| 摘要 |
PURPOSE:To reduce the noise generated by resonance by a method wherein, for the frequency command in accordance with the load condition or cooling condition of a transformer, the output frequency of a variable voltage frequency inverter is controlled in such a manner that it is relieved from the resonance point of the cooling of the transformer. CONSTITUTION:The load signal (a) detected by a current transformer 8 and a detector 9 is inputted to an arithmetic operation controlling section 10, the necessary cooling power corresponding to the load condition of a transformer 1 is calculated, and a signal which is turned to the output frequency of a variable voltage frequency inverter 7, with which the revolution number of the oil-feeding pump motor 3 and the fan motor 4 of a cooler 2 is sent to a level discriminating section 11. The level discriminating section 11 discriminates whether or not the above-mentioned signal is turned to the output frequency of the variable voltage frequency inverter 7 with which the cooler 2 resonates. When the signal corresponding to the resonance frequency, a control signal (b) is given to the variable voltage frequency inverter 5 in such a manner that the resonance point is avoided. |
