LIVE-LINE WORKING AND EVALUATION OF RISK ON 400kV TRANSMISSION LINE

197 Pages·2017·2.92 MB·English

by  Pietro Martini

LIVE-LINE WORKING AND
EVALUATION OF RISK ON 400kV
TRANSMISSION LINE
A THESIS SUBMITTED TO THE UNIVERSITY OF MANCHESTER
FOR THE DEGREE OF DOCTOR OF PHILOSOPHY
FACULTY OF SCIENCES AND ENGINEERING
2017
Pietro Martini
School of Electrical and Electronic Engineering
2
Table of Contents
ABSTRACT…………………………………………………………………………....19
DECLERATION ……………………………………………………………………...20
COPY RIGHT STATEMENT …………………………………………………….....21
AKNOWLEDGMENT ……………………………………………………………….22
TERMS, DEFINATION…………………………………………………………… 23
CHAPTER 1............................................................................................................... 27
1.1. Introduction ....................................................................................................... 27
1.2. Introduction to Live-line Working ..................................................................... 28
1.3. Live-line Working Tools and Methods .............................................................. 28
1.3.1. Hot stick ..................................................................................................... 28
1.3.2. Bare Hand (Potential Method) .................................................................... 29
1.3.3. Helicopter Techniques ................................................................................ 30
1.3.4. Ground-Based Robots ................................................................................. 31
1.4. Live-line Working Risk and Challenges ............................................................ 32
1.5. Minimum Approach Distance (MAD) ............................................................... 34
1.6. Objectives and Conclusion ................................................................................ 35
CHAPTER 2............................................................................................................... 37
2.1. IEC 61472, Live-line Working Safety Standards ............................................... 37
2.2. IEEE 516-1995 Standard ................................................................................... 39
2.3. IEC 61472 Description of Calculation Procedure............................................... 41
3
2.3.1. Correction Factors ...................................................................................... 44
2.4. Impact of Correction Factors on MAD .............................................................. 52
2.4.1. At Tower .................................................................................................... 53
2.4.2. At Mid-Span ............................................................................................... 54
2.5. Discussion of Standards .................................................................................... 56
CHAPTER 3............................................................................................................... 59
3.1. Introduction ....................................................................................................... 59
3.2. Travelling Waves .............................................................................................. 60
3.2.1. Wave Velocity on Overhead Lines.............................................................. 61
3.2.2. Wave Velocity on Cables............................................................................ 65
3.2.3. Wave Reflection and Line Characteristics Impedance ............................... 67
3.3. Transient Classification ..................................................................................... 70
3.4. Lightning Overvoltage....................................................................................... 71
3.5. Review of Main Sources of Switching Overvoltages ......................................... 71
3.5.1. Line Energisation, re-energisation and Disconnection: ................................ 72
3.6. Switching Impulse Strength ............................................................................... 82
3.6.1. Effect of Wave shape .................................................................................. 82
3.6.2. The “U-Curve” ........................................................................................... 84
3.6.3. Wave Polarity ............................................................................................. 87
3.6.4. Effect of Atmospheric Conditions ............................................................... 89
3.7. Discussion and Conclusion ................................................................................ 90
CHAPTER 4............................................................................................................... 92
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4.1. Introduction ....................................................................................................... 92
4.2. Simulation Methodology ................................................................................... 93
4.2.1. PSCAD Goodness-of-Fit Testing for Weibull Distribution.......................... 96
4.3. Parameters Influencing the Overvoltage on Transmission Line ....................... 98
4.3.1. Transmission Line Effect ............................................................................ 99
4.3.2. Type and Length of cable Section ............................................................. 100
4.3.3. Cable Section Position on transmission Line ............................................. 102
4.3.4. Capacitor bank.......................................................................................... 107
4.4. Network for Overvoltage Studies..................................................................... 112
4.5. Overvoltage Simulation Results....................................................................... 115
4.6. Calculation of Minimum Approach Distance ................................................... 120
4.7. Influence of Atmospheric Conditions .............................................................. 123
4.8. Influence of Floating object on Minimum approach distance ........................... 126
4.9. Discussion ....................................................................................................... 129
CHAPTER 5............................................................................................................. 131
5.1. Introduction ..................................................................................................... 131
5.2. Live-line Working Risk Evaluation ................................................................. 132
5.3. Risk Assessment ............................................................................................. 133
5.4. Methodology for Risk Assessment (Standard Switching Transient) ................. 134
5.4.1. Stress on the gap ....................................................................................... 135
5.4.2. Strength of the gap.................................................................................... 136
5.4.3. Intersection area ....................................................................................... 138
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5.5. Methodology for Risk Assessment (Non-standard Switching Transient) .......... 140
5.6. Evaluation of Risk Based on Simulation Results.............................................. 142
5.7. Discussion: ...................................................................................................... 147
CHAPTER 6............................................................................................................. 149
6.1. Conclusion ...................................................................................................... 149
6.2. Impact of different Parameters on Minimum Approach Distance ..................... 151
6.3. Future Work .................................................................................................... 153
References......................................................................................................................156
7. Appendices........................................................................................................ 166
Word Count: 43474
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Table of Figures
Figure 1-1: Live-Line Work Using Hot sticks, A: Fibre Glass Ladder, B: Hot Stick, C:
Bare Hand [1.12] ....................................................................................... 29
Figure 1-2: Live-Line Work Bare Hand or Potential Method, Where the Linesmen Are at
Same Potential as the Live Part and Isolated From the Earth [1.13] ............ 30
Figure 1-3: Live Men on 400kV Using the Live-lines Helicopter Method (Pictures
Provided by National Grid) ........................................................................ 30
Figure 1-4: Single Pick Robotic Arm which captures the Energized Conductor above the
H-Frame Structure [1.14-1.15]. .................................................................. 31
Figure 1-5: Typical Live-Line Working Task [IEC 624/13].......................................... 35
Figure 2-1: Flow Chart Illustrating the Calculation Procedure for the Minimum
Approach Distance .................................................................................... 40
Figure 2-2: Flow Chart Illustrating the Calculation Procedure for the Minimum
Approach Distance .................................................................................... 42
Figure 2-3: Electrical Distance for 0-1000m altitude at L6 tower, With and Without
Floating Object .......................................................................................... 53
Figure 2-4: Electrical Distance for 0-1000m Altitude at Mid-span L6 Tower, With and
Without Floating Object ............................................................................ 54
Figure 3-1: Pi-section Presentation of Overhead Line and Cable .................................. 61
Figure 3-2: Small Section of Transmission Line ........................................................... 61
Figure 3-3: Simple PSCAD Power System Model ........................................................ 62
Figure 3-4: Surge travelling time: Top: E_sending; The Voltage at the Sending and
Bottom: E_receiving; The Voltage at the Receiving End of the Line .......... 65
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Figure 3-5: National Grid direct buried cable diagram .................................................. 65
Figure 3-6: Impulse Generator Used in PSCAD ........................................................... 66
Figure 3-7: Voltage at Sending Point (Blue Curve) Due to Current Impulse where Ea and
Eb are the sending and receiving voltages respectively .............................. 67
Figure 3-8: PSCAD Simulation Travelling Wave; Top: Voltage at Beginning, Bottom:
Voltage at the End of Transmission Line ................................................... 68
Figure 3-9: Behaviour of Voltage Travelling Wave at Transition Point ........................ 68
Figure 3-10: Sum of reflected voltage and current and sending waves .......................... 73
Figure 3-11: Voltage at The Sending and Receiving End Due to Energisation of 60km
Line on 400kV System............................................................................... 75
Figure 3-12: PSCAD Simulation Model of Trapped Charge ......................................... 77
Figure 3-13: Energising of a Line, Top; Without Trapped Charge, Bottom; With Trapped
Charge ....................................................................................................... 77
Figure 3-14: Voltage Due to Top; Energisation, Middle; Re-energisation, Bottom;
Disconnection ............................................................................................ 79
Figure 3-15: Oscillatory Transient Due to Interruption of Fault Current on PSCAD
Model- ES: Voltage Sending Point, EL: Voltage along the Line, Earc:
Circuit Breaker Arc Voltage. ..................................................................... 81
Figure 3-16: Standards Switching Impulse Where V50 is a half the time to crest of Crest
of a Transient Wave [4.1] .......................................................................... 82
Figure 3-17: U-Curves Obtained with Impulse Voltages of Various Time-to-Crests (Tcr
µs) Applied to Rod-Plane Gaps. Atmospheric Humidity in These
Experiments Was Varied [3.22, 3.23]......................................................... 85
Figure 3-18: A; Switching Impulse Flashover Voltage of Rod-Plane Gap, B; Estimation
of CRIEPI’s Equation ................................................................................ 86
8
Figure 3-19: Rod-Plane Gap; 1- Minute Critical Withstand AC and DC Voltages; 50%
Percent Spark Over Voltage with Standard and Long Front Impulses [3.26].
.................................................................................................................. 88
Figure 4-1: Model of Event Occurrence in Simulation ................................................. 94
Figure 4-2: Switching Overvoltage Distribution (pu).................................................... 94
Figure 4-3: Overvoltage Weibull Distribution Plot ....................................................... 97
Figure 4-4: Sample PSCAD Model of Transmission Line ............................................ 98
Figure 4-5: Overhead Model ...................................................................................... 100
Figure 4-6: PSCAD Model of Line-Cable Combination ............................................. 100
Figure 4-7: Change of Overvoltage at Beginning and End of Cable Section Due to
Changing the Length ................................................................................ 101
Figure 4-8: Overvoltage at Beginning and End of Cable Section vs. Cable Type ........ 102
Figure 4-9: Schematic Model of Transmission Line ................................................... 103
Figure 4-10: Time Required for Wave to Travel along the Cable................................ 103
Figure 4-11: Overvoltage, Sending (Blue Curve) And Receiving (Green Curve) With
Cable Section at Beginning of the Line .................................................... 105
Figure 4-12: Schematic Model of Transmission Line with Cable Section Place in the
Middle of the Line ................................................................................... 106
Figure 4-13: Overvoltage, Sending (Blue Curve) and Receiving (Green Curve) With
Cable Section at Middle of the Line ......................................................... 106
Figure 4-14: Maximum Overvoltage, Sending (Blue Curve) and Receiving (Green
Curve) with Cable-Line at End of Transmission Line ............................... 107
Figure 4-15: Series Capacitor Bank Modelling with a 41.91µF series Capacitor ......... 109
Figure 4-16: Overvoltage with 20% Series Compensation .......................................... 110
Figure 4-17: Overvoltage with 50% Series Compensation .......................................... 111
Figure 4-18: Overvoltage with 80% Series Compensation .......................................... 111
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Figure 4-19: A; PSCAD Model of Transmission Line, B; Schematic diagram of the
network ................................................................................................... 113
Figure 4-20: Top; P-E, Bottom; P-P. Influence of Length of Transmission Line on the
Minimum Approach Distance .................................................................. 125
Figure 4-21: Top; P-E, Bottom; P-P - Minimum Approach Distance Influenced by
Altitude and Fault Levels ......................................................................... 126
Figure 5-1: Risk and Hazard Explanation [5.1]........................................................... 131
Figure 5-2: Risk Management Process ....................................................................... 132
Figure 5-3: Live-Line Working Risk Evaluation Process ............................................ 134
Figure 5-4: Switching Overvoltage Distribution ......................................................... 135
Figure 5-5: Flowchart Illustrating the Steps Undertaken for Calculation of Gap Strength
................................................................................................................ 136
Figure 5-6: Air Gap Voltage Breakdown Probability .................................................. 138
Figure 5-7: Combination of Air Gap Voltage Breakdown Probability and Switching
Overvoltage Distribution.......................................................................... 139
Figure 5-8: Risk as the Function of Time to Crest ...................................................... 142
Figure 5-9: Risk of Failure as a Function of Time to Crest on Different Towers for Top:
P-E and Bottom: P-P Voltage................................................................... 145
Figure 5-10: Risk of Failure for P-E Voltage as the Function of Changing the Gap Size,
Bottom: The Zoom in Graph of the Top Graph ........................................ 146
Figure 7-1: Conductor Coordinates of Overhead Line- Refer to Table 59 ................... 169
Figure 7-2: PSCAD Fault Type and Time Selection Modules ..................................... 171
Figure 7-3: PSCAD Overhead Line Model ................................................................. 171
Figure 7-4: P-E Calculation Design ............................................................................ 172
Figure 7-5: P-P Calculation Modules ......................................................................... 172
10
Figure 7-6: Rod to Plane Sparkover versus Gap Length D, CRIEPI_ Figure 5-2 [2.23]
................................................................................................................ 193
Figure 7-7: Switching Impulse Flashover Voltage of Rod-Plane Gap, Estimation of
CRIEPI’s Equation .................................................................................. 194