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Special transformers for transmission networks

HVDC Converter Transformers  

High Voltage Direct Current (HVDC) systems allow the transmission of energy over long distances and are also solutions for interconnection of networks with different characteristics and frequencies. To this end, Alstom Grid offers a wide range of dedicated special transformers that enableefficient and reliable electric power transmission. 

Direct current transformer components, usually superimposed on the AC ones, appear both during service and during factory testing, and generate high levels of stress on the valve windings that are connected to the rectifier bridge. The design and manufacture of HVDC converter transformers requires a fine mastery of insulation structure.The high harmonic content of the load current also demands a very specific knowledge of thermal design.We are the experts in this field and have HVDC converter transformers installed in Europe, India and Canada with ratings including 310 MVA and voltage levels up to 500 kV. 

TSO- pragnères transformers cells at site

Alstom Grid has been awarded an order for a 600 kV High Voltage Direct Current (HVDC) bipole for the Rio Madeira project in Brazil. This will be the world’s longest power transmission line, with a total length of 2,375 km. Alstom will supply 28 UHVDC Converter Transformers for complete converter stations, confirming its position as at the forefront in complex HVDC converter transformers market.

Transformers for Static VAR Compensators (SVC)  

Alstom Grid Static VAR Compensators (SVC) provide an elegant and flexible solution when improvements of power system efficiency and control of the reactive power balance of the network are made imperative by environmental considerations (for example, the construction of new transmission lines or the location of generating stations).

The SVC Transformers are used to connect SVC equipment to transmission lines. These transformers combine the complexity induced by DC components, even if they are moderate in this instance, with high levels of harmonic and rated currents.. In this way, mastery of insulation structures, thermal behaviour and magnetic field distribution are all part of the know-how infused into all Alstom Grid SVC transformers.

As High Voltage network systems are connected with each other at several points, the necessity of controlling the flow of energy increases. Classical voltage regulation without phase shifting is no longer sufficient for these situations.

For this reason, phase-angle regulating transformers are necessary. Phase-shifting transformers are divided in two families:

  • PST with one active part (single core)
  • PST with two active parts (dual core).

One active part permits independent phase angle and voltage regulation and is suitable for a limited voltage and power level. For higher power and voltages, a PST with two active parts is ideal.

  • Quadrature boosters (QB) 

As a variant of dual-core PST, quadrature boosters offer economical solutions when limited phase-shifting angles are required with voltage variations.

Since 1997, Alstom has supplied 9 QB transformers to UK's National Grid Co., with power ratings up to 2750 MVA (see picture).