IEEE 762:2006 pdf free download – IEEE Standard Definitions for Use in Reporting Electric Generating Unit Reliability,Availability, and Productivity
10.Capacity-weighted calculations for group performance indexes
When measuring the performance of a fleet of units of dissimilar size andor duty cycle, capacity-weightingis sometimes believed to better reflect the contribution of each unit to the fleet’s composite indexes.
Without weighting, smaller,infrequently run units will have the same impact on the performance indexesas larger，baseload units.However,there are also valid applications for using unweighted performanceindexes, even for group statistics (see Clause 9 for unweighted performance indexes).
To weight a performance measure, one does not simply take each unit ‘s performance measure(EFOR, forexample) and multiply that measure by the weight, add these products up, and divide by the sum of theweights. Each term in the equation must be multiplied by the weight, and then all those products must besummed over all the units before the rest of the calculation is performed.
NMC is the most common weight used in pooling performance indexes and is used in the formulas in thisclause. However, other weights are appropriate in some cases,particularly weights which consider theservice period of the unit as well as its size.
Capacity-weighted equations are not necessary for capacity and output factors (i.e.,GCF,NCF,GOF,NOF) becausc these factors are inherently energy-weighted. These equations are similar to those shown8.12 through 8.15.However, when calculating these factors for a group of units (or a unit that has a varyingcapacity value over time), do not simply average these factors. Apply the equations in 10.1 2 through 10.15for correct group performance measures.
These indexes are defined to be additive. Therefore, the total per-unit energy loss is the sum of the four indexes,and the remaining per-unit energy not lost is called equivalent availability factor (EAF).
In order for the four energy loss indexes to be additive, as in Equation (C.7), it is necessary that the capacity lossdue to each source be separated. In other words,for example, a unit cannot be simultaneously subject to fulloutage and unit derating.
Similarly, a unit cannot be simultaneously subject to both seasonal derating and full outage. In order toachieve nonoverlapping energy definitions, the IEEE 762 Working Group agreed to assign full (maximum) unitcapacity to the full outage state. In other words, both unit deratings and seasonal deratings are considered to endwhen a full outage starts, as far as the calculation of the unit derating factor and the seasonal derating factor areconcerned.
The electric industry in Europe and other parts of the world has changed reporting practices to distinguishlosses of generation caused by problems within and outside plant management control.However, afterreviewing the approaches used by others, the IEEE762 Working Group does not feel that such a distinctionis necessary in all reporting systems. If such a distinction is to be made within a particular reporting system,the outage events to be excluded or included may be distinguished based on location or cause, or both.
Some causes are internal to the plant operation and equipment while others are external and may beappropriate to exclude when calculating performance indexes for some reporting purposes. This standarddoes not set nor recommend a particular boundary between the generator and the transmission andordistribution to determine what equipment is “outside plant management control.”Such an equipmentboundary for a particular plant or generating unit may include all equipment up to the following:
a)The high-voltage terminals of the generator step-up (GSU) transformer and the station servicetransformers, as shown in Figure D.1
b) The GSU transformer or distribution system (load) side of the generator-voltage circuit breakers
c) Another location that may be reasonable considering the design and operating practices of the generating unit
lt may or may not be appropriate to assume that all problems within the power station boundary are withinplant management control. Therefore,rather than attempt to exhaustively identify the responsibilities ofplant management,the more feasible approach is to specify certain outage causes as outside plantmanagement control. With this approach, it is necessary within each particular reporting system to clearlyestablish the outage causes that are and are not deemed to be under plant management control. Thefollowing examples are offered as causes that may be considered as external,i.e.,outside of plantmanagement control.