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Power Division
Introduction |
| Powertech Transformers is the only manufacturer of large high voltage transformers in Africa. The company is owned 80% by Power Technologies Limited (Powertech), the largest power electrical group in Southern Africa and 20% by Power Matla. The power transformer business, which originated in the Swedish ASEA stable was established in South Africa in 1944 and has become dominant in that market. For a period from 1988 to 1992 the company was known as Brown Boveri Technologies (BBT) before the name changed to ABB Powertech Transformers in 1997. On 26 March 2008, the Competition Commission Tribunal gave the go-ahead for Powertech to purchase the 50% share that ABB held of the company and the name was changed to Powertech Transformers. With capacity in excess of 10 000MVA per annum and access to the most advanced technology available, the company is ideally positioned to service the whole sub-Saharan Africa power transformer and shunt reactor market. Each year more than 120 units with ratings from 20 to 800MVA and voltages up to 500kV are produced. |
Design |
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In practical transformer design the manufacturer has a choice between core type and shell type concepts. We, at Powertech Transformers, have manufactured mainly core-type transformers.
The majority of our transformers are designed according to the “TrafoStarTM” design which is the common ABB concept used for the design and manufacture of Power Transformers. It is based on the best practices and know-how acquired over several decades coupled with its global manufacturing experience.
The concept incorporates common electrical and mechanical design standards, global processes and quality norms. Every TrafostarTM transformer is built from standardised, service proven components and modules ensuring flexible, dependable and tailor-made transformer designs. The high reliability of these transformers ensures maximum availability, lower maintenance costs and reduced life-cycle costs.
Powerful and sophisticated software tools are used to develop the mechanical and electrical design of all transformers. These tools help in ensuring optimum electrical design and determining eddy current losses and short circuit forces accurately. A 3 dimensional modelling software (Pro-Engineer) used in developing the mechanical design enables designers to view the virtual prototype of a transformer (including tanking of the corecoil assembly) on the computer screen before production commences.
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Windings |
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Windings are designed to ensure high short circuit withstand capability, uniform surge voltage distribution and effective heat dissipation which are critical to transformer reliability.
The disc type design of the high voltage windings ensures better short circuit withstand capability, uniform surge voltage distribution and effective heat dissipation.
These windings can be used with different designs for both small and large transformers up to the highest voltage levels.
Using the latest developments in winding technology, we use “voltage stabilised” disc windings for the high voltage side. The individual winding turns in each group of discs are interleaved thereby increasing the winding series capacitance to get uniform voltage distribution. |
Core Construction |
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Cold-rolled grain oriented silicon steel laminations are used to ensure low no-load losses and suppression of vibrations resulting in lower noise levels. Using stepped sheet widths helps in achieving an almost circular cross section of the core.
Advanced step-lap core construction technique achieve precise core stacking with step lap joints at the corners. This technique also helps in stacking at precise angles thereby preventing the formation of air gaps in the core joints, which otherwise could lead to increased losses and noise generation.
Core form structure is used without any through bolts in the limb or yoke portion.
The core limb is wound with conducting resin impregnated glass tape to give rigidity to core and to get a minimum uniform circular section for inner winding. To avoid internal mechanical stresses, the core is set upright in the stacking device itself.
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Assembly
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Both the medium and large transformer assembly lines at Powertech Transformers are equipped with motorised personnel platforms capable of vertical and horizontal travel which allow the work of assembly and connecting up to be completed with minimum strain on personnel.
The core and windings are assembled using insulation material of the highest quality. Where required, correctly positioned magnetic shunts ensure the collection of stray flux preventing unwanted hotspots in the clamping structure and tank walls.
Jointing, both in the winding and external, is by high frequency welding, which is extremely rapid and reliable. These joints are taped and the leads fixed in position to withstand any stresses during test and service condition.
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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 |
| Computerised tank designs are fabricated from mild steel plate. Welds are dye-penetrant tested to ensure that there are no leaks and specific joints, which may be stressed during handling and transport, are ultrasonically tested. Stiffeners are added at calculated intervals to make the tanks vacuum and over-pressure proof. Tank interiors are painted a light colour to improve visibility. The tank exterior is treated and painted to customer requirements. Nitrile O-ring gaskets for pipe joints and inspection covers are a standard feature in order to avoid oil leaks developing later during service. Tank main covers are generally welded, but these can be offered as bolted covers if specifically requested. Where required, magnetic shielding is applied to the tank interior to prevent heating. Only accessories from approved suppliers are used on our transformers. |
Quality and Testing |
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Quality is built into every Powertech Transformers' product and acceptance testing is one of the final steps of the quality control measures. Powertech Transformers is an SABS ISO 9001-2008 listed and has a proven quality control system. Furthermore the company has ISO 14001-2004 accreditation for its environmental awareness.
Our testing facility includes an impulse generator, precision power analyser for transformer loss measurement, PD analyser and temperature data logger to carry out routine and type tests accurately.
A special motor-generator set-up is used to test transformers at 50Hz and 60Hz similar to the exact operating frequency which will enable us to obtain accurate results.
In addition to all routine tests, special and type tests that can be carried out in-house include:
. Temperature rise test
. Lightning & switching impulse test
. Induced over-voltage test with PD measurements
. Measurement of zero sequence impedance
. Noise levels
Modern data collecting systems and high-end testing instruments allow easy access to accurate results obtained from our test measurements.
Our transformers are subjected to all the necessary routine tests in accordance with IEC, ensuring they withstand conditions beyond normal operating conditions. The extremes to which the transformers are tested are a measure of the highest standards in quality and reliability built into every transformer
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Transport, Installation, Commissioning and Services |
| Powertech Transformers closely supervises the transport, installation and commissioning of its product to ensure customer satisfaction. Transformers are transported either oil or nitrogen filled. Once erected, transformers are filled under vacuum with highly purified transformer oil. Powertech Transformers also offers a wide range of services including, analysis of transformer oil samples, specialist technical advice and tap changer maintenance as well as transformer repairs. |
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