DETECTOR FOR LAYER SHORT-CIRCUIT OF FIELD WINDING OF SYNCHRONOUS MACHINE

PURPOSE:To surely detect a slight rare short-circuit by inputting an output from a primary delay circuit connected to the output side of a field voltage detector and the output signal of a field current detector, computing a resistance value and obtaining the change of the resistance value and deciding alarming or non-alarming. CONSTITUTION:The field winding 2 of the armature 1 of a synchronous electric machine is supplied with power from an exciter 3 and excited. Field currents at that time are detected by a shunt resistor 4, and a current signal Ifs is acquired by a field current detector 6. Field voltage Vf at that time is obtained by a field voltage detector 5, and input to a primary delay circuit 7 as a voltage signal Vfs. A resistance value Rf is acquired by a resistance computing means 8 from an output V'fs from the primary delay circuit 7 and the signal Ifs, and input to a decision device 9. The decision device 9 outputs a signal S when the change of the resistance value Rf is brought to a fixed value or more, and an alarm is given by an alarm circuit 11 when the signal S is detected for a specified time or more by a timer 10. Accordingly, even a slight rare short-circuit is surely detected.