PURPOSE: To prevent thermal dererioration of windings and to reduce the number of coolers being operated during low load by an apparatus wherein winding temperature is detected and, when it is judged that the detected temperature has exceeded its allowable limit, coolant of lower temperature is mixed with the coolant being forcibly circulated to restrict a rise in the winding temperature.
CONSTITUTION: When a load current is rapidly increased, a control circuit 100 outputs an operation command 17 to operate coolers 12 in the number corresponding to the load condition based on a detection signal from CT 15. The detected signal is compared with an allowable winding temperature θp, and when it is judged that the winding temperature θw has exceeded the limit, a mixing command 101 is issued to a driver 25 of mixing means 20. Then, the driver 25 causes a shut valve 24 to be switched to the side of a bypass pipe 21, so that cooling oil 6' within a coolant tank 18 is mixed with cooling oil 6 being forcibly circulated. The cooling oil 6' is immediately supplied to a winding 3 of a transformer 1 to reduce the temperature of the cooling oil 6. Thus, the actual winding temperature θw will not exceed the allowable winding temperature θp.
YAMAGUCHI MASANORI
KUMASAKA TAKAO
INUI YOSHIAKI
FURUYA YUTAKA
YOSHIDA YOSHIO
KUSUMOTO TOSHIO
HITACHI LTD