Online fault location on AC cables in underground transmission systems using sheath currents

• We provide field measurements of faults on a 38.4 km crossbonded cable.
• We present two methods for fault location on long crossbonded cables both using sheath current signals as input with very high accuracy.
• We discuss the practical issues that has to be taken into account when performing real-life fault location on cable systems.

This paper studies online travelling wave methods for fault location on a crossbonded cable system using sheath currents. During the construction of the electrical connection to the 400 MW off shore wind farm Anholt, it was possible to perform measurements on a 38.4 km crossbonded cable system. At 31.4 km, all cables were accessible which made it possible to apply a fault using an arc free breaker and measure the travelling waves at each end of the cable.On a crossbonded cable system, the sheaths are short circuited and grounded at both ends. This makes possible the use of low voltage Rogowski coils if the sheath currents contain the necessary information for accurate fault location. In this paper, this is examined by analysis of field measurements and through a study of simulations. The wavelet transform and a visual inspection method are used and the accuracy is compared. Field measurements and simulations are compared for testing the reliability of using simulations for studying fault location methods.