Abstract: A circuit for detecting the shorting of a diode in a circuit for rectifying AC current. A current transformer senses the current flowing through a diode. A DC bias current applied to the transformer secondary winding along with the unidirectional pulses normally passed by the diode cause saturation of the transformer core so that the normal current passed by the diode does not induce corresponding pulses in the secondary winding. In the event of diode shorting reverse current pulses will produce corresponding pulses in the secondary winding and those pulses are detected by a relay so that relay actuation occurs upon diode shorting.

Abstract: To detect system ground faults in a dual Y-connected output winding group polyphase alternator to direct current power supply system having direct current output circuitry isolated from a selected point of reference or ground potential, an electrical potential is applied across a selected point of reference or a ground potential and the alternator output winding group neutrals. A system ground fault completes a circuit through which this potential energizes the operating coil of an electrical relay having a pair of normally closed contacts connected in series in the alternator exciting field winding energizing circuit to effect the interruption of the alternator exciting field winding energizing circuit. To detect single phase operation faults, an auxiliary polyphase full-wave rectifier circuit is provided for each of the two alternator output winding groups.

Abstract: To detect system ground faults and shorted alternator output winding turn-to-turn faults, the series combination of a resistor and the operating coil of an electrical relay having a normally closed contact pair is connected between the neutrals of two parallel connected polyphase alternator output winding groups, the junction between the resistor and operating coil is connected through a resistor to ground and the normally closed relay contact pair is connected in series in the alternator exciting field winding energizing circuit. To detect open diodes in the main polyphase diode bridge type full-wave rectifier circuit, an auxiliary polyphase full-wave rectifier circuit having the operating coil and normally closed contacts of two relays in series in each leg is provided. Upon the failure of a diode of the main rectifier circuit, sufficient current to operate the corresponding relay in the auxiliary rectifier circuit is diverted therethrough.

Abstract: An AC generator or other AC source has two identical output sections which are connected through corresponding rectifiers to drive a DC load such as a group of DC traction motors connected in parallel for driving a locomotive. The rectifiers are selectively placed in parallel to provide a high current low voltage mode and in series to provide a low current high voltage mode, thus furnishing a wide range of voltage and current at a given power level to satisfy a broad range of motor requirements with a power source of limited size and capability. To effect smooth transition, one of the rectifiers includes SCR's to modulate the rectifier output voltage. During transition that rectifier is phase back to zero voltage, allowing the other rectifier to supply the full load requirements and then the rectifiers are switched from series to parallel or vice versa whereupon the modulated rectifier is returned to its full voltage.