Fault detection system for single phase double insulated equipment - uses internal conducting screen and high impedance sensitive detection circuit

摘要

Electrical equipment (1) and an electronic switch (2) are connected to a single phase AC supply typically 220 volts via a bridge rectifier (3). An equipment housing is made from a sandwich material presenting insulating material inside and out (4) and a conducting screen (5) in the centre. A detector circuit (6) with high impedance is connected to the screen and the electronic switch. In the event of a fault or breakdown in one or both insulating layers conductivity across the sandwich layer increases resulting in a small fault current. This is registered through the detector circuit and results in a switching signal (7) from the electronic switch to isolate the equipment and an alarm signal (8).