Motion Control & Drives


MV motors deliver reliability and better total cost

May 2023 Motion Control & Drives

Many critical industrial and other applications can benefit from medium voltage (MV) electric motors, due to their reliability and low total cost of ownership. According to Zest WEG sales specialist, Floris Erasmus, the benefits of MV electric motors include being purpose-designed and well protected. This makes them very reliable, and thus well suited for critical applications where the risk of failure-related disruption must be mitigated. “Any motor application – from pumps and fans to crushers and conveyors – can present a critical risk if a significant portion of the whole operation relies upon it,” he says. “In these cases, it is often worth considering the MV motor option in new projects or in circumstances where motors are being replaced.”

He adds that while the category of low voltage (LV) electric motors tends to end at about 1000 V, MV motors range from 1000 V up to as high as 33 kV. In the South African market, the upper end of the MV range is usually 11 kV. MV motors are generally not off-the-shelf, and are rather specially designed for their application. The construction is also different to an LV motor. The wire used in the windings, for instance, is more like a rectangular bar. Normally covered with mica tape, they make up form-wound coils. The coils are individually wrapped with thicker insulation to accommodate the higher voltage. There is only one turn in a slot, so there is no potential difference between turns; this means that there is less chance of an inter-turn failure or short circuit between coils.

An important difference in the winding of an MV motor is that it is conducted using vacuum pressure impregnation (VPI) and the use of an epoxy resin. Applying this resin in a vacuum allows all air and moisture to be removed. The absence of air allows the resin to flow more effectively into the spaces between the steel core and the copper winding. The incidence of air pockets in the slot of the stator is where many winding failures in motors begin. If resin is not effectively distributed, this can undermine the mechanical strength of the winding. The epoxy resin used in MV motors is very strong compared to varnish. In addition, the removal of moisture during the VPI process reduces the possibility of short circuits caused by water particles trapped inside the motor windings.

“Another benefit of MV motors is their low starting and operating current,” he continues. “The kilowatt rating of a motor – the power it consumes – is a function of the voltage; by raising the voltage, the amperage drawn in reduced. The starting current of a motor tends to be about six times higher than the operating current. By reducing the operating current, an MV motor helps to reduce the strain that high starting currents can place on the electrical system in a mine, plant or factory.”

The MV option also has a distinct advantage when it comes to the use of variable speed drives (VSDs). The transformers that are part of the MV motor installation ensure that no extra filters or add-ons are required to achieve near perfect sine waves. He notes that MV VSDs are also better at disrupting harmonics in the electrical system.

Protection systems on MV motors are an important aspect of ensuring their longevity. Erasmus explains that they are normally electrically protected with a smart relay, which is password protected. This makes it difficult to bypass the overload systems that protect the motor, and prevents the motor from being started under fault conditions. While this protection might slightly increase installation costs, it helps reduce total cost of ownership.

“In terms of our own MV offering, WEG has recently launched its W51 range, which includes MV motors,” he says. “This new range offers improved efficiencies and higher output to weight ratios, and the motors are suitable for VSD.” Availability is from a 315 to 450 frame, which, with four-pole motors, translates to a range of 132 to 1400 kW. The standard range reaches 6,6 kV but motors up to 11 kV can also be requested. The range includes motors for hazardous areas, where there may be gases which are susceptible to ignition.


Credit(s)



Share this article:
Share via emailShare via LinkedInPrint this page

Further reading:

First Tornado vertical lift module in SA
Motion Control & Drives
The first South African Gonvarri Tornado 9th-generation vertical lifting module was designed and installed for ACDC Dynamics, a market leader in the supply of electrical components for automation, commercial, industrial and mining sectors. It was designed to improve the efficiency of ACDC’s warehouse. It is an ultra-fast, virtually noiseless computer-controlled storage and transfer lift.

Read more...
Mammoet assembles world’s biggest land-based crane
Motion Control & Drives
Mammoet, the global leader in engineered heavy lifting and transport, has started assembling the world’s strongest land-based crane.

Read more...
Tapered roller bearings keep mining dump trucks rolling
SKF South Africa Motion Control & Drives
SKF designs, develops and manufactures a range of premium quality products to meet the demands of the mining sector, which is notorious for punishing conditions that test machines, equipment, and components to their very limit.

Read more...
First battery-electric trolley truck system for underground mining
ABB South Africa Motion Control & Drives
Boliden, Epiroc and ABB have passed a new technology milestone by successfully deploying the first fully battery-electric trolley truck system on an 800-metre underground mine test track in Sweden. This means the mining industry is a step closer to realising the all-electric mine of the future, with sustainable, productive operations, and improved working conditions.

Read more...
New lubrication-free rod ends
igus Motion Control & Drives
The constant need for relubrication of metallic bearing points on rod ends in industrial applications is a time-consuming and expensive exercise and poses a real contamination risk. As a result, igus has developed maintenance-free polymer-hybrid spherical bearings which are a safer and more cost-effective alternative.

Read more...
Prime gearbox solutions for pump applications
Bearings International Motion Control & Drives
I-MAK is a premium global brand in the stable of bearings and power transmission specialist, Bearings International. With more than a million references and hundreds of different product lines, the company’s unique power transmission solutions cater to a large range of applications in virtually all industrial segments.

Read more...
Millions of tons of grease and oil in our waterways
igus Motion Control & Drives
Shocking statistics reveal that approximately 50% of lubricants used on industrial machines and equipment eventually makes their way into the environment, where just one litre of used oil has the capacity to poison about a million litres of water.

Read more...
High performance in a small, new package
Bearing Man Group t/a BMG Motion Control & Drives
BMG, which celebrates 50 years of business this year, has recently released the new Danfoss iC2-Micro Drive into the African market. This advanced system delivers superior motor control and mechanical brake performance, is more intelligent and powerful than its predecessor, and is easier to use, install and commission.

Read more...
Future-proofing SMEs with cobots
Omron Electronics Motion Control & Drives
Many countries around the world are likely to experience skill shortages over the coming decade, especially technical specialists. At the same time, product lifecycles are becoming shorter. Collaborative robots are easy to set up, and offer a quick and cost-effective solution.

Read more...
Flexible transport solutions for materials handling
Omron Electronics Motion Control & Drives
Omron has added a Selectable Autonomy functionality to the core software for its line of autonomous mobile robots

Read more...