“High Voltage Direct Current Transmission”
Government polytechnic siwan
Rahl kumar madeshiya
3. Working OF HVDC Transmission System
4. Components of HVDC Transmission System
5. Advantages And Disadvantages
8. The Future Prospect
➢The word photovoltaic comes from “photo,” meaning light, and “voltaic,” which
refers to producing electricity.
➢PV cells are made of at least two layers of semiconductor material. One layer has a
positive charge, the other negative charge.
➢When light enters the cell, some of the photons from the light are absorbed by the
➢Freeing electrons from the cell’s negative layer to flow through an external circuit
and back into the positive layer.
➢This flow of electrons produces electric current.
➢In 1839 Alexandre Edmond Becquerel discovered the photovoltaic effect
which explains how electricity can be generated from sunlight. He claimed
that “shining light on an electrode submerged in a conductive solution
would create an electric current.”
➢However, even after much research and development subsequent to
the discovery, photovoltaic power continued to be very inefficient
and solar cells were used mainly for the purposes of measuring light.
How Does HVDC Transmission System Work?
➢ In generating substation, AC power is generated which can be converted into DC by
using a rectifier.
➢ In HVDC substationrectifiers and inverters are placed at both the ends of a line.
➢ The rectifier terminal changes the AC to DC, while the inverter terminal converts DC to
➢ The power remains the same at the sending and receiving ends of the line.
➢ DC is transmitted over long distances because it decreases the losses and improves
➢ A system having more than two converter stations and one transmission line is called
a ‘two terminal DC system’ or a ‘point-to-point system’.
➢ Similarly, if substationhas more than two converter stationsand interconnecting DC
terminal lines, it is called multiterminal DC substation.
Components of HVDC Transmission System
The main elements of an HVDC system are:
1. Converter unit
2. Converter transformer
3. AC filters & Capacitor banks
4. DC filters
5. Reactive Power source
6. Smoothing Reactor
7. Electrode Lines
Fig.- Main Components of HVDC Transmission System
➢Lighter and cheaper towers.
➢Lesser number of conductors and insulators, therefore reduced overall cost.
➢The direct current transfers only active power and thus causes lower losses than
➢ Due to the absence of the frequency factor on DC link,there is no skin effect.
➢ HVDC allows power transmission between unsynchronized AC transmission systems.
➢ The power flow through an HVDC link can be controlled independently under the
steady state condition.
➢ The disadvantages of HVDC are in conversion, switching and control.
➢ Expensive inverters with limited overload capacity.
➢ Higher losses in static inverters at smaller transmission distances.
➢ The cost of the inverters may not be offset by reductions in line constructioncost
and lower line loss.
➢ High voltage DC circuit breakers are difficult to build.
➢ Long distance bulk power transmission.
➢ Underground or underwater cables.
➢ Interconnectionsof AC systemsoperating at different frequencies.
➢ Control and stabilization of power flows in ac ties in an integrated power system.
➢ Renewable electricity superhighways such as offshore wind connections.
➢ Application of HVDC in INDIA:
1. Rihand-Delhi and Vindhyachal were the first long distance HVDC projects in INDIA.
2. In 1990 ,Rihand-Delhi (Singrauli) thermal power complex with a combined power
generation of several thousand MW was put in to service.
➢ Considering all the advantages of DC, it seems that HVDC lines are more
proficient than AC lines.
➢ But, the initial cost of HVDC substationis very high and their substation
equipment is quite complicated.
➢ For long distance transmission it is preferable.
➢ This system is economical and also improves the efficiency of the system.
The Future Prospect
➢ Next 25 years HVDC market will be dominated by “force commutatedconverter”.
➢ Self-commutatedconverters, more commonly known as "Voltage-Sourced
Converters" started to appear in 1997. This technology had captured a significant
proportion of the HVDC market.
➢In the future energy system based on renewables, HVDC is truly shaping the grid
of the future.
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2. I.J. Nagrath and D.P. Khothari ‘Power SystemEngineering’
3. H. Gambach, D. Retzmann, J. Dorn,IEEE Conferences 2011-12 Published in “The
International Conference on Advanced Power System Automation and
4. 2005 IEEE/PES Transmission and Distribution Conference & Exhibition: Asia and
Pacific Dalian, China
5. Ashfaq Hussain ‘Electrical Power Systems’-5th edition