Detecting differential currents for fault current circuit breaker - using magnetic flux induced state change in medium not contg. secondary winding

摘要

The conductor being monitored is fed through an annular core summation current transducer (1) of weakly magnetic material. A magnetic flux caused by an fault current causes a state change in a medium (3), which does not contain a secondary winding. The operating point is set by premagnetisation by a uniform field premagnetisation device (4). The core has an air gap in which is arranged a magnetoresistive sensor forming the medium, e.g. a field plate. A current source is connected to the sensor and its voltage is evaluated. If the voltage exceeds a threshold a relay (10) is triggered. USE - For mains independent current protection switches.