Speakers: Karl Zimmerman, SEL
Validating proper CT and VT wiring, terminations, and grounding is fundamental to successful performance of the protection system. Occasionally, errors in CT and VT connections can occur, like missing or broken neutral wires, multiple or missing ground connections, physical wiring errors, blown potential fuses or failures within the instrument transformers. These errors can lead to undesired operations of the protection.
This paper reviews fundamentals of CT and VT connections. We then show several actual field events of undesired or unexpected relay performance due to problems in the CT or VT circuit. These events include transmission line protection with distance and directional elements, high-impedance bus differentials, transformer differentials, and distribution feeders. We shall discuss several basic and advanced testing and commissioning approaches that can reduce errors and improve protection performance.