Protective Relaying of Power Systems Using Mathematical Morphology

The basic principle of protective relaying of power systems has not changed for more than half a century. Almost all power system protective relaying algorithms are dominated by integral transforms such as the Fourier transform and the wavelet transform. The integral transform can only provide an average attribute of the s- nals or their components. The accuracy of the attribute extraction is signi?cantly sacri?ced by the assumption of periodicity of the signals if the integral transform is appliedto transientsignals. Itis also wellknownthatthe signalsare liable to bec- taminatedbynoiseintheformofexponentiallydecayingDCoffsets,highfrequency transients, harmonic distortion, errors caused by non-linearityin the response of the sensors, and unwanted behaviour of power systems. This contamination is often provoked by fault conditions, just at the time when the protection relay is required to respond and trip the circuit breaker to limit damage caused by the fault. On the other hand, as we know, in most protection relays, complex computation has to be undertakenwithin a sampling interval, no matter how small the interval, to calculate the coef?cients relevantto the attributes of the signals byusing the integral transform based on a window of samples, and to calculate the relaying algorithms, which are derivedto representthe relationship betweenthese coef?cientsandpower system faults. If fast transients and high-order harmonics are to be addressed, - tra computing power and facilities are required. Therefore, it can be seen that the current power system relaying algorithms suffer from many problems including - curacy, fast responses, noise, disturbance rejections and reliability.

Professor Q.H. Wu is the chair of Electrical Engineering at The University of Liverpool, UK. He obtained an MSc(Eng) in Electrical Engineering from Huazhong University of Science and Technology (HUST), China and a PhD in Electrical Engineering from The Queen's University of Belfast (QUB). Before joining The University of Liverpool Professor Wu worked at both QUB and Loughborough University, UK. In 1994 he was awarded the Donald Julius Groen Prize for the best paper published in the Journal of Systems and Control Engineering, Institution of Mechanical Engineers. Professor Wu’s research interests include systems modelling, adaptive control, mathematical morphology, evolutionary computation, multi-agent systems and their applications for power system operation and control.

Z. Lu received an MSc(Eng) in Electrical Engineering from Huazhong University of Science and Technology, China. He obtained a PhD degree from The University of Liverpool and is currently a postdoctoral research associate with the Department of Electrical Engineering and Electronics at the university. His research areas include power system protection, mathematical morphology and evolutionary computation.

T.Y. Ji has received a BA in English and an MSc(Eng) in Signal and Information Processing from Xi'an Jiaotong University, China. She is currently studying for a PhD at the Department of Electrical Engineering and Electronics, The University of Liverpool, UK. Her research areas include mathematical morphology, signal processing and evolutionary computation.