A purpose-designed electrical house (E-House) from Zest WEG is driving one of the largest new High Intensity Grinding (HIG) mills in the southern hemisphere, which was recently installed at a platinum mine in South Africa’s North West province.
The size and operational parameters of the mill place demanding requirements on the equipment in the E-House, according to Tyrone Willemse, senior proposals manager at Zest WEG. Constructed in South Africa incorporating a range of products – produced and distributed by Zest WEG, the E-House design also delivers world class standards of safety and fire protection.
“The key benefit of the prefabricated E-House concept is the time it saves the customer and the high level of quality that can be ensured through its construction and testing under ideal workshop conditions,” he says. “The process is also streamlined as the complete project falls under a single provider, who takes full responsibility for delivering on-time and on-budget.”
This E-House includes the HIG mill’s variable speed drive (VSD) and all its associated auxiliary circuits and starters. A range of WEG transformers and motors are also part of this project. With its extensive in-house expertise, Zest WEG generates fully detailed designs for its E-Houses, using 3D computer assisted design (CAD) software.
“For this application, the E-House consists of a medium voltage (MV) room and a low voltage (LV) room,” he notes. “The MV room houses the well-known WEG MVW01 VSD, with an integral oil type 12 pulse transformer manufactured locally at our transformer manufacturing facility in Wadeville.”
Comprehensive fire detection
Willemse explains that the WEG MVW01 makes use of high voltage insulated-gate bipolar transistors (IGBTs), which lower the amount of power electronics needed. This also reduces the mean time to repair (MTTR), so that operations can be quickly restored in the event of a major fault on the system.
“The WEG MVW01 powers a WEG 3.75 MW MGR eight pole 3.3 kV directly-coupled squirrel cage induction motor,” says Willemse. “This motor is specially designed to be vertically mounted to meet the HIG mill’s operation and maintenance requirements.”
Both the motor and the VSD were designed to meet the aggressive torque requirements during some phases of the mill’s operation. The combination comfortably handles the torque requirements that periodically exceed 170% for more than three minutes, giving the customer the necessary flexibility. The LV room contains the motor control centre (MCC) that feeds all the auxiliary circuits of the mill.
“Importantly, we have installed the newly arc-proof type-tested IEC 61641 WEG board, which has the best rating for personal protection,” he says. “In the event of an internal arc, the MCC is fitted with an explosion duct that transfers any explosion safely out of the building.”
Another aspect of the safety features is a comprehensive fire detection and suppression system that meets the customer’s demanding standards. The two rooms are fitted with their own fully automated room-flooding suppression systems, which can flood the space with gas that douses electrical fires but is not dangerous to humans.
“The system can detect smoke at a very early stage, and can also check against false triggering,” he says. “More than two smoke detectors must react, activating a loud bell for evacuation or cancellation, before flooding takes place.”
The LV room also houses WEG CFW11 LV VSDs, which feed premium efficient WEG motors. The E-House’s small power and lighting circuits are fed by one of Zest WEG’s locally manufactured SANS780-compliant transformers.