Transformer Differential Protection
Lessons Learned from Commissioning and Analyzing Data
Ensuring correct setting and installation of a transformer differential relay is critical. Such a relay must detect internal faults, damaging overloads, and through-fault currents while remaining secure against misoperation. The ability to use wye-connected CTs with microprocessor-based relays has simplified installations, but it is still complicated. Installation and settings errors continue to be widespread, implying a need for more tests. Even with greater commissioning effort, occasional wiring problems develop over time, and these can best be resolved through analysis of relay event report data. In the interest of reducing transformer differential misoperations, we share in this article practical lessons we have learned through experience with commissioning and relay event report analysis.
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