The voltage applied to the motor may be reversed by backing the field current of generator through controller FC. When motor current increases, the control will disconnect the resistor and low speed torque is made available. Since speed is directly proportional to back EMF. Tapped Field Paralleling Field Coils: Variable Resistance in series with motor Series -parallel control method Flux Control Method In this flux control method, speed of the motor is inversely proportional to the flux.
Lesser the diverter resistance less is the field current, less flux therefore more speed. High current passes through the armature during the motor start up or when the motor is running at lower speed. Though speed can be increased above the rated value by reducing flux with this method, it puts a limit to maximum speed as weakening of flux beyond the limit will adversely affect the commutation.
This is commonly done with a special set of contactors direction contactors. A 5k ohm potentiometer is included. The Generator voltage can be varied by means of generator field regulator.
For these reasons, it is recommended not to operate the motor below its specified voltage rating. The higher number of turns of the shunt winding helps in generating a strong magnetic field.
In this method, the shunt field is connected to a fixed exciting voltage and armature is supplied with different voltages. Torque in the machine is generated by the interaction of the magnetic field of the windings and armature. Since N is directly proportional to the Eb. For a given constant load torque, if armature current is reduced then flux must increase.
It has a heavier gauge wire so it can support higher current. Unlike heavier gauges of wire in the winding in series motors, the shunt winding in this motor cannot carry very high current.
If the load is less, armature speed will increase. For a given constant load torque, if armature current is reduced, then flux must increase.
The shunt field windings of both DC machines are independently excited through variable resistors. In a shunt wound motor, the field coils are connected in parallel, or "shunted" to the armature coils.
By varying the current supplied to the rotor By varying the current supplied to the stator As the voltage around the rotor and stator is the same, the speed of the motor can be controlled by controlling the current through the stator or rotor.
Keeping these two above mentioned criterion in mind a DC shunt motor has been designed in a way, that the field winding possess much higher number of turns to increase net flux linkage and are lesser in diameter of conductor to increase resistance reduce current flow compared to the armature winding of the DC motor.
The field currents are much lower than the armature currents, allowing a moderate sized thyristor unit to control a much larger motor than it could control directly.
Speed control of series motor 1. Unlike series motors, the speed of the shunt motor is independent of the shaft load. Voltage Control Method a Multiple voltage control: A 5k ohm potentiometer is included More Information: Voltage Control Method Flux Control Method This method is very frequently used because it is very simple and economic.
In many applications, the motor-generator set was often left permanently running, to avoid the delays that would otherwise be caused by starting it up as required. This method of speed control is employed for DC series motor driving cranes, hoists, trains etc. In this method flux is reduced and speed is increased by decreasing the number of the turns of the series field winding.
Divertor is connected across the armature as in fig b.
In this method a number of tapping from field winding are brought outside. Field weakening is not used on its own but in combination with other methods, such as series-parallel control.In this system the armature of the DC Shunt motor is directly connected to a generator driven by a constant speed AC motor.
The field of the generator is supplied from the exciter (E). The field of shunt motor is supplied from a constant voltage exciter. Hence, a DC shunt motor is able to self-regulate its speed, and can be referred to as a constant speed motor.
When a load is applied to a DC shunt motor, its speed decreases, but the motor is able to self-regulate and quickly compensate for the lost speed.
A shunt DC motor has a feedback mechanism that controls its speed. As the armature rotates in a magnetic field, it induces electricity.
This EMF is generated in a reverse direction, thus limiting the armature current. Shunt Wound DC Motor | DC Shunt Motor on 24/2/ & Updated on 28/8/ The shunt wound DC motor falls under the category of self excited DC motors, where the field windings are shunted to, or are connected in parallel to the armature winding of the motor, as its name is suggestive of/5(10).
Speed control methods of DC motor Speed control of Shunt motor 1. Flux control method. It is already explained above that the speed of a dc motor is inversely proportional to the flux per pole.
Thus by decreasing the flux, speed can be increased and vice versa. Speed Control of DC Shunt Motor Rotating M-G sets are replaced by solid state converters to control DC motor speed. The converters used are choppers (in case of DC supply) or controlled rectifiers (in case of AC supply).
This method is not suitable for intermittent loads/5(9).Download