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Fault current limiter versus series reactor
Conference Paper · June 2017
DOI: 10.1109/EEEIC.2017.7977495
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Fault Current Limiter versus Series Reactor
Haidar Samet, Teymoor Ghanbari, Mohammad Amin
Jarrahi
Abdorasoul Ahmadi Beni, Bahram Kolkian, Arash
Ebtia, Mohammad Reza Banaeian Mofrad
Shiraz University
Shiraz, Iran
samet@shirazu.ac.ir, ghanbarih@shirazu.ac.ir,
mohammadamin.jarrahi@gmail.com
Mobarakeh Steel Company
Isfahan, Iran
a.ahmadibeni@msc.ir, b.kolkian@msc.ir, a.ebtia@msc.ir,
m.banaeianmofrad@msc.ir
Abstract— Mobarakeh Steel Company (MSC) in Isfahan/Iran
is one of the largest industrial complexes operating in Middle
East. In a development program in 10 kV feeder of MSC
distribution network, the short circuit capacity of the network
has been increased. Limitation of fault current in this network is
relegated to some series reactors in the tie feeders. Fault current
limiter (FCL) is an efficient alternative for the series reactors in
this application. In this paper, it is confirmed that using some
FCLs in suitable locations of network, the problems can be
resolved.
Keywords— FCL; series reactor; MSC; tie feeder.
I. INTRODUCTION
A. Motication and Literature review
The increasing development, growing electricity petition,
and rising complexity in industrial networks result in higher
fault currents. Thus, there is a significant interest in devices
which are capable of limiting fault currents [1]. Fault current
limiter (FCL) is an ideal option for limiting high fault currents.
An FCL is a device with low impedance at normal operation,
large impedance during fault and quick response characteristics
[2-4]. Utilization of FCL permits equipment to stay in use even
if their fault current exceeds the permissible value and shorttime withstand. In fact, capability of the increased fault current
interruption is provided by the FCLs for the power system
circuit breakers [5]. Using FCLs, replacement of over-rated
equipment can be avoided or at least moved to later [6-8]. In
case of newly planned systems, FCLs allow the usage of
equipment with lower ratings which results in possible
considerable cost saving [9].
FCLs have different types such as sold-state types and
superconductor types which among them, the superconductor
types have been more employed in industries. Using unique
quench characteristics of superconductor elements, the
superconducting FCL (SFCL) could suppress fault currents,
efficiently [2]. An SFCL has various merits such as automatic
excessive current detecting, automatic recovering, and faster
excessive current limiting actions. Furthermore, due to the lowloss nature in the superconducting state during normal
operation, they could be installed in the system to control
excessive current levels without any considerable losses and
nuisances [9].
FCLs can be placed in different locations of network for
different purposes as shown in Fig. 1 [10]. FCL in location A is
utilized to reduce the negative effects of upstream network on
downstream network in fault situations. Utilizing FCL in
location B is used for decreasing the interactions between two
adjacent networks. FCL in location C is aimed to decrease
effects of load R3 (which is in a feeder with high fault
probability) on network. FCL can be placed in location D for
protection of generator G from faults occurrence in the
upstream network.
As mentioned, one of the most suitable locations for
utilization of FCLs in industrial networks is in their tie feeders
[11]. The results of an analysis carried out by the CIGRE
Working Group regarding the preferred locations for installing
FCL is presented in Fig. 2 [12]. It can be observed that the
majority of FCLs have been installed in tie feeders.
A
FCL
FCL
B
A
FCL
FCL
D
FCL
C
G
R1
R2
Fig. 1. Suitable locations of FCL [2]
Incoming
generator
15%
Incoming
transformer
18%
Tie feeder
52%
Feeder
15%
Fig. 2. Preferred locations for installing FCLs [12]
978-1-5386-3917-7/17/$31.00 ©2017 IEEE
R3
B. Aim and Contribution
Mobarakeh Steel Company (MSC) is one of the biggest
steel producers in Middle East. Some problems have been
reported in MSC’s 10 kV distribution network development
program because of already installed series reactors in their tie
feeder locations. Some of series reactors reported shortcomings
are considerable conduction losses in normal condition,
remarkable voltage drop in case of heavy load start-up, and low
response time. FCLs can be a competent substitute for the
series reactors in this claim. In this paper, it is confirmed that
the suitable proposed solution for resolving MSC’s 10 kV
distribution network is replacing some FCLs with already
installed series reactors. For showing the performance of
proposed solution, the network with series reactors and FCLs is
simulated and analyzed in different conditions. The results
validate the proposed solution to overcome the network
problems.
C. Paper Organization
The rest of the paper is organized as follows: Section II
provides the operating principle of the FCL. In Section III, the
problem in MSC’s 10 kV distribution network and the
proposed solution are described. In Section IV, results and
discussions are presented. Design consideration of the utilized
FCL and its specifications are addressed in Section V.
Concluding remarks are provided in Section VI.
II. OPERATING PRINCIPLE OF FCL
Fig. 3 shows a simple equivalent circuit for discussing the
problem associated with fault current limitation in power
systems [13]. Regardless the load current passing through the
feeder prior to the fault, short-circuit current builds up with a
certain rate-of-rise depending on the parameters of the circuit
(source voltage U0 and source impedance ZS) and incipient
angle of the fault. When no limiting action takes place, a fault
current waveform denoted by i1 in Fig. 4 appears. This current
will be interrupted by a conventional circuit-breaker at t3. The
simplest way to limit the short-circuit current would be the use
of a source impedance ZS with an appropriate value. The
drawback of this solution is that it obviously also influences the
system during normal operation, i.e. it results in considerable
voltage drops at high load currents.
In order to be able to limit the first peak Î1 of the short
circuit current i1, it is necessary for the fault current limiting
device to operate within the time interval t1 and to cause a zero
or negative rate-of-rise of the current. This can be achieved by
inserting a voltage or an impedance with high enough value
into the circuit. Such an action requires the use of non-linear
elements and leads to currents of the shape i2 or i3, respectively,
depending on whether the current is only limited (i2) or limited
and interrupted (i3). Along with this current limitation an
overvoltage appears, which is proportional to the superimposed
di/dt.
Zs
U0
is
CB
Fault
Fig. 3. Equivalent circuit representing a fault condition
Fig. 4. Typical current waveforms due to a fault [13]
III. PROBLEM DESCRIPTION AND PROPOSED SOLUTION
10 kV feeder of MSC distribution network has three
63kV/10kV 40 MVA transformers which are shown in Fig. 5.
Each transformer feed its downstream busbar loads which they
work in parallel for applying power to each busbar.
Connections of busbars are already by a series reactor which a
bus tie is in its parallel position. Maximum tolerable current of
series reactors is about 600 A.
Problems that have been reported for this feeder are related
to start-up of compressors with 10 to 15 MW power
consumption. These compressors draw a huge inrush current at
start-up time from its supplying network which even with soft
starters, the current is about 3 or 4 times bigger than nominal
current of the network.
Presence of series reactors in tie feeders can be a problem
in this situation because of their considerable voltage drop.
Also the inrush current subsequent from heavy load start-up
can overload the series reactor and result in tripping it. The
transformer of each busbar should supplies its loads on its own
because of series reactor tripping. Consequently, transformer
draws a huge current from network because of this event and
therefore, an enormous voltage drop will be happened. Also in
this condition, voltage sensitive loads will be tripped.
The solution for solving this problem is replacing series
reactors with FCLs. With utilization of FCLs in place of series
reactors as shown in Fig. 6, feeder transformer contributions
for heavy loads start-up can be done without any problem. In
this situation, high inrush current is divided between three
transformers and mentioned problem won’t happen. FCLs act
as low impedance in heavy loads start-up situation and doesn’t
produce a considerable voltage drop. In fact, FCL’s effect on
network in normal situation and heavy load start-up situation is
insignificant. Although FCLs can have a better performance in
current limiting condition toward already installed series
reactors. FCLs can limit fault currents to an acceptable amount
that circuit breakers can properly perform.
Upstream
network
Upstream
network
Upstream
network
TR1
63kv/10kv
40 MVA
Bus1
Bus2
Bus3
Bus tie1
Other
loads
Heavy
loads
TR3
63kv/10kv
40 MVA
TR2
63kv/10kv
40 MVA
B. Scenario II
Bus tie2
Reactor1
Reactor2
Loads2
Loads3
Fig. 5. Single line diagram of 10 kV feeder of MSC’s distribution network
Upstream
network
Upstream
network
Upstream
network
TR1
63kv/10kv
40 MVA
TR2
63kv/10kv
40 MVA
TR3
63kv/10kv
40 MVA
Bus1
Other
loads
Heavy
loads
Bus2
FCL
Bus3
FCL
Loads2
MW compressor with a soft starter in Bus1 is simulated. At
first, the drawn inrush current is so enormous that a large
voltage drop is happened over series reactor1. After a few
moments, the series reactor1 is tripped because the inrush
current is much more than its tolerable current. After that
event, the other loads (voltage sensitive loads) are also tripped
as a result of voltage drop. The one phase voltage and current
waveform for Bus1 in this condition are shown in Fig. 7. and
Fig. 8.
Loads3
Fig. 6. Single line diagram of 10 kV feeder of MSC’s distribution network
with FCLs
IV. RESULTS AND DISCUSSIONS
For showing the proposed solution for MSC’s 10 kV
distribution network problem, the system is simulated in
PSCAD which four scenarios are considered:
 Scenario I: Simulating the reported problems of network
with already installed series reactors.
 Scenario II: Simulating the proposed solution by installing
FCLs in tie feeder locations.
 Scenario III: Simulating the system with series reactors and
FCLs to compare their effects on voltage drop.
 Scenario IV: Simulating the fault current limiting capability
of series reactors and FCLs.
The results for mentioned scenarios are described and
shown in following:
A. Scenario I
As mentioned in section II, heavy loads start-up is the
reason of network problems. For showing the problems, a 15
In this scenario, series reactors are replaced with FCLs to
overcome the network problems. In the heavy loads start-up
condition, FCLs performs as a low impedance and large inrush
current shared between three transformers capacities. Hence
the Voltage is increased in this scenario in compared to the
previous scenario. FCLs can handle the large current in this
situation and voltage sensitive load are still remain connected.
It should be noted that the current threshold that is selected for
FCL to act as large impedance is much more than maximum
inrush current which starting-up of heavy loads is drawn from
network. The one-phase voltage and current RMS waveform
for Bus1 in this condition are shown in Fig. 9. and Fig. 10.
C. Scenario III
In this scenario it is assumed that series reactor1 can
operate in heavy load start-up situation and don’t trip. A
considerable voltage drop will be occurred in this case due to
its large impedance. Presence of FCL in tie feeder can be a
perfect solution for this condition. FCL doesn’t produce
voltage drop because of it low impedance. Figure 11 compares
the voltage of Bus1 in presence of series reactor and FCL
during a start-up of the compressor.
D. Scenario IV
Comparing the fault current capability of series reactor and
FCL is done in this scenario. To fulfill this task, a three phase
fault is simulated on bus1 in system with series reactor and
FCL in bus tie location. In this scenario, FCL enters
considerable high impedance to system and limit the current to
an amount which the circuit breakers can cut the faulty section.
The one phase current RMS waveform for Bus2 in this
condition is shown in Fig. 12.
V. DESIGN CONSIDERATION OF FCL
Resistive and inductive types of SFCL are common
structures, which have been employed in industries.
Nowadays, the resistive type is more being attractive due to
some advantages addressed in [14-16]. Hence, the utilized FCL
in this application is selected as resistive type SFCL.
A well designed resistive FCL should meet the following
basic requirements:
1) limitation of the first peak of a fault current (transient
current);
2) limitation of the steady-state fault current;
3) low impedance under normal operation conditions of
the protected circuit;
4) low power loss under normal conditions
5) quick return to the low impedance state after the
limitation of fault currents;
6) high reliability and long lifetime similar to a
conventional power transformer;
7) no overvoltage related to the FCL operation
Based on the simulations, the main specifications for the
SFCL can be listed in Table I.
Considering the system conditions and the FCL
specifications, following design considerations should be taken
into account:
Fig. 9. Voltage RMS waveform for Bus1of 10 kV feeder of MSC’s distribution
network with FCL
 The device should be designed for normal voltage and
normal current of system which is in order 10 kV and 1.5
kA.
 Permissible voltage drop of the designed device should not
be more than 5% of nominal system voltage. In this
situation, the value of resistance in normal state can be
calculated which is 0.11 Ω for MSC’s 10 kV distribution
network.
 The designed FCL should operate in time interval of
quarter cycle after inception of fault. Knowing this fact,
FCL’s activation current should fulfill this condition.
Activation current for designed FCL is considered 3.5 kA.
 Designed FCL should limit the current to at least 50% of
maximum short circuit current. Resistance of device must
follow the mentioned subject. In this system, Resistance of
designed FCL is considered 1.8 Ω.
Fig. 10. Current RMS waveform for Bus1of 10 kV feeder of MSC’s
distribution network with FCL
Fig. 11. Voltage RMS waveform for Bus1of 10 kV feeder of MSC’s
distribution network with FCL and with series reactor
Fig. 7. Voltage waveform for Bus1of 10 kV feeder of MSC’s distribution
network
Fig. 12. Current RMS waveform for Bus2 of 10 kV feeder of MSC’s
distribution network with and without FC
Fig. 8. Current waveform for Bus1of 10 kV feeder of MSC’s distribution
network
TABLE I.
SPECIFICATIONS OF THE DESIRED FCL
device Specifications
Electrical characteristics
Normal voltage (kV)
Normal current (kA)
Number of phases
Resistance in normal state (Ω)
Activation current (kA)
Resistance in fault state (Ω)
Maximum tolerable short circuit current (kA)
Maximum tolerable time for current limiting (ms)
Limiting Speed (ms)
Time for return to normal state after limiting (ms)
Voltage drop in normal state (% of rated voltage)
Insulation class
Mechanical characteristics
Height (m)
Length (m)
Width (m)
Weight (tonnes)
Cryogenic characteristics
Superconductor element
Cooling liquid temperature in normal state (K)
Cooling liquid pressure in normal state (bar)
Cooling liquid level in normal state (%)
[3]
amount
10
1.5
3
0.11
3.5
1.8
12
120
2
10
5
H
[4]
1.1
0.9
0.9
3 to 5
[9]
[5]
[6]
[7]
[8]
[10]
YBCO
77
3
90
VI. CONCLUSION
The paper presents a solution for problems of MSC’s 10 kV
distribution network. The proposed solution is replacing some
FCLs with already installed series reactors in tie feeder
location. By installing FCL in the MSC 10 kV distribution
network, system interconnection is possible without the need to
raise the capacity of the circuit breakers, and facilities can be
configured for efficiency, among other benefits
[11]
[12]
[13]
[14]
ACKNOWLEDGMENT
The authors wish to thank the staff from MSC who have
contributed to the data and information contained herein. This
work was fully supported by Mobarakeh Steel Company under
grant number 48379316-2.
[15]
[16]
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