Post on 22-Jan-2022
transcript
Implications of Fault Current Limitation for Electrical Distribution Networks
Steven M. Blair, Andrew J. Roscoe, Campbell D. Booth, Graeme M. BurtInstitute for Energy and Environment,University of Strathclyde, Glasgow, UK
steven.blair@eee.strath.ac.uk
Anita Teo, Chris G. BrightStrategic Research CentreRolls-Royce Plc, Derby, UK
chris.bright@rolls-royce.com
The 10th International Conference on Developments in Power System Protection, Manchester, 29th March – 1st April 2010
The future need for fault current limitation
Case study network
Scale to number of
UK substations
Establish a generation
scenario that satisfies an 80% drop in
CO2 emissions by 2050:
Determine statistical fault level contribution for future generation mix
(based on typical interfaces and their fault
current contributions)
Account for “independent nodes”
Combine normal distributions: provides probability (or percentage) of
substations with fault level violations
Multiply by the number of substations in the UK, for each
voltage level
Technical issues with fault current limitation
An approach has been developed for estimating the number of UK substations that may require fault current limitation. Itis based on the statistical analysis of existing fault level headroom, combined with the potential future presence ofdistributed generation (DG) and energy storage.
% requiredTotal energy
requiredPeak capacity
Wind 60 % 22.7 GWa 64.9 GW
Tidal 20 % 7.8 GWa 18.6 GW
Wave 10 % 4.1 GWa 11.7 GW
Solar 5 % 2.7 GWa 22.2 GW
Despatchablerenewables
5 % 1.9 GWa 3.1 GW
Storage n/a 5.1 GWa 20.5 GW
Mean number of substations requiring fault current limitation:
11 kV 33 kV
All three DNOs 282 42
DNOs A and B 320 75
Statistical analysis of
present-day fault level
“headroom” (from public
DNO documents)
During a fault, the superconductor in a resistive superconducting faultcurrent limiter (SFCL) will rapidly transit from the superconducting stateto a resistive state. However, up to several minutes may be required forrecovery to the superconducting state, which leads to several issues.
Remote faults, such as F1, may causeundesired operation of an SFCL; theDG must “ride-through” until theappropriate protection operates.
Fault occurs
Protection operates
CB fully open Reclosure
CB fully closed
Re-sync and reclosure
CB fully closed
Dead time
Dead time and SFCL recovery
Time
Typical reclosure
Reclosure with SFCL recovery
Non-fault transients, such as transformerinrush, may cause spurious operation of SFCLs.Hence, SFCLs located at the grid infeed mustbe rated to operate only for “near” faults:
Comparison of reclosure times for a transient fault
Potential solutions include:• The use of SFCLs that can recover immediately after a fault,
or under load• Network automation could manipulate normally-
open/closed points to reduce the fault level• Islanding may help to supply loads during SFCL recovery• Islanding can help keep transformers energised, minimising
the risk of SFCL operation due to inrush
Conclusions:• Suggests a worldwide market for fault current limitation, for
countries facing similar future DG connection• Does not include the potential “intangible” benefits of
SFCLs: increased interconnection; increased security ofsupply; increased power quality; and reduced losses
-3500
-2500
-1500
-500
500
1500
2500
3500
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1
Cu
rre
nt
(A)
-20000
-15000
-10000
-5000
0
5000
10000
15000
20000
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1.1Cu
rre
nt
(A)
Inrush vs. 11 kV bus fault
Inrush vs. 33 kV bus fault
Transformer inrush
Three-phase to earth fault
Auto-reclosure schemes (e.g.,after a transient or semi-permanent fault at F2) may becomplicated by the presence ofSFCLs in the network: the deadtime may be unduly increasedby an SFCL’s recovery time.
G
33 kV
275 kV
N/O bypass
Local loads
SFCL
DG
DG
Grid
F2
F1
11 kV
11 kV
Overhead interconnector
DG
Current at a grid infeed to the 33 kV bus