| 摘要 |
PURPOSE:To ensure the cutoff of the shorted current within one cycle of the shorted current in the shorted fault at a low frequency region, by decreasing the field current of the synchronous machine at or below the frequency from which the temperature rise of an element due to the shorted current begins to increase rapidly during the regenerative braking. CONSTITUTION:A frequency detector 22 detects the frequency of a generator motor 7. An operation judging device 21 judges whether the generator motor 7 is starting or performing regenerative braking. When it is detected that the frequency (f) of the generator motor 7 becomes 50% or less during the regenerative braking by the detector 22 and the device 21, a field weakening command 30 is outputted to an exciting device 20 of the generator motor 7 and the field current If is decreased to 80%. The frequency (f) at which the field weakening command is issured to the exciting device and the decreasing width of the field current If are selected so that a temperature T of the element when an arm is shorted becomes an allowable element temperature or less which is determined under the condition that the fault current can be cut off at the time point when a forward voltage is applied after the conduction of one cycle of the shorted current. The optimum value should be selected for every case of the application. |
