Selection Of The Mains Filter Taking Into Account The Cable And Motor Leakage Capacitances - Keba ServoOne CM-P BG1 Operation Manual

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ID no.: 1400.201B.5-00
A.7.2 Selection of the mains filter taking into account the cable
and motor leakage capacitances
The effect of the mains filter is in general limited by the sum of all the leakage
capacitances in the components connected to the SO CM. This parasitic capacitance
is primarily determined by the motor cables connected. The capacitances in motors
connected form a further factor that cannot be ignored.
Therefore, typical application scenarios were assumed for the development of the filters
and the capacitances of KEBA motor cables and motors used as the basis to produce
typical total capacitances for which the filters were designed. For KEBA components the
following applies:
KEBA cables have a value of 0.47 nF/m
KEBA motors have a value less than or equal to 10 nF
For the 600 m filter variant, an application with 12 motors each with a cable length of
50 m is assumed for the design. With the above data, there is a total capacitance of
12 x 10 nF + 12 x 50 m x 470 pF/m = 402 nF. The total leakage capacitances for the
other mains filters are found similarly.
Overview of the permissible leakage capacitances for the mains filters
Permissible total leakage
Filter type
capacitance Cx [nF]
EMCxx.120 176
EMCxx.240 261
EMCxx.600 402
Table E.11 Total leakage capacitances on mains filters
Detailed consideration is necessary in applications with a larger number of axes or long
motor cables. Detailed consideration is also necessary if cables from other suppliers are
used and these cables are not designed to have low capacitance, and if motors from
other suppliers or special motors are used.
As the basis for the estimation of the permissible total cable length, use:
Lg = (Cx – Cm) / Ck
Date: 02/2020
Max. cable length that can be
connected for 12 axes [m]
120
300
600
Operation Manual Supply Unit SO CM-P BG1+2
Key:
Lg = Sum of the cable length for all axes connected [m]
Cx= Permissible total leakage capacitance of the mains filter (see table) [nF]
Cm= Sum of the parasitic capacitances in all motors connected [nF]
Ck = Capacitance of the motor cable used in [nF/m]
Example:
The SO CM system features the possibility of operating up to 24 axes on one supply
unit. Selected mains filter is in EMCxx.600.
Due to the capacitance contributed by the motors of 240 nF (24 x 10nF), a total cable
length of Lg = (402 nF-240 nF)/0.47 nF/m = 344 m is permissible.
That is an average per axis of 14.3 m on a "600 m filter".
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