Tag Archives: Trafo Power Solutions

TRAFO’S CAST RESIN TRANSFORMERS READY FOR ACTION AT ZUIKERBOSCH

Dry-type transformer specialist Trafo Power Solutions secured the order for 13 custom-designed cast resin units for Rand Water’s large Zuikerbosch Wastewater Treatment Works near Vereeniging.

The water purification and sedimentation facilities at Zuikerbosch will reportedly provide an additional 600 Ml per day to the system at a project value of R3 billion, as part of efforts to meet growing water demand in Gauteng due to steady population migration into the province.

The transformers being provided by Trafo Power Solutions range in size from 100 kVA to 1,600 kVA and have been modified to include earth fault protection and surge protection. This is in addition to the standard temperature protection features.

“The key advantages of dry-type transformers in this kind of application is their inherent safety and their ease of installation,” says Trafo Power Solutions managing director David Claassen. “The units can be installed inside built substations rather than having to be placed outdoors with their own civils and bunding infrastructure.”

Unlike conventional oil-cooled transformers, the dry-type units do not carry the risk of oil leaks or spillage and hence do not require special mitigation measures to protect the environment. The technology’s relative safety also makes them more versatile in terms of the locations in which they may be housed. The units are self-extinguishing and flame-retardant by nature, allowing them to be categorised as ‘F1’ in terms of international fire ratings.

“The transformers represent state-of-the-art technology from the leaders in cast resin transformer products, Hammond Power Solutions (HPS) who has been developing this field for a century,” says Claassen. “We have sourced our custom-designed units from the group’s manufacturing facilities in Italy, which boast world-leading expertise and equipment.”

While dry-type transformers have been around since the early 1900s, they are becoming increasingly popular in a variety of applications as the price differential compared to conventional transformers is no longer significant.

TAKE-UP BROADENS FOR DRY-TYPE TRANSFORMERS

As the market recognises the numerous benefits of dry-type transformers, specialist supplier Trafo Power Solutions has, in recent months, provided custom-designed units for a range of applications within South Africa and in other parts of the continent.

According to Trafo Power Solutions managing director David Claassen, an increasingly popular application for their transformers has been in large industrial companies which leverage solar power to augment their energy needs during daylight hours.

“Where companies have the roof or ground space to accommodate photovoltaic cells, many are taking advantage of solar power to reduce consumption from Eskom and cut their monthly electricity bill,” says Claassen. “With our experience in supplying the necessary specialised transformers for this purpose, we design and install units that are capable of supplying a 100% non-linear / inverter load while also providing electrostatic shielding between the medium voltage and low voltage sides of the transformer.”

Trafo Power Solutions recently installed and commissioned 1250 kVA and 1000 kVA units to serve large industrial bottling plants in Gauteng and Bloemfontein respectively

In another customised solution developed in response to a specific challenge faced by a customer, the company recently helped address the frequent voltage fluctuations in supply being experienced at the South African manufacturing facility of an international pharmaceutical company.

“Due to the instability of the electrical supply and frequent voltage fluctuations, it was decided the automatic on-load tap changer was the best solution for the customer,” he says. “We designed an integrated solution to automatically measure the supply voltage and change tap settings of the transformer in 9 steps of + and – 1,875% of on-load and without any interruption to the power supply feeding the facility.”

The supply and installation of two 1250 kVA transformers for this unique application was also completed in record time, including the commissioning and testing of the system within just three days of the units arriving from Hammond Power Solutions’ manufacturing facility in Italy.

There has also been steady demand for dry-type transformers in commercial buildings and hospitals, where users are looking to ensure high levels of safety in relatively confined spaces, while enjoying low maintenance requirements.

The absence of oil in the units gives them a higher safety rating than conventional oil-cooled transformers, and allows them to be installed indoors; users are also spared the cost of building special structures to accommodate the safety and environmental hazards related to oil-cooled units.

The upgrade of standby power generating facilities on two of the Johannesburg campuses of a leading South African university have also included four dry type transformers supplied by Trafo Power Solutions. The four transformers, two 2500 kVA and two 1000 kVA units, will step up the power supply from 400 V to 11 kV.

“We have also supplied numerous dry type lighting transformers for indoor and outdoor applications in the range of 25 kVA up to 200 kVA, as well as medium voltage outdoor potential transformers (PTs) or voltage transformers (VTs),” says Claassen. “These units are proving to be popular alternatives to the conventional oil-cooled transformer – due to their versatility in where they can be placed, and the avoidance of environmental risk.”

COPPER OR ALUMINIUM FOR DRY-TYPE TRANSFORMERS?

While many experts argue the respective pros and cons of using copper or aluminium in dry-type transformers, it is important to understand that innovations in transformer design have ensured that either of these two materials can today be applied with equal effect in most applications, according to David Claassen, managing director of Trafo Power Solutions.

Dry-type transformer specialists Hammond Power Solutions (HPS) – whose products are distributed in Africa by Trafo Power Solutions – has been using both copper and aluminium in the manufacture of conductors and bus bars in its low voltage and medium voltage transformers.

HPS has been a global leader in dry-type transformers for more than a century, and both materials have been used by HPS Europe in its production process for more than forty years.
The company has found no significant difference in the transformer lifespan delivered when using either copper or aluminium; from a technical point of view, the two materials are equivalent.

There is clearly a cost advantage to selecting aluminium as a conductor, as the commodity’s price tends to be significantly less expensive than copper, and more stable over time.
It is therefore not surprising that more than 80% of HPS Europe’s transformer production over the past 40 years – across all markets and applications – incorporates aluminium windings.

However, the argument is sometimes made that aluminium is inferior in terms of conductivity – as it has only 61% of the conductivity of copper – leading to higher energy losses.
Winding temperature is, of course, always a concern, but designers at HPS have been able to maintain temperatures below the insulation rating by designing aluminium winding transformers with conductors with larger cross-sectional areas than those made of copper.

Such design innovations in aluminium conductors have succeeded in reducing their energy losses to the same level as copper. This allows transformers of similar design and with the same temperature rise to exhibit roughly equivalent losses, regardless of the conductor material.

It is also argued that the thermal conductivity of copper is superior to that of aluminium in reducing hot-spot temperature rise in transformer windings. But this is true only when copper and aluminium windings of identical size, geometry and design are compared.

Claassen notes that, in fact, the thermal conductivity characteristics of aluminium can be very close to those of copper, for any given transformer kVA size.
The aluminium coil must just be designed and built 66% larger in its cross-sectional area, for the aluminium coils to achieve the same current-carrying capacity as copper.

HPS designs the cooling surface area, the coil geometry, the air ducting and the conductor shape to produce acceptable hot-spot gradients, regardless of the winding material used.

In terms of aluminium’s lower tensile and yield strength, there have been concerns expressed about its use in cyclic load applications – with aluminium demonstrating only 20% of the rupture stress capacity of copper.
In applications where loads draw high peaks of current, electromagnetic forces can cause movement of conductors and coil leads.

Again, the use of larger sized aluminium conductors addresses this issue, giving the aluminium windings almost the equivalent strength to copper windings.
HPS has found that the ability of its transformers to withstand the long-term mechanical effects of high impact loads or short circuits really depends more on adequate coil balance and lead support than on the choice of conductor material.

Expansion of aluminium due to changing temperatures has caused some problems when bolted connections are improperly installed, as aluminium expands nearly a third more than copper.
With the right type of spring-pressure connection, however, any loosening of joints can be avoided.
This can be done using either cupped or split washers, to provide the necessary elasticity at the joint without compressing the aluminium.
The result is that aluminium joints can perform equally as well as copper joints.

When it comes to connectivity, both copper and aluminium are prone to oxidation and other chemical changes when exposed to the atmosphere.

Cleaning and brushing with a quality joint compound to prevent oxidation is recommended for both materials but is more essential for aluminium.
HPS have a solution for aluminium and copper connectors that involves applying silver or tin-plating to either or both of the conductors in the bolted connection, or by putting a cupal transition plate between the materials.

Claassen emphasises that HPS has developed dry-type transformers for a range of industry applications – from distribution and marine vessels to railway, mining and off-shore rigs.

“Both aluminium and copper have been used in various applications for many years without any problem.
With our innovative design and production procedures, it is possible to avoid the technical limitations of aluminium conductors while retaining the advantages like cost and weight,” he concludes.