Correlation of Dga, Uhf Pd Measurement and Vibration Data for Power Transformer Monitoring

Reliability of electrical energy networks depends on quality and availability of electrical equipment like power transformers. Local failures inside their insulation may lead to catastrophic breakdowns. To prevent destroying events power transformers are e.g. tested on partial discharge (PD) activity. As testing is just snapshot information about transformers condition, permanent online monitoring is more frequently used to gain operational experiences. The paper presents a monitoring case study of an aged generator step-up transformer with PD activity. Different measurement methods considering different transformer parameters are introduced. Correlation of data for information gain regarding the insulation condition assessment is discussed with the help of a recorded incident with high PD level and followed rise in gas concentration. A Hydran sensor is used to measure the actual level and the trend of dissolved gasses. The presented monitoring system uses the electromagnetic PD measurement method, also known as UHFmethod. PD emitted electromagnetic waves are monitored with an oil valve sensor inside the transformer tank. Furthermore vibration monitoring is included, representing a new approach for transformer surveillance. In addition common measurements were performed for evaluation and correlation purpose, including load current, voltage, top-oil and ambient temperature of the transformer.