Low power stator core fault testing using EL CID

Generator stators are made from thin laminations with interlaminar insulation, defects in which permit damaging currents to flow. Traditional test methods require a substantial supply to excite the core at rated magnetic flux, temperature rises due to faults being detected by various means. The test is performed with the rotor removed and requires significant time and labour. The alternative low flux EL CID test is increasingly used by manufacturers and utilities worldwide. With low excitation power, faults are detected electromagnetically. Safety constraints are reduced and a further advantage is the ability to detect faults behind windings. Taking much less time than the rated flux test, it may be the only test option practicable in an outage. In some instances, tests may be carried out with the rotor in. Applicable to both turbogenerators and hydrogenerators, differences are mainly confined to test implementation and interpretation of spurious effects.