A synchronous motor-generator set forACtoDCconversion.Small synchronous motor and integral stepdown gear from a microwave oven Asynchronous electric motoris anAC motorin which, atsteady state,[1]the rotation of the shaft is synchronized with thefrequency of the supply current; the rotation period is exactly equal to an integral number ofACcycles. Synchronous motors containelectromagnetson thestatorof the motor that create amagnetic fieldwhich rotates in time with the oscillations of the line current. Therotorturns in step with this field, at the same rate. The synchronous motor andinduction motorare the most widely used types of AC motor. The difference between the two types is that the synchronous motor rotates in exact synchronism with the line frequency. In contrast the induction motor requires "slip", the rotor must rotate slightly slower than the AC current alternations, to develop torque. Therefore small synchronous motors are used in timing applications such as insynchronous clocks,timersin appliances,tape recordersand precisionservomechanismsin which the motor must operate at a precise speed. Synchronous motors are available in sub-fractionalself-excitedsizes[2]to high-horsepower industrial sizes.[1]In the fractional horsepower range, most synchronous motors are used where precise constant speed is required. In high-horsepower industrial sizes, the synchronous motor provides two important functions. First, it is a highly efficient means of converting AC energy to work. Second, it can operate at leading or unitypower factorand thereby provide power-factor correction. These machines are commonly used in analog electric clocks, timers and other devices where correct time is required. 1/11 Continue...
Posted on: Thu, 18 Jul 2013 08:17:45 +0000
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