Overcurrent protection for communications equipment mains ferro-resonant transformer - involves protecting transformer with current and voltage sensing units controlling solid state series switch also functioning as current controller

摘要

The protection method is for protecting a ferro-resonant transformer having a transformer primary (2) mains-fed (3) via a switching unit (7) controlled by current (8) and voltage (9) sensing units, the whole forming a self-contained power supply unit (11), with output from the transformer secondary (5) to the load (6). The switching unit operates "open" or "closed", or in a variable impedance mode. For a nominal 230V supply, comparators in the voltage sensing unit (9) pass "open" signals for excursions outside the band 170-270V, but only permit reclosing if voltage returns within the ferro-resonant transformer's design range, 180-266V, to avoid auto-oscillation. The switching unit is based on three MOSFET power transistors, controlled, with OR-logic, by the output signals of the other two units. ADVANTAGE - Provides stable power supply even during network transient variations.