SINAMICS S120
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
371/528
The required continuous braking power of the Braking Module P
DB
is calculated from the mean braking power P
mean
according to the following equation
P
DB
≥ 1.125 • P
mean
.
Note:
The factor 1.125 = 1 / 0.888 makes allowance for the fact that the permissible mean power for load duty cycles such
as the P
20
or the P
40
cycle equals only 88.8% of the permissible continuous braking power due to the thermal time
constants involved.
2. Checking the required peak braking power P
peak
In addition to the mean braking power P
mean
, the peak braking power P
peak
is also a determining factor in the
selection of a Braking Module. It is therefore important to check whether the Braking Module with the continuous
braking power P
DB
calculated according to 1. is also capable of producing the necessary peak braking power P
peak
during the specified load duty cycle. If it does not have this capability, the continuous braking power P
DB
requirement
must be increased as far as necessary to ensure that the peak braking power requirement is also covered.
The flowchart below illustrates the process for doing this.
Flowchart illustrating the process for calculating Braking Module and braking resistor
To reduce the voltage stress on the motor and converter, the response threshold of the braking unit and thus also the
DC link voltage V
DC link
which is generated during braking can be reduced in operation at low line supply voltages
within the relevant line supply voltage ranges (380 V to 400 V, 500 V or 660 V). However, this also means a
corresponding decrease in the attainable peak braking power due to P
peak
~ (V
DC link
)
2
/ R with the reduction factor
k = (lower response threshold / upper reponse threshold)
2
.
The upper response threshold is set in each case at the factory. The settable response thresholds and corresponding
reduction factors k are shown in the table below. Please take into account in the selection process that Braking
Modules for 500 V to 600 V 3AC or for 660 V to 690 V 3AC (depending on the line supply voltage on site) must be
provided for units with the supply voltage range from 500 V to 690 V 3AC.
Line supply voltage
Response threshold V
with associated reduction factor k
380 V – 480 V 3AC 774 V (k=1) or 673 V (k=0.756)
500 V – 600 V 3AC 967 V (k=1) or 841 V (k=0.756)
660 V – 690 V 3AC 1158 V (k=1) or 1070 V (k=0.853)
Response thresholds of Braking Modules and associated reduction factors k
For examples of how to calculate the required Braking Modules and braking resistors, please refer to chapters
"Converter Chassis Units SINAMICS G130" and "Converter Cabinet Units SINAMICS G150"
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