electric motor understanding

MOTOR TERMINALOGY

Rotating machines have an outside (stationary) part, called the stator.The inner (rotating) part is called the rotor. The rotor is centered within the stator, so that the rotor axis is concentric with that of the stator. The space between the outside of the rotor and the inside of the stator is called the air gap. The rotor is mounted on a stiff rod (usually steel), called a shaft. The shaft is supported in bearings so that the rotor is free to turn. The shaft extends through one or both of bearings to provide a means to connect the machine to the mechanical system. Note that the rotor is solidly fastened to the shaft so that the rotor and the shaft turn at the same speed. There the terms “rotor speed”, “shaft speed” or “machine speed” all mean the same thing and are used interchangeably. The rotor and the stator each have three basic parts: the core, the winding, and the insulation. Thus it is proper to speak of “the rotor core”, “the stator windings” “the rotor insulation system” and so on. The purpose of the rotor and stator cores is to conduct the magnetic field through the coils of the windings. The cores are almost always made of iron or steel. The windings conduct electric currents that are the source of the magnetic field and provide closed loops in which voltages may be induce by the magnetic field, in according Faraday’s law. If the current in a winding varies with the load on the machine , it is called load current. If the current in a winding merely provides a magnetic field and is dependent of the load , it is called magnetizing current, or exciting current. A winding that carries only load current is called an armature. A winding that carries only magnetizing current is called a “field winding”. The Current in field windings is almost always dc. A winding which carries current that Provides both load and magnetizing functions is called a primary and is usually the power-input winding. In such cases, the power output winding is called the secondary. A winding that carries load current must handled all of the power being converted or transformed by the device; however, the magnetizing power requirement is relatively small. The steady-state power input to a field winding is only about  to 2 percent of the rated power of the machine. This input to dc field windings is all consumed as I2R loss, except during the turn-on transient ,lasting at most a second or two, during which energy is being stored in the magnetic field. The winding conductors are almost always copper or aluminum. Depending on the amount of current to be carried, they may consist of coils of wire or heavy bars. Current of large amperage require conductors of large cross-sectional area. Each winding consists of several coils or bars in series or in series/parallel combination.

The ends of certain of the windings are brought out to terminals to permit easy connection to the electric system