3-phase Short Circuit Impact in Various Length of Power Line on

Transient Stability of Synchronous Generator BORIS CINTULA, ŽANETA ELESCHOVÁ, ANTON BELÁŇ

Institute of Power and Applied Electrical Engineering Faculty of Electrical Engineering and Information Technology

Slovak University of Technology in Bratislava Ilkovičova 3, 812 19 Bratislava

SLOVAKIA boris.cintula@gmail.com, http://www.fei.stuba.sk/

Abstract: - This paper presents the short circuit impact in various length of power line on the transient stability of synchronous generator. By the means of dynamic simulations are compared the same events on two power lines, the difference is at the fault distance on assessed power lines considering the generator. In the first part are compared the short circuit impacts and its tripping in fast zone of distance protection and in the second part is compared the short circuit tripping by protection failure at the end of assessed power line. All simulations are mutually compared in terms of the significance of their impact on transient stability of generator.

Key-Words: - Synchronous Generator, Transient Stability, 3-phase Fault, Fault Length, Power Line, Swinging, Relay Time Settings

1 Introduction During the power system operation occur a lot of fast changes and faults, which can cause a disproportion between production and consumption of electricity what also means significant changes of rotor angles [1]. The most common faults in the power system are statistically short circuits [2]. In terms of stability it is important how the power system responds to such disturbances, e.g. short circuit and power line tripping. “When such a fault

occurs, large currents and torques are produced

and often action must be taken quickly if system

stability is to be maintained.” [3] “Although many different forms of power system

stability have emerged and become problematic in

recent years, transient stability still remains a basic

and important consideration in power system design

and operation.“ [4]

2 Dynamic Simulations Dynamic simulations of 3-phase short circuit in various length of power line on the transient stability of synchronous generator are realised in according to simplified model of power system (Fig.1), where two basic states are assessed, i.e. short circuit tripping in fast zone (1st tripping zone) and short circuit tripping by distance protection failure at the end of assessed power line (V1, V3). The main difference between the short circuit on the power lines V1 and V3 is at a distance of a short

circuit on the power line considering the generator G1. For all simulations is considered protecting by distance protections, where the tripping characteristic time settings is defined for each zone as follows: 1st zone (100ms); 2nd zone (600ms); 3rd zone (V1=1,3s; V3=1,1s); 4th zone (V1=3,1s; V1=4,1s).

Fig.1 Model of Power System for 3-phase Short Circuit Impact Assessment on Transient Stability of Synchronous Generator (G-Synchronous Generators; G1-Assessed Generator; TR-Generator Transformers; QM1-QM8-Circuit Breakers; line-Power Lines; V1-V4-Assessed Power Lines) Dynamic simulations are realised for the following operational parameters of generator G1: SN=259MVA, UN=15,75kV, PG=235MW, QG=-1,55MVAr (underexcited state).

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3 Fault Tripping in Fast Zone (1st

Tripping Zone) of Distance Protection Dynamic simulations of fault tripping in fast zone of distance protection were realised for the short circuit on the power line in every 10% of power line length, where the simulation aim was to find a length when the generator swinging is the most significant. The tripping characteristic of fast zone of distance protection is shown in Fig.2.

Fig.2 Distance Protection Time Settings of 1st Tripping Zone on Power Lines V1 and V3 3.1 Fault Tripping on Power Line V1 Generator behaviour after the short circuit on power line V1 in length 10% and 50% and its consequent tripping is shown in Fig.3 and Fig.4, where the generator swinging is significant in both cases, but the short circuit in 10% of power line length has higher impact on transient stability. That is caused by the short circuit tripping at the end of the power line in time of 2nd tripping zone of protection, what is related with distance protection time setting (Fig.2).

Fig.3 Behaviour of the Synchronous Generator after the 3-phase Fault in 10% of Length of Power Line V1 by the 1st Zone Tripping (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

Fig.4 Behaviour of the Synchronous Generator after the 3-phase Fault in 50% of Length of Power Line V1 by the 1st Zone Tripping (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

Fig.5 Characteristic of Amplitude (sum [positive, negative]) of Generator Swinging amplitude from Length of Fault on Power Line V1

Fig.6 Characteristic of Amplitude (sum [positive, negative]) of Generator Swinging amplitude from Length of Fault on Power Line V1 by the 1st Zone Tripping on Both Sides of Power Line 3.2 Fault Tripping on Power Line V3 For assessment of short circuit impact on power line V3 tripped in fast zone are shown only two simulations, i.e. short circuit in 30% (Fig.7) and 90% (Fig.8) of length. Higher impact on generator swinging has short circuit in 90% of length, what is caused by its tripping in longer time (2nd zone of protection at the beginning of power line), when the generator contribution is higher into the short circuit.

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Fig.7 Behaviour of the Synchronous Generator after the 3-phase Fault in 30% of Length of Power Line V3 by the 1st Zone Tripping (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

Fig.8 Behaviour of the Synchronous Generator after the 3-phase Fault in 90% of Length of Power Line V3 by the 1st Zone Tripping (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

Fig.9 Characteristic of Amplitude (sum [positive, negative]) of Generator Swinging amplitude from Length of Fault on Power Line V3

Fig.10 Characteristic of Amplitude (sum [positive, negative]) of Generator Swinging amplitude from Length of Fault on Power Line V3 by the 1st Zone Tripping on Both Sides of Power Line

By the means of comparing of generator swinging after the short circuit tripping in the 1st zone protection in every 10% of power line length, it is possible to state that in case of power line V1 the generator swinging is smaller than in case of power line V3. This is caused due to closer distance of the power line V1 against the V3 in the same length of short circuit. In case of short circuit in 10% and 90% of power line length and its tripping in 2nd zone protection has an additional parameter impact on the size of swinging - topology of power system.

4 Fault Tripping by Distance

Protection Failure at the End of

Assessed Power Line (V1, V3) Dynamic simulations of fault tripping by the distance protection failure at the end of the power line V1 and V3 were realised for the short circuit on the power line in every 10% of power line length, where the simulation aim was to find a length when the generator swinging is the most significant. 4.1 Fault Tripping on Power Line V1 by

Distance Protection Failure at the End of

Power Line In Fig.11 and Fig.12 is shown the generator behaviour after the short circuit tripping on power line V1 and after distance protection failure at the end of the line in length 70% and 90%. Generator swinging is after these events in comparing with previous states (1st tripping zone) considerably higher, what is caused due to longer tripping times (Fig.13). By the means of mutual comparing of states by protection failure can be stated the generator swinging is higher by the short circuit in 90% of the power line length, when the generator contribution is higher into the short circuit because of tripping in 2nd zone at the beginning of this power line, i.e. in a longer time (Fig.13).

Fig.11 Behaviour of the Synchronous Generator after the 3-phase Fault in 70% of Length of Power Line V1 by the Failure of Distance Relay 2 (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

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Fig.12 Behaviour of the Synchronous Generator after the 3-phase Fault in 90% of Length of Power Line V1 by the Failure of Distance Relay 2 (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

Fig.13 Distance Protection Time Settings on Power Lines V1 and V2 by the Failure of Distance Relay 2

Fig.14 Distance Protection Time Settings on Power Lines V3 and V4 by the Failure of Distance Relay 2

Fig.15 Characteristic of Amplitude (sum [positive, negative]) of Generator Swinging amplitude from Length of Fault on Power Line V1 by the Failure of Distance Relay 2

4.2 Fault Tripping on Power Line V3 by

Distance Protection Failure at the End of

Power Line

Fig.16 Behaviour of the Synchronous Generator after the 3-phase Fault in 10% of Length of Power Line V3 by the Failure of Distance Relay 2 (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

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In case of simulation of a short circuit tripping on power line V3 by the protection failure at the end of power line are compared two most significant impacts on generator swinging, i.e. short circuit in 10% and 90% of length. Higher impact has a short circuit in 10% of length what is shown in Fig.16 and Fig.17. This is caused due to a longer tripping time. Short circuit in 10% of the length on the power line V3 is tripped in 1st zone protection and in 4th zone at the end of the line. Short circuit in of the length on the power line V3 is tripped 2nd zone protection and in 2nd zone at the end of the line. Tripping characteristic distance protection for this state is shown in Fig.14.

Fig.17 Behaviour of the Synchronous Generator after the 3-phase Fault in 90% of Length of Power Line V3 by the Failure of Distance Relay 2 (vt-voltage at the generator terminals; ang-rotor angle, efd-electromotive voltage; it-current; pg-active power; spd-frequency)

Fig.18 Characteristic of Amplitude (sum [positive, negative]) of Generator Swinging amplitude from Length of Fault on Power Line V3 by the Failure of Distance Relay 2

By the means of mutual comparing of generator swinging after the short circuit tripping on power line at the same distance by protection failure at the end of the power line can be stated that the generator swinging is smaller by the short circuit on the power line V3 than on the V1, what means electrically further short circuit, i.e. less impact on the transient stability of the synchronous generator G1.

6 Conclusion The above waveforms of dynamic simulations present only a graphic representation of generator

swinging, and therefore need to be supplemented with specific values of the operating generator parameters. These are in Table 1 and Table 2 for all simulations.

Table 1 Parameters Values for Simulation of Transient Stability of Synchronous Generator by the 1st Tripping Zone on Power Lines V1,V3 length

of

short

circuit

on

power

line

[pu]

power

line

voltage at

the

generator

terminals

[kV]

rotor angle [ °]

active

power

[MW]

frequency

[Hz]

min max min max

sum (positive, negative) amplitude

min max min max

0,1 V1 6,604 17,07 -47,8 17,29 65,075 23,63 369,6 49,49 50,37

V3 8,377 16,99 -49,7 11,09 60,801 13,59 368,8 49,52 50,39

0,2 V1 7,403 16,6 -17,4 13,71 31,131 52,85 367,3 49,75 50,31

V3 9,516 16,33 -14,6 8,679 23,2985 98,08 327,8 49,83 50,23

0,3 V1 8,064 16,56 -16,2 12,12 28,268 67,81 352 49,79 50,28

V3 10,33 16,19 -13,1 6,839 19,9391 116,2 313,1 49,86 50,2

0,4 V1 8,62 16,51 -15,3 10,85 26,123 79,91 340,1 49,81 50,26

V3 10,94 16,08 -11,9 5,524 17,4538 129,6 302,7 49,88 50,17

0,5 V1 9,089 16,46 -14,6 9,827 24,3872 90,02 330,9 49,82 50,24

V3 11,41 16 -11 4,545 15,5848 139,8 295,1 49,9 50,16

0,6 V1 9,491 16,4 -13,9 8,984 22,8938 98,55 323,6 49,84 50,23

V3 11,78 15,93 -10,4 3,795 14,1445 147,8 289,3 49,91 50,14

0,7 V1 9,836 16,34 -13,2 8,283 21,4925 105,8 317,6 49,85 50,22

V3 12,08 15,88 -9,81 3,214 13,0197 154,1 284,7 49,92 50,13

0,8 V1 10,13 16,29 -12,6 7,696 20,2564 112 312,5 49,86 50,21

V3 12,32 15,84 -9,37 2,758 12,1251 159,3 281 49,92 50,12

0,9 V1 7,473 17,4 -63,4 58,3 121,703 -190 562,1 48,88 50,73

V3 12,19 17 -33,5 11,01 44,499 107,8 331,9 49,67 50,25

Table 2 Parameters Values for Simulation of Transient Stability of Synchronous Generator by the Failure of Distance Relay 2 on Power Lines V1, V3 length

of

short

circuit

on

power

line

[pu]

power

line

voltage at

the

generator

terminals

[kV]

rotor angle [ °]

active

power

[MW]

frequency

[Hz]

min max min max

sum (positive, negative) amplitude

min max min max

0,1 V1 6,604 19 -108 26,01 134,205 33,89 361,3 49,49 50,35

V3 8,377 18,26 -98,3 11,09 109,381 72,18 357,8 49,52 50,28

0,2 V1 7,403 16,81 -62,4 13,2 75,561 52,85 365,2 49,52 50,31

V3 9,516 16,63 -52,3 7,095 59,3451 98,08 356,7 49,57 50,23

0,3 V1 8,064 16,73 -56,3 11,1 67,444 67,81 361,9 49,56 50,28

V3 10,33 16,57 -45,5 5,385 50,9254 116,2 346,3 49,63 50,2

0,4 V1 8,62 16,71 -53,3 9,81 63,0604 79,91 355,6 49,59 50,26

V3 10,94 16,44 -42 4,277 46,2372 129,6 336,3 49,67 50,17

0,5 V1 9,089 16,7 -51,7 8,88 60,5598 90,02 348,7 49,62 50,24

V3 11,41 16,59 -40,8 3,476 44,256 122,8 327,9 49,7 50,16

0,6 V1 9,491 16,69 -50,8 8,167 59,0067 98,55 342,2 49,65 50,23

V3 11,78 16,51 -39,6 2,877 42,4267 139,5 320,9 49,73 50,14

0,7 V1 9,836 16,68 -50,4 7,606 57,966 105,8 336,2 49,67 50,22

V3 12,08 16,43 -39 2,421 41,3814 153,5 315,1 49,76 50,13

0,8 V1 10,13 16,69 -52,9 7,154 60,074 112 330,7 49,68 50,21

V3 12,32 16,37 -38,9 2,073 40,9828 159,3 310,2 49,76 50,12

0,9 V1 7,911 17,34 -107 82,88 190,276 -149 509,4 48,81 50,58

V3 12,43 16,79 -64 21,06 85,092 126,1 384,8 49,62 50,2

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For the shown simulations and RMS values of monitored parameters it is possible to state the highest impact on generator swinging has the short circuit which occurs close to the generator. The size of generator swinging depends on the short circuit distance on power line and tripping time and therefore the protection time setting is very important indicator which can radically affect the transient stability of synchronous generator.

References:

[1] Cintula, B., Eleschová, Ž., Beláň, A., Liška, M., Transient Stability of Synchronous Generator for Selected Events, The 12

h WSEAS

International Conference on Electric Power

Systems, High Voltages, Electric Machines

(Power ´12), Prague, 2012, pp. 47-52, ISBN 978-1-61804-128-9.

[2] Reváková, D., Eleschová, Ž., Beláň, A., Prechodné javy v elektrizačných sústavách,

Bratislava, Vydavateľstvo STU, 2008, 180 s, ISBN 978-80-227-2868-3.

[3] Machowski, J., Bialek, J. W., Bumby, J. R., Power System Dynamics: Stability and Control,

Chippenham, Antony Rowe Ltd., 2008, 629 p, ISBN 978-80-227-2868-3.

[4] Grigsby, L. L., Power System Stability and

Control, New York, Taylor & Francis Group, 2007, 352 p, ISBN 978-0-8493-9291-7.

Acknowledgement These publications are the result of implementation of the project: “Increase of Power Safety of the Slovak Republic” (ITMS: 26220220077), supported by the Research & Development Operational Programme funded by the ERDF.

This work was done during implementation of the project Effective control of production and consumption of energy from renewable resources, ITMS code 26240220028, supported by the Research and Development Operational Program funded by the ERDF.

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