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Avoiding the non-detection zone of passive loss-of-mains (islanding) relays for synchronous generation by using low bandwidth control loops and controlled reactive power mismatches

Roscoe, Andrew and Burt, Graeme and Bright, C.G. (2014) Avoiding the non-detection zone of passive loss-of-mains (islanding) relays for synchronous generation by using low bandwidth control loops and controlled reactive power mismatches. IEEE Transactions on Smart Grid, 5 (2). pp. 602-611. ISSN 1949-3053

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Abstract

Generation connected to electrical distribution systems requires reliable and timely detection of loss of-mains (islanding). Passive loss of mains detection relays typically use measurements of parameters such as frequency, phase, and the magnitudes of voltage and current. If a part of the power network becomes islanded and there is a very close match between generation and demand of both active and reactive power, there is a risk that the relay will not be able to detect the loss of mains (LOM) event quickly, or perhaps at all. This is the “non-detection zone” or NDZ. This paper proposes a combination of 2 generator control techniques which allow the NDZ to be avoided even when the generator has significant inertia. Firstly, the natural instability (when islanded) of a grid-connected control scheme consisting of integral and droop controls is recognized and exploited. Secondly, a simple strategy is added which makes occasional small, steady-state adjustments to the reactive power output of the generator. The scheme has been tested in the laboratory and shows that the 2 second detection time required by IEEE 1547 can be achieved, even when an exact match of active power generation and demand is initially configured, and the generator has a significant inertia.