Abstract: A method of detecting faults in a traction motor installation having a plurality of AC traction motors powered from a common power source, each of the traction motors being connected by associated motor cables to a cable junction and the common power source being connected to the cable junction by main cables, includes disconnecting the power source from the main cables and performing initial short circuit to ground, short circuit between phases and leakage to ground tests on the traction motors through the main cables. When a fault is detected by the initial tests, at least one detailed test is performed by applying a predetermined voltage to the main cables and sensing current flow in the motor cables connected to each of the motors. The detailed test is one of a detail short circuit to ground test, a detail short circuit phase to phase test, and a detail leakage to ground test.

Abstract: A method of detecting faults in a traction motor installation having a plurality of AC traction motors powered from a common power source, each of the traction motors being connected by associated motor cables to a cable junction and the common power source being connected to the cable junction by main cables, includes disconnecting the power source from the main cables and performing initial short circuit to ground, short circuit between phases and leakage to ground tests on the traction motors through the main cables. When a fault is detected by the initial tests, at least one detailed test is performed by applying a predetermined voltage to the main cables and sensing current flow in the motor cables connected to each of the motors. The detailed test is one of a detail short circuit to ground test, a detail short circuit phase to phase test, and a detail leakage to ground test.

Abstract: A circuit for detecting a predefined reoccurring phase point an periodic electrical signal has an input stage which rectifies the signal into first and second complementary signals. A Schmitt circuit has an input connected to the rectifier stage and produces a first intermediate signal in response to the voltage of the first complementary signal. A complementary Schmitt circuit is connected to the rectifier stage and produces a second intermediate signal in response to the voltage of the second complementary signal. An output stage that is connected to the Schmitt circuit and the complementary Schmitt circuit, responds to the first and second intermediate signals by producing an indication of each occurrence of the reoccurring phase point in the periodic electrical signal.

Abstract: A circuit for measuring the frequency of an electrical signal includes a detector that senses a reoccurring phase point the electrical signal. A divide-by-M counter is connected to the detector and produces a control signal upon every Mth occurrence of the indication, where M is a positive number greater than one. A clock signal generator is provided. An output counter counts cycles of the clock signal between occurrences of the control signal and divides the count by M to produce an output count that corresponds to the frequency of the electrical signal.