JPH0468852B

PURPOSE:To detect the corona discharge during operation by a method wherein low resistance coating are provided close to main insulation layers of coils in a slot and metallic sensor electrodes are provided and connected to the coatings and the electrodes are connected to a corona measurement device. CONSTITUTION:Coil conductors 3, 3, covered by main insulation layers 4, are inserted into a slot 1 of a stator core 2 with spacers 6, 7, a layer spacer 8 and a lubrication layer 10 and fixed by a wedge 9. Low resistance coating layers 5 are formed around the main insulation layers 4 beforehand. Sensor electrodes 31, made of metallic materials, are provided between the low resistance coating layers 5 and the layer spacer 8 and connected to a corona measurement device 33 by a lead wire 32. High resistance metal, a slotted plate or a mesh electrode is used as the sensor electrode 31 in order to eliminate loss due to leakage flux. With this constitution, corona discharge can be detected during the operation and the deterioration of the insulation can always be observed.