1. 11 New Setting Free Algorithm for Out of Step Tripping Sept. 2009 MOSCOW H Kang – ART Areva T&D B Cvorovic, P Horton- SAS Areva T&D

2. 22 Introduction Recoverable and non-recoverable power oscillations

3. 33 Power Oscillations - Causes  What causes power oscillations?  Imbalance in generation and load  Faults (internal and external)  Load/Line switching

4. 44 Power Oscillations – Definition (1)  Nature and definition of power oscillations  Power oscillation that leads to system split is called: Out of step condition or pole slip or non-recoverable swing  Power oscillation that will not cause system split are called: Stable swings or Recoverable swings

5. 55 Power angle curve  Fast fault clearance increases power transfer Po and system stability by reducing Area 1 Curve 1 – Pre-fault transmitted power Po (via parallel lines) Curve 2 - Transmitted power reduced during ph-ph-N fault Curve 3 - New power curve upon opening parallel line  If Area 2>Area 1 – recoverable swings  If Area 2<Area 1 – OST condition P=(3VsVr/X)sinθ

6. 66 Power Oscillations – Definition (3)  Out of step condition  Occurs when two internal voltages of equivalent sources are in opposite direction  At that point the phase (swing) current is maximum  The position of the electrical centre will depend on Zs/Zr ratio  Recoverable swings  Two voltages typically oscillate between up to 120deg Vr Vs ZsZr OST condition: I=(Vs-Vr)/ZT=(Vs-(-Vr))/ZT~2Vn/ZT =Zs+Zline+Zr Electrical. center

7. 77  Elliptic shape: recoverable swing  Circle: OST condition Power Oscillations – Definition (4)

8. 88 Power Oscillations – Definition (5) Recoverable Non-Recoverable

9. 99 Traditional Out of Step Detection Methods

10. 10  Conventional methods:  Conventional methods use blinders to determine speed of impedance crossing the ∆R region (R6-R5). They may predict or detect OST condition.  If polarity of ‘R’ has changed on exiting Z5, it is Out of Step condition (already happened)  If positive sequence impedance crosses ∆Z region faster than ‘delta T’ set time the predictive OST is declared  Disadvantages  Difficulties to set blinders due to heavy loading  Setting dependant on system topology, thus settings may be inaccurate  Comprehensive system study required – increases the engineering time  Prone to unstable operation in series compensated lines during MOV operation Disadvantages

11. 11  New algorithm provides:  Setting free OST detection  CB tripping at a favourable angle New Algorithm

12. 12 New Algorithm - Principle Setting Free OST Detection Principle

13. 13 Setting Free OST Detection – Principle (1)  OST detection principle:  Recoverable swings: ∆R changes polarity when ∆I changes polarity  Non- recoverable swings: ∆R doesn’t change polarity when ∆I changes polarity

14. 14 Recoverable Swings Delta I and Delta R change polarity around same time Pole Slips When Delta I changes polarity, Delta R does not Recoverable SwingPole Slip Setting Free OST Detection – Principle (2)

15. 15 Tripping Angle Control Circuit breaker tripping angle control

16. 16 Tripping Angle Control VsVr Current Locus (I) 90 ° 180 ° (minimum Z) Vr locus Electrical Centre locus 0 ° 180 ° 90 ° 180 ° 90 ° X 270 ° ° °  Current locus during oscillation is a circle  Drawing taken from Westinghouse book

17. 17 Tripping Angle Control (1) Current during oscillation can be defined as: I swing=I MAX sin (θ/2) where θ is the angle between internal voltages of sources

18. 18 Tripping Angle Control (2) I trip=I MAX sin (240/2)=0.866 I MAX  Maximum phase (swing) current is recorded at the point when ∆I changes polarity (that point corresponds to minimum impedance)  Favourable (safe) split angle entered, for example 240 degrees  Tripping command is issued when phase current drops to:

19. 19 Supporting Elements(1) Power Swing Detection and Blocking

20. 20 Supporting Elements(2)

21. 21 Supporting Elements(3)

22. 22 Proof of Concept  Pole slip COMTRADES captured by the relays for various system tests were used to prove that the basic principle was sound  Modifications were made to the original principle to make it more robust.  Logic implemented to account for difference between the frequency of I and V during swings  Logic to make the algorithms immune to system disturbances and faults

23. 23 Test Results (1)  Numerous cases from different systems were applied  Algorithm remains stable during power system faults or recoverable swings  Both, balanced and open pole oscillation tested  No mal-operation recorded during evolving faults, sudden change of power flow, cross country faults and frequency variations  Angle set tripping compared with actual angle across the breaker proved to be accurate

24. 24 Test Results (3)

25. 25 Test Results (4)

26. 26 Test Results (2)

27. 27 Conclusions

28. 28  Setting free  All conventional methods require system studies and comprehensive settings  No blinders, no starters, thus no constraints on operating characteristics versus loading  Immune to topology changes  Security – Provides control over the angle at which the system is to be split.  Minimises chances of breaker opening at voltage maximum Advantages

29. 29 Thank You Questions?