Automatic testing of advanced transformer differential relays with multiple restrained inputs

Testing of advanced microprocessor based transformer differential relays with multiple restrained inputs presents a significant challenge to the protection engineer. The availability of multiple protection functions protecting the transformer for different internal, external and system fault or overload conditions make testing of multifunctional transformer protection relays a very complicated and time consuming task, which requires specialized equipment. The paper discusses the requirements for adequate testing of each of the specific protection functions. A report oriented approach to the automatic testing of the multifunctional multi-restrained transformer differential relay is described as well. The relays are tested for both internal or external faults. Phase-to-phase and phase-to-ground faults are considered. Hardware requirements and configuration for automatic testing are introduced. Definition of a transformer protection relay as a test object is presented. Different test methods are discussed in the last section of the paper