Performance of frequency relays with multiple synchronous based DG units

Anti-islanding protection is one of the main protection requirements for Distributed Generation (DG). Grid tied DG systems are equipped with an islanding detection method that is responsible for detecting the loss of mains in a timely manner in order to initiate DG disconnection. Frequency relays are commonly used in detecting an islanding condition for synchronous based Distributed Generation (DG). The effectiveness of frequency relays are assessed using performance curves which provide a relationship between the islanding detection time and the amount of active power mismatch. This paper examines the impact of operating multiple synchronous based DG units on the islanding detection capability and performance curves of frequency relays. The results show that, with multiple synchronous DG units, the performance curve of frequency relays will be altered depending on the equivalent inertia constant of the islanded DG system.