Temporary Overvoltages due to Harmonic Resonance in Long EHV Cables

With the increasing recourse to cables in EHV networks the likelihood of low-order harmonic resonance is becoming of even more concern. The scope of this paper is to analyze the overvoltages due to harmonic resonance at the no-load energization of a prospective 400kV-50Hz double circuit submarine cable line. ATP-EMTP analyses are carried out to predict the possibility of occurrence of low-order harmonic resonance; a phenomenon more liable to happen in case of EHV cables connected to low short circuit power networks. The occurrence of resonances is sought for in the frequency domain and overvoltages are calculated in the time domain for the no-load energization of the EHV double circuit cable line. A sensitivity analysis is carried out varying the switching instants of line circuit breakers and the network short circuit power, while load and operating configurations are taken as a parameter. The effect of shunt reactor saturation voltage on the harmonic overvoltages is also investigated. Operational and design countermeasure are proposed.