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Contents • ABSTRACT • INTRODUCTION • BASIC OPERATION OF ELECTRIC MOTORS • WRITTEN POLE MOTOR DESIGN • OPERATIONAL BENEFITS OF WRITTEN POLE MOTORS • CONCLUSION • REFERENCES ABSTRACT A new type of AC machine has been developed which can provide performance beyond the capability of conventionally designed machines. This new “Written-Pole” machine technology consists of a rotor design that has a layer of magnetic material that can be changed magnetically to any desired pole pattern while the machine is operating. The ability to electrically place the magnetic poles is any position allows a synchronous motor to be built that has a very low per-unit direct line starting current, high operating efficiency, and very high inertial load starting capacity. It can also provide generators where the output frequency is independent of rotational speed In the 1990’s, a new concept was developed in electric motors called the Written Pole® electric motor. This new motor type dramatically N reduces starting currents of single phase O motors. The motor uses an innovative approach I T of controlling the magnetic field of the motor to C reduce the starting current requirements. The U result is a motor that has starting current D requirements of only about twice the normal O running current and, as an added benefit, the R motors have efficiencies of 90% or better T N compared to conventional motors, which have I efficiencies of around 85%. Basic operation of electric motor To understand how an electric motor works, we must first understand the principles of magnetism and electromagnetism. An electromagnet is simply a piece of iron or other ferrous material that has been wound with a conductor through which an electric current can pass. When a current is passed through the conductor the iron is magnetized and acts just like a permanent magnetic. Consider two electromagnets and one permanent magnet aligned as shown in the figure below. TW0 POLE ELECTO- The top electromagnet is oriented MAGNETIC with the north-pole pointing up. The middle permanent magnet is oriented in the reverse fashion, with its north-pole pointing down and the bottom electromagnet has its north pole pointing up. There will be a force of repulsion between the centre magnet and the other two since the south pole of the top magnet is aligned with the south pole of the centre magnet and the north pole of the bottom magnet is aligned with the north pole of the centre magnet.
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