Detection of stator interturn fault of synchronous machine by rotor current analysis : A SIMULATION APPROACH

Abstract: One of the major electrical faults of synchronous machines is an interturn short circuit in the stator winding, due to winding insulation failure. A synchronous machine is designed to have electrical and mechanical symmetry in the stator and rotor. An interturn fault in a synchronous machine damages the symmetrical property, thereby inducing abnormal symptoms like varying torque, mechanical vibration, and deviation of stator and rotor terminal currents from their usual waveform. This last symptom is what is studied in this thesis, as an indicator of the presence of an interturn fault. An interturn fault during machine operation can lead to a catastrophic machine failure and consequent long outage, unless it is rapidly detected and the machine shut down. Prevention of such outages is an important concern for machine owners and power system operators. That is why early detection of interturn faults is desirable to prevent such machine failure. Several external sensors can be implemented to detect such interturn fault, which is costly. That is why it is desirable if the interturn fault can be detected by analyzing the measured currents that already are available to a protective relay. In this thesis a simulation approach is presented to observe the pattern and frequency spectrum of rotor field current in presence of a stator inter turn fault. All simulations have been performed using Matlab-based programs written during this thesis work in the Electromagnetic department (ETK) in KTH. The outcome of the thesis is that in the presence of an interturn fault in the stator, several even harmonic components are found in the frequency spectrum of the rotor field current. The presence of these harmonics is not a definitive sign of an interturn fault, as almost the same even harmonics are found in the rotor field current if the stator winding asymmetry is taken into account.