They are combined with a diode or thyristor rectifier. Applications range from large aluminum electrolysis to medium size operations. The transformers may have a built-in or separate voltage regulation unit.
Regulating and rectifier transformer combinations that are applied to primary aluminum production (smelters) are commonly known as 'rectiformers'. A typical aluminum potline is built as a 60-pulse system with five parallel 12-pulse rectiformers, each with different phase-shift windings; a 60-pulse system can be achieved by the following phase shift angles: +12°, – 6°, 0°, + 6° and +12°. As mentioned, one of the characteristics of rectiformers for aluminum plants is a very large regulating voltage range, from 0 Volts up to potentially 2,000 Volts (DC), depending on how many pots are connected in series.
The rectifier technologies employed in industrial applications are commonly known as double star (DSS) or double bridge (DB). DSS systems use an interphase transformer and are predominately applied as 6- or 12-pulse units where high currents are required with very low nominal voltages. DB systems are applied as 6-, 12-, 24-, 48- or 60-pulse systems, as required to suit the harmonic mitigation and process stability requirements. A higher number of pulse groups can be applied but tend to be less commercially attractive
Rectiformers can be supplied as a single tank solution for applications up to a rating of approximately 160 MVA, but for larger ratings transport limitations normally require that two transformers to be supplied as separate units.
- For applications in excess of 2,000 VDC (>100 kA)
- Installed base of over 20,000 MVA
- Double star (DSS), Double bridge (DB)
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