A study of fast decoupled load flow for underground cable systems with ill-conditioned branches

The ill-conditioned branches of a cable system are of several types since both small reactance and large resistance are known to exist. Furthermore, capacitance of conductors to earth is much larger than that of its overhead line counterpart. As a result, voltage instability accompanied by convergence difficulties may occur. Both series and parallel compensation schemes have been investigated. The approach has been to use an empirical investigation to determine the optimal compensation levels. No successful cases can be reported for the parallel scheme. For the series scheme, the optimal compensation level is voltage class dependent. After compensation, convergence speed is much slower than for the overhead line case. The reasons are discussed