Voltage-dividing DC circuit breaker and method

Abstract

The voltage dividing DC circuit breaker comprises serially connected high voltage and low voltage switches to carry load current. Serial capacitors are connected in parallel thereto and a crossed field switching device is connected in parallel to the low voltage switch. When the low voltage and high voltage switches are opened, current is forced through the crossed field switching device. When the crossed field switching device is turned off, the arcing high voltage switch is forced below its chopping current. The open circuit voltage is divided across the capacitors.

What is claimed is: 
     
       1. A voltage dividing DC circuit breaker for breaking a circuit against line voltage and having circuit breaking components of insufficient capability for withstanding open circuit line voltage comprising: first and second buses in said circuit breaker;   first and second serially connected switches connected between said buses and connected to an intermediate bus therebetween;   an electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.capable of offswitching all the current through said circuit breaker against voltage build up less than the open circuit voltage connected in parallel to said second switch between said intermediate and second buses; and   first and second serially connected capacitors connected to said first and second buses and at their intermediate point connected to said intermediate bus, so that in normal conduction current flows through said circuit breaker through said first and second switches in the closed condition, and when said first and second switches are opened, said first switch arcs and said second switch forces the circuit current through said electronic .Iadd.crossed field .Iaddend.switch .Iadd.device.Iaddend., and when said electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.is offswitched, current through said first switch decreases so that its arc extinguishes and current builds up with the standoff voltage divided between said first bus, and said intermediate bus and said second bus in accordance with the capacities of first and second capacitors. .[.2. The voltage dividing DC circuit breaker of claim 1 wherein said   
     
     
        electronic switch is a crossed field switch device..]. 3. The voltage dividing DC circuit breaker of claim .[.  2.]. .Iadd.1 .Iaddend.wherein said second capacitor has greater capacity than .[.sad.]. .Iadd.said 
     
     
        .Iaddend.first capacitor. 4. The voltage dividing DC circuit breaker of claim 1 further including a resistive circuit breaker branch comprising: a serial connection between said first and second buses comprised of a first resistor, and a third switch and a second electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.and a series connection of third and fourth capacitors connected in parallel to said third switch and said second electronic .Iadd.crossed field .Iaddend.switch device so that when said first and second switches are opened and said first electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.is turned off, current passes from said first bus to said second bus through said first resistor, said third switch and said second electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.to absorb energy in said first resistor and when said third switch is opened and said second electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.is turned off, voltage thereacross is divided in accordance with the capacity of said third and fourth capacitors.  .[.5. The voltage dividing DC circuit breaker of claim 4 wherein said electronic switch is a crossed field   
     
     
        switch device..]. 6. The voltage dividing DC circuit breaker of claim 4 further including a second resistive breaker branch connected between said first and second buses, said second resistive circuit breaker branch having the same type of components as said first circuit breaker branch. .[.7. The voltage dividing DC circuit breaker of claim 6 wherein the electronic switch in said second resistive circuit breaker branch is a 
     
     
        crossed field switch device..]. 8. The method of offswitching DC current flowing from a first bus to a second bus and where first and second serially connected switches are connected between the first and second buses and to an intermediate bus therebetween, with an electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.connected between the intermediate bus and the second bus, and with serially connected capacitors connected between the first and second buses and to the intermediate bus, comprising the steps of: permitting conduction through closed first and second switches for current flow from the first to the second bus;   opening the second switch to force current flow through the .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.so that the second switch ceases conduction;   opening the first switch so that it continues conduction of the circuit current through arcing;   turning off the electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.so that the current through the first switch is reduced sufficiently low so that arcing of the first switch deionizes; and   dividing the voltage rise across said first switch and said electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.resulting from cessation of conduction through said first switch and said electronic .Iadd.crossed field .Iaddend.switch .Iadd.device .Iaddend.in accordance with the series capacitors connected in parallel thereto.