Shpachuk O. Improving of method of protection from single-phase ground fault of the stator winding of synchronous generator which works in a block with a transformer

Object of the research – processes occurring during a single-phase-to-ground fault in a synchronous generator stator winding which operates in electric transformer block. The aim of the research is to enhance the reliability of onset, sensitivity and rapid response of a single-phase-to-ground fault protective system of a synchronous generator stator winding which operates in electric transformer block by determining the current value in the place of damage. Methods of research - theory of probability and mathematical statistics, were applied for analysis of damages and parameter variations of generator stator winding, methods of analysis of linear electric circuits, numerical methods for differential equations integration with application of computer simulation were applied for building of mathematical models of single-phase-to-ground fault current and current in interface, theory of reliability was used for evaluation of relay protection reliability, mathematical modeling methods were applied for analysis of the suggested protection system characteristics, methods of damage detection in discrete objects were applied for optimization of damage detection algorithm in protective relay. Theoretical results – It is the first time that the necessity of application of a set of emergency mode controlled parameters for protection from a single-phase-to-ground fault in a synchronous generator stator winding which operates in electric transformer block is substantiated and the mathematical model which considers the influence of those parameters on current value during a single-phase-to-ground fault and allows to reduce the possibility of protection system faulty actuations is elaborated; due to suggested systematized series of steps, namely: DC current superimpose, application of discharge current of preliminary charged condenser, monitoring of zero-phase-sequence voltage and considering the insulation capacitance of a synchronous generator stator winding which operates in electric transformer block aimed at provision of protection system reaction to current value in the place of damage the method of protection from a single-phase-to-ground fault in a synchronous generator stator winding which operates in electric transformer block was refined; the protection method of generator stator aimed at its disconnection was further developed in terms of simultaneous detection of rise in zero-phase-sequence voltage and decrease of transient resistance in the place of ground fault as evidence of emergency mode actuation and exceedance of programmed setting for actuation in response to current, which allows avoiding external short-circuit fault influence and disturbances in superimpose circuit. Practical result – the conceptual schemes of a system of synchronous generator stator winding protection from a single-phase-to-ground fault, which is based on combined method of DC current superimpose, application of discharge current of preliminary charged condenser, monitoring of zero-phase-sequence voltage and considering the insulation capacitance of a synchronous generator stator winding which operates in electric transformer block, was elaborated on the basis of theoretical results of the study; the parameters, values and characteristics of the elaborated system were estimated; the emergency modes of the devices were studied and the algorithms of detection of possible defects of the devices were elaborated; the comparative calculation of the potential results of control of synchronous generator stator winding insulation condition by means of protective systems which are based on different methods, including that elaborated by the author, which may be applied for reconstruction and replacement of old protective relay stations.The results obtained in the thesis are applied in the process of synchronous generator protective relay exploitation at State Enterprise "National Nuclear Energy Generating Company "Energoatom", Detached subdivision "Khmelnytska AES" and in educational process of Vinnytsia National Technical University when studying the subject "Protective Relay and Electrical Station Automation". Branch of application – electrical energy industry.