<P> Standardized NEMA & IEC motor frame sizes throughout the industry result in interchangeable dimensions for shaft, foot mounting, general aspects as well as certain motor flange aspect . Since an open, drip proof (ODP) motor design allows a free air exchange from outside to the inner stator windings, this style of motor tends to be slightly more efficient because the windings are cooler . A lower speed requires a larger frame . </P> <P> The method of changing the direction of rotation of an induction motor depends on whether it is a three - phase or single - phase machine . In the case of three - phase, reversal is straightforwardly implemented by swapping connection of any two phase conductors . </P> <P> In a single - phase split - phase motor, reversal is achieved by changing the connection between the primary winding and the start circuit . Some single - phase split - phase motors that are designed for specific applications may have the connection between the primary winding and the start circuit connected internally so that the rotation cannot be changed . Also, single - phase shaded - pole motors have a fixed rotation, and the direction cannot be changed except by disassembly of the motor and reversing the stator to face opposite relative to the original rotor direction . </P> <P> The power factor of induction motors varies with load, typically from around 0.85 or 0.90 at full load to as low as about 0.20 at no - load, due to stator and rotor leakage and magnetizing reactances. Power factor can be improved by connecting capacitors either on an individual motor basis or, by preference, on a common bus covering several motors . For economic and other considerations, power systems are rarely power factor corrected to unity power factor . Power capacitor application with harmonic currents requires power system analysis to avoid harmonic resonance between capacitors and transformer and circuit reactances . Common bus power factor correction is recommended to minimize resonant risk and to simplify power system analysis . </P>

What are the types of 3 phase induction motor