ground distance relay compensation based on fault resistance calculation

7/27/2019 Ground Distance Relay Compensation Based on Fault Resistance Calculation

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1830 IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 21, NO. 4, OCTOBER 2006

Ground Distance Relay CompensationBased on Fault Resistance Calculation

M. M. Eissa, Senior Member, IEEE

AbstractThe fault resistance introduces an error in the faultdistance estimate, and hence may create an unreliable operationof a distance relay. A new compensation method based on faultresistance calculation is presented. The fault resistance calculationis based on monitoring the active power at the relay point. Thecompensated fault impedance measures accurately the impedancebetween the relay location and the fault point. The relay hasshown satisfactory performances under various fault conditionsespecially for the ground faults with high fault resistance. Thisnew compensation method avoids the under-reach problem inground distance relays.

Index TermsActive power, distance protection, fault resistance,

impedance measurement.

I. INTRODUCTION

PROTECTION of an important transmission line is most

frequently performed using phase-and ground distance

relaying techniques. Distance relays effectively measures the

impedance between the relay location and the fault. If the

resistance of the fault is low, the impedance is proportional

to the distance from the relay to the fault. A distance relay is

designed to only operate for faults occurring between the relaylocation and the selected reach point and remain stable for all

faults outside this region or zone [1].

In developing distance relay equations, the fault under consid-

eration is assumed to be an ideal (i.e., zero resistance) [2][8].

In reality, the fault resistance will be between two high-voltage

conductors, whereas for ground faults, the fault path may con-

sist of an electrical arc between the high-voltage conductor and

a grounded object. The fault resistance introduces an error in the

fault distance estimate and, hence, may create unreliable opera-

tion of a distance relay [9].

The impedance seen by the relay is not proportional to the

distance between the relay and the fault in general, because of

presence of resistance at the fault location.Some techniques for arcing faults detection and fault distance

estimation are introduced in [10] and [11]. The techniques are

based on the voltage and current at one terminal in the time do-

main. The overhead line parameters and arc voltage amplitude

during the fault are given. The techniques have optimal applica-

tion in the medium voltage networks and symmetrical faults.

Manuscript received May 25, 2005; revised October 30, 2005. Paper no.TPWRD-00309-2005.

The author is with the Department of Electrical Engineering, Facultyof Engineering, Helwan University, Helwan, Cairo 11421, Egypt (e-mail:[email protected]).

Digital Object Identifier 10.1109/TPWRD.2006.874621

Fig. 1. Under reach of the distance relays.

A distance relay is set to operate up to a particular value of

impedance; for impedance greater than this set value the relay

should not operate. This impedance, or the corresponding dis-tance is known as the reach of the relay.

A distance relay may under-reach because of the introduction

of fault resistance as illustrated in Fig. 1. Relay at O is set for

protection up to Z. If a fault at Z occurs such that fault resistance

R is high and by adding this resistance the impedance seen by

the relay OZ such that Z lies outside the operating region of

the relay, then the relay does not operate. Fig. 1 shows the trip-

ping polygonally characteristic in case of high fault resistance.

Some techniques [12][17] are suggested for enhancing the high

fault resistance problem. These techniques accommodate this

problem by shaping the trip zone of the distance relay to ensure

the apparent impedance is included inside the trip zone.

In this paper, a new fault impedance compensation methodbased on fault resistance calculation is given. The fault resis-

tance is calculated using the active power at the sending end.

The relay uses a Fourier filter to derive the voltage and current

phasors. The problem of under reach in ground distance relays

is solved. The ground distance relay with this new compensated

method will be demonstrated. Theresults will show that the fault

impedance with high fault resistance is accurately zoned.

II. DOUBLE-END-FED EARTH FAULTS

Fig. 2 shows the phase current lags the phase current

by the angle because of the transfer of power from to .

Since the fault resistance can normally be neglected in the case

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EISSA: GROUND DISTANCE RELAY COMPENSATIONBASED ON FAULT RESISTANCE CALCULATION 1831

Fig. 2. Relationship between the phase voltages and phase currents.

Fig. 3. Diagram for illustrating the flow of sequence power quantities.

Fig. 4. Symmetrical component circuit for a line-to-ground fault (AAA 0 GGG

fault).

of phase-to-phase faults, it is sufficient to consider it only in the

case of earth faults particularly since the tower-to-earth resis-

tance, which under difficult ground conditions and the absence

of a continuous earth wire, can reach significant values.Consider a single unbalanced fault from line-to-neutral on

a system supplied through a grounded generator with pos-

itive-, negative-, and zero-sequence impedances of ,

and , respectively, and with a generated positive sequence

line-to-neutral voltages of and , respectively. Assume

that this system is supplying a fault resistance on phase

whose impedance is as illustrated in Figs. 3 and 4.

For a fault between phase A and ground, the symmetrical

component connection diagram is shown in Fig. 4. The phase

voltage and current can be expressed in terms of the symmet-

rical components, and the voltage of phase at the fault point

can be set as

(1)

(2)

where has been substituted for the sum and

has been substituted for the sum .

The impedance to the fault is given as

(3)

So the uncompensated fault impedance is

(4)

is a source of error in distance relays,

so the actual fault impedance is

(5)

In the same manner and for a three-line-to-ground fault

and symmetrical component circuit, the uncompensated fault

impedance for the distance relays is

(6)

is a source of error in distance relays, so

the actual fault impedance is

(7)

This paper aims to introduce compensated fault impedance

for (5) and (7) based on fault resistance calculation from the

active power and current measurements.

III. FAULT RESISTANCE CALCULATION

The voltages at the fault point can be expressed by

(8)

(9)

(10)

(11)

where

(12)

(13)

The total phase quantities at the point of fault are readily ob-

tained from the above sequence quantities with the following

results:

(14)

(15)



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The sequence power quantities per phase at the fault are

(16)

(17)

(18)

The total power quantities may be obtained by combining the

sequence quantities as

Also, from the single-phase solution, the total power quanti-

ties equal

(19)

From (19), it can be concluded that the total power in the fault

resistance equals the power in phase ( and );

(Fig. 3).

So

(20)

where and are the power in the fault resistance from thetwo sources for phase . So (20) can be expressed as

(21)

With minimal load flow at the time of the fault [18] and the

electromotive-force (emf) constant at the sending and receiving

ends ( and ), the current contribution at the receiving

end is almost in phase with the current at the sending end.

Thus, the phase relationship between the fault currents (

and ) and the voltages ( and ) can be described by

( ) and ( ).

From the above explanation, it can be concluded that the re-

lation between the total power at the receiving end is

directly proportional with a factor of the total power at the

sending end . So

(22)

where is defined as the distribution factor of the generated

power at the receiving end with respect to the generated power

at the sending end.

Consequently, the contribution power to the fault from the

receiving end is also a factor of the contribution power to the

fault from the receiving end. So

(23)

Also, the contribution current from the receiving end to the

fault is a factor from the contribution current to the fault from

the sending end

(24)

Hence, (21) can be described as

(25)

The total power in the fault is described as

(26)

From (25) and (26), the real part of the fault resistance is given

as

(27)

where is defined as the instantaneous power measured at the

sending end and is determined as [19] and [20].

According to the above explanation, the compensated fault

impedances for (5) and (7) are described, respectively, as

(28)

and

(29)

Equations (28) and (29) are the compensated fault impedance

calculation for the single and three earth faults, respectively.

IV. SIMULATION RESULTS

The power system used for testing the proposed new method

is a part of a 500-kV power system shown in Fig. 5. The system

includes two generating stations. A distance relay is located at

buses and as shown in Fig. 5. The voltage and current sig-

nals are the inputs to the relays, and 300 km is the line length.The results described on the R-X diagram (transient impedance

trajectory). The relay is set to protect 90% of the line. It forms

the first zone of the relay, corresponding to a maximum reach

of about 0.486 p.u., and has an arcing reverse of about 150%

[21][23]. The arcing reverse is the resistive allowance of the

trip area as a ratio of the inductive reactance. The reach of the

second zone is set at 120% of line-1. The power system is mod-

eled and different symmetrical and unsymmetrical faults with

solid and fault resistance are simulated using the Electromag-

netic Transients Program (EMTP).

The voltage and current signals are measured at the relay lo-

cations using a sampling frequency of 5000 Hz. The results ob-

tained from the tests are given here. The uncompensated andcompensated fault impedances given in (4) and (28) have been



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Fig. 5. Single-line diagram of the 500-kV power transmission system.

Fig. 6. Fault impedance trajectory forCCC 0 GGG

fault with fault resistance=

2 0 0

at 50 km from relay-S( FFF 1 )

.



1 0 0

at 150 km from relay-S( FFF 2 )

.

described as the single-phase earth faults while the uncompen-

sated and compensated fault impedances given in (6) and (29),

respectively, have been described as the three-phase earth faults.

The performance of the proposed technique was evaluated fordifferent types of internal and external faults, source impedance,


fault with a solid fault at 150 km

from relay-S ( FFF 2 ) .

Fig. 9. Fault impedance trajectory forBBB 0 GGG


2 0 0

at 320 km from relay-S (external fault atFFF 3

).

and fault resistance. Results showed faults are taken with a fault

resistance ranging from 0 to 300 .

The value of compensated and uncompensated fault imped-

ances seen by the phase to ground relay element is depicted

in Figs. 69. It is observed that if the compensated fault

impedance is used, the relay of fault is located exactly in its

proper zone. Whereas, if the uncompensated impedance is used

the fault impedance is misoperated and located out of its zone

or inaccurately located in its zone.

Figs. 10 and 11 show the fault trajectory for the 3L-G fault

(internal and external) protected zone. As seen in the figures, the

compensated fault impedance is properly identified as the zone

of fault and, thus, avoids misoperation in case of 3L-G faultsthrough high fault resistances.



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Fig. 10. Fault impedance trajectory for 3 LLL 0 GGG fault with fault resistance =

2 0 0 at 150 km from relay-S ( FFF 2 ) .

Fig. 11. Fault impedance trajectory for3 L

-G


2 0 0

at 370 km from relay-S (external fault atFFF 4

).

The suggested technique gives the solutions for the symmet-

rical and unsymmetrical faults with solid and fault resistances.

The presented technique does not depend on the line lengths,

so it can be applied on the long lines. The fault conditions such

as a dc component, sampling frequency, and point on wave do

not have an effect only on the relay performance. Moreover,

the compensated fault impedance accurately measures the

impedance between the relay location and the fault point. So,

the protective system will be very selective. These improve the

technique convergence properties.

V. CONCLUSION

The main objective of the paper is to find out the limitation of

the ground distance relay and the effect on the operating zoneof high fault resistance. This paper introduces a new method of

fault impedance compensation based on fault resistance calcu-

lation. The problem of under reach in ground distance relays is

solved. The investigation showed that the fault resistance detec-

tion could reach 300 . The results showed that the relay oper-

ates correctly for faults simulated within the first, second, and

third zones. The suggested technique gives the solutions for the

symmetrical and unsymmetrical faults. Fault impedance is ac-curately calculated; this will improve the relay selectivity. The

techniques can be used for medium and long lines.

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M. M. Eissa (M96SM01) was born in Helwan, Cairo, Egypt, on May 17,1963. He received the B.Sc. and M.Sc. degrees in electrical engineering fromHelwan University, Cairo, in 1986 and 1992, respectively, and the Ph.D. de-gree from the Research Institute for Measurements and Computing Techniques.Hungarian Academy of Science, Budapest, Hungary, in 1997.

Currently, he is an Associate Professor with Helwan University. In 1999, hewas invited to be a Visiting Research Fellow at the University of Calgary, Cal-

gary, AB, Canada. His research interests include digital relaying, application ofwide-area networking to power systems, and wavelet applications in power sys-tems.

Dr. Eissa received the Egyptian State Encouragement Prize in Advanced Sci-ence in 2002 and the best research in the advanced engineering science fromHelwan University in 2005.

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ground distance relay compensation based on fault resistance calculation

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