A new approach to switching, fault protection, and overload monitoring of distribution transformers

The major current monitoring and control functions for distribution transformers include: switching transformers in and out of the distribution system; sensing and interrupting secondary faults; sensing and interrupting primary faults; and monitoring transformer loading with indication and isolation capability. A novel primary switch and overcurrent protector device for handling all these requirements is presented. The device´s sensor element and magnet latch are described, and its testing and application are discussed. Although it is designed specifically for use in overhead, completely-self-protected transformers, it could be modified for use in pad-mounted transformers