Fault Development in Wet, Low Voltage, Oil-Impregnated Paper Insulated Cables

Abstract

Few studies have been carried out on the failure processes of low voltage distribution cables. This is mainly due to their excellent track record of high reliability, and their use of traditional technologies. Growing quantities of aged cable within the network now make management of these assets an important issue. This paper describes measurements of leakage current, partial discharges and arc formation within 400 V oil-impregnated paper insulated cable structures which have been artificially wetted by immersion in bulk water. A generic picture is produced to show the gradual evolution from a leakage current through discharge growth to final catastrophic failure. Rapid changes to the core temperature of a wet cable are shown to produce transient, high levels of leakage current. It is also shown that by increasing the core temperature more slowly these high levels can be reduced. It is suggested that the characteristics of individual arcs within successive half cycles may provide a basis for predicting whether an incipient fault will lead to failure in the short term.

Breakdown Behaviour of Damaged Low-Voltage Cables: Laboratory Experiments and Field Experience

“…There is a small difference between the positive and negative current cycles. Roughly similar characteristics are also observed in [7]. If the arc admittance is modelled as a linear relation with the current, the coefficient represents the reciprocal arc voltage, i.e.…”

Transition from alternating current to direct current low voltage distribution networks

“…Furthermore by increasing the voltage to the limit of the cable ratings will further increase the capacity. Increasing the voltage will inevitably increase the electrical stresses in the cable and may present a reliability problem in aged cables, especially in cases where moisture is already present in the cable [26, 27]. It has been shown that the bipolar configuration can carry more power in both 3‐ and 4‐core cables making it the better choice.…”

Corrosion in Low-Voltage Distribution Networks and Perspectives for Online Condition Monitoring

“…Statistics on the reliability of the Dutch electricity grid [3], which are collected annually, show that failures in the LV grid typically originate from an external factor, such as digging. Two mechanisms that may occur after such a damage has been inflicted (without an immediate outage as a result) have been identified, being corrosion of aluminum conductors [1], [8] and dry-band arcing resulting in intermittent current peaks [9]- [12]. The former may occur when a damaged component of the LV grid is submerged for a longer period of time and the latter may occur when small amounts of water can penetrate the component or in case the water is periodically present in the cable.…”