Rockwell Automation 825 Smart Motor Manager User Manual - Manual (Page 16)

1-2 Introduction
Publication 825-UM001B-EN-P January 2001
Operational Demands of the Motor/Drive
Temperature Rise
Motor designs and applicable standards require that, when a motor is operated under
specified loads and ambient conditions, the critical parts of the motor will remain within an
allowable temperature range and short-term overloads will not harm the motor.
The device protecting the motor must permit full use of the motor and its economical
operation. At the same time, the protective device must switch off rapidly if an overload
occurs.
Motor Operating Characteristics
Electric motors absorb electrical energy and supply mechanical energy. During this energy
conversion, losses are produced in the form of heat. The total loss consists of the following
separate losses:
• Losses independent of the current (these losses are virtually constant i.e., they also
occur at no load)
• Iron losses caused by remagnetization and eddy currents
• Mechanical losses caused by friction and ventilation
• Losses dependent on the current (these losses increase with load i.e., with the current
consumed by the motor)
• Heat losses caused by the current in the stator
• Heat losses caused by the current in the rotor
• Increased temperature rise caused by poor cooling (e.g., cooling fins are dusty or
damaged, coolant temperature is too high)