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Risk assessment of 170 kV GIS connected to combined
                      cable/OHL network
•Claus Leth Bak, Institute of ...
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Nordis Poster V02

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Nordis09 poster, lightning protection

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Nordis Poster V02

  1. 1. Risk assessment of 170 kV GIS connected to combined cable/OHL network •Claus Leth Bak, Institute of Energy Technology, Aalborg University, Denmark •Jakob Kessel, Energinet.dk, Denmark Simulations •Víðir Atlason, Landsnet, Iceland Front time Time to half Crest magnitude Soil Resistivity •Jesper Lund, NV Net, Denmark [ µs] [ µs] [kA] [ Ωm] SF 1,4 350 -41,8 92,5 Introduction BFO 10 350 -200 92,5 Danish power system has been decided to be cabled fully up to and including 170 kV. This makes planning of new network and GIS an urgent matter. Transmission system around city of Aalborg Simulation of a -41,8 kA 1,4/350 µs Shielding Failure Simulation of a -200 kA 10/350 µs Back Flashover To HVO To BDK To SBA IEC safety factor 15% makes admissible overvoltage level NVV Area 1 for transformers 565 kV. This is seen to be exceeded! Area 3 VHA To DYB Area 2 Effects of surge front time, soil resistivity and length of cable leading to ABØ the transformer are investigated: Aalborg HVV Surge front time Soil resistivity ADL Limfjord Varying lightning front time, Varying lightning front time, Varying soil resistivity, SF, Varying soil resistivity, SF, SF, closed breaker. SF, open breaker. closed breaker. open breaker. Denmark Cable length between GIS busbar and transformer Area 4 FER 170 kV outdoor substation 170 kV gas insulated substation To MOS To THØ Overhead lines 5 km Underground cables Planned 170 kV network 2014 Varying cable length to transformer, SF, closed breaker. Varying cable length to transformer, SF, open breaker. SBA C2 3,5 km DYB 420 kV JER Risk Assessment HVO S1 NVV S1 S1 S1 S1 S1 S1 S1 VHA S1 S1 S2 Soil resistivity 60 kV HVV ADL 60 kV T2 T2 S2 S2 S2 T1 T1 S3 ABØ 60 kV C2 1,8 km T1 T1 C2 C1 C1 10,6 km 8,7 km 1 km C1 C2 14,7 km 6 km R1 S2 S2 Transformer LIWL: S1 T3 S2 S2 60 kV MTBF vs. soil resistivity, BFO, MTBF vs. soil resistivity, SF, MTBF vs. soil resistivity, BFO, 650 kV open breaker. closed breaker. R2 C2 open breaker. 20 km S2 FER MOS THØ Front time Cable length Simulation taking into account: -Lightning parameters -Lightning current magnitude and rate of rise I tfront = - ÅBØ substation layout 1  24 ⋅  − 1 0.25 - Underground cable ÅBØ-NVV P  - Limfjord high tower crossing ABØ - Indoor GIS 60 kV busbar 170 kV busbar - Surge arrester precise model TF2 s.a. NVV -Dynamic grounding impedance Busbar 1 km UC breaker 1,5 km OHL MTBF vs. front time, SF, open MTBF vs. distance, SF, open MTBF vs. distance, BFO, open TF1 VHA breaker. breaker. breaker. -Voltage-time characteristics of insulators 6 km ADL 14,7 km -Implemented in PSCAD/EMTDC Conclusion Shielding failure and back flashover •MTBF above the acceptable limit of 1.000 years was obtained considered for Limfjord high tower for all cases. crossing •The steepness of the lightning surge did not prove to be a parameter of significance for this system. •Improved grounding resulted in a decrease of the voltage appearing at the transformer terminals. •Increased cable length yielded increased voltage magnitude to appear at the transformer terminals, for cable lengths up to 50 m.

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