What is a Rectifier Transformer ?


What is a Rectifier Transformer ?

Rectifier transformers are different from normal power and distribution transformers because they are special transformers made for industrial application.
  • A rectifier transformer is a transformer which includes diodes or thyristors in the same tank. Voltage regulation may also be included. Rectifier transformers are used for industrial processes which require a significant direct current (dc) supply.
  • Typical processes would include dc traction, electrolysis, smelting operations, large variable speed drive trains, etc.  The Rectifier Transformer is used in applications which require high DC power such as in DC Traction Systems and in processes such as electrolysis and smelting.

  • Voltage regulation is achieved using Tap Changers in the HV side.
  • Rectifier Transformers are sometimes also known as Rectiformers.
  • Rectifier Transformers are usually connected to a bank.  Each Rectifier-Transformer is designed with an inherent phase shift such that the transformers attain the peak voltage one after another.
  • This ensures a steady supply at peak voltage.  Thus a system with five banks of rectifier transformers with twelve pulses at a phase shift of +12°, – 6°, 0°, + 6° and +12° will result in a system  with 60 pulses.
  • For example, in 750 Volts DC traction system, we have a 33 kV/ 292–292 Volts rectifier transformer with a vector group of “ Dd0y5” and this “292–292 volts” is fed into a 12 pulse rectifier to get the required 750 Volts DC.

Operation of Rectifier Transformers

  • Rectifier transformers can be liquid-immersed, dry-type, or cast-coil technology. Dry type transformers were primarily used in distribution-voltage classes. Dry type and cast coil — are limited by voltage and kVA size.
  • However, liquid-immersed transformers can be built to all voltage levels and current levels. High-fire-point fluids can be used for fire-protection considerations.
  • Voltage regulation is achieved with no-load or on-load tap changers on the high voltage side. Fine levels of voltage regulation can be achieved using saturable reactors on the secondary side. Regulation units may be built in or separate.


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