电力需求与定价(15)

peak period consumers. Therefore, if the capacity costs of

base load generating units are included in the calculations, it

is very important to net out potential fuel savings due to

displacement of less efficient plant by these new base load

units (see Appendix for details). Even intuitively, it would not

be sensible to incorrectly charge peak consumers the highcapacity

costs of expensive base load units (e.g., nuclear), thus

encouraging them, for example to install their own captive gas

turbine plant.

Next, the LRMC of transmission and distribution (T&D) are

calculated. Generally, all T&D investment costs (except customer

costs-discussed later) are allocated to incremental capacity,

because the designs of these facilities are determined

principally by the peak kilowatt that they carry rather than

the kwh. However, particularly at the distribution level, the

size of a given feeder may depend on local peak demand which

may not occur within the system peak period and this could

complicate the problem of allocating distribution capacity

costs among the various rating periods [3]. The concept of

structuring by voltage level may be introduced at this stage.

Consider three supply voltage categories: high, medium, and

low (HV, MV, LV). Since consumers at each voltage level are

charged only upstream costs, capacity costs at each voltage

level must be identified.

The simplest approach is to use the average incremental cost

(AIC) method to estimate the LRMC of T&D. Suppose that in

year i, AMWi, and Ii are the increase in demand served (relative

to the previous year), and the investment cost respectively.

Then, the AIC of capacity is given by:

AIC = 1 i=o

where r is the discount rate (e.g., the opportunity cost of capital),

T is the planning horizon (e.g., 10 years), and L is the

average time delay between the investment and commissioning

dates for new facilities. We note that in the AIC method the

actual additional increments of demand are considered as they

occur, rather than the hypothetical fixed demand increment

AD used (more rigorously) in calculating generation LRMC.

However, because there is no problem of plant mix with T&D

investments, AIC and the hypothetical increment method will

yield similar results, while AIC is also usually much easier to

calculate using readily available planning data. An alternative

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