HVDC Transmission

Introduction & History HVDC stands for High Voltage Direct Current. HVDC transmission is an efficient technology designed to deliver large amount of electricity over long distances with negligible losses.

The world’s first commercial HVDC link situated between the Swedish mainland and the island Gotland was delivered by ABB.

Basic Transmissions of HVDC Back to Back Transmission. Point to point Overhead line Transmission. Point to point Underground Cable Transmission.

Point to point Sub marine Transmission.

Needs for HVDC The losses which occurs in the systems are comparatively low at all the stages (i.e) at generation , transmission & distribution level.

The losses at transmission level can be highly reduced by HVDC transmission.

Comparison of HVAC and HVDC Conventionally power transmission is affected through HVAC systems all over the world.

HVAC transmission is having sever limitations like, line length , uncontrolled power flow, over/low voltages during lightly / over loaded conditions, stability problems, fault isolation etc…

But HVDC have low transmission losses and it requires only two conductors.

Cont…

HVDC in IndiaHVDC LINK CONNECTING

REGIONCAPACITY

(MW)

Vindyachal North – West 2 x 250

Chandrapur West – South 2 x 250

Vizag – I East – South 2 x 250

Sasaram East – North 2 x 250

Vizag – II East – South 2 x 250

Parameters needed If DC is used in transmission, there need to be an inverter and the converter units.

Because the power generating stations is always generates Alternating Current.

Also the primary domestic appliances are designed to work on AC only.

AC-DC conversion : RectifierTransmission : DC

DC-AC conversion : Inverter

6 pulse Rectifier

Rectifier’s Waveform…

Transmission While transmitting the DC there are 3 types of links.

Types of DC links

Monopolar

Bipolar

Homopolar

Monopolar Links It uses only one conductor. Due to negative polarity, no corona effect occurs.

Bipolar Links It have two conductors. Junction between the conductors are grounded.

Can carry half the rated load, if fault occurs in one pole.

Homopolar Links It has two conductors are in same polarity (Usually negative).

The return path for such a system is through ground.

Inverter CircuitThe combinational circuit which converts DC-AC is referred as Inverter Circuit.

Advantages of HVDC Technical Advantage

System stability.less Corona Loss and no skin effect.

Greater Reliability.

Economical Advantages

Line cost is less.Tower Construction is narrow.

Cont…

Disadvantages Power loss in conversion, switching and control.

Expensive inverters. The high-frequency constituents found in direct current transmission systems can cause radio noise in communications lines that are situated near the HVDC transmission line.

Conclusion Recent studies indicate that HVDC systems are very reliable.

Very large investments Eg. In China and India shows that High Voltage Direct Current will very important in the future, especially in big and new-industries countries.

By Abuthahir T Arumugam A