J. M. LI ET AL. 47

ing power of the pumped storage units. On the other hand,

because the pumped storage units can replace thermal

power unit to be the variable load plant and improve the

operating conditions of thermal power unit. In this way,

it can reduce the auxiliary power rate and the coal con-

sumption rate of the thermal power unit, the difference

value between the two cases is the pumped storage power

station's shift peak and valley benefits. The calcu lation of

capacity benefit calculation is relatively simple, but cal-

culating shift peak and valley benefits is a complicated

problem which involves many factors.

In this paper, we choose the day with maximum load

as the typical day for every month and simulate the sys-

tem running in two cases of whether the pumped storage

power station is put into operation. The forecast of

pumped storage power station 24 point output curve in

the typical day bases on the data of historical average,

and in consideration of the development of installed ca-

pacity and load level, we revise the curve proportion ally.

The 24 point output curve of power from other areas de-

pends on the fixed power energy of the agreement. Spe-

cific steps to calculate the Static benefits are shown as

follows:

1) Determine the output curve of the other units in the

area except pumped storage unit. With the considering o f

load and emergency reserves, deduct pumped storage

power station output and power from other areas from

the load curve in the typical day (when the pumped stor-

age power station is on pumping state, its output is a

negative value).

2) Sort the units in the power grid. According to the

principle of energy-saving power generation dispatching,

clean energy unit such as hydropower unit, nuclear reac-

tors are arranged to put into operation first, and how to

decide the priorities of thermal power units depend on

the unit coal consumption rate.

3) Unit Commitment (UC). The priority listin g method

is used to solve the UC problem. The method initially

arranges the generating units based on lowest operational

cost characteristics. The predetermined order is then used

for UC such that the system load is satisfied [6,7].

4) Calculate shift peak and valley benefits of pumped

storage power station. Add the coal consumption of all

units in two cases respectively to get the total coal con-

sumption of the system, then we can obtain the shift peak

and valley benefits in the typical day by calculating the

difference between the two cases. So it is easy to figure

up the shift peak and valley benefits for month and year

with monthly unbalanced coefficient and seasonal un-

balanced coefficient.

3. Dynamic Benefits

Dynamic benefits of pumped storage unit include several

aspects, and in the simulation of system operation, they

are related to each other. At present, quantitative evalua-

tion algorithms for dynamic benefits usually adopt partial

summation model method; its main idea is dividing

pumped storage power station capacity into several parts

according to the function it undertakes. Then put forward

quantitative calculation formula for every part respec-

tively, and calculate the dynamic benefit, the total dy-

namic benefit of pumped storage power station is the

sum of all parts [8].

This paper adopts equivalent replacement method that

is widely used in the engineering economics. The first

step is calculating the basic program, namely studying

the system reliability index and annual cost when the

studied station provides dynamic benefit service; The

second step consider alternative program, namely calcu-

lating the annual co st that is needed to keep the reliability

index being same with the basic program when the stud-

ied station doesn’t provide dynamic benefit service.

Comparing with th e basic program, the excess part of the

annual cost in alternative program is the benefit annual

value. This paper focuses on two important items in dy-

namic benefit: emergency reserves benefit and frequency

modulat i on benefit.

3.1. Emergency Reserves Benefit

Starting with the overall system, this paper builds a pumped

storage power station accident emergency reserves benefit

evaluation model to analysis emergency reserves benefit

of pumped storage unit by dynamic simulating of system

accident pattern analysis and accident reflection of all

kinds of units after in the process of system accident. The

emergency reserves benefit evaluation model includes

two child models, the one is load model and the other is

the power generation model.

Load model. The load model is based on historical load

data of power system and the development of social eco-

nomic characteristics in the future. The load mode con-

sists of three parts: the annu al peak load, the annual load

curve, the typical daily load curve. The load on the ith

moment in the typical day can be calculated as follow:

max m

=

mt hmt

LL LL

(1)

where max is the annual peak load, m and hmt are

the annual load curve (seasonal unbalanced coefficient)

and the typical daily load curve, respectively.

LL L

Power generation model. Power generation model in-

cludes the analysis of system accident pattern and unit

response capability model. For simplicity, we count the

amount of power failure which need the pumped storage

unit response quickly and employ a quadratic fitting

method to evaluate the emergency capacity and accident

probability over the years. In addition, we assume that

load regulation speed of thermal power plants and gas-

powered plants are 2% and 7% of its rated capacity per

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