3 Assembly and installation
BU 0630 en-2020 35
Example
Given:
• Four 400 V SK 510P frequency inverters are connected to an electronic protective switching
device. Two inverters have a power of 5.5 kW and two have a power of 2.2 kW. All the inverters
are operated with a frequency of 6 kHz.
• The inverters are evenly distributed along the length of the cable.
• A two-wire shielded cable with a cross-section of 0.75 mm
2
and a total length of 100 m is used.
The smaller value is used for the maximum permissible cable resistance (in this case for 400 V,
5.5 kW, 6 kHz/application class B).
,
= 8 Ω
=
…
∗
= 19 Ω ∗
2
∗
0.1
0.75
2
= 2.53 Ω
The following formula applies for inverters which are evenly distributed along the length of the cable.
,
(
) =
,
∗
2
+ 1
,
(
) = 8 Ω ∗
2
4 + 1
= 3.2 Ω > 2.53 Ω =
=> OK!
24,
= 19.2 + 2.4 ∗
,
∗
+ 1
2
= 19.2 + 2.4 ∗
2.53 Ω
8 Ω
∗
4 + 1
2
= 21.1
Result: The cable resistance is low enough and the supply voltage must be at least 21.1 V.
Tip: If the calculated resistance is too high, the OSSD can be located in the middle of the cable
between the inverters. A star configuration with the OSSD at the centre of the star is also possible. In
this case, the cable capacity may be the limiting factor. In case of doubt, a larger cable cross-section
must be used.
Pos: 19 9 /Anlei tung en/El ektr onik/S afety /3. Fun ktions besc hreib ung/D etail s Sicher e Absc haltw ege/ Sicher er Absc haltw eg - Sichere Pulssperre und 24 V Versorgung_03 - EMV [SK 50 0P] @ 44\mod_1593157436188_388.docx @ 2638481 @ 3 @ 1
3.3.3 EMC
The EMC guideline values (see BU 0600) can be complied with by using an EMC-compliant wiring up
to a cable length of 100 m between the protective switching device and the frequency inverter.
Pos: 20 7 /Anlei tung en/El ektr onik/S afety /5. In betrieb nahm e/!Inbetriebnahme @ 15\mod_1486467478715_388.docx @ 2321059 @ 1 @ 1
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