What is the motor thermal model?

AuCom's motor thermal model offers precise motor protection normally only available from high-end motor protection relays.
- Protection is based on the motor's actual thermal capacity.
- Motor temperature is continually modeled.
- The thermal model accounts for different heating and cooling rates when the motor is in different operating states (starting, running or stopped).
- Both iron and copper losses are modeled.
The accuracy of the motor thermal model means the motor can be used to its maximum potential without nuisance tripping.
Thermal overload relays are imprecise because:
- The mass of the bimetal strips in the thermal overload is fixed and cannot be altered to match motor characteristics.
- They do not account for iron loss.
- They do not allow for different cooling rates at different stages of motor operation.
- The bimetal strips are affected by their ambient temperature, which is typically different to the motor’s ambient temperature.
- Adjustment is imprecise.
Inverse time-current and I2T electronic overloads offer limited protection because:
- The trip curves do not closely match motor heating.
- Inverse time-current protection does not account for motor temperature before the overload.
- They do not typically allow for differing cooling rates at different stages of motor operation.
- They do not account for iron loss.
- Adjustment is limited.