Power transfer unit for transferring power supplied to a load between

Abstract

Switching of three phase wye power can be efficiently completed without synchronization between two or more energy sources. The absence of synchronism can be overcome by switching one source off and then in a very short time frame restoring the power from the second power source. The duration of the outage can be controlled and minimized so that the load never loses energy long enough to cause an operational problem. The interruption time period in this description is limited to about 100 microsecond span; long enough to avoid interaction between the separate power sources, yet short enough to be transparent to the load. Electrical transfer of loads between power sources may be controlled precisely if the switching is accomplished using solid state electronic devices. Electronic switching is more reliable and does not generate the arcs during transfers that shorten the life span of mechanical contactors. Electrical switching devices are very efficient and handle high peak power levels; however, their internal losses dissipate heat. These resistive heating losses require cooling to avoid thermal destruction and this cooling adds significant weight and size penalties to a solid state switch. The power transfer unit (PTU) allows power contactors to transfer power from a number of power sources in a controlled manner to minimize disruption at the load. The PTU utilizes a logic controlled electronic switch in parallel with the contacts of a power control relay. The combination of an electronically controlled switch and an electro-mechanical relay provide precise switch timing with minimum power dissipation, in a package similar in size to that of a power relay alone. The physical package of the PTU relay may be similar in size to the present relay due to the elimination of arc quenching components and over-designed contacts.