Abstract
Presently there is a great interest in underground cable transmission lines in extra high and high voltage level networks. The undergrounding of the transmission system can lead to the decrease of the resonance frequencies resulting in high overvoltages and possible power system component damages. It is therefore necessary to analyze possible resonance problems in the mixed power transmission system. In this work a frequency dependent model for transmission systems is implemented and the frequency scan results are presented. In order to gain a better understanding of the nature and extent of the resonance, a resonance mode analysis is also executed. The proposed procedure is tested on two examples: a ten-node power system and the Swiss extra high voltage (EHV) power transmission system. Power systems comprising solely overhead lines and different variations of mixed power system are examined.
Highlights
Power transmission systems need to be expanded due to continuously rising demand and existing plans for increasing the generation share of renewable energy sources
4.2 Swiss extra high voltage (EHV) Power Transmission System The simulation of the actual Swiss EHV power transmission system was performed and the result of the frequency scan is shown on Fig. 6
The model was tested on two examples: the ten-node system and the Swiss power transmission system
Summary
Power transmission systems need to be expanded due to continuously rising demand and existing plans for increasing the generation share of renewable energy sources. Electronic components are often sources of harmonics and normally act like frequency-dependent current sources exciting system resonance frequency. Throughout this paper resonance frequency is understood as parallel resonance frequency (impedance is at its maximum). Because of their capacitive behavior underground (UG) cables can lead to a drop in resonance frequency. These facts increase significantly the risk of overvoltage in the system, which may in turn cause severe damage to network components. To prevent these problems a frequency analysis of the power transmission system should be done
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