电力需求与定价(13)

at each moment of time, may be estimated. The basic

MUNASINGHE: MODERN ELECTRICITY PRICING 331

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(b)

Fig. 5. (a) Typical annual LE. (b) Forecast of peak power demand.

concepts for calculating strict LRMC are summarized below,

while details of theory and illustrative case studies may be

foundin [311 and [551.

A. Cost Categories and Rating Periods

The three broad categories of marginal costs are: capacity

costs, energy costs and consumer costs. Marginal capacity costs

are basically the investment costs of generation, transmission

and distribution facilities associated with supplying additional

kilowatts. Marginal energy costs are the fuel and operating

costs of providing additional kilowatt-hours. Marginal customer

costs are the incremental costs directly attributable to

consumers including costs of hook-up, metering, and billing.

Relevant operation and maintenance costs (O&M), as well as

administrative and general costs (A&G) must also be allocated

to these basic cost categories. Furthermore, where appropriate,

these elements of LRMC must be structured by time of

use, voltage level, and so on.

The first step in structuring is the selection of appropriate

rating periods. The system load duration curves and generation

schedules, should be examined to determine periods during

which demand presses on capacity and supply costs are

highest. These cyclical critical periods may be due to daily

demand variations (e.g., evening lighting load), or seasonal

variations in both demand (e.g., summer airconditioning peak

load), and supply (e.g., dry season for hydro systems). To illustrate

the principles of structuring and calculating strict

LRMC, we begin with an all thermal system that does not exhibit

marked seasonability of demand, choosing only two

rating periods by time of day, i.e., peak and off-peak. Seasonal

variations in LRMC and the analysis of hydroelectric

systems are discussed later.

B. Marginal Capacity Costs

Consider in Fig. 5(a), the typical system annual load duration

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