Influence of instrument transformers on power system protection

摘要

Instrument transformers are a crucial component of power system protection.They supply the protection system with scaled-down replicas of current and voltagesignals present in a power network to the levels which are safe and practical to op-erate with. The conventional instrument transformers are based on electromagneticcoupling between the power network on the primary side and protective devices onthe secondary. Due to such a design, instrument transformers insert distortions in thementioned signal replicas. Protective devices may be sensitive to these distortions.The inuence of distortions may lead to disastrous misoperations of protective devices.To overcome this problem, a new instrument transformer design has been devised:optical sensing of currents and voltages. In the theory, novel instrument transform-ers promise a distortion-free replication of the primary signals. Since the mentionednovel design has not been widely used in practice so far, its superior performanceneeds to be evaluated. This poses a question: how can the new technology (design)be evaluated, and compared to the existing instrument transformer technology? Theimportance of this question lies in its consequence: is there a necessity to upgradethe protection system, i.e. to replace the conventional instrument transformers withthe novel ones, which would be quite expensive and time-consuming?The posed question can be answered by comparing inuences of both the noveland the conventional instrument transformers on the protection system. At present,there is no systematic approach to this evaluation. Since the evaluation could lead toan improvement of the overall protection system, this thesis proposes a comprehensiveand systematic methodology for the evaluation. The thesis also proposes a completesolution for the evaluation, in the form of a simulation environment. Finally, thethesis presents results of evaluation, along with their interpretation.