What do you mean by back emf in dc motor?
When the armature of the DC motor rotates under the influence of driving torque, the armature of the conductors moves through a magnetic field inducing an emf in them. The induced emf is in the opposite direction to the applied voltage and is known as the back emf.
What is eb in shunt motor?
DC Shunt Motor Equations
When the DC voltage (V) is applied to the field and armature winding, the back EMF (Eb) is induced in the armature winding which opposes the applied voltage. The applied voltage (V) is equal to the Ia*Ra voltage drop plus back EMF(Eb).
What will happen if back EMF is removed?
The only way for the back EMF of a motor that is still turning to vanish would be for the magnetic field to suddenly go to zero. This could happen if the stationary permanent magnets were suddenly removed, or in a field wound motor if the field winding was disconnected.
What is back EMF What is the importance of back EMF?
The presence of back emf makes the d.c. motor a self-regulating machine i.e., it makes the motor to draw as much armature current as is just sufficient to develop the torque required by the load. When the motor is running on no load, small torque is required to overcome the friction and windage losses.
Is back EMF AC or DC?
Back EMF can have either a sinusoidal (AC) or a trapezoidal (DC) waveform. The shape of the back EMF is important, as it determines the type of drive current and commutation method that should be used for the motor.
Why starters are required in a DC motor?
1. Why starters are required in a DC motor? … Explanation: Starting resistance of a DC shunt motor and DC compound motor is low. Well, that’s the reason why we use starters in a DC motors, in order to limit the armature current flowing through the armature and to protect machine circuitry.
Where is DC shunt motor used?
The applications of shunt DC motor include the following. These motors are used wherever stable speed is required. This kind of DC motor can be used in Centrifugal Pumps, Lifts, Weaving Machine, Lathe Machines, Blowers, Fans, Conveyors, Spinning machines, etc.
Why DC shunt motor is constant speed?
If the load on the motor increases armature speed reduces and thereby cause a reduction in the back emf. … Hence, a DC shunt motor always maintains a constant speed. Under no load condition, the back emf becomes nearly equal to the applied voltage.
Where is dc series motor used?
⇒ DC series motors are used where high starting torque required. These motors are only used where the variation of speed is possible. series motors are not suitable for constant speed applications. ⇒ DC series motor is used in a vacuum cleaner, traction systems, sewing machines, cranes, air compressors etc.
Is back EMF good or bad?
Back emf is a measure of energy conversion from electrical to mechanical in an electric motor. If you are able to make it zero no energy conversion to mechanical. … Eb is back emf, I armature current and R armature circuit resistance. So if you want energy conversion back emf is good.
What will happen if the back EMF in the DC motor absent?
64. What will happen if the back e.m.f. in the d.c. motor absent ? (a) Motor will run faster than rated value. Motor will burn.
What is back EMF formula?
The back emf is calculated based on the difference between the supplied voltage and the loss from the current through the resistance. The power from each device is calculated from one of the power formulas based on the given information. The back emf is ϵi=ϵS−I(Rf+REa)=120V−(10A)(2.0Ω)=100V.
What does back EMF depend on?
The back EMF depends, of course, on the speed of the motor — the change in magnetic flux that generates it increases with motor speed — so that as the motor begins to turn, the back EMF grows until the motor has reached its maximum speed, at which point the back EMF stays at its maximum value.
What is disadvantage of back EMF starter?
One disadvantage is that no back EMF is generated when the motor is stationary, so startup is affected by operating in open loop. Consequently, the motor can take a short time to settle and run efficiently.
What is the importance of a counter EMF?
The emf that opposes the flow of current. Just as the windings of a generator produce voltage, the rotor in a motor produces voltage that is counter or opposed to the supply voltage. This counter emf creates additional resistance that must be overcome by the supply voltage.