Glossary by "A"

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    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.

  • 128


    See: Diabatic

    Of, relating to, or being a reversible thermodynamic process that occurs without gain or loss of heat and without a change in entropy. 

  • 134

    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.

  • 135

    Alberta Electric System Operator

    Acronym(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.

  • 136

    Allowance for funds used during construction

    Acronym(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
  • 139

    Alternating current

    Acronym(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
  • 138

    American National Standards Institute

    Acronym(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.

  • 140

    Amp hours

    See: Ampere hours
    Source: ESA Technical Working Group
  • 141

    Ampere hours

    See: 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
  • 142

    Ancillary service

    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.)

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    See: American National Standards Institute
  • 143

    Area control error

    Acronym(s): ACE

    The instantaneous difference between a Balancing Authority

  • 144

    Asset utilization

    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
  • 145

    Automatic generation control

    Acronym(s): AGC

    Equipment that automatically adjusts generation in a Balancing Authority Area from a central location to maintain the Balancing Authority

  • 146

    Available transfer capability

    Acronym(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.

  • 147

    Average cost

    The revenue requirement of a utility divided by the utility.