17th International Conference on Electrical, Electronics and Systems Engineering ICEESE 2015 December 21 – 22, 2015 Istanbul, Turkey.

17th International Conference on Electrical, Electronics and Systems

EngineeringICEESE 2015

December 21 – 22 , 2015Istanbul , Turkey

Transient Stability Improvement in multi-machine system with using power

system stabilizer (PSS) and Static Var compensator (SVC)

presented by : Khoshnaw Khalid HAMA SALEH

Prof Dr. Ergun Ercelebi

University of Gaziantep, Dept. Of Electrical and Electronics Eng., 2015

OutlineINTRODUCTIONPOWER SYSTEM STATES

TRANSIENT STABILITY METHODS FOR IMPROVEMENT TRANSIENT STABILITY POWER SYSTEM STABILIZER (PSS) TYPES OF FACTS CONTROLLER STATIC VAR COMPENSATOR (SVC)

SIMULATION AND RESULTS CONCLUSION

REFERENCES

SIMULINK AND MATLAB SOFTWARE

APPENDIX

SYSTEM STABILITY

Modern power system is a complex non linear interconnected network. It consists of inter connected transmission lines, generating plants transformers and a variety of loads. With the increase in power demand nowadays some transmission lines are more loaded than their normal limits. With the increased loading of long transmission lines, the problem of transient stability has become a serious limiting factor.

The modern power system is complex that it becomes interest to power system stability, especially transient stability and small disturbance. Transient stability plays more effect role in stability of power system, during fault and large disturbance.

In this study proposes comparative of power system stabilizer PSS and static Var compensator SVC with to improve damping oscillation and enhance transient stability.

The effectiveness of a power system stabilizer PSS connected to the exciter and/or governor

in damping electromechanical oscillations of isolated synchronous generator is tested. The static Var compensator SVC device is a member of shunt FACTS (flexible alternating current transmission system) family, it is employed in power transmission system.

INTRODUCTION

POWER SYSTEM STATES

The power system is a highly nonlinear system that operates in a constantly changing environment; loads, generator outputs and key operating parameters change continually .

When subjected to a disturbance, the stability of the system depends on the initial operating condition as well as the nature of the disturbance.

Stability of an electric power system is thus a property of the system motion around an equilibrium set, i.e., the initial operating condition.

Steady state Dynamic state Transient state

Power system states

STEADY STATE In an interconnected power system, the rotors of each synchronous machine in the system rotate at the same average electrical speed. The power delivered by the generator to the power system is equal to the mechanical power applied by the prime mover, neglecting losses. During steady state operation, the electrical power out balances the mechanical power in.

DYNAMIC STATE Dynamic instability is more probable than steady state stability. Small disturbances are continually occurring in a power system (variations in loadings, changes in turbine speeds, etc.) which are small enough not to cause the system to lose synchronism but do excite the system into the state of natural oscillations. In a dynamically unstable system, the oscillation amplitude is large and these persist for a long time (i.e., the system is under damped)

TRANSIENT STATE For a large disturbance, changes in angular differences may be so large as to cause the machines to fall out of step. This type of instability is known as transient stability and is a fast phenomenon usually occurring within 1sec for a generator close to the cause of disturbance.

POWER SYSTEM STATES

SYSTEM STABILITY

STEADY STATE STABILITY

DYNAMIC STABILITY

TRANSIENT STABILITY

VOLTAGE STABILITY

Small- signal stability is the ability of the system to return to a normal operating state following a small disturbance

Dynamic stability refers to the ability of a power system subject to a relatively small and sudden disturbance

Transient stability is the ability of power system to maintain synchronism when it is suddenly subjected to a severe transient disturbance

Voltage stability is concerned with the ability of a power system to maintain steady acceptable voltages at all buses

SYSTEM STABILITY

Transient stability is the ability of the power grid system to maintain synchronism when subjected to severe disturbances.

Transient stability analysis is considered with large disturbances like :

1.Suddenly change in load.2.Generation or transmission system configuration due to fault.3.Switching.

TRANSIENT STABILITY

Regulated shunt compensation Generator tripping Rotor size and transfer reactance of line Dynamic braking resistor High Voltage DC (HVDC) Single- pole switching Fast excitation Control Fast governor action Independent-pole operation of circuit breaker SCR (Short Circuit Ratio) Load Tripping

METHODS FOR IMPROVEMENT TRANSIENT STABILITY

POWER SYSTEM STABILIZER (PSS) Power system stabilizer PSS are generator control used in fed back to enhance the damping of rotor

oscillation due to signal disturbance. The disturbance may be caused by the even small change in the reference voltage regulator exciter which results in ever increasing rotor oscillations.

The generic power system stabilizer PSS can be used to add damping to the rotor oscillation of the synchronous machine by controlling its excitation. To remain the power system in stability must be damped the electromechanical oscillation and also called power swing.

The input signal of PSS is machine speed division (dw) The output signal is additional input (Vstab) to the excitation system .

The generic power system stabilizer is modeled by the nonlinear system as shown in figure 1

Figure 1 block diagram of the PSS

ExciterAVR

PSS

Generator Voltage

Generator and Power Network

P

Figure 2 Structure of power system stabilizer (PSS)

PSS is the most excessively prevalence damping controller.

PSSused in all synchronous generators because it

has low cost.

power system stabilizer PSS is used to this important function damp these oscillation.

Its operates by adding a signal to the reference voltage signal, based on the automatic voltage regulator (AVR) and using power deviation, speed deviation, or frequency deviation with additional torque coaxial, for this reason, PSS is prepared, thus, it can increase the damping of low frequencies and developed the dynamic stability.

OPERATING PRINCIPLE OF PSS

Generally FACTS controllers are classified as: Series Controllers Shunt Controllers Combined Series-Series Controllers Combined Series -Shunt Controllers

TYPES FACTS CONTROLLS

Area 1

Area 2

Area 1

Area 2

Series FACTs device

Shunt FACTs device

Bus 1 Bus 2 Bus 1 Bus 2powerpower

Figure 3 Two-area power system with series FACTS device Figure 4 Two-area power system with shunt FACTS device

receiving endSending end

receiving endSending end

The Static VAR Compensator (SVC) is one of the shunt connected FACTS devices, which is based on power electronics.

It helps in : 1.voltage regulation, 2.reactive power control and improving the transient stability of the system.

The voltage regulation by SVC is done, by controlling the amount of reactive power injected into or absorbed from the power system.

STATIC VAR COMPENSATOR (SVC)

Figure 5 SVC structure

when the system voltage is low the SVC generates reactive power (capacitive mode).

when the system voltage is high the SVC absorbs reactive power (inductive mode).

Vinput vsystem

Vinput ystem

STATIC VAR COMPENSATOR (SVC) MODE

Leading current

Lagging current

Figure 6 Capacitive Mode of SVC

Figure 7 Inductive Mode of SVC

There are two basic types of SVCs, each having a different combination of the components

1.SVC of the TCR-FC type

As its name indicates, the SVC of the TCR-FC type consists of a TCR, which absorbs reactive power from the ac power system to which the SVC is connected, and several FCs, which supply reactive power to the system connected to the SVC. Figure 8 diagram of an SVC of the TCR-FC type

TYPES OF SVC

2.SVC of the TCR-TSC type

As its name indicates, the SVC of the TCR-TSC type consists of a TCR, which absorbs reactive power from the ac power system connected to the SVC, and several TSCs, which supply reactive power to the ac power system connected to the SVC.

TYPES OF SVC

Figure 9 diagram of an SVC of the TCR-TSC type

MODELS OF SVC

PHASOR MODEL DETAILED MODEL

MODELS OF SVC

It is more simple and simplified to described the SVC principle operation

It is use with phasor simulation of powergui

It is use for studying dynamic performance and transient stability of power system

Requires simulation times of 30–40 seconds or more

It is not simple like phasor model

It is use with discrete simulation of powergui

Typical applications include optimizing of the control system, impact of harmonics, transients and stresses on power components during faults.

Smaller time range (a few seconds)

CONTROL SYSTEM OF SVC The control system of SVC is shown in

Figure 10. It consists of a measurement system, voltage regulator and synchronizing system.

The measurement system measures the positive-sequence voltage to be controlled. A measurement system based on Fourier transformation is used.

A voltage regulator that uses the voltage error i.e the difference between the measured voltage Vm and the reference voltage Vref is used to determine the SVC susceptance B, which is needed to keep the system voltage constant.

The TSCs (and eventually TSRs) which are to be switched in and out, are determined by a distribution unit that computes the firing angle α of TCRs.

A synchronizing system consists of a phase-locked loop (PLL) and a pulse generator, sends appropriate pulses to the thyristors

Figure 10 Control System of SVC

Magnitude

Controller

Filters

𝑉 𝑖

Q

𝐼

𝑉 𝑟𝑒𝑓

+ -

α𝐵𝑒 (𝛼 )

𝑉

𝛼 :1

TRANSIENT STABILITY MODEL OF SVC

Figure 11 Transient stability model of SVC

The SVC model for transient stability can be obtained by assuming balanced, fundamental frequency operation with sinusoidal voltages . It can be represented by the following set of equations:

=

0 =

Most of the variables used in the above two equation are clearly defined on Figure 11

The control system variables and equations are represented by xc and fc(Xc,α,V,Vref),respectively.

These equations are used to represent limits not only on the firing angle, but also on the current I, the control voltage V and the capacitor voltage Vi, as well as control variables other types of controllers such as a reactive power Q control scheme .

It is integrated with MATLAB, enabling you to incorporate MATLAB algorithms into models and export simulation results to MATLAB for further analysis.

Simulink provides a graphical editor, customizable block libraries, and solvers for modeling and simulating dynamic systems

In this study used MATLAB 2014b

SIMULINK AND MATLAB SOFTWARE

SIMULATION TEST SYSTEM

The comparison between PSS and SVC was conducted in a multi-machine system, as shown in figure 12. This system consists of 4 machines and 6 buses.

The system was originally available in Matlab with two machines and three buses, but in order to consider more cases in this work, the number of machines and buses were increased.

The disturbance applied is three phase fault to ground near a generator 1 on bus 1 at t= 5s

SVC is used as a controller is phaser type, connected to B1 and taking those cases:

Figure 12 4 machine 6 bus test system modeled in Simulink/MATLAB

SIMULATION AND RESULTS

Case 1:

Comparison between using only PSS and PSS with SVC at maximum critical clearing time

When comparing between using only PSS and PSS with SVC for a critical clearing time (tc =148 ms),

the results show that the system loses stability when utilizing PSS alone, while it remains stable using both SVC and PSS.

Fig. 13-16 show the rotor angle difference of G1 of the test system, rotor angle difference of G3, the terminal voltage on B1 and transmission line active power of G1


0 1 2 3 4 5 6 7 8 9 10

0

50

100

150

200

250

300

Time (s)R

otor

Ang

le o

f G1

(deg

ree)

PSS

PSS + SVC

Figure 13 Rotor angle difference of G1 to G2

This Figure show the Rotor angle difference between generator 1 and generator 2

At tc = 148 ms With only PSS the system lost stability but with SVC stay in stability


0 1 2 3 4 5 6 7 8 9 10

-50

0

50

100

150

200

250

Time (s)

Rot

or A

ngle

of G

2 (d

egre

e)

PSS

PSS + SVC This Figure show the Rotor angle difference between generator 3 and generator 4


At tc = 148 msWith only PSS the system lost stability but with SVC stay in stability


0 2 4 6 8 10 12 14 16 18 20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

Time (s)

Term

inal

Vol

tage

on

B1

(p.u

)

PSS

PSS + SVC

Figure 15 Terminal Voltage on B1

This Figure show the Terminal Voltage of Generator 1 on B1



0 2 4 6 8 10 12 14 16 18 20

-1500

-1000

-500

0

500

1000

1500

2000

Time (s)Ac

tive

Powe

r of G

1 (M

W)

PSS

PSS + SVC

This Figure show the Transmission line power of generator 1

Figure 16 Transmission Line Active Power of G1



Using PSS solely and PSS with SVC (to enhance transient stability and dampen the oscillation), the system remained stable ,at clearing time(tc = 147 ms).

Table 1 lists the performance comparison between using (PSS) and (PSS with SVC). Furthermore, Fig. 17 and 18 shows the rotor angle difference of G1 and rotor angle difference of G3; SVC settled faster with settling time is (11s and 10.3s) than with only PSS (13s and 12.3s), and the peak amplitude of both rotor angle with SVC reduced with value is 118 and 93 degrees, respectively. With only PSS, the corresponding values are 130 and 128 degrees. Fig. 19 and 20 show that the terminal voltage on B1 and B6 with SVC oscillated less and stabilized with peak amplitudes of 1.115 p.u and 1.18 p.u, and settling times of 10s and 10s, compared to only PSS with peak amplitudes of 1.275 p.u and 1.25 p.u and settling times of 12s and 12s. Fig. 21 and 22 show the transmission line active power values of G1 and G3; it can be seen that the line with SVC has less oscillation and greater stabilization that that with only PSS.

Case 2: Comparison between using only PSS and PSS with SVC at clearing time = 147 ms


0 2 4 6 8 10 12 14 16 18 20

-40

-20

0

20

40

60

80

100

120

140

Time (s)

Roto

r Ang

le o

f G1

(deg

ree)

PSS

PSS + SVC



At tc = 147 msThe rotor angle is stabilized quickly with PSS and SVC


0 2 4 6 8 10 12 14 16 18 20

-40

-20

0

20

40

60

80

100

120

140

Time (s)

Roto

r Ang

le o

f G3

(deg

ree)

PSS

PSS + SVC





0 2 4 6 8 10 12 14 16 18 20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Time (s)

Term

inal

Vol

tage

on

B1

(p.u

)

PSS

PSS + SVC


This Figure show the Terminal Voltage 0f Generator 1 on B1



0 2 4 6 8 10 12 14 16 18 20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Time (s)

Term

inal

Vol

tage

on

B6

(p.u

)

PSS

PSS + SVC





0 2 4 6 8 10 12 14 16 18 20

0

200

400

600

800

1000

1200

1400

1600

1800

Time (s)

Act

ive

Pow

er o

f G1

(MW

)

PSS

PSS + SVC


This Figure show the Transmission Line Active Power of Generator 1

At tc = 147 msThe Active power is stabilized quickly with PSS and SVC


0 2 4 6 8 10 12 14 16 18 20

0

200

400

600

800

1000

1200

1400

Time (s)Ac

tive

Powe

r G3

(deg

ree)

PSS

PSS + SVC



At tc = 147 msThe Active power is stabilized quickly with PSS and SVC

Parameters

Rotor angle of G1

Rotor angle of G3

Terminal Voltage on Bus 1


Active power of G1

Active power of G3

Pea (deg.)

Ts(s)

Peak(deg.)

Ts(s)

Peak(p.u.)

Ts(s)

Peak(p.u.)

Ts(s)

Peak(MW)

Ts(s)

Peak (MW

Ts(s)

PSS 130 13 128 12.3 1.275 12 1.25 12 1470 12 1470 12

PSS + SVC 118 11 93 10.3 1.15 10 1.18 10 1700 10 1350 10

Table 1Comparison between PSS and PSS with SVC


SIMULATION AND RESULTSCase 3: Comparison between using only PSS and PSS with SVC at clearing time = 147 ms In this case the comparison between using PSS alone and two SVC with PSS in two

different locations was made. The first SVC was connected to the system in a location the same as the previous one, and the second was connected near G3 with bus 6.

The results show that using two SVCs is better than using only one; Table 2 lists comparison data between PSS and two SVC. Additionally, Fig. 23 and 24 show that rotor angle difference of G1 and rotor angle difference of G3 with SVC settled faster with settling time is (10s and 10s) than with only PSS (13s and 12.3s), and the peak amplitude of both rotor angle with SVC reduced with values of 115 and 85 degrees. With only PSS the settling time is 13 and 12.3s and the peak amplitude is 130 and 128 degrees. Fig. 25 and 26 show that the terminal voltage on B1and terminal voltage on B6 with SVC oscillates less and stabilizes with peak amplitude (1.175p.u and 1.16p.u) and settling time (10s and 9s) compared to only PSS, where the peak amplitude is (1.275p.u and 1.25p.u) and settling time (12s and 12s). Fig. 27 and 28 show the transmission line active power of G1 and line power of G3 with SVC oscillating less and stabilizing better than with only PSS


0 2 4 6 8 10 12 14 16 18 20

-40

-20

0

20

40

60

80

100

120

140

Time (s)Ro

tor A

ngle

of G

1 (d

egre

e)

PSS

PSS + 2 SVC



At tc = 147 msThe rotor angle is stabilized quickly with PSS and 2 SVC


0 2 4 6 8 10 12 14 16 18 20

-40

-20

0

20

40

60

80

100

120

140

Time (s)

Roto

r Ang

le o

f G3

(deg

ree)

PSS

PSS + 2 SVC





0 2 4 6 8 10 12 14 16 18 20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Time (s)

Term

inal

Vol

tage

on

B1 (p

.u)

PSS

PSS + 2 SVC





0 2 4 6 8 10 12 14 16 18 20

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Time (s)Te

rmin

al V

olta

ge o

n B

6

PSS

PSS + 2 SVC





0 2 4 6 8 10 12 14 16 18 20

0

500

1000

1500

2000

2500

Time (s)Ac

tive

Powe

r of G

1 (M

W)

PSS

PSS + 2 SVC



At tc = 147 msThe Active power is stabilized quickly with PSS and 2 SVC


0 2 4 6 8 10 12 14 16 18 20

0

200

400

600

800

1000

1200

1400

Time (s)

Activ

e Po

wer o

f G3

(MW

)

PSS

PSS + 2 SVC



At tc = 147 msThe Active power is stabilized quickly with PSS and 2 SVC

Table 1Comparison between PSS and PSS with SVC


parameters Rotor angle of G1

Rotor angle of G3



Active power of G1

Active power of G3

Pea (deg.)

Ts(s)

Peak(deg.)

Ts(s)

Peak(p.u.)

Ts(s)

Peak(p.u.)

Ts(s)

Peak(MW)

Ts(s)

Peak (MW

Ts(s)

PSS 130 13 128 12.3 1.275 12 1.25 12 1470 12 1470 12

PSS + 2SVC 115 10 85 10 1.175 10 1.16 9 2000 8.5 1300 10

CONCLUSION

This study discussed and investigated the transient stability enhancement by using a power system stabilizer PSS and static Var compensator SVC. The work shows a comparison between applied power system stabilizer PSS independently and combined with Static Var compensator SVC. The comparison examined test system, multi-machine consists of 4 machine 6 buses of MATLAB Simulink for studying, when occurred the three phases to ground fault on generator 1 and taking three cases ,first with at the critical clearing time the system lost the synchronism with only PSS and its remain synchronism with connected SVC with system as a controller. A second case at clearing time 147 ms the system in stable with both only PSS and PSS with SVC but the result is more better with used SVC for damping oscillation and final case is used two SVC and comparison with previous case the results shows better for improved transient stability and damping oscillation of several parameters such as Rotor angle and terminal voltage and transmission lines active power.

APPENDIX

The transmission System nominal voltage is 500 KV Rotor type (silent pole) Power rating of SVC = 200 MVAR

The generator parameters in per unit on the rated MVA and kV base are:

Xd = 1.305 X’d = 0.296 X”d = 0.252 Xq = 0.474 X”q = 0.243

Xl = 0.18 T’d = 1.01 T”d = 0.053 T”q = 0.1 H = 3.7

the parameters of the lines in per unit :

Resistance per unit length (Ohms/km) Inductance per unit length (H/km) Capacitance per unit length (F/km)

0.01755 0.8737e-3 13.33e-9

Distance of transmission lines :

M1 & M2 M3 & M4 M1 & M3 M2 & M4

700 km 700 km 400 km 400 km

Bus 2 Bus 3 Bus 4 Bus 5 Bus 6

PL = 100 MW PL = 4900 MW PL = 100 MW PL = 100 MW PL = 4900 MW

The loads on system for cases (Resistive Load) :

APPENDIX

REFFERENCES [1] G. Hingorani and L. Gyugyi, “Understanding FACTS, Concepts, and Technology of Flexible AC Transmission Systems”, Piscataway, NJ: IEEE Press, 2000. [2] A. A Edris, R Aapa, M H Baker, L Bohman, K Clark, “Proposed terms and definitions for flexible ac transmission system (FACTS)”, IEEE Trans. on Power Delivery, Vol. 12, No. 4, 1997, pp. 1848-1853.[3] P. Kundur, Power System Stability and Control, New York: McGraw Hill, 1994.[4] Dash. P. K, Selta Morris and Mishra. S, “Design of a nonlinear Variable Controller for FACTS Devices”, IEEE Transactions on Control System Technology, Vol. 12. No. 3, May 2004. [5] Patel, H. D,Majmudar, C,―Fuzzy logic application to single machine power system stabilizer,‖ Power Nirma University International Conference on Engineering, IEEE, Vol. 2, pp. 669- 674, Dec 2011.[6] M. A. Abido, “ Analysis and assessment of STATCOM based damping stabilizers for Power system stability enhancement” Electric Power System Research,73, 177- 185,2005[7] Mohan Mathur, Rajiv K. Varma , ―Thyristor-Based Facts Controllers for Electrical Transmission Systems, John Wiley &Sons, Inc. Publication, 2002, pp 93-138. [8] B T Ooi, M Kazerrani, R Marcean, Z Wolanski, F D Galiana, D. Megillis, G. Joos, “Mid point sitting of FACTS devices in transmission lines”, IEEE Tran. On Power Delivery, Vol. 1 No. 4, 1997, pp. 1717-1722. [9] S. M. Barakati, S. Khanmohamadi, S. H. Hosseini, “Improving the Power Stability using Fuzzy Logic Controlled Static Var Compensator”, The 4th Iranian Conference on Electrical Engineering, ICEE-97, 1996. [10] Mitsubishi Electric. (2010). Power system stabilizer PSS[11] Samuelsson, O. (1997). Power system damping-structural aspects of controlling active power. Lund University. [12] Liu, F. , Yokoyama, R. , Zhou, Y. , & Wu, M. Study on Oscillation Damping Effects of Power System Stabilizer with Eigenvalue Analysis Method for the Stability of Power Systems. [13] E. Z. Zhou, ―Application of Static Var Compensators to Increase Power System Damping, IEEE Transactions on Power Systems, Vol. 8, NO. 2, 1993. [14] M. H. Hague, ―Improvement of first stability limit by utilizing full benefit of shunt FACTS devices, IEEE Transactions On Power Systems, vol. 19, no. 4, pp. 1894 – 1902, 2004.[15] Arunkumar, Priya G, ―Power System Stability Enhancement using FACTS Controllers,‖ IEEE, 2012. [16] Claudio A. canizares, ―Power Flow and Transient Stability Models of FACTS Controllers for Voltage and angle Stability Studies, IEEE PES, 2000.

Thanks for your

attention

17th International Conference on Electrical, Electronics and Systems Engineering ICEESE 2015 December 21 – 22, 2015 Istanbul, Turkey.

Documents

power system stability

stability of power system

power transmission system

interconnected power

power system variations

electric power system

system motion

unstable system