Siemens SINAMICS G130 Engineering Manual page 173

Calculation example 2:
A SINAMICS S150 converter in degree of protection IP20 is to be operated as a centrifuge drive on a 400 V supply
system at a maximum ambient temperature of 40 °C at a maximum installation altitude of 1000 m. The motor current
I(t) and motor frequency f(t) over time are shown in the diagram below. In continuous batch process without
downtimes, therefore, the converter operates according to a regularly recurrent, periodic load duty cycle. The
converter is to be operated at the factory-set pulse frequency in vector control mode (drive object of Vector type).
Absolute value of motor current |I(t)| and motor frequency f(t)
1. Select the converter:
According to the diagram shown above, the converter must be capable of supplying a short-time current I
520 A. It therefore requires a base load current I
I / 1.5 = 520 A / 1.5 = 347 A.
ShortTime
For this reason, a converter rated for V = 400 V and I
a base load current I of 438 A and thus a short-time current I
H
frequency for vector control mode is 2 kHz. We shall now use a calculation to determine whether the selected
converter is suitable for the required periodic load duty cycle operating on the factory-set pulse frequency under the
conditions specified above.
2. Determine the current derating factor k
·
k : 1.0 (ambient temperature ≤ 40 °C, installation altitude < 1000 m, degree of protection IP20),
Temp
·
k : 1.0 (factory-set pulse frequency)
Pulse
·
k : 1.0 (not a parallel connection of S120 Motor Modules)
Parallel
·
k : This factor must be taken into account because of the periodic load duty cycle. According to the
IGBT
diagram above, the following applies:
- Current ratio ΔI = I
- Load duty cycle duration T = 300 s.
With ΔI ≈ 4.5 and T = 300 s, the derating factor is according to derating characteristic 3 which is
applicable to the SINAMICS S150 converter with V = 400 V and I
The current derating factor k
= ×
k k k
D Temp Pulse
3. Determine the permissible short-time current:
With a base load current I
H
= ×
I 1 5 .
Short Time
This value is slightly higher than the required maximum motor current of 520 A and is thus permissible.
Fundamental Principles and System Description
of at least
H
:
D
/ I
ShortTime BaseLoad
is therefore calculated as follows:
D
× × =
k k 1 . 0
Parallel IGBT
= 438 A and a derating factor k
× = × ×
k I 1 5 . 0 8 . 438 A
D H
T : Fill centrifuge
1
T : Accelerate to spin speed
2
T : Spin at spin speed
3
T : Decelerate to emptying speed
4
T : Empty centrifuge
5
T : Load cycle duration (T = T
= 490 A is selected which, according to catalog D 21.3, has
rated
of 1.5
ShortTime
= 520 A / 115 A = 4.52 ≈ 4.5.
× × × =
1 . 0 1 . 0 0 . 8 0 . 8
.
= 0.8, the permissible short-time current is
D
=
525 A
.
SINAMICS Engineering Manual – November 2015
Engineering Information
+ T + T + T + T
1 2 3 4
ShortTime
I = 657 A. The factory-set pulse
* H
= 490 A: k = 0.8.
rated IGBT
173/528
Ó Siemens AG
)
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