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Mobile switching stations for Eskom

The Zest WEG group has handed over to Eskom’s Central Region four 22 kV/11 kV unique mobile distribution switching stations, conceptualised and manufactured by Zest Energy. These fully integrated units were engineered to suit specific Eskom requirements including the ability to be used in different configurations.

The mobile distribution switching stations can be rapidly deployed to a site and quickly connected to support substation maintenance or emergency circumstances, improving the availability of Eskom’s electrical network. These units were also manufactured in accordance with South African road ordinance requirements to eliminate the need for special transportation permits.

“Zest Energy is involved in different types of substation and reticulation project work including fixed type conventional outdoor substations (typically up to 275 kV) as well as mobile substation solutions with a variety of configurations and voltages,” Alastair Gerrard, Zest Energy projects manager, says.

“Although the Zest WEG Group has been supplying transformers to Eskom on contract for several years, this is the first time that the group, through Zest Energy, has been tasked with innovating and developing an engineered solution of this type. Working with the Eskom project team, we developed this design from scratch to ensure that it met Eskom’s standards and specifications. The only off-the-shelf component in the entire mobile switching station is the MV switchboard.

“Part of the integrated solution is that all protection systems are on-board, as well as all supporting systems, to enable the operation of switchgear in a safe and controlled environment. This is essentially a fully-fledged switching station on wheels that runs on external auxiliary power supplied by the customer. There are other versions of mobile switching stations which involve putting switchgear into standard marine shipping containers and transporting them to site, but this product is a truly mobile solution that can easily be moved to site as, and when the need, arises.

Each mobile distribution switching station comprises two compartments, a medium voltage (MV) switchgear compartment and a switching control compartment, separated by an internal wall. Both compartments can be accessed directly from the outside of the trailer through fold-down single lever operated doors with fully incorporated handrails and steps. There are also sliding doors behind each main door to facilitate safe use of the switching station during extreme weather conditions.

Each mobile distribution switching station’s enclosure is custom built and integrated with a bi-axle, step-deck trailer which is, in turn, equipped with air suspension and ABS brakes. Each switching station incorporates an 11 panel, fixed pattern type MV switchboard (22 kV, 1 200 A, 25 kA/ 3s, 50 Hz) modified to accommodate standard Eskom protection schemes on board. The system is also integrated with other standard Eskom auxiliary systems, including metering, AC/DC power supply, BTU system with batteries and communication. Cable entry is designed as bottom entry through special access doors in the floor of each trailer and each cable can easily be terminated to the MV breaker terminals.

The switching stations can be used in coastal or polluted regions, owing to their double-insulated enclosure walls and roof as well as the non-corrosive materials of construction.