Assessing the Performance of ROCOF Relay for Anti-Islanding Protection of Distributed Generation Under Subcritical Region of Power Imbalance

• Published in: IEEE transactions on industry applications Vol. 55; no. 5; pp. 5395 - 5405
• Main Authors: Alam, Mollah Rezaul, Begum, Most. Tasneem Ara, Muttaqi, Kashem M.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-09-2019; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Active filters; Antiislanding technique; Australia; Computer simulation; Digital simulation; Distributed generation; Distributed power generation; Electric power distribution; Electric power systems; False alarms; Guidelines; Islanding; Islanding detection; load curve; nondetection zone (NDZ); Penetration; power imbalance; Rate of change of frequency relays; rate-of-change-of-frequency (ROCOF) relays; Reactive power; Relays; Reliability; Reliability analysis; Stress concentration
• ISSN: 0093-9994; 1939-9367
• DOI: 10.1109/TIA.2019.2927667

In practice, the load-curve and distributed generation (DG) penetration level determines the power imbalance level that a network can experience if islanding occurs. Therefore, with the prior knowledge of load-curve and DG penetration level, the setpoint of rate-of-change-of-frequency (ROCOF) relays can be adjusted so as to make them suitable for a real network. This paper first investigates the subcritical power imbalance region of ROCOF relays through analytical formulation followed by extensive simulation study in order to establish the maximum boundary limit of ROCOF's nondetection zone (NDZ) under all possible deficit/excess of active and/or reactive power imbalance scenarios. Second, ROCOF's reliability (assessed by detection rate and false alarm rate) is expressed analytically and then, validated numerically by simulating a test network of Australia in MATLAB and OPAL-RT real-time digital simulation platform. Finally, ROCOF's performance is assessed through receiver operating characteristics curves and a detailed reliability study under variable setpoints and detection time of the relays; the assessment considers the number of islanding events associated with the time-wise percentage of power imbalance level computed from the net load demand and variable DG penetration in a real network. All these test results demonstrate a clear operational guideline for ROCOF relay.