Abstract
Traditionally, extra high voltage (EHV) transmission systems consist exclusively of overhead lines (OHL) but in the recent years the utilization of high voltage AC (HVAC) power cables is increasing due to environmental, political and operational aspects. To study the impact of HVAC power cables on temporary overvoltages and slow front transients, a simulation model of the large-scale network is required. Guidelines concerning the modeling detail for the surrounding network need to be established to ensure sufficient accurate results. Existing guidelines for purely OHL transmission networks may not be adequate since the integration of HVAC power cables shift the harmonic impedance of the network to lower frequencies and that can affect the extent of the needed simulation model. Much effort can be saved from obtaining detailed data for an extensive but proper model, but a less detailed model might not describe the network behavior with sufficient accuracy. In this study, simplification options are considered, for which the time to construct and analyze a simulation model can be reduced. The simplification options are compared with the reference model (full detail), and judged based on three indicators for the level of accuracy: frequency and amplitude of the main resonance, and maximum over-voltage. As a result, guidelines on the extent of the simulated network and in which detail the model has to be built are proposed. The inverse approach, i.e. increasing level of detail until simulation results hardly change leads to similar results, but requires equivalent short-circuit networks for the rest of the grid. The method is tested for the Dutch 380kV grid where an underground cable connection of 10.8km length is introduced in 2013 and a second connection is planned for 2017.
Highlights
In the past, overhead lines (OHL) were the dominant means for transmitting electrical energy at HV and extra high voltage (EHV) levels
Existing guidelines for purely OHL transmission networks may not be adequate since the integration of high voltage AC (HVAC) power cables shift the harmonic impedance of the network to lower frequencies and that can affect the extent of the needed simulation model
For transmission networks solely consisting of OHLs there are proposed guidelines concerning the modeling depth needed for accurate results when simulating energization and reenergization transients, which state that the detailed model of the system must comprehend the part of the network up to the second substations behind that of the operating circuit breaker [8]
Summary
OHLs were the dominant means for transmitting electrical energy at HV and EHV levels. For transmission networks solely consisting of OHLs there are proposed guidelines concerning the modeling depth needed for accurate results when simulating energization and reenergization transients, which state that the detailed model of the system must comprehend the part of the network up to the second substations behind that of the operating circuit breaker [8] These guidelines might not be adequate when HVAC power cables are integrated in the studied network due to their different electrical properties (higher capacitance) which shift the harmonic impedance of the network to lower frequencies. The present study involves circuit response on switching transients, the reliability of predicting over-voltages depending on the detail level and extent of the network model This involves resonance frequencies typically up to 10 kHz. There are reasons to limit the extension of the simulated network.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have