4.2.5.3 Selection of the motor line
The correct cabling as well as the motor line itself play an important part in case of low
power in connection with long motor line lengths. Low-capacitance line
(phase/phase < 65 pF / m, phase / screen < 120 pF / m) at the inverter output have the
followingeects:
• allow major motor line lengths („4.2.5.4 Motor cable length and conducted interfer-
ences at AC supply“)
• better EMC properties (reduction of the common-mode output currents to earth)
PE
PE
PE
VU
W
The use of shielded motor lines with symmetrical structure is re-
quired for higher motor power (from 30 kW). In these lines the
protective earth conductor is tripartite and evenly arranged be-
tween the phase lines. A cable without protective earth conductor
can be used if local regulations so permit. Then the protective
earth conductor must be laid externally. Certain lines also permit
the shield for the use as protective earth conductor. For this, ob-
serve the details of the line manufacturer!
Figure 26: Symmetrical motor line
67
CONNECTION OF THE POWER UNIT
4.2.5.4 Motor cable length and conducted interferences at AC supply
The maximum motor cable length is depending on the capacity of the motor cable as
well as on the EMC emitted interference. External measures must be taken here (e.g.
theuseofalinelter).Thefollowinginformationisvalidfortheoperationunderrated
conditionsandtheuseofKEBlistedltersunderchapter„4.3.1 Filters and chokes“.
Device
size
Max. motor cable length shielded
in accordance with EN 61800-3
Category C2
Motor cable (low capacitance)
21
100 m
22
23
24
Table 33: Max. motor cable length
Thecablelengthcanbeincreasedsignicantbyusingmotorchokesormotor
lters.KEBrecommendstheuseofmotorchokesorltersforacablelength
upto 50 m.
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