rattus said:
There will be real power dissipated as well--friction, windage, resistance, and iron losses for example. Even an unloaded motor gets dissipates heat.
Motor loss components(typical data)
- Core or iron losses are comprised of the energy required to magnetize the laminated core and current losses from magnetically induced circulating currents inside the laminated core. Core losses make up about 25 percent of the total losses. Core or iron losses can be reduced by utilizing higher quality steels with low core loss characteristics found in high grade silicon steel, using thinner gauges of steel, and designing longer cores to reduce operating flux density.
- Stator losses are due to the heating effect of current flow through resistant stator windings. Stator losses are proportional to the current squared and multiplied by winding resistance in ohms. As current flow in the stator increases, so does power loss. Stator losses account for approximately 35 percent of total motor losses.
- Rotor losses are due to the heating effect of current flow in the rotor. Rotor losses are proportional to the current squared and multiplied by rotor resistance in Ohms. As current flow in the rotor increases, power loss, as well, increases. Rotor losses account for about 25 percent of total motor losses. Rotor losses diminish with the use of higher grade steel and larger conductor bars with increased cross sectional area, which lower the resistance of the rotor.
- Friction and windage losses comprise bearing friction, wind friction, the motor's cooling fan load, and any other source of friction or air movement in the motor. These losses are often appreciable in large and high speed totally enclosed fan cooled motors. Friction and windage losses typically make up about 5 percent of total efficiency loss. Friction and windage losses are less problematic with the use of high quality bearings and lubricants, and improved fan designs.
- Stray load losses are other losses in addition to core, stator, rotor and frictional losses. They are primarily due to leakage induced by load current, design flaws and manufacturing variables. Stray load losses make up about 10 percent of total motor losses. Optimizing motor design and enforcing strict quality control largely diminishes the extent of stray load loss.
