New Methods for Detecting Unintentional Islanding for a Distributed-Generation Inverter

Since the first adoption of IEEE Standard 1547 and UL Standard 1741, many connection schemes have been developed for tying a distributed- generation (DG) inverter to the Electric Power System (EPS). Unintentional islanding is not allowed. Quickly removing the DG inverter from the power system keeps the public safe, keeps line personnel safe, avoids EPS damage, and avoids damage to the distributed-generation inverter.  Recently, there are new methods to detect islanding that are faster and more reliable.  It is a challenge to detect an islanded condition quickly and reliably. Traditionally, voltage and frequency-limit elements have been used to disconnect the DG for an islanded condition. In this case study, protection elements for impedance (21), power-flow-controlled frequency rate of change (81ROC), and vector jump (78V) are used to detect an islanded condition and disconnect the DG inverter. These elements operate with greater speed and reliability than traditional methods. This paper presents initial islanding testing for an inverter driven by a high-speed, magnetic- levitation generator powered by waste heat from industrial processes.