Investigation into high-speed thermal instability testing of synchronous turbo-generator rotors

A thesis submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2017The research presented in this thesis conclusively shows that the most effective method to perform synchronous turbo-generator rotor Thermal Instability Testing is by utilising the current injection method of condition assessment. Analysis of the experiences of a local utility for well over a decade has uncovered a high number of rotors failing thermal instability testing in recent years. This trend has brought the current testing methodology into question. Two different assessment modes of testing have been found to be utilised internationally without preference, namely, current injection and friction/windage. By determining the method that is best suited to detect a thermally sensitive rotor a service provider can benefit by improved rotor reliability as well as cost saving. The evaluation is accomplished by utilising a scaled down experimental setup based on the model of a local testing facility as well as a 600 MW turbo-generator rotor. A direct thermal mapping technique has been devised utilising infrared thermography to capture the thermal distribution of the rotor surface under different test conditions. The results obtained have shown that the methods differ substantially with the friction method exhibiting a uniform surface distribution and the current-injection method exhibiting areas of higher temperature concentration around the rotor pole faces. However, weaknesses do exist in present-day testing techniques in the form of inaccurate temperature measurements during testing as well as little consideration given to external factors such as the interaction between the slip-ring and brush-gear that have the potential to influence test outcomes. A presented augmented method of performing thermal sensitivity testing taking advantage of infrared thermography is found to improve testing accuracy and aid in fault detection and location. Current thermal instability testing coupled with the direct thermal mapping method has been demonstrated to be the most effective means for performing rotor thermal sensitivity testing.MT201

Foreign material exclusion (FME) failures of large turbo alternators.

Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2009.Synchronous turbo alternators form the basic building block of a generation scheme. Turbo alternators are highly susceptible to foreign material ingress. In industry this phenomenon is on the rise. We evaluated the effects of foreign materials on the generator and condition monitoring equipment. The sources of foreign materials and methods to reduce ingress were investigated. We further evaluated industry best-practices on foreign material exclusion. Information is scarce, as no classic research material is available on foreign material exclusion. We therefore used industry foreign material exclusion best-practices and expert opinions were gathered. Eleven global incidents of foreign material exclusion failure were investigated. The areas of interest were: types of foreign material, area of ingress, condition monitoring response, component damage, root cause and prevention. We point out that turbo alternators are vulnerable to foreign material ingress mainly due to weak foreign material exclusion practices. We categorised the foreign materials and their effects on the operational parts of the turbo generator. We found that the air gap was the most susceptible to ingress. We identified the Generator Core Monitor as a possible solution to minimising foreign material damage