Siemens SINAMICS G130 Engineering Manual page 50

Fundamental Principles and System Description
Engineering Information
generators in order to reduce voltage harmonics. When Infeeds with regenerative capability (Smart Infeeds or Active
Infeeds) are supplied by diesel-electric generators, the appropriate parameters should be set to prevent the system
from operating in regenerative mode.
An extremely weak network would be, for example, a very low-output laboratory or test bay supply on which a high-
powered, variable-speed drive needs to be tested. If the drive were operated only under no-load conditions, there
could be no objection to this type of constellation. Very little active power is required under no load and the supply
system would not be overloaded in terms of power drawn. A basic prerequisite, however, is that the mains system
can supply the precharging current to precharge the DC link. The magnitude of the precharging current depends on
the unit type and is stated in the sections on specific unit types.
As long as the converter is designed as a 6-pulse rectifier without Line Harmonics Filter at the input side
(SINAMICS G130, G150 and S120 Basic Line Modules), the harmonic effects on the supply are also limited by virtue
of the low line currents, which means that this type of arrangement is perfectly suitable for test purposes. An
exception among the 6-pulse rectifiers is the SINAMICS S120 Smart Line Module, because this draws a significant
harmonic reactive current from the supply system, even under no-load conditions. For this reason, the regenerative
direction should be disabled in the firmware of Smart Line Modules if they are employed for the test purposes
described above.
Although 6-pulse drives with Line Harmonics Filters present no problems with respect to harmonics, there is still a
risk, as described above, that the fundamental wave of the line voltage will significantly increase due to detuning of
the filter, which means that the system can no longer function properly.
When high-power drives with Active Infeeds need to be tested (SINAMICS S150 or drives with S120 Active Line
Modules), an arrangement of this type is critical with respect to harmonics. The harmonics at the line side, which are
normally kept very low by the Clean Power Filter, can cause such distortions in the line voltage with RSC values of
< 5, even at no load, due to the high impedance of the weak network that the closed-loop control of the Active Infeed
starts to malfunction. In such cases, the system cannot operate properly, even if the Active Infeed closed-loop control
has been optimally parameterized.
SINAMICS Engineering Manual – November 2015
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