Since an electrical isolator is a mechanical switch, it often suffers from mechanical problems. To avoid such problems and to ensure reliable operations, proper maintenance of electrical isolators and earth switches is essential.
Isolators in a power system are those switches whose opened and closed positions are clearly visible. Normally we operate isolators in offload conditions. Although there is another type of isolators. We call this type as on load type isolators. We can operate these isolators, provided there must be a parallel path during operation.
The isolators have the main two parts. These are the insulating part and conducing part. So, we must take proper care for both of the parts.
Steps for Maintenance of Electrical Isolators
The following actions we need to take in the coerce of the maintenance of electrical isolators.
- We need to clean the support insulator body with removing salt cement and acid fumes if accumulated.
- Also, we need to inspect the contact surface. If we found any abnormality (burning of contacts), we must immediately replace the same with a new one. If the sign of burning is very small, we can remove those by rubbing with sandpapers.
- Also, we must check the proper alignment of the contact rods, etc during maintenance.
- We must check the tightness of bolts of the mechanisms as well as power connections and earth connections.
- By fully closing the isolators we need to check whether all the male contacts properly enter in the female contacts or not. If we find any abnormality we must adjust it immediately.
- Then we physically have to check whether the mechanical interlock is working properly or not. That means we have to try closing the earth switch after closing the isolator. If it is not possible physically, then we can ensure that the mechanical interlocking is all right. Otherwise, we need to check the mechanism and rectify it.
- Often, we need to lubricate the shaft bearing assembly including mechanical linkages of auxiliary switches.
- We may apply a thin layer of conductive lubricant on the contacts the auxiliary switches.
- We need to check the tightness off all the electrical control connections in the mechanism box. Also, we need to check the functionality of all auxiliary relays, in the mechanism box.
- We should measure the contact resistance of each contact of each phase. We may use a Digital Micro Ohm Meter for the purpose.
- Lastly, we must check the electrical interlocking scheme of each isolator and circuit breakers come under the interlocking scheme of that isolator.
Maintenance of Earth Switches
- We must check the alignment of the earthing blades.
- Also, we clean the blades including the female contacts of the switch.
- We need to check the aluminium and copper flexible bonds of the earth switch. If we find any defect, we should replace those without going for repairing. Because we should not compromise with the connection to the earthing.
- We also need to check for the proper tightness of the earthing connections of the supporting structure and mechanism box.
- We need to visually check the contacts, clean the control terminals in the marshaling kiosk.
- The space heater plays a significant role in marshaling kiosk. Because it keeps the inner space of the kiosk moisture-free. So proper checking of the healthiness of the space heater in the marshaling kiosk is essential.
- If we find any defect in the door gasket of the kiosk, we must repair or replace to avoid rainwater entry in the kiosk.
- Maintenance of Potential Transformer (PT and CVT)
- Maintenance of Minimum Oil Circuit Breaker
- Maintenance of SF6 Circuit Breaker
- Maintenance of Electrical Isolators and Earth Switches
- Maintenance of Current Transformer
- Maintenance of Lightning Arrestors (Lighting Arresters)