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Interfaces between insulating solids are generally weak regions particularly if the electrical stress is applied parallel to the interface. This paper presents the results from theoretical and experimental examinations on the partial discharge inception 50 Hz stress of the interface from XLPE samples between two Rogowski profile electrodes. Based upon the measurement of surface roughness, a model was developed to predict the average size of air enclosed surface voids using the elastic contact theory. The effect of surface roughness and mechanical interfacial pressure on partial discharge inception stress was investigated. The estimated results were found to be in good agreement with the experimental observations for interface with rough surfaces. However, in case of smooth surface, the estimated values were about 50 % higher than measured values, indicates probability of a few voids with larger size than the average estimated dimension.The surface roughness has a limited effect on the inception stress of interface, whereas increase of applied mechanical pressure from 3 bar to 8 bar raises the inception stress around 15 %.

Detection and location of any partial discharge signal requires an accurate frequency dependent cable model to correctly simulate the P.D. signal attenuation during its propagation in the cable. This model should be capable of simulating the semiconducting layers which have significant effects on P.D. signal attenuation and its propagation velocity. There is a substantial need for improvements in the flexibility of transient cable model through direct introduction of the two semiconducting layers in the cable model. This can be employed, in the next step to develop a 3 phase cable model for ATP. This paper has derived an impedance formula for the semiconducting layers. The propagation characteristics of the PD signal in a cable having two semiconducting layers are evaluated by applying the derived formula, and are compared with the related characteristics in a cable with no semiconducting layer. The propagation of a PD signal applied to the sending end of the core conductor is investigated. In application of the semiconducting pick-up sensor in the cable joint, there would be a considerable high frequency voltage across each semiconducting layers which can be used for study of PD phenomenon.

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