Loss of Mains (LOM) occurs when part of the utility network containing distributed generation (DG) is disconnected from the remainder of the system. Detecting LOM will become more important in the future as higher amounts of DG will be connected to increase the use of renewable energy sources, to reduce emissions and to reduce power transmission losses. In some cases, DG can be capable of supplying loads within an island and the islanded system can remain stable.However, safety issues arise if LOM persists and, accordingly, islanded operation is not permitted in the majority of utility systems throughout the world. Wide area monitoring systems, using synchronised phasor measurements, which are beginning to play an increasing role in monitoring and control in transmission networks, may offer opportunities to improve the performance of LOM protection in distribution networks, but may require some form of communications.A novel technique for LOM detection, using Phasor Measurement Unit (PMU) data, is described in this thesis. The technique, known as the Peak Ratio Analysis Method (PRAM), is shown to improve both the sensitivity and stability of LOM protection when compared to prevailing techniques.The technique is based on a Rate of Change of Frequency (ROCOF) measurement from M-class PMUs, but the key novelty of the method lies in the fact that it employs a new 'peak-ratio' analysis of the measured ROCOF waveform during any frequency disturbance to determine whether the potentially-islanded element of the network remains connected to the main system or not (i.e. it detects when islanding, or loss of mains, has occurred).The proposed technique is described and several examples of its operation are compared with three competing LOM protection methods that have all been widely used by industry and/or reported in the literature: standard ROCOF, Phase Offset Relay (POR) and Phase Angle Difference (PAD) methods. It is shown that the PRAM technique exhibits comparable performance to the others, and in many cases improves upon their abilities; in particular for systems where the inertia of the main power system is reduced, which may be the case in future systems with increased penetrations of renewable generation and HVDC infeeds.
|Date of Award||1 Jan 2014|
- University Of Strathclyde
|Sponsors||University of Strathclyde|
|Supervisor||Campbell Booth (Supervisor) & Graeme Burt (Supervisor)|