Electronic relay to protect motors and thyristors against symmet

Details Electronic relay to protect motors and thyristors against symmet Electronic relay to protect motors and thyristors against symmet

1993-12-09

1994-11-15

Deboer, Todd

Electricity: electrical systems and devices

Safety and protection of systems and devices

Motor protective condition responsive circuits

361 93, 3241581, H02H 708

Patent

active

053653947

ABSTRACT:
A protective electronic relay is disclosed of the type which includes a feed source with a one-phase transformer, rectifying bridge, filter condenser and voltage regulator. Pickups are provided where one-phase signals are generated, connected to some diodes, connected to some capacitors and to a zener diode for the purpose of obtaining rectified, filtered and limited signals with a voltage level proportional to the line intensity of the protected motor. A multiple microswitch connected to some resistors permits presetting of the voltage level and nominal triggering intensity of a relay. An R-C network that can be timed in various scales comprised of resistors a capacitor and another multiple microswitch allows adjustment of the triggering time constant and is applied to that voltage level at the non-inverting input of an operational amplifier whose inverting input is at a reference voltage. Upon the non-inverting input of the operational amplifier reaching the reference voltage, due to a symmetric overload, the output of the operational amplifier passes to logic state 1. This sends a positive signal to the gate of a thyristor, driving it into conduction and depolarizing the base of a transistor making it pass from saturation to cut-off. As a result a relay connected to the collector of the transistor is triggered, changing the state of its contacts and causing disconnection of the protected motor.

REFERENCES:
patent: 4345288 (1982-08-01), Kampf et al.
patent: 4584623 (1986-04-01), Bello et al.
patent: 4683513 (1987-07-01), Miller
patent: 4710844 (1987-12-01), Scott et al.
patent: 4967307 (1990-10-01), Dougherty

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