To achieve rotation, there has to be some interaction between magnetic flux produced by electromagnetism within the motor. Armature Diverter : Rheostat Divider is connected across the armature of the coil as shown in fig b. The shaft torque Tsh is less than armature torque Ta due to. Universal motors for commercial are usually of small capacity, not more than about 1 kW output. This is due to the fact that the rotor is constructed in a manner resembling a squirrel's cage. Series Motor Speed Control Motor speed control is achieved by controlling the voltage applied to the motor. Further if you have any queries you can call us on the toll free no.
Therefore series motors are not suited for the application where load on the motor is completely removed and where motors are driving the belts. And for this reasons series motor becomes essential as the starter motor in industrial applications which deal with heavy mechanical loads like huge or large metal chunks. As heavy currents flow through the very thick series field windings, large torques are produced in series motors. This method of speed control is not economical due to considerable power losses in speed controlling resistances. Cookies are not enabled on your browser. This method is known as Ward Leonard System.
If we add resistance in series with the armature, the armature current Ia decreases and hence speed decreases. Slip is a measure of the difference between the synchronous speed of the stator field rotation and the rotor field rotation. Therefore, before magnetic saturation of the field, flux ɸ is directly proportional to Ia. The basic adjustable armature voltage control method of speed d control is accomplished by means of an adjustable voltage generator is called Ward Leonard System. Where, I is the input line current Ia is the armature current Ish is the shunt field current Equation 1 is the current equation. This method is quite efficient. Series motors are not suitable when a constant speed is required.
This essentially controls the torque developed by the motor. The drawback is speed regulation. The motor can be connected in two arrangements: cumulatively or differentially. Speed control of series motor 1. Flux control method To control the flux, a rheostat is added in series with the field winding, as shown in the circuit diagram.
Hence, for small currents speed is inversely proportional to ɸ. Armature speed is approximately proportional to the voltage across the armature. They are Shunt motor, Series motor and Compound motor. Because this field is fixed, it cannot be adjusted for speed control. Since the armature voltage and the field direction reverse at the same time, torque continues to be produced in the same direction.
To carry this huge load, field windings are very thick and have few turns. The number of times this occurs per unit of time is referred to as frequency. Series motors can develop very high starting torque and provide excellent torque characteristics under load. This feature is used to slow down and recharge batteries on and electric cars or to return electricity back to the electric grid used on a street car or electric powered train line when they slow down. Therefore, when armature current is very small the speed becomes dangerously high. Torque of the series motor is proportional to square of the field current i. This high electromagnetic torque produces motor speed, strong enough to lift heavy load overcoming its initial inertial of rest.
Variable Resistance In Series With Armature Method In this method, an R is series with the armature of motor. It is seen that for a 4 pole motor, the speed of the motor can be obtained easily. An induction motor has a rotor rotating part and a stator stationary part within the motor housing. Please note that the interconnection of the field stationary winding and armature rotating winding determine the machine's operating characteristics. Since the speed is not related to the line frequency, universal motors can develop higher-than-synchronous speeds, making them lighter than induction motors of the same rated mechanical output. M2 is the motor, it controls the speed of the generator.
In this method the output from the generator G is fed to the armature of the motor M2 whose speed is to be controlled. This has restricted the practical application of this type of motor. Rotor has a central axle about which the rotor rotates in relation to the stator. By varying the rheostat diverter , any speed below the normal speed can be achieved. Series Wound Motor In the series motor, the field winding is connected in series with the armature winding.