A Unified Approach to Controlled Switching of Power Equipment Gabriel Benmouyal, Normann Fischer, Douglas Taylor, Mark Talbott-Williams, and Ritwik Chowdhury Schweitzer Engineering Laboratories, Inc.

Overview Comprehensive methods for controlled closing and opening of breakers Transformer configuration considerations Controlled switching devices (CSDs)

What Is Controlled Switching? Methods to reduce or eliminate voltage and current transients from breaker operation

Four Closing Settings Per Phase Definition Units TClose Compensated breaker pole closing time ms TCarc Difference between electrical arcing and mechanical contact Degrees TCpow Voltage point-on-wave closing angle TCdel Additional closing delay Cycles

Controlled Closing Timing

Single-Phase Closing

Optimal TCpow Settings Equipment Configuration TCpow.a TCpow.b TCpow.c TCdel.a TCdel.b TCdel.c Shunt capacitors Yg 0° 180° Y, D 30° 150° Reactors 90° 270° 60° 300° 0.5 • N

Example of Closing on Three Independent Power Inductors (Single Phase)

Closing on Three Independent Power Inductors

Relation Between Voltage and Prospective Flux

TCpow for Single-Phase Transformer With Residual

How Do We Measure Residual Flux?

Closing on a Wye-Delta-Connected Transformer With Residual Flux

Simulated Magnetizing Curve

Delayed Closing Strategy Calculate residual fluxes in all three phases Close phase with the highest flux Close other two phases (0.5 • N cycles later) when Corresponding fluxes are equal First closed phase is at zero voltage

TCpow With Wye-Grounded Transformers Magnetically Dependent Cores Maximum Flux TCpow.a TCpow.b TCpow.c TCdel.a TCdel.b TCdel.c A 60° 300° 0.5 • N B C 240° 120°

Controlled Closing Fluxes

Final Settings Supplied to Closing Algorithm

Controlled Closing Magnetizing Currents

Random Closing Magnetizing Current

Breaker Opening Reignition Constraints

Breaker Pole Opening Settings Units TOpen ms TOarc Degrees

Breaker Pole Opening Timing

Conclusion Controlled closing Controlled opening Eliminates voltage or current transients Improves power quality Protects equipment Makes protective relays more reliable Controlled opening Eliminates breaker restrike or reignition Protects equipment

Conclusion Breaker closing settings Breaker opening settings TClose TCarc TCpow TCdel Breaker opening settings TOpen TOarc

Questions?