HVDC Transmission

Tashfain YousufFasih ur Rehman

Shayan Ahmad KhanHafiz Hashir Awan

Abdullah Amir

Contents• Introduction of HVDC transmission• Advantages of HVDC over AC transmission• Disadvantages• Components and Diagram• Applications

Introduction• Direct Current for transmission.• Long Distance.• Underwater.• Technology developed in 1930s in Sweden by ASEA.• Early Installations in 1951 between Moscow and Kashira, and 10-20

MW system between Gotland and Mainland Sweden in 1954.

HVDC Transmission• Full form High Voltage Direct Current Transmission.• Two AC systems having different frequencies can be linked up

together by means of HVDC link.• It is used to transmit electricity over long distances.• High Voltage Thyristors in converters.

Why HVDC transmission?• Less line losses.• Only Two conductors required.• Less expensive.• Long range transmission.

Thyristor Valves• Solid State device.• Thyristors require an external circuit(in HVDC applications) to turn

them off.• DC conversion.

Capacitor Commutated Converters• On AC Primary or Secondary side.• Series capacitors offset the commutating inductance of converter and

help to reduce fault currents.• Inverter voltage drop causes DC current surge.

Principle• Rectify the AC power to a voltage level of say 200 kV and then

converting it at the other end.

Components• Converting transformer.• Converter bridge.• Surge arresters.• Smoothing reactors.• AC and DC filters.

Construction• 12 Pulse converter.• 3 Pulsed transmission.• AC Filter.• Converters in Rectifying and inverting mode.• Thyristor valves in series.

Advantages• Occupies less space.• Economical.• Synchronization of two AC power supply.• Does not transmit short circuit current.

Disadvantages• Complexity of control.• Inability of transformers to change voltage levels.• High cost of convention equipment.• Difficulty of breaking DC current which results in high cost of DC

currents.

Applications• Long distance bulk power transmission.• Under ground or under water cables.• Asynchronous interconnection of two AC power supplies.

Conclusion• Control of power flow in terms of direction and level.• Power grid interconnection.• Long transmission.• HVDC overland links are usually bipolar, on overhead lines.