Emerson PACMotion IC830DP 01207, Руководство по аксессуарам

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PACMotion™ Servos Accessories Guide Section 8
GFK-3173C December 2020
Motor Chokes 22
Section 8: Motor Chokes
8.1 Shielded Motor Cables
For electromagnetic compatibility, the motor must be supplied with power using a shielded cable. The
structure of a cable with 100% shielding and the capacity equivalent circuit diagram (to earth) are shown
below.
Figure 21: Shielded Motor Chokes
8.1.1 Why use motor chokes?
•
To compensate for high capacitive charge/discharge currents typical of shielded motor cables
approximately 25 m and longer.
•
To reduce current alternation noise in the motor.
•
To reduce the current ripple in the motor.
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 rising of the motor current, thereby reducing the current transferred to the
shield.
8.1.2 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
equivalent resistance can reduce the oscillation tendency of the LCR oscillating circuit
(drive/choke/cable/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.