Calculation of Grounding Grids Parameter at Arbitrary Geometry
NEUTRAL POINT GROUNDING MODES FOR 10KV GRIDS IN SHANGHAI
Transcript of NEUTRAL POINT GROUNDING MODES FOR 10KV GRIDS IN SHANGHAI
Prague, 8-11 June 2009
NEUTRAL POINT GROUNDING MODESFOR 10KV GRIDS IN SHANGHAI SHINAN AREA
Weibin Wang
Shinan Power Supply Company of SMEPC, P.R.China
2009-6-11
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Introduction 1
Estimate on Capacitive Current2
Analyse of Main Factors 3
Criterion on Grounding Mode Determination4
Examples Verification 5
Conclusion 6
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
1. Introduction
Shinan Area
(48% of Shanghai)
Table 1 The Growth of Sold Electricity
6.14%11.37%11.7%17.12%Growth(%)
34.5532.5529.2226.16Sold Electricity(billion KWh)
2008200720062005Year
2005 2006
Sold Electricity (billion)
26.1629.22
2007 2008
32.55 34.55
Introduction of Shinan Area
Because of the worldwide financial crisis, the sold electricity declined in 2008.
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
1. Introduction
Table 1 The Capacitive Current of Some Typical Substations
22%7272.72468226%2 / 846.28Ⅲ
21%6849.32567229%2 / 741.97ⅡJiuting
32%7998.81692429%2 / 751.43ⅢSheshan
46%11149.31293450%4 / 851.13ⅠRongxin
93%21696.4170290%9 / 1086.93Ⅱ
74%21016.8727180%8 / 1092.23ⅠQichang
34%8363.11597067%4 / 657.75ⅡShuyin
71%12922.4519957%4 / 761.72Ⅱ
77%16749.2490275%6 / 863.26ⅠGuangang
72%9666.9375567%4 / 649.96Ⅲ
53%9633.8840857%4 / 766.81ⅡBaonan
59%10090.9704543%3 / 776.64Ⅲ
55%11396.3942043%3 / 775.48ⅡLi’an
43%10145.71337850%4 / 875.52Ⅲ
72%11433442750%4 / 891.46ⅡYindu
CableLength
Rate
Cable Feeders Length
(m)
Overhead Line Feeders
Length (m)
Cable Feeders
Rate
Cable Feeders/ All Feeders
Capacitive Current (A)
10kV Bus No.Substations
Rapid Growth of Capacitive Current
Increased rapidly even to 100 A.
Over-voltage and potentialaccidents when single phase earthed.
Prague, 8-11 June 2009
Estimate on Capacitive Current 2
Introduction1
Analyse of Main Factors 3
Criterion on Grounding Mode Determination4
Examples Verification 5
Conclusion 6
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
2. Estimate on Capacitive Current
Why to estimate the capacitive current?
Formulas
Based on the actual capacitive current values, wefit out the formulas with an acceptable error limitrange for estimating other capacitive currents in
choosing the grounding mode.
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Table 2 Comparison between Estimate and Actual Values of Capacitive Current
12922.441.2-2.71%60.04661.72Ⅱ16749.261.21.46%64.18963.26Ⅰ
Guangang
10090.931.6-5.69%72.27976.64Ⅲ11396.331.61.80%76.83675.48Ⅱ
Li’an
10145.741.83.08%77.84875.52Ⅲ1143341.8-0.97%90.57791.46Ⅱ
Yindu
10732.611.30.78%58.30458.76Ⅲ7739.801.3-6.11%37.80040.26Ⅱ
Kungang
7998.811.62.91%52.93051.43Ⅲ10326.401.6-2.65%62.01963.71Ⅱ
Sheshan
7272.721.6-3.14%44.82846.28Ⅲ
6849.321.6-3.24%40.61141.97ⅡJiuting
Cable Length(m)
Cable Feeders Number
αErrorEstimate Value(A)
Actual Value(A)
10KVBus No.Substation
The errors are acceptable.
2. Estimate on Capacitive Current
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Analyse of Main Factors3
Introduction1
Criterion on Grounding Mode Determination4
Examples Verification 5
Conclusion 6
Estimate on Capacitive Current2
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Device Insulation Level
Feeders Rate & Length Rate of Cable
Capacitive Current
Grid Structure and Development
Reliability+Cost/Benefit
3. Analyse of Main Factors
Core and aspects for analyse and balance
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Capacitive Current
3. Analyse of Main Factors
ro L
BN
C
ACa Cc Cb
Ic ↗,the over-voltage may increasewhen single phase grounded, potentialaccidents.Ic ↗,it maybe influence the dynamic compensation ability ofthe arc suppression coil.
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Cable feeders rate ↘ ,overhead lines rate ↗ ,instantaneous single phase earthing faults ↗ ,the grounding mode through coil is more suitable
Length rate is a supplement for a accurate and general description of the actual complicated grids
Cable feeders rate ↗ ,overhead lines rate ↘ ,instantaneous single phase earthing faults ↘ ,the change from coil to low resistance will lead to few influences on reliability
Reliability
Feeders Rate & Length Rate of Cable
3. Analyse of Main Factors
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Grid Structure & Development
3. Analyse of Main Factors
Connections, loads transfer capacity
Multi-power supply source
Reserve capacity of clients
Capacitive current growth in future
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 20093. Analyse of Main Factors
Lightning over-voltage curve
They can’t bear the over-voltage
Accidents maybe occur which may lead to a long time blackout
Great cost and difficulty to rebuild these old substations and equipments in large scale
Low resistance mode is more suitable
Poor insulation:
Capable of bearing a higher over-voltage
Grounding through arc suppression coil mode is more suitable for a better reliability
Better insulation:
Equipments Insulation Level
Working on site
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Criterion on Grounding Mode Determination4
Introduction1
Examples Verification 5
Conclusion 6
Estimate on Capacitive Current2
Analyse of Main Factors 3
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 20094. Criterion on Grounding Mode Determination
Pure Cables Grid: Cable Feeders Rate 100%
ο/Cable Length Rate: ≥80%
ο/οCable Length Rate: <80%Cable Feeders Rate: > 80%
ο/οCable Length Rate: >80%
ο/ο/οCable Length Rate: [50%,80%]
ο/οοCable Length Rate: <50%Cable Feeders Rate:[50%, 80%]
ο/οοCable Length Rate: ≥50%
οοοCable Length Rate: <50% Cable Feeders Rate: <50%
οοPure Overhead Lines Grid: Cable Feeders Rate 0%
> 100[50,100]< 50Capacitive Current (A)Grid Situation
ο: Arc suppression coil : Low resistance
ο/ :To be decided depending on grid structure, loads transfer capacity, insulation level, et al.
Mix
ed G
ridCriterion in Different Power Grids
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 20094. Criterion on Grounding Mode Determination
The criterion has been promulgated after discussedby experts in 2005.
The criterion becomes a guidance for adjustment ofgrounding modes.
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Introduction1
Examples Verification5 Examples Verification
Conclusion 6
Estimate on Capacitive Current2
Analyse of Main Factors 3
Criterion on Grounding Mode Determination4
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Low Resistance in the Transformer Room in Xuefu substation
5. Examples Verification
The grounding mode was adjusted to low resistance in December 2007.
It has run good still now.
Rebuilding & Operation
Prague, 8-11 June 2009
Conclusion6
Introduction1
Estimate on Capacitive Current2
Analyse of Main Factors 3
Criterion on Grounding Mode Determination4
Examples Verification 5
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
6.Conclusion
1
Neutral point grounding modes should be accorded with the actual situation of power grid.
2
With the development of regional economy and power structure, the grounding modes should be adjusted in timely.
3
The criterion has been proved feasible by two actual substations, and it will be implemented widely in future.
Weibin Wang-China Session 3 Paper 0132
Prague, 8-11 June 2009
Thank You!Welcome to Shanghai
for EXPO 2010!
Weibin Wang-China Session 3 Paper 0132