The speed of a dc motor is changed by changing the current in the field or by changing the current in the armature. When the field current is decreased, the field flux is reduced, and the counter emf decreases. This permits more armature current. Therefore, the motor speeds up.
What happens when the speed of DC motor is increased?
When the speed of a DC motor increases, emf will get increases and hence the current drawn will get decreases.
When the speed of a DC motor increases back emf?
Since V and Ra are usually fixed, the value of Eb will determine the current drawn by the motor. If the speed of the motor is high, then back e.m.f. Eb (= PφZN/60 A) is large and hence the motor will draw less armature current and vice-versa.
What factors increased the speed of DC motor?
The speed of rotation of the coil in a D.C. motor can be increased by: (i) Increasing the strength of the current, (ii) Having more turns in the coil, (iii) Increasing the area of the coil, (iv) By increasing the strength of the magnetic field.
Why does motor speed increases?
By Ohm’s law, the amount of “extra” current will initially be the the (new) supply voltage minus the (old) induced voltage, all divided by the armature resistance. This increased armature current will increase the motor torque, which will cause the motor to speed up, which will increase the back emf.
When the speed of DC motor increases its armature current A increases B decreases C remains constant D None of the mentioned?
A 4 pole, 500V shunt motor has 720 wave connected conductors on its armature. The full load armature current is 60A and flux per pole is 0.03Wb.
| Q. | When the speed of dc motor increases , its armature current —- |
|---|---|
| B. | decreases |
| C. | remains constant |
| D. | none of the above |
| Answer» b. decreases |
How speed of the DC shunt motor can be increased?
So, the back emf is directly proportional to speed. We can control the speed by increasing armature resistance.
What is back emf of a DC motor?
back EMF in Electrical Engineering
Back EMF is the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates. When the speed varies, the winding characteristics may fluctuate, resulting in variation of back EMF.
Can we increase the speed of motor?
Increasing the speed can be achieved by increasing the supply frequency as the speed and frequency are directly proportional; however, there are two constraints.The maximum motor torque in the over-speed region is inversely proportional to the speed.
What are the factors that affect the speed of a DC motor explain how the speed can be controlled above and below base speed?
Thus, the speed of a DC motor can control in three ways: By varying the flux, and by varying the current through field winding. By varying the armature voltage, and the armature resistance. Through the supply voltage.
What affects motor speed?
The rotating speed of an electric motor depends on two factors: its physical construction, and the frequency (Hz) of the voltage supply. Electrical engineers select the speed of a motor based on the needs of each application, similar to how the mechanical load determines the horsepower required.
How does DC motor increase RPM?
You can increase the rotational speed of the DC motor by increasing the excitation current over the field coil of that motor or by increasing the field fluxes in the airgap of the motor ..
How does DC motor speed change?
Thus, the speed of a DC motor can be controlled in three ways:
- By varying the supply voltage.
- By varying the flux, and by varying the current through the field winding.
- By varying the armature voltage, and by varying the armature resistance.
What is the relationship between DC motor speed and DC motor current?
In general the speed of a shunt DC motor is directly proportional to the armature voltage and inversely proportional with the field current, disregarding inherent losses. Ideally, for constant armature voltage and field current, the motor speed should be constant, despite of the armature current.
When speed of a DC generator decreases the armature current?
When the speed of the DC generator decreases, the armature current increases. This is due to the generation of back emf in armature.
Why does speed decrease when current increases?
When field current increases, the motor speed will decrease because there is higher EMF. When armature voltage increases, the speed will increase.
Which of the following will decrease when the supply voltage of a DC motor is increased?
Easiest explanation: When supply voltage is increased full load current will decrease in order to keep output power constant, which will decrease torque at that moment, while starting torque will remain as it is, irrespective of any change in supply voltage.
Why the speed of a DC shunt motor decreases as the load increases?
In case of DC shunt motor, the flux per pole is considered to be constant, torque increases with the increase of load current. If the load current increases then the armature current also be increased and the speed slightly falls due to increase in voltage drop in armature.
How speed of the DC shunt motor can be increased decreasing the field current increasing the field current decreasing the load current increasing the armature current?
The speed of a dc motor is changed by changing the current in the field or by changing the current in the armature. When the field current is decreased, the field flux is reduced, and the counter emf decreases. This permits more armature current. Therefore, the motor speeds up.
Is the speed of a DC shunt motor is increased the back emf of the motor will?
So, the back emf is directly proportional to speed. Hence, when the speed of a DC shunt motor is increased, then the back emf of the motor will increase.
Which DC motor is preferred for constant speed?
Which D.C motor is preferred for machine tools? Explanation: DC shunt motor is a constant speed motor tool machine such as lathe machine requires being run at a constant speed. As lathe machines roll down iron pieces reducing Diameters at a constant speed.
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