Detect and Evaluation of Corona Defects on Generator Stator Winding Overhangs

摘要

The defects of corona or discharge are important factors to result maybe in failures on stator winding. It is meaningful to detect the corona defects at the early stage of faulty coming on. This paper presents a new method to detect and evaluate the corona defects on stator winding overhangs. A test bench that consists of real stator bar spare, ultraviolet radiation detector and partial discharge measurement instrument has been developed in the laboratory. Corona would be brought on at selected areas of spare stator bars under the controllable test situation. Ultraviolet radiation and partial discharge of the corona are measured simultaneously. Test environment and distance between ultraviolet radiation detector and corona defect should also be important parameters. The statistical relation between partial discharge and ultraviolet radiation is analyzed based on tests. The parameters of saturation intensity of corona are developed to describe the corona area and corona intensity. Under the basis of data relation, the ultraviolet radiation of corona is able to corresponding to the partial discharge. It is a way to evaluate the crisis of corona. Because ultraviolet radiation imaging and measurement system can take on the advantage of visualization, it is convenience to locate the corona areas accurately. The paper also presents the principle of evaluating the failure risk of stator winding in the next 5~6 years based on above measurement. Difference repair and maintenance schemes can be adopted according to the risk level of corona defects. Up to date, over 20 large Generators have been inspected and evaluated.