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    Glossary of terms

    Common electricity terms, explained

    Want to know the meaning of the terms we use? You’ll find explanations right here.

    For terms used in independent system operator rules, or Alberta Reliability Standards, read our Consolidated Authoritative Document Glossary.

    Start typing a term to filter, or browse terms alphabetically.

    • Alternating current (AC)

      A current that flows alternately in one direction and then in the reverse direction. In North America, the standard for alternating current is 60 complete cycles each second. Cycles per second is also referred to as Hertz (Hz).

    • Baseload generation

      Generation capacity normally operated to serve load on an around-the-clock basis.

    • Biomass

      Organic matter that is used to produce synthetic fuels or is burned in its natural state to produce energy. Biomass fuels include wood waste, peat, manure, grain by-products and food processing wastes.

    • Brownfield

      Land previously or currently used for industrial or certain commercial purposes.

    • Capacitor/capacitor bank

      A device used to control voltages by eliminating a voltage drop in the system.

    • Capacity market model

      A market model where generators are paid for having generation available to supply, whether or not any energy is actually produced and supplied.

    • Carbon offset

      A financial instrument representing a reduction in greenhouse gas (GHG) emissions.

    • Circuit

      A conductor or a system of conductors through which electric current flows.

    • Cogeneration

      The simultaneous production of electricity and another form of useful thermal energy used for industrial, commercial, heating or cooling purposes.

    • Combined-cycle

      A system in which a gas turbine generates electricity and the waste heat is used to create steam to generate additional electricity using a steam turbine.

    • Competitive process

      A tendering process that enables all qualified bidders to compete in a fair, transparent and open environment for the right to develop, design, build, finance, own, operate and maintain major transmission infrastructure in Alberta. 

    • Conductor

      A metallic wire or combination of wires through which electric current is intended to flow.

    • Control area

      A defined region of the electricity grid for which supply and demand are kept in balance by the control area’s system operator.

    • Converter station

      A location where electric energy is converted to direct current (DC) from alternating current (AC) or vice versa.

    • Cooling Degree Day (CDD)

      The number of degrees that a day’s average temperature is above a threshold temperature.

    • Cost-of-service model

      A traditional electric utility model where a utility is allowed to set rates based on the cost of providing service to customers and the right to earn a limited profit, all as set by a regulator such as a utilities commission.

    • Customer sectors

      Types of electric load classified according to type of use. Four sectors commonly used are residential, commercial, farm and industrial.

    • Cutplanes

      An imaginary line, often depicted on a map, that cuts across the transmission lines connecting two or more areas. The loading on these lines is summed together to measure the power flow across the cutplane.

    • De-rate

      A reduction in a generating unit’s or other piece of electric equipment’s net capacity.

    • Deregulation

      An absence of a monopoly or central planning, where consumers can choose their supplier, similar to other common household service providers.

    • Direct assigned to TFOs

      In a regulated monopoly, projects are assigned to a transmission company based on their service territory. 

    • Direct current (DC)

      Current that flows continuously in the same direction (as opposed to alternating current). The current supplied from a battery is direct current.

    • Double circuit

      A line of supporting structures that carries two power circuits.

    • Dynamic stability

      The characteristic of a power system that, when disturbed from an original state through events such as short circuits, allows recovery to a normal state through damping of the oscillations generated by the disturbance events.

    • Emission intensity

      The ratio of a specific emission (such as carbon dioxide) to a measure of energy output. For the electricity sector, emission intensity is usually expressed as emissions per megawatt hour (MWh) of electricity generated.

    • Energy-only

      A market model where power plants are paid only for the energy they actually produce.

    • Equilibrium price

      A market price established through competition at the point where the quantity sought by buyers is equal to the amount produced by sellers. This price is also often called the competitive price or market clearing price.

    • Frequency excursion

      Any deviation, up or down, of the base frequency of a power system. In North America, the base power system frequency is 60 Hertz (60 cycles per second).

    • Gas turbine

      See simple-cycle.

    • Geothermal energy

      Where the prime mover is a turbine driven either by steam produced from hot water or by natural steam that derives its energy from heat found in rocks or fluids beneath the surface of the Earth.

    • Gigawatt (GW)

      One billion watts.

    • Gigawatt hour (GWh)

       One billion watt hours.

    • Greenfield

      Land being considered for development that has not previously been used for commercial or industrial purposes.

    • Greenhouse gas (GHG) emissions

      Gases that trap the heat of the sun in the Earth’s atmosphere, producing a greenhouse effect.

    • Gross domestic product (GDP)

      One of the measures of national income and output for a given country’s economy. GDP is defined as the total market value of all final goods and services produced within the country in a given period of time (usually a calendar year). It is also considered as the sum of the value added at every stage of production (the intermediate stages) of all final goods and services produced within a country in a given period of time and is given a monetary value.

    • Heat rate

      A measure of generating plant thermal efficiency generally expressed as units of energy input per unit of energy output.

    • Heating Degree Day (HDD)

      The number of degrees that a day’s average temperature is below a threshold temperature.

    • High-voltage direct current (HVDC)

      The transmission of electricity using direct current.

    • Holding restrictions

      A legislated limit on the market share a company may hold.

    • Index to the pool price

      A premium or a discount to the pool price.

    • Injection-withdrawal model

      A market model where access to the transmission system is allocated based on consumption (for loads) and dispatch (for suppliers).

    • Kilowatt

      1,000 watts.

    • Kilowatt hour (KWh)

      1,000 watt hours. Imagine 10 lamps, lit with 100-watt bulbs for one hour. At the end of the hour, the lamps will have used one kilowatt hour of electricity. Electricity retailers typically bill households in kilowatt hours.

    • Levelized unit electricity cost (LUEC)

      The constant price required to cover all expenses incurred over the lifetime of a generating unit.

    • Load (electric)

      The amount of electric power used by devices connected to an electric system.

    • Load factor

      A measure of the average load, in kilowatts, supplied during a given period. It is generally used to determine the total amount of energy that would have been used if a given customer’s maximum load was sustained over an extended time period and, through comparison, show what percentage of potential load was actually used.

    • Megawatt (MW)

      One million watts.

    • Megawatt hour (MWh)

      One million watt hours. A megawatt hour measures the amount of electricity a generator produces in one hour.

    • Merchant transmission

      Transmission line(s), constructed by proponents that are not regulated utilities, for the purpose of selling transmission capacity to third parties such as generators or load customers who wish to make transactions over the line.

    • Nuclear generation

      Where heat produced in a reactor by the fissioning of nuclear fuel is used to create steam in a boiler. This steam is then used to drive a turbine, which in turn drives the electric generator.

    • Offset

      See carbon offset.

    • Parallel path

      Electric power flows on all interconnected parallel paths in amounts inversely proportional to each path’s resistance. This also refers to the flow of electric power on one electric system’s transmission facilities resulting from scheduled electric power transfers between other electric systems.

    • Peak load/demand

      The maximum power demand (load) registered by a customer or a group of customers or a system in a stated time period. The value may be the maximum instantaneous load or, more usually, the average load over a designated interval of time such as one hour, and is normally stated in kilowatts or megawatts.

    • Peaking capacity

      The capacity of generating equipment normally reserved for operation during hours of the highest daily, weekly, or seasonal loads. Some generating equipment may be operated at certain times as peaking capacity, and at other times to serve loads on an around-the-clock basis.

    • Power Pool of Alberta

      The not-for-profit entity responsible for the operation of the wholesale electricity market from 1998 through 2002.

    • Premium price

      Price paid to an operating reserve provider that gives the AESO the option to call on the reserve if required.

    • Price fidelity

      A price that reflects economic fundamentals, free from distortion or intervention.

    • Price-quantity pairs

      Price-sensitive bid block information that consists of a quantity of megawatts and the available dollar price for the megawatts.

    • Service territories

      Geographic areas of the province served by a regulated electricity provider.

    • Simple-cycle

      Where a gas turbine is the prime mover in a plant. A gas turbine consisting typically of one or more combustion chambers where liquid or gaseous fuel is burned. The hot gases are passed to the turbine where they expand, driving the turbine that in turn drives the generator.

    • Single circuit

      A transmission line where one circuit is carried on a set of structures (poles or lattice towers).

    • Solar (power)

      A process that produces electricity by converting solar radiation into electricity or to thermal energy to produce steam to drive a turbine.

    • Substation/switching station

      A facility where equipment is used to tie together two or more electric circuits through switches (circuit breakers). The switches are selectively arranged to permit a circuit to be disconnected or to change the electric connection between the circuits.

    • T-2

      Two hours prior to the delivery hour, when the ability to change offers in the market is closed.

    • Tap

      A point of connection along a transmission line between substations.

    • Thermal overload

      A condition where the thermal limit of a piece of electrical equipment such as a conductor or transformer is exceeded.

    • Transformer

      An electrical device for changing the voltage of alternating current.

    • Transmission losses

      Energy that is lost through the process of transmitting electricity. 

    • Transmission path

      One or more transmission lines that form the transmission connection between two points on the system.

    • Transmission tag(s)

      An electronic identifier which contains specific transactional information on transmission, distribution and retail operations.

    • Vertically integrated

      In the case of electricity, a vertically integrated company owns generation, transmission, distribution and retail operations.

    • Voltage

      The difference of electrical potential between two points of an electrical circuit expressed in volts. It is the measurement of the potential for an electric field to cause an electric current in an electrical conductor. Depending on the amount of difference of electrical potential, it is referred to as extra low voltage, low voltage, high voltage or extra high voltage.

    • Voltage stability

      Operation within acceptable voltage ranges. Normal voltage limits are defined as the operating voltage range on the interconnected system that is acceptable on a sustained basis. Emergency voltage limits are defined as the operating voltage range on the interconnected system that is acceptable for the time sufficient for system adjustments to be made following a facility outage or system disturbance.

    • Voltage violation

      A measured or calculated condition where the voltage at a point on the transmission system is outside the acceptable limits as described in the criteria.

    • Watt

      The unit of power equal to one joule of energy per second. It measures a rate of energy conversion. A typical household incandescent light bulb uses electrical energy at a rate of 25 to 100 watts.

    • Watt hour (Wh)

      An electrical energy unit of measure equal to one watt of power supplied to or taken from an electric circuit steadily for one hour.

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