Risk assessment of 170 kV GIS connected to combined cable/OHL network
420 kV
ADL
MOS
DYB
HVV
60 kVABØ
NVV
VHA
60 kV
FER
SBA
THØ
HVO
60 kV
60 kV
C11 km C2
6 km
C1
14,7 km
C1
8,7 km
C2
1,8 km
C2
10,6 km
T1
T1
T2
T3
R1
R2
C2
3,5 km
C2
20 km
S1 S1 S1 S1 S1
S1 S2
S1
S1
S2
S2
S2
S2S2
S2
S2
S2
T1
T1
S3
JER
S1 S1S1
T2
NVV
1 km UC
1,5 km OHL
60 kV busbar
s.a.
170 kV busbar
ABØ - Indoor GIS
TF2
TF1
Busbar
breaker
VHA
6 km
ADL
14,7 km
Transmission system around
city of Aalborg
Planned 170 kV network 2014
Simulation taking into account:-Lightning parameters-Lightning current magnitude and rate of rise- ÅBØ substation layout- Underground cable ÅBØ-NVV- Limfjord high tower crossing- Surge arrester precise model-Dynamic grounding impedance-Voltage-time characteristics of insulators-Implemented in PSCAD/EMTDC
Transformer LIWL:650 kV
Shielding failure and back flashover
considered for Limfjord high tower
crossing
Introduction
IEC safety factor 15% makes admissible overvoltage level for transformers 565 kV. This is seen to be exceeded!
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.
Risk Assessment
MTBF vs. front time, SF, open breaker.
MTBF vs. soil resistivity, SF, open breaker.
MTBF vs. soil resistivity, BFO, open breaker.
MTBF vs. soil resistivity, BFO, closed breaker.
MTBF vs. distance, SF, open breaker.
MTBF vs. distance, BFO, open breaker.
Conclusion
•MTBF above the acceptable limit of 1.000 years was obtained for all cases.•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.
Simulations
Front time[ µs]
Time to half[ µs]
Crest magnitude[kA]
Soil Resistivity[ Ωm]
SF 1,4 350 -41,8 92,5
BFO 10 350 -200 92,5
Simulation of a -41,8 kA 1,4/350 µs Shielding Failure Simulation of a -200 kA 10/350 µs Back Flashover
Varying lightning front time, SF, closed breaker.
Varying lightning front time, SF, open breaker.
Varying soil resistivity, SF, closed breaker.
Varying soil resistivity, SF, open breaker.
Varying cable length to transformer, SF, closed breaker. Varying cable length to transformer, SF, open breaker.
Surge front time Soil resistivity
Cable length between GIS busbar and transformer
Effects of surge front time, soil resistivity and length of cable leading to the transformer are investigated:
25.0front
11
24
−⋅
=
P
I
t
Soil resistivity
Front time Cable length
•Claus Leth Bak, Institute of Energy Technology,
Aalborg University, Denmark
•Jakob Kessel, Energinet.dk, Denmark
•Víðir Atlason, Landsnet, Iceland
•Jesper Lund, NV Net, Denmark
NVV
ADL
FER
HVV
5 km
ABØ
VHA
Overhead lines
Underground cables
170 kV outdoor substation
170 kV gas insulated substation
To HVOTo SBA
To DYB
To MOSTo THØ
To BDK
Aalborg
Limfjord
Area 3
Area 2
Area 1
Area 4
Denmark
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