Transient thermal performance of e.h.v.-cable joints

In the first part of the paper, temperature changes in the straight joints associated with single-core oil-filled cables are determined for a number of transient operating conditions. These conditions include normal load changes and, in artificial-cooling schemes, the loss of coolant flow. In particular, 400 kV, 1935 mm2 cables with several different cooling systems, i.e. normally buried separate water pipe and integral cooling, have been analysed. The thermal field in the joint and adjoining cable is examined by means of a number of finite-element networks in two dimensions. In the second part, the onset of thermal instability in e.h.v.-cable systems with integral cooling has been predicted, using a digital computer. The studies show that both the time and position at which instability occurs can be obtained for a range of input conditions. The changes in temperature prior to instability do not indicate if and when instability will occur; thus the monitoring of cable and joint temperatures will not give useful prior warning of the onset of thermal instability.