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New Setting Free Algorithm for Out of Step Tripping

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. Introduction. Recoverable and non-recoverable power oscillations. Power Oscillations - Causes. What causes power oscillations?

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New Setting Free Algorithm for Out of Step Tripping

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  1. 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. Introduction Recoverable and non-recoverable power oscillations

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

  4. 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. Electrical . center Vs Vr Zs Zr OST condition : I =( Vs - Vr )/ ZT =( Vs - ( - Vr ))/ ZT ~ 2 Vn / ZT ZT = Zs + Zline + Zr 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

  6. Power Oscillations – Definition (4) • Elliptic shape: recoverable swing • Circle: OST condition

  7. Power Oscillations – Definition (5) Recoverable Non-Recoverable

  8. Traditional Out of Step Detection Methods

  9. Disadvantages • 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

  10. New Algorithm • New algorithm provides: • Setting free OST detection • CB tripping at a favourable angle

  11. New Algorithm - Principle Setting Free OST Detection Principle

  12. 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

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

  14. Tripping Angle Control Circuit breaker tripping angle control

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

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

  17. Tripping Angle Control (2) • 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: I trip=IMAX sin (240/2)=0.866 IMAX

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

  19. Supporting Elements(2)

  20. Supporting Elements(3)

  21. 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

  22. 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

  23. Test Results (3)

  24. Test Results (4)

  25. Test Results (2)

  26. Conclusions

  27. Advantages • 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

  28. Thank You Questions?

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