At one of 66/11 KV Grid Sub-Station, it was observed with burning of CT clamp causing red-hot at the 66 KV CT Stud.
Observation
1. This CT (Current Transformer) was connected with the Gantry mounted beam structure and fitted with pad clamp of proper size.
2. The current on the CT was very less of 200 Ampere for the 600/1 Ampere CT.
3. As the stud was of annealed Copper metal, so required Bi-metallic strip was also wrapped through the clamps.
4. But it was observed with heating on the clamp and resulted with red-hot on the termination point.
5. So, the rectification action was taken. The clamp was removed for checking and found with burning pits on the bi-metallic strips.
6. No other deformity was observed.
Analysis
1. The Clamp was of proper size, connected with even bi-metallic strip in the system.
2. On checking it was found with burning of Bi-metallic strip due to generation of heat.
3. Before opening of the clamp, the tightness of the nuts was also checked and found in order.
4. Only one issue was there in the way of connection of the conductor jumper to the clamp.
5. The jumper was connected such the water droplet during drizzle rain was getting entry to the stud and getting deposited at the end mouth of the clamp and stud.
6. In this case the jumper connection was the culprit and deposition of the water droplet with gradual heating was resulting the red-hot and burning of the bi-metallic strip as like shown in the fig 2.A.
7. The jumper connection was changed to such that gradual sippage/ingress of water droplet got blocked. (Fig 2.B)
8. The new clamps were also changed using bi-metallic strips to avoid further heating of the clamps.