Analysis on the Operation of 750kV Controllable Shunt Reactor

in Gansu Power Grid of China

Rong Xiaoyun

1,2

, Shao Chong

3,4

, Wang Weizhou

, Hou Yanpeng

, Liu Fuchao

Jia Cunxi

and Li Zhengyuan

North China Electric Power University, Zhuxinzhuang, Dewai, Beijing, China

The University of Edinburgh, School of Engineering, The King's Buildings,Edinburgh, U.K.

Gansu Electric Power Research Institute, Qilihe District, Lanzhou, P.R. China

Gansu Electric Power Maintenance Company, Anning District, Lanzhou, P.R. China

Keywords: Controllable Shunt Reactor, 750kV Super-high Voltage Grid, Operation, Wind Power.

Abstract: Super High Voltage is the efficient way to achieve low power losses in long distance power transmission,

but power frequency overvoltage and secondary current still exist. In order to improve the stability of the

system, high voltage controllable shunt reactor (CSR) is added to the system. This thesis was based on the

large amount of data about the 750kV controllable shunt reactor operated in the 750kV substation of

Dunhuang, which is the first CSR applied in 750kV super-high voltage grid in China. The relationship

between the variation of the voltage and the switching on/off of CSR was analized, the actual impacts of the

CSR on the reactive power distribution and the active power loss were studied. Furthermore, a certain

theory basis for the CSR maintenance was provided.

1 INTRODUCTION

Northwest of China is rich in wind power, a 10GW

wind farm has being developed. In order to transmit

and transform the large scale wind power, two

750kV super high voltage transmission lines have

been constructed. Because of the long distance

transmission of large scale power and the dramatic

intermittency and unpredictability of wind power,

the reactive power balance and voltage control

problem of the grid became prominent (Wang,

2009).

As the controllable shunt reactor (CSR) can

adjust reactive power of the system flexibly, inhibit

overvoltage and secondary arc current, reduce

network loss (IEEE Standard Requirements, 2008),

improve the stability and the delivery capacity of the

system (Belyaev and Smolovik, 2005), it becomes

the first choice to solve the problems relating to the

large scale wind power integration from long

distance in Northwest China, especially in Jiuquan,

Gansu (Pan et al., 2007). In November, 2011, the

750kV CSR, which has the highest operating voltage

in the world, self-developed by China, was

successfully put into comercial operation in

Dunhuang substation of Jiuquan (Liu et al., 2012).

The map of the position of Dunhuang and Jiuquan is

as shown in Figure 1, marked with read circle.

Figure 1: Map of Dunhuang and Jiuquan.

It has solved the reactive power and voltage

fluctuation of the 750kV Dunhuang substation

effectively, and improved the utilization rate of the

750kV wind power delivery system, as the 750kV

Dunhuang substation is one of the main substations

with large scale wind power integrated into power

105

Xiaoyun R., Chong S., Weizhou W., Yanpeng H., Fuchao L., Cunxi J. and Zhengyuan L..

Analysis on the Operation of 750kV Controllable Shunt Reactor in Gansu Power Grid of China.

DOI: 10.5220/0004358801050109

In Proceedings of the 2nd International Conference on Smart Grids and Green IT Systems (SMARTGREENS-2013), pages 105-109

ISBN: 978-989-8565-55-6

 2013 SCITEPRESS (Science and Technology Publications, Lda.)

grid concentratedly (Li et al., 2010).

This thesis was based on 340 sets of data,

measured from the related power system when the

operation state of CSR in Dunhuang is changed .

Later, combined with the actual operation state, the

voltage of the 750kV Bus and the reactive power of

the system, the operation states and the effectiveness

of CSR were analysed, and the advises for operation

and maintenance were given.

2 DUNHUANG CSR PROJECT

2.1 CSR Introduction

According to the different constitutions and basic

principles, the CSR in the world can be classified

into magnetic control CSR and high-impedance

transformer CSR (Bryanteev et al., 2006). And

according to the different applications, it can be

sorted into the bus shunt reactor and the line shunt

reactor (Xie and Chen, 2008).

Magnetically controllable shunt reactor has

advantages like continuously adjustable reactive

power, small and low harmonic component, and

economical control system. It is mainly used as bus

shunt reactor. But because of low response speed, it

is not suitable for line shunt reactor, and can not be

used in 750kV wind power delivery system

characterised by frequent fluctuation of power (Zhou

et al., 2003) .

High-impedance transformer CSR (stepped

controllable shunt reactor) always has great losses,

high-level harmonics and noises when applied into

super high voltage system. Compared with

magnetical CSR, high-impedance CSR has simple

principle, faster dynamic response speed, easier

operation and maintenance. When its control system

is in failure, it can operates as fixed reactor (Zhou et

al., 2007). The structure principle of the 750kV CSR

is as shown in Figure 2. This kind of CSR is

appropriate for large scale wind power concentrated

integration in Hexi area in Gansu province of China

(Li et al., 2010).

Figure 2: Structure Principle of the 750kV CSR.

2.2 750kV Dunhuang Substation

At present, about 5.5GW wind power as the first-

stage construction of JiuQuan super wind power

base in Gansu have been integrated into 330kV

power system and connected with the 750kV system

through seven 330kV booster stations and two

330kV transformer stations. Expected total wind

power in 2015 will reach to 1270 million watts

[1-3]

At that time, 750kV Dunhuang substation would be

rated as the biggest capacity and highest voltage

level single substation in the world for the wind

power integration, as almost all the wind power of

Jiuquan would integrate into its 330kV bus (Zhou et

al., 2006).

As wind power fluctuate frequently, the highest

voltage of the 750kV bus of the Dunhuang

substation had reached 802kV and the lowest 755kV.

The voltage and reactive power adjustment of the

power grid is very difficult.

In order to enhance the voltage stability, balance

reactive power, reduce grid losses, improve the

reliability and security of the systems operation, the

300Mvar stepped CSR was developped as the

750kV bus CSR of 750kv Dunhuang substation.

The adjustable range is 25％, 50％, 75％, 100％ of

the nominal capacity (Pan et al., 2007).

2.3 Operational Data of the CSR

This thesis is based on the CSR operational data,

collected from 14 January, 2012 to 6 August, 2012,

340 valid sets altogether. Contents mainly included

are actuation time, adjustment level, voltage change

and the reactive and active power in high and

medium voltage side of the primary transformer. For

example, at 04:24, 6 August, 2012, the capacity of

the CSR was adjusted from 75% to 50%

automatically, bus voltage was adjusted from 755kV

to 758kV, the active and reactive power in high

voltage side of the primary transformer 2 were -

735MW and 156Mvar, in medium voltage side were

736MW and 56Mvar. As for primary transformer 3,

the active and reactive power in high voltage side

were -734MW and 156Mvar, in medium voltage

side were 736MW and 57Mvar.

3 DUNHUANG CSR OPERATION

STATE ANALYSIS

The voltage level and power capacity of 750kV

Dunhuang substation CSR are both the highest in the

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world. Its operating environment is really harsh

(plateau section, gobi desert). A plentiful operational

data has been accumulated, after one-year running.

Operational data mining has great practical

significance for the improvement of the operation

and maintenance performance of this CSR and for

the optimal structure designing of other CSR.

3.1 CSR Capacity State Analysis

The adjustment level of CSR illustrates its capacity,

operation states and corresponding action of

thyristor. The analysis of this sets of data is

conducive to the maintenance of CSR.

15%

33%

35%

17%

25%

50%

75%

100%

Figure 3: Percentage of Capacity States.

Figure 3 is the percentage of the four different

capacity states which is obtained from 340 sets of

statistical data. It is obvious that 50% and 75%

accounts for the largest percentage, nearly reach to

the twice of 25% and 100%. The state that the whole

capacity is out of service never shows up.

Figure 3 indicates that the capacity of this CSR

was reasonably designed, as more than half of the

capacity is utilized. The rated capacity put into

operation also happened but in a small proportion.

Figure 3 also shows that the valve bodies which

control the 75% and 50% capacity act relatively

frequent, so they should be treated as key elements

during maintenance. And because 25% capacity is

always put into operation, so it also needs more care.

3.2 Analysis of CSR Action Conditions

Figure 4 is derived from the action time statistics of

CSR, and it is useful to design maintenance and

inspection time.

Figure 4 is the distribution density of the total

action times for these four different levels at

different period. The action (put or cut) of the CSR

mainly occurred between March and July, especially

between early May and the end of June.

Taking the weather during this period in

Dunhuang as reference, it is clear that the main

reason which causes this variation is the wind speed

in Dunhuang was really unstable from May to July,,

causing grid connection capacity of wind power

fluctuated frequently and the varying of voltage and

reactive power of system, finally leading to the CSR

switching frequently.

02/01 03/22 05/11 06/30

0.05

0.1

0.15

0.2

0.25

期

Figure 4: Numbers of Action and it’s Time Distribution.

This indicates that the best maintenance time of CSR

in Dunhuang is between January and March or May

and July. Strengthened inspection of equipment must

be done to prevent potential accident which may

caused by the frequent switching.

4 CSR IMPACT ON VOLTAGE

The switching of CSR will cause the change of bus

voltage.

100 to 75

75 to 50

50 to 25

25 to 50

50 to 75

75 to 100

-20

-10

adjust level

voltage

times

Figure 5: The Influence of CSR Switching on Voltage.

Distribution density

Date day/mouth

AnalysisontheOperationof750kVControllableShuntReactorinGansuPowerGridofChina

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In theory, when CSR level is adjusted from low

to high, the reactive capacity increases and the

voltage decreases, vice verse. Three dimensional

scattering projection diagram 5 is derived from 340

sets of statistic data. This figure reflects the

occurrence number of some certain voltage

difference caused by the change of capacity.

4.1 Main Impact on Voltage

When the operating capacity of CSR decreases, most

of the voltage increases although the amplitude are

generally small. Nearly 90% of the voltage

differences are concentrated between 1kV and 6kV.

Voltage differences reach to 10kV or 20kV also

occurred, but most are 2kV. When the operating

capacity increases，most of the voltage decreases.

Nearly 90% of the voltage drops are concentrated

between 1kV and 6kV. Voltage drops reach to 10kV

also occurred, but most are 2kV as well. From above,

CSR with total capacity of 300Mvar, switching at

75Mvar of each level, do not significantly affects the

voltage of 750kV bus, as amplitude of variation

always within 1%, tending to nominal value.

Through the analysis of the data, putting the CSR

into operation and its frequent switching won’t

influence the operation of 750kV equipment.

4.2 Analysis of Special Circumstances

As stated, after the switching of CSR, some voltage

differences are not within 6kV. Two main classes,

one is the amplitude of variation bigger than 6kV.

For example, within the 340 sets of data, voltage

differences (increase) reach to 20kV appeared twice,

12kV appeared twice. Voltage differences (decrease)

reach to 9kV appeared once, 8kV appeared once.

Although they conform to the theory but are

different from normal situation. Another is when the

operating capacity increases, bus voltage also

increases and when the operating capacity decreases,

bus voltage also decreases, opposite to the theory, as

shown in Figure 5 within red circles.

In the first situation, increasing 20kV for

example, referring to the nearby switching actions

and corresponding weather information, wind speed

changed rapidly at that time so the grid connection

capacity of wind power is bigger. At 14:29,

31/03/2012, the operation capacity of CSR dropped

from 100% to75%, causing voltage increase from

756kV to 758kV, 2kV increment. Then at 14:38，

31/03/2012, the operation capacity dropped from

75% to 50%, causing voltage increase from 758kV

to 778kV, 20kV increment. This phenomenon

appears many times within small period furing 340

sets of data, and always accompanied with large

amplitude of voltage variation. This phenomenon

indicates that the primary causes of large amplitude

of voltage variation after CSR put into operation are

the big variation of grid connection capacity of wind

power and lacking of CSR switching capacity within

one operation time. Introducing short term wind

power predicting outcomes into control logic of CSR

is a promising method to solve this problem.

In the second situation, the variation of voltage

goes against the theory. Firstly, because all the data

were recorded manually, so man-made faults won’t

be eliminated. What’s more, another possibility is if

wind power changes quite fast, bus voltage

fluctuated frequently, so during a small period the

voltage increments or decrements caused by the

wind power grid connection is bigger than the

voltage decrements or increments caused by the

switching of the CSR, so the variation of voltage

goes against the theory.

5 CONCLUSIONS

CSR is the effective means in solving voltage and

reactive power problems of the power grid caused

by the large scale wind power integration. This

thesis combines with the actual operation states of

300Mvar stepped CSR in Dunhuang 750kV

substation of China, analyzed its operating

characteristics, summarized the impact of switching

actions on bus, the conclusion is as follows:

(1) 300Mvar CSR is sufficient in solving the voltage

and reactive power fluctuation problems of the

power grid of Dunhuang.

(2) The switching times of CSR is relatively high

during the period when wind power fluctuates

frequently. It is suggest that maintenance

between January and March and strengthened

inspection of equipment between May and July

be arranged.

(3) The thyristor switching of 50% and 75%

capacity act relative frequently and 25% capacity

is always put into operation, so they all should be

treated as emphasis during the maintenance.

(4) After putting the CSR into operation, the

variation of bus voltage is limited nearly within

the acceptable range. That means CSR don’t

have large impact on bus voltage.

(5) As wind power changes with large amplitude and

frequently, large amplitude of voltage variation

after the variation of CSR capacity may

occurred. Introducing short term wind power

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predicting outcomes into control logic of CSR is

a promising method to solve this problem.

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