BRIEF ON THE REPORT OF CIGRE WG B4-45 – TECHNOLOGICAL ASSESSMENT OF 800KV HVDC APPLICATIONS...
-
Upload
priscilla-campbell -
Category
Documents
-
view
215 -
download
0
Transcript of BRIEF ON THE REPORT OF CIGRE WG B4-45 – TECHNOLOGICAL ASSESSMENT OF 800KV HVDC APPLICATIONS...
BRIEF ON THE REPORT OF CIGRE WG B4-45 – TECHNOLOGICAL ASSESSMENT OF 800KV
HVDC APPLICATIONS
(Authors: R N Nayak, Mohammed Rashwan, R P Sasmal)
UHV Symposium Delhi, Jan 2009
Background: Formation of WG
Converter Configuration
Ground electrode station
Insulation Co-ordination
External Insulation
Reliability and Availability
Interference Levels
Conclusion
PRESENTATION SUMMARY
Background
• WG14.32 formed to review the current state of HVDC converter stations up to 600kV and requirement to expand the technology to voltages above 600kV and specifically to 800kV.
• Several studies and meetings confirmed 800 kV HVDC transmissions - a feasible voltage step (IEEE and Cigré in the late 80’s, Cigré 2002, Power Grid Corporation of India Ltd. Workshop in Delhi, February 2005)
• New WG B4-45 formed in 2005 for “ Technological Assessment of 800kV HVDC Applications “
The main driving forces for 800 kV HVDC systems:
Cost of power losses on overhead lines. Need for Bulk power evacuation over very long
distances. Technological constraints of other EHV options. Right of way constraints. Techno-economic drive necessitates development of 800
kV HVDC
Background
The amount of power to be transmitted The transmission distance Staging consideration of the project Location of converter station The amount of power to be transmitted at the different
stages of the project Reliability and availability requirements Loss evaluation Size and weight of the converter transformers for
transport
Converter Configuration
Decided by Utilities / planners
3,000 MW
3,750 A400 kV
800 kV
400 kV
3,000 MW
800 kV 3,750 A
1,875 A1,875 A
Possible 800 kV Arrangements- Series and Parallel
• Two similar rating parallel 12 pulse converters per pole
• Two dissimilar rating parallel 12 pulse converters per pole.
• One single 12 pulse converter per pole
• Two similar MW rating series connected 12 pulse converters per pole
• Two dissimilar MW rating series connected 12 pulse converters per pole
Converter Configuration
3,000 MW
3,750 A800 kV
600 kV
400 kV
200 kV
12 x 300 MVA
The advantages/disadvantages one of the valve groups insulated for
400 kV only;
only one among four transformer groups have full insulation at 800 kV
In case, one 12 – pulse bridge fails, half of the pole power can still be
transmitted (no ground return), voltage level will be half of nominal losses would be high;
No practical staging scheme; installation at full power done at once;
4 spare units needed per station unless provisions made for 600 KV and 800 KV units to fit in the space of 200 KV and 400 KV units
Series converters
Converter Configuration
3,000 MW
800 kV
Advantages / disadvantages:
loss of a converter means still the operation at 800 KV; with unbalanced ground current
Metallic return can not be used unless the same polarity parallel converter is removed from service
The staging in power, possible by installing one 12 – pulse bridge for each pole, later on, a second one
Possible to make rectifiers and inverters at different location i.e Multi-terminal stations.
2 spare units required, as minimum, per station;
Parallel convertersConverter Configuration
Earth Electrode station Design Criteria
Life expectancy : 50 yrsUnbalance current during normal operationPole outage condition Due consideration for parallel /multi-terminal operationPossibility of Metallic return to avoid ground current
Selection of Suitable site Close to HVDC terminal to reduce cost Soil resistivity upto the depth of 10 kms.
Ground Electrode
Natural sources located in the magnetosphere and ionosphere,
Earth being conducting natural sources, induce secondary fields in the earth.
Vector nature of electromagnetic fields enables to estimate the tensor form of the resistivity structure by measuring five components time series data consisting of three magnetic (Hx, Hy , Hz ) and two electric (Ex, Ey ) components.
Magnetotelluric (MT) measurement based on natural electromagnetic (EM) fields & it delineate the electrical structure of the earth
Natural EM fields contain a wide spectrum of signals Deeper resistivity information by recording low frequency
content of the signal for a longer duration of MT time series recording
Magnetotelluric measurement Ground Electrode
Good Conductivity up to the depth of 4150m except the top layer of about 100m
Typical result of Soil Resistivity
Ground Electrode
neutral
800 kV DC
D
10
E1
V3
V3
V2 72
V1
92
valve hall boundary
C2
C1
V3
V3
V3 71
V3
valve hall boundary 81
AC Bus- 1
A
52
62 A
- 1
A
51
61 A
91
A2
E2
400 kV DC
82
M
SR
AC Bus
• Converter transformer arrester “A2”
• Converter group arrester type “C1” and “C2”
• Mid point arrester type “M”
• Smoothing arrester type “SR”
Provide higher safety and reliability to the equipment.
Insulation Co-ordination
Arrester arrangement for series Converters
E1
9
valve hall boundary
V2
V2
V2
7
V1
C
AC-Bus 1
A
5
6 A
AC-Bus 1
A
5
6 A
A2
V2
V2
V2
7
V1
valve hall boundary
81
M
800 kV DC
D
10 SR
neutral
E2
82
800 kV DC
D
10 SR
neutral
E2
82 81
E1
9
Converter transformer arrester “A2”
• Converter group arrester type “C”
• Mid point arrester type “M”
• Smoothing arrester type “SR”
Provide higher safety and reliability to the equipment.
Insulation Co-ordination
Arrester arrangement for parallel Converters
SIWL kVpk 1600
LIWL kVpk 1900
DC withstand test voltage
kV 1200
Polarity reversal test voltage
kV 1020
Insulation Co-ordination
Insulation levels depends upon:
Particular layout, arrester arrangement arrester datasystem parameters
Typical Minimum Insulation Values:-
External Insulation
External insulation Creepage distance
• Pollution level• Surface material of insulators or equipment
housing Shed profile
Corrections for Altitude
Converter station equipment: The conditions well defined
Transmission line: conditions vary along the route ( 2000 – 3000 km) as the line pass through all kinds of terrain, including polluted areas and high altitudes > 1000 m.
Established procedure of calculation of availability and reliability for HVDC projects already established and being monitored and reported Worldwide
Characteristics of a reliable HVDC project: long continuous operations without fault
being fault tolerant, that is, being able to recover from faults quickly
only partial and acceptable loss on major faults
well integration in the AC system.
Availability and Reliability
Availability and Reliability
Typical forced outage rate used as design base in the recent HVDC projects: • Pole outage : 5 – 6 per year per pole• Bipole outage: 0.1 per year
Possible target values with series valve group :• 12 pulse bridge (Converter) outage: 2 - 2.5 per
year per converter • Pole outage : 2 – 3 per year per pole• Bipole outage: 0.1 per year or less
Possible target parallel valve group converters :• Pole outage : 5 – 6 per year per pole• Bipole outage: 0.1 per year
Interference Levels
Electric Field : 25kv/m – 30 kV/m
Ion current Density : 100 na/ m2
Minimum conductor height: 18 / 20 mtrs
Magnetic Field limit• Occupational exposure: 200 mT• Public Exposure: 40 mT
FOR HVDC TRANSMISSION LINE
FOR HVDC TERMINAL Electric Field : 30kv/m
Ion current Density : 100 na/ m2
Conclusion
Availability and reliability of Large HVDC system plays a major role in system stability, Needs proper planning for converter configuration
Experience gained from the initial 800 kV HVDC projects must be suitable incorporated in future projects
R & D activities must be continued to reduce the overall cost of the HVDC systems
Converter transformer design, wall bushing and external insulations needs special care during design.
THANK YOUTHANK YOU