Voltage-current-time inverse-based protection coordination of photovoltaic power systems

Increasing share of distributed energy resources (DERs) in power networks results in dynamic network topology and short-circuit fault levels. Low fault infeed in PV connected power network will rarely damage any power components, but detection of faults is of prime importance. The existing over-current, voltage, and impedance-based relays may fail to detect/clear the faults. However, it is observed that PV infeed networks are generally weak and experience a collapse in terminal voltage with increase in current during the system faults. In this article, variation in fault currents and voltages is utilised for formulating a new voltage-current-time inverse (VCTI) mathematical relay model. The proposed relay model enhances the operating time of the relays and maintains the protection coordination for weak power networks, especially powered with high PV generation. Using this relay model, a cluster-based protection coordination scheme for PV-dominant penetrated power network is presented. The performance of the proposed relay model and coordination schemes is compared with inverse definite minimum time (IDMT) relays and other relying models. Based on the proposed relay model, a hardware relay prototype model has been developed and it is found that hardware results are highly stable and are within 3% accuracy of simulated results.