The purpose of this indicator is to monitor industry progress in minimizing outage time and power reductions that result from unplanned equipment failures or other conditions. This indicator reflects the effectiveness of plant programs and practices in maintaining systems available for safe electrical generation.

Unplanned capability loss factor is defined as the ratio of the unplanned energy losses during a given period of time, to the reference energy generation, expressed as a percentage.

Unplanned energy loss is energy that was not produced during the period because of unplanned shutdowns, outage extensions, or unplanned load reductions due to causes under plant management control. Causes of energy losses are considered to be unplanned if they are not scheduled at least four weeks in advance. Causes considered to be under plant management control are further defined in the clarifying notes.

Reference energy generation is the energy that could be produced if the unit were operated continuously at full power under reference ambient conditions throughout the period. Reference ambient conditions are environmental conditions representative of the annual mean (or typical) ambient conditions for the unit.

• Unplanned energy losses expressed in units of megawatt-hours (electric). The definition of unplanned energy losses is included as part of the Unit Capability Factor indicator description.
• Reference energy generation, expressed in units of megawatt-hours (electric).

The unplanned capability loss factor is determined for each period as shown below:

• UEL = Total unplanned energy losses for the period
• REG = Reference energy generation for the period

Note: The total unplanned energy loss for the period is the sum of the losses from all unplanned events.

• Unplanned energy loss: UEL = å(UPL x HRU)
  Where:
  • UPL = Unplanned power loss: the power decrease in megawatts due to an unplanned event
  • HRU = Hours operated at reduced power (or shutdown) due to the unplanned event
• Value for the industry = Median of the unit values
• Unplanned capability loss factors for individual units will be presented for a three-year period to maintain consistency with the three year Unit Capability Factor.

Data for new units is included in the calculation of industry values beginning January 1 of the first calendar year following commercial operation.

• The reference energy generation is determined by multiplying the reference unit power by the period hours.
• The reference unit power is the maximum power capability of the unit under reference ambient conditions. 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 design changes that affect the capacity are made to the unit.
• The reference ambient conditions are environmental conditions representative of the annual mean (or typical) ambient 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.
• Unplanned energy losses caused by the following conditions should be included when computing the unplanned capability loss 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
• Unplanned energy losses due to the following causes should not be included when computing the unplanned capability loss factor because these losses are not considered to be under the control of plant management:
  • Grid instability or failure
  • Lack of demand (reserve shutdown, economic shutdown, or load--following)
  • Environmental limitations (such as low cooling pond level, water intake restrictions , earthquake or deluges that could not be prevented by operator action)
  • Labor strikes (see clarifying note below)
  • Fuel coast downs
  • Seasonal variations in gross dependable capacity due to cooling water temperature variations
• The values of planned or unplanned 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 unplanned outages and start-up following these outages, the reference unit power should be used as the basis for computing power losses.
• If energy losses during an event occur due to a combination of causes under management control and causes outside of management control, the portion of the total losses that are unplanned and are under management control should be identified and used when computing the unplanned capability loss factor.
• Outages or load reductions caused by labor strikes that occur while the unit is operating are normally not included as unplanned 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. If a labor strike occurs during an outage, any outage extensions are included as energy losses 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 and 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 clarification 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 that occur while entering and recovering from an unplanned outage will be considered as unplanned 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.
• Either net or gross energy may be used; however, consistency must be maintained for all energy terms. The use of gross energy is more meaningful in certain situations. For example, it is less confusing for multi-unit stations that may power the station electrical loads from one unit.
• Planned Capability Loss Factor (PCLF) : The planned capability loss factor can be calculated from the relationship:

  UCF + UCLF + PCLF = 100% Over a specific time period

  Where:
  
  • UCF = Unit capability factor (%)
  • UCLF = Unplanned capability loss factor (%)

  Note: PCLF Replaces the formerly used planned energy unavailability factor (PUF)