Short circuit detecting circuitry for three=phase machine - uses relays with resistors and filters to detect displacement voltages of third harmonic and fundamental frequency

摘要

A ring 6-phase transformer (2) has its prim winding (21) between a star point of the three-phase electrical machine (1) and earth. A three-phase transformer (3) has its prim, winding (31,33,35) connected together to an earthed star point, their other sides being connected to output terminal poles of the machine winding (11, 12, 13). The sec winding (32,34,36) of the three-phase transformer are connected to an open triangle. One terminal pole of the latter is connected to impedance, (41,42) forming a voltage divider (4). Another terminal pole (6) is connected to the sec winding (22) of the single-phase transformer and co earth. ADVANTAGE - Detects both earth and winding short circuit.