First of all, we would like to thank God for his blessing, and we also express our deep sense of gratitude to Mr. Birhanu B. (Msc) for encouraging us to work on this project and providing his support and guidance throughout this project. Our deepest appreciation also goes out to school of Electrical & Computer engineering who gave us many needed support, encouragement and help, and our friends who struggling with us exploring this scope. Finally, thank you to all those involved directly and indirectly helping us out during our design & simulation which we can’t state out every one of them.
Now a day’s power demand and population growth is very high due to this rising electric power networks have been highly growing and striving. To satisfy the escalating loads so, we investigating Power system based Thyristor control series capacitor is a system used to control transmission system dynamic performance for the system disturbance and well regulate system voltage. This system addresses the problem with mechanically switched reactive power compensator which cannot match with the rapid changing of system voltage and slow switching speed. Also the system use voltage and current transformer to measure the current & voltage on the transmission line to calculate the power factor of the system. In our compensation when voltage lead the current or when the inductive reactive power high on the transmission line the capacitor bank is automatically connected to the system and compensate the reactive power. If the over compensation occurs the inductor bank connected to the system and also lower the pf of the system. This thyristor control series capacitor used for power system dynamic stability enhancement used for different place but in our case it has been used for transmission line from gibe generation system to Jimma substation. All the simulation result are obtained using matlab Simulink.
Presently due to the absence of power regulation industry and the limitation faced by power industry due to energy, environmental and regulatory issues, the main challenge is to improve the power transfer capability and also to improve the system integrity of the given transmission facility. To solve such kinds of problem using TCSC is incomputable option. Series compensation when familiarized in power systems encouragements the power flow in a particular network segment which reduces active power losses and also prevents system sub-synchronous oscillations. Recent development of power electronics introduces the uses of flexible AC transmission system (FACT) controllers in power system. Commonly use this device in power system for to improve power transfer capability, voltage stability and power oscillation damping 1 2.
Now a day thyristor controlled series capacitor is used as series compensation device. The series inductive reactance of ac transmission lines is one of the factors which govern the maximum amount of power that can stably be transferred by these lines under steady-state conditions 3 4.
One method of developing the steady-state maximum power transfer capability of an AC line is to reduce its net series inductive reactance, and in real world this can be achieved by connecting a fixed capacitive compensating reactance in series with the line using static capacitor banks. However, if the capacitive reactance provided by such a series compensator can be dynamically controlled it is possible not only to increase the steady- state power transfer capability of a transmission system, but also to improve the ability of the system stability.
For many years SC technique is used to adjust the power transfer between two stations by adjusting the net series impedance of the line. Connection of a Series capacitor is a conventional and recognized method of growing transmission line capacity, by reducing the net series impedance, thus increasing power transmission. But, due to the restriction of its slow switching time it is substituted by Thyristor controllers, which are fast acting devices due to which
Fast and non-stop control of line compensation is possible. In our country the transfer of high amount of electricity via long transmission lines is required as well as interconnection of power systems.
1.2 Problem statement and justification of project
In long transmission line there is high inductive reactance is induced in the line, the induced inductive reactance causes high reactive power in the system and that decrease the active power, and that means increase power loss. Due to this problem there is system disturbance in the system. This cause, that some lines are extremely overloaded, it causes the occurrence of non-stable voltage. On the other hand, power transfer problems have occurred frequently within large variation of loads. These issues are important in effective power supply system to ensure normal operation of the electric load.
1.3 Objective of this project
1.3.1 General objective
The main objective of this project is to improve power system stability by using thyristor controlled Series capacitor (TCSC).
1.3.2 Specific object
Varying the firing angle to control the TCSC
Connect thyristor back to back so that they can operate in all quadratic region.
To determine the power factor from receiving and sending end voltage.
1.4 scope of project
This project entitled with power system stability enhancement by using series compensator mainly concerned in reactive power compensation usage to the electric supply using TCSC and simulates the system by Mat lab Simulink. Our project scope limited up to stabilizing of the sending and receiving voltage
1.5 significances of the project
The significance of this project to stabilize flow of power system by placing thyristor controlled series capacitor in the transmission line and by equalizing the sending and receiving end of voltage as much as possible. And also increase the transmission line efficiency by reducing power loss on the line and increase the active power.
This part is the overall process or steps to accomplish the project and it is explained in terms of flow chart.0560259Gathering information, data, document and research necessary (relevant) for the study
Reading and analyzing information’s and interpreting to our goal
List out hardware and Software components we used
Software assembling using Mat lab
Result and analysis
Conclusion and recommendation
Gathering information, data, document and research necessary (relevant) for the study
Reading and analyzing information’s and interpreting to our goal
List out hardware and Software components we used
Software assembling using Mat lab
Result and analysis
Conclusion and recommendation
Fig, 1 overall methodology of our project
Several studies show that also many thyristor control series capacitor used for improving voltage stability. Some of the studies have investigated and are proposing new model of TCSC.
S.Meikandasivam, Rajesh Kumar Nima and Shailendra Kumar, proposed on their paper?Behavior Study 0f TCSC presented in World Academy of Science Engineering and technology 2008 World’s first 3 phases 5, 2 X 165 MVAR, TCSC was installed in 1992 in Kayenta substation, Arizona. It raised the transmission capacity of transmission line by 30%, but it was soon realized that the device is also a very effective means for providing damping of electromechanical power oscillations 6.
S.V.N Jithin Sundaret, also proposed and presented his research on the controlled shunt reactor for bus voltage management in EHV system. As the permanent connection of the shunt reactors leads to reduced voltage levels and decreased transmission capacity of the lines during full load conditions 7.
Pasi Vuorenpaa et, al, proposed his research dynamic modeling of Thyristor Controlled Series Capacitor in PSCAD and RTDS. In his research, the main target is to develop new modeling techniques for Thyristor Controlled Series Capacitor (TCSC) and to investigate the interaction phenomena between TCSC and surrounding network, is presented and the effect of control system structure and surrounding network on operational characteristics of TCSC 8.
After reviewing various paper, finally came to know that the shunt compensation is the better reactive power compensation technique. Now my proposed work is based on shunt compensator i.e. thyristor control series capacitor (TCSC) in order to compensate the reactive power Impedance of series compensating capacitor cancels the portion of the actual line reactance ; effective transmission impedance is reduced. As if the line was physically shortened or we can say that in order to increase the current in the given circuit series impedance of the actual physical line, the voltage across this impedance must be increased.
This can be accomplished by an appropriate series connected circuit element such as capacitor, the impedance of which produces a voltage opposite to the prevailing voltage across the series line reactance and thus causing later voltage to increase .So Series compensator provides desired series compensation voltage when and where required if installed. They implement their project for distribution center 220v short distance. But we do this project for transmission system for voltage 132kv (from gibe generation station to jimma substation) and the circuit they used is complex and we try to use simple circuit for many people easily understand.
SYSTEM BLOCK DIAGRAM
In this chapter we will discuss the characteristics, operation, and advantage of power system with TCSC component. We will start by discussing the basic technological configurations of power system with TCSC. Then the chapter explains the characteristics of the components; capacitor bank, inductor bank, power supply, Traic (TCR), and transmission line parameter. These are the relevant components used in the power system with TCSC studied in this project.
1127760993140001739900701675Transmission line parameter
0Transmission line parameter
Fig 3.1 block diagram of power system with TCSC
3.1 system component description
3.1.1 Triac (TCR)
This traic is a kinds of device used for switching the inductor bank when it gain signal from opto copular. A correction action is adjusted or initialized to compensate for angle difference by continuous changing the firing angle of TCR via opto isolator TRIAC driver circuit
3.1.2 Capacitor bank
Capacitor bank is the basic component that delivers capacitive reactance, which is negative reactive power. Capacitor is group of several capacitor of the same rating that is linked in series or parallel with each other. Most of the power system has inductive loads thus generally only lagging power factor occurs hence capacitors are used to compensate by producing leading current to the load to reduce the lagging current. It is unit is MVAR. Advantage of capacitor bank is:
It reduces line current of the system.
Improves voltage level of the system.
Reduces system losses.
3.1.3 Inductor bank
Inductor bank is the element that supplies inductive reactance. This is positive reactive power. Inductors bank are used to compensates by absorbing leading current from the load for reducing leading current there by shrink the phase angle length between the real power and apparent. The function of shunt inductor is to deliver lagging (inductive) kvars to an electrical system when and where wanted.
3.1.4 Power supply
A power supply is an electric source that supplies electric power to an electrical system. And also we use 132kv AC. input to the transmission line.
3.1.5 Transmission line parameter
Transmission line parameter is the element that we use or exist on the line through the process of transmission system. Most of them are listed below;
Resistance: It is the opposition of line conductors to flow of current. The resistance is distributed uniformly along the entire length of the line. However, the performance of a transmission linecan be analyzed appropriately if distributed resistance is considered as lumped.
Capacitor: A capacitor (originally known as a condenser) is a passive two-terminal electrical part used to store energy electrostatically in an electric field. The forms of capacitor in real-world is vary widely, but all contain at least two electrical plates separated by a dielectric (i.e., insulator). The conductors can be thin films of metal aluminum foil or disks, etc. The non-conducting dielectric acts to increase the capacitor’s charge capacity.
Reactive power: is a power moves between the source and load of the circuit. This power is not doing any useful on the loads. It is produced for maintenance of the system. It is the power used to sustain the electromagnetic field in inductive and capacitive equipment. This power is supplied for many purposes by condensers, capacitors, and similar devices, which can react to changes in current flow by releasing energy to normalize the flow. In a purely reactive circuit, voltage and current are 90 degree apart. The cosine of 90 degree angle is zero that is the power factor is zero. This means the circuit returns all energy received from the source to the source. The reactive power can be calculated as
Q=I2*X or V2/X…………………………………………………..3.1
Where; Q= reactive power
V= voltage supplied
I= system current
Reactive power is measured in volt amperes reactive (VAR).
Long transmission line: When the length of an overhead transmission line is more than 150 kmand line voltage is very high (> 100 kV), it is considered as a long transmission line. For thetreatment of such a line, the line constants are considered uniformly distributed over the wholelength of the line and rigorous method are employed for solution.
Receiving end voltage (Vr): the voltage obtained at the receiving end on a transmission line.
Sending end voltage (Vs): the voltage obtained at the sending end of a transmission line. Both are used to calculate transmission efficiency in power transmission line.
Transmission efficiency the power obtained at the receiving end of a transmission line is generally less than the sending end power due to losses in the line resistance. The ratio of receiving end power to the sending end power of a transmission line is known as the Efficiency transmission of the line i.e. % age Transmission efficiency,
?T= receiving end voltage/sending end voltage*100%
= VRcos?R = VRcos?R/VRcos?S*100%…………………………………………3.2
Where VR, IR and cos ?R are the receiving end voltage, current and power factor while VS, ISand cos ?s are the corresponding values at the sending end.
Bus bar: In electrical power distribution, a bus bar are used to conducts electricity within a switchboard, distribution board, substation, battery bank, or other electrical apparatus. Its main purpose is to conduct a substantial current of electricity, and not to function structural member. Bus bars are the basic components in electrical power grid because they can reduce the power loss via reducing the corona effects. This is because bus bars have bigger surface areas compared to wires.
3.2 Operation of thyristor
3.2.1 The thyristor controlled series compensator (TCSC)
TCSC is one of the most important and best known series FACTS controllers. TCSC (thyristor controlled series capacitor) has one parallel inductor and series connected capacitor with a transmission line. It provides continuous variable capacitive reactance and variable inductive reactance to control the transmission line parameters. It has basically use for enhance system stability. The basic module of a TCSC is shown in bellow Fig3.2 It consists of three components: capacitor banks C, bypass inductor L and bidirectional thyristors T1 and T2. The firing angles of the thyristors are controlled to regulate the TCSC reactance in accordance with a system control algorithm, normally in response to some system parameter variations.
Fig. 3.2 configuration of thyristor in transmission line
There are three modes of operation of TCSC depending upon the firing angle of the pulses fed to the thyristor namely 9:
Thyristor blocked mode
Thyristor by passed mode
Vernier operating mode.
Thyristor blocked operating mode: When the thyristor valve is not triggered, the TCSC is operating in blocking mode. In this mode, the TCSC performs like a fixed series capacitor. Thyristor Bypass Operating Mode:-in this mode the TCSC module behave like a parallel capacitor combination. The value of inductor higher than the capacitor. This mode is employed for central purpose and initiating certain protective function.
Vernier operating mode: Vernier control the TCSC dynamics are varied continuously by controlling the firing angle. The firing angle is possible from 0 to 90 degree for each half cycle when it is generated from the zero crossing of the line current hence divided into two parts:
Fig. 3.3 Equivalent circuit of TCSC in Vernior mode
Advantage of TCSC: Regulation of power flow in prescribed transmission line. Secure loading of transmission line nearer to their thermal limits. Prevention of cascading outages by contributing to emergency control. Damping of oscillation that can threaten security or limit the usable line capacity.
4.1 Data collected
The data collected for our design from gibe power generation station to jimma substation is listed or shown on the appendix.
4.2 Reactive and active power flow
Fig 4.1 active and reactive flow diagrams
Is= sending end current
Ir= receiving end current
Es= sending end voltage
Er= receiving end voltage
R=Transmission line resistance
X= Transmission line reactance Transmission line impedance
Transmission line impedance Z = R + jX = |z|<?…………………………………………..4.1
Sending end current
Ss= sending end complex power= VsIsSs=Vs<?Vs<?-X-Vr<-?|z|…………………………………………………………………….4.4
Real power or active power flow from sending end is
Ps= real (Ss)
Reactive power at sending end is
Qs= imaginary (Ss)
Qs=v2sin?|z|-VsVrsin(?+?)|z|Power system transmission lines have small resistance compared to the reactance i.e. R/X ratio is very small. Also power loss in the transmission line is negligible.
R=0; Z= |X|<900
Ps= VsVrsin?/= |X|……………………………………………………………………….4.6
Qs= VsVs-Vrcos?/ |X|…………………………………………………………………..4.7
If Es leads Er , then load angle ? is positive and real power flows from sending end to receiving end.
If Es lags Er, then load angle ? is negative and power flows from receiving end to sending end. If resistance R = 0, then maximum real power flow from sending end occurs at ? = 90° the maximum power flow is given by.
4.3 principles of AC power control
Relating a voltage in series with the line and in phase quadrature with the current flow, may can increase or decrease the amount of current flow. As the current moves lags the voltage by 90°, there is injection of reactive power in series.
If a voltage with variable level or magnitude and a phase is applied in series, then changing the amplitude and phase angle can control both active and reactive power. This needs injection of both active power and reactive power in series.
Decreasing and increasing the value of the reactance X can also decrease and increase the power height of both active and reactive power.
Power flow can also be controlled by regulating the size of sending and receiving end voltages Vs and Vr. These kinds of control have much effect on reactive power flow than active power flow.
4.3 Mathematical model
The Process of getting a capacitance of fixed capacitor (FC) for compensation of the inductive reactive power on the transmission line it wants a capacitor bank which gives negative reactive power for the compensation of the reactive power. For providing the capacitive reactance it needs the capacitor. The real capacitor in farads can be designed using the following equation 10.
Where; Q= capacitor unit rating in VAR
C= capacitor in farad
f= frequency in Hz
V= line voltage
The TCSC is calculated with sufficient capacity to supply at least the reactive power absorbed by the nonlinear load (Qtcsc? QL).
For Q= Qmax +10% QmaxHere of load from the appendix table is 10Mvar at 132kv for three phase
Q= 10MVAR+ 10%*10MVAR
Now, C= 11MVAR/ (2*3.14*50*(76.2KV) 2)
So, capacitor to absorb 11M VARs at 76.2kv = 12.066 µF
4.3.1 Traic Controlled Reactor (Variable Inductance) Branch
The triac controlled reactor consist of the variable inductor by changing the firing angle instant it is possible to control the current in the reactor , and also control the capacity of the reactive power absorbed by the TCR. The current flowing through the reactor can be controlled by varying the firing angle of the triac and is given by 10:
Where; ?= firing angle of triacThe reflected inductance can be varied and its value as a function of firing angle thus is given by:
L (?) = ?/ (2?-2?+sin2?)…………………………………………………………..4.10
Where the firing angle (?) is bounded as (?/2) < ? < ?The reflected reactance thus can be given by below and its value as a function of firing angle can be varied as,
X1(?) = 2?f1 (?/ (2?-2?+sin2?))………………………………………………4.11
It can be seen from the from the above equation that the reflected reactance of TCR branch is a function of firing angle (?)and the reflected reactance increases with increase in firing angle, the reflected reactance is ? for ? =1800.
4.3.2 Determination of inductance of TCR reactance
At 100% or unity load power factor the TCSC does not interchange any reactive power with the ac system, under this operative condition the total reactance of TCSC compensator should neither capacitive nor inductive i.e. the reactance of FC capacitor branch be equal to the reactance of the TCR controlled branch 11.
I.e. Xc= XL (?)
For C= 6.033µF and ?= 1300
Xc= 1/ (2*3.14*50*13.066*10-6)
From the above Xc= X (l)
L= Xc*(2?-2?+sin (2?))/ (2?2f)
4.3.3 Reactive Power Compensation
Reactive-power compensation is arranged with a TCSC joined in series with the transmission line. The overall reactive power of the TCSC is given by 11.
Q (?) =V2 (Bc-BL (?))
Where; Bc= ?oC BC=2?fc
The suspectance of TCR as a task of firing angle is given by:
BL=1woL B=12*?*fl =12*3.14*50*0.20479 = 0.0155MOH
Where the firing angle (?) is bounded as (?/2) < ? < ?
The table blew show the variation of reactive power with respect to the firing angle. Variation of Q with the firing angle ?
Table4.1 Peak load data from Gilgel gibe to Jimma
No. ?in degrees BL(? ) im MOH Q (?)=V2(Bc-BL(?))
1 900 0.01555 -68,291,282.77
2 1000 0.01212846 -48,424,316.3
3 1100 0.008911213 -29,743,563.28
4 1200 0.0060779103 -13,292,162.19
5 1300 0.0037618951 155,641,1582
6 1400 0.0020341173 +10,187,879.16
7 1500 0.000894576955 +16,804,551.82
8 1600 0.00027232392 +20,417,626.72
9 1700 0.00034015603 +21,801,349.7
10 1800 0 +21,998,859.23
The reactive power of the TCSC is may can positive or negative, as shown from the above table the sign of the reactive power depends on the firing angle of the TCR. If Bc<Bl(? ) , the sign of the reactive power is negative thus the TCSC provides lagging reactive power i.e. the TCSC acts as inductive reactance where as if the sign of the reactive power is positive thus the TCSC provides leading reactive power i.e. the TCSC acts as capacitive reactance. Generally from the above table the reactive power of TCSC varies w.r.t firing angle (?). And we can calculate the power factor at different firing angle the pf also different for instance 12. From the above calculation the Pf goes from lagging to leading for after that the pf start to lag.
4.4 Power transfer
The active power transferred by the uncompensated and compensated transmission line is compared as follow:
a) Without series compensation
b) With series compensation
Fig.4.2 voltage profile for radial circuit without SC and with SC
4.5 Circuit diagram of the system
The supply given to our medium transmission line from gibe generating station is 132kv. A tcsc is placed on this line and it consists of a fixed capacitor and a parallel TCR in each phase. The system we use is capacitive mode the firing angle becomes 90deg (using only capacitor). At this point nominal compensation are 75%. By the nature normal oscillatory frequency of TCSC IS 163Hz this means around 2.7 times of fundamental frequency 7. It has two operating mode either capacitive or inductive mode. When it’s in capacitive mode the firing angle is between 69-90 degree and in inductive 0-49 degree.
Fig .4. Overall circuit diagram of power system with TCSC
4.6 simulation result and discussion
Simulation result is performed in MATLAB Simulink software. Simulation diagram of purposed system and its output waveform is shown in figure below
Fig. 4. Sending end voltage generating from station
The above figure is shows the total voltage supply to the transmission line (sending end voltage).
Fig. 4 receiving end voltage with TCSC
The receiving end voltage with TCSC is almost the same as with sending end voltage because TCSC is reduces transmission line loss and make stable the receiving and sending end voltage. This means when TCSC connected current lead to voltage in case the reactive power is compensated due to capacitor and inductor effect on the line. Fig. 4 receiving end voltage without TCSC
Receiving end voltage without TCSC is much less than sending end voltage. This indicates that the voltage drop is high and the voltage is less stable as compared from receiving end voltage with TCSC. That is before connected TCSC voltage lead to current in case the reactive power is not compensated on the line. In this case the reactive power is inductive mode on the line.
Generally; Addition of TCSC device to one of the lines changes the power flow in given lines according to level desired. This change is accomplished by changing the impedance of line, in which is installed TCSC device. With the access values of angle switching thyristors ?, TCSC can change the impedance of the line and thus normalizes the power flow as necessary.
CONCLUSIONS AND RECOMMENDATIONS
This project improves stability and enhancement of active power transfer capability by using thyristor controlled series capacitor. The circuit in the design measure the current and voltage from the line. Thyristor controlled series capacitor (TCSC) is a kinds of variable impedance series compensator and seriously connected with the transmission line to increase capability of power transfer by reducing transmission losses. In this project, when voltage lead the current or when the inductive reactive power is high on the transmission line the capacitor is connected automatically to the system and compensate the reactive power.
Generally, when using a thyristor controlled series capacitor the active and reactive power is increased from the original active and reactive power value. This implies TCSC increase the power transfer capability and stabilize the voltage.
The system can be deployed where it’s necessary to compensate the reactive power in order to stabilize the system. This system can also be upgraded with the use of TSC (thyristor switch capacitor) and harmonic suppressor in order to enhance the switching frequency of the capacitor bank and to eliminate the harmonic distortion due to high switching frequency. The power system computational complexity of transient stability problems have kept them from being run in real-time to support decision making at time of a disturbance. If a transient stability analysis could run in real time or faster than real time, faster transient stability simulation implementations may significantly affect. Therefore the load flow analysis may be carried out for the model under investigation using gauss-siedel, newton raphson and fast-decoupled.
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Table 2 line data from gibe to jimmaNo. Line data Value
1 Node 1 Gilgel gibe
2 Node 2 Jimma 500kv
3 Element name Jimma gilgel gibe
4 Network level 500kv
5 Type Gilgel gibe – jimma6 Line type Overhead
7 Length(km) 71.2
8 Resistor (ohm/km) 0.1905
9 Reactance (ohm/km) 0.4373
10 Capacitor (µf/km) 8.4
11 Line voltage(kv) 132
12 Maximum voltage(kv) 145
13 Conductor type Aluminum
14 Frequency(Hz) 50
Table 3 Peak load data from Gilgel gibe to JimmaNo. Transformer Secondary(KV) Real power(MW) Reactive power(MVAR)
1 JIMMA132/15 KV 15 14.5 Max =10, Min= 2
2 JIMMA132/33/15 KV 33 Currently= 6