Energy and Power Engineering, 2013, 5, 579-583
doi:10.4236/epe.2013.54B111 Published Online July 2013 (http://www.scirp.org/journal/epe)
Fault Location Method and Simulation Analysis of
Parallel Compensating Capacitors
Daquan Du1, Na Zheng2, Zhiming Su3
1Hebei Electric Power Research Institute, Shijiazhuang of Hebei, China
2Hebei Shijiazhuang Power Supply Company, Shijiazhuang of Hebei, China
3School of Electrical and electronic engineering, North China Electric Power University, Baoding of Hebei, China
Received March, 2013
ABSTRACT
At present, the operational parallel compensating capacitors can only through the protection action for the information,
so we can‘t location the fault capacitor. In order to obtain every parallel capacitor running status information and
meanwhile according to internal structure and the operation mode of film capacitor, this paper established the physical
model on the single capacitor and the capacitors and simulated different forms of capacitor fault model and calculated
currents changes which flow through the capacitor in every group. According to the above situation, we established
fault criterion matrix of capacitors. The simu lation results show that the fault criterion matrix can reflect capacitor run-
ning state information accurately, and it positioned fault capacitor effectively.
Keywords: Parallel Capacitor; Physical Model; Fault Locatio n; Fault Matrix
1. Introduction
As a kind of very important reactive power compensation
equipment, capacitor improved the power system struc-
ture and the power quality. The stable operation of ca-
pacitors is a very important guarantee for the power sys-
tem security.
At present, the transformer substation under the juris-
diction of the power supply company, which has large
numbers of capacitor. So it is difficult to monitor single
capacitor’s electric capacity effectively in the operation
and maintenance. When the capacitor failure o ccurs, only
relying on capacitor protection device movement, this
method is an afterthought method, and only reflects the
fault information of the capacitors. Location the fault
capacitor need for detected individually[1-3].
Currently, the running parallel capacitor is lack of ef-
fective online testing means. Reference [4] applied high
potentials in taking energy and wireless synchronization
acquisition and transmission technology to design a par-
allel capacitor’s capacitance online monitoring system.
Based on th e each curr ent f low through capacitor, we can
realize the change trend of every capacitor’s capacitance.
In order to obtain the capacitor in the parallel capacitor
banks operating status information and locate on the fault
capacitor effectively, this paper modeled a single capaci-
tor and the entire group of capacitors physical model,
which according to the internal structure of the film ca-
pacitors and field operation. We simulated different
forms of capacitor fault model and calculated currents
changes which flow through the capacitor in every group.
According to the above situation, we established fault
criterion matrix of capacitors. The simulation results
show that the fault criterion matrix can reflect capacitor
running state information accurately, and it positioned
fault capacitor effectively.
2. The Internal Structure and Operation
Mode of the Parallel Capacitor
Currently, film capacitors have been widely applied be-
cause of their excellent performance in the power sys-
tem .The internal core electrode of a film capacitor is a
metal foil, and use polyethylene, polypropylene, poly-
styrene or polycarbonate plastic film wound into a cylin-
drical shape from the overlap of the ends, then through
Press-fit, connection, packaging, packing, capping means
to create .Internal core of the single capacitor connected
M and N series. In the actual running of the site, the
three-phase connection of the parallel capacitor bank is
generally star wiring. In each phase, it also takes the
form of capacitors in series and parallel combinations to
meet the requirements of various parameters. Figure 1 is
a common wiring for parallel compensation capacitor,
the double-star wiring, the neutral point ungrounded. In
each phase, the connection of each star capacitor is 10

D. Q. DU ET AL.
580
and 4 series, and the rated capacity of each capacitor is
29.55 uF, a discharge coil is used to discharge and cater
to the voltage transformer[5].
Capacity of the capacitor changes in two forms, the
increase and decrease of the electrical capacity. The ca-
pacitance of the capacitor increase is due to the break-
down or partial discharge of the internal components and
at this time the amount of increase of the electric capac-
ity is often at least 10%, even larger. But the reasons for
the reduction of the capacitor capacity are element
through a larger current, which exceeds the predeter-
mined value cause internal fuse blown. If one or two
components blown fuse, a change in capacitance value is
generally less than 5%.
According to the relevant protocols of the parallel ca-
pacitors at current, when the capacity change of the ca-
pacitor exceeds a certain threshold value is considered to
be the fault of the capacitor. When the capacitor fault
occurs, the fuse will be blown and it will isolate fault
original from intact original, meanwhile the capacitance
of the capacitor will change accordingly. Capacitor ca-
pacity changes can be reflected in the current from flow-
ing through the capacitor, based on this to determine the
operating state of the capacitor from the monitoring of
the capacitor current.
3. The Model of Capacitor and Simulation
In order to obtain the run state trend information of ca-
pacitor in parallel capacitor bank, we assumed that the
internal fuse blown to simulate the electrical capacity
changes in the amount of 5% in this paper. By analyzing
the current flowing through the capacitor and according
to the relationship between the capacitance of the ca-
pacitor and the current value to obtain the trend of the
electric capacity of the capacitor and position the capaci-
tor whose electrical capacity has a large change.
Modeling capacitor parameters: type BAM12/2-334-
1W, rated voltage 6 kV, rated capacity 29.55 uF and in
the form of internal fuse protection. The internal struc-
ture of the capacitor is 12 and 4 series as shown in Fig-
ure 2.
C
C
C
C
TV
C
C
C
C
TV
QG1
FV
L
Figure 1. Main wiring diagram of the parallel compensation
capacitor bank.
Figure 2. Equivalent circuit diagram of single capacitor.

D. Q. DU ET AL. 581
Capacitor bank shown in Figure 1 as an example, the
connection of each group-phase capacitors is 10 and 4
series, and every capacitor is 12 and 4 series in each in-
side element. Simulation of the electric capacity change
within 5% of the capacitor, it may be has a variety of
fusing forms according to different fuse blown fuse[6].
Fault simulation in this pap er is based on the Simulink
public module library and electricity systems profes-
sional module library of the Matlab simulation platform.
The Simulink simulation language is one of the most
famous integrated simulation environment in the field of
dynamic system simulation, also it uses advanced graph-
ics technology, has a good user interface, provides a
large number of systems built-in modules, simulation
concise and practical[7].
3.1. The Fuse Blown Only Occurs in a Capacitor
The equivalent diagram of single capacitor shown in
Figure 2, the connection of elements is 12 and 4 series,
and the capacity of the capacitor is 29.55 uF. Assuming
that the each element of capacitor has the same capacity,
a capacitance value of each element can be calculated as
9.85 uF according to the series-parallel relationship of
the capacitive element.
As shown in Figure 2, the connection relationship of
each capacitor element has obvious symmetry, when
there is a blown fuse, we assume L11 fuse (denoted as
case 1), according to the series-parallel relationship of
capacitance the value of the capacitor can be calculated
as 28.8933uF. When the two fuse are blown, it is as-
sumed that L11 and L12 at the same time fuse (denoted
as case 2), or L11 and L21 at same time fuse (denoted as
case 3), the electrical capacity of the capacitor reduce to
28.2652 uF and 28.1429 uF respectively.
The single-phase equivalent circuit of 10 and 4 series
capacitor is shown in Figure 3. Apply Simulink tool to
simulate and calculate the current flowing through the
capacitor bank shown in Figure 3. Assuming the blown
fuse occurs in the C11 capacitor, and we denoted the
current which flowing through C11 as I11, and C12 as
I12, and the current following other capacitors and so on.
Current calculation results shown in table 1, I11 is the
current flowing in the failure capacitor, and I12 is the
current flowing in non-failure of a capacitor of the fault
parallel segments, I21, I31, I41 are current flowing
through the o ther parallel section capacito r. Figure 4 is a
curve, which reflects the relationship between the current
flowing through capacitor and capacitance chang e.
From Table 1 and Figure 4, the calculated result, we
Figure 3. Single-phase equivalent circ uit of the 10 and 4 series capacitor bank.
Figure 4. Curve reflects the relationship between the cur-
rent and capacitance change.
Table 1. Current flowing through capacitor.
I11 I12 I21 I31 I41 Total current
No fault33.15433.15433.154 33.154 33.154 397.842
Case 132.46233.20033.138 33.138 33.138 397.658
Case 231.79933.24433.123 33.123 33.123 397.481
Case 331.66933.25333.121 33.121 33.121 397.447

D. Q. DU ET AL.
582
can see in the three fault case, the currents flowing
through the failure of a capacitor are reduced, which is
same as trend of the capacitor capacity.
3.2. The Fuse Blown Happens in Different
Capacitors
Such cases mainly consider the fuse blown in two ca-
pacitors, because the connection of the capacitor group is
10 and 4 series, and taking the symmetry of the capacitor
connected relationship into account, there are two cases
in the failure of a capacitor:
1) Two failure capacitors occur in a same series, may
set as C11 and C12;
2) Two failure capacitors occur in the different series,
may set as C11 and C21;
While a change in capacitance of each capacitor has
three forms, i.e. a blown fuse in the element(case 1 in
2.1), two blown fuse in the same series (case 2 in 2.1)
and two blown fuse in the different series (case 3 in 2.1).
The different points of the three fuse case only a reduc-
tion of the capacitor capacitance values are different, but
have the same regularity, so only consider the first two
cases described above analyze. The current variation in
other circumstances can be got in the same way.
Apply Simulink tool to simulate, and compare no fault
current and fault current flowing capacitor group, the
results shown in the table below.
In Tab le 2 , the failure capacitors of the fault 1 are C11
and C12, the failure capacitors of th e fault 2 are C11 and
C12, the failure capacitors of the fault 3 are C11 and C21,
the failure capacitors of the fault 4 are C11 and C21. As
can be seen from Figure 5 When the capacitor failure
occurs, the change of current is very obvious compare
with the normal capacitor current, an d total current of the
capacitor bank will has a dramatic change correspond-
ingly, and the current ch ange in no fault capacitor is very
small.
4. Fault Location of Capacitor
The relationship between a change in capacitance and the
current flowing through the capacitor bank can be ob-
tained in section II. Current changes can be demonstrated
in the form of a matrix, for the previous embodiment the
capacitor bank can be established a 10-row by 4 column
matrix, and we defined that when the capacitor current
increases the value of the corresponding position is 1,
when the capacitor current is decreased the value of the
corresponding pos ition is -1.we can judge the fault of the
capacitor bank through observing the change of the ma-
trix values easily. If we need to know th e fuse number of
the capacitor element, we can judged by reduce or in-
crease of the current.
Established discrimination matrix based on data in
Table 2, the four fault a matrix as follows:
Figure 5. Comparison of each capacitor current changes.
Table 2. Current flowing through each capacitor.
I11 I12 I13 I21 I22 I31 I41 I（total current）
No fault 33.154 33.15433.15433.15433.15433.15433.154 397.842
Fault 1 C11（case 1）
C12（case 1） 32.507 32.50733.24633.12333.12333.12333.123 397.473
Fault 2 C11（case 1）
C12（case 2） 32.550 31.84333.29033.10833.10833.10833.108 397.296
Fault 3 C11（case 1）
C21（case 1） 32.447 33.18433.18432.44733.18433.12333.123 397.474
Fault 4 C11（case 1）
C21（case 2） 32.432 33.17033.17031.78433.22933.10833.108 397.297

D. Q. DU ET AL. 583
1
1111
1111
1 111
1 111
1 111
1 111
1 111
1 111
1 111
1 111
A





 



















2
1111
1111
1111
1111
1111
1111
1111
1111
1111
1111
A





 
















 
















3
1111
11 11
11 11
11 11
11 11
11 11
11 11
11 11
11 11
11 11
A























 

4
1111
11 11
11 11
11 11
11 11
11 11
11 11
11 11
11 11
11 11
A


























The working condition of the individual capacitors in
the capacitor group can be seen from 4 matrixes above.
When the matrix va lue in a colu mn is the same show th at
the respective capacitors segments have no faults; when
the positive and n egative value appear in a column in th e
discrimination matrix it shows that has a fault in this ca-
pacitor section, and the capacitance value is reduced in
the corresponding position of negative value, shows that
the capacitor internal fuse has blown. According to the
current changes and its corresponding relationship, we
can determine the number of fault capacitor fuse blown.
5. Conclusions
In order to obtain operating state information and the
failure of a capacitor effectively positioning of the vari-
ous capacitors in shunt capacitor bank, and according to
the operation mode and the capacitor’s internal structure
we establish the physical modeling of a single capacitor
and the entire group of capacitors in this paper, and si-
mulate different form of capacitor failure model, and
calculate the change current flowing through the capaci-
tor bank, and establish the failure discrimination matrix
on this basis. The simulation results show that the ca-
pacitor failure discrimination matrix can reflect the run-
ning state of the capacitor in the group accurately, and
locate the failure capacitor effectively.
6. Acknowledgements
The paper is supported by the opening funding of Na-
tional Engineering Laboratory for Ultra High Voltage
Engineering Technology (Kunming, Guangzhou).
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