Siemens SINAMICS G130 Engineering Manual page 174

Fundamental Principles and System Description
Engineering Information
2
4. Determine the I t value of the motor current:
According to the time characteristic of the motor current as shown by the diagram above, the I
é
æ
1 I
ê ç ç
= ×
2
t I value 1
×
T I k
ê
è
ë
Rated D
é
æ
1 115 A
= × ê ç ç
2
t I value
300 s 392
ê
è
ë
1
[
2 = × +
t I value 5 . 2 s
300 s
2
The calculated I t value of 90 % is below the acceptable value of 100 % and is therefore permissible.
5. Determine the permissible current during interval T
During interval T the converter is operated at an output frequency of 5 Hz, a frequency which is lower than 10 Hz.
5
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
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 is thus calculated as follows:
5
=
I ( T )
5
This value is higher than 350 A. The converter may therefore be operated continuously with 350 A at 5 Hz during
interval T within the periodic load duty cycle T.
5
The selected SINAMICS S150 converter rated for V = 400 V and I
application with the given periodic load duty cycle provided it is operated at the factory-set pulse frequency.
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2 2
ö æ ö
I
÷ ÷ ç ç ÷ ÷
× + × +
T 2 T
1 × 2
I k
ø è ø
Rated D
2 2
ö æ ö
520 A
÷ ÷ × + ç ç ÷ ÷ ×
60 s 60
A 392 A
ø è ø
+ + +
105 . 6 s 5 . 2 s 105 . 6 s
:
5
× = ×
. 0 75 I . 0 75 490
Rated
2
æ ö æ
I I
ç ç ÷ ÷ ç ç
× +
3 T 4
× 3 ×
I k I k
è ø è
Rated D Rated
2
æ ö æ
115 A 520
+ ç ç ÷ ÷ × + ç ç
s 60 s
392 A 392
è ø è
270 s
]
× = ×
47 . 8 s 100 % 100
300 s
5:
=
A 368 A .
= 490 A is thus suitable for the centrifuge
rated
2
t value is
ù
2 2
ö æ ö
I
÷ ÷ ç ç ÷ ÷ ú
× + ×
T 5 T
4 × 5
I k
ú
ø è ø
û
D Rated D
2 2
ö æ ö
A 350 A
÷ ÷ × + ç ç ÷ ÷ ×
60 s 60 s
A 392 A
ø è ø
.
=
% 90 %
•
100 %
ù
•
100 %
ú
ú
û