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DEFINITION
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The “energy availability factor” over a specified period, is the ratio of the energy that the available capacity could have produced during this period, to the energy that the reference unit power could have produced during the same period.
The energy that the available capacity could have produced is equal to:
REG – PEL – UEL – XEL
Where:
- REG = Reference energy generation(net) (MW(e).h) for the period
- PEL = Total planned energy losses (MW(e).h)
- UEL = Total unplanned energy loss (MW(e).h)
- XEL = Total external energy losses (beyond the plant management control)
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DATA ELEMENTS
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The following data are required to determine each unit's value for this indicator:
- Reference energy generation (net), expressed in units of megawatt-hours (electric)
- Planned energy loss: the energy that was not produced during the period because of planned shutdowns or load reductions due to causes under the plant management control. Energy losses are considered to be planned if they are scheduled at least four weeks in advance, generally at the time when the annual overhaul, refueling, or maintenance program is established. Energy losses considered to be under plant management control are further defined in the clarifying notes. Planned energy loss is expressed in units of megawatt-hours.
- Unplanned energy loss: the energy that was not produced during the period because of unplanned shutdowns, outage extensions, or load reductions due to causes under plant management control. Energy losses are considered to be unplanned if they are not scheduled at least four weeks in advance. Energy losses considered to be under plant management control are further defined in the clarifying notes. Unplanned energy loss is expressed in units of megawatt-hours.
- External energy loss (energy loss due to causes external to the plant): the energy that was not produced during the period due to constraints external to the plant. These constraints are those considered to be beyond the control of the plant management. Energy losses considered to be beyond the plant management control are further defined in the clarifying notes.
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CALCULATIONS
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The energy availability factor is determined for each period as shown below:
| Value of a unit, |
EAF (%) = |
REG - PEL - UEL - XEL x 100 |
| REG |
Where:
- REG = Reference energy generation(net) (MW(e).h) for the period
- PEL = Total planned energy losses (MW(e).h)
- UEL = Total unplanned energy loss (MW(e).h)
- XEL = Total external energy losses (beyond the plant management control) (MW(e).h)
Note: The total planned, unplanned energy losses and energy loss due to causes external to the plant for the period is the sum of the losses from all planned, unplanned and external events, respectively.
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DATA QUALIFICATION REQUIREMENTS
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Data for new units is included in the calculation of annual values beginning January 1 of the first calendar year following commercial operation.
Data for units in commercial operation at the end of the commercial operation period is included in the calculation of annual values ending December 31 of the last calendar year preceding shutdown.
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CLARIFYING NOTES
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- The reference energy generation (net) is determined by multiplying the reference unit power (net) by the reference period hours.
- Reference unit power (former maximum electrical capacity) is the maximum power capability of the unit under reference ambient conditions, i.e. the maximum power that could be maintained or is authorized to be maintained throughout a period of continuous operation, in practice 15 hours or longer. If a maximum power capability has been determined by formal test, the reference unit power is determined by correcting test results to reference ambient conditions. If a formal test has not been performed, the reference power should be based on design values, adjusted for reference ambient conditions. The reference unit power is expected to remain constant unless, following design changes, or a new permanent authorization, the management decides to amend the original value. The reference unit power may be gross or net. (It is recognized that the reference unit power may be set up by an authorized reference unit thermal power, and in these cases the net "reference" unit power corresponding to the authorized reference thermal power should be used for simplicity in the calculations.)
- Reference unit power (net) (former maximum net electrical capacity) is the maximum power that can be supplied measured at the unit outlet terminals, i.e. after deducting the power taken by unit auxiliaries and the losses in the transformers that are considered integral parts of the unit.
- Nuclear thermal power is the unit nuclear thermal power as derived from whatever is the most accurate heat balance measurement.
- The reference ambient conditions are environmental conditions representative of the annual mean (or typical) conditions for a unit. It is expected that historical heat sink temperatures will be used to determine the reference ambient conditions. The same reference ambient conditions will generally apply for the life of the unit. Periodic review of these reference conditions is not required.
- The reference period hours are the total number of hours in the pre-defined calendar time.
- For units in power ascension at the end of the period, the clock hours from the beginning of the period or the first electrical production, whichever comes last, to the end of the period.
- For units in commercial operation at the end of the period, the clock hours from the beginning of the period or of commercial operation, whichever comes last, to the end of the period or permanent shutdown, whichever comes first.
- Planned energy losses (those scheduled at least four weeks in advance) caused by the following conditions should be included when computing the energy availability factor because they are considered to be under the control of plant management:
- Refueling or planned maintenance outages
- Planned outages or load reductions for testing, repair, or other plant equipment or personnel-related causes
- Energy losses due to tests may be considered as planned if they are identified at least four weeks in advance and are part of a regular program, even if the precise time of the test is not decided four weeks in advance.
- Unplanned energy losses caused by the following conditions should be included when computing the energy availability factor because they are considered to be under the control of plant management:
- Unplanned maintenance outages
- Unplanned outages or load reductions for testing, repair, or other plant equipment or personnel-related causes
- Unplanned outage extensions
- Unplanned outages or load reductions that are caused by, or prolonged by, regulatory actions taken as a result of plant equipment or personnel performance, or regulatory actions applied on a generic basis to all like plants
- “External” Energy losses caused by the following conditions should be included when computing energy availability factor.
- Environmental limitations (such as low cooling pond level, or water intake restrictions that could not be prevented by operator action)
- Labor strikes (see clarifying note below)
- Fuel coast downs
- Seasonal variations in net dependable capacity due to cooling water temperature variations, low river or tidal waves
- Restrictions on fuel supply as a result of external constraints, for example, disputes in fuel industries or by fuel rationing
- The values of planned, unplanned or external power losses to be used in computing energy losses due to a particular event are the losses that would have occurred if the unit were operating at the reference power level at the time of the event. The power losses relative to the reference power may be determined by one of the following techniques:
(1) Subtracting the actual power level during the event from the power level immediately prior to the event when the power was at or near the reference power level,
(2) Computing the power level reduction that would have occurred with the unit at the reference power level, or
(3) Using historical data from similar events occurring at the reference power level.
For example, if a unit experiences a 10 MW power loss due to an equipment problem while operating at 75 % of the reference power, and it is determined from calculations or from similar events that have occurred at the reference power that the same equipment problem would have resulted in a 20 MW power loss at the reference power level, then 20 MW should be used when computing the energy loss.
- For events involving planned, unplanned or external outages and start-up following these outages, the reference unit power should be used as the basis for computing power losses.
- Outages or load reductions caused by labor strikes that occur while the unit is operating are normally included as external energy losses because these energy losses are not under the direct control of plant management. However, if during the strike the unit becomes incapable of starting or operating because of equipment failures, maintenance, overhauls, or other activities such as refueling, then the energy losses during the time the unit is inoperable are included as planned or unplanned. If a labor strike occurs during an outage, any outage extensions are included as energy losses (planned or unplanned) as long as the unit is incapable of being restarted because of equipment failures, maintenance, overhauls, or other activities such as refueling.
- In general, changes in an outage or load reduction start date must be announced at least four weeks in advance to be considered as "planned". However, if the grid dispatcher requests a change in the start date less than four weeks in advance, the outage or load reduction is considered to be planned.
The same rule may be used if the change in the start date is decided by plant management, assuming this decision is due to all of the following reasons or circumstances:
The unit is operating in a deregulated environment, and the management decision to modify the planned outage start date is solely to take advantage of economic situations to maximize, on a short term basis, the economic benefit coming from selling the plant electricity output.
This economic benefit can be applied to the entire production system of the Utility, not only to the specific unit under consideration.
- The unit is considered as able to run at maximum power during the four-week period prior to the initial planned outage start date.
- Any forced or unplanned outage occurring during this four-week period (or before the new start date) shall not become the reason for putting forward the planned outage.
- If a unit begins an outage or load reduction before the scheduled start date, the energy loss from the beginning of the outage or load reduction to the scheduled start date is an unplanned energy loss.
- If an outage extends beyond the scheduled start-up date, either to complete originally scheduled work or to complete corrective maintenance work on equipment required for start-up, all energy losses associated with the outage extension should be considered as unplanned. However, outage extensions to complete discretionary work (i.e., preventive maintenance or modifications) not originally scheduled for completion during the outage should be considered as planned if the work is scheduled at least four weeks in advance. Extended outages can be reclassified from unplanned to planned once corrective maintenance activities required for start-up are completed if any remaining planned activities were scheduled at least four weeks in advance. This classification also applies to load reductions.
- The scheduled start and end dates of planned outages and load reductions are those dates negotiated with and agreed to by the network and/or grid dispatcher. These dates may differ from dates shown on the detailed schedule of activities used at the unit for directing the outage.
- Energy losses related to load reduction preceding a shutdown and load increases following the shutdown should be categorized as planned or unplanned depending on whether the shutdown is planned or unplanned. For example, energy losses while entering and recovering from a planned outage will be considered as planned losses. If an outage extension (unplanned outage) occurs at the end of a planned outage, the energy loss during recovery from the outage will still be considered as a planned loss because the shutdown was originally caused by a planned outage. Energy losses due to required tests following refueling are considered planned losses.
- A unit that is in reserve shutdown will be considered as available if it can be restarted within the normal time required for unit start-up. If work on plant equipment is undertaken that would prevent a restart, the energy that potentially could have been produced while the plant was unavailable should be computed and used when determining the energy availability factor, even if the plant was not actually required to start-up during the period.
- Energy Unavailability Factor (EUF) : Energy unavailability factor can be calculated from the relationship:
EUF = 100 - EAF over a specific time period
Where:
EAF = Energy availability factor
Note: Formerly EUF was defined as follows:
EUF = PUF + UUF + XUF
Where:
- PUF = Planned energy unavailability factor
- UUF = Unplanned energy unavailability factor due to causes in the plant
- XUF = Unplanned unavailability factor due to causes external to the plant
New definition of EUF (valid since January 1 1991, covering data for the year 1990):
EUF = PCLF + UCLF + XCLF
Where:
- PCLF = Planned capability loss factor (%)
- UCLF = Unplanned capability loss factor (%)
- XCLF = External capability loss factor (%)
- External Capability Loss Factor (XCLF) : External capability loss factor can be calculated from the relationship:
UCF = EAF + XCLF over a specific period
Where:
- UCF = Unit capability factor (%)
- EAF = Energy availability factor (%)
Note: XCLF replaces the formerly used unplanned unavailability factor due to causes external to the plant (XUF)