Transcript HVDC(high voltage DC)

Seminar on
H I G H V O LTA G E D . C . T R A N S M I S S I O N S Y S T E M
www.fakengineer.com
WHAT IS HVDC ?
 In a HVDC (High voltage D.C.) transmission system, electricity is taken
from an AC power network, converted to DC in a converter station and
transmitted to the receiving point by a transmission line (overhead) or
cable(underground). It is then converted back to AC in another
converter station and injected
into the receiving AC network. HVDC enables the power flow
to be controlled rapidly and
accurately, and improves the
performance, efficiency and
economy of the connected AC
networks.
POINTS TO BE DISCUSSED
 Introduction.
 History of HVDC.
 HVDC goes global.
 India adopts HVDC.
 Why HVDC ?
 Advantages of HVDC over HVAC:
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Disadvantages of HVDC.
Cost of HVDC.
Components of HVDC.
Types of HVDC links.
Application of HVDC.
Recent advances in HVDC technology.
Conclusion.
INTRODUCTION
• Now a days large blocks of power are needed to be
transmitted over very long distances.
•There arises some technical problems of transmitting power
to such a long distance using A.C.
•In the view of the drawbacks of a.c system the HVDC
transmission has come into picture.
•It is useful for bulk power transmission and interconnecting
incompatible grids.
History of HVDC
 Firstly concept was developed by a swiss engineer ‘Rene Thury’ during
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the end of 19th century.
Earlier mercury-arc valves were used in Converters which later get
replaced by Thyristor-valves.
In 1941 a 60MW 115km ‘Elbe-project’ was designed
in Berlin(Germany),but couldn’t be completed.
Above equipments were moved to Soviet Union &
in 1951, first HVDC link was established between
Moscow and Kashira.
However in 1954 first successful HVDC 20MW
96km commercial installation was done between
the Gotland island and Sweden.
This transformer converted the first
HVDC transmission in Gotland.
This transformer converted
the first HVDC transmission
in gotland
HVDC goes Global
 Currently there are some more than 100 of HVDC systems
across the whole world ,out of which 6 are in India.
 Some of them are as follows:
-Between Sweden & Denmark.
-Between south & north islands of New Zealand.
-Between Italy & Sardinia.
-Between Los Angeles & Oregon.
-Between north African deserts & central Europe.
-Between UK & western Europe.
 Proposal of a.c transmission across the English channel was
abandoned and get replaced by HVDC system
HVDC IN INDIA
 In India presently 6 HVDC systems are in operation.
 India- Pioneer developer of HVDC since 1990 with the first
HVDC set up of 1000MW 814Km Rihand-Dadri line between
U.P & Rajasthan.
 2000MW 1440Km Talcher-Kolar link is biggest so far connecting
four states-orissa,andhra pradesh,tamilnadu and karnataka.
 In march 2000,Power-grid(largest power transmission utility of
India) awarded a new long distance HVDC transmission project
to SIEMENS,Germany.
 More greater plans are cooking to add 1lakh MW of power by
2012 in which HVDC will play vital role to transmit these powers
to all corners of India.
Main data
Commissioning year:
1990
Power rating:
1 500 MW
No. of poles:
2
AC voltage:
400 kV (both ends)
DC voltage:
±500 kV
Length of overhead DC 814 km
line:
Main reason for
Long distance, network
choosing HVDC:
stability
FACTS & FIGURES
Data of Rihand-Dadri line
Data of Talcher-Kolar line
14th Feb 2003
1500MW
Commissioned
year
No. of poles
2
Power rating
2000MW
AC voltage
400KV(both
ends)
No. of poles
2
DC voltage
500KV
No. of towers
5651
Length of overhead
DC line
814Km
Amount of steel
10,000 metric tone
Amount of cement
80,000 metric tone
Length of line
1400Km
Cost of project
Rs.700 crore
Commissioned year
1990
Power rating
Reason for choosing Long distance,
HVDC
Network stability.
Comparison between the prices of AC & DC
Transmission
ADVANTAGES
Advantages of HVDC can be classified as:
Advantages of dc
transmission
Technical
Advantages
Economic
Advantages
Technical Advantages
 Reactive power requirement
 System stability
 Short Circuit Current
 Independent Control of ac system
 Fast change of energy flow
 Lesser Corona Loss and Radio interference
 Greater Reliability.
•No limits in transmitted distance
•Direction of power flow can be changed
very quickly
Economic advantages
•DC lines and cables are cheaper than ac lines or
cables.
•The towers of the dc lines are narrower, simpler
and cheaper compared to the towers of the ac
lines.
•Line losses in a dc line are lower than the losses
in an ac lines.
Types of DC links
Monopolar
Homopolar
Bipolar
Monopolar link
Bipolar Link
Incorporating HVDC into AC systems
 Two terminal DC link point to point transmission.
 Back to Back DC link
 DC line in Parallel with AC link.
 Multi-Terminal DC link.
GROUND RETURN
• Most dc transmission lines use ground return for reasons of
economy and reliability
 Ground return are used by the monopolar and the bipolar link
for carrying the return current.
 The ground path has a low resistance and, therefore low power
loss as compared to a metallic conductor path provided the
ground electrodes are properly designed.
 The resistance of the ground path is independent of the depth
of the line.
CONVERTER STATION EQUIPMENT
 Thyristor valves
 Converter Transformer
 DC Reactor
 Harmonics Filtering Equipment
 Control Equipment
 Reactive power compensation
PROBLEMS
 The Design of grounding electrodes for low cost of
installation and maintenance
 Location and screening of electrodes so that ground
currents cause negligible electrolytic corrosion of
buried and immersed metallic structures.
ADVANCES RECENT
 GTO’s have come into use.
 Use of active ac and dc filters.
 Advanced fully digital control systems using
optical fibers.
CONCLUSION
 Recent studies indicate that HVDC systems are very
reliable.
 The data collected from 31 utilities says that forced
unavailability of energy due to the converter station
is 1.62%
 The scheduled unavailability of energy is about
5.39%.