Figure 3-2 Logic Diagram: Motor Thermal Overload Protection (49) - Siemens 7SR17 Rho Manual

Chapter 1) 7SR17 Rho Description Of Operation
Gn 49 Char (Thermal Characteristic)
The IEC thermal characteristic of the Rho conforms to IEC60255-8 (Thermal Electrical Relays).
A user definable thermal curve is available to allow matching of the relay thermal characteristic to all motor and
cooling system types.
'Starting' and 'cooling' constants modify the thermal heating time constant during motor run-up and stopped
conditions.
The thermal state may be reset from the fascia or externally via a binary input.
Thermal overload protection can be inhibited from:
Inhibit 49 A binary or virtual input,
Figure 3-2 Logic Diagram: Motor Thermal Overload Protection (49)
Gn 49 TauH Heating Constant (Heating Time Constant)
Used during normal motor running conditions and overloads.
Gn 49 TauS Starting Constant
Multiple of heating time constant takes into consideration the reduced cooling available during motor starting.
Gn 49 TauC Cooling Constant
Multiple of heating time constant takes into consideration the reduced rate of cooling of a stopped motor.
Page 28 of 78 ©2014 Siemens Protection Devices Limited