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EMC filter `will work with unscreened cables 600m long`

01 February, 2000

EMC filter `will work with unscreened cables 600m long`

Most filters designed to tackle EMC (electromagnetic compatibility) problems from AC inverters will work only with motor cables less than 50m long. Now, the EMC specialist Schaffner has come up with a new type of filter which, it says, will work with screened cables up to 200m long and unscreened cables up to 600m.

As well as allowing the use of cheaper unscreened cables, Schaffner says that its device, which combines matched input and output filters in a single package, will reduce stress levels on motors, extending their lives. The ability to handle long runs of cable means that the FN 5100 filter can also be used in installations where several motors are driven from one inverter.

Schaffner claims it can cope with up to six paralleled motors, each having 40m long cable. Another promising application is where an existing motor is being linked to a new inverter. Normally, the existing unscreened cabling would have to be replaced using costly screened materials. Schaffner says that the new filter will allow the unscreened cable to be kept, cutting both materials and labour costs.

The new filter can also be used with applications such as borehole and down-well pumps where the motor is often located several hundred metres from the inverter. Combining the input and output filters in a single module avoids the problems of resonance that can occur with separate, unmatched filters, and saves space and installation work, according to Schaffner.

The exact length of motor cable that the filter will support depends on the switching frequency of the inverter, the motor frequency and the operating temperature of the filter. The higher the frequency, the shorter the cable length. The FN 5100 can handle voltages up 480V AC and comes in seven different current ratings from 6-33A. The filter can be used with most three-phase inverters with switching frequencies in the range 10-20kHz and with 50Hz or 100Hz motors.

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