Distributed measurement of conductor temperatures in mine trailing cables using fiber-optic technology

Mine trailing cables operated above safe thermal limits can cause premature insulation failure, increasing electrocution and fire hazards. Previous US Bureau of Mines (USBM) Pittsburgh Research Center research showed that, under static test conditions, electrical current levels permitted under present regulations may not limit cable temperatures to less than the 90°C rating of reeled trailing cable. The USBM began a study of thermal characteristics of reeled trailing cable using dynamic test conditions more representative of field conditions where operators constantly reel in and pay out cable. This research is in support of efforts by industry associations and the Mine Safety and Health Administration to establish safety guidelines for cyclically rated reeled machines. The paper describes a unique approach to measuring temperatures within reeled cable under dynamic test conditions. Fiber-optic sensors embedded within the metallic conductors measure temperatures at 1-m intervals along the entire length of cable. Temperature measurements are reported to be accurate to within ±1°C. The test setup requires access to only one end of the trailing cable, allowing researchers to freely reel in and pay out cable while temperature measurements are made, simulating field conditions. Manufacture of a fiber-optic-embedded trailing cable is described along with initial test results that indicate the fiber optic approach is viable