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In dc motor, the armature conductors are revolving in the magnetic field and emf is induced in the armature conductors. The direction of the induced emf is in opposite direction to the applied voltage as per Flemings left hand rule. So, the induced emf in motor is called as back emf or counter emf.
Vydehi
Wiki User
∙ 13y ago
Wiki User
∙ 11y agoThe backing EMF of a DC motor is the voltage produced in a conductor that tends to neutralize the present voltage. It is what a motor generates and it increases with speed. It stops the motor from turning infinitely quickly.
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Why is a starting current in a DC motor very high?
A rotating d.c. motor generates a back-emf which opposes the supply voltage and reduces the current drawn by the motor. When the motor is stationary, it cannot generate this back emf and, so, the only opposition to current is the resistance of its windings which is relatively low. So, on startup, the current is large; as the machine starts to run, the resulting back emf, acts to reduce the current.
Is there any application of Lenz law in DC motor?
yes lenz law states that every current opposes the reason which cause the generation of that current . it is very useful for considering back emf in dc motor. The lenz law also help us to determine the supply voltage of DC motor.
Why a diode is connected parallel to a dc motor in its speed control circuit?
A motor is a mass of wires classified as a coil. Coils have a decency to generating reverse voltage when commutation the diode therefore is there for clipping this harmful back EMF
What determines the magnitude and polarity of the counter-emf in a dc motor?
the magnitude is decided by the amount of flux, number of conductors, speed of the motor and the type of the winding used. the polarity is decided by the direction of rotation of the motor and the direction of armature current flowing in the motor.
What would the power loss be if the series field winding of dc motor connected directly across the 240 V dc supply?
Detailed Solution. For a constant back emf, flux is inversely proportional to the speed of the motor. If field winding is disconnected accidentally, the speed would dangerously increase in order to maintain the back emf of the motor
The back emf indcuced in the armature is AC or DC?
only in dc motor...
What is the difference between Counter-electromotive force and back emf?
They are Same for dc motor
What is the difference between a DC motor and a generator in terms of EMF?
During the operation of a DC motor, EMF is created across its terminals using an external source. Whereas, in a DC generator EMF is created across its terminal based on principle of dynamically induced EMF. So talking in terms of EMF, in DC motor EMF is consumed by the motor coil and utilized to rotate the axle. On the other hand, in DC generator EMF developed across coil is transfered to a load or a battery and consumed by them.
Why Back EMF occur in only dc motor?
It doesn't. It exists in all electrical machines, d.c. or a.c., motor, generator, or transformer.
How much emf is needed for running a dc motor?
It depends entirely on the design of the motor.
Why is a starting current in a DC motor very high?
A rotating d.c. motor generates a back-emf which opposes the supply voltage and reduces the current drawn by the motor. When the motor is stationary, it cannot generate this back emf and, so, the only opposition to current is the resistance of its windings which is relatively low. So, on startup, the current is large; as the machine starts to run, the resulting back emf, acts to reduce the current.
When pole flux of dc motor is zero what is its speed?
when the pole flux is zero there is no induced emf in the armature conductor of dc machine as a result of this there is no back emf for controlling action so speed become dangerously high or we can say it will be infinite.
What is the significance of emf?
According to motor eq. Eb=v-Ia.Ra.And the speed of motor is directly proportional to back EMF.At starting of motor speed is 0,so that Eb is also 0.As the speed increases ,Eb also increases,so that armature current decreases.As the Eb decreases ,so that Ia increases.In this way the back EMF makes the motor self regulating to take armature current as per requriment of motor.Because of this reason EMF also called governor principle of DC motor.This is most important significance of Back EMF. The back EMF is Explaned with lenses Law
What is significance of back emf?
According to motor eq. Eb=v-Ia.Ra.And the speed of motor is directly proportional to back EMF.At starting of motor speed is 0,so that Eb is also 0.As the speed increases ,Eb also increases,so that armature current decreases.As the Eb decreases ,so that Ia increases.In this way the back EMF makes the motor self regulating to take armature current as per requriment of motor.Because of this reason EMF also called governor principle of DC motor.This is most important significance of Back EMF. The back EMF is Explaned with lenses Law
What is emf induced in a motor's coil that tends to reduce the current in the coil of the motor?
BACK emf induced in a motor's coil that tends to reduce the current in the coil of the motor. The answer should be 'back'.
Is there any application of Lenz law in DC motor?
yes lenz law states that every current opposes the reason which cause the generation of that current . it is very useful for considering back emf in dc motor. The lenz law also help us to determine the supply voltage of DC motor.
Why is the starting current high in DC motor?
The starting current is high because when the motor is not rotating no back-emf is generated, leaving the starting current to be determined by the armature resistance, which should be low.
