DRIVES AND CONTROLS
The WEG W22Xd flameproof motor, available from Zest WEG Group, meets worldwide standards for use in hazardous applications including the mining sector
classified for Group I( mines susceptible to firedamp) and Group II( surface industries), for gases Group IIB and IIC, is suitable for use in hazardous areas defined as Zone 1 and Zone 2 – Gases and Vapours, and Zone 21 and Zone 22 – Combustible or Ignitable Fibres.
The advantage of one motor carrying dual certification for gas and dust facilitates a reduction in inventory costs for users as a common motor frame can be used with different types and sizes of terminal boxes.
Developed in 2002, the initial range of WEG flameproof motors covered the larger power output segment for low, medium and high voltage supplies up to 11 kV. Following the introduction of motors in frame sizes 315 to 500, the range was extended in 2014 to include larger sizes through to a 710 frame.
Complying with the latest editions of IEC / EN 60079 standards, the WEG W22Xd range allows Zest WEG Group to provide a comprehensive range of hazardous area motor products from IEC frame sizes 71 to 710.
Features of the WEG W22Xd 560 to 710 frame design include a stainless steel tube array which provides air ducts allowing both axial and radial flow paths which optimise cooling of the rotor, stator and critical components such as the bearings. The motor is fitted with an aerodynamic fan and cover for efficient air flow with minimum noise.
Designed using finite element analysis( FEA) software, the cooling system on the WEG W22Xd flameproof motor provides outstanding heat dissipation. This reduces thermal stress on the insulating materials facilitating longer life. It also eliminates hot spots by providing a uniform temperature distribution throughout the frame.
The redesigned main terminal box of the WEG W22Xd flameproof motor incorporates fixing bolt housings that provide protection from impact and other environmental damage. This also prevents accumulation of water whilst providing generous space for easy connections.
There are multiple options available for the main power terminal box and accessory terminal boxes for connecting motor protections such as current transformers, surge arrestors or surge capacitors.
The WEG W22Xd flameproof motor is available with two, four, six or eight poles – with higher
polarities available on request- in low and high voltage versions and with a range of outputs from 500 kW to 4,500 kW. The frame has a robust welded steel construction and features solid integral feet to minimise vibration, complementing the low noise outputs.
With the WEG W22Xd range, Zest WEG Group has the capability to provide flameproof motor solutions for applications in virtually all extreme conditions including those with ambient temperatures from-55 ° C to + 60 ° C and altitudes up to 5,000 m above sea level.
“ Zest WEG Group’ s product line-up includes low and high voltage electric motors, vibrator motors, variable speed drives, softstarters, power and distribution transformers, MCCs, containerised substations, mini-substations, diesel generator sets, switchgear and cogeneration and energy solutions as well as electrical and instrumentation engineering and project management services.”
Elsewhere, Shaw Controls, a Zest WEG Group company, reports the successful completion of its contract to supply a containerised electrical solution to a gold mine in West Africa. Kirk Moss, Medium Voltage Manager at Shaw Controls, says the containerised solution will supply power to drive a mill on this new mine.
“ Containerised electrical solutions are becoming increasingly popular as these allow for speed of installation and are a particularly cost effective option for mine and plants operating in Africa,” Moss says.
The custom engineered sub-station comprises a medium voltage( MV) WEG Variable Speed Drive( VSD) and a dry type phase shift transformer driving a 2 000 kW, 6 pole, 6,6 kV squirrel cage WEG electric motor. The VSD is housed in the container while the oil cooled transformer is housed outside of it to facilitate heat dissipation.
Retrofitting variable frequency drives
When metallurgical processing plants are designed and built, equipment specification is usually tailored to meet the maximum expected operating conditions. XPS Process Control states:“ This can present challenges when operating at turndown conditions unless some means of adjusting equipment performance can be incorporated. In new plant designs, Variable Frequency Drives( VFDs) are often applied to rotating equipment such as slurry pumps to match the pump characteristics to the process duty. This technology was either not available or prohibitively expensive when many older plants were designed, and plant performance can suffer at turndown conditions. However, retrofitting
VFDs to existing pumps can provide significant benefits.”
Alan Hyde, Principal Engineer XPS Process Control, said in a recent article that a typical ball mill grinding circuit closed by cyclones was equipped with fixed speed cyclone feed pumps, one operating and one standby. Performance was good at high mill feed rates, but at reduced feed rates the cyclone feed pressure was very unstable. The fixed pump capacity made it impossible to maintain sufficient head in the pumpbox, resulting in pump surging. This was confirmed in the plant, with cyclic variations observed in the cyclone overflows, as well as audible cycling in the pump noise and vibration. Improved performance was obtained when running an identical pump equipped with a VFD, operating at reduced speed to maintain an appropriate pumpbox level. The benefits were estimated as potentially up to 0.5 % additional pay metal recovery in flotation from a more consistent flotation feed flow and quality, as well as energy savings of up to 8 % from the reduced pump speed and improved efficiency.
Marthinusen & Coutts consolidating position in Africa
Marthinusen & Coutts, a division of ACTOM( Pty) Ltd, says it is consolidating its role as an integrated electrical and mechanical services provider across Africa, and internationally. Together with subsidiary, ACTOM Turbo Machines, the division offers the full range of maintenance, repair and special manufacturing services for electric motors, generators, turbo machinery and other high speed mechanical rotating equipment.
Richard Botton, Divisional CEO, Marthinusen & Coutts, says both Marthinusen & Coutts and ACTOM Turbo Machines have a long and proud history of serving customers on the continent. He ascribes the ongoing success to a combination of diligent planning, a culture of problem solving and providing innovative solutions; a sense of urgency, industry-leading skills, and having the necessary infrastructure and resources in place, both in South Africa and in strategic African countries.
Marthinusen & Coutts is unique in that it is the only independently-owned service provider that is capable of providing extensive maintenance, repair and special manufacturing solutions for all electrical and mechanical rotating machinery.
“ We are well positioned to carry out critical projects both in Africa and globally, having access to all our resources in South Africa as well as our well-equipped facility in Zambia, which provides immediate services to our customers in that region, with all the sought-after advantages of a local facility, plus the full backup of M & C and ACTOM’ s resources in South Africa,” Botton says.
Marthinusen & Coutts has an extensive
10 International Mining | NOVEMBER 2017