A Real-Time Conductor Sag Measurement System Using a Differential GPS

A real-time and “direct” method of measuring the absolute value of sag on a transmission-line conductor using a differential global positioning system (DGPS) is presented. The method includes a real-time data-processing module integrated into the DGPS system. The GPS signals corresponding to physical movement of the midspan of a transmission-line conductor were obtained so that conductor-to-ground clearance could be recorded in real time. Several field tests were designed and implemented to test the DGPS method under varying conditions of the transmission-line current. A comparison of results obtained from the DGPS method with those from a laser-range finder indicates an accuracy of 1 in.