Siemens SINAMICS S120 Installation And Start-Up Manual page 264

Basic Information about the Drive System
Monitoring and protective functions
Example
The factory setting for the alarm threshold for chip temperature monitoring is
15 °C. Temperature monitoring for the heat sink and inlet air is 5 °C, that is, the
"Overtemperature, overload" alarm is triggered at 15 °C or 5 °C below the shut-
down threshold.
The parameterized responses are induced via p0290 simultaneously when the
alarm is output.
Possible responses include:
S Reduction in pulse frequency (p0290 = 2, 3)
This is a highly effective method of reducing losses in the power section, since
switching losses account for a high proportion of overall losses. In many
applications, a temporary reduction in pulse frequency is tolerable in order to
maintain the process.
Disadvantage:
Reducing the pulse frequency increases the current ripple which, in turn, can
increase the torque ripple on the motor shaft (with low inertia load), thereby
increasing the noise level.
Reducing the pulse frequency does not affect the dynamic response of the
current control circuit, since the sampling time for the current control circuit
remains constant.
S Reducing the output frequency (p0290 = 0, 2)
This variant is recommended when you do not need to reduce the pulse
frequency or the pulse frequency has already been set to the lowest level.
The load should also have a characteristic similar to the fan, that is, a
quadratic torque characteristic with falling speed. Reducing the output
frequency has the effect of significantly reducing the converter output current
which, in turn, reduces losses in the power section.
S No reduction (p0290 = 1)
You should choose this option when neither the pulse frequency nor the output
current needs to be reduced. The converter does not change its operating point
once an alarm threshold has been overshot, which means that the drive can be
operated until it reaches its shutdown values. Once it reaches its shutdown
threshold, the converter switches itself off and the "Overtemperature, overload"
fault is output. The time until shutdown, however, is not defined and depends on
the degree of overload.
To ensure that an alarm can be output earlier or that the user can intervene, if
necessary, in the drive process (e.g. reduce load/ambient temperature), only
the alarm threshold can be changed.
Function diagram for thermal monitoring and overload responses
S 8014
7-264
Thermal monitoring power section
SINAMICS S120 Installation and Start-Up Manual, 12/04 Edition
E Siemens AG, 2004. All rights reserved