Short circuit limiting equipment for multi-machine bus=bar - incorporates current transformer with switchable load and is controlled by electronic switch

摘要

The application is typically to a multi machine busbar feeding a variety of loads, installed on a ship or aircraft. The busbar is divided into a series of machine and load groups by short circuit current limiters and isolators. The limiter comprises a current transformer whose secondary winding output is rectified and applied to a circuit consisting of an electronic switch and parallel resistor. A supervisory equipment monitors the secondary current and regulates the electronic switch. Normally the switch is conducting and the secondary winding of the current transformer is short circuited. If the current rises beyond a set threshold due to a fault on the busbar, the switch is opened and the resistance is inserted into the secondary circuit. This sudden large increase in load causes a large volt drop across the primary winding, and the consequent increase in impedance limits the fault current. Very fast operation is possible with the electronic switch.