-
A New Fault Location Algorithm for Distribution Systems with
Distributed Generations
S. Jamali and V. Talavat
Centre of Excellence in Power System Operation and Automation
Iran University of Science and Technology Narmak, Tehran
16846-13114, Iran
Email: [email protected], [email protected]
Abstract- This paper presents a new fault location algorithm for
radial distribution systems with distributed generation (DGs),
which uses the fundamental component of voltages and currents
recorded at the head of main feeders in a substation. In the
proposed fault location algorithm after calculating the internal
voltages of the distributed generations, the accurate fault
location is estimated by an iterative process. The accuracy of the
proposed algorithm has been validated by simulation studies carried
out for different fault conditions by using the EMTP software for a
205-node 20 kV radial distribution system containing three DGs. The
studies considers the effects of fault type, fault resistance, load
variation, DGs injected power uncertainty and penetration level of
DGs, which are shown very remarkable fault location results
presented in the paper.
I. INTRODUCTION
Power distribution systems are subjected to fault conditions
caused by various sources. It is important for the electricity
companies to locate the fault quickly for achieving customers
satisfaction by enhancing service reliability and power
quality.
Fault location in distribution systems with distributed
generations is more complicated, which is mainly because of lack of
effective protection coordination in presence of DGs.
During the last fifteen years, several fault location methods
for distribution systems have been proposed in the literature. Most
of the methods deal with conventional radial distribution systems,
and only recently very little attention has been paid to fault
location in distribution systems consisting distributed generations
which are briefly explained as follows.
The idea proposed by penkov et al [1] describes a fault location
algorithm based on symmetrical components. The presented method can
be applied to three phase short circuit faults in balance
systems.
Bretas et al presented a fault location algorithm for
distribution systems with DGs which uses the positive sequence
apparent impedance [2]. The authors have not explained how to find
the internal DGs voltages and also they have not considered the
non-homogeneity of distribution lines.
This paper presents a new fault location method for radial
distribution systems with distributed generations, which overcomes
the above mentioned difficulties. The proposed fault location
algorithm is based on the fundamental
frequency components of voltages and currents recorded at the
main relaying point of the networks.
The proposed algorithm consists of two sequential steps. In the
first step, known as the pre-fault processing, by using the
pre-fault voltage and current phasores and having scheduled DGs
active and reactive power in PQ-based, or active power and bus
voltage in PV-based load flow, the internal voltages of the DGs are
estimated. In the second step, known as the post-fault processing,
after removing DC offset components of the voltage and current
samples, the fault location algorithm is performed by an iterative
process.
In order to show the accuracy of the proposed fault location
algorithm, simulation results are presented for a 205-node 20 kV
radial distribution network having several laterals and three DGs
with up to 46% level of penetration. The simulation study considers
the effects of fault type, fault resistance, load variation, DGs
injected power uncertainty and penetration level of DGs. The
results indicate that the algorithm has remarkable accuracy and
robustness for being applied to any radial distribution systems
with distributed generations.
II. FAULT LOCATION ALGORITHM
To illustrate the new proposed fault location algorithm,
consider a faulted line section in radial distribution system with
distribution generations, as shown in fig .1, where VS=[Va Vb Vc]t
is the sending-end voltage phasor quantity and IS=[Ia Ib
Ic]t/IR=[I'a I'b I'c]t are the upstream/downstream current infeed
phasor quantities.
Based on the faulted line section in Fig. 1, the voltages at the
sending-end VS can be expressed in term of the upstream/downstream
current infeed phasor quantities and fault distance d.
( )RSSS IIRdZIV += (1) Fig. 1. faulted line section
If
d
Ic
Ib
Ia
Vc
Vb
Va
(1-d)
Ifa Rfa
V'c
V'b
V'a
Rfb Rfc Ifb Ifc
Rf
I'c
I'b
I'a
MilosHighlight
MilosHighlight
MilosHighlight
MilosHighlight
MilosHighlight
MilosHighlight
-
where:
=
333231
232221
131211
zzzzzzzzz
Z
+
+
+
=
ffcff
fffbf
ffffa
RRRRRRRRRRRR
R
In the above equation, the quantities of fault resistances
(Rfa, Rfb, Rfc and Rf) can be varied from zero to infinity
depending on fault types and phases involved [3]. For instances, in
case of the single-phase-to-ground fault on phase A, only fault
resistance is Rf and the quantities of Rfa, Rfb and Rfc are zero,
infinity and infinity respectively.
Appling the quantities of fault resistances, equation (1) can be
rewritten for the assumed fault as following:
( ) ( )aafc13b12a11a IIRIzIzIzdV +++= (2) Given the quantities
of Va, IS and I'a, separating equation
(2) into real and imaginary components as equation (3) and
solving them, the fault distance d and fault resistance Rf can be
estimated.
( ) ( ) ( )( ) ( ) ( ) faac13b12a11a
faac13b12a11a
RIIImdIzIzIzImVImRIIRedIzIzIzReVRe
+++=
+++= (3)
Similar equations can be obtained for phase-to-phase,
phase-to-phase-to-ground and three phase faults.
In the above equations, each quantities of VS and IS of faulted
line section, which are calculated using data available at the
substation, are known and the quantity of IR due to existence only
one measuring point in distribution system is unknown. Proposed
fault location method by using of the following iterative algorithm
calculates each unknown quantities such as d, IR and fault
resistances.
1. Initialize d=0, that is fault point is assumed at the
beginning of line section.
2. Calculate the quantity of IR by using of the new circuit
solution procedure on downstream subsystem of fault point.
3. Determine fault distance d and fault resistances using
equation (1).
4. Keeping on algorithm until the estimated fault distance
converges, that is
-
By forming the impedance matrix ZB for assumed subsystem, the
following steps are describing the above mentioned procedure.
In the first step, after isolating all internal DGs voltages,
the conventional power flow algorithm is performed on the
subsystem, which is considered that DGs fault current infeed are
equal to zero. By calculating isolated DGs points voltages Vi and
subtracting from the DGs scheduled internal voltages, DGs fault
current infeed can be derived using equations as in follows:
iDGii VVV = (7)
[ ] [ ] [ ]VZI 1BDG = (8) where: VDGi: scheduled internal
voltage of the ith distributed
generation Vi: calculated isolated DGs points voltages. In the
next steps, conventional power flow algorithm is
applied to the subsystem by considering DGs fault current infeed
using equation (8). The above process is repeated until the
mismatches of V in sequential iterations become less than a
threshold.
III. DISTRIBUTED GENERATION MODELING
In order to modeling of distributed generations, ideal
synchronous generators connected to distribution system by
transformer are used. The applied post-fault synchronous generators
model, which is shown in Fig. 3, are consisted of the internal
voltage E"g behind subtransient reactance X"s. The above internal
voltage E"g has been formed by performing pre-fault power flow
algorithm based on scheduled DGs active and reactive power in
PQ-based, or active power and bus voltage in PV-based DGs [6].
IV. SIMULATION RESULTS
To evaluate the performance of the proposed fault location
algorithm, an actual radial distribution feeder, commonly found in
Iran, is studied. The 205-node 20 kV radial distribution test
feeder, which is shown in Fig. 4, contains 71 km overhead lines and
110 distribution transformer 20/0.4 kV as constant impedance loads
definition. In the above test feeder distribution transformers have
totally installed loads of 11160 kVA and the maximum length of
transformers to the beginning of the feeder is 24 km.
In order to describe the sensitivity of the fault location
algorithm results to transformer loading variations, the above test
feeder has been presented in three different cases with various
transformer loading factors (LFs) and power factors (PFs).
Fig. 3. Post-fault ideal synchronous generator model
In the above test system three distributed generations with
nominal power capacities 1.25, 1.25 and 1.6 kVA, which are
connected to nodes 104, 164 and 205 respectively, have been used.
The inserted distributed generations are presented as 400 V
synchronous generators connected by a 0.4/20 kV transformers with
the same related synchronous generators capacities. Table I
illustrates the characteristics of the connected distributed
generations.
In order to show the accuracy of the proposed fault location
algorithm, several simulations were performed on the mentioned test
feeder using EMTP software. The simulated fault points contain
different fault types such as single-phase-to-ground
phase-to-phase, phase-to-phase-to-ground and three phase
faults.
Table II shows the fault point information such as sending and
receiving end of the faulted section line, the length from the
beginning of the faulted section line and the length from the
beginning of the test feeder.
In the following the effect of fault type, fault resistance,
load variation, DGs injected power uncertainty and penetration
level of the DGs on the accuracy of fault location algorithm has
been studied.
Fig. 4. 205-node 20 kV radial distribution system
TABLE I Distributed generations characteristics
DG node Scheduled active power(MW) Scheduled reactive
power(MVAr) Xs(pu) X"s(pu)
104 0.8 0.6 1.8 0.18 164 0.8 0.6 1.8 0.18 205 1 0.75 1.8
0.18
154 156 167169
7 8 5 69
234 1
2728 2629
23
202119
2224
25
1011
163031 32 33343639414749 5153
13
84
86
46
4445
4342
48
5254
50
3840
35
59
71
76
77
105 82
12
15 1418 17
37
5558
57
56
61
63
67
73
60
72
66 65 6462
69 68
7570
74
104103102100 101
85
8081 7879
106107
9088
87
999798
9189
92 9493
9596
83
108109
111
110112 113114 116 118 122
123124125126
120
121117115 119127
132 130
129128
131
134133 142
135
137 136
139138
140
141
146145
144143
147
148
149
150
186
185184183 152 153
157
151168
170 155 162
163
164
165166158159161
160
171175176
177 173
174
189
200199198
201
202
197196
204205 182
178
172
203
181
179
180
187188
190193
194
195
192191
DG1
DG3 DG2
E"g X"s
Vt
-
TABLE II Simulated fault points parameters
Sending-end node
Receiving-end node
Length from beginning of the
section(m)
Length from beginning of the
feeder(m) 11 13 550 4172 71 76 425 11432
100 102 250 13967 153 155 630 15592 186 189 225 20922
A. Effect of fault Resistance Variations To evaluate the
accuracy of fault location algorithm some
simulations on fault points shown in Table II with five fault
resistance varying from 0 to 50 by 10 step, have been performed in
EMTP software. The simulation results obtained from fault location
algorithm are summarized in Fig. 5.
B. Effect of LFs and PFs Variations In order to investigate the
performance of the proposed
fault location algorithm, several simulations were performed for
radial distribution test feeder depicted in Fig. 4 with three
various transformer LFs and PFs. Fig. 6 shows the above fault
location algorithm results, which contain the phase-to-phase-to
ground faults with 5 Rf value and 10 Rfa and Rfb values.
It can be noticed that the error estimation in the proposed
fault location algorithm are different in various quantities of
transformers LFs and PFs.
Fig. 5. Errors for fault resistance variations Fig. 6. Errors
for LFs and PFs variations
C. Effect of DGs Active and Reactive Powers Uncertainty As the
DGs active and reactive powers are different from
their scheduled quantities, the fault distance estimation errors
are increased. In order to describe the above concept, different
single-phase-to-ground faults with 10 Rf have been tested. The
obtained fault location results for different DGs active and
reactive power for five DGs active and reactive powers error
varying from -20% to 20% by 20% step, has been presented in Fig.
7.
It can be seen from Fig. 7 that the DGs active and reactive
power deviations scheduled quantities are increasing the fault
location errors. For instance, by using of the -20% DGs active and
reactive power error in scheduled quantities, the fault location
algorithm has 19% error estimation.
D. Effect of Penetration Level of the DGs To study the effect of
DGs penetration levels, most
simulations have been presented on the radial distribution test
feeder with three different cases. The above first case only
contains DG1, the second case have DG1 and DG2 and the third case
contain all DGs on the test feeder, whose penetration level powers
are 11, 24 and 46 percent of total powers. The performed simulation
results, which are shown in Fig. 8 and Fig. 9, contain
single-phase-to-ground faults with 10 Rf.
It can be observed from the obtained results, as the actual used
DGs active and reactive powers are not equal to their scheduled
quantities, increasing the DGs penetration levels cause the higher
estimation error.
Fig. 7. Errors for DGs active and reactive powers uncertainty
Fig. 8. Errors for real DGs active and reactive powers
4172 11432 13967 15592 209220
0.005
0.01
0.015
0.02
0.025
0.03
0.035
0.04
Fault Distance(m)
Erro
r(%)
LLG Faults
Case1Case2Case3
4172 11432 13967 15592 209220
2
4
6
8
10
12
14
16
18
20
Fault Distance(m)
Erro
r(%)
LG Faults
PQ-Error=-20%PQ-Error=-10%Real PQPQ-Error=+10%PQ-Error=+20%
4172 11432 13967 15592 209220
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.1
Fault Distance(m)
Erro
r(%)
LG Faults
1-DG, Real-PQ2-DG, Real-PQ3-DG, Real-PQ
4172 11432 13967 15592 209220
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Fault Distance(m)
Erro
r(%)
LG Faults
Rf=0Rf=10Rf=20Rf=30Rf=40Rf=50
-
Fig. 9. Errors for unreal DGs active and reactive powers
V. CONCLUSION
In this paper a novel fault location algorithm for electric
distribution systems containing distributed generations has been
presented. The proposed method includes a new sub procedures such
as DGs-contained lateral current calculation algorithm. The
algorithm has been tested for a 205-node 20 kV radial distribution
feeder having three distributed generations, where the effects of
fault type, fault resistance, load variation and penetration level
of DGs has been studied.
The simulation results indicate that the presented fault
location algorithm has acceptable accuracy and robustness for
applying to any radial distribution systems with distributed
generations.
REFERENCES [1] D. Penkov, B. Raison, C. Andrieu, J. P. Rognon,
B. Enacheanu, DG
impact on three phase fault location. DG use for fault location
purposes?, International Conference on Future Power Systems, 16-18
Nov., 2005.
[2] A. S. Bretas, R. H. Salim, Fault location in unbalanced DG
systems using the positive sequence apparent impedance,
Transmission and Distribution Conference and Exposition, Latin
America, Aug., 2006.
[3] Z. Jun, D. L. Lubkeman, A. A. Girgis, Automated fault
location and diagnosis on electric power distribution feeders, IEEE
Transactions on Power Delivery, vol. 12, Issue 2, April, 1997, pp.
801-809.
[4] L. Seung-Jae, C. Myeon-Song, K. Sang-Hee, J. Bo-Gun, L.
Duck-Su, A. Bok-Shin, Y. Nam-Seon, K. Ho-Yong, W. Sang-Bong, An
intelligent and efficient fault location and diagnosis scheme for
radial distribution systems, IEEE Transactions on Power Delivery,
vol. 19, Issue 2, April, 2004, pp. 524-532.
[5] E. C. Senger, G. Jr. Manassero, C. Goldemberg, E. L.
Pellini, Automated fault location system for primary distribution
networks, IEEE Transactions on Power Delivery, vol. 20, Issue 2,
Part 2, April, 2005, pp. 1332-1340.
[6] C. S. Cheng, D. Shirmohammadi, A three-phase power flow
method distribution system analysis, IEEE Transactions on Power
Systems, vol. 10, No. 2, May, 1995, pp. 671-679.
4172 11432 13967 15592 209220
2
4
6
8
10
12
14
16
18
20
Fault Distance(m)
Erro
r(%)
LG Faults
1-DG, PQ-Error=-20%1-DG, PQ-Error=+20%2-DG, PQ-Error=-20%2-DG,
PQ-Error=+20%3-DG, PQ-Error=-20%3-DG, PQ-Error=+20%
