Digital Elcid Testing On Generator Stator Core Application: Lab

The stator core of a typical generator is built from thousands of thin steel sheets (laminations) and the winding is formed from electrically insulated copper conductors bars which are embedded in slots between teeth around the bore .The core is held together by steel building bars, usually on its outside. The laminations are coated with a thin layer of electrical insulation to prevent eddy currents being induced between them by rotating magnetic flux produced by the spinning rotor.
Defects in the inter-laminar insulation cause fault currents to flow locally in the core. These currents can produce dangerous local overheating or hot spots in the damaged areas and the damage to the core may become progressively worse. In extreme cases sufficient heat is generated to melt small parts of the core and even modest rises in core temperature adjacent to the winding can result in the premature failure of the winding insulation. These hot spots should be detected and repaired during routine machine overhauls.
Earlier test methods known as Rated core ring flux test requires the core to be excited to its normal working level for a considerable time. The temperature rise of hot spots due to the core fault was then measured. In this method many disadvantages like running of high current / high voltage cables, mechanical stresses, possibility of increased damage etc. were found.