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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY 2008
Dynamic Performance Comparison of
Synchronous Condenser and SVC
Sercan Teleke, Tarik Abdulahovic, Torbjörn Thiringer, and Jan Svensson, Member, IEEE
Abstract—In this paper, a comparison of the dynamic performance between a conventional synchronous condenser, a
superconducting synchronous condenser, and a static var compensator (SVC) is made in a grid setup by simulating different cases
that affect the performance of reactive power compensation. The
results show that the SVC injects more reactive power and has a
better dynamic performance during faults that cause a moderate
or minor voltage drop on its terminals, such as single-phase to
ground faults in weak grids. The synchronous condensers, on
the other hand, bring the voltage to the nominal value quicker
and show a better dynamic performance for severe faults such as
three phase to ground faults in stiff grids. The superconducting
synchronous condenser injects up to 45% more reactive power
compared to the conventional synchronous condenser during a
nearby three phase to ground fault.
Index Terms—Static var compensator (SVC), superconducting
synchronous condenser, synchronous condenser.
Fig. 1. Single-line diagram with a synchronous condenser connected to grid.
The purpose of this paper is to compare the dynamic performance of a conventional synchronous condenser, a superconducting synchronous condenser (SuperVAR) and an SVC during
various grid set ups and fault types.
II. PRESENTATION OF REACTIVE
POWER COMPENSATION DEVICES
I. INTRODUCTION
EACTIVE power compensation is defined as the reactive
power management with the aim of improving the performance of ac power systems [1]. Reactive power compensation is
viewed from two aspects: load compensation and voltage support. In load compensation, the objectives are to increase the
power factor, to balance the load and to eliminate current harmonics from nonlinear industrial loads [2], [3]. Voltage support
reduces voltage fluctuation at a given terminal of a transmission line [1] and improves the stability of the ac system by increasing the maximum active power that can be transmitted. It
also helps to maintain a substantially flat voltage profile at all
levels of power transmission, increases transmission efficiency,
controls steady-state and temporary over-voltages [4], and helps
to avoid catastrophic blackouts [5], [6].
As reactive power compensation is an effective way to improve the electric power network, there is a need for controlled
reactive power compensation which can be done either by synchronous condensers or static var compensators (SVCs), which
utilize power electronic devices.
R
Manuscript received April 16, 2007; revised September 9, 2007. This work
was supported by ABB FACTS, Västerås, Sweden. Paper no. TPWRD-002162007.
S. Teleke is with the Department of Electrical and Computer Engineering, North Carolina State University, Raleigh, NC 27606 USA (e-mail:
steleke@ncsu.edu).
T. Abdulahovic and T. Thiringer are with the Department of Energy and Environment, Chalmers University of Technology, Göteborg SE-412 96, Sweden
(e-mail: abdulaho@student.chalmers.se; torbjorn.thiringer@chalmers.se).
J. Svensson is with ABB FACTS, Västerås SE-721 64, Sweden (e-mail: jan.r.
svensson@se.abb.com).
Digital Object Identifier 10.1109/TPWRD.2007.916109
In this section, the synchronous condenser and the SVC are
presented.
A. Synchronous Condensers
Synchronous condensers have played a major role in voltage
and reactive power control for more than 50 years [7]–[12].
In this section, conventional and superconducting synchronous
condensers are described.
1) Conventional Synchronous Condenser: A synchronous
condenser is a synchronous motor without any mechanical load
[13]. Its field is controlled by a voltage regulator to generate or
absorb reactive power to support a system’s voltage or to keep
the system power factor at a specified level. Synchronous condensers installation and operation are identical to large electric
machines. A single-line diagram with a synchronous condenser
is shown in Fig. 1.
2) Superconducting Synchronous Condenser (SuperVAR):
Only the field winding of the synchronous condenser utilizes
a high-temperature superconductor winding cooled with a
cryocooler subsystem to about 35–40 K [14]. The cryocooler
modules are placed in a stationary frame and helium gas is
used to cool the rotor of the machine. The stator winding is
a conventional copper winding. However, the winding is not
placed in conventional iron core teeth, since the iron core
saturates due to the high magnetic field, typically 1.5–2.0 T,
imposed by the field winding. Only the stator yoke (back iron)
uses magnetic iron to provide magnetic shielding and to carry
flux between adjacent poles. The absence of iron in most of
the magnetic circuits in these machines results in a very low
synchronous reactance (typically 0.3–0.5 p.u.). More details of
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TELEKE et al.: DYNAMIC PERFORMANCE COMPARISON OF SYNCHRONOUS CONDENSER AND SVC
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Fig. 2. Single-line diagram of the SVC used in the simulations.
Fig. 3. Single-line diagram of the used grid setup.
the SuperVAR, including performance features, design configurations, and maintenance challenges can be found in [15].
B. Static VAR Compensator (SVC)
Maintenance requirements of conventional synchronous condensers rose interest in the development of static VAR systems
[16]. Several papers have studied modeling [17]–[20] and the
application of SVCs [16], [21], [22]. A typical SVC, composed
of thyristor-switched capacitors (TSCs) and thyristor-controlled
reactors (TCRs), together with filters, is shown in Fig. 2. The
filters (FCs) are used to remove low-frequency harmonics produced by the TCR and to produce reactive power. With proper
coordination of the capacitor switching and reactor control, the
reactive power output can be varied continuously between the
capacitive and inductive ratings of the equipment.
The compensator operates to regulate the voltage of the transmission system at a selected terminal. However, the maximum
obtainable capacitive current decreases linearly with the system
voltage since the SVC becomes a fixed capacitor when the maximum capacitive output is reached. Therefore, the conventional
thyristor-controlled SVC rapidly deteriorates its voltage support
capability with the decrease of system voltage.
III. SETUP OF PERFORMANCE STUDY
A. Setup of Compensators
For comparison of the SuperVAR [15], the conventional synchronous condenser and the SVC, a grid setup using PSCAD is
made, where the parameters are given in the Appendix. The conventional synchronous condenser and the SuperVAR are using
the type DC2A exciter and the type ST1A exciter, respectively.
The 32 Mvar SVC consists of two TSC banks where each bank
has 35.8% of the rated power, two 3rd and 5th harmonic filters
where each carries 10.2% of the rated power and two 7th and
11th harmonic filters where each carry 4% of the rated power.
For reactive power consumption, one TCR with the size of 38%
of the rated power is employed. In the connection of the SVC
coupling transformer with the size
to the network, a 10%
of rated reactive power is used, where the high voltage side was
connected with Y grounded.
B. Grid Setup
The grid setup used to compare the performance of the SuperVAR, the conventional synchronous condenser and the SVC,
is shown in Fig. 3. The setup shows a factory, where the main
load consists of two sets of 50 induction machines of 500 HP
with 0.9 power factor; 10 kV with inertia constant of 2 s. These
units are connected to a 36 kV substation via 25 MVA transformers (10% leakage reactance, 36/10 kV). Moreover, a resistive and an inductive load of 16 MW and 12 Mvar are also connected to the substation via a 25 MVA transformer (10%, 36/10
kV). A capacitor bank of 8 Mvar is connected to each 10 kV
load bus in order to keep the 10 kV bus within 95% to 100%
of nominal voltage during full load operation. The short-circuit
ratio (SCR), which is the ratio between the short-circuit power
measured at the 36-kV bus and the load total apparent power, is
3.9 which represents a medium strong system.
Four 8 MVA synchronous condensers or one 32 Mvar SVC
are/is connected to the 36 kV bus via a 32 MVA transformer
(10%, 13.8/36 kV), to provide reactive power compensation, especially in case of faults occurring in the network that transfers
the power from the generator to the factory. The network consists of two 200 km lines with an X/R ratio of 15 where the fault
occurs in one of the lines, which will cause the breakers to open
after a 250 ms delay, and accordingly to disconnect the faulted
line and connect it back 500 ms after the fault is cleared.
In the 36 kV substation, there is a 70 MVA step down transformer (10%, 130/36 kV) that adapts the voltage level to the
factory. Finally, the 130 kV source is an infinite bus.
IV. SIMULATION RESULTS FROM THE STUDY
To compare the synchronous condensers with the SVC, the
parameters of the grid have been altered. The configuration
without any reactive power compensation is denoted by WOC.
The cases with conventional synchronous condensers and
SuperVARs connected to the 36 kV bus are denoted by CON
and SCO, respectively. Finally, the configuration with the SVC
connected to the 36 kV bus is denoted by SVC.
A. Different Fault Types
In this section, single-phase-to-ground, two-phase-to-ground,
and three-phase-to-ground faults are simulated and analyzed.
1) Single Phase to Ground Fault: To determine the performance of the different compensators, a single phase to ground
fault in the middle of one of the two lines is applied. The resulting positive-sequence voltage, reactive power injection and
the speed of the induction machines are displayed in Figs. 4–6.
From Fig. 4, it is clear that without any reactive power compensation, the system collapses and with compensation it survives. Moreover, after the fault, the SVC brings the voltage back
to 1 p.u. quickly and accurately.
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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY 2008
Fig. 6. Speed of the induction machines. Single-phase-to-ground fault.
Fig. 4. Positive-sequence voltage using the synchronous condensers and the
SVC. Single-phase-to-ground fault.
Fig. 7. Positive-sequence voltage using the synchronous condensers and the
SVC. Two-phase-to-ground fault.
Fig. 5. Reactive power injected (20 Hz LP-filter) by the synchronous condensers and the SVC. Single-phase-to-ground fault.
The reactive power injections are shown in Fig. 5. The SVC
injects reactive power after a delay caused by the delay in the
controller, whereas the synchronous condensers react instantaneously due to the change in the terminal voltage. However,
after the initial delay, the SVC injects more reactive power
due to faster voltage control compared to the synchronous
condensers that have significantly larger time constants due to
their field windings.
It can be observed that at the instant of the fault, the SuperVAR injects more reactive power than the conventional
synchronous condenser, which is the consequence of the lower
synchronous reactance. However, as we reach the instant of
the fault clearance, the conventional synchronous condenser
reaches the performance of the SuperVAR. This is the result of
the quicker exciter utilized for the conventional synchronous
condenser. It can be seen in Fig. 6 that the induction machines
collapse without any reactive power compensation and the
speed of the induction machines recover quicker with the SVC.
2) Two-Phase-to-Ground Fault: The resulting positive-sequence voltage, reactive power injection and the speed of the
induction machines for a two phase to ground fault are displayed
in Figs. 7–9.
Now, the positive-sequence voltage drops more with the SVC
compared to the case using the synchronous condensers. Moreover, the positive-sequence voltage reaches the nominal value
quicker with synchronous condensers. The explanation is that
the SVC injects less reactive power during and after the fault
Fig. 8. Reactive power injected (20 Hz LP-filter) by the synchronous condensers and the SVC. Two-phase-to-ground fault.
Fig. 9. Speed of the induction machines. Two-phase-to-ground fault.
until the line is connected back. This is due to that the SVC provides reactive power proportional to the square of its terminal
voltage, so severe voltage drops on its terminals limit its reactive power injection. And, this also means that the speed of the
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TABLE I
MINIMUM POSITIVE-SEQUENCE VOLTAGE DURING THE FAULT AT 36-kV BUS
TABLE II
MAXIMUM INJECTED REACTIVE POWER BY SYNCHRONOUS CONDENSERS
AND SVC DURING THE FAULT
Fig. 10. Positive-sequence voltages in the presence of the synchronous condensers and the SVC. Three-phase-to-ground fault.
Fig. 11. Reactive power injected (20 Hz LP-filter) by the synchronous condensers and the SVC. Three-phase-to-ground fault.
To observe the effect of reactive power compensation on minimum voltage levels more clearly during different fault types,
minimum positive-sequence voltage levels at 36 kV bus during
the fault are put on Table I.
The maximum injected reactive power during the fault for
the conventional synchronous condenser, the SuperVAR and the
SVC can be observed in Table II.
It should be mentioned that the values marked with * are obtained with a 40 MVA SVC (where the system did not collapse)
due to collapse with a 32 MVA SVC during the three phase to
ground fault. It can be seen from Table I and II that the SVC injects more reactive power when there is less voltage drop on 36
kV bus whereas, when the voltage drops more, such as the case
observed in two phase and three phase to ground faults, synchronous condensers inject more reactive power than the SVC.
B. Different Fault Location
Fig. 12. Speed of the induction machines. Three-phase-to-ground fault.
induction machines drops more with the SVC due to the lower
positive-sequence voltage.
3) Three Phase to Ground Fault: The resulting positive-sequence voltage, reactive power injection and the speed of induction machines for a three-phase-to-ground fault are displayed
in Figs. 10–12. Here, the positive-sequence voltage drops even
more with the SVC and it can be noticed that the system collapses due to insufficient injection of reactive power.
However, the reactive power injected by the synchronous condensers is increasing. The larger the positive-sequence voltage
drop, the more reactive power is provided by the synchronous
condensers due to that the injected reactive power is proportional to the difference of terminal voltage and the internal machine voltage induced in the stator by the rotating magnetic field.
The speed of the induction machines drop more with the SVC
and hence the induction machines can not recover their speed
after the fault has been cleared.
To determine the sensitivity of the fault location, the fault
location is changed to 50 km from the source which corresponds to 25% of the line length and 150 km from the source
which corresponds to 75% of the line length and a single phase
to ground fault is applied. The minimum positive-sequence
voltage during the fault for different fault locations is shown
in Fig. 13, which displays that the minimum positive-sequence
voltage drops more when the fault location is far away from the
source. Moreover, the synchronous condensers perform better,
while the performance of the SVC drops. This is in spite of the
fact that the positive-sequence voltage only drops to 0.86 p.u.
As the fault is closer to the load, the reactive power injection performance drops slightly with the SVC, while the performance of the synchronous condensers improves during the
fault (Fig. 14). However, after the fault has been cleared and the
line is restored, the voltage rises up, which helps the SVC to inject more reactive power due to its quicker response, while the
synchronous condensers react slower due to their field winding
dynamics.
The minimum speed of the induction machines drops more
when the fault is closer to the load, as shown in Fig. 15. The
minimum speed is strongly related to the minimum positive-
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IEEE TRANSACTIONS ON POWER DELIVERY, VOL. 23, NO. 3, JULY 2008
Fig. 13. Minimum positive-sequence voltage at the 36 kV bus. Different fault
locations on the transmission line.
Fig. 16. Positive-sequence voltage at the 36 kV bus. SCR = 2:4.
Fig. 17. Positive-sequence voltage at the 36 kV bus. SCR = 5:8.
Fig. 14. Maximum injected reactive power by the synchronous condensers and
the SVC. Different fault locations on the transmission line.
Fig. 15. Minimum speed of the induction machines. Different fault locations
on the transmission line.
sequence voltage. When the fault is closer to the source, the
speed is higher due to larger reactive power injection by the
SVC. This advantage diminishes as the fault is closer to the load
and the voltage drop during the fault is increased.
C. Different SCR
To observe the effect of different SCR, the short-circuit capacity seen at the 36 kV bus is changed to have a SCR of 2.4
(double line length to 400 km) and 5.8 (half line length to 100
km). The results are obtained by applying a single phase to
ground fault while keeping the other parameters unchanged.
It takes more time for the synchronous condensers to bring the
voltage level back to the nominal value by decreasing the SCR
to 2.4 (Fig. 16). Also it can be seen that the voltage during the
fault drops only 10% which represents a small error for the exciters, resulting in a small increase in the field current of the synchronous condensers. When the fault is cleared, the induction
machines begin to consume a lot of reactive power to recover
their speed. Due to this fact and to the slow response of the synchronous condensers for low voltage changes, the voltage continues to drop and it takes more time for the synchronous condensers to bring the voltage back to the nominal value. The SVC
shows better performance in this case and keeps the voltage at
1 p.u. even during the fault, but due to the measurement delay it
produces overvoltages during instants of the fault clearance and
the line restoration.
For the system when the SCR is increased to 5.8, which corresponds to a strong system, the system will not collapse even
if it is not supported by reactive power compensation devices,
which can be noticed in Fig. 17. However, reactive power compensation units help in restoring the voltage in the 36 kV bus
quicker. In Fig. 17, the advantages and disadvantages of each
device mentioned before can be confirmed.
Injection of more reactive power by the SVC during and
after the fault, which is seen in Fig. 18, explains the reason for
bringing the voltage back to the nominal value quicker with the
SVC which can be noted in Figs. 16 and 17. Trends shown in
Fig. 18, clearly underline the better performance of the SVC in
the case of weak grid systems.
V. CONCLUSION
In this paper, it was found that the SVC injects more reactive
power and shows better performance during faults that caused
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TABLE VI
PARAMETERS OF SUPERVAR
Fig. 18. Maximum injected reactive power by the synchronous condensers and
the SVC. Various SCRs.
TABLE VII
EXCITER PARAMETERS FOR SUPERVAR
TABLE III
PARAMETERS OF CONVENTIONAL SYNCHRONOUS CONDENSER
REFERENCES
TABLE IV
SATURATION DATA OF CONVENTIONAL SYNCHRONOUS CONDENSER
TABLE V
EXCITER PARAMETERS OF CONVENTIONAL SYNCHRONOUS CONDENSER
less voltage drop on its terminals, such as single phase to ground
faults or faults in weak grids. However, during severe faults,
such as three phase to ground faults and severe faults in stiff
grids, the synchronous condensers perform better and bring the
terminal voltage to the nominal value quicker. This is especially
true for the case with the SuperVAR, which injects up to 45%
more reactive power compared to the conventional synchronous
condenser.
Moreover, for future studies, it will be very interesting to expand the analysis and comparison to include the STATCOM and
the authors are planning to present a paper on this subject.
APPENDIX
Tables III and IV are used for the conventional synchronous
condenser.
Table V is used for the exciter DC2A of the conventional
synchronous condenser.
Table VI is used for calculating parameters for the SuperVAR.
Table VII is used for the exciter ST1A of the SuperVAR.
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Sercan Teleke was born in Ankara, Turkey, in 1983.
He received the B.S. degree in electrical and electronics engineering from Middle East Technical University, Ankara, in 2005 and the M.S. degree in electric power engineering from Chalmers University of
Technology, Göteborg, Sweden, in 2006. He is currently pursuing the Ph.D. degree in electrical engineering at North Carolina State University, Raleigh.
His research interests are in the areas of powerelectronics applications to power systems and design
and control of special purpose electrical machines.
Tarik Abdulahovic was born in Srebrenik, Bosnia
and Herzegovina, in 1976. He received the B.S
degree from the University of Tuzla in 2001 and
the M.S. degree in electric power engineering
from Chalmers University of Technology (CTH),
Gothenburg, Sweden, in 2006, where he is currently
pursuing the Ph.D. degree.
The main focus of his research is the generation
and propagation of high-frequency disturbances in a
sea-based wind park consisting of modern convertercontrolled wind turbines.
Torbjörn Thiringer received the Ph.D. degree in
1996 from Chalmers University of Technology,
Gothenburg, Sweden.
Currently, he is a Professor in the Department of
Energy and Environment at Chalmers University
of Technology. His areas of interest are issues pertaining to grid integration of wind energy into power
systems as well as power-electronic converters in
general.
Jan Svensson (S’96–M’98) received the M.Sc., Lic.
Eng., Ph.D., and D.Sc. degrees from Chalmers University of Technology, Göteborg, Sweden, in 1991,
1995, 1998, and 2002, respectively.
From 1998 to 2002, he was an Assistant Professor
with the Department of Electric Power Engineering,
Chalmers University of Technology. Currently, he
is with ABB Power Systems, Västerås, Sweden,
involved in development of FACTS and HVDC
transmission, especially design and control of
light-concept devices. His interests include control
of power electronics in power systems, power quality, energy storage, and wind
power.
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