TRANSIENT STABILITY ENHANCEMENT BY USING DSSC AND PSS

http://www.iaeme.com/IJEET/index.asp 40 [email protected]

International Journal of Electrical Engineering & Technology (IJEET)

Volume 7, Issue 3, May–June, 2016, pp.40–48, Article ID: IJEET_07_03_004

Available online at

http://www.iaeme.com/ijeet/issues.asp?JType=IJEET&VType=7&IType=3

ISSN Print: 0976-6545 and ISSN Online: 0976-6553

Journal Impact Factor (2016): 8.1891 (Calculated by GISI) www.jifactor.com

© IAEME Publication

TRANSIENT STABILITY ENHANCEMENT

BY USING DSSC AND PSS

S. I. Barde

Department of Electrical Engineering,

BRHCET, Vangani, India

ABSTRACT

Synchronous operation of generators in power system is required to supply

continuous electricity to customers. Proper transient stability must be

maintained for stable operation of power system. To enhance the transient

stability of power system FACTS or D-FACTS technology can be used. In this

paper, Distributed Static Series Compensator (DSSC) which, belongs to D-

FACTS technology is used to enhance the transient stability of two-machine

system with Power System Stabilizer (PSS) as an auxiliary controller and it is

found that DSSC along with PSS is able to maintain required transient

stability during severe three-phase to ground fault.

Key words: Distributed Static Series Compensator, D-FACTS, FACTS Power

System Stabilizer, Synchronous operation, Transient stability.

Cite this Article: S. I. Barde, Transient Stability Enhancement by Using

DSSC and PSS. International Journal of Electrical Engineering &

Technology, 7(3), 2016, pp. 40–48

http://www.iaeme.com/ijeet/issues.asp?JType=IJEET&VType=7&IType=3

1. INTRODUCTION

Transient stability in power system can be defined as, the ability of power system to

remain in synchronism during severe fault conditions [1]. It means ability of power

system to regain its original pre-fault equilibrium position or another equilibrium

point which is generally in vicinity to pre fault equilibrium point. In 1920, power

system stability is recognized as crucial and important problem [2].

Demand of electrical power is increasing tremendously and it is expected that, in

India the total requirement of electrical power can cross 950,000 MW by year 2030

[3]. Therefore, to supply electrical power continuously to customers, new generation

and transmission system should be developed. But in India, constructing new

transmission line is not always feasible. In addition to the high capital cost involved in

development of transmission system other hurdles are Right of Way (ROW), scarce

land availability and forest clearance, and getting forest clearance takes considerable

Transient Stability Enhancement by Using DSSC and PSS


time in India due to lengthy process and involvement of different levels of

permissions [4].

Hence, there is need to use existing transmission system efficiently. To enhance

transient stability without compromising active power flow through transmission line

technically proven FACTS controller can be used [5]. But, these FACTS controllers

have some limitations. To overcome these limitations D-FACTS devices were

introduced. The D-FACTS controllers are distributed in nature and these controllers

are connected along the high voltage (HV) or extra high voltage (EHV) transmission

line [6]. Deepak M. Divan and et al. has introduced concept of D-FACTS technology

to relieve congestion and to improve power flow capabilities [6]. S. Golshannavaz and

et al have discussed effect of Distributed Static Series Compensator (DSSC) on

transient stability [7]. In this work, DSSC with fuzzy controller is used to improve the

transient stability of two machine system.

2. SERIES COMPENSATION AND POWER ANGLE

The power system is highly non-linear system and maintaining adequate transient

stability margin is complex phenomenon. Hence, proper power system design and

planning is required to ensure proper system operation during contingencies. In case

of, transient stability contingencies considered are short circuit faults which are

further classified as line to ground fault (LG), line to line ground fault (LLG) and

three phase fault (LLLG) [2].

To ensure stable operation of power system, system operator must maintain proper

transient stability. Practically power angle is maintained at 30° [8]. To enhance the

power flow without compromising transient stability, series FACTS or D-FACTS

controllers can be used. These controllers consist of voltage source inverter [5, 7].

Series controllers inject voltage in series with transmission line and phase angle

between injected voltage and line current is 90°. By operating these controllers in

capacitive mode, inductive reactance of the transmission line can be neutralized

partially [9].

Figure 1 Phasor diagram for uncompensated transmission line

Figure 2 Phasor diagram for series compensated transmission line

S. I. Barde


(1)

Where, Vs & Vr = Bus voltages

δ = Power angle

Xl = Line impedance

From equation (1) and phasor diagram (fig. 1 and 2) it is evident that by

decreasing transmission line reactance we can increase the power flow through

transmission line and similarly, effect of series compensation on power angle δ can be

observed. Due to decrease in transmission line reactance the δ angle is also reduced

which means we are transmitting more power with reduced power angle. The limits

for power angle δ are 0° < δ < 90° [10].

3. DTRIBUTED STATIC SERIES COMPENSATOR

A. Voltage Source Inverter

All FACTS and D-FACTS controllers are based on voltage source inverter. The

voltage source inverters are preferred due to their better performance and less cost as

compared to current source inverter. Hence, in case of DSSC single phase voltage

source inverter is used. The circuit schematic of DSSC system is shown in figure 3.

By changing polarity of dc current power flow can be changed in either direction.

Therefore, voltage source inverter uses bidirectional devices such as GTO or IGBT

with parallel diode connected in reverse [5].

B. Single Turn Transformer (STT)

STT is important part of DSSC. STT is designed in such a way that it will clamp on

transmission line. STT has high turn ratio, say 100:1 or 75:1. This design protects VSI

under fault condition. If the fault current is 30 kA or 50 kA, the inverter current is

only 300 A or 500 A respectively. This is well below the current rating of available

GTO or IGBT [11].

Figure 3 Circuit schematic of DSSC system



C. Contol System

The main objective of control system of DSSC is to maintain charge of DC capacitor.

Also to inject voltage in transmission line, in such a way, that injected voltage will be

orthogonal to line current [12]. In this work fuzzy controller is developed to achieve

conditions. Rotor angular difference between two generators and power angle is used

as an input to fuzzy controllers. Block diagram of control system is shown in fig 4.

Figure 4 Control system for DSSC

4. SIMULATION RESULTS

To study effect of DSSC on transient stability two-machine system, shown in fig. 5 is

considered. The system considered consist of two generator with 1000 MVA and

5000 MVA rating. Length of transmission line is 700 km. To study effect of DSSC on

transient stability following two different cases are considered.

Figure 5 Two-machine system

A. Without DSSC

The three-phase to ground fault is created at T= 1.1. In this case DSSC is not active in

circuit. Due to three phase fault created near generator one power angle goes on

increasing after T=1.2 and two generators losses synchronism (fig. 6).

S. I. Barde


Figure 6 Varitation of power angle during 3-phase fault

As two generators losses synchronism its effect on rotor angular speed and

machine voltage can be observed in fig.7 and 8. generator one accelerates and

generator two decelerate.

Figure 7 Varitation of rotor speed during 3-phase fault.

Figure 8 Varitation of generator voltage during 3-phase fault.



B. With DSSC

Same fault condition is used to study effect of DSSC on power angle, rotor angular

speed and machine voltage. If system is subjected to severe three phase fault of

duration 0.1 then alone DSSC is unable to maintain synchronism as its primary work

is to enhance power flow capability of transmission line and not transient stability

enhancement. Hence, auxiliary POD controller or power system stabilizer (PSS) is

needed in system to damp oscillation in the rotor speed. In this work, PSS is used to

provide auxiliary damping signal to maintain transient stability.

As shown in fig. 9 power angle oscillates between 73° to 37° and become stable

after T=4 completely and attains the pre fault equilibrium. Similarly effect of fault on

machine voltage and angular speed is shown in fig. 10 and 11. From these results it is

clear that DSSC along with auxiliary controller can maintain transient stability.

Figure 9 Varitation of power angle during 3-phase fault with DSSC and PSS.

Figure 10 Varitation of generator voltage during 3-phase fault with DSSC and PSS.

S. I. Barde


Figure 11 Varitation of rotor speed during 3-phase fault with DSSC and PSS

Voltage and current generated by voltage source inverter is shown in fig. 12 and

13 and output voltage of DSSC is shown in fig. 14.

Figure 12 Output voltage of single phase voltage source inverter

Figure 13 Output current of single phase voltage source inverter.



Figure 14 Output voltage of DSSC

5. CONCLUSION

To supply continuous electrical power to the customers, maintaining transient stability

is very important. D-FACTS technology provides more reliable approach to enhance

power transfer capabilities and transient stability of power system than FACTS

technology. From two-machine power system simulation results, it is evident that

DSSC along with auxiliary controller can be used to enhance transient stability

without compromising active power flow through transmission line. We have shown,

In case of three phase fault, if DSSC is not active in system, the two generators losses

synchronism. Whereas, if DSSC is active in system during three phase fault, system

stabilizes after few oscillations and generators do not lose synchronism. DSSC

provides cost effective method to enhance the transient stability. In this work, we

have proved that, DSSC with fuzzy logic controller can be used along with PSS as

supplementary controller to mitigate the transient stability problem and by using

DSSC we can transmit more power without violating the transient stability limits.

REFERENCES

[1] Kothari, D. P., and I. J. Nagrath. Power system engineering. Tata McGraw-Hill,

2008.

[2] Kundur, Prabha. Power system stability and control. Edited by Neal J. Balu, and

Mark G. Lauby. 7. New York: McGraw-hill, 1994.

[3] Manoj kumar Gupta. Power Plant Engineering. PHI Learning pvt. ltd. 2012.

[4] National Electricity Plan (Volume – II) Government of India Ministry of Power

Central Electricity Authority. http://www.cea.nic.in/reports/powersystems

/nep2012/transmission_12.pdf

[5] Hingorani, Narain G., and Laszlo Gyugyi. Understanding FACTS: concepts and

technology of flexible AC transmission systems. Wiley-IEEE press, 2000.

[6] Divan, Deepak, William Brumsickle, Robert Schneider, Bill Kranz, Randal

Gascoigne, Dale Bradshaw, Michael Ingram, and Ian Grant. A distributed static

series compensator system for realizing active power flow control on existing

power lines. In Power Systems Conference and Exposition, 2004. IEEE PES, pp.

654-661. IEEE, 2004

S. I. Barde


[7] Golshannavaz, Sajjad, M. Mokhtari, Mojtaba Khalilian, and Daryoosh

Nazarpour. "Transient stability enhancement in power system with distributed

static series compensator (DSSC). In Electrical Engineering (ICEE), 2011 19th

Iranian Conference on, pp. 1-6. IEEE, 2011

[8] Gupta, B. R. Power system analysis and design. S. Chand & Company, 1998

[9] Fajri, Poria, Morteza Farsadi, Daryoush Nazarpour, and Arash Tavighi. A novel

strategy for controlling a group of distributed static series compensators. In

Electrical and Electronics Engineering, 2009. ELECO 2009. International

Conference on, pp. I–119. IEEE, 2009.

[10] Kimbark, Edward Wilson. Power system stability. Vol. 1. John Wiley & Sons,

1995

[11] Johal, Harjeet, and Deepak Divan. Design considerations for series-connected

distributed FACTS converters. Industry Applications, IEEE Transactions on 43,

no(2007): 1609–1618

[12] Gaber Shabib and Youssef A. Mobarak, Coordinated Design of A Mb-Pss and

Statcom Ontroller To Enhance Power System Stability. International Journal of

Electrical Engineering & Technology, 3(2), 2012, pp. 352–372.

[13] Sameer S. Mustafa, Mohammad A. Abdullah and Bilal A. Nasir, the Influence of

Optimum Generation on Transient Stability. International Journal of Electrical

Engineering & Technology, 4(4), 2013, pp. 118–128.

[14] Mukesh Kumar Kirar, Ganga Agnihotri, Transient Stability Enhancement by Ann

Based Adaptive Load Shedding. International Journal of Electrical Engineering &

Technology, 3(3), 2012, pp. 200–210.

[15] Fajri, Poriya, and Saeed Afsharnia. A PSCAD/EMTDC model for distributed

static series compensator (DSSC). In Electrical Engineering, 2008. ICEE 2008.

Second International Conference on, pp. 1–6. IEEE, 2008.

TRANSIENT STABILITY ENHANCEMENT BY USING DSSC AND PSS

Engineering

Transcript of TRANSIENT STABILITY ENHANCEMENT BY USING DSSC AND PSS