PURPOSE: To minimize the total loss of a transformer by a method wherein the signals of a load current and oil temperature of the transformer are inputted and are converted into the signals proportional to a loss of a main body thereby controlling a variable voltage and variable frequency inverter so as to minimize the total loss for operation of an electric motor for cooling.
CONSTITUTION: The transformer 1 for an electric power is provided with the current transformer 2 for detecting a load current and the temperature sensor 3 for detecting an oil temperature. Also, the electric motor for cooling of a cooling device 4 for a transformer is controlled by a variable voltage and variable frequency inverter 60. A control circuit comprises a signal input circuit 10, an analog calculator 20, an optimization coefficient setting circuit 30, a composition circuit 40 and an output circuit 50. The calculator 20 calculates the outputs of a load current signal V1, an oil temperature signal T and an unloading loss setting device 23 and outputs the main body loss signal composed of the total of the unloading loss and the loading loss corrected the temperature. The circuit 30 inputs the output of the calculator 20, a signal T and the d.c. voltage for setting a constant to determine the optimization coefficient for minimizing the total loss. Thus, an external surge voltage and an electrical noise prevent an operation error thereby minimizing the total loss of the transformer.
SAKAKI KIYOSHI
ABE MASAAKI
| JPS58225618A | 1983-12-27 |