Free State Transformers offers a wide range of Distribution transformers , Miniature substations and Special Application transformers.
Special Application Transformers :

CONVERTER 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.

FURNACE TRANSFORMERS

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.

RECTIFIER TRANSFORMERS

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.



DISTRIBUTION AND POWER TRANSFORMERS

These Transformers are the popular and commonly produced type of Transformers. They range from small pole mounted transformers to very large transformers seen openly in distribution yards and substations. Typically robust oil-natural, air natural (ONAN) cooling is used due to the remoteness of the installation site and added complexity of other cooling options.
 

LARGE DISTRIBUTION TRANSFORMERS :

RANGE: 5000kVA to 20 000kVA

PRIMARY VOLTAGES: up to 33kV

TAPPINGS: Off-circuit Tap switch (OCTS) or on-load Tap Changers (OLTS)

TAPPING RANGE 2,5% to 5% (OCTS) or 5% to 15% (OLTS)

TERMINATION: HV & LV Outdoor open bushings or

: HV & LV cable boxes

TANK CONSTRUCTION: Free breathing with bolted on lids, flat under base or Skid base

COOLING: ONAN/ONAF

FITTINGS: Lifting lugs, earth terminal, surge arrestor brackets when requested, rating & diagram plate, drain & filter valve, Jacking pads, Oil level indicator, Oil temperature indicator, winding temperature indicator, dehydrating breather.

STANDARDS: SABS, SANS 780

SMALL and MEDIUM TRANSFORMERS

RANGE: 5kVA – 5000kVA

PRIMARY VOLTAGES: up to 33kV

TAPPINGS: External Tapping connection (single phase) or of circuit Tap-switch (OCTS)

TERMINATIONS: HV Outdoor open bushings or HV & LV cable boxes

TANK CONSTRUCTION: Sealed welded cover or sealed bolted cover.

COOLING: ONAN

MOUNTING ARRANGEMENT: Pole mounting with brackets or flat base for pole mounting platform mounting

STANDARDS: SABS, SANS 780

MINIATURE SUBSTATIONS :

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 .




SPECIAL APPLICATION TRANSFORMERS

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.