What are the advantages of HVDC over HVAC transmission and Applications of HVDC

What is the aim of electric power supply

To supply electrical power which is required for all the customers in an entire geographical area at all the time continuously and it must be done in low cost the geographical area coverage should be maximum. The security of the supply needs to be maximum and the fault duration should be short. The supply of the power must be in the targeted limit of frequency in case of AC supply. The power supplied must be in specified limits of voltage

Why DC transmission is used instead of AC transmission

The transmission of power through the Ac lines is not easy to control and the reactive power losses are high and the voltage drop due to the AC transmission is more

Limitation of HVAC

  • Reactive power loss
  • Less stability
  • Less current carrying capacity when compared to HVDC
  • Power flow control is not possible
  • Skin and Ferranti effect

WHAT IS HVDC

It is a long distance direct current transmission system which uses DC voltages up to about 1 MV to keep the transmission losses down. Due to the losses in AC transmission HVDC is used for a better power transmission

In earlier days power transmission is done through AC but it has many limitations like line length, uncontrolled power flow, overloaded conditions, stability problems, fault isolation… the DC transmission requires conversion at both ends from AC to DC at the sending end and from DC to AC at the receiving end. The conversion is done through rectifier at the sending end and in the receiving end it is done by the inverter station at the receiving end

Advantages of HVDC over HVAC transmission

  • Controlled power flow can be easily possible
  • Asynchronous operation is possible between regions having different electrical parameters
  • There is no restriction on line length because there is no reactance in DC power lines
  • Cable transmission possible only with HVDC
  • It is cheaper than the HVAC system because of fewer transmission lines and less right of way for the same number of power transmission
  • No charging problem
  • No skin & Ferranti effect
  • It requires less space when compared to AC for same voltage rating and size
  • Ground can be used as the return conductor
  • Less corona loss and radio interference
  • No switching transient
  • No transmission of short circuit power
  • Fast fault clearing time

Disadvantages of HVDC

  • Cost of terminal equipment is high
  • Harmonics are generated by inverters and rectifiers
  • Blocking of reactive power
  • Point to point transmission
  • Limited overload capacity
  • The reactive power requirements are huge at the converter terminal
  • There is heat loss In converter substation

Applications

  • Long distance transmission
  • Bulk power transmission
  • Asynchronous interconnections
  • Long submarine cables
  • Control and stabilize the power system with power flow control

Components of HVDC system

  • Rectifiers and inverters (converters)
  • Converter transformers
  • AC filters
  • DC filters
  • Smoothing reactor
  • Thyristor

What are the transmission line investment coasts

  • Right of way
  • Transmission towers
  • Conductors
  • Insulators
  • Terminal equipment