Siemens SINAMICS G130 Engineering Manual page 100

Fundamental Principles and System Description
Engineering Information
Key to equation:
•
I(t) RMS value of the output current of the converter or inverter as a function of time
(In the case of parallel connections of S120 Motor Modules, I(t) is the RMS value of the output
current of a partial inverter resp. one Motor Module.)
•
I Rated output current of the converter or inverter
Rated
(In the case of parallel connections of S120 Motor Modules, I
partial inverter resp. one Motor Module, not taking into account the derating factor for parallel
operation.)
•
k Current derating factor (see below for its definition)
D
•
T Load duty cycle duration which must not exceed the 300 s setting for the standard load duty cycle
For the practical calculation of the I
current in each case as an approximate substitute to the output current time characteristic required by the application.
This simplifies the calculation as the integration is replaced by a simple summation.
⎡
⎛
1
⎜ ⎜
= ⋅ ⎢
2
I t value
⎢
⎝
T
⎣
i.e. the sum of all phases T
illustrates the correlations:
Approximation of the current characteristic over time using time phases with constant current
The current derating factor k
current of the converter or inverter to be reduced:
Key to equation:
•
k
D
•
k
Temp
•
k
Puls
•
k
Parallel
•
k
ShortDutyCycle
The derating factors k
Temp
engineering manual. The derating factor k
The derating factor k
ShortDutyCycle
SINAMICS G130, G150 and S150 converters and S120 Motor Modules (Chassis and Cabinet Modules), which are
described in this engineering manual.
SINAMICS Engineering Manual – May 2008
100/396
© Siemens AG
2
t value, it is generally helpful to apply a finite number n of phases of constant
2
⎞ ⎛
I I
⎟ ⎟ ⎜ ⎜
⋅ +
1 2
T
⋅
1
⎠ ⎝
I k I
Rated D Rated
where
equals the load duty cycle duration T, where T must be ≤ 300 s. The diagram below
to T
1 n
specified in the equations takes into account all of the factors that require the output
D
= ⋅
k k k
D Temp
Current derating factor (total derating factor)
Derating factor for increased ambient temperatures of from 40 °C to 50 °C
Derating factor for pulse frequencies greater than the factory setting
Derating factor for parallel operation of S120 Motor Modules
Derating factor for short load duty cycles with T < 60 s).
and k can be found in the relevant catalogs or device-specific sections of this
Puls
has generally the value of 0.95 for SINAMICS S120 Motor Modules.
Parallel
for short load duty cycles with T < 60 s has generally the value of 0.9 for the
2
⎞ ⎛
I
⎟ ⎟ ⎜ ⎜
⋅ + +
T ......
⋅
2
⎠ ⎝
k I
D Rated
n
∑
=
T T
,
n
1
⋅ ⋅
k k
Puls Parallel ShortDutyC ycle
is the rated output current of a
Rated
⎤
2
⎞
⎟ ⎟
⋅ ⎥
•
n
T
100 %
⋅
n
⎥
⎠
k
⎦
D
.