2010 International Conference on Power System Technology

A Novel Algorithm of Wide Area Backup Protection Based on Fault Component Comparison

Zhiqin He, Zhe Zhang, Xianggen Yin, Hua Wang

Abstract--This paper proposes a novel wide area back-up pro­tection algorithm that measures synchronized information from

different buses in region. The amplitude of voltage fault com­ponent from different buses is compared, and the bus with

maximum magnitude will be selected. Hence, suspected fault line

set could be established according to the sub-graph and complete incidence matrix of selected buses. Then, voltage fault component

amplitude at two sides of each suspected line could be calculated from another side, and the amplitude comparison between

computed and measured value could be implemented. The ratio would be 1 when external fault occurs, and it would be greater

than 1 when internal fault occurs. Thus, the fault line could be

identified finally. The technique doesn't need high precision synchronization of wide area information, and could response to

different faults. The simulation of lO-unit and 39-bus New England system using PSCADIEMTDC illustrates the effective­

ness of this method.

Index Terms--Wide area protection, phasor measurement

unit(PMU), fault component comparison, lO-unit and 39-bus

New England system, PSCADIEMTDC.

I. INTRODUCTION

PROTECTIVE relaying is the "first defense line" of bulk power grid. If relay device could trip correctly and reliably,

the stability and security of grid could be sustained. Otherwise,

the emergency would be amplified [1]. The wide area blackout events in worldwide in Recent 30 years demonstrate

that protection mal-operation and cascading trips caused by

flow transferring is one of the significant factors which accelerate wide area blackout. In addition, traditional relay set

values off-line. This setting style couldn't keep sensitivity and

selectivity at the same time for system's complicated network topology. And the setting value rectifying work depends on

manual work, so hidden failure would exist [2]. Therefore,

researching fault rapid location and isolation algorithm and improving traditional setting method is the focus for relay

engineers in future. Meanwhile, these discussions are the main

self-healing function of smart gird [3]. The blackout investigators found that remote backup

protection (such as: Zone3 of distance protection) contribute

This work was supported by the National Natural Science Foundation of China (No. 50837002 and No. 5087703 1), and the National High Technology Research and Development of China (863 Programme) (2009AA05Z208).

Z. He, Z. Zhang, X Yin, and H. Wang are with the Electrical Power Security and High Efficiency Lab, Huazhong University of Science and Technology, Wuhan 430074, China (e-mail: zhiqinhe@smail.hust.edu.cn).

978-1-4244-5940-7/1 0/$26.00©20 1 0 IEEE

to the acceleration of the blackout. However, if a contingency

of a failure of the station battery occurs, Zone3 still is the most effective method to protect grid [4]. A flow transferring

identification algorithm with consideration of flow transfer

factor (FTRF) based on phasor measurement unit (PMU) is presented in [5]. The transfer current value caused by single

feeder could be calculated off-line. Then, the flow transferring

could be found by comparing measured current value and calculated value.

Wide area protection is a new path for relay engineer to

explore. Because of the time delay problem, wide area backup

protection is easier to realize than main protection. Genetic algorithm is used to identify fault location in [6]. Information

fault tolerance could be obtained, and protection device could

make proper decision even the information distortion reaching 5/32. Traditional current differential protection and direction

pilot protection are introduced to wide area backup protection

in [7]-[10]. The protection Agent has fault forecast and identification functions. Traditional main relay operation

information and wide area current differential protection are

combined to use [8]. The differential protection needs wide area data to be high precise synchronized measured. On the

contrary, directional comparison protection only need transmit

logic component, it is easier to realize in actual gird [9]. Utilizing bus positive sequence voltage to reduce calculation

scope is presented in [11]. But it is hard to reflect high

resistance fault. Negative and zero sequence voltage could be used to locate fault position. However, they could only

identify asymmetrical fault [12].

There are two structure types have been discussed: distributed and centralized. The former sets every intelligent

electronic device (lED) as a trip decision making unit. Each

lED only communicates with relative IEDs which belong to its protection scope [7]. However, producing high intelligent

lED and using it widely is a long term scheme for the price

and technology problem. Existing wide area protection

systems are all based on regional centralized structure [13]­[15]. The idea is setting a critical substation as central station

to realize wide area protection function. Information from

other substations will be transmitted to central station in order to realize fault location and implement trip strategy.

A novel wide area protection algorithm is proposed in this

paper. It is based on region centralized structure and only uses voltage and current fault component amplitude to locate fault

position. Firstly, positive voltage superimposed component,

negative and zero sequence voltage are used to select the bus

which is the most adjacent to fault line. Then, sub-graph and

complete incidence matrix of this bus is utilized to find suspected fault line set. Finally, the ratio between estimated

and measured value of bus voltage is calculated in order to

locate fault line. This method couldn't be affected by high

grounding resistance, and doesn't have high demand to data synchronization.

II. SUSPECTED FAULT LINES SELECTION

A. Bus Sort f

VM(l)

�1I(2)

(a) Phase to phase fault

(b) Single-phas grounding fault

�/(I)

(c) Two·phase grounding fault

Fig. 1. Sequence voltage distribution of two source system Post-fault

As is shown in Fig.1, when asymmetrical fault occurs in

the middle of transmission line, the sequence voltage

distribution has several characteristics as follows: • The peak value of positive sequence voltage is at equ­

ivalent source point. In contrast, the minimum value is at

fault point;

• The peak value of negative and zero sequence voltage

could be found at fault point. When the measured point is further, the magnitude of negative and zero sequence

voltage would be smaller. At source point, negative se­

quence voltage value falls to zero. Zero sequence voltage

would fall to zero on the delta side of transformer.

According to above characteristics, the amplitude of posit­

ive sequence voltage superimposed component, negative and

zero sequence voltage from each buses in power grid could

be sorted. Then, the buses which are most incident to fault line could be found. The pickup criterion is as follows:

(iw .... 1 "KU, ) u (lu .... 1 " KU, ) u (iu, .. 1 " KU, ) (1)

Where I'.U"

., , u"

., and u"., are the amplitude of positive

sequence voltage superimposed component, negative and zero

sequence voltage of bus n. u, is the rated phase voltage of bus

n. K is a proportional coefficient. It's value ranges 0.3 to 0.5.

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Let the pickup bus number is I, m, k. These buses would

be sorted, and the bus which has maximum value of fault

superimposed component would be selected. The sort criterion

is:

{MAX = (il'.u.,l.ll'.u ,.I. ... ll'.u.I)} u

{MAX = (lu,,l.lu,,I. ... lu,,.I)} u (2)

{MAX = (iu ... ,I,lu",I. ... lu . ...I)} Where the amplitude of positive sequence voltage sup­

erimposed component, negative sequence voltage and zero

sequence voltage are measured synchronously by PMU of

each substations in regional girdo If the voltage of one bus is

the maximum, it represents that this bus is the nearest bus to

fault point. If there is more than one bus satisfY formula (2), the

subsequent calculation should be implemented according to

these buses.

B. Suspected Fault Lines Search Let bus m is chosen after former step. Then, all the tran­

smission lines connected to bus m would composite suspected

fault line set. These lines could be found according to the sub­

graph and adjacent matrix of bus m. the sub-graph represents protection scope of IEDs in bus m.

Fig.2 shows IEEE 3-unit and 9-bus system structure. A

fault occurs on Line 6 about 10% of total length. B8

B3

L6

IED7 IED5

L2 L4

IED8 [ED6

B5 B6 IEDI! IED9

LI L3

IEDI2 IEDIO -_ ........ _--..,.....--_ ...... - B4

TI

--t-- BI

01

Fig.2. 3-unit and 9-bus system with line fault

Let Bus8 is selected, and the scope of line protection doesn't exceed transformer low voltage side. The sub-graph

could be obtained as follow:

Bus5

e8

Line2

e7 e2

Bus7 Line5

Fig.3. Sub-graph of Bus8

el e3 e4 Bus9

Bus8 Line6 e5

Line4 e6

Bus6

In this paper, the buses and transmission lines compose

vertexes and the intelligent electric devices (lED) compose edges in sub-graph. The direction of each lED is from bus to

feeder. The sub-graph scope of BusS should extend to Line2

and Line6, because el and e3 which represent lED 1 and IED3

should play remote backup protection role. The complete incidence matrix M of this sub-graph is:

el e2 e3 e4 e5 e6 e7 e8

B8 1 0 0 0 0 0 0

L6 0 0 -I -I 0 0 0 0

B9 0 0 0 0 0 0

L5 -1 -1 0 0 0 0 0 0 (3)

M=B7 0 0 0 0 0 0

L4 0 0 0 0 -1 -1 0 0

B6 0 0 0 0 0 0 0

L2 0 0 0 0 0 0 -I -1

B5 0 0 0 0 0 0 0 1

The feeders and IEDs which is incident to BusS could be search as follow steps:

• Searching non-zero elements in row BS. Then, el and e3

could be found;

• Non-zero elements in column el and e3 could be found.

And L5 and L6 could compose suspected fault line set; • Searching non-zero elements in row L5 and L6, and el,

e2, e3, e4 could be found. These edges represent the IEDs

which are needed to implement subsequent calculation in

order to find fault line finally.

Apparently, the sub-graph and complete incidence matrix

could be formed off-line and rectified accompany with grid topology's change.

III. FAULT LOCATION BASED ON VOLTAGE COMPARISON

A. Theory of Algorithm The method is using voltage and current fault component

from relative buses and feeders to form criteria. Fault com­ponent could be classified to two types: superimposed com­

ponent (positive sequence) and stable state component

(negative and zero sequence). The superimposed component could reflect symmetrical and asymmetrical faults. However,

it could only exits in a short time (about 40ms) after fault

occurring. Thus, it is necessary to add stable state component

to improve this criteria.

If the transmission line operates normally, one side voltage

could be calculated by relative variables from another side.

For instance, the negative voltage of side M and N of one line could be calculated as follows:

(4)

Where Uw and u;, represent bus negative sequence

voltage estimated value. U'M ' U,. represent bus negative

sequence voltage actual value. i'M , i,. represent branch

current, of which the positive direction is from bus to feeder.

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z" represents line impedance.

When external fault occurs, the negative sequence network could be presented as follow:

ZM2 Uw

Fig.4. Negative Sequence network

Where a is a coefficient in order to present fault location.

It's value is [0, I]. Z, is transitional impedance. The relation

formulas are as follows:

. • ZM 2U2! U2M = (-I2M)ZM2 = -----....:::..:--"-----Zg + (ZM 2 + aZL2) / /(ZN2 + (1- a)ZL2) ZN2 + (1- a)ZL2

ZM 2 +aZL2 ZM 2 + ZL2 + ZN2

(5)

(6)

According to (5), (6), (7), the ratio between U;M and

U2M could be presented as follow:

��M=(l+�). ZN2 ZM2+aZL2 (S) U2M ZN2 ZN2+(1-a)ZL2 ZM 2 Where transient impedance component disappears, and the

final equation could be acquired:

U2M ZN2 +(I-a)ZL2 ZM 2 (9)

{ I�;M I=I ZN2+ZL2 . ZM 2+aZL2 1 I�;N I=I ZM 2+ZL2 . ZN2 +(I-a)ZL2 1 U2N ZM 2 + aZL2 ZN2

When internal fault occurs, the value of lu,l!lu,1 at two

sides would be higher than I. In contrast, when external fault

occurs, this value would be equal to 1 approximately. Let the

margin is 20%, the fault location criterion is:

IMY I lv' I lv' I «� > 12)u(� > 12)u(� > 12» ILlUIM I IU2M I IUOM I ILlV' I lv' I lv' I U« __

IN_ > 12u�> 1.2u(� > 12» ILlV IN I IV2N I IVON I

( 10)

This is a comprehensive criterion which consists of six

small criteria. The logic relationship among these small

criteria is "or". It means that the protection would operate if any criteria could be satisfied. Apparently, this criterion only

uses voltage amplitude without angle to identifY fault. Thus, it

doesn't need a high demand to data synchronization.

B. System Impedance Influence Analysis According to formula (9), it is clear that the value of

lu,. I u,.1 and Iv,. I U,.I is affected by the ratio between system

impedance and line impedance. If the ratio in Fig. 4 is:

(1 I)

Hence, the influence of system and line resistance is

neglected. The following equation could be deduced:

U2M U'M (I-a)x+xy (12)

{ I�;M I = �;M = (1+ y)(a+x)

I�;N I = �;N = (1+X)[(1-a)+ y ] U2N U'N ay+xy In order to find the extreme value of (12), an equation

should be supposed:

V;M = V;N V'M V'N

� (x-y)a' -2a(x+xy)+x+xy = 0

The value of a is:

a= x(y + I) ± .Jx(y + I)y(x + I) x-y

( 13)

(14)

(15)

(15) could be substitutes into (12) , and a new expre-

ssion is as follow:

v'", V;N (x + Y + I) [ .J x(y + l)y(x+ I) -y(x + I)] -=-=1+ (I6) V'M V2N Y[ x(x+ I) -.J x(y + I)y(x+ I) ] Let K = .J x(y + I)y(x + I) , and the value of ( 16) is lower

than 1.2. It could be deduced as:

[y + (x + I)]K -[x + (y + I)] y(x + I) "'---'--.;.;;....-"---"--;.;;.;...-'----'- < 0.2

y[x(x + I) -K ] (x+I)[K -y(y+l)]

�-I <0.2 Y[K-x(x+l)] The final formula could be presented as follow:

x+1 -1+--· y

( 17)

(18)

CI9)

I I � (1+-)'( 1+-) <1.44 (20) x y If the scope of x, y is [1, 5], (20) could be presented as

follow figure:

• •

FigS Extreme value distribution of voltage fault component ratio

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Where z axis represents the value of Iv; I / lv, I . It can be

seen that the extreme values of Iv; I / lv, I are all above the sec­

tion which value is 1.44.

IV. CASE STUDY

A. Simulation Model This paper build 10-unit and 39-bus New England test

system model to test the performance of this algorithm using

PSCADiEMTDC software. The voltage level of transmission line is 345kV. The frequency of power grid is 60HZ and fault

point is set in the middle of the line between bus 4 and bus 14.

Six types of fault are tested, and the protection programme is compiled using MATLAB 2009.

Let bus16 represents area central station of wide area

backup protection system. The single line figure and bus

number of simulation system is as follow:

39

9 _L...-...I....

Fig.6. lO-unit and 39-bus New England test system

B. Bus Sort Test There is only listing the voltage amplitude variable quantity

of bus3, 4, 5, 13, 14 and 15 for paper length restriction. The test results are shown in Table I-III.

When metal fault occurs, the positive sequence voltage

superimposed component, negative sequence and zero sequence voltage of the buses which are adjacent to fault point

are changes in different extent. Bus4 and 14 change more

remarkable than other buses for they are more adjacent to fault point than other buses. Positive sequence voltage super­

imposed component could reflect all types of metal faults. But,

it couldn't reflect high resistance grounding fault. Negative sequence voltage could reflect all types of metal asymmetrical

faults and has the same problem with the former.

Only the zero sequence voltage of bus 14 starts up normally

when high resistance grounding fault occurs. Therefore, add­ing zero sequence voltage is helpful to identify nonmetal fault

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in power grid. fault point is in the middle of line. Thus, it is possible that bus

According to the sort criteria presented before, bus 14 could 4 and 14 would be both selected in actual grid. But it would be selected as the bus which is the most adjacent to fault point. not add too large calculation scale and would not miss any

The value span between bus 14 and 4 is small, because the suspected event.

TABLEr POSITIVE SEQUENCE VOLTAGE SUPERIMPOSED COMPONENT RATIO OF BUSES

Fault ILw,l/kv Type

Bus3 Bus4 Bus5 Bus 13 Busl4 Busl5

AG 17.529 34.754 18.550 25.425 35.535 18.2 12

AG(3000)

Be 38.342 76.090 40.545 55. 185 77.683 39.622

Be (250) 24.934 45.009 26.208 34.068 45.627 25. 179

BeG 45.007 89.349 47.709 64.787 9 1.328 46.694

ABe 76.56 1 152.202 8 1.225 1 10.303 155.603 79.325

TABLE II NEGATIVE SEQUENCE VOLTAGE OF BUSES

Fault lu,! IkV Type

Bus3 Bus4 Bus5 Bus 13 Busl4 Busl5

AG 17.866 34.954 18.88 1 25.345 35.654 18.409

AG(3000)

Be 38.778 76.268 41. 13 1 55.395 78.025 39.885

Be (250) 29. 123 57.278 30.865 4 1.605 58.59 1 29.964

BeG 32.067 63.070 33.996 45.754 64.488 32.930

ABe

TABLE III ZERO SEQUENCE VOLTAGE OF BUSES

Fault Type

Bus3 Bus4 Bus5

AG 37.08 1 79.026 27. 15 1

AG(3000)

Be

Be (250)

BeG 28.234 56.563 20.696

ABe

C. Fault Location Test There is only listing the ratio result of line 4-14, 3-4 and

14-15 which are incident or sub-incident to bus 14. The test results are shown in Table IV-VI.

As is shown in test results, the ratio of positive voltage seq­

uence superimposed component, negative and zero sequence voltage from two sides of line 4-14 could be higher than 1.200

lu,! IkV Bus 13 Busl4 Busl5

39.689 79.3 13 3 1.704

6.207

30.205 60.0 19 24.055

when grounding fault happens, and the sensitivity of zero sequence criterion is higher than others. The voltage ratio of

line 3-4 and 14-15 is near 1.000. The transient resistance

couldn't affect this algorithm. So the mal-operation and refu­sing operation could be forbidden reliably.

When phase to phase and symmetrical fault occurs, posi­

tive sequence voltage superimposed component or negative

voltage criterion could identifY fault line correctly.

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TABLE IV POSITNE SEQUENCE VOLTAGE SUPERIMPOSED COMPONENT RATIO

Fault ILlU;I/ILlUII

Type Bus3 Bus4 Busl4 Bus4 Busl5 Busl4 (L3 .. ) (L3-4) (LI4 .. ) (LI4 .. ) (LI4-l5) (LI4-1S)

AG 1.000 1.003 1.602 1.599 1.008 1.003

AG (300n) 1.006 1.004 1.609 1.592 1.008 1.005

BC 1.002 1.003 1.609 1.595 1.009 1.004

BC (25n) 0.996 1.002 1.6 1 1 1.594 1.0 10 1.00 1

BCG 1.005 1.00 1 1.608 1.597 1.006 1.003

ABC 1.004 1.00 1 1.608 1.594 0.999 1.00 1

TABLE V NEGATIVE SEQUENCE VOLTAGE RATIO

Fault lu;l/lu,1 Type Bus3 Bus4 Busl4 Bus4 Busl5 Busl4

(L3 .. ) (L3 .. ) (LI4 .. ) (LI4 .. ) (LI4-1S) (LI4-1S)

AG 1.000 1.003 1.602 1.599 1.007 1.002

AG (300n) 1.006 1.002 1.609 1.589 1.006 1.005

BC 1.00 1 1.003 1.609 1.595 1.009 1.004

BC (25n) 0.997 1.002 1.607 1.593 1.009 1.00 1

BCG 1.005 1.005 1.6 1 1 1.598 1.005 1.005

ABC

TABLE VI ZERO SEQUENCE VOLTAGE RATIO

Fault Type Bus3 Bus4 Busl4

(L3 .. ) (L3-4) (LI4 .. )

AG 0.999 1.005 1.862

AG (300n) 1.000 1.005 1.88

BC

BC (25n)

BCG 1.033 0.992 1.859

ABC

V_ CONCLUSION

The paper proposes a novel wide area backup protection algorithm for power grid fault location using PMU technique

based on centralized system structure. This algorithm could

realize region grid fault location by two steps and has been proved its effectiveness in simulation test. It could be adopted

with wide area differential current protection as protection

double configuration for many reasons. • The relay only uses voltage and current fault component

amplitude information to identify fault position and doe-

lu; I/luo I Bus4 Busl5 Busl4 (LI4-4) (LI4-1S) (LI4-1S)

1.826 1.0 14 0.998

1.826 1.020 1.00 1

1.806 1.0 18 0.994

sn't have a strict demand to data synchronization;

• The relay criterion doesn't affected by transient resistance and system non-all phase operation;

• Only the sub-graph and complete incidence matrix of all

buses should be calculated in central station off-line. There are many further work should be done for improving

this algorithm. The next work is as follows:

• Test and improve this algorithm in order to meet different power system operation condition. Such as: flow

transferring, system oscillation, multi-fault and so on;

• Simulate actual communication network and test the

communication delay of this method in order to verify its

real-time performance.

VI. REFERENCES

[I] Damir Novosel, George Bartok, Gene Henneberg, et al. "IEEE PSRC report on perfonnance of relaying during wide-area stressed conditions," IEEE Trans. Power Delivery, vo1.25, pp.3-16, Jan. 20 10.

[2] AG.Phadke, Synchronized Phasor Measurements and Their Applications, New York: Springer, 2008, p.2 1 1.

[3] Li Bin, Bo Zhiqian. "Investigation on Protection and Control of Smart grid," Automation of Electric Power Systems(in Chinese), vo1.33, pp.7-12, Oct. 2009.

[4] S. H. Horowitz, A G. Phadke. "Third zone revisited," IEEE Trans. Power Delivery, vo1.2 1, pp.23-29, Jan. 2006.

[5] XU Huiming, BI Tianshu, HUANG Shaofeng, et al. "Flow transferring identification algorithm for Multi-branches removal event with consideration of transient phenomena," Proceedings of the CSEE(in Chinese), vo1.27, pp.24-30, Aug. 2007.

[6] WANG Yang, YIN Xianggen, ZHAO Yijun, et al. "Regional power network intelligent protection based on genetic algorithm," Automation of Electric Power Systems(in Chinese), voL32, pp. 40---44, Sep. 2008.

[7] SU Sheng, K. K. Li, W. L. Chan, et al. "Agent-based self-healing protection system," IEEE Trans. Power Delivery, vo1.2 1, pp.6 10-618, Apr. 2006.

[8] Xiaoyang Tong, Xiaoru Wang, Kenneth Hopkinson. "Agent-based self­healing protection system," IEEE Trans. Power Delivery, vo1.24, pp.6 1-72, Jan. 2009.

[9] Cong Wei, Pan Zhencun, Zhao Jianguo. "A wide area relaying protection algorithm based on longitudinal comparison principle," Proceedings of the CSEE(in Chinese), vo1.26, pp.8-14, Jul. 2006.

[ 10] Yang Zengli, Shi Dongyuan, Duan Xianzhong. "Wide-area protection system based on direction comparison principle," Proceedings of the CSEE(in Chinese), vo1.28, pp.77-8 1, Aug. 2008.

[II] M. M. Eissa, M. E1shahat Masoud, M. Magdy Mohamed Elanwar, et al. "A novel back up wide area protection technique for power transmission grids using phasor measurement unit," IEEE Trans. Power Delivery, vo1.25, pp.270-278, Jan. 20 10.

[ 12] Zhang Yagang, Zhang Jinfang, Ma Jing, Wang Zengping. "Fault detection and identification based on DFS in electric power network," KAM Workshop IEEE International Symposium, 2008, pp.742-745.

[ 13] Miao Shihong, Liu Pei, Lin Xiangning, et al. "A new type of backup protective system in wide area network based on data network," Automation of Electric Power Systems(in Chinese), voL32, pp.32-36, May. 2008.

[ 14] Zhao manyong, Zhou hongjiang, Chen Zhaohui, et al. "A new wide-area Integrated protection scheme based on IEC6 1850," Automation of Electric Power Systems(in Chinese), vo1.34, pp.58--{50, Mar. 20 10.

[ 15] Xiangning Lin, M. Zhengtian Li, Kecheng Wu, et al. "Principles and implementations of hierarchical region defensive systems of power grid," IEEE Trans. Power Delivery, vo1.24, pp.30-37, Jan. 2009.

VII. BIOGRAPHIES

Zhiqin He was born in Jiangxi province, China, on February 5, 1982. He received the B.S. and M.S. degrees from East China Jiaotong University, Nanchang, in 2003 and 2006. He is currently pursuing the Ph.D degree in electrical power engineering at the Huazhong University of Science and Technology, Wuhan, China.

His research interests include power system wide area protection and control.

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