Switchgear undervoltage protection circuit - has relay and tripping drive preceded by limiter and additional protective relay

摘要

The monitoring circuit for a quick acting switch, which includes a low voltage release coil (1) controlled by a relay (12) followed by a release coil (2), interconnected with a motor drive (3), and including a switching transistor (11), has a limiter (6) located between a capacitor (4) across the load (5) and the first relay (12) acting as the low voltage monitor, which gives a switching signal when the voltage falls below a given value, for application to the relay system (1, 2). Connected to the limiter is a further relay (8) and switch (8a, 8b) arrangement controlled by a protective stage (7) as an additional safety device against a defect in the release mechanism or capacitor operation.