VOLTAGE SENSING DEVICE CONNECTABLE TO THREE-WIRE OR FOUR-WIRE VOLTAGE SOURCES

摘要

An automatic transfer control device for selectively energizing an electrical distribution system from a pair of electrical power sources. The device includes voltage sensors for sensing electrical conditions on each of the sources. The device may be used on either three-wire or four-wire systems. The voltage sensors comprise an operational amplifier for artificially generating a phase-to-phase voltage from two phase-to-ground voltages. The artificially generated voltage is used to detect sequence reversal on the sources being monitored. Separate means are provided to select a source from which to draw control power for the device, the control power criterion being different from the transfer criterion.