Considerations for sending a breaker trip command over great distances for the purpose of arc flash mitigation

Abstract

When analyzing arc flash hazards in an electrical distribution system, it is not uncommon for equipment with high incident energy levels to be a great distance from the immediate upstream interrupting device. Adding more complexity to the problem is the fact that the immediate upstream interrupting device is at a higher voltage level, so the upstream protective device senses a small fraction of the actual arcing fault current. In some cases, this means that the arcing fault must be detected by a device at the low voltage equipment, and a trip signal must be sent several thousand feet to the upstream breaker. This paper analyzes the advantages and disadvantages of different media which can be used to transmit this transfer trip signal. The reader is advised of different methods of alarming to alert operations personnel that the protection scheme is not operational, either due to communications channel or protective device failure. Different design architecture concepts are explored to advise how to achieve maximum reliability, and different failure scenarios are examined to show how increased message delays for certain failures can dramatically increase incident energies.