Electric terminology index

A

Allocation.

Power generation or consumption commitment resulting from a market.

Ancillary services.

Services which are necessary to ensure the electricity supply under the suitable conditions of security, quality and reliability. These include: primary regulation, secondary regulation reserve, tertiary regulation and voltage control of the transmission grid (in the future the Service Restoration will be developed as an ancillary service).

Auto-producer.

A natural or legal person who generates electricity mainly for own use. Under the terms of 2818/1998 RD this translates into an average annual minimum of own consumption equivalent to:

30% of the electrical energy produced if the power of the installation is inferior to 25 MW.
50% of the electrical energy produced if the power of the installation is equal or superior to 25 MW.

In order that the electrical surpluses of these facilities may be included under the special regime, they must be included in one of the following groups:

Waste energy power stations.
Co-generation power stations.

B

Bay.: A set of equipment comprising of switches, switchgear, measurement and protection tools whose purpose is to manoeuvre and protect a circuit (line, transformer, etc.).
Bilateral contracts.: The producers, auto-producers, external agents, distributors, traders, consumers or representatives of whichever of them, as participants in the production market may formalise bilateral contracts regarding the physical delivery of an electrical energy supply.
Block.: Energy bid by a Bidding Unit for one specific hour within a market session. For certain types of bids (secondary and tertiary), several blocks per hour are allowed.
Busbar.: The power plant busbar, is that point beyond the generator but prior to the voltage transformation point in the plant switchyard, it is the starting point of the electric transmission system. The nominal net electrical output is measured at these points and the electricity for auxiliary and house loads consumed in any way related to the generation are deducted.

C

Capacity auction.: Process used to allocate interconnection capacity based on market mechanisms by means of explicit annual auctions, monthly auctions, daily and intraday auctions.
Capacity payments.: Regulated payment to finance the medium and long-term power capacity service, offered by the generation facilities to the electricity system.
Closed-cycle pump storage generation.: Production of electrical energy carried out by the hydroelectric power stations whose higher elevation reservoir does not receive any type of natural contributions of water, but uses water solely from the lower elevation reservoir. When the water is released, from the higher elevation reservoir, energy is created by the downflow, and later the water is pumped back from to the the lower elevation reservoir to the upper reservoir, process that usually takes place overnight when national electricity demand is at its lowest.
Combined cycle.: Technology for the generation of electrical energy in which two thermodynamic cycles coexist within one system: one involves the use of steam, and the other one involves the use of gas. In a power station, the gas cycle generates electrical energy by means of a gas turbine and the steam cycle involves the use of one or more steam turbines. The heat generated by combustion in the gas turbine is passed to a conventional boiler or to a heat-recovery element which is then used to move one or more steam turbines, increasing the yield of the process. Electricity generators are coupled to both the gas and steam turbines.
Commercial exchange capacity.: Technical maximum import and export capacity of a country's power system with a neighbouring country's system, and that is compatible and complies with the safety criteria established for each system.
Compensatory energy.: Energy withdrawn from the market matching as compensation for the energy added due to grid restrictions, or vice versa.
Congestion incomes.: Revenues derived from the allocation of interconnection capacity, destined in the first instance to guarantee the real availability of the assigned power and the rest will be included in the income/costs for the calculation of the access tariffs.
Congestion: A situation in which the link which interconnects two national transmission grids is not able to accept all the resulting physical flows of the international trade which has been requested by market participants. This is done through bilateral contracts or as a result of the Market Splitting process, due to an insufficient interconnection capacity of the elements and/or the own national transmission grids in question.
Consumers.: Natural or legal persons who buy energy for their own use. Those consumers who acquire energy directly from the production market are known as Direct Market Consumers.
Consumption of pumps.: Electrical energy used by pumped storage hydroelectric plants for elevating water from the lower to the upper reservoir for the generation of electricity.
Control band.: Energy band established by the system for controlling and maintaining the generation-demand balance, correcting unintentional deviations which take place during operation in real time with the European system, or of the frequency deviations of the system with respect to the programmed values.
Control deviations.: Deviations which occur between two electrical systems and are measured as the difference between the scheduled international exchanges and the physical international exchanges.
Coordinated Balancing Action (also called Counter Trading).: Programme of exchanging energy between two electricity systems. This is established in real time and is carried out in a coordinated way between both system operators. This is super-imposed on the firm exchange programmes, upholding these, in order to solve a congestion situation identified in real time in the interconnection.

D

Daily horizon.: Limit of 24 hours for which the different hourly programmes are devised. A weekly horizon also exists which considers the following seven days and the rolling annual horizon, which considers the next 12 months, with a weekly breakdown.
Daily market.: This is the market in which the purchasing and sales transactions of electrical energy for the following day are carried out.
Demand at busbar.: Energy injected in to the transmission grid from the ordinary and special regime power stations and imports, after deducting the pumping consumption and exports. In order to transport this energy to the consumption points it would be necessary to remove the losses originated in the transmission and distribution grid.
Deviation management.: The mechanism of deviation management is an optional service managed and remunerated by market mechanisms. The objective is to resolve the deviations between generation and demand superior to 300 MWh which could appear in the period between the end of one intraday market and the beginning of the next intraday market horizon.
Discharging.: A situation in which a transmission grid facility (line, transformer, busbar, etc.) is disconnected from the rest of the electricity system and, therefore, does not allow the flow of electricity through it. Additionally, the facility during unloading is earthed at one or more points with the purpose of assuring that their voltage differential remains at zero. This way, works of any type can be carried out on the element without risking the security of the people carrying them out.
Disparo (Trigger).: Non-programmed interruption of the electricity supply.
Distributors.: Those mercantile societies which have the function of distributing electrical energy, as well as to construct, maintain and operate the distribution facilities to required to transfer and distribute the energy at the consumption points.

E

Electricity control centre.: This is the centre responsible for the coordination, operation and supervision of the security of the whole of the Spanish electricity system. Amongst its functions are the scheduling of the coverage for electricity demand and programming of international exchanges, as well as zone operation and remote control. It is also the sole regulator of the Peninsular Shared Control (RCP). More information ...
Energy capability factor.: The ratio of energy capability to mean energy capability, and both referred to the same period and hydroelectric generation set.
Energy capability.: The energy capability or potential energy of a hydro-electric head installation during a given period of time is the maximum quantity of electrical energy which all the observed corrected inflows, limited to the plant capacity flow, would enable it to produce under the most favourable conditions.
External agents.: Are those introducing electrical energy in to or taking electrical energy from exterior systems. This is done under the terms set out in articles 9 and 13 of Law 54/1997. Law 17/2007 establishes that, as of 2008, the figure of the external agent no longer exists and that its role is now included in that of the commercial agent. The application of this measure requires prior legal development.

F

Functioning base programme (PBF).: Is the result of aggregating to the base matching programme (resulting from the daily market), the special regime energy purchased by distributors and the bilateral contracts executed. It also includes the breakdown of the generation anticipated by the group of generators. This breakdown is a pre-requisite that is necessary in order to perform the PBF security analysis.

G

Generation consumption.: Energy used by the auxiliary elements of power stations, necessary for the everyday functioning of the production facilities.
Generation market.: This is comprised of the set of commercial purchase transactions and the sale of energy and other services related to the supply of electrical energy. It is structured on forward markets, daily market, intraday market, non-organised markets and system adjustment services, understanding as such the resolution of technical restrictions of the system, ancillary services and deviation management.
Generation-consumption deviations.: These are the deviations originated by the modifications in the generation schedule due to the total or partial non-availability of one or several generators, variations in demand forecast of the energy buying agents, or by a new demand forecast carried out by the System Operator and which differs from the total demand matched resulting from the previous session of the Intraday Market.
Generator terminals.: Are the terminals of the main and auxiliary generator/s. The gross electrical energy production is measured at the generator terminals.
Generic units.: Programming units used to conduct operations in the market as a portfolio (by company) in the daily market and bilateral contracts.

H

Hourly programmings.

Chronologically, these are the different demand forecasts in the daily horizon.

Base daily programme (PBC): Daily generation and demand programme, with hourly breakdown, carried out by the Market Operator based on the matching process between generation and demand bids received from market agents. This programme also includes, in an individualised manner, the programmed energy excepted from the obligation to present bids in the daily market.
Provisional viable daily programme (PVP): Daily programme, with hourly breakdown, which incorporates the modifications introduced in the PBC to solve technical restrictions.
Definitive viable daily programme (PVD): Daily programme, with hourly breakdown, in which the performed allocations of secondary regulation reserve have been included.
Final hourly programme (PHF): Programming established by the Market Operator resulting from the matching of bids for the sale and purchase of electrical energy formalised for every period of programming as a result of the viable daily programme and of the matching of the successive intraday markets.
Operative hourly programme (PHO): Operative programme which the System Operator establishes each hour until the end of the programming horizon and that is published 15 minutes before each change of hour.

Hydroelectric reserves.

The hydroelectric reserve of a reservoir is the quantity of electrical energy that could be produced in its own power plant and in all the power plants situated downstream, with the total drainage of its current useable water reserves and providing that drainage occurs without natural contributions. The annual regime reservoirs are those in which complete drainage would take place in less than one year. Hyper-annual regime reservoirs are those in which the total drainage time takes more than one year.

I

IFE Rules.: Rules that establish the terms and conditions which govern allocation, by means of auctions, of the capacity available in both directions in the France-Spain interconnection.
Installed power.: Maximum power that a production unit can reach, during a determined period of time, measured at the generator terminals.
International physical exchanges.: The movements of energy which have taken place across lines of international interconnection during a certain period of time. It includes the loop flow of energy as a consequence of the grid design.
International programmed exchanges.: These are the programmes that are established between two electricity systems as a consequence of a set of programmed individual transactions in the market or by means of bilateral contracts.
Interruptibility.: Is a demand management tool managed by Red Eléctrica as system operator and used to provide an efficient and rapid response to the needs of the electricity system. The concept of interruptibility has changed into that of demand management in which large consumers who acquire energy through the electricity market can take part and establish the corresponding service level contracts with the system operator. These companies obtain discounts on their invoices in exchange for a reduction in their electrical consumption, upon demand, and under special circumstances as determined by the system operator. In any case, the reductions of consumption to which these consumers must agree to are typified in the regulation and have as fundamental variables, the notice period, its duration and the number of times it can happen in an electrical year (November 1 - October 31).
Intraday market.: The objective is to manage the adjustments occuring in the generation and demand of energy which may be produced after having fixed the daily market.
IPE Rules.: Rules that establish the terms and conditions which govern the allocation, by means of auctions, of the capacity available in both directions in the Portugal-Spain interconnection.

L

Load factor.: Measures the relationship between the energy produced during a period of time and that which would have been produced in this period working at normal power.

M

Marginal price.: Price of the last sell offer which was necessary to be assigned in order to cover the demand in a market session. This price is the one which all the producers receive and the one which all the consumers who participate in this session pay.
Market agent.: Entity which may access the Spanish electricity market as a participant, not just to buy energy, but also to sell it. The following may act as market agents: electricity producers, distributors and commercial agents, qualified electricity consumers, and also companies or consumers who reside in other countries and have the external agent qualification.
Market clearing.: Daily generation and demand programme, with hourly breakdown, carried out by the Market Operator based on the matching process between generation and demand bids received from market agents. This programme also includes, in an individualised manner, the programmed energy excepted from the obligation to present bids in the daily market.
Market Operator.: Mercantile society which assumes the management of the bid system for the purchase and sale of electrical energy in the daily and intraday market under the established regulations.
Market splitting.: Management mechanism for the exchange capacity between two or more electricity systems which is carried out simultaneously with the Iberian generation market and uses as its criteria the economic efficiency of the spare capacity between the electricity systems. In the case of congestion between the systems, the market splits into zones of differing price. In the contrary case, an overall unique price for the market exists.
Measured deviation.: Difference between the energy measured at the busbars and the energy scheduled in the market.
Measured deviations to lower.: Measured deviations to lower are those which result when the production measured at the busbar is smaller than that scheduled in the market or when the consumption measured at the busbar is higher than that scheduled in the market, therefore the system must manage that difference by increasing production through the adjustment markets in real time.
Measured deviations to raise.: Measured deviations to raise are those which result when the production measured at the busbar is greater than that scheduled in the market or when the consumption measured at the busbar is lower than that scheduled in the market, therefore the system must manage that difference by reducing production through the adjustment markets in real time.

N

National demand in free market.: Electrical energy demand (measured at busbar) of the consumers on the peninsula who directly contract energy from a trader or in the market.
National demand in regulated market.: Electrical energy demand (measured at busbar) of the consumers on the peninsula who contract energy from with an energy distributor on a tariff.
Net energy.: Maximum energy which a production unit can reach measured on exiting the power plant, that is to say, deducting the electricity for auxiliary, pumping and house loads consumed in any way related to the generation.
Net generation.: Production of energy measured at the generator terminals, minus the consumption in the auxiliary services and the losses in the transformers.
Net national consumption.: This is energy introduced into the electrical transmission grid from the ordinary regime power plants (conventional), special regime (cogeneration and renewables) and from the balance of the international exchanges. In order to transfer this energy to the point of consumption it would be necessary to deduct the losses originating from the transmission and distribution grid.
Non-availability factor.: Relationship between the energy that has not been produced due to shutdowns or power reductions, scheduled or non-scheduled, attributable to the energy that could have been produced during the same period working at nominal power.
Non-renewable energies.: Those obtained from fossil fuels (liquid or solid) and their derivatives.
Non-supplied energy (NSE).: This is the energy not introduced into the electricity system due to service interruptions occurred in the transmission grid.

O

Offer.: Set of blocks associated to a Bidding Unit for a certain session of the market.
Operation Markets.: The objective is to adapt the resulting generation programmes for the daily and intraday markets to the technical needs of quality and security required by the supply of electrical energy. These are composed of the solution of technical restrictions, the allocation of the ancillary services and deviation management. These markets are managed by Red Eléctrica in its role as system operator.
Ordinary regime.: The production of electrical energy from all those facilities which are not included under the special regime.

P

Participant.

Entity which participates in the capacity allocation auctions, buying physical capacity rights (PCR) or later selling them directly to other entities.

These entities are subject to the arranged operating (P.O. 4.1 and P.O. 4.2) and in the Rules of Capacity Allocation of the France-Spain Interconnection (IFE Rules) or Rules of Capacity Allocation of the Portugal-Spain Interconnection (IPE Rules).

The participants are the counterparts of the respective TSO in the Declaration of Acceptance of Rules IFE/IPE.

Power guarantee.

Regulated payment that is included in the price of the peninsular demand to guarantee the availability of sufficient power, in the long term, to cover of the supply of electrical energy. Since 1 January of 2008 it has been replaced by the Capacity Payment whose object is to guarantee that there exists sufficient available power to cover the supply of electrical energy in all of the grid nodes, both in the medium and long term.

Price.

Hourly value of the generation/demand balance resulting from a market session.

Producible energy.

Maximum quantity of electrical energy that theoretically could be produced considering the water supplies registered during a specific period of time and once the supplies used for irrigation or uses other than the production of electrical energy have been deducted.

Producible hydroelectric index.

This is the quotient between the producible energy and the average producible energy, both related to the same period and to the same hydroelectric equipment.

Producible hydroelectric.

Maximum quantity of electrical energy that theoretically could be produced considering the water supplies registered during a specific period of time and once the supplies used for irrigation or uses other than the generation of electrical energy have been deducted.

Production at busbars.

Energy measured at the generator terminals having deducted the electricity for auxiliary, pumping and house loads consumed in any way related to the generation.

Production at generator terminals.

The electricity production of a generation unit, measured at the generator terminals.

Production unit.

Thermal group, pumping power station, management unit of hydroelectric power stations or management unit of a set of wind mills in a wind farm which evacuate energy in the same grid node.

Programming unit.

(PU) Minimum element with capacity to bid in a market.

Pump consumption.

Electrical energy used by pumped storage hydro plants for elevating water from the lower to the upper reservoir for the generation of electricity.

Pumped storage.

This is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power is used to run the pumps. During periods of high demand of electricity, the stored water is released through turbines.

Q

Qualified consumers.: Is a consumer who can choose the supplier of their electrical energy in accordance with Royal Decree Law 6/2000 of 23 June. As from 1 January 2003 all consumers of electrical energy are considered as qualified consumers. With Law 17/2007 of 4 July coming in to force, which modified Law 54/1997, the figure of qualified consumer disappeared and remained integrated under the concept of consumer. In accordance with the cited law, consumers who acquire energy directly from the generation market are known as Direct Market Consumers.

R

Real time restrictions.

Process carried out by the system operator consisting of the resolution of the technical restrictions identified during real time operation by means of the modification of the programmes of the programming units.

Re-dispatching.

Variation on the energy matched in the daily market, as a result of the execution of the successive intraday markets or ancillary services.

REE Contract.

This corresponds to the existing agreements prior to the implementation of the electricity market between Spain and France, Portugal, Morocco or Andorra. Entities have been created separating importing from exporting. They cannot access the regulation markets.

Regulation band.

Energy band established by the system for regulation. This is done with the objective of maintaining the generation-demand balance, correcting involuntary deviations which take place during operation in real time with the European system, or of the frequency deviations of the system with respect to the programmed values.

Regulation deviations.

Deviations which occur between two electrical systems and are measured as the difference between the programmed international exchanges and the physical international exchanges.

Renewable energies.

Those obtained from natural resources and both industrial and urban waste. These different types of energy sources include mini-hydroelectric, solar, wind, solid industrial and urban residues, and biomass.

Requirement.

Detected needs which are attempted to be covered during a market session.

Restriction.

Any limitation derived from the situation of the transmission grid or the system so that the supply of electricity can be carried out under the defined conditions of security, quality and reliability in the procedure of operation P.O. - 1.1. Additionally, restrictions a can take place due to:

Insufficient secondary and tertiary regulation reserve.
Insufficient reserve capacity for voltage control.
Insufficient reserve capacity for service restoration.

For the resolution of these types of restrictions, the mechanisms established in the corresponding ancillary services shall be applied.

Rolling year.

The period of time elapsed in the last twelve months.

S

Secondary market of capacity.: Mechanism which allows the transfer and resale, on behalf of a participant, of acquired physical capacity rights in the annual and monthly auctions or by means of transfers.
Secondary regulation band and secondary regulation.: The secondary reserve is an optional ancillary service with the objective of maintaining the generation-demand balance, correcting deviations with respect to the anticipated exchange programmes between Spain and France, and frequency deviations. Its temporary action horizon stretches from 20 seconds to 15 minutes. This service is remunerated by means of market mechanisms via two concepts: availability (regulation band) and usage (energy).
Secondary regulation.: An ancillary service whose purpose is to maintain the balance between generation and demand, correcting the involuntary unintentional deviations which occur in the real-time operation of exchanges with the European system or the deviations in the system frequency with respect to the programmed values. Its temporal working horizon ranges from 30 seconds to 15 minutes. It is remunerated under two concepts: capacity (regulation band) and usage (energy).
SEIE.: Insular and extra-peninsular electricity systems. Refers to the electricity systems of the Balearic Islands, the Canary Islands and autonomous cities of Ceuta and Melilla.
Session.: Meeting of the Market.
Simel.: Electric Power Measurement Information System. More information...
SIOS.: System Operator's Information System. More information...
Special regime.: Production of electrical energy which falls under a unique economic regime, originating from facilities with installed power not exceeding 50 MW whose production originates from cogeneration or other forms of electricity generation associated with non-electrical activities, if and when, they entail a high energy yield: Groups that use renewable non-consumable energies, biomass or any type of biofuel as a primary energy source: Groups which use non-renewable or agricultural waste, livestock and service sector waste as primary energy sources, with an installed power lower than or equal to 25 MW, when they entail a high energy yield.
Support exchanges.: Programmes which are established between two electricity systems to guarantee the conditions for supply security of either of the two interconnected systems. This is done in case of emergency to solve a specific risk situation in the operation of one of the systems and with the previous agreement between the respective operators and in the absence of alternative means of resolution in the system requiring support.
Surplus/deficit of deviations.: Difference between the amount of the settlements of the deviations and the energy used to maintain the generation-demand balance.
System adjustment services.: Services necessary to ensure the electricity supply under the conditions of quality, reliability and security. The adjustment services can have obligatory or optional character. These are understood as adjustment services such as the resolution of technical restrictions of the system, ancillary services and deviation management.
System operation processes.: Those system adjustment services which are necessary to assure the electricity supply under the necessary conditions of quality, reliability and security. The adjustment services can have obligatory or optional character. Adjustment services are understood as the resolution of technical restrictions of the system, ancillary services and deviation management.
System Operator.: Mercantile society whose main function is to guarantee the continuity and security of the electricity supply as well as the correct coordination of the generation and transmission system. It carries out its functions in coordination with the operators and agents of the Iberian Electricity Market under the principles of transparency, objectivity and independence. In the current Spanish model, the system operator is also the manager of the transmission grid.

T

Technical restrictions PBF.: Mechanism integrated in the electrical energy production market carried out by the system operator consisting of the resolution of the technical restrictions identified in the Daily Base Functioning Programme by means of the modification of the programmes of the programming units and the subsequent process of re-balancing generation-demand.
Tertiary regulation.: An optional ancillary service, that if subscribed to, is accompanied by mandatory bid, managed and compensated by market mechanisms. Its objective is to resolve the deviations between generation and consumption and the restitution of the secondary regulation reserve which has been used. This is done by means of the adaptation of the operating programmes of the programming units corresponding to generation plants and pumped storage consumption facilities. The tertiary reserve is defined as the maximum variation of power generation that a generation unit can carry out within a maximum of 15 minutes, and which can be maintained for at least 2 hours.
Thermal line rating.: The maximum energy which can be transported by an electrical line without breaking the established safety distances. This value depends on the characteristics of the line and on the environmental characteristics (temperature, wind and solar heating).
TIEPI.: This is the time of interruption equivalent to the installed power in the medium voltage transformation centres.
TIM (Average Interruption Time).: Time, in minutes, which results from dividing the ENS (energy not supplied to the system due to interruptions of the service occurred in the transmission grid), by the average power of the peninsular system.
Traders.: Those mercantile societies that, accessing the transmission or distribution grid, acquire energy to sell to consumers, to other system participants or to carry out international exchange operations under the terms established in Law 54/1997.
Transmission grid availability rate.: Indicates the percentage of total time in which each element of the transmission grid has been available for service. It is calculated from the nominal power of each installation once the downtime due to preventive and corrective maintenance, unforeseen unavailability, or other causes (such as the construction of new facilities, renovations and improvements) have been deducted.
Transmission grid.: Set of lines, parks, transformers and other electrical elements with 220 kV or more, and those other facilities, regardless of their power, which fulfil transmission functions, international interconnections and the interconnections with the Spanish peninsular and extra-peninsular electricity systems.

U

Unavailability of the production units.: A production unit is completely available if it can participate in production without any limitation in generation capacity or, when applicable, pump consumption. Otherwise, it is considered unavailable, being such unavailability of a partial or total nature. The net unavailable power of a group is determined by the difference between the installed net power in the plant terminals and the net power truly available.
Unavailability rate.: Indicates the percentage of time during which the transmission lines have not been in service.

V

Voltage control.: This is an ancillary system service whose aim is to guarantee the suitable voltage control in the nodes of the transmission grid, so that the operation of the system meets the established security and reliability requirements, ensure that the energy supplied to the final consumers is in compliance with the required quality and that the generators can work in the established conditions for its normal operation.