Download Voltage leval improment by using Static VAR compensator (SVC)

International Journal of Current Trends in Engineering & Research (IJCTER)
e-ISSN 2455–1392 Volume 2 Issue 4, April 2016 pp. 342 - 348
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Voltage Leval Improment by Using Static VAR
Compensator (SVC)
Wagh Vijay R.1 , Jadhav Sunil A.2 , Dange Sagar A.3
1,2,3
Electrical Engineering , S.B.Patil C.O.E.
Abstract—This paper will discuss how static Var compensator successfully been applied to control
transmission system. The voltage level of the system changes when there is a change in load and the
drop in load voltage lead to demand for the reactive power. Static VAR Compensation under FACTS
uses TCR (Thyristor Control Rector) based on shunt compensation duly controlled from a
programmed microcontroller.
Shunt capacitive compensation - This method is used improve the power factor. Whenever an
inductive load connected to the transmission line, power factor lags because of lagging load current.
To compensate, a shunt capacitor is connected which draws current leading the source voltage. The
net result is improvement in power factor. The time lag between the zero voltage pulse and zero
current pulse duly generated by suitable operational amplifier circuits in comparator mode are fed to
two interrupt pins of the microcontroller where the program takes over to actuate appropriate number
of opto-isolators duly interfaced to back to back SCR at its output for bringing shunt capacitors into
the load circuit to get the power factor till it reaches 0.95. The microcontroller used in the project is
of 8051 family which is of 8 bit. The power supply consists of a step down transformer 230/12V,
which steps down the voltage to 12V AC. This is converted to DC using a Bridge rectifier. The
ripples are removed using a capacitive filter and it is then regulated to +5V using a voltage regulator
7805 which is required for the operation of the microcontroller and other components
Keywords—FC-TCR type SVC, SVC control, dynamic control of reactive power, FACTS
Controllers, Microcontroller based control of Reactive power, TCR control, Single
I. INTRODUCTION
There is a continuous rise in demand of electrical power. To meet this rise, the growth in
generation is stability, voltage collapse and grid failure. To provide stable, secure and quality power
supply to end users and to utilize available transfer capacities in better way, Flexible AC
transmission systems (FACTS) controllers are used to enhance power system stability along with
their main application of power flow controlessential, which is not always possible due to various
limitations like environmental, financial, resources, land, etc. Expansion of transmission network is
always not easy. Due to these problems, the entire power system is operated at its highest capacity
which may generate problems of of stability, voltage collapse and grid failure. To provide stable,
secure and quality power supply to end users and to utilize available transfer capacities in better way,
Flexible AC transmission systems (FACTS) controllers are used to enhance power system stability
along with their main application of power flow control
In this paper, the design and fabrication of 1- phase fixed capacitor-thyristor controlled
reactor (FC- TCR) type SVC based on microcontroller have been developed in the laboratory for
Bulp Load Test System.The Static Var Compensator (SVC) is an early generation of FACTS
Controllers and a proven technology for voltage stability and power factor correction. The SVC is
composed of a fixed capacitor (FC) and a thyristor controlled reactor TCR. This paper deals with the
Design, Fabrication and Testing of Microcontroller based SVC along with Automatic Control
circuit Hardware. The laboratory setup of the Bulp Load test system with and with out SVC
Automatic control circuit have been Developed. SVC is comprised of a thyristor controlled reactor in
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International Journal of Current Trends in Engineering & Research (IJCTER)
Volume 02, Issue 04; April – 2016 [Online ISSN 2455–1392]
parallel with capacitor. The test results to inject or absorb VArs into the system for maintaining
constant voltage profile have been presented in this paper. This fine tuning is accomplished by
varying the firing delay angle (α) of the reactor, thus modifying the TCR VArs absorbed. if α = 0 is
defined as the zero crossing of the applied voltage, then firing angles will be in the range of (π / 2) ≤
α ≤ π for each half-cycle
II.
STATIC VAR COMPENSATOR
A) Configuration of SVC :SVC provides an excellent source of rapidly controllable reactive shunt compensation for dynamic
voltage control through its utilization of high-speed thyristor switching/controlled devices . A SVC is
typically made up of coupling transformer, thyristor valves, reactors, capacitance (often tuned for
harmonic filtering).
b) Advantages of SVC:The main advantage of SVCs over simple mechanically switched compensation schemes is their
near-instantaneous response to change in the system voltage. For this reason they are often operated
at close to their zero-point in order to maximize the reactive power correction . They are in general
cheaper, higher-capacity, faster, and more reliable than dynamic compensation schemes such as
synchronous compensators (condensers). In a word:
1)
2)
3)
4)
5)
6)
Improved system steady-state stability.
Improved system transient stability.
Better load division on parallel circuits.
Reduced voltage drops in load areas during severe disturbances.
Reduced transmission losses.
Better adjustment of line loading.
In its simplest form, SVC is used as Fixed Capacitor-Thyristor Controlled Reactor (FC-TCR)
configuration as shown in Fig. 1. The TCR branch provides continuously controllable reactive
power only in the lagging power-factor region. To extend the controllable range to the leading
power-factor region, a fixed-capacitor bank is connected in shunt with the TCR. The TCR VAr is
rated larger than the fixed capacitor to compensate the capacitive VAr and provide net inductivereactive power should a lagging power-factor operation be desired
Fig.1: Configuration of FC-TCR
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International Journal of Current Trends in Engineering & Research (IJCTER)
Volume 02, Issue 04; April – 2016 [Online ISSN 2455–1392]
The fixed-capacitor banks, generally connected in a star configuration, are split into 3-phase
group. Each capacitor consists of a small tuning inductor which is connected in series and tunes the
branch to work as a filter for a specific harmonic order.
III. HARDWARE IMPLEMENTATION
Here the hardware setup is done on medium transmission line model and under variable RL
load condition firing angle is set to change the requirement of reactive power injection into the
system. The firing angle is generated using microcontroller 89C51 (8051). The pulses are generated
based on Zero crossing detector circuit input of ZCD is given to controller based on ZCD output
microcontroller generates pulses and that is given to antiparallel connected thyristor with isolation
using coupler ICs. In actual single pulse is generated that is inverted and given to second thyristor
of same leg with assurance of avoiding short circuit of the thyristor pair leg.
Fig.2: Project Block Diagram
Experimental setup of the hardware is shown in Fig. is very similar to system with
Microcontroller based control of Reactive power, TCR and FC control, Single phase. Load in
laboratory setup is chosen as RL load and value of Fixed Capacitor is 2.5mf and inductive load of
40watt, 230V AC ,0.4A,Sending end voltage is set to 230Volt and receiving end voltage is measured
for various load condition Voltage regulation is provided by means of a closed-loop controller. SVC
control circuit consists following blocks, such as step down/up transformer, rectifier bridge circuit,
active power filter, voltage.
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International Journal of Current Trends in Engineering & Research (IJCTER)
Volume 02, Issue 04; April – 2016 [Online ISSN 2455–1392]
Hardware Circuit Implementation of Automatic Control of Static Var Compensator (SVC)
using Micro Controller regulator, gate pulse generating unit (i.e.firing unit)The gating or ‗turn on‘
signal to each thyristor isdelayed by α, the firing or conduction angle, from the zero crossing of the
source voltage
Fig.3:Hardware implementation of TCR
After implementing hardware circuit with full wave bridge rectifier and zero crossing detector
using dual operational amplifier output signals are obtained as shown in figure 3 at each zero
crossing pulses are generated from operational amplifier the same pulses are given to microcontroller
unit and then processed for delay operation for firing of thyristor Ultimately with increase in firing
angle current decreases. So the system reactive power can be varied by varying the firing angle α.
Fig.4:Comparison of rectifier output with ZCD pulses
IV. PERFORMANCE SVC CONTROLLER
An SVC is a controlled shunt susceptance (B) as defined by control settings that injects
reactive power (Q) into the system based on the square of its terminal voltage. illustrates a TCR
SVC, including the operational concept. The control objective of the SVC is to maintain a desired
voltage at the high-voltage bus. In the steady-state, the SVC will provide some steady-state control
of the voltage to maintain it the high-voltage bus at a pre-defined level. If the high-voltage bus
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International Journal of Current Trends in Engineering & Research (IJCTER)
Volume 02, Issue 04; April – 2016 [Online ISSN 2455–1392]
begins to fall below its set point range, the SVC will inject reactive power (Qnet) Into thereby
increasing the bus voltage back to its net desired voltage level.
If bus voltage increases, the SVC will inject less (or TCR will absorb more) reactive power,
and the result will be to achieve the desired bus voltage. +Qcap is a fixed capacitance value,
therefore the magnitude of reactive power injected into the system, Qnet, is controlled by the
magnitude of –Qind reactive power absorbed by the TCR
Fig 5.Controlling scheme for SVC branch
V. OPERATION OF TCR
The fundamental operation of the thyristor valve that controls the TCR is described here. The
thyristor is self commutates at every current zero, therefore the current through the reactor is
achieved by gating or firing the thyristor at a desired conduction or firing angle with respect to the
voltage waveform. The gating or ‗turn on‘ signal to each thyristor is delayed by α, the firing or
conduction angle, from the zero crossing of the source voltage as illustrated in . As current lags the
voltage across the reactor by 90°, so a firing angle of ninety degrees results in maximum, that is,
continuous reactor current. For a firing angle of 180°, the reactor current will be zero. As the
thyristor firing angle is increased from 90 towards 180 degrees, the current in the reactor is reduced.
Therefore, the firing angle can be in the range of 90° ≤ α ≤ 180° to vary the TCR current from zero to
its maximum by phase angle control of the thyristors. The reactor is connected in series with two
antiparallel thyristors. The conduction interval is reduced from maximum to zero.
In terms of suseptance,
ISVC = j BSVCV
Where: BSVC = BTCR + B c
Bsvc = BL((π-2α-sinα)/π) + B c
Where, B c = 1/ Xc
BL = 1/XL
In terms of reactance, X SVC =XCXTCR/XC+XTCR
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International Journal of Current Trends in Engineering & Research (IJCTER)
Volume 02, Issue 04; April – 2016 [Online ISSN 2455–1392]
Where, X TCR = π X L /σ- Sinσ
X SVC = πXCX L / (XC (σ- Sinσ) - π X L)
Where, σ = 2(π- α)
XSVC= πXCX L/ XC [(2(π -α)- Sin2σ)- π X L]
X SVC =VBus2/ Q SVC
QSVC = VBus2 (XC [2π- σ+ Sin2σ] - π X L)/ πXCX L
Generally, by changing the firing angle ‗α‘the fundamental reactance X L of the reactor is changed.
XL =V/ I FL1
VI. RESULT ANALYSIS
So the system reactive power can be varied by varying the firing angle α. Readings are taken for
various load condition tabulated and table 1 and table 2 withour SVC and with SVC(variable firing
angle α).
Table 1: Voltage Variation without SVC
Terminal
voltage
S.No
Load current
Power Factor
Time(ms)
Io(Amps)
VL (V)
Output
Power
(Watts)
1
195
1.56
0.985
0
299.67
2
197
1.53
0.95
0-1
286.33
3
198
1.47
0.8
1-2
232.84
4
197
1.51
0.929
1.246
276.34
5
197
1.50
0.917
1.253
270.97
Table 2: Voltage Variation with SVC
S.No
Terminal
voltage
Load
current
Power Factor
Time(ms)
Output
Power
(Watts)
VL (V)
Io(Amps)
1
192
1.77
1
0
339.84
2
193
1.67
1
0
322.31
3
195
1.61
1
0
331.95
4
197
1.55
1
0
305.35
5
198
1.53
1
0
302.94
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International Journal of Current Trends in Engineering & Research (IJCTER)
Volume 02, Issue 04; April – 2016 [Online ISSN 2455–1392]
VII. CONCLUSION
Simulation results are verified using hardware implementation and it is found that FC-TCR is
effective compensation technique compare to mechanical operated or other dynamic power flow
controllers. Also it is observed that in closed loop system the performance of system improved as
well response time of system is very fast Dynamic performance and voltage control analysis will
continue to be a very important process to identify system problems and demonstrate the
effectiveness of possible solution.
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2013)
T. Vijaykumar, A.Nirmalkumar ―Experimental Results of Microcontroller Based FC-TSR-TCR Systems‖
International Journal of Electrical and Electronics System Research vol 3 June 2010
Dr. SA Khaparde, Mr. S.M. Brahma, "Flexible AC Transmission System (FACTS): An Overview", Transmission and
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