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Proceedings of the International Conference on Recent Advances in Electrical Systems, Tunisia, 2017
Editors: Tarek Bouktir&RafikNeji
Fault Resistance Effect on Distance Protection in High Voltage
Transmission Lines
Samira Seghir, TaharBouthiba, RebihaBoukhari, SamiaDadda and AbdelhakimBouricha
LaboratoireOptimisation des RéseauxElectriques
University of Sciences and Technology of Oran Mohammed Boudiaf, USTO
B.P. 1505 El-Mnaouar, Oran 31000 - Algeria
seghirsamira3@gmail.com tbouthiba@yahoo.comboukhari.nabila@yahoo.com sam91tee@hotmail.com
abdelhakim.bouricha@univ-usto.dz
Abstract--Distance relay is the main protection of power
transmission lines and make an important role in power
system stabilization if it operates selective and instantaneous.
The distance relay measures impedance between relay and
the fault point. As the impedance is proportional to the
distance between the fault point and relay so the relay is
directly indicates the distance of the fault location. A fault
resistance during ground faults can depreciate the reliability
of standard-distance protection algorithms. DFT algorithm is
used to measure phasor quantities to obtain apparent
impedance. Distance relays having quadrilateral
characteristics are most suitable for EHV transmission lines
for different types of faults. In this paper, quadrilateral
distance characteristic of the relay Micom Alstom P442 is
implemented for the protection of 220 kV Algerian
transmission lines network using Matlab/Simulink. A study
of the fault resistance effect on the performance of distance
protection is done.The results are presented in graphical
form using an R-X diagram.
Index Terms--Distance protection, fault, fault resistance,
transmission lines, zone protection, quadrilateral characteristic,
Micom Alstom P442 relay.
1. INTRODUCTION
A digital distance relay uses sampled voltage and current
data from the relaying pointfor measuring the apparent
impedance and then uses an appropriate characteristic
tomake proper decisions to disconnect a faulted line.
Because different networkconditions correspond to
different remote-end infeed/outfeed behavior and since
this isnot measurable at the relaying point, the traditional
distance relays have faced severestatic under-reach and
overreach problems. In general, the first zone reach of a
non-pilotdistance relay is set to cover 80-90% of the line
length to the nearest remoteterminal to avoid relay
overreach under all operating conditions. The relay,
however,may not even extend beyond the tee point in
some under-reaching cases [1].
The distance protection uses, to locate a fault, a distance
protection measurement between the latter and the point
where it is installed. This distance is determined by
measuring the impedance of the line, if the line becomes
weak, it gives to the breaker the command to open to turn
off the default line. A default line this protection is based
on digital distance relays.
The principle of distance protection is that the post-fault
impedance estimate is proportional to the fault distance
[2–4]. All discrete distance protection algorithms calculate
this impedance accurately if the input voltages and
currents of the protection relay are purely sinusoidal.
2. DISTANCE PROTECTION PRINCIPLE
Distance protection determines the fault impedance from
the short-circuit voltage and current at the location where
the relay is installed (Fig. 1).
Fig. 1. Distance protection principle, measurement of fault
impendence
The measured fault impedance is compared with the
known line impedance. If themeasured fault impedance is
smaller than the set line impedance, a fault is detected
anda trip signal sent to the circuit-breaker. This means that
the distance protection in itssimplest form operates by
measuring the voltage and current at the relay location.
Noadditional information is required for this basic
distance protection, and the protectiondoes not have to
depend on any additional equipment or transmission
signal. Becauseof inaccuracies in distance measurement,
which are the result of measurement errors,transformation
(CT, PT)errors and inaccuracies in line impedance, in
practice it is impossible toset the protection to 100% of
the line length. A security limit (10 % to 15 %) from
theend of the line must be determined for the so-called
under-reaching zone (1st zone) inorder to ensure
protection selectivity due to internal and external faults,
which can beseen in Fig. 2.
The rest of the line is covered by an over-reaching zone
(2nd zone)which, in order to ensure selectivity, must have
a time delay with respect to theprotection of the
neighboring line. In the case of an electro-mechanical
protection, thisdifference in time is 400-500 ms, and 250-
300 ms in the case of analog static andnumerical
Proceedings of the International Conference on Recent Advances in Electrical Systems, Tunisia, 2017
Editors: Tarek Bouktir&RafikNeji
protection.This time delay includes the operating time of
the circuitbreaker,delay of the distance measuring
elements as well as the security limit.
Fig. 2. Protection zones of distance relay.
In contrast to differential protection which is completely
selective (its protectionzone is entirely defined by the
location of the current transformers at both line ends),the
distance protection in its simplest form (without
telecommunication supplements)does not provide absolute
selectivity. Selective tripping must be ensured by time
delayrelative to the neighboring protection. However,
distance protection has the possibilityof reserve protection
for the neighboring lines. The second stage (over-reaching
stage)is used for this purpose. It reaches the neighboring
busbars and a part of neighboringlines. The next, 3rd stage
is usually used for protecting the entire length of the
neighboring lines (Fig. 2). The arrangement of the stages
and time settings is obtained with a time-length diagram
[5,6].
Performance of the conventional ground distance relaying
scheme is adversely affected by different types of ground
faults, such as single line to ground, double line to ground.
This effect is more pronounced due to the considerable
value of fault resistance [7-9]. The work presented in this
paper addresses the aforementioned problems encountered
by the conventional distance relaying scheme when
protecting doubly fed transmission lines.
3. USED METHOD
A. Phasor estimation: Discrete Fourier Transform
The signal of the voltage V (t) can be written:
(1)
with: w0 fundamental pulsation.
T: period (T=20ms)
(2)
(3)
(4)
n = 1: Fundamental harmonic (at f = 50 Hz)
n = 0 :Continuous harmonic (f= 0)
n: nth harmonic
Equation (1) becomes:
(5)
With :
For n=1 (fundamental frequency at 50 Hz)
(6)
(7)
Let: N be the number of samples per period T:
T = N*∆t
(8)
(9)
(10)
(11)
(12)
(13)
;
We do the same for the current and we find:
;
B. Impedance calculation
The fault impedance is calculated by (Fig 1):
Proceedings of the International Conference on Recent Advances in Electrical Systems, Tunisia, 2017
Editors: Tarek Bouktir&RafikNeji
(14)
For single-phase fault at phase ‘a’:
(15)
(16)
Where:
: Current at source K after fault in phase ‘a’.
: Residual current, which is equal to the sum of the
currents of the three phases.
(17)
Earth coefficient.
(18)
and are zero and positive impedance line
respectively.
For double-phase fault to ground at phases ‘a-b-g’:
(19)
(20)
4. SIMULATION AND RESULTS
A. Study network
The study network is the west Algerian network as
indicated in Fig.3.The protected transmission line is of
100 km assumed between node T (Tiaret) and node S
(Saida) with a voltage of 220 kV (Fig.4).
Fig. 3: Study network, the west Algerian network
Fig. 4: Transmission line to protect: Tiaret-Saida.
The transmission line is supposed with distributed
parameters.
Positive sequence resistance line :RdL= 0.01273 Ω/km
Positive sequence inductance line :LdL= 0.9337 mH/km
Positive sequence capacitanceline :CdL= 12.74 nF/km
Zero sequence resistance line :RoL= 0.3864 Ω/km
Zero sequence inductance line :LoL=4.1264 mH/km
Zero sequence capacitanceline :CoL=7.751 nF/km
The «Matlab-Simulink» software is used to regenerate
voltages and currents signalsat node T (relay position).
Regardingthat distance relay is an impedance element it
needs samplingcurrent and voltage to calculate impedance
using these values.This current and voltage sampling was
done via CT (currenttransformer) and PT (voltage
transformer). These equipmentshave certain accuracy
class and in the fault moment thissampling may be
disturbed by problems CT saturation or CVTtransient fault
(capacitor voltage transformer) and it willinfluence
distance relay performance [10].
Thecurrents and voltages signals are filtered using the
antialiasing filter (Butterworth low-pass) and are sampled
at 1 kHz.
Fig.5. shows the original and filtered signal of the faulty
voltage. The filtered currents and voltages signals are used
for fault location. The current and voltage waves are
sinusoidal after the fault. The applicate methods can be
used for network with complexes loads and unbalanced
cases.
Fig.6 and Fig.7 show filtered signal voltages and current for a
single and double phase to ground fault, respectively.
Fig.5: Signal voltage: original and filtered signals
0 0.05 0.1 0.15 0.2 0.25 0.3
-2
0
2x 105
Times (s)
Signal (Volt)
Original signal
0 0.05 0.1 0.15 0.2 0.25 0.3
-2
0
2x 105
Times (s)
Signal (Volt)
Filtered signal
Proceedings of the International Conference on Recent Advances in Electrical Systems, Tunisia, 2017
Editors: Tarek Bouktir&RafikNeji
Fig.6: Signal voltages and currents for single phase fault see by
the relay T
Fig.7: Signal voltages and currents for double phase to ground
fault see by the relay T
For the calculation of the currents and voltages at the
relay, the Fourier transform method was used and
impedance fault ZF is calculated.
The reference impedance for each zone is defined as:
Z1ref = ZL* 80% = 1.016 + j 23.4 Ω.
Z2ref= ZL*120% = 1.5276 + j 35.1818 Ω.
Z3ref= ZL*150% = 1.9095 + j 43.9772 Ω.
B. Results
The following figures give the values of the resistances RK
and reactancesXK of the loop of the faulty line as a
function of the actual fault location for several fault
resistance Rf in order to determine the tripping zone of the
circuit breaker with quadrilateral characteristic of Micom
Alstom P442 relay.
Figure 8shows the fault impedance for single phase fault
see by the relay for different fault resistances Rf.
Fig. 8 Fault impedance for single phase fault see by the relay for
different fault resistancesRf.
Figure 9shows the fault impedance for double phase fault
see by the relay for different fault resistances Rf.
Fig. 9 Fault impedance for double phase fault see by the relay for
different fault resistancesRf.
C. Results interpretation
In this section, the distance protection was studied as a
function of the fault resistance RF in order to see its
influence on the zones of the protection. We took the
quadrilateral characteristic of Micom Alstom P442 relay.
It is noted that for all fault types the increase of the fault
resistance causes a localization error which explains the
presence of the fault impedances outside the desired zone
and the zone is not detected correctly.
For example, for a RF= 10 Ω fault in zone 1, it is seen by
the relay as a fault in zone 2. The same for a fault in zone
2, it is seen by the relay as a fault in zone 3. These errors
are due to the algorithm used by the relay, the type of fault
and the resistance of the fault.
To improve this protection, it is necessary to play on the
tripping time of each zone by estimating the fault
0 0.05 0.1 0.15 0.2 0.25 0.3
-2
-1
0
1
2x 105
Times (s)
Voltage (V)
Single-phase fault
0 0.05 0.1 0.15 0.2 0.25 0.3
-5000
0
5000
Times (s)
Current (A)
0 0.05 0.1 0.15 0.2 0.25 0.3
-2
-1
0
1
2x 105
Times (s)
Voltage (V)
Double-phase to ground fault
0 0.05 0.1 0.15 0.2 0.25 0.3
-1
-0.5
0
0.5
1x 104
Times (s)
Current (A)
-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80
-30
-20
-10
0
10
20
30
40
50
60
70
Resistance ()
Reactance ()
Single phase fault
Line characteristic
Zone 1
Zone 2
Zone 3
Rf = 0
Rf = 5Rf = 10
-70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80
-30
-20
-10
0
10
20
30
40
50
60
70
Resistance ()
Reactance ()
Double phase fault
Line characteristic
Zone 1
Zone 2
Zone 3
Rf = 0Rf = 5
Rf = 10
Proceedings of the International Conference on Recent Advances in Electrical Systems, Tunisia, 2017
Editors: Tarek Bouktir&RafikNeji
resistance RF by another algorithm. If the estimated
resistance is low (RF<10Ω) the trip time of each zone is
maintained, if it is high (RF> 10Ω), a setting is proposed in
the tripping times.
5. CONCLUSION
Distance protection is based on the principle of the three
zones, the impedance calculation is constantly compared
with reference impedance values in order to detect the
faulty zone and thereafter to know the tripping time of the
circuit breaker. A quadrilateral distance characteristic of
the relay Micom Alstom P442 was implemented for the
protection of 220 kV Algerian. The performance of
quadrilateral characteristics is evaluated for different fault
location with different fault resistance for single and
double phase faults.Thevariation in fault resistance affects
the performanceof the distance relay.Satisfactory results
have been obtained for low fault resistances. For high
fault resistances, the results are not satisfactory, it was
necessary to propose a technique of estimating the fault
resistance to adjust the tripping times of the circuit
breaker.
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