ENGINEERING OPTIMAL ENERGY SOLUTIONS FOR AFRICA

Zest WEG Group combines its local manufacturing capability with WEG’s range of world class products to engineer energy solutions for customers around Africa, according to the group’s integrated solutions executive, Alastair Gerrard.

Gerrard also emphasises Zest WEG Group’s extensive network of agents and distributors across the continent, who provide vital insights into local conditions, needs and constraints.

“Our solutions are not off-the-shelf, and are tailor made for individual application requirements,” he says. “Our team spends time gaining an in-depth understanding of what the customer really needs, and what the operational constraints are.
In this process, we collaborate with reliable, in-country partners who have local knowledge and experience. This local presence also facilitates quick response times and 24/7 after-sales support.”

Gerrard also emphasises the use of parent company, WEG’s range of motors, variable speed drives and soft starters, as well as its low voltage and medium voltage switchgear.
These products are an integral part of the fit-for-purpose solutions, as is Zest WEG Group’s South African manufacturing capability in terms of generator sets, transformers, substations and other mobile energy solutions.

“Operating a local gen set manufacturing facility staffed by experienced engineers allows us the flexibility to package this offering with an engine and alternator combination to suit the customer preference,” he says.
Zest WEG Group also offers a standard off-the-shelf range of gen sets.

Forming part of Zest WEG Group’s manufacturing operations in South Africa is WEG Transformers Africa which has two facilities capable of producing transformers up to 45 MVA/132 kV and a range of mini substations up to 33 kV.
Also, part of the group is Shaw Controls which is a leading local manufacturer of custom electrical panels, motor control centres (MCCs), containerised electrical solutions and E-houses. He says that E-houses have become popular in Africa as these are pre-assembled and tested in a factory prior to being transported to site by truck.

The focus is on providing integrated solutions in four main areas, says Gerrard, being power generation, electrical infrastructure, mobile energy solutions and group product packages.
Power generation options include diesel, gas, steam, hydro and renewable energy generation solutions, while the electrical infrastructure offering ranges from supply and refurbishment of outdoor and indoor substations to the provision of overhead lines.

Mobile energy solutions, which are engineered to meet specific customer and site needs, are popular in the mining industry but are relevant to any application where operations need flexibility when deploying their electrical systems such as gen sets, substations, skid type solutions or circuit breakers.

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.

INDUSTRIAL, FOOD APPLICATIONS NOW BIG FOR SCREEN SPECIALISTS KWATANI

Known mainly for its large screens and feeders for mining, Kwatani has in recent years expanded substantially into various industrial and food sectors – currently providing screening solutions for almost 50 different materials and products.

According to Warren Mann, Kwatani’s business development manager – industrial division, the company is involved in screening a wide range of materials and foodstuffs from wax beads, carbon and bunker sand to tea, coffee, pet food and rice.

“Our strength is the ability to test the customer’s product or material in our own materials testing laboratory,” says Mann. “This is part of our solution-focused approach to deliver a customised machine that will add optimal value to the customer’s operation.”

These in-house facilities are vital in selecting the correct separator for each application.
By analysing and testing under simulated production conditions it is possible to determine the appropriate machine size and configuration as well as the optimum screen openings.

He highlights that Kwatani has for decades invested heavily in its local design and manufacturing capacity.
In 2012, it also acquired the assets of Lockers Engineers, and continues to supply Lockers customers with the full product range including vibrating screens and feeders, electromagnetic super feeder drives, controllers, vibrating trough conveyors and fluidised bed dryers.

The company’s rectangular R-type separators have a typical application in the sugar industry and are capable of screening 50 to 200 tonnes per hour of sugar to remove lumps and foreign material before grading and packaging.

“Spices and tea processing are other applications where we are actively involved, providing sizing and scalping screens that can handle up to 10 tonnes per hour,” he says.

Food safety comprises a key element in the design and manufacture of the screens that are used in food-related applications, and Kwatani has standardised on using stainless steel.
In addition, its workshop facilities have been optimised accordingly to achieve cost savings in the final assembly.

“We use high-grade stainless steel for any food contact surface, as mild steel tends to rust when exposed to excessive moisture and is not suitable in many food processing applications,” he says. “There are also specific plastics we use that are non-toxic and food-safe, adhering to hygiene and quality standards.
We offer a bonded screen mesh with food-safe epoxy, rather than a bolt down screen mesh, in order to eliminate the risk of bolts coming loose and entering the product stream.”

Kwatani’s S-type round separators are highly versatile and used in many different industries and have a special application in high temperature environments and liquid separation such as removing foreign particles from hot cooking oil.

Industrial products handled by Kwatani screens include the sizing of wax beads that are used in exfoliating creams. Clays such as bentonite and kaolin are also scalped.

“We have screens that can clean the sand in bunkers on golf courses, removing contaminants like grass and soil that have been tramped in by golfers,” says Mann. “In this instance we provide a mobile solution, so the screen can be easily moved to site, and powered by a small generator.”

The range of fine-screen meshes – with apertures of just 38 microns in size – can even separate blood from water and are used in environments like abattoirs.

Kwatani has a low-profile separator option with lower heights than the standard design. This allows it to fit into spaces too small for the standard design where installation space is limited.

Kwatani separators can also be used as safety screens as a last line of defence to remove off-spec product before it is packed.
This reduces the volume of returns and raises satisfaction levels among end-users.

“Manufacturing our own products promotes job creation and skills development, and also gives us the ability to offer high levels of product support, we know the products inside out,” says Mann.