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


Introduction 1

Estimate on Capacitive Current2

Analyse of Main Factors 3

Criterion on Grounding Mode Determination4

Examples Verification 5

Conclusion 6



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.



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.


Estimate on Capacitive Current 2

Introduction1




Conclusion 6



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.



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



Analyse of Main Factors3

Introduction1



Conclusion 6




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



Capacitive Current


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.



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




Grid Structure & Development


Connections， loads transfer capacity

Multi-power supply source

Reserve capacity of clients

Capacitive current growth in future


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




Introduction1


Conclusion 6




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


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.



Introduction1

Examples Verification5 Examples Verification

Conclusion 6






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


Conclusion6

Introduction1







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.



Thank You!Welcome to Shanghai

for EXPO 2010！


neutral point grounding modes for 10kv grids in shanghai

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