GB1254882A - A.c. electric motor apparatus - Google Patents

Abstract

1,254,882. Protective arrangements. COMPAGNIE DES COMPTEURS. 6 Dec., 1968 [6 Dec., 1967], No. 58205/68. Heading H2K. An asynchronous motor is provided with an arrangement for producing a signal representative of the slip of the motor by determining an impedance characteristic of the motor, the arrangement comprising means producing first and second signals related respectively to a current and a voltage of the supply to the motor and means for producing a third signal which is a function of the first and second signals and corresponds to an impedance characteristic relating to the slip of the motor. In the arrangement shown, the terminals 105, 106 and 107, 108 would be connected to current and voltage transformers (not shown) in the motor supply circuit. The current signal at terminal 105, 106 is applied through a current transformer 31 to an impedance 32, 33 representative of that of the motor when stationary. The current signal is also applied to a mutual inductance 30 having identical secondary windings 30b, 30c representative of a reference impedance. An isolating transformer 35 connected to the terminals 107, 108 has its secondary winding 35b in series with the winding 30c. The resulting voltages at points α, b are applied to a coincidence circuit formed by diodes 41, 42, 47, 48 connected to the base of a transistor 44 which conducts when the voltages are simultaneously positive. An indicating instrument 55 or a relay indicates or responds to the mean value of the collector-emitter voltage of the transistor 44. In a further arrangement, Fig. 3 (not shown), current and voltage transformers supply a rectifier comparator circuit. A relay connected to this circuit becomes operative to cause tripping of a circuit-breaker only after a time delay imposed by current-responsive relay, the delay being sufficient to avoid incorrect operation during the starting of a motor. Positive sequence current and voltage filters may be used in applications where the supply to the motor might be unbalanced.