Ac Motors.

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  • Topic: Electric motor, Induction motor, Three-phase electric power
  • Pages : 13 (4115 words )
  • Download(s) : 122
  • Published : April 9, 2013
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INTRODUCTION
AC Motor
AC motors is a motor that uses alternating current to produce rotation. AC motors have several advantages, ac motors have only two bearings that can wear. Secondly, there are no brushes to wear because the motor doesn’t have a commutator. Maintenance is minimal. Also no sparks are generated to create a hazard in the presence of flammable material. The main parts of an ac motor are rotor and stator. A rotor is the rotating part of an ac motor. Stator is the stationary part of an ac motor. There are two main types of AC motors, depending on the type of rotor used. The first type is the induction motor, which runs slightly slower than the supply frequency. The magnetic field on the rotor of this motor is created by an induced current. The second type is the synchronous motor, which does not rely on induction and as a result, can rotate exactly at the supply frequency or a sub-multiple of the supply frequency. The magnetic field on the rotor is either generated by current delivered through slip rings or by a permanent magnet. Other types of motors include eddy current motors, and also AC/DC mechanically commutated machines in which speed is dependent on voltage and winding connection. AC Motors Theory

A universal motor is a single-phase series motor, which is able to run on either alternating current (ac) or direct current (dc) and the characteristics are similar for both ac and dc. The field windings of a series motors are connected in series with the armature windings. Basic principles of Universal Motors

The electrical design areas of a universal motor are the magnetic circuit, the field and armature windings, the commutator and brushes, the insulation and the cooling system.

Commutation Process of Universal Motors

Performance Characteristics of Universal Motors

PRINCIPLE OF AC MOTOR
Single-phase motors, used in ship. 3 phase motors are used in application ranging from fractional horsepower to over 500hp. Three phase motor are used because they are simple in construction require little maintenance and cost less to operate than 1phase or dc motors. The most common 3 phase used is the induction motor. An induction motor is a motor that has no physical electrical connection to the rotor. Induction motors have no brushes that wear or require maintenance. Current in the rotor is induced by the rotating magnetic field of the stator. In 3phase motor, a rotating magnetic field is set up automatically in the stator when the motor is connected to 3 phase power. The coils in the stator are connected to form 3 separate windings phases. Each phase contains one-third of the total number of individual coils in the motor. Each phase is placed in the motor so that it is 120 from the other phases. A rotating magnetic field is produced in the stator because each phase reaches its peak magnetic strength 120 away from the other phases. Three phase motors are self starting and don’t require an additional staring method because other rotating magnetic field in the motor. To develop a rotating magnetic field in a motor. The stator windings must be connected to the proper voltage level. This voltage level is determined by the manufacturers. 3 phase motors are designed as either single voltage motors or dual voltage. Single voltage 3 phase motors is a motor that operates at only one voltage level. Single voltage motor are less expensive to manufacture than dual voltage motors but are limited to locations having the same voltage as the motor. Common single voltage, 3 phase motor ratings are 230v 460v and 575v. Other single 3 phase motor ratings are2oo v 208v and 220v. All 3 phase are wired so the phase connected in either a wye or delta configuration. In a single voltage, wye connected 3 phase motor one end of each of the three phases is internally connected to the other phases. The remaining end of each phase is brought out externally and connected to a power line. The leads that are brought out externally are...
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