80 Program features Motor thermal protectionThe control program features two separate motor temperature monitoring functions.The temperature data sources and warning/trip limits can be set up independently foreach function.The motor temperature can be monitored using• the motor thermal protection model (estimated temperature derived internallyinside the drive), or• sensors installed in the windings. This will result in a more accurate motor model.In addition to temperature monitoring, a protection function is available for ‘Ex’ motorsinstalled in a potentially explosive atmosphere.Motor thermal protection modelThe drive calculates the temperature of the motor on the basis of the followingassumptions:1. When power is applied to the drive for the first time, the motor is assumed to be atambient temperature (defined by parameter 35.50 Motor ambient temperature).After this, when power is applied to the drive, the motor is assumed to be at theestimated temperature.2. Motor temperature is calculated using the user-adjustable motor thermal time andmotor load curve. The load curve should be adjusted in case the ambienttemperature exceeds 30 °C.Note: The motor thermal model can be used when only one motor is connected tothe inverter.Temperature monitoring using PTC sensorsOne PTC sensor can be connected to digital input DI6.The resistance of the PTC sensor increases when its temperature rises. Theincreasing resistance of the sensor decreases the voltage at the input, and eventuallyits state switches from 1 to 0, indicating overtemperature.1…3 PTC sensors can also be connected in series to an analog input and an analogoutput. The analog output feeds a constant excitation current of 1.6 mA through thesensor. The sensor resistance increases as the motor temperature rises, as does theDI6+24VDT
