ANALYSIS OF SYNCHRONOUS MACHINE TURN-TO-TURN FAULT CURRENTS

In the event of internal faults in turbo generators large currents flow in the windings due to the unsymmetrical magnetic linkage between the stator windings of the lap-connected generators. This causes severe damage to the windings, shaft and coupling of the machine. Extensive study on these faults can help mitigate the damage caused by these faults by allowing design of protective schemes that detect faults more quickly. This thesis, backed by experimental results, proposes a method that depends on the negative sequence voltage, negative sequence current quantities and field currents to distinguish from internal or external faults as well as focusing on the analysis of internal faults in synchronous machines. The limitations of the existing protection practices in detecting the turn-to-turn faults were also researched. The main motivation for the work is to overcome the present limitations by using a new approach for modelling of generators for internal faults. Information on the magnitude of internal fault current can help validate the synchronous machine internal faults models based on a modified winding function theory approach and the multi-loop method. The work deals with development of a test setup for measuring the turn-to-turn fault currents of the salient pole synchronous generator in the lab. The process is initiated by calculating the approximated currents using the design aspects of the machine. These calculations are compared to the measured currents during various combinations of turn-to-turn faults. This thesis discusses the sensitivity of protection schemes applied for detecting turn-to-turn in the generator. The zero sequence voltage based approach, negative sequence differential protection and the proposed advanced rotor double frequency harmonic current based detection methods were each analyzed to determine their sensitivity for internal faults by varying from the number of shorted turns from 1 turn to 10 turns.masters, M.Engr., Electrical and Computer Engineering -- University of Idaho - College of Graduate Studies, 201