Transient Overvoltages in Cable Systems Part 2 – Experiments on fast transients in cable systems

Abstract

In this thesis work, transient overvoltages in cable systems are characterized through both simulations in PSCAD and laboratory experiments on a system of limited extension at medium voltage. The system includes a longer and a shorter cable, a vacuum circuit breaker in between and two transformers, on the supply side and load side, respectively. Modeling of the transformer for proper representation of high frequency components is a key point, which is dealt with in detail in the report. For the laboratory setup, which includes two single-phase cables, an extensive analysis of the measurements done is presented. These include open and close operation of the vacuum circuit breaker at no load, with resistive load and inductive load, respectively. The experimental results are also compared with simulations made in the software PSCAD/EMTDC. A number of simulated cases for a similar system including threephase cables are also presented. It was found that certain conditions must be fulfilled in order for the reignitions to occur. In opening operations, for example, reignitions are more likely to happen if the contact separation starts just before the current zero crossing. However, for the closing operation it has been difficult to determine an instant in which the reignitions are more frequent.