Protection of systems containing IBR from asymetrical ground faults using zero sequence current

As more renewables join and contribute to the power system, Inverter Based Resources (IBR) are adding challenges to the protective system. The relatively small power output of these generators and the corresponding fault currents they produce present problems for traditional protective relaying schemes, causing relay mal-operation, and issues with protective system coordination and operation. The majority of distribution protection schemes are based on over-current protection, where when a current threshold is exceeded, a trip signal is generated by the relay indicating a fault. The addition of distributed generation to the power system complicates protective relaying in a number of ways: the magnitude of the fault current will be altered based upon the location of the fault relative to the IBR, and the response of the IBR sources to a fault will be much different than the traditional synchronous generator. The biggest change that the introduction of an IBR to an existing system produces is that the currents experienced during a fault by the protection system will not be the same as the system was originally designed for, since the IBR sources have a much lower fault current with IBR fault currents typically in the 1.2 - 1.5 p.u. range. The relatively low fault current of IBR sources present a difficulty in differentiating faults from increased loads. Additionally negative sequence relays may fail in the presence of IBR's due to the negligible negative sequence current produced by the IBR during a fault.IBR sources may also alter the flow of fault current from what the protective system was designed around. This paper presents a novel method to allow the sub-cycle detection, and determination of the relative location, of asymmetrical ground faults (single line to ground and double line to ground) in systems containing IBR sources through the use of phasor analysis of the zero sequence current. Least Error Squares Estimation is then applied to the fault currents to give a phasor estimation to improve the detection time of these faults. The proposed method uses a phasor analysis rather than an Artificial Intelligence (AI) or a machine-learning based technique to keep the protection scheme aligned closely with current practices at utilities. Non-ground faults are detected using overcurrent protection with a transfer-trip communication system.