Development of Cable Space Charge Measurement Device through Using Pulse Electro-acoustic Method

Abstract: The existence and accumulation of space charge within the cable insulation pose great threat to the conductance characteristics, aging and breakdown of polymer power cables. Hence, it is of significance to study the distribution and accumulation of space charge. In the paper, the basic principle of pulse electro-acoustic (PEA) is presented and a new device that can be used for measuring the cable sample PEA space charge is developed. It is possible for the device to measure cables with different insulation thicknesses and radius thanks to the use of flat electrode. The system is used to test a new 10kV XLPE cable and a 10kV XLPE cable which has been in service for 20 years. It is found that the space charges accumulated in the cable which has been running for a long time are more than the new one under the same test conditions. 

Key words:  pulse electro-acoustic method (PEA), space charge, flat electrode, stray capacitance, data processing       

Introduction

The XLPE electric cable is widely used in the high voltage transmission line and medium-low distribution network thanks to a series of advantages, including good electric performance, high breakdown field strength and simple to install and maintain. However, people always focus on the insulation aging and breakdown problem under long-term condition. The distribution and movement of space charge have big effect on the characteristics such as conductance, aging and breakdown. It is widely accepted that space charge and electric field distortion is one of main causes for insulation aging and breakdown. The development of space charge research is based on space charge measurement technology. The non-destructive measurement technology especially advances the development of space charge research and equipment production. Non-destructive methods include pressure wave expansion, laser intensity modulation and pulse electro-acoustic (PEA) method. Of them, the pulse electro-acoustic is the most widely applied method in the world.