 Open Access
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 Authors : Kunj Thekdi , Vishwajeetsinh Varnamiya , Deep Desai
 Paper ID : IJERTV8IS010010
 Volume & Issue : Volume 08, Issue 01 (January – 2019)
 Published (First Online): 05012019
 ISSN (Online) : 22780181
 Publisher Name : IJERT
 License: This work is licensed under a Creative Commons Attribution 4.0 International License
Congestion Management in Transmission Lines using FACTS Devices
Congestion Management in Transmission Lines using FACTS Devices
Kunj Thekdi
BE Electrical 2018
Faculty of Technology & Engineering, The Maharaja Sayajirao University of Baroda
Vadodara, Gujarat, India
Vishwajeetsinh Varnamiya
BE Electrical 2018
Faculty of Technology & Engineering, The Maharaja Sayajirao University of Baroda
Vadodara, Gujarat, India
Deep Desai
BE Electrical 2018
Saradar Vallabhbhai Patel Institute of Technology, Vasad, Vadodara, Gujarat, India
Abstract This report presents a mathematical model of Available Transfer Capability (ATC) deals with congestion management situation in transmission lines. This report contains the simulation of IEEE 9bus system in software Power World Simulation EducationEvaluation 20 , which defines whether the system is in congestion or not using the values of ATC in every case. ATC can be calculated using Power Transfer Distribution Factor (PTDF) which is taken from standard IEEE 9bus system data from Power world simulator. This report also contains modeling of a FACTS device i.e. Thyristor controlled series capacitor (TCSC). This report also contains that using this device in series with the line, it changes the susceptance of line and ultimately it improves the ATC of the line hence congestion is managed.
Keywords Available Transfer Capacity(ATC), Power Transfer Distribution Factor(PTDF), Flexible AC Transmission System(FACTS), Thyristor Controlled Series Capacitor(TCSC)

INTRODUCTION
In all over the world, interconnections and loadings in the modern power system networks are growing. Power utilities are facing a major challenge in maintaining desired security of power supply. Power system security and analysis forms an essential part of modern energy management system. The economic downturn coupled with environmental and ecological pressures have obliged the electric utilities, all over the world, to serve the augment in load demand without corresponding increase in generation and transmission facilities. This has forced the utilities to operate their generators and transmission systems to their maximum capabilities. And system running under its maximum capabilities is called system under congestion. Hence, the re regulation of the power system has been derived for getting maximum economical benefits to the society.

CONGESTION MANAGEMENT IN TRANSMISSION LINES

Congestion Management
In deregulated environment all simultaneous transactions will pull the power system in unstable state or it is in congestion. Any violations in physical or operational constraints will results congestion. The constraint has been listed as under:

Voltage Limits

Thermal Limits

Stability Limits


Available Transfer Capability (ATC)
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AVAILABLE TRANSFER CAPABILITY (ATC)
AND EQUATIONS
In deregulated environment all simultaneous transactions will pull the power system in unstable state or it will be in congestion. Any violation in physical or operational constraints will result in congestion. The physical structure of transmission line cannot modify as it requires a huge amount of investment. Hence, power can be imported and exported in open access market with the same lines in congestion management. The possible boundaries that may be violated in case of congestion are:

Thermal limits of transmission lines

Emergency ratings of the Transformer

Voltage limits

System stability.

ATC Calculation using PTDF [1]
One way of calculating ATC from node A to node B is to use DC load flow (explained later) repetitively by increasing the amount of transaction until a limit of any of the corridor is reached. However, this is computationally inefficient. Instead, the Power Transfer Distribution Factor (PTDF) can be used to calculate the maximum allowable flow for a given pair of injection and takeoff points. It is also necessary to consider the effects of contingencies like line outages. This can be achieved using Line Outage Distribution Factor (LODF). Let us first see the details of DC load flow model.

DC Load Flow Model [1]

With the assumptions, power flows over transmission lines connecting bus i and bus j is given as:
Where,
line inductive reactance in per unit phase angle at bus l
reference bus. The angles in equation 4.3 can be found out as
Thus, power flow over line lm can be found out using this equation.
A. ATC calculation Using PTDF
ATC is determined by recognizing the new flow on the line from node l to node m, due to a transaction from node i to node

The new flow on the line is the sum of original flow and the change.
Where, is the base case flow on the line andis the magnitude of proposed transfer. If the limit on line lm, the maximum power that can be transferred without overloading
line lm, is , then,
phase angle at bus m
The total power flowing into the bus i, Pi, is the algebraic sum of generation and load at the bus and is called a bus power injection. Thus,
This can be expressed in a matrix form as:
Where, the elements of the susceptance matrix BX are functions of line reactances. One node is assigned as a reference node by making its angle zero and deleting
corresponding row and column in matrix. Thus,
The dimension of obtained is . Let us augment it by adding zero column and row corresponding to
is the maximum allowable transaction from node i to node j constrained by the line from node l to node m. ATC is the minimum of the maximum allowable transactions over all lines.
Using the above equation, any proposed transaction for a specific hour may be checked by calculating ATC. If it is greater than the amount of the proposed transaction, the transaction is allowed. If not, the transaction must be rejected or limited to the ATC.
Using the above equation, any proposed transaction for a specific hour may be checked by calculating ATC. If it is greater than the amount of the proposed transaction, the transaction is allowed. If not, the transaction must be rejected or limited to the ATC.


STANDARD DATA AND NORMAL CONDITION: IEEE 9 BUS SYSTEM
IEEE 9 bus system in normal condition
FROM BUS
TO BUS
Absolute % PTDF
5
4
89.59
6
4
10.41
7
5
10.41
9
6
10.41
7
8
10.41
8
9
10.41
PTDF values of IEEE 9 bus system from POWER WORLD SIMULATOR.
Further figure shows a model of a transmission line with a TCSC connectedbetween buses i and j. The transmission line is represented by its lumped equivalent parameters connected between the two buses. During the steady state, the TCSC can be considered as a static reactance jXC. This controllable reactance, XC is directly used as the control variable to be implemented in the power flow equation. [5]
Line flows

Without TCSC
Gij + jBij = [ rij / ( rij2 + xij2) ] + j[ xij2 / ( rij2 + xij2) ]

With TCSC (jxc)
Gij+ jBij = [1/{rij + j(xij xc)]*[rij j(xij xc)]/[rij
– j(xij xc)]
Where,
Bij = [(xij xc) / {rij2 + (xij xc)2}] Gij = [rij/{rij2 + (xij xc)2}]
IEEE 9 bus system in congested condition


FACT DEVICE TCSC
Thyristorcontrolled series capacitor (TCSC) is a capacitive reactance compensator, which consists of a series capacitor bank shunted by a thyristor controlled reactor in order to provide a smoothly variable series capacitive reactance.
Assumptions

We have taken Xc =0.9153 pu and using this we have calculated the Bij which comes out to be Bij
=1.18 pu. So, After connecting TCSC in series with the line 45 the new Bij is 1.18 pu instead of the previous values (0.176 pu) . Now , whenever we use TCSC the line susceptance between 45 will be Bij=1.18 pu.

We have taken Gij=0 pu .


CASES

CASE I NEGATIVE ATC
IEEE 9 bus system in congested condition without TCSC
IEEE 9 bus system in congested condition with TCSC

CASE II CRITICAL ATC
IEEE 9 bus system in congested condition without TCSC
IEEE 9 bus system in congested condition with TCSC

CASE III POSITIVE ATC
IEEE 9 bus system in congested condition without TCSC
IEEE 9 bus system in congested condition with TCSC


RESULT TABLE
CASES
ATC WITHOUT TCSC in MW
ATC AFTER USING TCSC (IMPROVED ATC) in MW
I negative
13.56
12.98
II – critical
0.0446
0.5692
III – positive
3.18
3.73

CONCLUSION
It concludes that the development of the AC Power Transmission Congestion Distribution factor (PTCDF) suitable for computing change in any line quantity for a change in MW bilateral transaction. With PTCDF ATC can be calculated. For multiple transactions ATC calculation is very important and mandatory too. ATC calculations can be used to solve congestion problem in restructured electrical power network.
In case of negative ATC where ATC falls below zero i.e. negative in congested situation, as discussed in chapter 5:caseI, can be improved in negative as well, though it is not a good situation for the transmission system.
In case of critical ATC, before using TCSC, ATC is negative and it can be brought to positive using TCSC and it is quite useful method in practice. The results for the same are described in chapter 5:caseII.
While in case of positive ATC, it can be improved using TCSC and the results for the same is shown in chapter 5:case III, which is the situation, market faces frequently.
In all cases, TCSC injects MVAR to the line that reduces the real power flow in the line.

APPENDIX
IEEE 9BUS DATA

REFERENCES
IJRET, eISSN: 23191163  pISSN: 23217308
[5] K. R. Padiyar, FACTS controller in power transmission and distribution [6] Manisha Chadar, Thesis on Mitigation of voltage sag by thyristor controlled series capacitor and PWM generator and their comparision, IJTPD, vol. 1, issue 1, PP: (7198) [7] Liangzong Yao, Phill Cartwright, Laurent Schmitt, XiaoPing Zhang, Congestion Management of Transmission systems using FACTS, IEEE Conference 2005, pp 15