scope:

Purpose

This Handbook describes the tests to be carried out on current transformers during both stage 1 and stage 2 commissioning (TP106).

The following tests must be carried out with strict adherence to ensure the integrity of the CT installation including the associated secondary circuits. Numerous system incidents have been encountered in the past relating to incomplete commissioning practices in this area.

The driving flux of a CT is always present when load current is flowing and therefore, if the secondary load is inadvertently disconnected (open circuit), very high voltages will be developed across the secondary winding with the risk of injury to personnel and damage to the equipment. Even with the primary circuit out of service a hazard may still be present because of the potential for current to flow in the CT in the event of a system fault or if the primary circuit is Earthed for maintenance (NSI12).