MODELING AND ANALYSIS OF CUSTOM POWER PARK BY PSCAD/EMTDC
PROGRAM
Özel Amaçlı Güç Parkının PSCAD/EMTDC Programında Modellenmesi ve Analiz
Edilmesi
Mehmet TÜMAY
Elektrik Elektronik Mühendisliği
Yusuf Alper KAPLAN
Elektrik Elektronik Mühendisliği
ABSTRACT
The advances in power electronics based devices to improve power quality
have been increased the interest on Custom Power Park (CPP). CPP concept
means the integration of multiple CP Devices within the Industrial/Commercial
Park, which offers customers high quality of power at the distribution system
voltage level. CPP is one of the most useful solutions to prevent voltage
sags/swells and harmonics from distribution lines.
In this thesis, CPP has been modeled by using PSCAD/EMTDC program.
CPP is composed of Static Transfer Switch (STS) and Dynamic Voltage Restorer
(DVR). The operation principles of STS and DVR have been explained in detail
and then they have been modeled with PSCAD/EMTDC program. Simulation
results have been comprehensively investigated. Different types of faults are
applied for STS and DVR in CPP and the response of the system for these
disturbances are examined.
Keywords: Power Quality, Custom Power Park, Dynamic Voltage Restorer,Static
Transfer Switch
ÖZET
Güç kalitesini iyileştirmek için kulanılan güç elektroniği tabanlı
donanımlardaki gelişmeler, Özel Amaçlı Güç Parkına olan ilgiyi arttırmıştır. Özel
Amaçlı Güç Parkı, endüstriel ve ticari park dahilinde çoklu özel amaçlı güç
aygıtlarının bütünlüğü anlamına gelip, dağıtım sistemindeki gerilim seviyesinde
müşterilere kaliteli güç sunar. Dağıtım hatlarında oluşan gerilim düşümü/yükselimi
ve harmonikleri önlemek gerekmektedir ve bunun için Özel Amaçlı Güç Parkı
uygulamaları en uygun çözümlerden biridir.
Bu tezde Özel Amaçlı Güç Parkı PSCAD/EMTDC programı kullanılarak
modellenmiştir. Özel Amaçlı Güç Parkı, Statik Transfer Anahtarı (STA) ve Dinamik
Gerilim İyileştirici (DGİ) kullanılarak oluşturulmuştur. STA ve DGİ’ nin çalışma
prensipleri detaylı olarak anlatıldıktan sonra PSCAD programında modellenmiş ve
simulasyon sonuçları incelenmiştir. Özel Amaçlı Güç Parkının STA ve DGİ
* Yüksek Lisans Tezi -MSc Thesis
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kısımlarında değişik hatalar uygulanmıştır ve bu hatalara sistemin tepkisi
incelenmiştir.
Anahtar Kelimeler: Güç Kalitesi, Özel Amaçlı Güç Parkı, Dinamik Gerilim
İyileştirici, Statik Transfer Anahtarı
Introduction
Custom power is the employment of power electronic or static controllers in
medium voltage distribution systems for the purpose of supplying a level of
reliability and/or power quality that is needed by electric power customers sensitive
to power quality variations. In other words custom power is intended to protect the
customers from interruptions and voltage reductions originating in the utility system
as well as those transfered to customers from other customers via the utility system
and even internal disturbances. Custom power devices, or controllers, include
static switches, DVRs, injection transformers, energy storage modules that have
the ability to perform current interruption and voltage regulation functions in a
distribution system to improve reliability and/or power quality (Daniel and Sannino,
2003).
Electric power is a form of energy we have come to depend on, so much
so, that in many automated product line businesses can not tolerate its loss for
even a few tens of milliseconds. With the ever-increasing role of electricity in
improving the quality of life, productivity of manufacturing and service industries,
and efficient energy use, power electronics will play significant part (Narain G,
1998).
Custom Power is a concept based on the use of power electronic
controllers in the distribution system to supply value-added, reliable, high quality
power to its customers. For many customers this is a preferred alternative to the
customer improvising utility power by their own means, mostly in a band aid
manner with numerous uninterruptable power supplies, as is done now. Many
utilities are moving in the direction of value-added Custom Power service to their
large customers.
Simulation study of a custom power park (CPP) is presented. It is assumed
that the park contains unbalanced and nonlinear loads in addition to a sensitive
load. Two different types of compensators are used seperately to protect the
sensitive load terminal voltage. Additional issues such as the load transfer through
a static transfer switch, detection of sag/fault etc. are also discussed. The concepts
are validated through PSCAD/EMTDC simulation studies on a sample distribution
system.
Power Quality Problems
Power quality can be defined as having a bus voltage that closely
resembles a sinusoidal waveform of required magnitude. Increasing number of
sensitive devices to variations, the requirement for reducing losses and the
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behaviors of interconnected networks are some reasons which increase the
importance of power quality concept. In the industry, power quality polluting loads
are increasing day by day. The main reasons for concern with power quality (PQ)
are as following (Dong, 2004):
 End user devices become more sensitive to PQ due to many
microprocessor based controls.
 Complexity of industrial processes; the re-startup is very costly.
 Large computer systems in many businesses facilities.
 Power electronics equipment used for enhancing system stability,
operation and efficiency. They are major source of bad PQ and are
vulnerable to bad PQ as well.
 Deregulation of the power industry.
 Complex interconnection of systems, which results in more severe
consequences if any one component fails.
 Continuous development of high performance equipment; Such
equipment is more susceptible to power disturbances.
Voltage sag is a fundamental frequency decrease in the supply voltage for
a short duration.
Voltage swell is defined as the increase of fundamental frequency voltage
for a short duration.
An interruption occurs when the supply voltage (or load current) decreases
to less than 0.1 per unit for a period of time not exceeding 1 minute.
Figure 1 shows the common voltage disturbances.
Figure1 Voltage Disturbances (Ghosh, 2005)
Custom Power Park Concept
The layout of the custom power park is shown in Fig.2 The power to the
park is supplied either by source vs1 through the preferred feeder or through the
source vs2 through the alternate feeder. Of these, during normal operations, v s1
supplies power through the preferred or primary feeder (PF). During a fault or long
duration voltage sag in the preferred feeder, the STS rapidly transfers the supply to
vs2 through the alternate feeder (AF).
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Figure 2 Layout of Custom Power Park (Ghosh, 2005)
The loads in the park are divided into three categories. Load L–1 is
unbalanced, load L–2 is a rectifier load, which draws harmonic current, and load L3 is both balanced and harmonic free. Load L–3 is sensitive or critical, and needs
continuous uninterrupted supply. To facilitate this, a power electronic-converterbased device is connected at the CPP bus.
The DVR can inject a voltage in series to cancel the unbalance and
harmonics created in the CPP bus so that load L–3 gets balanced supply.
Therefore all three loads get balanced voltage irrespective of harmonics and
distortion in L–1 and L–2. As a consequence, the current drawn through the feeder
is balanced and sinusoidal. The capacitor Cf is provided to bypass the harmonic
currents generated by the nonlinear load L-2.
The custom power park is also equipped with a thyristor based STS, which
can transfer the CPP load from the PF to the AF in case of a voltage sag or fault in
the PF. In case of a catastrophic failure in which both feeders are lost, the diesel
generator (DG) set is turned on for auxilary supply. In the interim period when the
feeders are off and the DG is not on, the solid state converter based device (DVR )
regulates the voltage of the critical load L–3 (Ghosh, 2005).
Static Transfer Switch
The STS is used in uninterruptible power supply systems and in distribution
networks to provide connection to alternate sources of ac power for critical loads
when the main sources fail.
The STS can be used very effectively to protect sensitive loads against
voltage sags, swells and other electrical disturbances. The STS ensures
continuous high-quality power supply to sensitive loads by transferring, within a
time scale of milliseconds, the load from a faulted bus to a healthy one.
To ensure continuity of electrical power supply with sensitive process
controls, a critical load is normally supplied from two independent sources, one
being the primary selection. Tradiationally, the sources are often connected to
mechanical switches incorporating controls that can recognize loss of the main
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power source and then automatically transfer to the alternate source, thus
maintainig a highly reliable source of power.
However, as processes and process controls have become increasingly
sensitive not only to loss of the power source but also to fluctuations in the voltage
supplied (i.e. voltage sags and swells), mechanical transfer switches can not
transfer quickly enough to eliminate customer interruptions when such interruptions
occur.
The Static Transfer Switch (STS) essentially consists of a pair of back-toback thyristor switches. It takes the place of the mechanical transfer switch and
enables a seamless transfer of energy from the main source to the alternate
source in order to avoid service interruption. As a result, this arrangement can
provide reliable power to the customer (Mokhtari, Dewan and Iravani, 2002).
Dynamic Voltage Restorer
The dynamic voltage restorer (DVR) is a power quality device that has
gained an increasing role in protecting industries against disturbances such as
voltage sags and swells related to remote system faults.
Power quality has become an increasingly important topic in the
performance of many industrial applications. One of the major issues in improving
power quality in distribution networks is the mitigation of voltage sags. The effect of
voltage sag can be very expensive for the customer because it may lead to
production downtime and equipment demage. Voltage sag can be mitigated by
voltage and power injections into the distribution system using power electronics
based devices. Different approaches have been proposed to limit the cost causes
by voltage sag. One approach to address the voltage sag problem is the use of
dynamic voltage restorer (DVR) which is a custom power device employing gate
turn off thyristors. During a sag disturbance, the DVR uses a power electronic
inverter to inject voltage in series with the source. The amplitude and the phase
angle of the injected voltages are variable thereby allowing control of the real and
reactive power exchange between the device and the distribution system. Short
time energy storage is used to provide the supplemental energy through the
inverter to keep the load voltage at acceptable levels.
The voltage sensitive equipment in industrial sector has made industrial
processes more vulnerable to supply voltage deviations. Such voltage deviations in
the form of voltage sag, swell or temporary outage cause severe process
disruptions resulting in millions of dollars of loss of revenue. Therefore power
supply authorities as well as customers have been desperately looking for a cost
effective solution currently to ride through momentary power supply disturbances.
As such, the preposition of a novel custom power device called dynamic voltage
restorer (DVR) for compensating voltage disturbances in distribution systems has
generated a great deal of interest recently. Apart from the DVR, some researchers
have proposed several other devices to mitigate momentary disturbances.
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Modeling Of CPP By Using PSCAD/EMTDC
Figure 3 shows the PSCAD modeling of Custom Power Park. The power to
the park is supplied either by source vs1 through the preferred feeder or through the
source Vs2 through the alternate feeder, the STS rapidly transfers the supply to V s2
through the alternate feeder. The DVR can inject a voltage in series to cancel the
unbalance and harmonics created in CPP. The custom power park also equipped
with a thyristor based STS, which can transfer the CPP load from the preferred
feeder to the alternate feeder.
System Quantities
System frequency
Source Vs1
0º
Source Vs2
0º
Preferred feeder (PF) impedance
Alternate feeder (AF) impedance
Values
50 Hz
12 kV (L-L), phase angle
12 kV (L-L), phase angle
0.05 + j0.0048 
0.05 + j0.0048 
PSCAD/EMTDC Simulation Tool
PSCAD/EMTDC is an industry standard simulation tool for studying the
transient behaviour of electrical networks. Its graphical user interface enables all
aspects of the simulation to be conducted within a single integrated environment
including circuit assembly, run-time control, analysis of results, and reporting. Its
comprehensive library of models supports most ac and dc of power plant
component and controls, in such a way that, custom power systems can be
modeled with speed and precision
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NaI
VaInv
NbI
VbInv
A
B
C
3 Phase
RMS
2
1
g4
2
1
2
3
g6
2
3
2
5
2
g2
2
2
5
2
dcVltg
A
B
2
#2
g2
50.0 [MVA]
6
#1
2
gatepa
gatepb
A
B
C 12.0 [kV]
C
0.380 [kV]
6
Vpa1
gatepc
2
Ipb
Vpb1
g6
Ipa
Ipc
4
A
B
2
200.0 [MVA]
#2
VpuSe
4
#1
NaR
VpuR
Ilc
VaRec
NcR
VcRec
2
A
B
3 Phase
RMS
5.97e-4 [H]
NbR
5.97e-4 [H]
0.402 [ohm ]
VbRec
56.25 [ohm]
IacB
VpuI VpuRe
VloadA0.0014 [H]
56.25 [ohm]
56.25 [ohm]
IacC
VloadA
0.0014 [H]
IacA
0.0014 [H]
Figure 3 CPP Model in PSCAD
Ip1
0.05 [ohm] 0.004806 [H]Vx
0.05 [ohm] 0.004806 [H]
A
B
C
dcCur1
Fault
Ip2
Ip3
Timed
Fault
Logic
A
A
Ip1
200.0 [MVA]
Ip2
B
Vpc1
gateaa
gateab
g4
A
#2
Iaa
Iab
g1
131
#1
A
C 115.0 [kV]
C
12.0 [kV]
200.0 [MVA]
Vaa1
g3
5,66 [uF]
0.164 [H]
B
0.05 [ohm] 0.004806 [H]
A
B
g5
#2
Ip3
A
B
0.01 [H]
Icap
5.97e-4 [H]
0.402 [ohm ]
Vb_a
VcInv
10.0 [ohm ]
T
T
T
T
0.402 [ohm ]
Vc_b
#1
B
200.0 [MVA]
0.05 [ohm] 0.004806 [H]
Vab1
Iac
A
B
#2
Via_c
Ilb
Va_c
g1
#2
#1
C 12.0 [kV]
C
115.0 [kV]
A
B
#2
Vac1
1.0 [MVA]
#2
Ila
C
g3
#1
Vic_b
NcI
Vib_a
C
A
B
#1
C 115.0 [kV]
C
12.0 [kV]
A
#1
2 [kV]
g5
5.660 [uF]
0.164 [H]
10.0 [ohm ]
10.0 [ohm ]
5,66 [uF]
0.164 [H]
#2
0.05 [ohm] 0.004806 [H]
0.05 [ohm] 0.004806 [H]
gateac
B
C 12 [kV]
5000.0 [uF]
T
T
T
T
T
T
#1
C 12.0 [kV]
C
115.0 [kV]
Iaa
Iab
Iac
gateaa
T
T
B
C
A
0.000003
0.003
[H] [ohm ]
B
0.000003
0.003
[H] [ohm ]
FAULTS
CABC->G
0.000003
0.003
[H] [ohm
]
Simulation Results of STS Part
Figure 4 and Figure 5 shows the addition of line currents of preferred
source and alternate source which were measured from the high voltage side of
the transformer.Figure 5 represents preferred source currents and figure 6
represents alternate source currents. It is seen that load is feed from only one of
the sources, there isn’t any source paralleling and there is not any cross currents.
The critical load is supplied from the alternate feeder at the fault time.
Fig 4 shows the Valt signal at the fault time. Vprf is “off ” and Valt signal is “on” at the
fault time. After fault they return their initial values
Figure 4 Valt Signal at the fault time
Fig 5 shows the preferred phase currents at the fault time. It can be seen from Fig. 4
and Fig. 5 that even though the interruption occurs at 0.2 s and the transfer signal is
generated at the fault time.
Main : Graphs
0.0250
Ipa
Ipb
Ipc
0.0200
0.0150
0.0100
y (kA)
0.0050
0.0000
-0.0050
-0.0100
-0.0150
-0.0200
-0.0250
0.00
0.10
0.20
0.30
0.40
0.50
...
...
...
Figure 5 Preferred Phase Currents
Figure 6 shows the alternate phase currents at the fault time. It is clearly seen that
load is supplied from alternate feeder at the fault time. After the fault load is supplied from
the preferred feeder.
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Main : Graphs
Iac
0.0250
Iab
Iaa
0.0200
0.0150
0.0100
y (kA)
0.0050
0.0000
-0.0050
-0.0100
-0.0150
-0.0200
-0.0250
0.00
0.10
0.20
0.30
0.40
0.50
...
...
...
Figure 6 Alternate Phase Currents
Figure 7 shows the load phase currents it can be seen that the fault has no effect on
the load phase currents.
Main : Graphs
Ilc
2.00
Ilb
Ila
1.50
1.00
y (kA)
0.50
0.00
-0.50
-1.00
-1.50
-2.00
0.00
0.10
0.20
0.30
0.40
0.50
...
...
...
Figure 7 Load Currents
Simulation Results of DVR Part
Figure 8 shows the load voltage. There is a fault at 0.16 sec and it is 0.05 sec duration. It is
seem that at the fault duration the load voltage is undisturbed. Simulations have been carried
out to evaluate the performance of the DVR in a distribution system under various operating
conditions. From the simulation results, the designed DVR responded well in compensating
voltage sags. The harmonics generated in the DVR can be significantly reduced by
connecting a pasive filter to the system.
8.0
VFault
6.0
4.0
2.0
y
0.0
-2.0
-4.0
-6.0
-8.0
Figure 8 Phase Voltage Before DVR
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Figure 9 illustrates the phase load voltage after the DVR. The result shows that fault
has no effect on the CPP load voltage at the fault time. At the fault time DVR injects a
voltage to the system.
8.0
VLoad
6.0
4.0
2.0
y
0.0
-2.0
-4.0
-6.0
-8.0
Figure 9 Phase Voltage After DVR
CONCLUSIONS
This thesis has presented electromagnetic transient models of a custom power park.
The park is composed by STS and DVR. The highly developed graphic facilities available in
PSCAD/EMTDC were used to conduct all aspects of model implementation and to carry out
extensive simulation studies.
Custom power park offers to the customer; no interruptions, low harmonic
voltages, and acceptance of fluctuating and non-linear loads without effection terminal
voltage.
In this thesis custom power park concept has been studied. Advantages of custom
power devices have been pointed out. CPP has been modeled by using PSCAD/EMTDC
program. CPP is composed of Static Transfer Switch (STS) and Dynamic Voltage Restorer
(DVR). The operation principles of STS and DVR have been explained in detail and then
they have been modeled with PSCAD/EMTDC program. Simulation results have been
comprehensively investigated. Different types of faults are applied for STS and DVR in CPP
and the response of the system for these disturbances are examined. The methodolgy of
the integration of the custom power devices to the park is also discussed.
134
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