4.1.4
Requirements for cables
Power cable
1. Only shielded medium-voltage cables may be used as power cables. Due to the low
capacitance, it is preferable to use single-phase cables, e.g. Protothen N2XS2Y. You can
also used armored cables of the type that are standard in some regions/industries. You
should, however, observe the dimensioning criteria regarding maximum capacitances and
inductances.
2. Lay the cables in a 3-phase bundle.
a)
Laying the cables in a 3-phase bundle
b)
Laying three parallel cables (to accommodate each phase)
Figure 4-3
Laying cables
The method used for laying the parallel cables is not critical as far as EMC is concerned.
However, to avoid damage in the event of a short-circuit current, you should fasten the
cables in the appropriate way.
3. Take into consideration the line-to-line voltage to ground (√3* U) when selecting the cable
voltage class. The converter can run even if a ground fault is present. In this case, the
voltage to ground is the line-to-line voltage.
4. Where the current is concerned, take into account the rms value for dimensioning purposes,
as the rms value also contains the harmonic currents.
Cable capacitance and inductance
Cable capacitances and inductances can influence the commutation. The cable capacitance
has an influence on the dl/dt limit required (toroidal cores). Add the cable inductance to the
effective motor inductance.
The project-specific dimensioning provides the max. permissible capacitance and the max.
permissible inductance with respect to the commutation process. Both specifications can be
found in the "Plant-specific data". Pay attention to this information.
Determining the effective values in the case of commutation
Effective cable capacitance in the case of commutation:
C = C’ (in μF/km) * cable length * number of parallel cables / 2
Preparations for use
4.1 Notes for system integrators
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