Transformer Protection

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5/29/2015Schweitzer Engineering Laboratories1Copyright SEL 2015IEEE SF Power and Energy SocietyMay 29, 2015Transformer ProtectionAli Kazemi, PERegional Technical MangerSchweitzer Engineering LaboratoriesIrvine, CASources of Transformer Stresses Thermal cycling Vibration Local heating due to magnetic flux Impact due to through-fault current Heating due to overload or inadequate coolingSource: IEEE Std. , IEEE Guide for Protecting Power Transformers5/29/2015Schweitzer Engineering Laboratories2Transformer Failure Statistics1983 1988 Winding failures37% Tap changer failures22% Bushing failures11% Terminal board failures3% Core failures1% Miscellaneous failures26%Source: IEEE Std. , IEEE Guide for Protecting Power TransformersTransformer Protection Differential Protection Current Transformer Performance Through Fault Protection Mechanical Protection5/29/2015Schweitzer Engineering Laboratories3Design Considerations for Transformer Differential Protection CT ratio and CT voltage class selection CT connections Current phase shifts across Transformer Inrush detection Differential pickup settings Zero-sequence currents Slope High excitation currentsDesign Considerations for Transformer Backup Protection Overcurrent Directional overcurrent External faults Sudden pressure Hot spots Loss of coolers5/2

Compensation With Digital Relays Current Scaling and Phase-Shift Compensation Are Internal • Exact current scaling • Phase-shift compensation for all transformer connections ... Transformer Thermal Monitoring Optimizes Operation • Transformer protection • System operation • System planning • Capital investment.

  Phases, Early, Monitoring