The sheer size of mining and minerals processing operations frequently means cable lengths between drives and motors are long. Both VLT® and VACON® drives are designed to provide trouble-free operation with cable lengths up to at least 150 m for screened cables and 300 m for unscreened cables. And, as no additional output filters are required with these cable lengths, this saves space, installation time and costs compared to more traditional drive solutions. With built-in RFI filters, they comply with EMC standards, ensuring reliable operation of all other electrical equipment on the same installation. This more compact solution often results in considerable initial project cost savings as a result of being able to use smaller, lower cost switchrooms and substations.
Harsh, dusty conditions and extreme temperatures are common and can create challenges for any electronic product. Although it is common practice on modern mine sites to install drives in relatively clean, pressurized, air conditioned switchrooms and substations, it has become well-recognized that a drive designed for harsh environments will have a significantly longer, trouble-free lifetime. This ultimately ensures better asset availability and saves maintenance costs for the mining company. Both VLT and VACON drives are available with coated PCBs ensuring they are suitable for installation in harsh environments as defined by IEC 60721-3-3 Class 3C2 at least.
AC drives are increasingly being used to efficiently control equipment on mine sites. To protect them from the harsh environment, they are often installed in sealed switchrooms. This creates challenges as the more drives there are in a room, the bigger the challenges with heat loads. Larger and more expensive air conditioning systems might be needed to control the heat loads in switchrooms and substations. However, the unique back-channel cooling design of higher power VLT drives and availability of VACON liquid-cooled drives can result in significantly reduced heat loads in switchrooms, enabling the use of smaller, lower-cost air-conditioning systems.
VLT drives rated 90 kW and higher incorporate an innovative back-channel cooling design. There are separate cooling paths for the power components and control electronics, separated by an IP54 seal. Back-channel cooling removes approximately 85% of the power loss directly through the heatsink, leaving only 15% of the total loss to be dissipated in the switchroom. Although separate cooling paths themselves are not innovative, the innovation in our VLT drives comes from ensuring they are separated by an IP54 seal and making it easy to duct outside air into and out of the back-channel air path.
When outside air quality on the mine site is suitable, using the heatsink cooling fans and appropriate mounting and ducting, filtered external air at temperatures up to 50°C can be used to exhaust approximately 85% of the heat loss from the VLT drives. The heat loss can easily be exhausted directly outside the switchroom with no effect on the switchroom pressurization. The switchroom air-conditioning system only needs to be sized for the remaining 15% heat losses into the switchroom, saving significant costs for the switchroom and on-going operating costs of the air conditioning.
In addition, the compact size of VLT and VACON drives, both designed as standard for long motor cables without requiring additional options, often means smaller switchrooms can be built, providing further opportunities for significant switchroom cost savings.
While AC drives help optimize production, save energy and extend equipment lifetime, they also introduce harmonic currents to the mine site grid. If not kept under control, these harmonics can affect the performance and reliability of generators and other equipment.
Reliable estimation of the harmonic impact of AC drives on the mine site electrical system, combined with the use of the optimum mitigation equipment, helps plants avoid the hidden and often expensive consequences of harmonic distortion.
All VLT and VACON drives supplied for mine site installations incorporate a DC link choke or AC choke, first level, harmonic filter as standard. If required, additional harmonic filters and other harmonic mitigation solutions, as well as software tools for calculating harmonic mitigation requirements, are also available.
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