Prototype implementation of an islanding detection relay based on pattern classification of current and voltage transients

Abstract

A prototype islanding detection relay, which uses decision tree classifier to categorize the transient generating events as ‘islanding’ or ‘non-islanding’ was implemented and tested. It consisted of two basic stages of signal processing to extract the required feature vectors for the classification. The first stage involved signal filtering and in the second stage signals were processed by rectifying, summing, and lowpass filtering to get the energy content in the three phases during a selected time-frame. A simple radial medium voltage distribution system having a single distributed generator was simulated in PSCAD/EMTDC to obtain the transient waveforms, and the performance of the relay was tested with signals generated using an RTP real-time waveform playback instrument. The experimental results showed high accuracy in detecting islanding events within a response time of less than two cycles. The proposed relay can be implemented with a very low cost and is simple in construction. Therefore, this could be an acceptable low cost substitute for the expensive and complex transfer trip schemes, which are commonly in use with the distributed generation. loads and distributed energy resources (DER) remains energized while isolated from the remainder of the utility system’ (IEEE, 2003). Unintentional islanding resultsin several safety and power quality' issues including abnormal variations in frequency and voltage, possibility of creating ungrounded systems, and potential safety hazards for repair crews. In formulating guidelines and/or rules for interconnecting DGs in the distribution systems, the most common practice is to adopt the IEEE standard 154 (IEEE, 2003). These otional practice standards have been developed with an underlying assumption that thepower system is radial. In the past, the power available from DGs was not essential to support the load on the system. Hence, the standards suggest to disconnect the DGs for any ‘significant’ fault (a fault that could require the protection to be provoked) on the distribution system and thus, maintaining the radial nature of the system. Consequently, the islanding detection relays are designed to avoid power islanding, and these relays are referred to as anti-islanding relays (Xu et al., 2004; Mahat et al., 2008). However, there is a change in the approach towards islanding with the initiatives on microgrids (Chowdhury et al., 2009; Lidula & Rajapakse, 2011). The performance of the power-islanding detection methods in a microgrid setup is more demanding as the microgrid is designed to operate as a stable power island. Many powerislanding detection methods in practice would find it difficult to meet the qualities demanded by micorgrids (Katiraei et al., 2005) without the use of expensive telecommunication facilities. Keywords: Active filters, decision tree classificat