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Page 1: [IEEE 2012 China International Conference on Electricity Distribution (CICED) - Shanghai, China (2012.09.10-2012.09.14)] 2012 China International Conference on Electricity Distribution

.<@>. 2012 China International Conference on Electricity Distribution (CICED 2012) Shanghai, 5-6 Sep. 2012

A Reasearch of Feeder Protection 10k V Distribution

N eteorks Including Distributed Generation

menghua Deng jun Qian zhenping Van tao Yu jiaqing Zhou junchao Zhang Liyi LI

No. 1651, Yishan Road, Xuhui District, Shanghai

Abstract-More and more distributed generation (DG) is being connected into distribution network with the

development of power grid. The connection of DG will

impact the feeder protection directly. It may lead to loss of

protection's selectivity or decrease of protection

sensitiveness. More badly, the protection may refuse to act

or act mistakenly. In this paper a practical distribution

network with DG which exists in the power grid of SHINAN

Power Supply Company is proposed. Based on this example

grid, what impact the DG brings to the feeder protection

and how it affects the feeder protection are studied deeply.

An improved protection scheme is proposed considering the

impact of DG. New protection scheme includes two major

changes. Firstly directional unit is added to the feeder

protection which may act mistakenly. Secondly, two sets of

setting value are applied to some feeders' protection and the

protection can switch to one or the other setting value

depending on whether DG is interconnected to the

distributed network. An ATP model of the example

distributed network is built and a large number of

simulations are made which covers all fault situations which

may occur in the network. The simulation result indicates

the proposed protection scheme can meet all of the need in

protection sensitiveness and selective ability. In summary,

the new protection scheme can solve the problem that the

connection of DG brought to distribution network's feeder

protection.

Keywords-distributed generation, distribution networks, 10 kV level feeder 's protection

I. INTRODUCTION

Distributed generation is paid more and more attention to with the development of solar energy power generation, photovoltaic generation and wind power generation. The sustainable development of earth requires the growing up of DO; because DO makes good use of renewable energy and it behaves friendly to environment. Power supply mode of traditional distribution network changes greatly because of DG. The electrical structure is changed by the connection of DG. And fault current will be supplied both by system and DO when fault takes place on network. All of these will affect the protection of feeder greatly.

Paper[2-5] analyze influences brought to distribution network protection by DO from several aspects. Paper 6

proposes a way that distance pilot protection is introduced into distribution network. Although distance pilot protection has absolute selectivity and can act quickly, it will lead to cost increase that adding communication apparatus to the protection. Paper 7 proposes a protection scheme which changes the line impedance when fault happens by using current limiter. This method can ensure that the protection have selectivity and enough sensitivity. A method is proposed in paper 8 which can guarantee the protection act selectively when fault happens at the end of line or at the forward of next stage line. Paper 9 proposes a method based on wide area network (WAN). The protection judges faulted area by information provided by the WAN firstly. Then it sends a signal to isolate the fault point.

A whole protection scheme is put in this paper based on a practical distribution network example. It provides two set of setting value for some feeder current protection I and adds directional unit to related feeder protection. It can solve the problem that protection act without selectivity or enough sensitivity resulted by DG. And it is simple and viable because no new type of protection and no additional hardware are needed.

II. INFLUENCE ON 10KV FEEDER PROTECTIONS

BROUGHT BY DG

A practical 10kV level distribution network which exists in Shanghai network is proposed as in figure 1. 35kV level station S 1 supplies 10kV level station S2 by feeder AB. S2 contains several 10kV level outgoing feeders (e.g. BC, BF) but no transformer. A solar energy power generation is connected to 10kV bus of station S2. Station S3 is powered by S2 through line Be. S3 contains both transformers and 10 kV outgoing feeders. As the same, station S4 is powered by S2 through line BF. However, there is no 10kY outgoing feeder in S4. It is must be allowed that figure 1 do not shows all feeders of the practical network. But all typical feeders are included.

If the solar energy power generation is not connected to the network, in accordance with the regulation of 10k Y distribution network protection setting, protection of lines and transformers in figure 1 will be set as follow. Transformers of station S3 and S4 are at the end of all the 10k Y protection, so they adopt over current protection as main protection which is set according to the principle of

CICED2012 Session 4 Paper No CP0200 Page 1/5

Page 2: [IEEE 2012 China International Conference on Electricity Distribution (CICED) - Shanghai, China (2012.09.10-2012.09.14)] 2012 China International Conference on Electricity Distribution

-@>- 2012 China International Conference on Electricity Distribution (CICED 2012) Shanghai, 5-6 Sep. 2012

escaping maximum load current. All 10k V level feeders are configured with current protection 1 and over current protection. Current protection 1 is set to escape the maximum short-circuit current when fault takes place at the end of line. Over current protection is set to escape maximum load current. And neighbor over current protections cooperate with each other at the time setting value. Connection of DO affects the protections as follow:

( 1) Fault happens at F 1

------------- ------, E --<-+---:::-:-'7-----+ 4 F 5

As DO is connected to S2, short-circuit current on protection 1 will increase. So sensitivity of both its current protection and over current protection will increase. As the same, short-circuit current on protection 2 will increase. And this may lead to current protection 1 of protection 2 acting without selectivity. As the over current protection of protection 2 has a bigger time setting value than protection 1, it will not act. However, as the make up protection of line CD, its sensitivity will increase.

10kY level station S4 r-----------------1

r-------------- : , , I

i l-----""--T----+-i,--r---Lo-CID : 5 c _________________ �

: r-------------------j , " : 4 ------. 17\\ : ,

: 7- "-1U :: �-t----�+---+-�---���� f4 B 2

, , , , , , , ,

-------------- -------

35kV level station S I 10kY level tation S2

PI , , , ,

� _____ - - - _________ - __ I

10k V level station S3

D

Figure I A practical I OkV distribution network

(2) Fault happens at F2 Short-circuit current on protection 2 increases while

on protection 3 decrease by the affection of DO. This will increase the sensitivity of both current protection 1 and over current protection of protection 2. For protection 3, its current protection 1 would not act because of the decrease of short-circuit current. But as the make up protection of line BC, the sensitivity of it's over current protection will decrease. However, because the maximum load current is much less than short-circuit current, the sensitivity can still meet the requirement.

(3)Fault happens at F3 Affection of DO to protection 5 and protection 3 is the

same as (2). When fault takes place on transformer of S4 or on its low-voltage side, current protection I of protection 5 may act mistakenly as the increase of short-circuit current on it. Over current protection of protection 5 will not act because it has a bigger time setting value than protection of transformer in S4.

(4)Fault happens at F4 Short-circuit current on protection 3 does not change

as the connection of DO. So, whether protection 3 act or not is irreverent with the DO. But because that short-circuit current still flow to faulted point through line BA from DO, fault can not be insulated completely when protection 3 acts to cut-off breaker 3.

(5)Fault happens at F5 Short-circuit current on protection 4 increases by the

influence of DO, which lead to the increase of its sensitivity. Part of the short-circuit current supplied by DO flows through protection 3 on reverse direction. This reverse short-circuit current may make protection 3 act under some given situation.

To sum up, disadvantageous influence DO brings to feeder protection contains the follow notes mainly: CDWhen fault happens on the latter line which located after the point DO connected to, current protection I of latter line may act incorrectly and sensitivity of over current protection of anterior line may decrease when it acts as make up protection of latter line. 0When fault happens on the anterior line which located before the point DO connected to, misoperation may takes place because of the reverse short-circuit current. Cutting off breaker at the side of system only can not isolate the fault point completely when fault takes place on the anterior line which is connected to DO directly.

III. NEW PROTECTION SCHEME OF 1 OKV FEEDER OF

DISTRIBUTION NETWORK WITH DG

A new protection scheme is proposed based on the analysis of influence brought to 10k V feeder protection by DO as described in 1. New protection scheme contains:

(1) All 0 f the 10k V feeders are still configured with current protection 1 and over current protection. Over current protection is set in accordance with the regulation that it can escape maximum load current. Current protection 1 is still set to escape the maximum short-circuit current when fault happens at the end of line.

(2) Two sets of setting value are equipped with the current protection I of the latter line which may act mistakenly (as protection 2, protection 5 in figure 1 ).The first set of value is set under the situation that DO is not connected to the network. The second set of value is calculated in a new network that contains the DO. Protection setting value is switched to the first set through

CICED2012 Session 4 Paper No CP0200 Page 2/5

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Page 3: [IEEE 2012 China International Conference on Electricity Distribution (CICED) - Shanghai, China (2012.09.10-2012.09.14)] 2012 China International Conference on Electricity Distribution

-@>- 2012 China International Conference on Electricity Distribution (CICED 2012) Shanghai, 5-6 Sep. 2012

adjusting the protection clamp when DO is connected to network and switched to the second set when DO is not connected to.

(3)Other protections which do not act mistakenly because of the connection of DO are equipped with just one set of setting value. And the setting value is calculated without regard to the DO. Directional unit is added to the protection of anterior line which is connected to the DO directly (as protection 3 in figure 1). The protection can not start if the fault current on it is reverse. And it intertrips breaker at the end of the line when it acts.

Taking the network in figure 1 as example, how the protections act when the new protection scheme is adopt is showed as follow. The directional unit can not startup when fault happens on F5 because the short-circuit current on protection 3 is on the reverse direction. Protection 3 will act to isolate the fault point completely by cutting off breakers on both side of line AB when fault takes place at F4. Current protection 1 of protection 2 would not act when fault happens at F 1 because it is switched to the second set of setting value when DO is connected to the network. As the same, current protection 1 of protection 5 will not act when fault happens on transformer 4 or at its low-voltage side.

The new protection scheme does not introduce new type of protection. It still adopts current protection 1 and over current protection. The setting of current protection I and over current protection is a mature technique. And they do not involve communication problem of several ends. In a word, the new protection scheme is simple, viable and economical.

IV. SIMULATIONS

Parameters of lines and equipment in figure 1 are as

follow. System impedance in maximum operating mode

looked in from Station S 1 's 10kV bus is X,,'" =0.0960 while

in minimum mode is x"'wx = 0.142 0. Line AE is an overhead

line, reactance per km is Xl = 03550/ km, resistance per km

is Rj = 0.2650/ km , and length is LlJc = 4 km. Line AB, BC, BF,

CD are cable line, reactance per km is Xl = 0.0890/ km resistance per km IS R, = 0.2530/ km lengths are

LAB = 12km LHe = tkm LIiF = 6km LCJ) = 4km · d , , In or er.

Capacity of DO is 1 OMY A. Transformer impedance in

station S3 and S4 calculated to 10k V side is x,

= 1. 920 .

Maximum load on line AB, AE, BC, BF, CD are 400A,

380A,280A, 160A, 180A in order.

Simulation model built with ATP as figure 2:

44kl11 '"

Zs 3 - 12km A

E 5 6kl11 2 7km

B '" IOMVA

F f6-aD baD

C I 4km D

Figure 2 ATP simulation model

Based on the new protection scheme, setting and calculation of all feeder line protections in figure 1 are carried out. Results of all protection setting value as table 1.

Table 1 Protection setting value of 10kV feeders in figure 1

Current Protection I 2014A Protection 1

Over current protection 326.1A Current Protection I 2431A

(First Set)

Protection 2 Current Protection I 3806A (Second Set)

Over current protection 507.4A Current Protection I 3812A

Protection 3 Over current protection 724.8A

Current Protection I 6785A Protection 4

Over current protection 688.6A Current Protection I 2564A

(First Set)

Protection 5 Current Protection I 4115A (Second Set)

Over current protection 289.9A A large number of fault sImulatIOns are carned out

when fault happens on different lines. Faulted current measured by simulation as follow:

(1) When three-phase short-circuit fault happens at 50% distance of line CD, current measured on protection 1 and protection 2 are:

I) = 12 = 2758.2A

Compare faulted current with protection setting value as table 2:

Table 2 Comparing of Protection Setting Value and Faulted Current

Protection Setting Value Faulted Current

On Protection(A)

Current Protection I 2014 2758.2 Protection 1

Over Current Protection 326.1 2758.2 Current Protection I ( First Set) 2431 2758.2

Protection 2 Current Protection I ( Second Set) 3806 2758.2 Over Current Protection 507.4 2758.2

CICED2012 Session 4 Paper No CP0200 Page 3/5

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Page 4: [IEEE 2012 China International Conference on Electricity Distribution (CICED) - Shanghai, China (2012.09.10-2012.09.14)] 2012 China International Conference on Electricity Distribution

.<@>. 2012 China International Conference on Electricity Distribution (CICED 2012) Shanghai, 5-6 Sep. 2012

According to table 2, faulted current is greater than over current protection setting value of protection 1 and protection 2, so both protections would startup. Current protection I of protection 1 will act because faulted current exceed its setting value. For protection 2, it will act if first set of setting value is adopt while it do not act if the second set of setting value is used. It can be concluded that protection 2 will act mistakenly if it adopt the first set of value when DO is connected to the network.

(2) When fault takes place on low-voltage side of transformer in station S4, faulted current on protection 5 as:

15 = 221O.4A The second set value of current protection I for

protection 5 is 4115A as showed in table 1 which is much bigger than faulted current. So the protection will not act which is correct. And the first set value is 2264A. This value is very close to the faulted current, so it is quite likely that protection 5 will act incorrectly when capacity of DO or impedance of the transformer change properly.

(3) Faulted currents on protection 2 and 3 are as follow when fault happens at 50% distance of line BC.

i2=4300.7A 1, = 2048.3A , Over current protection of protection 2 and 3 will

startup b)[ comparing to the setting value in table 1. Faulted current 3 is far greater than over current protection setting value of protection 3, although it decreases a lot by the affection of DO. So over current protection of protection 3 still has enough sensitivity while it behaves as make up protection of line Be. And current protection I of protection 2 will act while protection 3 would not act by

REFERENCES:

[ 1] WU Jing, JIANG Hao. Applying and prospect of distributed

generation system . Rural Electrification, 2003( 7) : 19- 20.

[2] ZHANG Chao, JI Jian ren, XIA Xiang, et al. Effect of distributed

generation on the feeder protect ion in distribution network. Relay,

2006, 34( 13) : 9-12.

[3] BARKE R P P, DE MELLO R W. Determining the impact of

distributed generation on power systems : Part 1 radial distribution

systems/ / Proceedings of Power Engineering Society Summer

Meeting, July 16-20, 2000, Seat tie, WA,USA: 1645-1656.

[4] REN Biying, ZH ONG Yanru, SUN Xiangdong, et al. Islanding

detection method based on the alternate current disturbances . Automat

ion of Electric Power Systems, 200S, 32( 19) : SI- S4.

[ 5] HU ANG Wei, LE I Jinyong, XIA Xian g, et al . Influence of

distributed generation on phase-t 0- phase short circuit protection in

distribution network . Automat ion of Electric Power Systems,200S,

32( 1) : 93-97.

comparing the faulted current with setting value. In summary, protection 2 and protection 3 can act correctly at this time.

(4) When fault happens at 50% distance of line AE,

faulted currents on protection 3 and 4 are:

13 = 60S.SA 14 = 10340A ,

Faulted current on protection 4 exceeds setting value of current protection I greatly which is caused by the connection of DO. Reverse faulted current on protection 3 is slightly less than the over current protection setting value of protection 3. So the reverse faulted current may lead to misoperation of protection 3 with large possibility if faulted place, operating mode or DO parameter changes a little.

V. CONCLUSION

Deep and detailed analysis is made about the influence brought to 10k V feeder line protections by DO in distribution network. All of the analysis is based on a practical distribution network. A new protection scheme is proposed. It is simple and viable because that it just need a little adjustment on the old one. A large number of simulations when fault takes place on different lines are made. By comparing faulted current measured in simulation experiment with protection setting value, the results indicate that the protection scheme proposed can satisfy all requirements. It solves the misoperation and sensitivity decrease problem of protection brought by the connection of DO.

[ 6] VIA WAN F A, K ARLSSON D, SANNINO A, et al .Protection

scheme for meshed distribution systems with high penetration of

distributed generation/ / Power Systems Conference: Advanced

Metering, Protect ion Control ,Communication, and Distributed

Resources, M arch 14- 17,2006, Clemson, SC, USA: 99- 104.

[ 7] WU Gang, LU Yuping, H UA Lidan, et al. Impact of fault current

limiter t 0 the performance of relay protection in distributed

generation. Jiangsu Electrical Engineering, 2007,26( 2) : 1- 4.

[ S] ZHANG Yanxia. DAI Fengxian. New Schemes of Feeder Protection

for Distribution Networks Including Distributed Generation. Automat ion

of Electric Power Systems, 2009, 33( 12) : 71- 74.

Deng Menghua (19S4-), Male, Yunnan Shanghai, Graduate, Engineer,

Research Direction: Power system relay protection, Email :

[email protected]

CICED2012 Session 4 Paper No CP0200 Page 4/5

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