An interesting case occurred at one of the medium-voltage facilities. The 10 kV busbars were fed by a powerful 110/10 kV step-down transformer. To reduce short-circuit currents on 10 kV side, reactors were installed there between the transformer and 10 kV busbars. The transformer and reactor were connected using single-core cables (about 50 m length, 4 cables per phase).

After the facility was commissioned, the 10 kV terminations at the cable connection point to the reactor were periodically damaged. This attracted increased attention to the assembly, and it was found that the cables and the terminations were significantly heated. To reduce the heat, it was decided to abandon the solid bonding of the screens and use single-point bonding – this was quite acceptable, since the cable line was short, and AC 50 Hz induced voltages on the screens did not exceed several Volts.

Although the temperature of the cables and terminations was lowered, the damage to the terminations had not stopped. Then three additional causes of damage were considered:
1️⃣ The terminations are too bent.
2️⃣ The terminations have the wire screens going up, which makes it possible for condensate to penetrate between the wires of the screen down into the termination.
3️⃣ The terminations are in the range of the reactor’s electric field, and this field distorts the field distribution inside the terminations.

To eliminate factors 1️⃣-2️⃣-3️⃣, the cable terminations were reinstalled 5 meters away from the reactors, closer to the transformer, where they were mounted vertically, without bends. Then the new 10 kV terminations were connected to the reactor using a rigid bushing of a 5 m length.

This solution made it possible to eliminate damage to the 10 kV terminations, but it is still not fully clear which of the three factors 1️⃣-2️⃣-3️⃣ was the main cause of damage to the terminations shown in the photo. Or maybe there were additional factors which were not mentioned?

Was it possible for electric field of the dry reactor (with open air-ventilated windings) to influence the cable terminations connected to it? I would be grateful if you could share your opinion in LinkedIn group “High Voltage Cable Lines“, and here is the link to the post about damaged terminations.

Thank you