Leveraging its considerable in-house expertise and local manufacturing capability, Zest WEG recently custom designed and manufactured one of the largest mobile substations ever built in South Africa.

The 50 MVA mobile substation – destined for Guinea – includes a dual voltage rated mobile transformer produced by WEG in Brazil, according to Bernard Mitton, engineering team leader for integrated solutions at Zest WEG. The substation will be commissioned early in 2022.

“This is a full turnkey project procured by Robustrade in Dubai for the Utility Company of Guinea, called Electricité De Guinée,” says Mitton. “Our in-house team co-ordinated the electrical, civil and mechanical designs, as well as the engineering solutions for the customer.”

The full project includes three trailers of equipment, and allows the end-user to step down power from the main national grid at various geographic points as required. High voltage power is tapped from existing overhead line with a specifically designed and manufactured tee-off solution connecting the supply into the mobile substation, where it is stepped down from 110 kV or 60 kV to 20 kV or 30 kV depending on requirements.

“From the 50 MVA mobile substation, the supply is then distributed to a 30-20 kV mobile switching station, containing an incomer and five feeders,” he says. “Mini-substations can be fed directly, or a cable can feed to a junction box in the field, usually where there is an existing cable in the ground.”

As part of the project, Zest WEG designed and supplied a cable reel trailer with all power and control cabling needed for the mobile transformer and mobile switching station. Included on this trailer are 30 kV field junction boxes to assist with the cable connection between exiting cables already installed and the supply cables from the mobile switching station. These boxes allow for up to three feeder cable connections. The advantage of this design, he notes, is that the junction box becomes a termination point. The termination ends of the on-site cable do not need to be redone, and all that is necessary is a bolt-on connection.

“This mobile substation solution is suitable for both temporary and permanent installations, so it can be used in a range of applications,” Mitton says. “For emergencies, it can replace an existing substation transformer in the event of failure, and for standby applications it can handle temporary overloads at substations.”

It can also be put to use during routine maintenance, to manage the loads of existing substations being maintained, repaired or inspected. This minimises the delay in taking out the unit due to load and other system constraints. The mobile substation can even be used to provide power for large project sites or mining sites of high importance.

He highlights that the design and construction of solutions for mobile applications, including mobile generators, is one of Zest WEG’s strengths. The expertise and capability within the business allows these units to be custom-designed to suit customer requirements. In fact, none of the mobile solutions provided to date have been identical.

“We have acquired valuable experience from many years of designing, manufacturing and supplying mobile solutions in modular configurable designs – mainly for Africa and Latin America,” he says.

“These are not off-the-shelf products, but are custom-engineered solutions to technically comply with user’s specifications, integral requirements, the operational environment, logistical requirements and the safety of the operating personnel.”

The mobile substation includes innovative design features such as the integration of several functions into a compact, modular design. New technologies such as hybrid circuit breakers have been employed, along with disconnectors, earthing switches, ring-type current transformers, inductive voltage transformers and surge arresters.

“All the functionalities are included in a single prefabricated solution, while space requirements for switchgear bays are reduced through high integration of components,” says Mitton. “The substation’s transformer was specifically designed and manufactured by WEG in Brazil for mobile applications.”

Other special features include bushings made of composite silicon rubber, as well as an advanced mechanical and electrical safety interlock system. The modular design simplifies on-site installation, as all equipment has been pre-fabricated, pre-wired and pre-tested before shipping.

“This enhances the reliability of the solution, which translates into high availability and less maintenance,” he says. “It also simplifies the transport, logistics and commissioning.”

The order for the mobile sub-station was placed just before the Covid-19 lockdown in early 2020, so the project had to be managed under challenging conditions. The factory acceptance testing of key components, for instance, could not be done in person due to travel restrictions – so this was successfully done through virtual platforms across different time zones.

“All in all, we embraced the new communication technologies and proved once again that we could deliver to customer requirements even under unprecedented conditions,” Mitton says.

“Being able to meet the stringent requirements of Electricité De Guinée, through close collaboration with the Robustrade team, ensured the project was a success, proving this solution suitable for use across the region,” he concludes.

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