Transient behaviour modelling of underground high voltage cable systems

The behaviour of voltage and current transients when a high voltage (HV) cable is first energised is a problem of practical significance to utilities. Modelling of this behaviour on a suitable simulation platform is an attractive approach, in many cases, provided that the results closely match real-world behaviour. This thesis presents modelling and analysis of transients resulting from energisation of an unloaded cable using PSCAD®/EMTDC™ simulation software. An assessment of the applicability of existing frequency-dependent (FD) cable models is given. The impact of transients on a simulated cable system is also presented and discussed. In cable system modelling, system components must be accurately modelled, primarily the underground cable. Two common frequency-dependent cable models are based on the travelling wave method, namely the FD-Mode and FD-Phase models. These models are investigated by comparing their ability to predict energisation current transients resulting from the switching of an unloaded 132 kV underground cable. The simulated results are validated by comparison with the measurement data. It was found that, the FD-Phase model provides more accurate results compared to the FD-Mode model. This model is widely applicable and suitable for use in modelling a wide range of frequencies. The FD-Phase model was used in this study to analyse the distribution of overvoltages at sending and receiving ends of the cable system. Specifically, statistical analysis has been carried out correlating the overvoltage magnitudes induced and the closing behaviour of the circuit breaker (CB). Two statistical switching techniques have been applied, namely the deterministic and probabilistic approaches. Based on the approaches studied, results from probabilistic techniques are recommended owing to the fact that it is closer to reality.