* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Power Oscillations – Definition (1)
Portable appliance testing wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Stray voltage wikipedia , lookup
Buck converter wikipedia , lookup
Power factor wikipedia , lookup
Wireless power transfer wikipedia , lookup
Immunity-aware programming wikipedia , lookup
Electrical substation wikipedia , lookup
Utility frequency wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Power over Ethernet wikipedia , lookup
Audio power wikipedia , lookup
Control system wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Power electronics wikipedia , lookup
Electric power system wikipedia , lookup
History of electric power transmission wikipedia , lookup
Electrification wikipedia , lookup
Distribution management system wikipedia , lookup
Mains electricity wikipedia , lookup
Three-phase electric power wikipedia , lookup
New Setting Free Algorithm for Out of Step Tripping 4 3 2 1 0 -1 -2 -3 Sept. 2009 MOSCOW -4 H Kang – ART Areva T&D B Cvorovic, P Horton- SAS Areva T&D 1 1 Introduction Recoverable and non-recoverable power oscillations 2 2 Power Oscillations - Causes What causes power oscillations? Imbalance in generation and load Faults (internal and external) Load/Line switching 3 3 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: 4 Stable swings or Recoverable swings 4 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 Electrical . center Vs Vr Zs Zr OST condition : I=(Vs -Vr )/ ZT =(Vs -(-Vr ))/ZT ~2 Vn /ZT ZT = Zs +Zline +Zr 6 6 Power Oscillations – Definition (4) Elliptic shape: recoverable swing Circle: OST condition 7 7 Power Oscillations – Definition (5) Recoverable Non-Recoverable 8 8 Traditional Out of Step Detection Methods 9 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. +jX Z6 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 Z5 Predictive Out of step trip ZL Recoverable swing Out of step trip R6' R5 R5' R6 R Disadvantages Difficulties to set blinders due to heavy loading Setting dependant on system topology, thus settings may be inaccurate Z5' Z6' Comprehensive system study required – increases engineering time the Prone to unstable operation in series compensated during MOV operation 10 lines 10 New Algorithm New algorithm provides: Setting free OST detection CB tripping at a favourable angle 11 11 New Algorithm - Principle Setting Free OST Detection Principle 12 12 Setting Free OST Detection – Principle (1) OST detection principle: Recoverable swings: Non- recoverable swings: jX ∆R changes polarity when ∆I changes polarity ∆R doesn’t change polarity when ∆I changes polarity ∆I=IN+1-IN ∆R=RN+1-RN I=positive sequence current R=positive sequence resistance RECOVERABLE SWING : Point when both, ∆I and ∆R change polarity R NON RECOVERABLE SWING : Point when ∆I changes polarity and ∆R polarity remains unchanged 13 13 Setting Free OST Detection – Principle (2) Recoverable Swings Pole Slips Delta I and Delta R change polarity around same time Recoverable Swing 14 When Delta I changes polarity , Delta R does not Pole Slip 14 Tripping Angle Control Circuit breaker tripping angle control 15 15 Tripping Angle Control Current locus during oscillation is a circle 0 Vs Vr 90 90 270 180 (minimum Z) 180 90 270 Electrical Centre locus Vr locus 180 270 Current Locus (I) X Drawing taken from Westinghouse book 16 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 90 180 0 Imax I240 240 270 17 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 18 Supporting Elements(1) Power Swing Detection and Blocking 19 19 Supporting Elements(2) 20 20 Supporting Elements(3) 21 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 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 23 Test Results (3) 3 2 1 Swing /Pole Slip I 0 1 254 507 760 1013 1266 1519 1772 2025 2278 2531 2784 3037 3290 3543 3796 OST -1 -2 -3 24 24 Test Results (4) 25 25 Test Results (2) 26 26 Conclusions 27 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 28 Thank You Questions? 29 29