HVDC Transmission System Basics, Block Diagram, Working

HVDC Transmission System:

One of the important power electronics field application is High Voltage DC [HVDC] Transmission System.
For large power transmission over long distances, the HVDC proves to be economical and efficient over High Voltage AC [HVAC] transmission system.

In this post let us see how HVDC transmission system works....

HVDC Transmission System- Block Diagram

The block diagram of HVDC transmission system is shown below. Click the image to see enlarge view...

  • As shown two AC systems A and B are interconnected by the DC line.
  • From the system-A three phase AC supply is first passed through a AC filter.
  • The AC filters reduced the current harmonic generated by the converters from entering into the AC systems.
  • Then the supply stepped up through the step-up transformer.
  • This gives high AC voltage which is ready for transmission.
  • The high voltage AC is converted into high voltage DC by the converters that are connected in series.

If power flows from system A to B, then converter-A operates as rectifier and converter-B operates as an inverter.
If the power flows in reverse manner (i.e., B to A) then converter-B acts as rectifier and converter-A acts as an inverter.

Normally, 12 pulse configuration is used for converter A and B to reduce the ripple voltage.

  • The DC output of the converter is filtered by DC filters and smoothing inductors to eliminate the DC ripples.
  • Thus ripple free high voltage DC is obtained. This high voltage DC is then transmitted over the DC transmission line.
  • The DC line has +kV and -kV with respect to ground.
  • This is done in purpose to balance the voltage the voltage of two transmission lines with respect to earth.
  • The center point of converters A and B are  earthed with one line at +kV and the other line -kV with respect to earth. This done to get the +- kV system.
  • At the receiving station, the high voltage DC is again filtered and passed to converter B (which act as an inverter).
  • This inverter output is stepped down, passed through AC filters. Thus the three phase AC supply is obtained at the receiver side finally.

Thanks for reading about HVDC Transmission System... 

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