Functions; Analog Value De-Coupling; Thermal Motor Protection - Siemens SINAMICS G120 Operating Instructions Manual

Functions

8.1

Analog value de-coupling

3 analog values can be connected-up in the chemical industry module. These involve, from
the system perspective (field side) one setpoint (frequency/speed) and two measured values
(motor current, motor frequency). Current signals DC 0/4 to 20 mA on the field side are used
as carrier signals for these values. On the field and CU side, the analog values have a
common reference potential. The setpoints and the two measured values are de-coupled
from one another through a high-ohmic path (>10 MΩ).
In the CM, the analog values are isolated between the field (motor side) and the CU (inverter
side). Maximum insulation voltages of 891 V (peak value, continuous operation) and 1670 V
(peak value, max. 1 s, discharge) are reached.
8.2

Thermal motor protection

Thermal motor protection (TMP) is used to directly monitor the motor winding temperature.
To realize this, the motor manufacturer integrates temperature-dependent resistors (PTC)
directly in the motor winding. When it reaches its limit temperature, the resistance of the PTC
suddenly changes (as a step function).
An evaluation unit is integrated in the chemical industry module for motors with integrated
temperature protection (type A PTC sensor). This ensures that the motor operating
temperature (when responding and switching back) is in conformance with IEC 60034-11-2
(DIN EN 60947-8).
Figure 8-1
Chemical industry module CM240NE with CU250S-2 DP
Operating Instructions, 03/2014, A5E34142527B-AA
TMP characteristic
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