电力需求与定价(16)

method of determining marginal T&D costs at several different

voltage levels would be to use historical data to fit regression

equations such as:

(Transmission Costs) = a + b - (Peak Demand).

However there is no guarantee that such past relationships

would hold true in the future, as the system expands.

Assume that the AIC of EHV and HV transmission has been

computed and annuitized over the lifetime of the plant (e.g.,

30 years) to yield the marginal costs ALRMCHV. Then, the

total LRMC of capacity during the peak period, at the HV

level would be:

where LHV% is the percentage of incoming peak power that is

lost in EHV and HV network. This procedure may be repeated

at the MV and LV levels. The LRMC of T&D calculated

in this way is based on actual growth of future demand,

and averaged over many consumers. However, facilities associated

with given generating sites or loads should be specifically

allocated to these uses rather than averaged out, e.g.,

transmission spur line, exceptionally low or high distribution

costs for one or moreg iven customers.

C. Marginal Energy Costs and Treatment of Losses

The system lamda concept is useful ,in calculating marginal

energy costs. The LRMC of peak period energy will be the

running costs of the machines to be used last in the merit

order, to meet the incremental peak kilowatt-hour represented

by AD. In our model, this would be the fuel and operating

costs of gas turbines, adjusted by the appropriate peak loss

factors at each voltage level. Similarly, the LRMC of off-peak

energy would usually be the running costs of the least efficient

base load or cycling plant used during this period. Exceptions

occur when the marginal plant used during a rating period was

not necessarily the least efficient machine that could have

ELECTRICITY PRICING 339

been used. For example, less efficient plants which have long

start-up times and are required in the next rating period, may

be operated earlier in the loading order than more efficient

plant. This would correspond to minimization of operating

costs over several rating periods rather than on an hourly basis.

Again since the heat rate of the plants could vary with output

level, the simple linear relationship usually assumed between

generation costs and kilowatt-hours may need to be replaced

by a more realistic nonlinear model [361. We note that the

loss factors for adjusting off-peak costs will be smaller than the

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