Glossary by "T"

  • 558

    T&D I

    See: I

    Energy losses that occur within electric transmission and distribution (T&D) systems.

    Source: ESA Technical Working Group
  • 559


    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.

  • 560

    Tap changer

    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
  • 561

    Taper charge

    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
  • 562


    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
  • 564


    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.

  • 565


    The parts of a cell/battery to which the external electric load is connected and through which current flows.

    Source: ESA Technical Working Group
  • 17

    Test entry

    Acronym(s): TE

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  • 566

    Texas Reliability Entity

    Acronym(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.  

  • 567

    The North American Electric Reliability Corporation

    Acronym(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.

  • 568

    The North American Synchrophasor Initiative

    Acronym(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.

  • 569

    Thermal rating

    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.

  • 570

    Thermal runaway

    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.  

  • 571

    Three-phase line

    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
  • 572


    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
  • 573

    Tie line

    A circuit connecting two Balancing Authority Areas.

  • 574

    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
  • 576

    Total harmonic distortion

    Acronym(s): THD

    The ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency. See harmonic distortion.  

    Source: Wikipedia
  • 577

    Total transfer capability

    Acronym(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.

  • 578

    Transfer capability

    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  

  • 579


    Energy that couples to other parts of the system, typically appearing as a short burst of oscillation of possibly various frequencies

    Source: Wikipedia
  • 580


    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.  

  • 581

    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
  • 582

    Transmission constraint

    A limitation on one or more transmission elements that may be reached during normal or contingency system operations.

  • 583

    Transmission line

    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.

  • 584

    Transmission operator

    The entity responsible for the reliability of its “local” transmission system, and that operates or directs the operations of the transmission facilities. 

  • 585

    Transmission planner

    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.

  • 586

    Transmission reliability margin

    Acronym(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.

  • 587

    Transmission service

    Services provided to the transmission customer by the transmission service provider to move energy from a point of receipt to a point of delivery.

  • 588

    Transmission service provider

    Acronym(s): TSP

    The entity that administers the transmission tariff and provides transmission service to transmission customers under applicable transmission service agreements.  

  • 589

    Trickle charging

    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