Power Ratings Of Sinamics Converters And Inverters / Definition Of The Output Power - Siemens SINAMICS G130 Engineering Manual

1.1.5

Power ratings of SINAMICS converters and inverters / Definition of the output power

SINAMICS converters produce an electrical three-phase system at their output, the power of which – taking into
consideration factor √3 – can be calculated from the output voltage and the output current, whereby any phase angle
can exist between output voltage and output current, depending on the load characteristics. Therefore electrical
output power, for which the converter's output is designed, presents an apparent power as a result of the existing
phase angle. This apparent power can be calculated from the obtainable output voltage and the continuously
permissible thermal output current, which is the rated output current I
SINAMICS converters in the vector control mode reach at the output almost the value of the incoming supply voltage
by using pulse-edge modulation, the apparent output power of the converter can be calculated using the following
formula:
This apparent output power of the converter is a physically correct value, but it is not really suitable to allow a simple
correlation between the converter output power and the rated motor power as the apparent power of the converter
(given in kVA) and the mechanical shaft power (rated power) of the motor (given in kW) do not directly correspond
because current, power factor and efficiency of the motor are required.
A much simpler option for the coordination of the output power of the converter and the rated power of the motor is
the definition of an active output power for the converter, which is deduced from the mechanical shaft power (rated
power) of a typical three-phase asynchronous motor which can be operated by the converter.
Definition of the output power for SINAMICS converters and inverters
The active output power of a SINAMICS converter or inverter is defined as the mechanical shaft power (rated power)
of a typical, 6-pole, asynchronous motor, which can be operated by the converter or inverter at its rated point, without
overloading the converter or inverter. As 2 and 4-pole motors always have a better power factor and also equal or
lower rated currents, all 2, 4 and 6-pole motors are covered by the definition of the output power given above with
regard to the coordination of the power between converter and motor.
In the SINAMICS catalogs and operating instructions (equipment manuals), usually several values for the output
power of the converters or inverters are given:
·
Output power on the basis of the base load current I
·
Output power on the basis of the base load current I
Each value for the output power of converters and inverters applies to motors with rated voltages of 400 V, 500 V or
690 V as well as a rated frequency of 50 Hz. (The definition of the standard load duty cycles – low overload and high
overload – and the definition of the corresponding base load currents I
cycles"). It is particularly important with SINAMICS S120 and S150 units with the wide input voltage range of 500 V -
690 V 3AC that the values for the output power of these units are depending on the voltage. Therefore they are
significantly different for 500 V and 690 V.
The following example should clearly illustrate how the output power for a SINAMICS converter is determined:
Converter data:
Line supply voltage
Rated output current
Base load current I for low overload
L
Base load current I for high overload
H
Rated outputs and rated currents of SIMOTICS TN series N-compact 1LA8
asynchronous motors listed in the catalog for operation with 400 V / 50 Hz:
Number of 200 kW
poles
p
2 -
4 -
6 345 A
Fundamental Principles and System Description
S = √3 • V
rated
250 kW 315 kW 355 kW
- 520 A 590 A
430 A 540 A 610 A
430 A 540 A -
When it is taken into consideration that
rated.
• I .
line rated
for low overloads
L
for high overloads
H
and I
L
380 V – 480 V
605 A
590 A
460 A
400kW
660 A
690 A
690 A
SINAMICS Engineering Manual – November 2015
Engineering Information
is given in the section "Load duty
H
Ó Siemens AG
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