Siemens SINAMICS G130 Engineering Manual page 377

Dimensioning example:
A braking power as shown by the diagram below is periodically injected into the DC busbar of a system which is
supplied from a 400 V power supply network over a rectifier without regenerative feedback capability. Within a load
duty cycle duration of 100 s, the braking power reaches a peak value of 1300 kW for 10 s.
A SINAMICS S120 Motor Module suitable as a Braking Module for this application must be selected. The data of the
required braking resistors must also be calculated.
1. Select a suitable S120 Motor Module
The required peak braking power P
current. The maximum DC link voltage V
The smallest Motor Module capable of producing the required peak braking power of 1300 kW at the selected
response threshold of 774 V is chosen from the table of technical data:
·
Output power 710 kW at 400V / rated output current 1260 A.
As a 3-phase Braking Module, it is capable of producing a peak braking power of 1669 kW > 1300 kW.
The next step is to check whether the mean braking power of the given load duty cycle is below the permissible
continuous braking power of the selected Motor Module. In this case, it is 1140 kW.
·
P = (200 kW • 20 s + 1300 kW • 10 s + 800 kW • 30 s + 0 kW • 40 s) / 100 s = 410 kW < 1140 kW.
mean-Brake
The selected Motor Module is therefore suitable, both in terms of peak braking power and continuousbraking power.
2. Calculate the data of the braking resistors
The minimum value R
BR-min
Motor Module, it is
·
R (cold state) = 0.18 Ω .
BR-min
The maximum value R
BR-max
and the maximum braking power P
·
R (operating temperature) = [ 0.49 • (V
BR-max
The resistance specification is therefore as follows:
·
Resistance value:
·
The three resistors R
power of 1300 kW for 10 s in a 100 s cycle. Each individual resistor must therefore be dimensioned for one
third of the power values stated above.
= 1300 kW must be provided by a Motor Module with the lowest possible
max-Brake
= 774 V is therefore selected as the response threshold.
DC-max
of the three braking resistors can be found in the table of technical data. For the selected
of the three braking resistors is calculated from the response threshold V
= 1300 kW of the given load duty cycle to be
max-Brake
DC-max
0.18 Ω (cold state) < R
operating in unison must be capable of a continuous power of 410 kW and a peak
BR
Engineering Information
2
) ] / P = [ 0.49 • (774 V)
max-Brake
< 0.2258 Ω (operating temperature).
BR
SINAMICS Engineering Manual – November 2015
SINAMICS S120
= 774 V
DC-max
2
] / 1300 kW = 0.2258 Ω .
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Ó Siemens AG