HVDC BACK TO BACK CONNECTION FOR
POWER EXCHANGE BETWEEN ELECTRICAL GRIDS
by
MD. ARIFUR RAHMAN
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING
DHAKA UNIVERSITY OF ENGINEERING AND TECHNOLOGY
GAZIPUR
December-2014
HVDC BACK TO BACK CONNECTION FOR
POWER EXCHANGE BETWEEN ELECTRICAL GRIDS
A Project Report
Submitted in partial fulfillment of the requirements for the degree of
Master of Electrical and Electronic Engineering
By
MD. ARIFUR RAHMAN
Student No: 022219 Session: 2003-2004
Supervised By
Dr. Md. Bashir Uddin
Professor
DEPARTMENT OF ELECTRICAL AND ELECTRONIC ENGINEERING
DHAKA UNIVERSITY OF ENGINEERING AND TECHNOLOGY
GAZIPUR
December-2014
Declaration
It is hereby declared that this project or any part of it has not been submitted elsewhere for the award of any degree or diploma.
Candidate’s Signature
(Md. ArifurRahman)
ii
Acknowledgement
It is a great pleasure of the author to acknowledge respect and gratitude to the supervisor Dr. Md. Bashir Uddin, Professor, Department of Electrical and Electronic Engineering, DUET, Gazipur, for his kind cooperation, constant encouragement, valuable advice and guidance throughout the project work. Dr. Md. Bashir Uddin provided with information, comments, corrections and criticisms pertaining to the preparation of this project hand note. Without his whole-hearted supervision, this work would not have been possible.
I am grateful to Dr. Md. AnowarulAbedin,Professor & Head, Department of Electrical and Electronic Engineering for providing the opportunity of completion of M. Engineering degree through extending my student-ship.
I am thankful to Project Director, Manager and Engineer Colleagues of Grid Interconnection Project, Power Grid Company of Bangladesh Ltd. for providing the information against HVDC and Grid Interconnection.
I am also thankful to the Engineers of Siemens AG Germany, COBRA Instalaciones Y Servicios Spain and Power Grid Corporation of India Ltd. who have provided the information by training on HVDC station, AC transmission line and Grid Interconnection.
I am grateful to my family and friends who have provided support and encouragement during my studies.
Finally I am grateful to Almighty Allah that I have completed the project successfully.
iii
Abstract
The demand of electrical power reserve capacity in Bangladesh is increasing continuously day by day. This has led to increase in the generation and transmission structure to meet the increasing demand. The imperatives of supplying energy have led to the establishment of generating stations. An alternate way to meet the requirements is to import electrical energy from neighboring countries like India, Nepal, Bhutan,
Myanmar etc. To meet the growing demand for electricity and keep the country’s
economic growth unhurt, the Bangladesh government is taking different strategies to minimize the difference between demand and supply of electricity and importing electricity from India is one of them. The regional cooperation is necessary for development and to strengthen South Asian union, country and their motto of cooperation, long term economic analysis etc.
In technical consideration electrical energy will be imported through grid interconnection system with HVDC link. However, as generation and utilization of power remain at alternating current, for this the HVDC link requires conversion at two sides, from AC to DC at the sending side called rectification and DC to AC at the receiving side called inversion. For long distances DC line is required in between rectification and inversion
station. In economical consideration, the distances less than “break even” value, HVAC
transmission tends to be economical than HVDC transmission and more expensive for longer distances.For short distance two grids should be connected with AC transmission line, where two converter stations are at one end of the line called “HVDC back to back station” and AC switching station at the other end. In back to back DC link’s the rectification and inversion processes are carried out in the same converter station mainly in the same building.
iv
The development of solid state electronics paved the way for facilities the conversion of high voltage AC (HVAC) to high voltage DC (HVDC) and vice-versa in power system operation. The converters use high powered thyristors connected in series to give the required voltages. For reduction of number of series connected thyristors, the AC voltages are reduced by step down transformers in both of the AC sides. For constant AC voltages at both of rectifier and inverter ends, transformers are used with On Load Tap Changing (OLTC) mechanism. In order to obtain smooth DC in AC to DC conversion process, DC filters or smoothing reactors are used in between rectifier and inverter. Due to generation of harmonics caused by AC to DC and DC to AC conversion, AC harmonic filters are used at both of the AC sides.
The physical process of conversion is such that the same station can switch from rectifier to inverter by simple control actionby changing firing angle of thyristors, thus facilitating power reversal.Hench the HVDC back to back station can be called power exchange center and used in transmission section for interconnection between grids.
v
Contents
Page No.
Chapter – 1: Introduction
1.1 1.2
Introduction Objectives
….
13
….
Chapter – 2: Power Grid Interconnection
2.1 2.2 2.3 2.4 2.5 2.6 2.7
Interconnected Power Grid
…. …. …. …. …. …. …. …. …. …. …. …. ….
4
General Benefits of Grid Interconnection Economics of Grid Interconnection
57
Features and Functions of HVAC and HVDC Comparison of HVAC and HVDC
910 11 12 13 14 15 16 16 17
Advantages and Disadvantages of HVDC Possible Configurations for HVDC Interconnection 2.7.1 HVDC Connection with DC Overhead Line 2.7.2 HVDC Connection with DC Sea Cable 2.7.3 HVDC Back to Back Connection
- HVDC Link in Neighboring Country
- 2.8
2.8.1 HVDC Link with Overhead Line in India 2.8.2 HVDC Back to Back Connection in India
Chapter – 3: Back to Back Converter Station
- 3.1
- Converter Station Layout
…. …. …. …. …. …. ….
19 20 21 22 23 24 26
3.1.1 Converter Station Equipment
- AC Switch-yard Equipment
- 3.2
- 3.3
- AC Filter, Shunt Capacitor and Shunt Reactor
3.3.1 Necessity of AC Filter
3.4 3.5
Converter Transformer in HVDC System DC Filter/ Smoothing Reactor
vi
- 3.6
- Thyristor Valve
…. …. ….
27 27 29
3.6.1 Thyristor Valve Layout 3.6.2 Physical Arrangement of Thyristor Valves 3.6.3 Power Thyristor and Thyristor Evolution 3.6.4 ThyristorSnuber Circuit
…. ….
31 32
- 3.6.5 Grading Resistor and Thyristor Monitoring Electronics ….
- 34
35 36 37
3.6.6 Grading Capacitor
…. …. ….
3.6.7 Saturable Reactor 3.6.8 Thyristor Valve Cooling System
Chapter – 4: HVDCThyristor Converters
- 4.1
- HVDC Link between AC Grids
…. …. …. …. …. …. …. …. …. …. ….
39 40 41 42 43 44 45 46 49 51 53
4.1.1 DC Voltages at Both Converters are Positive 4.1.2 DC Voltages at Both Converters are Negative Three Phase Twelve Pulse HVDC Configuration Three Phase Twelve Pulse Converter
4.2 4.3
4.3.1 Operation Sequence for Twelve Pulse Converter
- Three Phase Six Pulse Converter
- 4.4
4.4.1 Operation Sequence for Six Pulse Converter
- Converter DC Voltages
- 4.5
4.6 4.7
Converter Operation as Rectifier and Inverter AC Line Current for 12-Pulse Converter Operation
Chapter – 5: Converter Controland Protection
5.1 5.2 5.3 5.4
Control Function and Power Control Power Flow Direction Control
…. …. ….
55 57 59 62
Rectifier and Inverter Voltages Characteristics DC Voltage and Current Control for Change of AC Voltage ….
vii
5.5 5.6
AC Filter Sub-Bank Control 5.5.1 Reactive Power Control 5.5.2 AC Voltage Control
…. …. …. …. …. ….
65 66 68 69 71 72 73 74 75 76 77
5.5.3 Voltage Limitation Control 5.5.4 Harmonic Performance Control HVDC Protection 5.6.1 Valve Short Circuit Diff. Protection (87CSY, 87CSD) …. 5.6.2 Bridge Differential Protection (87CBY, 87CBD) 5.6.3 Group Differential Protection (87CG) 5.6.4 DC Differential Protection (87DCB) 5.6.5 AC Over-current Protection (50/51C)
…. …. …. ….
5.6.6 DC Over-voltage/ Open Converter Protection (59/37DC)… 78
5.6.7 DC Under-voltage Protection (27DC) 5.6.8 AC Over-voltage Protection (59AC) 5.6.9 AC Under-voltage Protection (27AC)
…. …. ….
79 80 81 82 83
5.6.10 AC Valve Winding Ground Fault Supervision (59ACVW). 5.6.11 Fundamental Frequency Protection (81DC 50Hz)
….
Chapter – 6: Technical Exposure of HVDCBack to Back Connection
- 6.1
- Bangladesh - India Grid Interconnection
….
84
6.1.1 Transmission in Bangladesh Side 6.1.2 Transmission in India Side
…. ….
85 85
6.2 Transmission Line of Bangladesh-India Grid Interconnection
6.2.1 Transmission Line Length
…. …. …. …. ….
86 86 87 87 88
6.2.2 Transmission Line Physical and Electrical Data 6.2.3 Transmission Line Conductors 6.2.4 Line Earth Wire and Optical Ground Wire 6.2.5 Transmission Line Insulators
viii
6.2.6 Clearance to Obstacles from Lines 6.2.7 Types of Tower
…. …. …. ….
88 89 89 90
6.2.8 Height of Towers for Different Type 6.2.9 Different Type of Towers Used in Bangladesh Side
- Converter Station at Bheramara
- 6.3
6.4
- 6.3.1 Power, Voltage and Current Rating of HVDC Station ….
- 91
92 93
6.3.2 Technical Data ofThyristor Valves
…. ….
6.3.3 Technical Data ofConverter Transformers 6.3.4 Data of AC Filters, Shunt Capacitors and Shunt Reactors.. 94 AC Switch-Yard Equipments at Converter Station 6.4.1 Technical Data of Bus-Bars
…. ….
94 95 96 97 98 99
6.4.2 Technical Data ofCircuit Breakers 6.4.3 Technical Data of Capacitive Voltage Transformers …. 6.4.4 Technical Data of Current Transformers AC Harmonic Filters at Converter Station
…. …. ….
6.5
- 6.6
- Double Tuned AC Filter in 400kV Side (DT 12/24)
6.7 6.8
Double Tuned AC Filter in 230kV Side (DT 12/24) Double Tuned AC Filter in 230kV Side (DT 3/12)
…. ….
106 113
Chapter – 7: Economical Exposure of HVDC Back to Back Connection
7.1 7.2
Cost of Imported Electrical Energy Cost of HVDC Back to Back Station
…. ….
119 121
7.2.1 Calculation of Cost of HVDC Back to Back Station Cost of AC Switching Station
…. …. …. …. ….
124 127 130 133 135
7.3 7.4
7.3.1 Calculation of Cost of AC Switching Station Cost of AC Over-head Transmission Line 7.4.1 Calculation of Cost of AC Transmission Line
7.5 7.6
Information against HVDC & HVAC Costs and Losses Transmission Line Losses
…. ….
137 140
ix
7.7 7.8
Calculation of Losses in Grid Interconnection System Running Cost for Energy Transmission
…. ….
142 144
- 7.9
- Calculationof Transmission Costfor Interconnection System ….
- 147
7.10 Calculation of Transmission Costfor Total System
…. ….
149 154 156
7.11 Bangladesh – Nepal Electrical Grid Interconnection
7.11.1 General Costs for Bangladesh – Nepal Grid Interconnection ...
7.11.2 Calculation of Cost of HVDC Back to Back Station
….
159
7.11.3 Calculation of Cost of AC Switching Station 7.11.4 Calculation of Cost of AC Transmission Line
…. ….
162 165 167 169
170
7.11.5 TotalCostfor Bangladesh – Nepal Grid Interconnection..
7.12 Bangladesh – Myanmar Electrical Grid Interconnection
….
7.12.1 General Costs for Bangladesh – Myanmar Grid Interconnection
7.12.2 Calculation of Cost of HVDC Back to Back Station 7.12.3 Calculation of Cost of AC Switching Station 7.12.4 Calculation of Cost of AC Transmission Line
…. …. ….
173 176 179
- 181
- 7.12.5 TotalCostfor Bangladesh–Myanmar Grid Interconnection
Chapter – 8: Discussion
8.1 8.2
Discussion References
…. ….
183 184
x
List of Figures
Sl. No. 1. Fig -2.1 : Variation of cost with distance for AC & DC transmission 2. Fig- 2.2 : Configuration of HVDC connection with DC overhead line ….
- Description:
- Page No.
….
813 14 15
3. Fig-2.3 : Configuration of HVDC connection with DC sea cable 4. Fig- 2.4 : Configuration of HVDC back to back connection
…. ….
5. Fig. 3.1 : Convertor station layout for HVDC back to back station 6. Fig. 3.2 : Converter transformer
…. …. …. …. …. …. …. …. ….
19 25 25 26 28 29 30 30 31
7. Fig. 3.3 : Converter transformer winding & core arrangement 8. Fig. 3.4 : DC filter / smoothing reactor 9. Fig. 3.5 : Thyristor valve layout 10. Fig. 3.6 : Physical arrangement of thyristor valves 11. Fig. 3.7 : Double valve arrengement 12. Fig. 3.8 : Quadruple valve arrengement 13. Fig. 3.9 : Light triggered power thyristor 14. Fig. 3.10: Evolution of power thyristors 15. Fig. 3.11: Thyristorsnubber circuit 16. Fig. 3.12: Snuber resistor
…. …. …. …. …. …. …. …. …. …. …. ….
32 33 33 33 34 35 36 37 38 39 40 41
17. Fig. 3.13: Snuber capacitor 18. Fig. 3.14: Thyristor monitoring electonics 19. Fig. 3.15: Grading Capacitor 20. Fig. 3.16: Saturable reactor 21. Fig. 3.17: Cooing components 22. Fig. 3.18: Parallel cooling system 23. Fig. 4.1 : HVDC link between ac grids 24. Fig. 4.2 : Current and power are in same direction 25. Fig. 4.3 : Current and power are in opposite direction
26. Fig. 4.4 : HVDC monopole configuration
….
42
xi
27. Fig. 4.5 : HVDC bipole configuration
…. …. …. …. …. …. ….
42 43 44 45 46 46 47 47 48 48 49 52 52 53 54 56
57 58
59 60 61 62
64
67 68 72
28. Fig. 4.6 : Three phase’s twelve pulse bridge converter circuit
29. Fig. 4.7 : Thyristor operation sequence for 12 –pulse converter
30. Fig. 4.8 : Three phase’s six pulse converter circuit
31. Fig. 4.9 : Thyristor operation sequence for 6 –pulse converter 32. Fig. 4.10: Zero (0) degree firing points for 6 –pulse converter 33. Fig. 4.11: Three phase six pulse converter valves 1& 2 conducted 34. Fig. 4.12: Three phase six pulse converter valves 1, 2 & 3 conducted …. 35. Fig. 4.13: Three phase six pulse converter valves 2 & 3 conducted …. 36. Fig. 4.14: Three phase six pulse converter valves 3 & 4 conducted ….
37. Fig. 4.15: Three phase six pulse converter voltages with ‘α’ firing angle…
38. Fig. 4.16: Idealized controlled six pulse converter voltage
….
39. Fig. 4.17: Relationship between DC voltage “Ud” and firing angle “α” ….
40. Fig. 4.18: AC line current of star and delta transformer for every 6-pulse.. 41. Fig. 4.19: AC line current on transformer primary side for 12-pulse 42. Fig. 5.1 : HVDC control function
…. ….
…. ….
…. …. …. ….
….
…. …. ….
43. Fig. 5.2 : Two ac systems coupled with HVDC link 44. Fig. 5.3 : Direction of power flow with dc voltages
45. Fig. 5.4 : Two ac systems connected with 12-pulse HVDC link 46. Fig. 5.5 : Rectifier and inverter operation 47. Fig. 5.6 : Converter (rectifier & inverter) characteristics
48. Fig. 5.7 : DC voltage control for change of rectifier side acvoltage 49. Fig. 5.8 : DC voltage control for change of inverter side acvoltage
50. Fig. 5.9 : AC filter switching in reactive power controlmode 51. Fig. 5.10: AC filter switching in ac voltage control 52. Fig. 5.11: HVDC protection zone
53. Fig. 5.12: Valve short circuit differential protection zone
….
73
xii
54. Fig. 5.13: Bridge differential protection zone
…. …. …. …. …. …. …. …. …. …. …. …. …. …. …. …. …. ….
74
- 55. Fig. 5.14: Group differential protection zone
- 75
- 56. Fig. 5.15: DC differential protection zone
- 76
- 57. Fig. 5.16: AC over-current protection zone
- 77
58. Fig. 5.17: DC over-voltage/ open converter protection zone 59. Fig. 5.18: DC under-voltage protection zone
78 79
- 60. Fig. 5.19: AC over-voltage protection zone
- 80
- 61. Fig. 5.20: AC under-voltage protection zone
- 81
62. Fig. 5.21: AC valve winding ground fault protection zone 63. Fig. 5.22: Fundamental frequency protection zone 64. Fig. 6.1 : Bangladesh-India grid interconnection system 65. Fig. 6.2 : Double tuned ac filters (DT 12/24 and DT 3/12) 66. Fig. 6.3 : Double tuned ac filter in 400kV side (DT 12/24) 67. Fig. 6.4 : Double tuned ac filter in 230kV side (DT 12/24) 68. Fig. 6.5 : Double tuned ac filter in 230kV side (DT 3/12) 69. Fig. 7.1 : Interconnected grid systems with HVDC 70. Fig. 7.2 : Transmission line route from Bangladesh to Nepal 71. Fig. 7.3 : Transmission line route from Bangladesh to Myanmar
82 83 84 98 99 106 113 145 155 170
Abbreviations & Notations
xiii
- A
- - Ampere
- AC
- - Alternating Current
- Alternating Current Filter - Bangladeshi Taka - Back to Back
ACF BDT BtB
- CB
- - Circuit breaker
- CT
- - Current Transformer
- - Direct Current
- DC
DCF DS
- Direct Current Filter - Disconnecting Switch
- - Double Tuned
- DT
ENR ER
- East-Northern Region - Eastern Region
- ES
- - Earthing Switch
ESOF ETT
- Emergency Switch Off - Electrically Triggered Thyristor
FACTS - Flexible Alternating Current Transmission Systems FCL HVAC HVDC IPC
- Fault Current Limiter (Series Reactor) - High Voltage Alternating Current - High Voltage Direct Current - Individual Phase Control
- - Kilo Ampere
- KA
- KG
- - Kilo Gram
- KM
- - Kilo Meter
- KN
- - Kilo Neutron
- KV
- - Kilo Volt
xiv
KVA KVAR KW
- Kilo Volt Ampere - Kilo Volt Ampere Reactive - Kilo Watt
KWH LA
- Kilo Watt Hour - Lightning Arrester
- LTT
- - Light Triggered Thyristor
- - Mega Volt Ampere
- MVA
- MW
- - Mega Watt
- NR
- - Northern region
ODAF OLTC PT
- Oil Dynamic Air Force - On Load Tap Changer - Potential Transformer - Reactive Power Control - Southern Region
RPC SR SVC TCSC USD VBE VSC WR
- Static VAR Compensator (Parallel)
- Thyristor Controlled Series Compensator
- United State Dollar - Valve Base Electronics - Voltage Source Converter - Western Region
xv
1
Chapter – 1 Introduction