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Special Transformers


These Transformers are used to supply variable speed drives (VSD) for motor control. A VSD typically injests a whole spectrum of harmonics into the supply lines, and the transformers design needs to accommodate these harmonics. A convertor transformer is typically rated at 100% capacity, when a Distribution transformer is typically rated at 80% capacity. VSD drives are based on power electronic and usually require a neutral line, hence the most common vector group is DYn11, i.e. a Delta Primary with a star Secondary with the neutral point brought out.


The smeltering Industry uses AC & DC processes depending on the Arc Furnace application. DC Electric Arc Furnace (EAF) Transformers are similar in design to rectifier transformers, but have many more taps and on-load tap-changers. AC (EAF) transformers are subjected repeat short circuit conditions that require a more conservative design. They too have many taps and on-load tap changers. The AC (EAF) Transformers are generally manufactured as single phase units which allow the furnace design and process to be optimised.


These transformers cover a large range of configurations. The IEC60076 standards lists 19 configurations, most of the configurations were developed in the era of Mercury-arc rectifiers and have less relevance since the development of high current thyristors (silicon controlled rectifiers) and more advanced devices such as GTOs & IGCTs. The two commonly used rectifiers are the three phase bridge rectifier and the 6 phase double star with inter-phase transformer (IPT) which requires a dual secondary winding transformer design. The normal bridge rectifier uses a normal 3 phase design. We offer extended delta, phase shifted transformers where impedance and voltage matching is critical in a twelve pulse plant.



Our Miniature Substations are of modular design and can be customised to contract requirements .

Our designs offer options for SF6 and oil filled high voltages wich gear with custom build low voltage and auxiliary feeder circuits . Standard ratings range from 100kVA to 1600kVA with voltages up to 22kV.

Miniature substations with primary voltage rating of 33kV can be supplied withouthigh voltage switch gear .


Transformers supplying dedicated or non - distribution type loads are designed to customer specific requirements .

A large range of specialized application transformers can be designed and manufactured .

Some of the more frequent applications are, transformers supplying 6 pulse and 12 pulse rectifier circuits, Earthing transformers with auxiliary voltage supply, Isolation transformers , Auto - wound transformers with either primary or secondary voltage variation, Neutral Earthing resistors and many more .

A dual voltage Mobile Substation (specially manufactured for Eskom) is used in open cast mines where the primary of the transformer can be temporarily connected to an overhead line.


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