From the editors' desk

Abstract

The first article in this issue is "Special Requirements of High Frequency Current Transformers in the On-Line Detection of Partial Discharges in Power Cables," by Yang Xu, Xiao Gu, Bin Liu, and Baojun Hui of the State Key Laboratory of Electrical Insulation and Power Equipment, Xi'an Jiaotong University, Xi'an, China; Zhigang Ren of the Beijing Electric Power Research Institute, Beijing, China; and Shaoxin Meng of the China Electrical Power Research Institute, Wuhan, China. The article discusses some special requirements of high frequency current transformers and the instrumentation in the on-line detection of partial discharge (PD) in cables. Four types of defects representing typical situations in the field were created in a 110-kV cable and joint for PD detection. Based on the frequency analysis of the PD signals, the upper frequency of a measuring instrument needs to be higher than 40 MHz and the lower frequency no less than 500 kHz. The lower frequency limit is recommended to avoid power line interference. Provided that the high frequency current transformer satisfies the bandwidth requirement, a high transfer impedance is preferred. A sensitivity better than 100 pC is expected in on-site PD detection and in high noise environments. The article compares eight PD measuring instruments based on high frequency current transformer detection with respect to lower and upper limit frequencies, sensitivity, PD pattern recognition functions, and PD signal attenuation. Among the existing functions, the PD pattern recognition function needs to be improved for on-line cable tests. In addition, the article concludes that there still is a need for an on-line calibration method based on high frequency current transformer sensors.