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In fully networked, intelligent factories, the requirements in terms of electromagnetic compatibility (EMC) almost inevitably increase. Especially in industrial plants where frequency converter-controlled motors are used, undesired currents increasingly occur on the equipotential bonding cables or protective earth cables. The Stuttgart cable experts at LAPP therefore set themselves the goal of investigating the physical coupling mechanisms within motor connection cables and deriving a new type of cable design from this. Visitors to HANNOVER MESSE 2023 will be able to see for themselves to what extent this project has been crowned with success - and those who are particularly curious will already find out when they read on.

New approaches to cable design

In developing the zeroCM technology - an innovative EMC solution, according to LAPP - the company took a completely new approach. Instead of solving the problem of EMC via the shielding, as is usually the case, the complete cable design of the ÖLFLEX SERVO FD zeroCM was rethought. Three phase conductors are now arranged symmetrically and stranded in an inner layer. In addition, the protective conductor is stranded in an outer layer with opposite stranding direction around the three phase conductors in a specific lay length ratio. The insulation of the conductors is capacitance-optimised and consists of polyethylene, polypropylene or a foamed variant. There is a separating fleece between the inner layer and the outer layer. "This special, innovative stranding technique achieves perfect electrical symmetry, which reduces magnetic radiation and greatly reduces internal couplings," explains Stefan Hilsenbeck, Senior Engineer Advanced Technology at LAPP Holding AG.

According to LAPP, the advantages of the invention are clear: the EMC-optimised cable design is easy to implement and offers the best protection against EMC-related interference currents. "The cable is asymmetrical in terms of visual appearance, but we achieve 100% electromagnetic symmetry and thus even get by with less shielding," Hilsenbeck emphasises.

Cause without effect

In summary, zeroCM technology does not eliminate the cause of EMC interference, but it does address one of the significant points where interference is introduced into the system environment. On the one hand, the new cable design enables equalising currents to be reduced by up to 80 percent at the frequency converter output and on parallel paths such as data lines. On the other hand, reduced cable-charging currents ensure reduced load on and in the frequency inverter itself. For example, longer cable lengths should be possible without the frequency inverter being operated outside its (EMC) specifications. In addition, zeroCM technology prevents the occurrence of voltage levels on the ground/earth potential (ground voltage) on the consumer side. This is particularly important when, for example, sensitive sensors such as analogue encoders are used.

Research project confirms effectiveness

The effectiveness of the new type of line has already been confirmed within the framework of the "PEPA" research project of the Federal Ministry of Economics and Climate Protection. In addition to LAPP, the companies SEW-EURODRIVE, BLOCK, Danfoss, MAGNETEC and the Technical University of Darmstadt are involved in the project. The best values in terms of leakage current at the inverter output were achieved by the low-capacitance design of the zeroCM cable. In addition, the interference current flowing via a parallel signal line was investigated: Here, too, the use of the zeroCM cable favours the lowest possible interference currents.

Favourable cost factor

In addition to the advantages described above, users can also save costs because costly filter technology can be dispensed with and the system runs more stably. "Although the new cable may seem unfamiliar when it is first assembled, the cabling remains as simple as usual, or the effort is even reduced compared to the earth-symmetrical cables with a third protective conductor that are currently still common on the market," says Hilsenbeck. LAPP plans to further expand its portfolio with zeroCM technology. The next focus will be on hybrid cables. Hybrid cables, bus cables or one-cable solutions contain, in addition to the power cores, also data, resolver or control core pairs, which up to now have been elaborately shielded from the power cores. The zeroCM technology results in a completely new freedom of arrangement of the construction elements, which should reduce the use of materials and increase performance.