Introduction |
| The distribution transformer business, partly originated in the Swedish ASEA stable in 1944 and within Desta Transformers, in 1953. Desta Power Matla, commenced operation in July 1999 in the original Desta Transformers premises in Booysens, Johannesburg. Other operations were situated in Pretoria West and Cape Town (previously Power Engineers). In 2009, Desta Power Matla (DPM) joined forces with Powertech Transformers (PTT). At the same time, PTT’s shareholding changed significantly. Power Matla, DPM’s BEE partner of many years, increased its investment in the transformer industry by buying a 20% stake in the new Powertech Transformer company. |
Technical Data |
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The transformers comply with SANS 780 and/or IEC 76, BS 171 and NRS 027.
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Windings |
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All distribution transformer high voltage windings are made of copper. The low voltage windings are made of copper strip, but in certain ranges copper or aluminium foil is used. Diamond dot paper is used for interlayer insulation on the foil windings as it adds mechanical strength to it. Core and winding assemblies are clamped by means of top and bottom yoke clamps.
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| Core Construction |
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All distribution transformers cores are made of grain oriented, low loss magnetic cold-rolled silicon steel. Both sides of steel sheets are laminated with ceramic insulation. The core construction is optimised for cold-rolled steel properties so that best parameters for magnetic circuit are obtained, i.e. minimum no-load losses and small magnetising power. |
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Corrosion Protection
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The exterior and interior surfaces of the transformer tank, cover and conservator (when fitted) are carefully degreased. Rust and millscale are removed by a process of acid pickling or phosphating.
The exterior surfaces of inland units are thereafter given a coat of high build primer, followed by a coat of high build alkyd base full gloss enamel giving a total dry film thickness of at least 75µm. The method employed is either flow coating or spray painting.
Coastal units are shot blasted and hot zinc metal sprayed prior to painting to a finish of 125µm.
The standard colour is Avocado colour C12 to SANS 1097.
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| Processing |
| Windings are dried under vacuum and, on large units, oil impregnated before assembly. The complete active part is processed in an autoclave to obtain less than 0,5% moisture content. Within the prescribed time following the drying cycle, pressure is applied to the windings and the unit is tanked and filled, under vacuum, with heated, degassed and purified oil. |
Cooling |
| Powertech Transformers offers a wide range of cooling methods such as ONAN, ONAF, OFAF, OFWF or combinations thereof. Forced cooling can be activated by temperature or loading pattern. |
Tanks |
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Hermetically sealed transformers incorporate a tank with corrugated or tube radiator fins.
The transformer tank has a sturdy design that allows for normal transportation of an oil-filled transformer without any damage resulting from vibration.
Free breathing transformers have removable panel radiators and isolating valves.
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Quality Assurance |
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The transformers and miniature substations carry the SABS mark of approval. The distribition transfomer factory in Johannesburg and Cape Town has received the ISO 9001 version 2000 listing and as such a stringent quality assurance programme in accordance with the very specific requirements is rigidly adhered to. This ensures a product of the highest quality.
Testing
Routine tests to SANS 780 are made on every transformer prior to despatch:
• Measurement of winding resistance
• Measurement of voltage ratio and verification of polarity and connection symbol
• Measurement of impedance voltage and load loss
• Measurement of no - load loss and no - load current
• Induced overvoltage withstand test
• Separate - source voltage withstand test
• Measurement of paint thickness
• Test for effectiveness of sealing
Type tests to SANS 780 can be undertaken on request:
• Full impulse voltage withstand test
• Full and chopped impulse voltage withstand test
• Temperature rise test
• Tank stiffness test
Special tests to SANS 780 can also be made on request
• Short circuit withstand test (subject to limitations of SABS high current laboratory equipment)
• Measurement of audio sound level
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| Transport |
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Transformers are delivered to the customer fully assembled and ready for operation.
During transport, transformers must be securely placed in vertical position and firmly fastened to prevent any displacement. The transformer undercarriage has small pulling eyes designed for ropes or fastening belts.
Warranty
All our products are backed by a 1 year warranty period.
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