This paper presents experimental and theoretical analyses used to establish electrical features that can be utilized as indicators of armature winding, field winding or rectifier diode deterioration in brushless three-phase synchronous generators before the imperfection progresses to become a ground fault. The paper begins with the description of a 5 kVA synchronous generator specifically designed and constructed to allow for simulation of armature winding, field winding or rectifier diode deterioration in a brushless machine. Subsequently, a description of the experimental methodology and the results of experiments are presented. Specific features that can be used as indicators of the deterioration are described and a theoretical basis for them is provided. The proposed features can be obtained continuously during normal generator operation. As such, they can be used as a basis for both winding brushless and brush-fed synchronous generator health monitoring applications.

Condition Monitoring of Brushless Three-Phase Synchronous Generators With Stator Winding or Rotor Circuit Deterioration

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

The design principles of a new relay for detection of grounds on the stator windings of generators is discussed. The relay provides 100% coverage of the stator windings with measurement of the fundamental and third harmonic components of the residual voltage at the terminals of the generator and the voltage across the grounding resistor at the neutral of the generator. The design concepts of the detectors utilizing the third harmonic components of the above signals are based on measurements of these signals on a number of Ontario Hydro thermal units.

Design Principles of a New Generator Stator Ground Relay for 100% Coverage of the Stator Winding

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

In this paper, a novel adaptive stator-ground fault protection scheme based on third-harmonic differential voltages is implemented on a lab scale synchronous generator. The lab scale generator is used to emulate the fault characteristics of industrial generators along the stator windings. Simulations based on finite element analysis methods were used to design and tune the laboratory testbed. Experimental results prove the expected fault characteristics as well as fault detection capability of the adaptive stator-ground fault protection scheme.

Modeling and Experimental Verification of a 100% Stator Ground Fault Protection Based on Adaptive Third-Harmonic Differential Voltage Scheme for Synchronous Generators

The paper shows how the normally generated third-harmonic voltage can be used to protect the lower ten to twenty percent of generator stator windings against ground faults. A method of determining the applicability of the scheme to a given machine is described which takes into account the design of the generator and its externally connected apparatus. The effects of finite resistence ground faults are also investigated and other advantages of the scheme, such as protection of the neutral, are also highlighted.

G. W. Buckley

Papers

Performance of Third Harmonic Ground Fault Protection Schemes for Generator Stator Windings