Abstract
“System modelling and harmonics”, starts by proposing a method that can be used when deciding how much of the network to model when doing a simulation of an energisation/restrike together with the possible limitations of the method.The chapter continues by analysing the frequency spectrums of cable-based networks which have lower resonance frequencies than usual because of the larger capacitance of the cables. At the same time, a technique that may help save time when plotting the frequency spectrum of a network is proposed.The chapter ends by proposing a systematic method that can be used when doing the insulation co-ordination study for a line, as well as the modelling requirements, both modelling depth and modelling detail of the equipment, for the study of the different types of transients followed by a step-by-step generic example.
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- 1.
The data were kindly provided by the Danish TSO: Energinet.dk.
- 2.
The exceptions are explained in Sects. 5.2.4 and 5.2.5.
- 3.
For more information on equivalent networks see Sect. 5.2.6.
- 4.
We do not intend to say that the standard is wrong, just that it is necessary to be careful for some configurations and be always critic of the results that are obtained in the simulations.
- 5.
The speed of the coaxial mode and intersheath mode shown in the table are slightly larger than the usual ones for reducing the risks of an incorrect estimation of the modelling depth.
- 6.
However, a transformer as well as the busbar in the other side of the transformer should be included in the model, when a transformer is inside or in the boundary of the area being modelled.
- 7.
Ideally it would be 0.5, but it is given a security margin for the case of a reflection reaching the cable immediately after the expected peak time, which can increase the voltage magnitude.
- 8.
This assuming that we are interested in an accurate simulation of the voltage. The same is not true for the current where it would be necessary to consider the intersheath mode currents generated by the coaxial current.
- 9.
It will usually be less than 80 m/μs (for example, it was around 60 m/μs for the example shown in Sect. 3.4.2).
- 10.
We should remember that we can use the precise intersheath mode velocity of each cable if we have enough information available.
- 11.
There is a small reflection because of the grounding of the cable’s screen.
- 12.
We are considering the presence of an ideal voltage source in this point.
- 13.
The term long distance is seen in comparison with the size of the line being energised. For a 1 km long line, 10 km is a long distance, but the same is not true for a 50 km long line.
- 14.
As an example, if we are modelling a transmission network we are not going to model also the several distribution networks, we will instead use an equivalent network.
- 15.
Remember that these values may change in future iterations of the standard.
- 16.
We have to remember that changes in the thicknesses also correspond to changes in the resistivity and permittivity as seen in Sect. 1.1.
- 17.
As previously explained in Sect. 5.2.5 we should have more lines than required in order to avoid this inaccuracy. In this case, this was not done on purpose in order to demonstrate the problem.
- 18.
References and Further Reading
Morched AS, Brandwajn V (1983) Transmission network equivalents for electromagnetic transients studies. IEEE Transactions Power Apparatus Syst 102(9):2984–2994 September 1983
Wiechowski W, Børre Eriksen P (2008) Selected studies on offshore wind farm cable connections—challenges and experience of the danish TSO. In: Conference on IEEE-PES General Meeting, Pittsburgh
Martinez-Velasco Juan A (2010) Power system transients—parameter determination. CRC Press, Boca Raton
Watson Neville, Arrillaga Jos (2003) Power systems electromagnetic transients simulation. IEEE Power and Energy Series, United Kingdom
Arrillaga Jos, Watson Neville (2001) Power system harmonics, 2nd edn. John Wiley & Sons, England
IEC 62067 (2004) Power cables with extruded insulation and their accessories for rated voltages above 30 kV (Um = 36 kV) up to 150 kV (Um = 170 kV)—test methods and requirements, 3rd edition
IEC 60840 (2001) Power cables with extruded insulation and their accessories for rated voltages above 150 kV (Um = 170 kV) up to 500 kV (Um = 550 kV)—test methods and requirements, 1st edition
IEC TR 60071-4 (2004) Insulation co-ordination–Part 4: Computational guide of insulation co-ordination and modelling of electrical networks
Cigre Joint Working Group 21/33 (2001) Insulation co-ordination for HV AC underground cable system. Cigre, Paris
Cigre Working Group C4–502 (2013) Power system technical performance issues related to the application of long HVAC cables. Cigre, Paris
Cigre Brochure 39 (1990) Guidelines for Representation of Network Elements when Calculating Transients, Working Group 02 (Internal overvoltages) Of Study Committee 33 (Overvoltages and Insulation Coordination), Cigre, Paris
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da Silva, F.F., Bak, C.L. (2013). System Modelling and Harmonics. In: Electromagnetic Transients in Power Cables. Power Systems. Springer, London. https://doi.org/10.1007/978-1-4471-5236-1_5
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DOI: https://doi.org/10.1007/978-1-4471-5236-1_5
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