Industrial solutions provider Rand Technical Services (RTS) reports that it supplied a variable speed drive (VSD) system to mechanical products and control manufacturer Danfoss last year. The VSD system was used in a dust extraction system on diversified miner Anglo American’s Kumba Iron Ore’s Sishen opencast mine, in the Northern Cape.

“This semi-arid area, renowned for its extreme ambient temperatures of up to 42 ºC, needed a suitable system for its conditions, which RTS assisted in supplying,” says RTS MD Ian Fraser.
“The Sishen project required that we provide a maintenance-free system that would ensure low dust levels, and a reliable flow of air at a rate specified by Danfoss’ engineers. “In addition, each of the eight containerised units had a different layout so we needed to design and engineer the spin filters to fit specific applications,” says Fraser.

VSD’s are able to electronically vary the speed of electric motors; however, challenges can arise as VSD’s rely on semiconductors – which at times can be unreliable – to generate heat, explains Fraser.

“VSDs are placed inside containerised or brick motor control centre (MCC) rooms on mine sites in order to protect them from the environment, owing to the fact that ambient temperatures on site are, generally, very high, making the inside of the container excruciatingly hot. “The system’s self-generated heat results in specification oversized air con- ditioners,” says Fraser.

For this reason VSD’s have a back- channel cooling system, which enables one to channel ambient air from outside the control room, through the VSD, and vent it back to the atmosphere.

“The system saves up to 85% of the heat extracted, thus drastically reducing cooling costs. “Furthermore, this cooling air only passes over the heat sink surfaces, and avoids contact with the internal elec- tronic components, preventing contamination of the control electronics, thereby extending the life of the system,” states Fraser, who cautions that dust build-up on the heat sink surfaces over an extended period of time could impair heat transfer capabilities.

“Moreover, the air-conditioning units pump cool air into the area around the VSD panels, which wastes energy since all of the energy absorbed by the air conditioner is used to maintain a reasonable temperature within the container or MCC room,” explains Fraser adding that the technology allows for smaller air-conditioning units to be fitted and, therefore, a reduction in elec- tricity consumption.

The units are self-cleaning and energy- efficient, as only the auxiliary purge fans, that direct the polluted air out of the air stream, require power.

“Our ability to adapt our product to the specified requirements of our customers is our major differentiator in an industry driven by boxed products, and by working closely with customers, we are able to engineer solutions that provide them with the results they require,” Fraser concludes.