Siemens SINAMICS G130 Engineering Manual page 151

The calculation formula given above allows for arrangements in which a large-cross-section cable is taken from the
converter to a subdistributor to which motors are connected by small cross-section cables, as well as arrangements
in which the cables to individual motors are directly connected to the converter. In systems without a subdistributor,
the term n C (A) l must be set to "0".
D * D * D
The formula is valid for converters and inverters with one or two motor reactors at the output and for shielded and
unshielded motor cables. Allowance for the number of motor reactors (1 or 2) and the cable type (shielded or
unshielded) is made exclusively by the value l
in the relevant columns of the tables two pages above. It must however be taken into account that this formula is not
suitable for calculating mixtures of shielded and unshielded cables, e.g. in cases where a shielded cable is used up to
the subdistributor and unshielded cables to the motor.
Since only the ratio of capacitance values of motor cables with different cross-sections is relevant in the formula
rather than the absolute capacitance value itself, the capacitance per unit length values for cable type Protodur
NYCWY stated in the table below as a function of the cable cross-section can be applied for all shielded and
unshielded cable types for the purposes of this calculation.
Cross-section A
2
]
[mm
3 x 2.5
3 x 4.0
3 x 6.0
3 x 10
3 x 16
3 x 25
3 x 35
3 x 50
3 x 70
3 x 95
3 x 120
3 x 150
3 x 185
3 x 240
Capacitance per unit length of shielded, three-wire, motor cables
of type Protodur NYCWY as a function of the cable cross-section A
Calculation example:
A roller table with 25 motors, each with an output power rating of 10 kW, is to be supplied by a SINAMICS G150
converter. A converter with a supply voltage of 400 V and an output power of 250 kW is selected for this application.
The roller table application data are as follows:
The converter is sited in an air-conditioned room and will supply a subdistributor via two parallel, shielded cables,
50 m in length, each with a cross-section of 150 mm
cables, each on average 40 m in length with a cross-section of 1 x 10 mm
Since this is a multi-motor drive with a large number of parallel motor cables, it is absolutely essential to install a
motor reactor. We shall now use a calculation to check whether the selected converter combined with a motor reactor
can fulfill the requirements.
1st step:
Calculation of the quantities n
"Converter Cabinet Units SINAMICS G150" or the specifications in Catalog D11 by applying the information in the
above table of capacitance per unit length as a function of the cable cross-section:
According to Catalog D 11, a maximum of two parallel motor cables, each with a maximum cross-section of 240 mm
can be connected to the motor terminals of converter type SINAMICS G150 / 400 V / 250 kW. The maximum motor
cable length for shielded motor cables in combination with one motor reactor is 300 m according to Catalog D 11.
From this data we can calculate:
Fundamental Principles and System Description
, which is specified according to the configuration to be calculated
S max
Capacitance per unit length
[nF/ m]
0.38
0.42
0.47
0.55
0.62
0.65
0.71
0.73
0.79
0.82
0.84
0.86
0.94
1.03
2
. 25 motors are connected to the subdistributor via shielded
, C (A ) and l
S max S max max S max
Engineering Information
2
.
for single-motor drives from the data given in the chapter
SINAMICS Engineering Manual – November 2015
151/528
Ó Siemens AG
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