Why does a DC motor increase in speed when its field strength is decreased?
Table of Contents
- 1 Why does a DC motor increase in speed when its field strength is decreased?
- 2 What increases the speed of a DC motor?
- 3 What happens to the DC motor speed when the field current is reduced?
- 4 How does a decrease in flux produce an increase in speed in a linear machine?
- 5 How do you reduce motor speed?
- 6 Does the speed of a shunt motor increases or decreases when the armature current increases?
Why does a DC motor increase in speed when its field strength is decreased?
If the field flux of a DC motor is decreased, the motor speed will increase. The reduction of field strength reduces the CEMF of the motor, since fewer lines of flux are being cut by the armature conductors, as shown in below Equation. This increased torque causes the motor to increase in speed.
What increases the speed of a DC motor?
You increase the speed by increasing the frequency. If a motor base speed is 60 Hz, raising the frequency to 120 Hz will double the speed of the motor.
What will happen to the speed of DC shunt motor when the flux is increased?
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.
Why speed decreases as load increases?
As the load torque increases the electromagnetic torque decreases and vice versa.. Power is always same for constant power operation.. .. So if the load torque increases the speed decreases and vice versa… In this way speed of the motor decreases with the increasing of load in rotor shaft…
What happens to the DC motor speed when the field current is reduced?
Magnetic flux in turn is related to field current by the magnetisation characteristics. Hence speed of DC Shunt motor increases with decrease in field current.
How does a decrease in flux produce an increase in speed in a linear machine?
1 Answer. The instant flux is reduced, the back emf reduces and this causes the armature to increase current. More current means a higher driving torque and this accelerates the armature to run at a higher speed until the speed equation is in balance again.
Why is speed inversely proportional flux?
In case of series motors torque is directly proportional to the flux and current (diagram below). When we add a resistance across the armature then armature current decrease and since torque is constant so flux increases… Now speed is inversely proportional to the flux so when flux increses speed decreases..
How does DC motor speed increase and decrease?
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.
How do you reduce motor speed?
So, if you want to decrease speed, decrease voltage. If you want to decrease torque, decrease current. If you increase torque (say by putting a brake on the motor), you are increasing motor torque. But if you don’t change the supply of electrical power, then the mechanical power also won’t change.
Does the speed of a shunt motor increases or decreases when the armature current increases?
From the equation. (3) we can say, speed is inversely proportional to armature current. Thus, when the speed of the dc motor is increased, the armature current will decrease. So, the correct answer is “Option B”.
Why does motor speed drop?
As the load increases, to maintain the voltage at a constant value, current decreases, due to which the strength of magnetic field produced by the Internal Winding of DC motor decreases. This results in a decreased interaction of the two magnetic fields and thus Decrease in Speed of motor is observed.