Commonwealth Edison recently conducted a survey of the utility industry on how to determine energy created during arc flash events. The limited information available focused on selecting arc-rated clothing rather than determining the parameters for calculating the incident heat energy. ComEd’s research also revealed the industry was not aligned on the best methodology to use when estimating the incident heat energy, according to an article in Transmission & Distribution World magazine.
ComEd contacted the Kinectrics High Current Testing Lab in Toronto, Canada, and arranged to conduct primary underground cable and joint fault testing to measure the incident energy created during a fault.
Prior to the primary underground cable and joint fault testing, ComEd established two objectives:
- To measure the incident heat energy so accurate parameters, such as arc gap and adjustment factors, could be developed for ARCPRO to calculate the energy from a primary cable system failure in an enclosed space.
- To determine the ability of an electrical arc safety blanket to contain the arc, given attachment constraints.
The article goes on to explain the process and results of the testing, including the arc shape, the arc length and adjustment factors.
The test results found incident energy is dependent on the cable type and the arc length was much larger than anticipated. Standard arc lengths and adjustment factors were determined for use with the ARCPRO program. Electrical arc safety blankets block a majority of the incident energy produced during a 12.47-kV cable fault using typical fault current on the ComEd distribution system.
The increased level of protection could be achieved through minimal installation practices. Based on this testing, ComEd modified the level of arc protective clothing required for entry into manholes and is field-testing the use of arc suppression blankets.
