Modern Mining April 2020

Modular construction Mining plant construction is currently seeing a drive towards assembling as much as possible in a con- trolled environment, where testing is possible. The modular skids are then shipped to site, often in remote areas, where they are incorporated into the rest of the plant. “The cost of civil construction in many other African countries can be high,” says Claassen. “With these transformers, the brick and mortar require- ment is limited to just a support – no more bund wall needed to contain oil spills.” Electrical substations at industrial plant or mines are often housed either in converted shipping con- tainers or in custom-built e-house substations. “We have a strong engineering capability and we look at the complete solution around the transformer. We often supply a complete substation – a contain- erised, modular-type solution where we install the medium-voltage switchgear, the transformer, surge protection and others, to ensure the solution is fit for purpose.” Dry-type transformers are also designed sturdier and lighter than oil transformers as they are loaded and unloaded at harbours and transported to site by road. In many African countries, mines tend to be in remote areas, which means the transformers are trucked over long distances of bumpy, dusty road.

remote areas where the skills and equipment required for proper maintenance aren’t always avail- able,” says Claassen. Dry-type transformers, on the other hand, have a low maintenance requirement as they contain no oil and require no gas sensors. The temperature sensors fitted to dry type transformers are straight- forward PT100 probes which are easily removed and replaced if required. “Basically, all you do with dry-types during main- tenance shut-downs is to use an air compressor to blow the dust out of the windings.” Trafo does the complete winding of its cast-resin transformers, through its partner, TMC Transformers, a specialist in dry type transformer technology, in either aluminium or copper, depending on the ratio between factors such as the number of turns and the number of coils used. “The coils,” says Claassen, “are wound around a mould. The mould then goes into a vacuum chamber, where the resin is poured and cast. This process is the internal protection of the cast-resin transformer.” Upon completion of the process, Trafo runs par- tial discharge testing to ensure that factors such as temperature, vacuum and pressure were correct throughout. The partial discharge result should be <10 pC in compliance with the IEC, but the measured results are frequently <5pC.

A mobile modular process plant with cast resin transformers housed in electrical substations.

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April 2020  MODERN MINING  27