COMPUTER MODELLING OF DIGITAL DISTANCE AND DIRECTIONAL RELAYS
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With recent advances in microelectronics, the use of micro-processor based relays for power system protection has received much attention from power system researchers. To develop micro-processor relays suitable for use in power systems, their performance must be evaluated during the design stage. For achieving this, two approaches can be used. One approach is to design a prototype of the relay and test it. This procedure will be expensive if it becomes necessary to change the design several times. The second approach is to develop models of the relay and its expected performance on, a digital computer. This procedure will allow an engineer to check the performance of several designs without building prototypes. Moreover, the design process will take less time than the time required to optimize the designs using the first option. This thesis is concerned with the development of an interactive software which implements the models of digital distance and directional relays on a digital computer. The software uses four techniques for implementing the models. These are amplitude comparison, phase comparison, impedance estimation and memory mapped targeting techniques. The software facilitates the execution of the programs in two modes of operation. In the first mode, the computations are performed using the floating point format of numbers. In the second mode, the effects of analog to digital converters, truncations or roundings and bit shift multiplications are incorporated. The capabilities of the software are demonstrated by including cases of transmission line shunt faults. The movement of the trajectory of the calculated line impedances from the pre-fault to the post-fault states shows the speed with which a relay detects faults that are in its operating zone.