A relay based high speed transfer scheme for UPS system

Abstract

A load transfer mechanism is essential for every UPS system whether it is on-line or off-line. In the present transfer system, a small, fast, 6-Ampere relay is used as a transfer switch. To achieve faster operation, a 6 V-relay coil has been chosen as a low voltage relay coil has a lesser number of turns, implying less inductance. Here the duration of the peak current of the relay coil has been assumed to be the duration for transfer of the load from main to auxiliary source. Only one change over relay contact is enough for the low power transfer switch. The faster relay has minimum physical gap between the contacts. It is not as fast as a static switch, implying relatively larger interruption time, especially at the time of load transfer between mains source to auxiliary. Using suitable speedup circuit, a 6-millisecond transfer time is achieved. This timing tallies with the simulated transfer time.