Recently, a client of ours encountered a trip event from their transformer protections, for a fault that was external to the differential zone. This seemed odd to us, and forced us to power up the test lab and see what was happening!
Fortunately, we were able to simulate the same fault in our controlled test lab environment to help diagnose the problem.
After vigorous testing and evaluation, it was discovered that the differential protection settings required adjustments to better suit the system. The winding compensation settings for the differential protection needed to be adjusted to account for the phase shift in the transformer. Because of the existing winding compensation settings, the relay was tricked to believe there was in fact enough differential current to trip, rather than being restrained and allowing the downstream feeder to trip instead.
We then provided new recommended settings, followed by field testing, which allowed our client to re-energize the station in a timely manner!
Black and McDonald ETS division is always happy to help our clients troubleshoot unique scenarios, and restore power safely and efficiently.
Retired TC Energy
9moLooks like a lot of fun , what a wonderful way to spend a day