Due to their design, the contact resistance measurement of dead tank circuit breakers requires a different approach comparing to the live tank circuit breakers. A DC current used for this measurement flows directly through the current transformers mounted on the bushings. Presence of current transformers (CT) on this type of circuit breakers may introduce errors during a test because of CT magnetizing process. For this reason, it is necessary to saturate a CT prior to performing a measurement.
For this reason we implemented a new test mode called DTRtest in our Micro Ohmmeters (RMO-A, RMO-G and RMO-D series) and in the CAT devices with the built-in micro ohmmeter. This testing mode is specially designed for resistance measurement of the dead tank circuit breakers.
Process of measurement parameters setting and testing in this mode is very simple and does not differ much from live tank circuit breakers.