Maximum step out of AC cables to offshore installations

Abstract

The task of supplying an offshore installation with power is one that can be solved in several different ways. This thesis suggests a compensated AC subsea cable as the power from shore solution. At a length of 200km, the cable is stretched to its limits in order to provide sufficient power offshore. The simulation was carried out sing ATP, a graphical preprocessor to the ATP version of the Electromagnetic Transients Program (EMTP).

Using a fixed series and shunt compensation, it was possible to meet the demands of a 50MW offshore load. Even accounting for load rejection, the compensation meant the system was able to run within its operating limits. The need for both onshore and offshore compensation became apparent during no load conditions. At a transmission voltage of nearly 100kV, the voltage drop across the cable was no more than 7\%. The transmission losses across the whole system amounted to 11\%. There does however seem to be little encouragement for even longer cable lengths.

As the compensation of the system was realised, the problem of SSR came to the fore. Using a frequency scan, one could observe that the introduction of fixed series compensation in to the system introduced resonant SSR frequencies. This could partially be solved by using the premise of a very simplified STATCOM device connected to the system.