This thesis concerns the study of a novel method of power system digital distance protection, which may provide the breakthrough required for the implementation of faster and more accurate protection schemes than presently available. The method employs a frequency domain impedance measurement technique based upon a simplified line model and the use of finite Fourier transform coefficients in the analysis of very small amounts of information. Unlike previously proposed methods, the algorithm does not rely on any periodicity in the relaying signals and, as a result, it is capable of performing in high transient conditions using data of short duration. Operating times of 10 msec and less can be achieved and it is envisaged that the method will have considerable advantages in short and long line distance protection. The work embraces considerations of the general philosophy behind digital protection schemes, performance studies of the new method and the investigation of various implementation proposals. The performance of the finite transform technique is studied in some detail and, in the analysis, a quasi-optimal relationship is developed by which conditions may be chosen to ensure acceptable response in the presence of noise and various numerical errors. The studies show that offset fault current conditions can cause some problems in the performance of the algorithms. These conditions are studied in detail and a number of practical solutions are investigated. Recently developed frequency domain power system simulation techniques are used in studying the performance of the new method and the importance of such facilities in the development of fast operating protection schemes is demonstrated. The implementation studies are concerned with the practical requirements of hardware and software for protection schemes employing the new method. A brief investigation of data acquisition techniques and signal levels is made and consideration is given to the speed of the various software procedures based on currently available processing equipment.
|Date of Award||1977|