Presented in this paper is a theoretical review of the relationships that should exist between electrical winding parameters and the mechanical vibration of AC machine elements under normal and faulted operating conditions. Also included are data from an experimental study that relate stator vibration and bearing vibration to selected winding faults in a synchronous machine. Consideration of these results indicates a significant relationship between electrical deterioration and mechanical vibration and, thus, provides the motivation for additional study and a basis for future applications.

https://stacks.cdc.gov/view/cdc/8665/cdc_8665_DS1.pdf

Detection of A-C machine winding deterioration using electrically excited vibrations

Equivalent circuits based on the actual connection of coil-groups of generators are used to study the characteristics of various generator stator ground fault protection schemes presented in the literature. The evaluation and the comparison of the characteristics of those schemes are given by means of protection coverage-critical resistance curves. Although these schemes are successful in practice, they suffer the disadvantage of low sensitivity, which is strongly related to generator operating conditions. To overcome this disadvantage, two adaptive stator ground fault protection schemes based on digital techniques are developed. Compared to conventional third-harmonic voltage schemes, they can automatically track the change of generator operating conditions before a ground fault occurs. Test results from a digital simulation show that they can keep high sensitivity during all operating conditions. >

Adaptive ground fault protection schemes for turbogenerator based on third harmonic voltages

This paper introduces a new differential protection scheme based on zero-sequence voltages with 100% coverage for generator stator ground faults. Analysis shows that the Delta-fundamental zero-sequence voltages and the Delta-third-harmonic voltages at the generator neutral and the terminals will change simultaneously, and they present some similar characteristics. According to that, the new scheme that exploits the fault information of both the zero-sequence fundamental voltage and the third-harmonic voltage is described. As it combines the information of the zero-sequence fundamental voltage and the third-harmonic voltage, the scheme can detect the ground fault with high sensitivity in 100% coverage winding. Simulation and field test results show that the proposed scheme can obtain higher sensitivity than the traditional schemes

Differential Protection Based on Zero-Sequence Voltages for Generator Stator Ground Fault

The results of the analysis of zero-sequence currents flowing in generator neutral and at ground-fault location during the generator normal operation and during ground faults in the stator windings are presented. The influence of different methods of grounding the generator neutral on these currents in the primary circuits for different parameters of generators, transformers, and additional capacitance to ground of the generator breakers was determined. This influence was analyzed for generators with ungrounded neutral, for generators with the resistance in neutral, and for generators with ground-fault neutralizer (GFN) grounding the generator neutral. The analysis has been done for real resistance of the breakdown channel during ground faults along the whole length of the generator stator winding. It has been found that the applied method of grounding the generator neutral, the parameters of generator and transformer, the additional capacitance to ground of the generator breakers, the level of fault resistance and ground-fault location have a substantial influence on currents flowing in the generator neutral and at ground-fault location in the breakdown channel in the main insulation of generator stator winding.

Ground-fault currents in unit-connected generators with different elements grounding neutral

The paper presents a novel adaptive stator ground fault protection scheme with fault location capability for high-impedance grounded synchronous generators. The protection scheme uses already available neutral grounding signals in the existing subharmonic injection protection to obtain a Kalman adaptive filter (KAF) for real-time stator insulation parameter estimation. The KAF estimator yields a method of continuous tracking of stator insulation condition during healthy operations. This information is then used for real-time stator ground fault detection as well as fault location. The effectiveness of the proposed method is verified using extensive experiments performed on a lab-scale unit-connected generating station.

Pope

Papers

A Comparison of 100 Percent Stator Ground Fault Protection Schemes for Generator Stator Windings