The noise effect in conducting on-line partial discharge testing in distribution-class cables

Power cables used in the distribution system, power plants and production facilities often are operated at voltages from 4 kV to 15 kV. These cables are laid next to each other in open or closed trays. In the distribution system, they are terminated to transformers at both ends or to an overhead line at one end and transformer at the other end. In power plant and production facilities, they are terminated to stepdown transformers at one end and often are terminated to high voltage motors at the other end. Partial discharge (PD) pulses measured from one of these cables also could be the results of PD activities in the adjacent cables, motors and transformers, or could be the results of electromagnetic interference from nearby equipment. This makes conducting on-line PD testing almost impossible. In such environments, off-line PD testing is also difficult to perform because it requires shutting down almost the entire system to minimize the interference effect. In this paper, a new approach to conduct on-line PD testing in a noisy environment is presented. The new approach is based on conducting PD measurements in both the time and frequency domains. The PD data collected in both domains are used to identify the PD source