Title :
The effect of ageing on the thermal conductivity of stator coil overhangs in medium generators
Author :
Wheeler, J.C.G. ; Lissenburg, M.L.
Abstract :
The authors evaluate coil overhang conductivity and see how it varied with cyclic operation at up to 155°C under accelerated conditions in a laboratory environment. The coils on a typical Class F 155°C generator of about 25 MW rating are cooled by air at a speed of 10-20 m/s and at a maximum temperature of 40-45°C. Heating in the overhang region derives from I2R losses in the copper. Typically the heat dissipation from the coil will be in the region of 2000 W/m2 of copper surface area. These conditions were reproduced as closely as possible in the ageing of two samples of overhang from a Class F machine. They were cycled on a two-hourly programme between 40°C and 150°C and for 2500 hours at this simulated the most severe feature of their operating regime over the period of their service lives. The coils were suspended at the end of a short wind tunnel. The air speed over the samples was approximately 10 m/s. Thermal cycling appears to have consolidated the insulation and increased the high temperature thermal conductivity
Conference_Titel :
Dielectric Materials, Measurements and Applications, 1988., Fifth International Conference on
Print_ISBN :
0-85296-359-9