End to end testing of transformer protection IEDs using smart testing philosophy: Case study and recommended solutions implemented at 400kV substation, Madhya Pradesh, India

Transformers are critical assets of power system network and their adequate protection is a matter of vital importance. Modern protection relays are usually defined as intelligent electronic device (IED) s, and they provide huge flexibility and enhanced protection features to assure correct operation of the equipment. Transformer protection IEDs are equipped with key features such as differential and restricted earth fault (REF) protection along with several other functionalities as per the guidelines of IEEE C37.91. These functions are available with enhanced facilities such that it can incorporate the difference in phase angle based on vector rotation, ratio correction of current transformers used, interposing CT corrections etc… The increase in flexibility of the IED has also increased the complexity of programming it where a trivial error in the configuration will result in unwarranted operation causing loss of power and reduction of equipment life. Perfect implementation of protection needs proper testing of all programming and configurations, where the complexities of transformer vector shift, magnitude compensation, 2nd harmonic interlock, differential and restrain algorithm of various manufacturer with unique characteristic complicates the testing procedure. This paper discusses about testing vector groups and the facilities in IEDs to adapt to it, along with different field cases where the IEDs have misbehaved due to improper testing, and to address the same various methodologies and features available in modern testing kits, through which the testing of IEDs is standardized ensuring proper commissioning of the system.