An Adaptive Fuzzy Mho Relay for Phase Backup Protection With Infeed From STATCOM

This paper presents a fuzzy-logic-based scheme for the operation of generator-phase backup distance protection, otherwise popularly known as the “phase 21” function, in the presence of a STATCOM installed at the generator bus. The presence of STATCOM impacts the normal functioning of the distance relay based on its location as well as that of the fault. The method introduced here counters its adverse effects by formulating an adaptive mho relay for the phase 21 function, which accounts for the fast and dynamic compensation provided by the STATCOM throughout the operating time domain. Fuzzy logic is used in this paper to handle this varied compensation with its capability to process uncertain variation using linguistic variables to good effect. Two particular feature inputs from the STATCOM which have a direct impact on the reach of the relay are considered as the fuzzy system inputs. The objective is to counter and minimize the effect of current infeed from the STATCOM, on the apparent reach observed by the phase 21 relay and, thus, achieve the desired coordination. Electromagnetic transient simulations were used for the studies. The interaction between the simulation and the fuzzy system is performed online to further enable a closed-loop approach. Further furnished results validate the same interaction.