This paper discusses cable modeling for long highvoltage ac underground cables. In investigating the possibility of using long cables instead of overhead lines, the simulation results must be trustworthy. Therefore, model validation is of great importance. This paper gives a benchmark case for measurements on a 400-kV cable system with cross-bonded sheaths. This paper describes in detail the modeling procedure for the cable system and compares simulation results with the transient field test results. It is shown that although the main characteristics of the waveforms are well reproduced in the initial transient, there are significant deviations between the simulation and measurement results. An analysis indicates that the main cause for the deviation is inadequate representation of the current distribution on conductors since the modeling approach does not take proximity effects into account. The measurement results can be received by contacting the first author of this paper.
Recent studies of long EHV cables show the importance of performing temporary overvoltage analyses. As the switching of EHV cables can trigger temporary overvoltages, it is important to find the dominant frequency component contained in the switching overvoltages of these cables. Since there are no theoretical formulas to find the dominant frequency, it is generally found by means of time domain simulations or frequency scans. The derivation of theoretical formulas has been desired as the formulas would be useful in verifying the results of time domain simulations or frequency scans. Additionally, the formulas could eliminate the necessity of building simulation models of some network components. In order to address this need, this paper derives theoretical formulas to find the dominant frequency in long cable energization overvoltages. The accuracy and practical usefulness of the formulas are confirmed by comparing with the results of time domain simulations.
The Danish power system is characterised by a high share of wind power production. Most of the wind power has so far been distributed onshore and connected to the lower voltage levels. The recent tendency is to group it in large offshore wind farms. The wind farms are often connected directly to the high voltage network via long AC cable lines compensated by shunt reactors. These cable connections impose some additional challenges that should be considered in the planning stage. This paper presents the recent experience of the Danish TSO with long cable connections of wind farms and shows the results of selected simulation studies made of the planned Horns Rev B wind farm connection.
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