1 Applica>on of a Protec>on Scheme to Mi>gate the Impact of Load Rejec>on in a 500 kV Transmission System Waruna Chandrasena and David Jacobson System Planning Department Manitoba Hydro IEEE 2011 Electrical Power and Energy Conference
2 Introduc>on • 500 kV Transmission system – 535 km long – 50% series compensa>on – 1800 MW transfer from Dorsey to Forbes IEEE 2011 Electrical Power and Energy Conference
3 Temporary Overvoltages (TOV) • 500 kV breaker opera>on • TOV due to line capacitance (about 650 Mvar) • Designed for 600 kV con>nuous opera>on IEEE 2011 Electrical Power and Energy Conference
4 Temporary Overvoltages (TOV) • 230 kV breaker opera>on • TOV due to line capacitance (650 Mvar) and ter>ary capacitors (220 Mvar) • Possible ferroresonance condi>ons • Stresses dielectric and thermal withstand capability of equipment IEEE 2011 Electrical Power and Energy Conference
5 Protec>on Scheme at Dorsey • Low side load rejec>on (LSLR) Protec>on • Trigger event: 230 kV trip coil energiza>on • Opens 500 kV and 46 kV breakers at Dorsey • Transfer trips breakers at Forbes IEEE 2011 Electrical Power and Energy Conference
6 Riel Sec>onaliza>on Project • Riel Sta>on • About 50 km from Dorsey; 485 km to Forbes • 720 MVA autotransformer • 220 Mvar shunt capacitors and 225 Mvar shunt reactor IEEE 2011 Electrical Power and Energy Conference
7 Temporary Overvoltages (TOV) Exis>ng system or Riel out-­‐of-­‐service Dorsey out-­‐of-­‐service IEEE 2011 Electrical Power and Energy Conference
8 Temporary Overvoltages (TOV) Riel 230 kV side open 1. Riel 230 kV side open 2. Dorsey 230 kV side opens IEEE 2011 Electrical Power and Energy Conference
9 A Protec>on Scheme at Riel? • Energy dissipa>on in arresters • 436 kV arresters have 6 MJ energy discharge capability • Time to dissipate 6 MJ Sta>on Before Riel Aaer Riel Dorsey 340 ms 75 ms Riel -­‐ 100 ms • An overvoltage relay typically takes about 100 ms to detect IEEE 2011 Electrical Power and Energy Conference
10 LSLR Protec>on Scheme at Riel • Period – 3 ferroresonance • Transfer tripping required (for stuck breaker condi>ons) IEEE 2011 Electrical Power and Energy Conference
11 LSLR Protec>on Scheme at Riel • 230 kV side open at Riel • Block 500 kV breaker opera>on if line 603 is in service • Use current measurement on line 603 as a status indicator • Open 46 kV breakers IEEE 2011 Electrical Power and Energy Conference
12 LSLR Protec>on Scheme at Riel • 230 kV side open at Riel • Block 500 kV breaker opera>on if line 603 is in service • Use 200 A threshold • De-­‐block if line 603 current is less than 200 A IEEE 2011 Electrical Power and Energy Conference
13 Simula>on Model • PSCAD Control Sequence IEEE 2011 Electrical Power and Energy Conference
14 LSLR Protec>on Scheme at Riel • Simula>on Results – LSLR at Dorsey – Precondi>on: Riel 230 kV and 46 kV breakers open – Time to dissipate 6 MJ in arresters Shunt Reactor Shunt Capacitor Minimum >me (s) Maximum >me (s) 1 Riel 220 0.78 1.21 2 Dorsey 220 0.71 1.08 3 Both reactors out-­‐of-­‐service 220 0.26 0.46 0 0.18 0.40 4 IEEE 2011 Electrical Power and Energy Conference
15 LSLR Protec>on Scheme at Riel • Simula>on Results – LSLR at Riel – Precondi>on: Dorsey out-­‐of-­‐service – Time to dissipate 6 MJ in arresters Shunt Reactor Shunt Capacitor Minimum >me (s) Maximum >me (s) 1 Riel 220 2 Dorsey 220 0.07 0.09 3 Both reactors out-­‐of-­‐service 220 0.07 0.09 0 >2.0 >2.0 4 < 3 MJ (no ferroresonance observed) IEEE 2011 Electrical Power and Energy Conference
16 Conclusions • Inves>gated the impact of sec>onalizing a transmission line on temporary overvoltages • Applica>on of a protec>on scheme to mi>gate the impact on equipment was studied • Recommended a new protec>on for Riel and to retain the exis>ng scheme at Dorsey • Study results formed the basis for func>onal specifica>on of the new protec>on scheme • Several opera>ng restric>ons were recommended IEEE 2011 Electrical Power and Energy Conference
17 Thank You! IEEE 2011 Electrical Power and Energy Conference