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Although extremely unlikely, if during a heavy through fault the incoming stab-in contact gets welded to the contact plate, then adopt the following procedure to remove the unit from the MCC and replace the stab-in contacts and the contacts plates.
When the contacts weld, do not try to force the unit out by exerting excessive force on the racking handle, as that would damage the racking mechanism.
Removal
De-energise the MCC completely by switching off the incoming feeders. ENSURE THAT THE BUS IS COMPLETELY DEAD.
In case of single front, open the rear doors to disconnect the contact plates from the dropper and remove the unit in the usual manner.
In case of double front section, approach the dropper contact plates of Front1 (F1) through the wire/way of Front2 (F2) after removing the barriers behind the droppers of F1.
Having removed the unit from the MCC, the drawout power contacts can then be easily removed from the unit.
Replacement
Bolt the new contact plates to the vertical droppers. Anti-corrosion contact grease must be used at the joint. Hindustan Petroleum MPL (EXXON) or its equivalent contact grease is recommended.
Replace the busbar barriers and supporting tray.
Check the insulation with the help of a Megger.
Follow the directions given under ‘Instructions Before Energising’.
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