Water Tree Detection in Underground Cables Using Time Domain Reflectometry

This paper proposes to use time domain reflectometry (TDR) to detect water trees in underground residential distribution (URD) cables. Water trees are very dangerous to underground cables. They can grow for years without any change on the performance of the cable, and then can cause the cable to fault unexpectedly. Therefore, a method to detect water trees in URD cables is proposed in this paper. The method implements an optimal pulse generator placement algorithm on a distribution feeder for performing TDR. It can determine the exact location of a water tree in a cable, and it does not rely on the length of the cable or the type of cable used. The method can also detect multiple water trees on the same cable, and can be installed on existing systems, since it does not require data of the healthy system. It is a periodic monitoring system where pulses are sent throughout the year. The proposed method has been verified using multiple case studies on a real distribution feeder. Using TDR, optimal pulse generator placement, and subtraction of cables´ measured signal in time domain with similar measured signals a critical distribution feeder´s health has been monitored successfully.