Extending the Service Life of Electric Motors with HELUKABEL

April 18, 2022

DCS HELUKABEL Extending Service Life of Electric Motors 1 400

When operating electric motors with frequency converters, undesirable bearing currents often occur that can significantly impact the service life of the rolling contact bearings. Scientists at TU Darmstadt have investigated these bearing currents - and found out that they can be reduced in some cases with the help of screened motor supply cables.

Bearing currents are undesirable currents that occur during the operation of electric motors. They flow through the roller bearings that connect the movable rotor to the fixed motor stator. Bearing currents occur mainly in drives where the speed is changed with the help of a frequency converter and can cause considerable damage to the bearings. Particularly in cases that have an inappropriate grouding concept, bearing currents with high current densities can occur, which melt or even steam the metal in the bearing ring. The result is craters and so-called riffles in the roller bearing, which become noticeable with increased vibrations and wear even faster. As a result, the bearing often fails only a few months after installation.

There are four kinds of bearing currents, each of which is influenced by different factors and has varying degrees of impact:

•Capacitive bearing currents are caused by the voltage across the bearing changing and compensating the currents flowing. These are typically too small to be harmful.
•Discharge bearing currents (EDM) are pulsed discharge currents. They can occur if the voltage increases in the bearing across the lubricant film until it is electrically broken.
•Circular bearing currents are circular currents in the electrical machine. This is caused by a high-frequency magnetic ring flux around the shaft, which induces a voltage along the shaft.
•Rotor-to-ground bearing currents can occur if the rotor of the electric drive is additionally grounded through a gearbox or another device and its ground impedance is lower than that of the stator. The current flows proportionally from the motor housing through the bearings into the shaft and across the ground connection of the rotor.

However, by designing the bearing appropriately, using hybrid or ceramic bearings as well as brushes, filters and grounding rings, design engineers have some options to reduce and avoid these unwanted currents.

Shielding Makes the Difference

DCS HELUKABEL Extending Service Life of Electric Motors 2 400

A decisive criterion is the selection of the right motor cable - this was the result of a study by the Institute for Electrical Energy Conversion at the Technical University of Darmstadt, carried out with the cooperation of HELUKABEL. The scientists compared the occurring bearing currents for cable types with and without screening in several test setups. In the process, they found out that rotor-to-ground bearing currents in particular can be significantly reduced by using shielded cables.

Shielded cables are a simple and effective method to protect rolling-contact bearings from premature wear and failure. An additional advantage: their shielding also prevents unwanted electrical radiation to other devices and thus contributes to the electromagnetic compatibility (EMC) of the entire system.

In its tests, the team from the TU Darmstadt used HELUKABEL motor cables of the type TOPFLEX®-EMV-UV-3 PLUS 2YSLCYK-J. This double-shielded cable is designed for interference-free operation of frequency converters. Furthermore, it is UV and weather resistant and therefore suitable for outdoor use. HELUKABEL's TOPFLEX® series comes in many versions according to different requirements - and has an extensive range of servo and feedback cables for industry and mechanical engineering.

UL/CSA motor cable products include:

•TOPFLEX® 600 VFD: XLPE Insulation, EMC-preferred Type, Flexible Motor Power Supply Cable, Oil-resistant, NFPA 79 Ch. 4
•TOPFLEX® 650 VFD: XLPE Insulation, EMC-preferred Type, Flexible Motor Power Supply w/ Control Conductors, Oil-resistant, NFPA 79 Ch. 4
•TOPFLEX® 1000 VFD: XLPE Insulation, EMC-preferred Type, Flexible Motor Power Supply w/ 3 Symmetrical Ground Conductors, Oil-resistant, NFPA 79 Ch. 4
•TOPSERV® 600 VFD: XLPE Insulation, EMC-preferred Type, Highly Flexible Motor Power Supply Cable, Oil-resistant, NFPA 79 Ch. 4
•TOPSERV® 650 VFD: XLPE Insulation, EMC-preferred Type, Highly Flexible Motor Power Supply w/ Control Conductors, Oil-resistant, NFPA 79 Ch. 4

Source

Put to the Ultimate Test – Part 1: Torsion Tests by HELUKABEL

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Cables and wires in industrial robots and other moving machine parts are often required to withstand extreme stresses caused by torsion. Constant repetitive movements put materials under considerable strain. At the same time, operators expect components to function perfectly and reliably throughout their entire service life to avoid disruptions, outages and safety hazards.

For this reason, at HELUKABEL, we simulate intensive and continuous torsion stresses under realistic conditions with our high-tech testing equipment in Windsbach. We have several types of apparatus for doing this because some of our customers, for example those in the automotive industry, have very precise specifications for how a torsion test is carried out. The tests show that our cables and wires withstand speeds up to 1,000°/s, accelerations up to 2,000°/s² and torsion angles up to 720°. Hence, we make sure that each product always meets our customers’ high standards, and that they receive the impeccable quality they rightly expect from us as a leading supplier of cables, wires and accessories for more than 40 years.

What Is Torsion?

To learn the answer, click here

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Festo Didactic at the Forefront of Developing Canada’s Future Work Force

DCS Festo Didactic at the Forefront of Developing Canadas Future Workforce 1 400x275

With Canadian manufacturing suffering from a growing labour shortage, the participation of industry in skills development is emerging as a vital component in hiring and retention.

The needs are stark: The Canadian Exporters and Manufacturers Association says almost 40% of its members have jobs they can’t fill. Five years from now, 60% expect to be short-staffed, especially when it comes to skilled trades. Statistics Canada forecasts the country’s labour force growth rate will remain below 0.2% for the rest of the decade, below replacement levels.

This growing shortage is affecting companies of all sizes. Already, some manufacturers acknowledge losing out on contracts because they can’t find the manpower to fulfill them.

In reality, the challenge is two-fold: to replenish and expand the workforce to help close the gap between the number of job seekers and vacancies through 2030 when the last baby boomers reach age 65, and ensure workers get opportunities throughout their careers to upgrade or add to their skillset as current technologies evolve and new ones emerge. Festo, through Festo Didactic, one of the world leading provider of equipment and solutions for technical education, intends to help Canada meet this challenge on both fronts. In essence, the approach Festo has always taken is that the learning never stops.

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