Rating and Heating of Motors:
Continuous Duty Motor : There are two types of Continuous Duty Motor — continuous duty at constant load and continuous duty with variable load cycle. In the former the load torque remains constant for a sufficiently longer period corresponding normally to a multiple of time constant of the drive motor. The drive motor is therefore loaded for a sufficient amount of time continuously, till it attains thermal equilibrium. While driving such a load a motor should have a rating sufficient to drive it without …
Electric Motor Cooling and Heating : The geometry of an Electric Motor Cooling is too complex to predict accurately the heat flow and temperature distribution. This is a difficult task. A portion of the conductors of armature winding are embedded in slots and some portion is outside the iron material as overhang. The heating calculations are also complicated by the loading of the motor. The direction of heat flow does not remain the same at all loaded conditions. At no-load or lightly …
Electric Motor Power Loss and Heating : An Electric Motor Power Loss and Heating occurring in its various parts such as copper losses occurring in armature and field and eddy currents in the magnetic material used as a core, and mechanical losses due to friction and windage. These unavoidable Electric Motor Power Loss cause localized heating and are responsible for temperature rise of the motor. The heat flows from the point of origin to the external surface where it is dissipated to …
Periodic Intermittent Duty : The class of duty making use of the ability of electric motors to operate with overload is called Periodic Intermittent Duty. The load on the motor is a sequence of identical duty cycles as shown in Fig. 5.17. The drive motor is loaded at constant load for a period ton. At the end of ton the machine is switched off for a period of toff. The machine heats during ton and cools during toff. The time toff is …
Short Time Intermittent Duty : Another class of duty for normally occurring loads is Short Time Intermittent Duty in which the load requires a constant power for a short interval of time and rests for sufficiently longer time. When a motor is used for this purpose, duration of the load on the motor is less than the heating time constant of the motor or the time required for obtaining thermal equilibrium. The period of rest is sufficient enough to cool the motor …