Experimental and Theoretical Analysis of Cable Discharge

This paper focuses on the phenomenon of discharge of HVAC cables, which is a concern for utilities when performing AC/DC tests, during maintenance works, and more recently when switching cables for grid voltage control. The study is based on field and laboratory tests of 275 kV pressurized-oil-filled (POF) cables, analytical calculations, and simulations. The contributions of this paper are: field and laboratory measurements of voltages and leakage currents during cable discharge, including a field test carried out in 2015 by the National Grid (UK) on a 275 kV POF cable of 21 km; a method for estimating the leakage resistance and the time required to discharge a cable system using simple parallel RC circuit theory; and typical values of leakage resistance, leakage current, and discharge time for 275 kV cable systems. The influence of temperature, electric field, and humidity on cable discharge is also discussed and a correction factor to account for the impact of humidity is proposed.