Study of corona spaces in cable

This paper describes four methods of studying corona spaces in high voltage cables, principally polyethylene cables. These involve: A. The manometric test for corona around the conductor B. Silver mapping on the conductor C. Capacitance increase when the conductor spaces are filled with water D. Change in corona level produced by gas substitution Test A depends on the pressure decrease caused by absorption of oxygen activated by corona. Figure 1 shows the set-up for a balanced test which eliminates troublesome fluctuations due to diffusion or changes in ambient temperature and pressure. Figure 2 shows single sample tests on a 46 KV cable with no strand shielding. Absorption is shown by the jumps during stress periods. In an improved KV cable corona absorption was slight even at 120 KV AC. After bending (11.5 × 0.D.) corona onset was between 75 and 90 KV. In principal there appears to be no voltage limit to the test.