Investigation of STATCOM effects on synchronous generator impedance based LOF relay with considering a realistic model for the excitation system of the generator

This paper studies the effects of static synchronous compensator (STATCOM) on synchronous generator conventional loss of field (LOF) protection. To accomplish a comprehensive study, a typical and realistic excitation system is considered for the generator by using the phase-domain generator model available in the real-time-digital-simulator. Using such a system, LOF phenomenon is realistically studied in accordance with IEEE Standard C37. 102-2016, and the generator dynamics along with the LOF relay performance are investigated through different types of complete and partial LOF failures. It is shown that STATCOM presence can cause two major impacts on the LOF protection; i) It imposes an additional time delay on the relay performance to detect the LOF failures, while the amount of such a time delay is dependent on the generator initial loading and the type of LOF failure, and ii) It might lead the generator to reach a new stable operating point (NSOP) during change-over from AVR to MVR mode. Both impacts and the related consequences are discussed in the paper and some solutions are suggested to deal with the probable negative aspects. The solutions comprises 1) employing an overloading relay to avoid thermal impacts on the stator windings and 2) employing an alarming scheme to avoid the undesirable effects, that the generator may experience during prolonged under-excitation operation in the probable NSOPs.