Fundamental Principles and System Description
Engineering Information
SINAMICS Engineering Manual – November 2015
Ó Siemens AG
174/528
4. Determine the I
2
t value of the motor current:
According to the time characteristic of the motor current as shown by the diagram above, the I
2
t value is
ú
ú
û
ù
ê
ê
ë
é
×
÷
÷
ø
ö
ç
ç
è
æ
×
+×
÷
÷
ø
ö
ç
ç
è
æ
×
+×
÷
÷
ø
ö
ç
ç
è
æ
×
+×
÷
÷
ø
ö
ç
ç
è
æ
×
+×
÷
÷
ø
ö
ç
ç
è
æ
×
×=
5
2
5
4
2
4
3
2
3
2
2
2
1
2
1
2
1
T
kI
I
T
kI
I
T
kI
I
T
kI
I
T
kI
I
T
valuetI
DRatedDRatedDRatedDRatedDRated
• 100 %
ú
ú
û
ù
ê
ê
ë
é
×
÷
÷
ø
ö
ç
ç
è
æ
+×
÷
÷
ø
ö
ç
ç
è
æ
+×
÷
÷
ø
ö
ç
ç
è
æ
+×
÷
÷
ø
ö
ç
ç
è
æ
+×
÷
÷
ø
ö
ç
ç
è
æ
×= s
A
A
s
A
A
s
A
A
s
A
A
s
A
A
s
valuetI 60
392
350
60
392
520
60
392
115
60
392
520
60
392
115
300
1
22222
2
• 100 %
[ ]
%%%..... 90100
300
270
100847610525610525
300
1
2
=×=×++++×=
s
s
sssss
s
valuetI
.
The calculated I
2
t value of 90 % is below the acceptable value of 100 % and is therefore permissible.
5. Determine the permissible current during interval T
5:
During interval T
5
the converter is operated at an output frequency of 5 Hz, a frequency which is lower than 10 Hz.
Since the duration of this interval is 60 s and it occurs periodically in a 300 s cycle, it corresponds to 20 % of the total
operating period and is thus significantly higher than 1 % to max. 2 % of the total operating period of the centrifuge.
Therefor the derating characteristic described in subsection "Operation without overload with frequent periods of low
output frequencies < 10 Hz" in section "Power cycling capability of IGBT modules and inverter power units" must
therefore be applied to interval T
5
:
Permissible output current with frequent periods of low
output frequencies as a function of output frequency
According to this derating characteristic, the converter may be operated at a maximum of only 75 % of its rated
current in operation at 5 Hz output frequency if premature failure of the unit is to be avoided. The permissible current
during interval T
5
is thus calculated as follows:
AAITI
Rated
36849075.075.0)(
5
=×=×=
.
This value is higher than 350 A. The converter may therefore be operated continuously with 350 A at 5 Hz during
interval T
5
within the periodic load duty cycle T.
The selected SINAMICS S150 converter rated for V = 400 V and I
rated
= 490 A is thus suitable for the centrifuge
application with the given periodic load duty cycle provided it is operated at the factory-set pulse frequency.
To Next Page
Loading...
