Arc flash detection apparatus and electrical system including the same

Abstract

An electrical system includes first, second and third busses; a first interrupter electrically connected between the first and second busses; at least one of a shorting apparatus operatively associated with the first or second bus, and the first interrupter comprising a trip coil; a current sensor to sense a fault current flowing in the first bus and responsively output a first signal; a number of light sensors to sense an arc flash operatively associated with a number of the first, second or third busses and responsively output a second signal; a second interrupter electrically connected between the second and third power busses and output a third signal; and a circuit to invert the third signal to provide a fourth signal, and to operate the at least one of the shorting apparatus and the trip coil responsive to an AND of the first, second and fourth signals.

What is claimed is: 
     
         1 . An electrical system comprising:
 a first power bus;   a second power bus;   a third power bus;   a first circuit interrupter electrically connected between the first power bus and the second power bus;   a shorting apparatus operatively associated with the first power bus or second power bus;   a current sensor structured to sense a fault current of at least a predetermined magnitude flowing in the first power bus and responsively output a first signal;   a number of light sensors structured to sense an arc flash operatively associated with a number of the first power bus, second power bus and the third power bus and responsively output a second signal;   a second circuit interrupter electrically connected between the second power bus and the third power bus, the second circuit interrupter being structured to move contacts from a closed position to an open position responsive to detecting an overcurrent condition and responsively output a third signal when the second circuit interrupter is about to clear a fault; and   a circuit structured to receive the first signal, the second signal, and the third signal and to selectively activate or not activate the shorting apparatus dependent on receiving at least one of the signals.   
     
     
         2 . The electrical system of  claim 1 , wherein the circuit is configured to activate the at least one of the shorting device or the first circuit interrupter responsive to receiving the first signal and the second signal without having first received the third signal. 
     
     
         3 . The electrical system of  claim 1 , wherein the circuit is configured to activate the shorting apparatus responsive to receiving the second signal without having first received the third signal. 
     
     
         4 . A circuit for use in an electrical system having at least one of a shorting device or a first circuit interrupter, a second circuit interrupter, and an enclosure, the circuit being configured to:
 receive a first signal indicative of the presence of a fault current in the electrical system;   receive a second signal indicative of the presence of light in the enclosure;   receive a blocking signal indicative of commencement of movement of the second circuit interrupter from a closed position toward an open position when the second circuit interrupter is about to clear the fault; and   selectively activate or not activate the at least one of the shorting device or the first circuit interrupter dependent on receiving at least one of the signals.   
     
     
         5 . The circuit of  claim 4 , wherein the circuit is configured to activate the at least one of the shorting device or the first circuit interrupter responsive to receiving the first signal and the second signal without having first received the blocking signal. 
     
     
         6 . The circuit of  claim 4 , wherein the circuit is configured to activate the at least one of the shorting device or the first circuit interrupter responsive to receiving the second signal without having first received the blocking signal. 
     
     
         7 . The circuit of  claim 4 , further comprising an auxiliary contact associated with the second circuit interrupter, wherein the blocking signal originates from the auxiliary contact. 
     
     
         8 . The circuit of  claim 4 , further comprising a device monitoring a trip shaft or a trip actuator of the second circuit interrupter, wherein the blocking signal originates from the device. 
     
     
         9 . The circuit of  claim 4 , wherein, upon receipt of the blocking signal, the circuit is configured to prevent activation of the at least one of the shorting device or the first circuit interrupter. 
     
     
         10 . A method of operating an arc flash detection system, comprising:
 receiving a blocking signal from a circuit interrupter indicative of movement of the circuit interrupter toward an open position, and   preventing operation of a shorting device in response to receiving the blocking signal.   
     
     
         11 . The method of  claim 10 , further comprising the step of operating the shorting device in response to: receipt of a signal indicative of an overcurrent condition in an electrical system, receipt of a signal indicative of the presence of light in an enclosure of the electrical system, and the failure to receive the blocking signal. 
     
     
         12 . The method of  claim 10 , wherein the blocking signal originates from an auxiliary contact associated with the circuit interrupter. 
     
     
         13 . The method of  claim 10 , wherein the blocking signal originates from a device monitoring movement of the trip shaft or a trip actuator of the circuit interrupter. 
     
     
         14 . The method of  claim 10 , further comprising the step of preventing operation of an upstream circuit interrupter in response to the blocking signal.