Previous projects in conjunction with projects currently running have studied the use of capacitive couplers, Radio Frequency Current Transformers and Rogowski coils. The aim of this project is to assess the suitability of directional couplers for on line monitoring in comparison to established methods. A directional coupler is essentially a screened conducting plate placed on the outer layer of the semi-conducting material of the cable, with outputs from each end of the sensor being fed to a scope. Due to both the capacitive and inductive effects between the two plates one output from a sensor will be greater than the other, hence the direction from which the discharge emanated from can be determined. The advantage directional couplers offer over other methods is this two-channel output per each sensor, so discharge sites can be pin-pointed, however also means that twice as much data is collected and then needs to be analysed.