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AKD2G/AKD/S700 Accessories Manual | 12 Motor Chokes
12 Motor Chokes
12.1 Shielded Motor Cables
For electromagnetic compatibility, the motor must be supplied with power using a shielded cable. The struc-
ture of a cable with 100% shielding and the capacity equivalent circuit diagram (to earth) are shown below.
Why use motor chokes?
To compensate for high capacitive charge/discharge currents typical of shielded motor cables approx-
l
imately 25 m and longer.
To reduce current alternation noise in the motor.
l
To reduce current ripple in the motor.
l
The digital drives' high switching frequencies and steep switching edges give rise to the transfer of capacitive
currents to the shield by the three phases (U, V, W). These currents flow from the shield to earth. Depending
on the cable length and cable capacity, this can lead to the generation of shield currents with peak values of
up to 20 A. These shield currents place a load on the drives and motor and, on large systems, lead to shifts in
potential which can damage other components. This effect is evident in particular on systems with multiple
drives operating in parallel on the same mains filter. The motor chokes slow down the rate of rise of the motor
current, thereby reducing the current transferred to the shield.
Why is the cross-section of the motor cable important?
Motor cables longer than 50 m with a small cross-section (such as 4x1.0mm²) and therefore a higher equi-
valent resistance are able to reduce the oscillation tendency of the LCR oscillating circuit (drive/choke/c-
able/motor). This cross-section can also be advantageous for cable lengths shorter than 50 m if the cable
capacity and motor inductance are very high. However, the current loading of the cable must always be within
the limits specified by industry standards.
50 Kollmorgen™ | kdn.kollmorgen.com | November 2019
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