but is usually subject to approval by state and regional bodies who may override the exemption if it is felt that this is in the public interest and require a generator to sell within a certain price range or to a certain customer or group of customers.
Extended range electric vehicleAcronym(s): EREV
An extended-range electric vehicle (EREV) operates as a battery electric vehicle for a certain number of miles. After the battery has been discharged, a gas engine powers an electric generator for several hundred miles of
Expenses, costs, or potential costs which are not included in cost analyses, cost/benefit studies or prices, usually because they cannot be readily quantified, determined or allocated. Typically the term externalities refer to social and environmental costs, but they can be any costs which are not incurred by the responsible party.Source: ESA Technical Working Group
The maximum or minimum voltage, current, frequency, or real or reactive power flow through a facility that does not violate the applicable equipment rating of any equipment comprising the facility.
Fast area regulationSee: Fast frequency regulationSource: ESA Technical Working Group
Fast frequency regulation
A fast version of area regulation. Ideally fast frequency response resources can respond robustly to the ACE signal, thus output changes every few seconds.Source: ESA Technical Working Group
An event or condition occurring on an electric system such as a short circuit, a broken wire, or an intermittent connection.
When an excessive amount of current flows in an uncontrolled manner through the electrical system.Source: U.S. Department of Energy (DOE)
Federal Energy Management ProgramAcronym(s): FEMP
U.S. Department of Energy - Office of Energy Efficiency and Renewable Energy - Federal Energy Management Program (U.S. DOE-FEMP) The program assists federal government agencies to reduce energy use and cost, increase energy efficiency, use renewable energy, and conserve water. FEMP’s three primary areas of concentration are project financing, technical assistance, and planning, reporting, and evaluation.Source: ESA Technical Working Group
Federal Energy Regulatory CommissionAcronym(s): FERC
FERC is an independent agency regulating the interstate transmission of electricity, natural gas and oil, and responsible for maintaining system reliability, ensuring electricity is transmitted in an unbiased manner, and establishing the price of ancillary services necessary for reliable system operation.
An electrical wire/circuit which “feeds” energy to the next lower level of distribution. A feeder may be an underground or an overhead wire.Source: ESA Technical Working Group
That portion of the Demand that a power supplier is obligated to provide except when system reliability is threatened or during emergency conditions.
Firm transmission service
The highest quality (priority) service offered to customers under a filed rate schedule that anticipates no planned interruption.
A cost or expense incurred without regard to whether or how much a respective service, facility or equipment is used (i.e., unlike variable costs; fixed costs are incurred irrespective of how much the service, facility or equipment is used).Source: ESA Technical Working Group
An electrical discharge through air around or over the surface of insulation, between objects of different potential, caused by placing a voltage across the air space that results in the ionization of the air space.
Robust responses to changing needs and opportunities that are enabled by use of a device or technique that is adaptable, versatile and, in some cases, transportable.Source: ESA Technical Working Group
Flexible alternating current (ac) transmission systemAcronym(s): FACTS
FACTS enables control of power flow on ac transmission lines and to optimize utilization of existing transmission facilities by allowing operation at or near equipment’s thermal operating limits without sacrificing reliability. Core FACTS technologies are thyristors though FACTS also incorporates sophisticated controls, communication and monitoring devices and computer algorithms.Source: ESA Technical Working Group
Generating capacity whose output can be varied as needed. Flexible generation is said to be dispatchable.Source: ESA Technical Working Group
For electrochemical batteries; recharging during which batteries are connected to a constant-voltage supply that maintains the cell in fully charged condition.Source: ESA Technical Working Group
Florida Reliability Coordinating CouncilAcronym(s): FRCC
A not-for-profit corporation in the state of Florida whose mission is to ensure that the bulk power system in Peninsular Florida is reliable, adequate and secure. The FRCC serves as a regional entities with delegated authority from the North American Electric Reliability Corporation (NERC) for the purpose of proposing and enforcing reliability standards within the FRCC Region. See also regional entities.
The amount of area required for the storage system.Source: ESA Technical Working Group
1. The removal from service availability of a generating unit, transmission line, or other facility for emergency reasons. 2. The condition in which the equipment is unavailable due to unanticipated failure.
A value, usually expressed in megawatts per 0.1 Hertz (MW/0.1 Hz), associated with a balancing authority area (BAA) that approximates the BAA
A change in Interconnection frequency.
The difference between the actual and scheduled frequency.
(Equipment) The ability of a system or elements of the system to react or respond to a change in system frequency. (System) The sum of the change in demand, plus the change in generation, divided by the change in frequency, expressed in megawatts per 0.1 Hertz (MW/0.1 Hz).
A combination of electrodes, separated by electrolyte, that is capable of producing electrical energy by electrochemical action.
The manner in which electricity is generated. The electricity that flows through California
Generation and transmission cooperativeAcronym(s): G&T co-op
A not-for-profit entity that is owned by several distribution cooperatives. A G&T cooperative supplies and transmits electricity to member co-ops.Source: ESA Technical Working Group
Generator shift factorAcronym(s): GSF
A factor to be applied to a generator
One billion Watts of power.Source: ESA Technical Working Group
A measure involving one billion watts being generated, transmitted, distributed or used continuously for one hour. (Note the difference between GigaWatt-hours of energy and a GigaWatt of power where power reflects the rate at which electric energy is generated, transmitted, distributed or used).Source: ESA Technical Working Group
Gravitational potential energy
Potential energy associated with a mass due to the mass’ vertical position or height. The energy is stored as the result of the gravitational effect of the Earth on the mass.Source: ESA Technical Working Group
Changes to the voltage waveform in an alternating current (AC) system, from a simple sinusoidal waveform to a complex waveform. Harmonic distortion can cause overheating of and damage to electrical equipment and suboptimal performance of electricty-using equipment.Source: ESA Technical Working Group
A measure of thermal generation conversion efficiency expressed as the amount of fuel (energy) input for a given electric energy output. Typically heat rate is expressed as the number of BTUs of fuel input per kWh of output (energy).Source: ESA Technical Working Group
Host balancing authority
1. A Balancing Authority that confirms and implements Interchange Transactions for a Purchasing Selling Entity that operates generation or serves customers directly within the Balancing Authority
The electric power futures market that is established one-hour before delivery to end-user customers.
Hour-ahead priceSee: Hour-ahead market
Price for electricity in an hour-ahead market.Source: ESA Technical Working Group
Any chemical compound comprised of hydrogen and carbon. Familiar examples include elements of wood, petroleum, coal, natural gas and propane.Source: ESA Technical Working Group
The process using flowing water to turn turbines to generate electric power.
Energy losses associated with current flow through electric transmission and distribution systems. Also known as resistive losses. resistive losses. As the name implies: ISource: ESA Technical Working Group
The cost of the next kilowatt-hour of generated energy, also referred to in the industry as the next unit. Incremental costs change as production increases or decreases, but these changes don’t always occur in a predictable pattern. As an example, incremental costs typically decrease as production rises to comfortable capacity. But once that limit is reached, incremental costs increase because additional costs (construction of new facilities, costs of stressing production facilities, etc.) need to be factored into the cost of the next unit. Incremental cost is often used interchangeably with marginal cost, but incremental cost is a strict value applied to the next unit only, whereas marginal costs are often expressed as averages of large numbers of next units.Source: ESA Technical Working Group
Independent power producerAcronym(s): IPP
A generation company that is not part of a regulated vertically-integrated utility company that sells output under a long-term contract.
Independent system operatorAcronym(s): ISO
An organization formed at the direction or recommendation of the Federal Energy Regulatory Commission (FERC) to coordinate, control and monitor operation of the electrical power system. An ISO’s jurisdiction may be for one state or multiple states. Note: RTOs typically perform similar or the same functions as ISOs, but RTOs tend to have jurisdiction over larger geographic areas than ISOs. Some ISOs and RTOs also administer the marketplace for wholesale electricity.Source: ESA Technical Working Group
Independent System Operator New EnglandAcronym(s): ISO-NE
A non-profit organization that ensures the constant availability of electricity by 1) ensuring the day-to-day reliable operation of New England’s bulk power generation and transmission system, 2) overseeing and ensuring the fair administration of the region’s wholesale electricity markets, and 3) managing comprehensive, regional planning processes.
Induce (current)See: Inductance
The ratio of the voltage to the rate of change of current, which has units of henries (H).
A passive two-terminal electrical component which resists changes in electric current passing through it. It consists of a conductor such as a wire, usually wound into a coil. When a current flows through it, energy is stored in a magnetic field in the coil. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor, according to Faraday
Institute of Electrical and Electronics Engineers, Inc.Acronym(s): IEEE
IEEE a professional association that is “dedicated to advancing technological innovation and excellence for the benefit of humanity” and to “inspir[ing] a global community through IEEE’s highly cited publications, conferences, technology standards, and professional and educational activities.”
Integrated gasification combine cycle plantAcronym(s): IGCC
IGCC power plants add to the electricity supply, replace aging coal power plants and replace expensive natural gas power plants. Using coal, IGCC plants produce a synthetic gas, the pollutants are removed and electricity is generated using combined cycle technology.
Integrated resources planningAcronym(s): IRP
A holistic/comprehensive electric resources planning framework that addresses all existing and possible electric supply resources including those owned and controlled by entity doing the planning and other resources that can be provided by other providers. Addressed are supply and demand side alternatives. The objective is to identify the most optimal portfolio of electric resources (i.e. the mix that yields to the lowest possible cost, possibly including environmental and societal externalities). Historically IRP was used as aSource: ESA Technical Working Group
Energy transfers that cross Balancing Authority boundaries.
The responsible entity that authorizes implementation of valid and balanced Interchange Schedules between Balancing Authority Areas, and ensures communication of Interchange information for reliability assessment purposes.
An agreed-upon Interchange Transaction size (megawatts), start and end time, beginning and ending ramp times and rate, and type required for delivery and receipt of power and energy between the source and sink balancing authorities involved in the transaction.
An agreement to transfer energy from a seller to a buyer that crosses one or more Balancing Authority Area boundaries.
The physical and electrical connection between an electricity source and an external power system (i.e. the electric power grid).Source: ESA Technical Working Group
Interconnection reliability operating limitAcronym(s): IROL
A system operating Limit that, if violated, could lead to instability, uncontrolled separation, or cascading outages that adversely impact the reliability of the bulk electric system.
One of three types of generation, intermediate generation moves up and down throughout the day.
The resistance to the flow of electric current within an electrochemical cell or battery.Source: ESA Technical Working Group
Interruptible load or interruptible demand
Demand that the end-use customer makes available to its Load-Serving Entity via contract or agreement for curtailment.
Inverted block rate
An energy pricing structure involving prices for energy prices that increase commensurate with increasing energy use. Typically; inverted block rates apply to energy delivered to customers that use a large portion of energy during peak demand periods, especially if additional capacity is needed to meet the customer’s electricity needs. The opposite of declining block rate.Source: ESA Technical Working Group
Investor owned utilityAcronym(s): IOU
A utility whose assets are owned by investors (as distinct from public power agencies, cooperatives and municipal utilities).
IslandingSee: Electrical island
The process of operating an electrical island.Source: ESA Technical Working Group
Automatic generation control (AGC) of jointly owned units by two or more balancing authorities.
A common measure of energy. One joule equals one watt-second, or 1/3,600,000th of a kilowatt-hour.Source: ESA Technical Working Group
A unit of power equal to one thousand Watts.Source: ESA Technical Working Group
A measure involving one thousand watts being generated, transmitted, distributed or used continuously for one hour. The kiloWatt-hour is perhaps the most common unit of electric energy; it is used by utilities for billing. (Note the difference between kiloWatt-hours of energy and a kilowatt of power where power reflects the rate at which electric energy is generated, transmitted, distributed or used).Source: ESA Technical Working Group
The energy of motion. Any mass that is in motion has kinetic energy. Some forms of kinetic energy include vibrational, rotational and translational (i.e. due to motion from one location to another).Source: ESA Technical Working Group
Least-cost planningSee: Integrated resources planningSource: ESA Technical Working Group
Levelized costSee: Levelized cost of energySource: ESA Technical Working Group
Levelized cost of energyAcronym(s): LCOE
A common metric used to compare the “levelized” or “annuity equivalent” cost per unit to generate electric energy, over a specified period (number of years), given assumed cost-of-capital, start year prices and cost/price escalation rates. The two primary components are 1) capital plant and equipment related cost and 2) expense related costs such as maintenance and fuel. Importantly, LCOE is used to make comparisons between generation alternatives assuming comparable bases. So they reflect relative cost—and are unlikely to reflect actual cost—for a specific alternative or circumstance.Source: ESA Technical Working Group
Actions taken to extend the useful life of utility equipment, primarily by reducing peak demand served by the equipment. For most equipment types that involves reducing the equipment’s maximum and on-peak operating temperatures. For underground power cables a key result is reduced ground faults.Source: ESA Technical Working Group
The element within a “system” that: 1) is operating at its appropriate rating or 2) would be following the limiting contingency. Thus, the limiting element establishes a system limit.
Line faultSee: FaultSource: ESA Technical Working Group
An end-use device or an end-use customer receiving electric power and using electric energy from the electrical system (grid). Note: The term load is sometimes treated as a synonym for demand, which is the measure of power that a load receives or requires.Source: ESA Technical Working Group
A specific geographical area where electric load is concentrated, especially areas within a utility’s service area where demand is highest.Source: ESA Technical Working Group
Load managementSee: Demand side managementSource: ESA Technical Working Group
A graphical representation of electric demand over time.Source: ESA Technical Working Group
Load-serving entitiesAcronym(s): LSE
Utilities, marketers or aggregators who provide electric power to a large number of end-use customers.
Local publicly owned electric utilities
A municipal corporation, a municipal utility district, an irrigation district or a joint power authority (which can include one or more of the agencies mentioned above) furnishing electric services over its own transmission facilities, or furnishing electric service over its own or its members
Locational marginal priceAcronym(s): LMP
A method of setting prices in an ISO market whereby prices at specific locations on the grid are determined by the marginal price of generation of power available to that specific location. Prices vary from location-to-location based on transmission congestion and losses.
Long-term fixed contract
A bilateral transaction, often for an extended period of time at a set amount. Contracts may be one, five or 10 years and could be for peak or off-peak hours or a full-day contract.
A description of the magnetic effect that electric currents and magnetic materials have on their surroundings. The magnetic field is a vector field meaning that it is characterized by both the direction and a magnitude of the magnetic influence.Source: ESA Technical Working Group
Marginal costSee: Incremental costSource: ESA Technical Working Group
Market clearing price
In any exchange, sellers prefer to part with their assets for the highest price possible while investors interested in buying the same asset desire the lowest purchase price possible. At some point, a mutually agreeable price is reached between buyers and sellers. It is at this point that economists say the market has “cleared” and transactions take place. Thus, the clearing price of an asset is the price at which it was most recently traded.
A unit of power equal to one million watts.
A measure involving one million watts being generated, transmitted, distributed or used continuously for one hour. The MegaWatt-hour a common unit of electric energy. (Note the difference between MegaWatt-hours of energy and a Megawatt of power where power reflects the rate at which electric energy is generated, transmitted, distributed or used).Source: ESA Technical Working Group
Merit order rank
Ranking of electric supply resources according to their availability and the price that will be applied to the energy they produce.Source: ESA Technical Working Group
A combination of co-located distributed electric resources that can operate as one entity that either 1. interacts with the greater electric grid (if available) or 2. as an autonomous power system that is not connected with a large power system (i.e. in “island” mode).Source: ESA Technical Working Group
Midwest Independent Transmission System Operator, Inc.Acronym(s): MISO
An Independent System Operator (ISO) and Regional Transmission Organization (RTO) providing open-access transmission service and that monitors the high voltage transmission system throughout the Midwest United States and Manitoba, Canada.
Midwest Reliability OrganizationAcronym(s): MRO
Midwest Reliability Organization (MRO) is a non-profit organization dedicated to ensuring the reliability and security of the bulk power system in the north central region of North America, including parts of both the United States and Canada. MRO is one of eight regional entities in North America operating under authority from regulators in the United States through a delegation agreement with the North American Electric Reliability Corporation (NERC) and in Canada through arrangements with provincial regulators. The primary purpose of MRO is to ensure compliance with reliability standards and perform regional assessments of the grid
The lowest level of production that a generating unit can maintain before it ceases to be cost-effective to keep online.
Transportable substation equipment designed for use as temporary infrastructure when a permanent substation is not practical or is out of service such as to provide temporary electric service at construction sites or emergency service.Source: ESA Technical Working Group
Modular pumped hydroelectric electricity storageAcronym(s): MPHS
Pumped hydroelectric storage systems with small or relatively small rated power and whose components.Source: ESA Technical Working Group
Municipal electric utilityAcronym(s): muni
A municipal corporation, municipal utility district, an irrigation district or a joint power authority furnishing electric services over its own transmission facilities, or furnishing electric service over its own or its members
Must take resource
An electric supply resource, including generation and power purchase agreements (PPAs) with “minimum energy take requirements” whose output must be purchased, without regard to the purchasing entity’s need for the output..Source: ESA Technical Working Group
Exogenous Event involving Loss of a major line or transformer
Exogenous Event involving Coincident loss of two major lines or transformers
National Association of Regulatory Utility CommissionersAcronym(s): NARUC
An advisory council in the United States consisting of members from state utility regulatory agencies in all 50 states, the District of Columbia, Puerto Rico, and the US Virgin Islands. NARUC’s mandate is to “serve the consumer by seeking to improve the quality and effectiveness of public regulation in America.” NARUC also advises state and federal agencies regarding utility-related legislation.Source: ESA Technical Working Group
National Electrical CodeAcronym(s): NEC
A regionally adoptable standard for the safe installation of electrical wiring and equipment in the United States. The NEC, while having no legally binding regulation as written, can be and often is adopted by states, municipalities and cities in an effort to standardize their enforcement of safe electrical practices within their respective jurisdiction. In some cases, the NEC is amended, altered and may even be rejected in lieu of regional regulations as voted on by the governing bodies of any given locale.
The end-use customers that the Load-Serving Entity is obligated to serve.
A mixture of hydrocarbon gases occurring with petroleum deposits, mainly combining methane with varying quantities of ethane, propane, butane and other gases. Used as a fuel and for manufacturing organic compounds. This type of gas generates about 38-percent of the stateSource: ESA Technical Working Group
The terminal of a battery from which electrons flow, through the load, during cell/battery discharge.Source: ESA Technical Working Group
Net actual interchange
The algebraic sum of all metered interchange over all interconnections between two physically Adjacent Balancing Authority Areas.
Net energy for load
Net Balancing Authority Area generation, plus energy received from other Balancing Authority Areas, less energy delivered to Balancing Authority Areas through interchange. It includes Balancing Authority Area losses but excludes energy required for storage at energy storage facilities.
Energy use metering involving measurement of energy used and energy fed into the utility grid by a customer with generation capacity. So, in essence, each unit of energy fed into the grid directly offsets use and cost incurred for one unit of energy purchased from the grid. So a customer that participates in a net metering program may actually produce more energy than needed. In some cases the utility pays the same price for energy from the customer as the customer pays for purchased electricity from the utility. Increasingly, though, utilities pay a lower price to producers than they receive from customers. Net metering may require two separate meters.Source: ESA Technical Working Group
Net scheduled interchange
The algebraic sum of all Interchange Schedules across a given path or between Balancing Authorities for a given period or instant in time.
Network integration transmission service
Service that allows an electric transmission customer to integrate, plan, economically dispatch and regulate its network reserves in a manner comparable to that in which the Transmission Owner serves Native Load customers.
New Brunswick System OperatorAcronym(s): NBSO
A not-for-profit independent (Canadian) corporation whose primary responsibilities are to ensure the reliability of the electrical system and to facilitate the development and operation of a competitive electricity market in New Brunswick.
New York Battery and Energy Storage Technology ConsortiumAcronym(s): NY-BEST
The New York Battery and Energy Storage Technology (NY-BEST
Voltage of a fully charged cell/battery when it is discharged at its rated current.
Non-firm transmission service
Transmission service that is reserved on an as-available basis and is subject to curtailment or interruption.
Non-Spinning Reserve is off-line generation capacity that can be ramped to capacity and synchronized to the grid within 10 minutes of a dispatch instruction by the ISO, and that is capable of maintaining that output for at least two hours. Non-Spinning Reserve is needed to maintain system frequency stability during emergency conditions.
Cells or batteries which do not contain water, such as those with molten salts or organic electrolytes.Source: ESA Technical Working Group
A protection system operates as designed and the fault is cleared in the time normally expected with proper functioning of the installed protection systems.
The rating as defined by the equipment owner that specifies the level of electrical loading, usually expressed in megawatts (MW) or other appropriate units that a system, facility, or element can support or withstand through the daily demand cycles without loss of equipment life.
North American Electric Reliability CorporationAcronym(s): NERC
North American Electric Reliability Corporation (NERC) develops and enforces reliability standards; assesses adequacy annually via a 10-year forecast and winter and summer forecasts; monitors the bulk power system; and educates, trains, and certifies industry personnel. North American Electric Reliability Corporation (NERC) is a self-regulatory organization, subject to oversight by the U.S. Federal Energy Regulatory Commission and governmental authorities in Canada. North American Electric Reliability Corporation (NERC) is a non-government organization which has statutory responsibility to regulate bulk power system users, owners, and operators through the adoption and enforcement of standards for fair, ethical and efficient practices. More specifically; North American Electric Reliability Corporation (NERC) has authority to enforce reliability standards with all users, owners, and operators of the bulk power system in the United States, and makes compliance with those standards mandatory and enforceable.
North American Energy Standards BoardAcronym(s): NAESB
An organization that serves as an industry forum for the development and promotion of standards which will lead to a seamless marketplace for wholesale and retail natural gas and electricity, as recognized by its customers, business community, participants, and regulatory entities.
Northeast Power Coordinating Council, Inc.Acronym(s): NPCC
A not-for-profit corporation responsible for promoting and improving the reliability of the international, interconnected bulk power system in Northeastern North America. See also regional entities.
Nuclear power plant
Generating about 14.5-percent of California
Obligation to serve
A regulatory obligation of a utility to provide electric planning services for all customers and to assure adequate supply of electricity now and in the future.
Those hours or other periods defined by NAESB business practices, contract, agreements, or guides as periods of lower electrical demand.
Times when demand for electricity is highest (a.k.a peak demand). Typically on-peak times occur during weekdays during the hottest summer months, when normal demand is high and when air conditioning is operating. Similarly, in some areas on-peak times may be in the winter when high normal demand is combined with high heating-related power use.
Ontario Independent Electricity System OperatorAcronym(s): OIESO
A not-for-profit independent (Canadian) corporation that monitors the system and identifies what is required to maintain reliability in the future, reporting on these recommendations through regular publications. The IESO 1. assesses generation and transmission facilities’ adequacy, 2. prepares the Ontario Reliability Outlook, which reports on the progress of interrelated generation, transmission and demand-side projects underway to meet Ontario’s reliability requirements and 3. coordinates emergency preparedness for the province’s electricity systemSource: ESA Technical Working Group
Markets in which energy end-users can pay to have energy that purchased from a third party transmitted via transmission systems owned by other entities. Open access prevents a transmission owning utility from controlling the energy supply. Open access differs from direct access in that direct access refers to acquisition of actual energy, whereas open access refers only to access to transmission systems used to transport it.Source: ESA Technical Working Group
Open access same time information serviceAcronym(s): OASIS
An electronic posting system that the transmission service provider maintains for transmission access data and that allows all transmission customers to view the data simultaneously.
Open access transmission tariffAcronym(s): OATT
Electronic transmission tariff accepted by the U.S. Federal Energy Regulatory Commission requiring the Transmission Service Provider to furnish to all shippers with non-discriminating service comparable to that provided by Transmission Owners to themselves.
A battery to which nothing is connected.Source: ESA Technical Working Group
The difference in electric potential (voltage) between the terminals of a cell or battery when the circuit is open (i.e., nothing is connected).Source: ESA Technical Working Group
Operating expenseAcronym(s): OPEX
A category of expenditure that a business incurs as a result of performing its normal business operations. One of the typical responsibilities that management must contend with is determining how low operating expenses can be reduced without significantly affecting the firm’s ability to compete with its competitors. Also known as “OPEX”.
A document that identifies specific steps or tasks that should be taken by one or more specific operating positions to achieve specific operating goal(s). The steps in an operating procedure should be followed in the order in which they are presented, and should be performed by the position(s) identified. A document that lists the specific steps for a system operator to take in removing a specific transmission line from service is an example of an Operating Procedure.
The voltage level by which an electrical system is designated and to which certain operating characteristics of the system are related; also, the effective (root-mean-square) potential difference between any two conductors or between a conductor and the ground. The actual voltage of the circuit may vary somewhat above or below this value.
Operations and maintenanceAcronym(s): O&M
Expenses related to operation and maintenance of equipment or facility.Source: ESA Technical Working Group
The cost of an alternative that must be forgone in order to pursue a certain action. Put another way, the benefits you could have received by taking an alternative action.
Any interruption of current flow (and thus electric service) in a T&D system. Note that most parts of the electric grid are designed to allow current flow to be routed around affected parts of the grid to reduce or avoid service interruption. See also forced, planned, sustained, scheduled and unplanned outage.Source: ESA Technical Working Group
A condition involving generation output that exceeds the system demand. Aside from adverse effects on the grid (stability) overgeneration is undesirable because excess energy has no value if it is not put to productive use. In fact, in some cases “negative prices” are used to encourage use of excess energy.Source: ESA Technical Working Group
Overlap regulation service
A method of providing regulation service in which the Balancing Authority providing the regulation service incorporates another Balancing Authority
Chemical reactions resulting in release of electrons by an electrode’s active material. The opposite of reduction.Source: ESA Technical Working Group
Cells or batteries connected as follows: all positive terminals are connected together and all negative terminals are connected together. An important effect is that the output current from cells/battery connected in parallel is additive whereas the voltage remains at the characteristic voltage.Source: ESA Technical Working Group
The maximum power draw from end-user loads during specified times. For example, most utilities experience peak demand during hot summer afternoons.Source: ESA Technical Working Group
An electric supply resource, typically a combustion turbine generator or reciprocating engine, whose primary purpose is to generate electricity when peak demand occurs.Source: ESA Technical Working Group
Performance based ratemakingAcronym(s): PBR
Regulated rate-of-return is established primarily based upon the utility’s “performance objectives,” rather than cost.Source: ESA Technical Working Group
Performance-based regulationAcronym(s): PBR
Regulatory provisions that sets a utility’s authorized rate-of-returns and profit based on the degree to which the utility meets or exceeds specified performance criteria which may include emission control, public benefits, labor practices and cost of service, among others. In some cases utilities that meet PBR criteria may be allowed to reduce or maintain energy prices and in other cases the utility may be allowed to operate under fewer regulatory or legal constraints.Source: ESA Technical Working Group
Phasor measurement unitAcronym(s): PMU
A device that enables synchronized measurement of electrical wave forms on the electricity grid. Synchronization is accomplished using a common time source for synchronization (e.g. global positioning system). That synchronization enables real-time measurements of status/conditions for geographically diverse points within the grid. PMUs may be separate devices or they may be incorporated into a protective relay or other device. PMUs are poised/expected to be an important element of the smarter, more diverse, more distributed electricity grid of the future. PMUs are also known as synchrophasors.Source: ESA Technical Working Group
An interruption of electric generation, transmission or distribution operation which is planned.Source: ESA Technical Working Group
The responsible entity that coordinates and integrates transmission facility and service plans, resource plans, and protection systems.
Plug-in electric vehicleAcronym(s): PEV
An electric vehicle that can be connected to the electric grid for charging and/or to supply electricity to the gridSource: ESA Technical Working Group
Plug-in hybrid electric vehicleAcronym(s): PHEV
A hybrid electric vehicle that can be connected to the electric grid for charging and/or to supply electricity to the gridSource: ESA Technical Working Group
Point of deliveryAcronym(s): POD
A location that the Transmission Service Provider specifies on its transmission system where an Interchange Transaction leaves or a Load-Serving Entity receives its energy.
Point of receiptAcronym(s): POR
A location that the Transmission Service Provider specifies on its transmission system where an Interchange Transaction enters or a Generator delivers its output.
Point to point transmission serviceAcronym(s): PTP
The reservation and transmission of capacity and energy on either a firm or non-firm basis from the Point(s) of Receipt to the Point(s) of Delivery.
The terminal of a battery into which electrons flow, through the load, during cell/battery discharge.Source: ESA Technical Working Group
The stored energy associated with a mass that is related to the mass’ position. See also elastic potential energy and gravitational potential energy.Source: ESA Technical Working Group
The rate at which energy is generated, converted, transmitted, distributed or delivered.Source: ESA Technical Working Group
The level of power that a storage system can provide per unit volume occupied by the system.Source: ESA Technical Working Group
Electronic devices, methods and systems used to convert power with a specific form to power with a desired form. For example, power electronics is used to convert direct current electric power to alternating current electric power and vice versa.Source: ESA Technical Working Group
Power exchangeAcronym(s): PX
A marketplace for sale and purchase of wholesale electricity (energy and capacity).Source: ESA Technical Working Group
the ratio of real power to apparent powerSource: ESA Technical Working Group
Power factor adjustment
A charge levied on commercial and industrial electricity end-users that reflects metered power factor that is lower than a specified threshold.Source: ESA Technical Working Group
Power factor correction
Adjusting the power factor towards unity, through the injection or absorption of reactive poweralso provide power factor correction.Source: ESA Technical Working Group
Power qualityAcronym(s): PQ
A measure of the level of voltage and/or frequency disturbances.
A battery comprised of primary cells. A non-rechargeable battery.Source: ESA Technical Working Group
A cell whose an electrochemical reaction is not intended to be reversible (i.e., once the cell is fully discharged it is not or cannot be recharged. Primary cells may be classified based on the electrolyte involved.Source: ESA Technical Working Group
Pro forma tariff
Usually refers to the standard OATT and/or associated transmission rights mandated by the U.S. Federal Energy Regulatory Commission Order No. 888.
Protective relays, associated communication systems, voltage and current sensing devices, station batteries and DC control circuitry.
Services provided or offered by utilities “for the public good.” Public benefits may include, for example, cost reductions associated with energy efficiency programs, use of renewable energy resources, assistance for low-income customers, research and development, programs that improve environmental quality and services which enhance reliability of transmission systems.Source: ESA Technical Working Group
Public benefits charge
A modest charge added to customer’s electricity billing commensurate with costs related to services that a utility provides “in the public interest.” They apply, for example, if a utility is required—by law and/or regulation—to provide public interest services which may include education, assistance for low-income customers, environmental and efficiency programs and research and development. Before deregulation; public interest charges were collected and managed by the utility, with regulatory oversight or public-interest organizations. After deregulation; it is increasingly common for charges to be placed into a public trust, to be managed by an independent third party or advisory board, possibly with regulatory oversight.Source: ESA Technical Working Group
Public utility commissionAcronym(s): PUC
The state agency that regulates the activities of investor-owned utilities (and also municipal utilities in some states).
The entity that purchases or sells, and takes title to, energy, capacity, and Interconnected Operations Services. Purchasing-Selling Entities may be affiliated or unaffiliated merchants and may or may not own generating facilities.
Qualified facilitiesAcronym(s): QFs
An individual or corporation owning and/or operating a generation facility, but not primarily engaged in the generation or sale of electric power. QFs are either renewable power production or co-generation facilities that qualify under Section 201 of PURPA.
Qualifying facilityAcronym(s): QF
A class of electric energy producer characterized by 1. small-scale “self-generation” for commercial loads and that may generate surplus energy or 2. self-generators that generate excess electric energy, incidental to other activities such as heat production. Such facilities that meet requirements established by the Federal Energy Regulatory Commission’s regarding ownership, power and efficiency may sell electricity to the utility which is required to purchase the energy at a price that is based on the utility’s avoided cost. That arrangement tends to be favorable to the producer. A key driver for establishing this class of producers was to reduce air emissions, increase fuel efficiency and to reduce dependence on imported sources of energy.Source: ESA Technical Working Group
RadialSee: Radial circuit
A transmission line, distribution line, or transmission/distribution subsystem which is not interconnected with other systems. So named because it radiates outward from another transmission system without bridging any other systems.
RampSee: Ramp rateSource: ESA Technical Working Group
1. The rate at which power output can be changed. Typically ramp rate is expressed in units of MW/minute. 2. The rate at which output from a generator or demand associated with loads varies. Ramp rates can involve variation ranging from several percent over a few seconds to significant percentages over timeframes of one or a few minutes. 3. The rate at which power output can be changed. Typically ramp rate is expressed in units % of maximum power per minute. 4. (Schedule) The rate, expressed in megawatts per minute, at which the interchange schedule is attained during the ramp period. 5. (Generator) The rate, expressed in megawatts per minute, that a generator changes its output.Source: ESA Technical Working Group
A proposed ancillary service that involves electric resources whose output can be varied rapidly to offset ramping of other resources. See also ramp rate and ramping.Source: ESA Technical Working Group
The asset (property) value of a given utility. Rate base is used as a benchmark value to determine how much a utility can be permitted to earn (its rate of return). Whether public or private, utilities will likely have debts investments that must be repaid over time, and without a rate base, it is impossible to determine how much income a public utility will require to sustain itself. Rate bases may also used to determine the point at which a private utility in a regulated environment graduates from reasonable profitability to obscene profitability, or to calculate a utility’s worthiness for funds which may be needed for expansion or upgrading of equipment.
An administrative proceeding—and related documents—used by a regulated entity to justify and apply for cost-recovery and rate changes. Rate case proceedings take place before the relevant regulatory agency or committee thereof.Source: ESA Technical Working Group
A group of utility customers that is categorized based on the type of rate structure (tariff) they are subject to.Source: ESA Technical Working Group
Rated electrical operating conditions
The specified or reasonably anticipated conditions under which the electrical system or an individual electrical circuit is intended/designed to operate.
The operational limits of a transmission system element under a set of specified conditions.
The portion of electricity that establishes and sustains the electric and magnetic fields of alternating-current equipment. Reactive power must be supplied to most types of magnetic equipment, such as motors and transformers. It also must supply the reactive losses on transmission facilities. Reactive power is provided by generators, synchronous condensers, or electrostatic equipment such as capacitors and directly influences electric system voltage. It is usually expressed in kiloVoltAmp-reactive (kVARs or MegaVoltAmp-reactive (MVARs).
Reactive supply and voltage control from generation service
Electric supply resources used to supply reactive power to the grid to manage the grid voltage. Typically generators used for this service are equipped with a synchronous condenser. One of six ancillary services specified by the FERC under Order 888. See voltage support.Source: ESA Technical Working Group
The portion of electricity that supplies energy to the load.
Real time pricingAcronym(s): RTP
Prices for wholesale electricity that are specific to the time when the electricity is purchased.Source: ESA Technical Working Group
Present time as opposed to future time. (From Interconnection Reliability Operating Limits standard.)
The competitive generation market controlled and coordinated by the ISO for arranging real-time imbalance power.
Receiving balancing authority
The balancing authority importing the Interchange.
Cells or batteries that can be recharged.Source: ESA Technical Working Group
A somewhat sophisticated circuit breaker that protects electrical T&D systems from overloading, voltage surges and other undesirable phenomena and that can “reclose” once the problem is cleared to restore normal operation. The reclosure process is typically designed so they are prevented from reclosing if the same fault occurs several times in succession over a short period. That reduces the chance of repetitive line faults (i.e. so electric service is not turned off repeatedly, in part to reduce damage to or accelerated wear of electrical equipment. and to avoided temporary outages caused by short duration phenomena like lightning strikes or transmission switching.Source: ESA Technical Working Group
State in which the gases normally formed within the battery cell during its operation, are recombined to form water.
A chemical process that results in the acceptance of electrons by an electrode’s active material. The opposite of oxidation.Source: ESA Technical Working Group
Eight organizations in North America with delegated authority from North American Electric Reliability Corporation (NERC) to safeguard the reliability of the bulk power systems throughout North America. (WECC, MRO, SPP, TRE, FRCC, SERC, RFC and NPCC).Source: ESA Technical Working Group
Regional reliability organization
1. An entity that ensures that a defined area of the Bulk Electric System is reliable, adequate and secure. 2. A member of the North American Electric Reliability Council. The Regional Reliability Organization can serve as the Compliance Monitor.
Regional reliability plan
The plan that specifies the Reliability Coordinators and Balancing Authorities within the Regional Reliability Organization, and explains how reliability coordination will be accomplished.
Regional transmission organizationAcronym(s): RTO
Regional transmission organizations are established to operate the high-voltage interstate transmission system in a reliable, non-discriminatory manner, and to coordinate with other critical entities, such as participating utilities and generators, neighboring RTOs/ISOs and power exchanges. See also Regional Transmission Organizations/Independent System Operators.
Regional Transmission Organizations/Independent System OperatorsAcronym(s): RTO/ISO
Independent System Operators grew out of FERC Orders Nos. 888/889 where the Commission suggested the concept of an Independent System Operator ISO) as one way for existing tight power pools to satisfy the requirement of providing non-discriminatory access to transmission. Subsequently, in Order No. 2000, the Commission encouraged the voluntary formation of Regional Transmission Organizations to administer the transmission grid on a regional basis throughout North America (including Canada). Order No. 2000 delineated twelve characteristics and functions that an entity must satisfy in order to become a Regional Transmission Organization. RTO/ISO regions in the U.S.: CAISO, ERCOT, SPP, MISO, PJM, NYISO and ISO-NE. RTO/ISO regions in Canada: AESO, NBSO and OIESO.
An amount of reserve responsive to Automatic Generation Control, which is sufficient to provide normal regulating margin.
Regulation and frequency response serviceSee: Frequency response
One of six ancillary services specified by the FERC under Order 888.Source: ESA Technical Working Group
The process whereby one Balancing Authority contracts to provide corrective response to all or a portion of the ACE of another Balancing Authority. The Balancing Authority providing the response assumes the obligation of meeting all applicable control criteria as specified by North American Electric Reliability Corporation (NERC) for itself and the Balancing Authority for which it is providing the Regulation Service.
The degree of performance of the elements of the bulk electric system that results in electricity being delivered to customers within accepted standards and in the amount desired. May be measured by the frequency, duration and magnitude of adverse effects on the electric supply.
The entity that is the highest level of authority who is responsible for the reliable operation of the Bulk Electric System, has the Wide Area view of the Bulk Electric System, and has the operating tools, processes and procedures, including the authority to prevent or mitigate emergency operating situations in both next- day analysis and real-time operations. The Reliability Coordinator has the purview that is broad enough to enable the calculation of Interconnection Reliability Operating Limits, which may be based on the operating parameters of transmission systems beyond any Transmission Operator
Reliability coordinator area
The collection of generation, transmission, and loads within the boundaries of the Reliability Coordinator. Its boundary coincides with one or more Balancing Authority Areas.
ReliabilityFirst Inc.Acronym(s): RFC
A not-for-profit company whose mission is to preserve and enhance electric service reliability and security for the interconnected electric systems within the ReliabilityFirst geographic area. See also regional entities.Source: RFC
Contingency operation that provides capacity (power) if a generator or transmission line fails unexpectedly, called after Non-spinning Reserve. Response is typically required 30-60 minutes after the failure. Also known as Supplemental Reserve.
Reserve sharing group
A group whose members consist of two or more Balancing Authorities that collectively maintain, allocate, and supply operating reserves required for each Balancing Authority
Resistive lossesSee: ISource: ESA Technical Working Group
Resource adequacyAcronym(s): RA
The degree to which electric supply resources are capable of delivering the needed energy and power.Source: ESA Technical Working Group
The entity that develops a long-term (generally one year and beyond) plan for the resource adequacy of specific loads (customer demand and energy requirements) within a Planning Authority Area.
The Ramp Rate that a generating unit can achieve under normal operating conditions expressed in megawatts per minute (MW/Min).
The amount of time required for a storage system output to transition from no discharge to full discharge.Source: ESA Technical Working Group
The practice by retail electricity end-users of purchasing electricity from a supplier other than the retail utility and then using utility transmission systems to “wheel in” the purchased energy.Source: ESA Technical Working Group
The amount of revenue required to cover all utility costs—including those related to electric supply, transmission, distribution and customer service—including capital-related expenditures, operating expenses, taxes, interest on and return of debt, and, if applicable, the authorized rate of return on and return of stockholder equity.Source: ESA Technical Working Group
A corridor of land on which electric lines may be located. The Transmission Owner may own the land in fee, own an easement, or have certain franchise, prescription, or license rights to construct and maintain lines.
Exposure to or the existence of potential danger, harm, or loss related to something of value.Source: ESA Technical Working Group
Round trip efficiency
The amount of energy that a storage system can deliver relative to the amount of energy injected into the system during the immediately preceding charge. (Also referred to as efficiency.)Source: ESA Technical Working Group
Rural electric cooperativeSee: Electric cooperativeSource: ESA Technical Working Group
Rural Utilities ServiceAcronym(s): RUS
An organization within the U.S. Department of Agriculture whose purpose is to be the U.S. federal government’s lead agency regarding matters related to rural infrastructure (electricity, water and telecommunications).Source: ESA Technical Working Group
An interruption of electric generation, transmission or distribution operation that are planned well in advance to, for example, undertake regular or routine maintenance or to inspect equipment.Source: ESA Technical Working Group
An entity authorized to submit to the ISO a balanced generation or demand schedule on behalf of one or more generators and one or more end-user customers.
An entity responsible for approving and implementing Interchange Schedules.
The Transmission Service arrangements reserved by the Purchasing-Selling Entity for a Transaction.
Scheduling, system control and dispatch service
An ancillary service involving scheduling of movement of electricity through, out of, within, or into a Control Area. It is provided the operator of the Control Area in which the transaction occurs. One of six ancillary services specified by the FERC under Order 888.Source: ESA Technical Working Group
The structural part of a galvanic cell that restricts the escape of solvent or electrolyte from the cell and limits the ingress of air into the cell.
A battery comprised of secondary cells. A battery that can be recharged numerous times.
A cell whose an electrochemical reaction is reversible (i.e., the cell can be recharged.)Source: ESA Technical Working Group
A device similar to a recloser that serves as a “bypass switch” for sections of the transmission or distribution systems with faults. They remain open (i.e. no current can flow) until there is no voltage on the line, due, for example, to tripping of a breaker or reclosure. When their is a fault in the primary circuit, the sectionalizer switches current flow to another circuit that provides a path around the section with the fault. The use of sectionalizers ensures that service is not interrupted to critical portions of the grid even when serious faults disable the primary transmission path(s).Source: ESA Technical Working Group
Storage discharge that occurs while the battery is in an open-circuit condition.
Sending balancing authority
The Balancing Authority exporting the Interchange.
Cells or batteries connected as follows: positive terminals are connected to the negative terminal of the next cell/battery. An important effect is that the output current from cells/battery connected in series is the same as the current from one cell/battery whereas the voltage of the cells/batteries is additive.Source: ESA Technical Working Group
Electric service line between the utility’s distribution cables and the customer’s home or business. Typically they are comprised of two 120 Volt lines whose output can be combined to produce a 240 Volt service, and a neutral third line. When these three lines are used in the same cable run, they are referred to as triplex cable.Source: ESA Technical Working Group
For a dry cell or battery comprised of dry cells; the amount of time during which the cell/battery can retain a specified percentage of its original energy content, under specified conditions. For example; shelf life might be specified assuming that cell retains at least 90% of its original energy content if stored within a specified temperature range.Source: ESA Technical Working Group
A capacitor or group of capacitors which are placed across an Electric Power line or Electric Appliance to provide a voltage increase or to improve the power factor of the circuit. A switchable shunt may be disconnected from the circuit when conditions warrant, while a fixed shunt is permanently connected to the power line.Source: ESA Technical Working Group
Silicon controlled rectifierAcronym(s): SCR
A semiconductor device that functions as an electrically controlled switch. The SCR is one device type in the family of semiconductors that includes transistors and diodes. The basic purpose of a SCR is to function as a switch that can “switch” power on and off. SCRs do not have any mechanical parts. SCRs consist of a semiconductive path and what is called a bridge. When a voltage is applied across the bridge, the semiconductive path becomes conductive and carries the current until something interrupts the current ahead of the SCR. Then the path becomes semiconductive again. They are used in many electronic appliances. For grid applications they are used on the secondary side of electricity supply transformers, effectively isolating customers’ electric service from the grid. SCRs are considered to be very reliable and inexpensive.Source: ESA Technical Working Group
Sink balancing authority
The Balancing Authority in which the load (sink) is located for an Interchange Transaction. (This will also be a Receiving Balancing Authority for the resulting Interchange Schedule.)
Collectively; devices, practices and protocols that enable rich monitoring and situational awareness and flexible and robust control of various parts of or entire power systems under varying conditions. Among other objectives, Smart Grid is expected to reduce peak demand, increase energy efficiency and increase electric service reliability and power quality.Source: ESA Technical Working Group
Heat and light generated from sunlight.
Source balancing authority
The balancing authority in which the generation (source) is located for an Interchange transaction. (This will also be a Sending balancing authority for the resulting Interchange schedule.)
Southern Electric Reliability CouncilAcronym(s): SERC
A nonprofit corporation responsible for promoting and improving the reliability, adequacy, and critical infrastructure of the bulk power supply systems in all or portions of 16 central and southeastern states. Owners, operators, and users of the bulk power system in these states cover an area of approximately 560,000 square miles and comprise what is known as the SERC Region. See also regional entities.
Southwest Power PoolAcronym(s): SPP
A not-for-profit organization that serves as both the reliability entity and the independent system operator One of nine Independent System Operators/Regional Transmission Organizations (ISOs/RTOs) and one of eight North American Electric Reliability Corporation (NERC) regional entities. SPP is mandated by FERC to ensure reliable supplies of power, adequate transmission infrastructure, and competitive wholesale prices of electricity. See also regional entity and independent system operator.Source: Southwest Power Pool (SPP)
The amount of energy that a storage system can deliver per unit mass of the system.Source: ESA Technical Working Group
The level of power that a storage system can generate per unit mass of the system.Source: ESA Technical Working Group
Spot marketSee: Real-time marketSource: ESA Technical Working Group
The ability of an electric system to maintain a state of equilibrium during normal and abnormal conditions or disturbances.
The maximum power flow possible through some particular point in the system while maintaining stability in the entire system or the part of the system to which the stability limit refers.
“Back-up” electric service provided to end-users that normally produce their own electricity. Historically the price for standby service has been prohibitive, reducing the likelihood that end-users would use on-site generation extensively. As a result of deregulation, utility customers in some areas may be able to purchase “supplementary” energy on the spot market at prices significantly lower than those associated with traditional standby service.Source: ESA Technical Working Group
State of chargeAcronym(s): SOC
The degree to which storage is charged relative to the maximum possible amount of energy that can be stored by the system, typically expressed as a percentage.Source: ESA Technical Working Group
Static VAR compensatorsAcronym(s): SVCs
A static VAR compensator (or SVC) is an electrical device for providing fast-acting reactive power on high-voltage electricity transmission networks. SVCs are part of the Flexible AC transmission system device family, regulating voltage and stabilising the system. Unlike a synchronous condenser which is a rotating electrical machine, a static VAR compensator has no significant moving parts (other than internal switchgear). Prior to the invention of the SVC, power factor compensation was the preserve of large rotating machines such as synchronous condensers or switched capacitor banks.
The energy available in the storage system to perform physical work through the conversion of its chemical or mechanical energy, stated in kWh or MWh.Source: ESA Technical Working Group
Substation onsite power
Power required at substations so there is sufficient power needed to continue operations (e.g. control and communication) during interruptions on the part of the grid where the substation is located.Source: ESA Technical Working Group
An electrical resonant frequency on an alternating-current transmission line that is less than the line frequency, and results from the insertion of series capacitors to cancel out part of the line and system reactance.
Part of an electricity transmission and distribution system whose voltage is lower than that of the transmission system and higher than that of the distribution system. Subtransmission circuits are usually arranged in loops so that a single line failure does not cut off service to a large number of customers for more than a short time. Subtransmission circuits usually involve overhead lines though some circuits are underground. Typical subtransmission voltages range from 69 kV to 115 kV and sometimes as high as 138 kV.Source: ESA Technical Working Group
Supervisory control and data acquisition acquisitionAcronym(s): SCADA
A system of remote control and telemetry used to monitor and control the transmission system.
Supplemental operating reserve
The portion of operating reserve consisting of: 1. Generation (synchronized or capable of being synchronized to the system) that is fully available to serve load within the disturbance recovery period following the contingency event; or 2. Load that is fully removable from the system within the disturbance recovery period following the contingency event. See also operating reserve and synchronized operating reserve.
Supplemental regulation service
A method of providing regulation service in which the Balancing Authority providing the regulation service receives a signal representing all or a portion of the other Balancing Authority
The extra generating capability that an electric utility needs, above and beyond the highest demand level it is required to supply to meet its users needs.Source: California Energy Commission
Supplemental reserve service
One of six ancillary services specified by the FERC under Order 888. See operating reserve and supplemental operating reserve.Source: ESA Technical Working Group
A transient variation of current, voltage, or power flow in an electric circuit or across an electric system.
The de-energized condition of a transmission line resulting from a fault or disturbance following an unsuccessful automatic reclosing sequence and/or unsuccessful manual reclosing procedure.
A substation through which energy is routed from different sources and/or to different customers. Consider a switching station located near a load center that allows the load center to switch between various energy providers. Another example is a switching station that is located near a generation facility that switches some or all of the generator’s output among regions.Source: ESA Technical Working Group
Synchronized Reserve service supplies electricity if the grid has an unexpected need for more power on short notice. The power output of generating units supplying synchronized reserve can be increased quickly to supply the needed energy to balance supply and demand; demand resources also can bid to supply synchronized reserve by reducing their energy use on short notice.Source: PJM Interconnection LLC (PJM)
Synchronized reserve service
One of six ancillary services specified by the FERC under Order 888. See operating reserve and synchronized operating reserve.Source: ESA Technical Working Group
In electrical engineering, a synchronous condenser (sometimes called a synchronous capacitor or synchronous compensator) is a device identical to a synchronous motor, whose shaft is not connected to anything but spins freely. Its purpose is not to convert electric power to mechanical power or vice versa, but to adjust conditions on the electric power transmission grid. Its field is controlled by a voltage regulator to either generate or absorb reactive power as needed to adjust the grid’s voltage, or to improve power factor.
Machines that operate at “synchronous speed” meaning that the rotational frequency (rpms) of the equipment’s rotor matches the frequency of the power system to which it is connected (e.g. 60 cycles per second in the U.S.)Source: ESA Technical Working Group
SynchrophasorSee: Phasor measurement unitSource: ESA Technical Working Group
System operating limit
The value (such as MW, Mar, Amperes, Frequency or Volts) that satisfies the most limiting of the prescribed operating criteria for a specified system configuration to ensure operation within acceptable reliability criteria. System Operating Limits are based upon certain operating criteria. These include, but are not limited to: 1. Facility Ratings (Applicable pre- and post- Contingency equipment or facility ratings) 2. Transient Stability Ratings (Applicable pre- and post-Contingency Stability Limits) 3. Voltage Stability Ratings (Applicable pre- and post- Contingency Voltage Stability) 4. System Voltage Limits (Applicable pre- and post- Contingency Voltage Limits)
An individual at a control center (Balancing Authority, Transmission Operator, Generator Operator, Reliability Coordinator) whose responsibility it is to monitor and control that electric system in real time.
T&D ISee: I
Energy losses that occur within electric transmission and distribution (T&D) systems.Source: ESA Technical Working Group
Any terminal where an electric connection is established. Most commonly a terminal is a connection that draws a rated amount of current from a circuit. Just as a water tap allows one to draw a certain amount of water from the total supply, an electrical tap serves the same function for drawing electricity from a source of supply. Tapping a circuit can mean to 1. run/string a line or cable from a point in a circuit or 2. draw electricity from that circuit.
A device that can increase or decrease a transformer’s operating voltage to vary the amount of current that the transformer draws (taps) from the circuit supplying the electricity.Source: ESA Technical Working Group
Cell or battery charging involving a relatively charge rate (current) when the cell or battery is at a low state of charge and a tapering off of the charge rate (current) as the battery reaches a higher state of charge.Source: ESA Technical Working Group
A document that characterizes types and magnitude of levies that are assessed (e.g. electric service prices) and related terms and conditions such as eligibility. Utility tariffs are amended periodically and are approved by regulatory agencies. Also known as a , tariff schedule.Source: ESA Technical Working Group
The process by which measurable electrical quantities from substations and generating stations are instantaneously transmitted to the control center, and by which operating commands from the control center are transmitted to the substations and generating stations.
The parts of a cell/battery to which the external electric load is connected and through which current flows.Source: ESA Technical Working Group
Test entryAcronym(s): TE
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Texas Reliability EntityAcronym(s): Texas RE
Texas RE develops, monitors, assesses, and enforces compliance with North American Electric Reliability Corporation (NERC) Reliability Standards within the geographic boundaries of the ERCOT region. Texas RE is also authorized by the Public Utility Commission of Texas (PUCT) and is permitted by North American Electric Reliability Corporation (NERC) to investigate compliance with the ERCOT Protocols and Operating Guides, working with PUCT staff regarding any potential protocol violations.
The North American Electric Reliability CorporationAcronym(s): NERC
Mission: Ensure the reliability of the North American bulk power system. North American Electric Reliability Corporation (NERC) is the electric reliability organization (ERO) certified by the Federal Energy Regulatory Commission to establish and enforce reliability standards for the bulk-power system. North American Electric Reliability Corporation (NERC) develops and enforces reliability standards; assesses adequacy annually via a 10-year forecast, and summer and winter forecasts; monitors the bulk power system; and educates, trains and certifies industry personnel. ERO activities in Canada related to the reliability of the bulk-power system are recognized and overseen by the appropriate governmental authorities in that country.
The North American Synchrophasor InitiativeAcronym(s): NASPI
A consortium of government and industry that is working to prevent another major blackout in North America by installing synchrophasors that will provide real-time situational awareness of electric grid conditions by helping to get the most out of projects funded by the Smart Grid Investment Grants awarded as part of the 2009 American Recovery and Reinvestment Act.
The maximum amount of electrical current that a transmission line or electrical facility can conduct over a specified time period before it sustains permanent damage by overheating or before it sags to the point that it violates public safety requirements.
A condition whereby a cell on charge or discharge will destroy itself through internal heat generation caused by high overcharge or high rate of discharge or other abusive conditions.
Electrical energy supplied by 3 out of phase sinusoidal voltage wave forms that are 120 degrees out of phase. Usually used in industrial applications and may have some energy efficiency characteristics.Source: ESA Technical Working Group
A solid-state semiconductor device that incorporates four layers of alternating N and P-type semiconductor material. Thyristors act as “bistable switches” that conduct when a current trigger is applied to their “gate,” They continue to conduct until the voltage across the device is reversed (i.e. while they are forward biased). See also silicon controlled rectifier.Source: ESA Technical Working Group
A circuit connecting two Balancing Authority Areas.
Time of use (energy prices)Acronym(s): TOU
Price for electric energy that is specific to the time (season, day of week, time-of-day) when the energy is purchased.Source: ESA Technical Working Group
Total harmonic distortionAcronym(s): THD
The ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. See harmonic distortion.
Total transfer capabilityAcronym(s): TTC
The amount of electric power that can be moved or transferred reliably from one area to another area of the interconnected transmission systems by way of all transmission lines (or paths) between those areas under specified system conditions.
The measure of the ability of interconnected electric systems to move or transfer power in a reliable manner from one area to another over all transmission lines (or paths) between those areas under specified system conditions. The units of transfer capability are in terms of electric power, generally expressed in megawatts (MW). The transfer capability from
Energy that couples to other parts of the system, typically appearing as a short burst of oscillation of possibly various frequencies
An interconnected group of lines and associated equipment for the movement or transfer of electric energy between points of supply and points at which it is transformed for delivery to customers or is delivered to other electric systems.
Transmission access charges
Fees/charges imposed on parties seeking to use another party’s transmission system to “wheel” electricity from the source to the end-use location.Source: ESA Technical Working Group
A limitation on one or more transmission elements that may be reached during normal or contingency system operations.
A system of structures, wires, insulators and associated hardware that carry electric energy from one point to another in an electric power system. Lines are operated at relatively high voltages varying from 69 kV up to 765 kV, and are capable of transmitting large quantities of electricity over long distances.
The entity responsible for the reliability of its “local” transmission system, and that operates or directs the operations of the transmission facilities.
The entity that develops a long-term (generally one year and beyond) plan for the reliability (adequacy) of the interconnected bulk electric transmission systems within its portion of the planning authority area.
Transmission reliability marginAcronym(s): TRM
The amount of transmission transfer capability necessary to provide reasonable assurance that the interconnected transmission network will be secure. TRM accounts for the inherent uncertainty in system conditions and the need for operating flexibility to ensure reliable system operation as system conditions change.
Services provided to the transmission customer by the transmission service provider to move energy from a point of receipt to a point of delivery.
Transmission service providerAcronym(s): TSP
The entity that administers the transmission tariff and provides transmission service to transmission customers under applicable transmission service agreements.
Electrochemical cell or battery charging involving a continuous or an intermittent constant-current supply which keeps the cell/battery fully charged while the cell/battery is not being used (discharged).Source: ESA Technical Working Group
Separating a utility
Unit commitment (generation)
A specific generating unit that has been “committed” to provide electricity. The unit commitment process involves a determination of which generator will be needed to serve the expected load during a specified period of time. Often unit commitment is scheduled one day in advance. A generation unit is said to be committed once operation of the generator starts although a committed unit may not be dispatched unless it is actually needed.Source: ESA Technical Working Group
An interruption of electric generation, transmission or distribution operation which is not scheduled.Source: ESA Technical Working Group
Delay the need to replace or enhance equipment within the grid, usually by using a power source or load management to reduce the peak load served by the equipment to below the equipment’s rated power. See also life extension and transmission and distribution upgrade deferral.Source: ESA Technical Working Group
A specific deployment of a storage system for one or more applications and/or one or more benefits.Source: ESA Technical Working Group
Utility distribution companyAcronym(s): DISCO
A distribution wired business and a regulated retailer who serves end-use customers
One or more individual benefits associated with a specific use. A value proposition is said to be attractive if the total value of all benefits exceeds all costs, including required return on investment, if any.Source: ESA Technical Working Group
Costs which change in proportion to the amount of energy generated or used. Variable costs may be associated with the cost for fuel, variable operating expenses, variable equipment and facility maintenance and depreciation from equipment wear.Source: ESA Technical Working Group
Vertically integrated utility
A utility that owns and operates all elements of the utility infrastructure and that provides all customer services.Source: ESA Technical Working Group
Virtual power plantAcronym(s): VPP
A combination of electric resources including distributed generation and storage and demand response that can be aggregated and operated in concert such that they operate as if they were one entity (i.e. a virtual power plant). The aggregated resources may be used to manage the supply and demand balance and/or they may used as a merchant or wholesale electric resource.Source: ESA Technical Working Group
In electric power transmission and distribution, volt-ampere reactive (var) is a unit used to measure reactive power in an AC electric power system. VAR control manages the reactive power, usually attempting to get a power factor near unity (1).Source: Smart Distribution Wiki
VAR optimization manages the reactive power, usually attempting to get a power factor near unity (1).Source: Smart Distribution Wiki
Voltage conservationSee: Conservation voltage reduction
Western Electric Coordinating CouncilAcronym(s): WECC
The organization responsible for coordinating and promoting bulk electric system reliability in the Western Interconnection. In addition, WECC provides an environment for coordinating the operating and planning activities of its members as set forth in the WECC Bylaws.
A cell whose electrolyte exists in liquid form so it is free to flow and move within the cell.Source: ESA Technical Working Group
The process of converting kinetic energy from the wind (air in motion) into different types of energy, including thermal, mechanical and electrical, with wind turbines..