Interferences can eventually limit or even interrupt the performance of electrical installations
An electromagnetic interference (EMI) is the phenomenon where two or more waves combine to form a resulting wave of greater, lesser, or equal measure to the original component waves. Whatever the case, the resulting wave is different to the original waves and as such, potentially unsuitable for its purpose.
Electromagnetic interferences are the interruptions that can occur in any electronic circuit, component, or system due to the presence of undesired voltages or currents, which are caused by internal or external radiation coming from signals radiated from electric motors, high voltage power lines, radio stations, etc., and even natural phenomena, which disturb, reduce, or limit the systems' performance.
Shielded cables with concentric wires
Shielded cables with concentric wires, whose spiral shape surrounds the whole conductor, work effectively for frequencies up to 20kHZ, with higher frequencies producing an inductive effect in the spiral which causes it to lose efficiency.
The shields, made from one layer of aluminium and polyester, provide the 100% coverage that is necessary for electrostatic protection. In addition to the metal layer, they should have an additional conductor in electrical contact with this same layer to facilitate earthing.
These shields can be longitudinal or spiral shaped, but with their lower inductance, longitudinal shields are advisable. These shields are light and flexible, and their most suitable function is to shield individual pairs of two-conductor cables or paired cables.
Shielded cables with copper braiding
Polished or tinned to facilitate soldering, they are effective at low frequencies because of their lower resistance, with the coverage necessary for electrical applications being 60%, while for signal, coverage at around 80% should be recommended.
Shielded cables with copper wire braiding have important technical characteristics that define them: braiding angle, wire diameter, number of wires per braid, as well as the number of braids. This copper must be earthed, with the most effective way being to solder it 360º around the conductor, although normally it will be twisted, forming a unipolar conductor which is what makes the connection.
Normally a layer of aluminium and polyster, and wire braiding means that coverage is boosted to 100%, with low resistance to the direct current, and the mechanical solidity of the shielding is improved.
Because of their special design, these cables (distributed earthing, shielding combined with 100% coverage for high frequencies and 85% coverage for lower frequencies) are the most suitable ones for frequency converter power supply. A variable frequency drive (VFD) is the control system for the rotational velocity of an alternating current motor, by means of varying the power frequency supplied to the motor. This equipment is being employed more and more frequently in all processes, with the aim of reducing electric consumption, as well as prolonging the motors' service life.
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