Efficient Networks Siemens Sinamics S120 - Manual (Page 292)

Monitoring and protective functions
8.2 Thermal monitoring and overload responses
Drive Functions
292
Function Manual, (FH1), 07/2007 Edition, 6SL3097-2AB00-0BP4
8.2 Thermal monitoring and overload responses
Description
The priority of thermal monitoring for power unit is to identify critical situations. If alarm
thresholds are exceeded, the user can set parameterizable response options that enable
continued operation (e.g. with reduced power) and prevent immediate shutdown. The
parameterization options, however, only enable intervention below the shutdown thresholds,
which cannot be changed by the user.
The following thermal monitoring options are available:
● I
2 t monitoring - A07805 - F30005
I 2 t monitoring is used to protect components that have a high thermal time constant
compared with semi-conductors. An overload with regard to I 2 t is present when the
converter load r0036 is greater than 100% (load in % in relation to rated operation).
● Heat-sink temperature - A05000 – F30004
Monitoring of the heat-sink temperature (r0037) of the power semi-conductor (IGBT)
● Chip temperature - A05001 - F30025
Significant temperature differences can occur between the IGBT barrier junction and the
heat sink. These differences are taken into account and monitored by the chip
temperature (r0037).
If an overload occurs with respect to any of these three monitoring functions, an alarm is first
output. The alarm threshold p0294 (I 2 t monitoring) can be parameterized relative to the
shutdown (trip) values.
Example
The factory setting for the alarm threshold for chip temperature monitoring is 15 Kelvin (K).
Temperature monitoring for the heat sink and inlet air is set to 5 K, that is, the
"Overtemperature, overload" alarm is triggered at 15 K or 5 K below the shutdown threshold.
The parameterized responses are induced via p0290 simultaneously when the alarm is
output. Possible responses include:
● Reducing the pulse frequency (p0290 = 2, 3)
This is a highly effective method of reducing losses in the power unit, 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.
● 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. Further, the load should also have
a characteristic similar to the fan, that is, a quadratic torque characteristic with falling speed.