Mell Why will a series motor over speed when it is started at no load?
With no mechanical load on the series motor, the current is low, the counter-EMF produced by the field winding is weak, and so the armature must turn faster to produce sufficient counter-EMF to balance the supply voltage. The motor can be damaged by overspeed.
What happens to an unloaded series motor?
series-wound motor, suddenly unloaded, will accelerate – its armature’s back EMF will rise and increase its effective impedance, so cuts the current flowing through the field windings connected in series, and decreases the magnetic flux through the armature.
When a series motor will over speed?
If a sudden heavy load is thrown on the motor, the series field winding will draw a heavy current from the supply and thus cause the total flux to reduce to a very small value. The motor will now attain a dangerously high speed like a series motor.
Can you overspeed a DC motor?
Because the speed of DC motor is inversely proportional to the magnetic field, once the magnetic field is less than the minimum allowable value. The speed of the motor will exceed the maximum allowable value. Therefore, an overspeed switch is installed on the axis of the DC motor.
Can an electric motor overspeed?
Average 2 pole industrial motors can safely exceed its base speed by 25%. Many manufacturers balance their 2 pole and 4 pole rotors to the same speed – 25% over the 2 pole base speed. A 2 pole motor may therefore operate up to 125% over base speed before reaching its balance limit.
Which braking is not possible in?
1. Regenerative braking is not possible in a series motor. Explanation: In regenerative braking, the motor acts as a generator. The back emf is more than the terminal voltage in case of regenerative braking.
What causes a series wound motor to overspeed?
The field current is low and motor will overspeed. If a series wound motor has an insufficient load it will cause it to overspeed, especially if its a larger motor. Or, if its a compound wound motor (which has both a series and shunt winding) and the shunt winding open circuits it will become a series motor effectively.
What are the disadvantages of series wound DC motors?
Series DC motors, when their output shaft is unloaded, will continue to accelerate until they destroy themselves. This is a consequence of wiring the field winding in series with the armature, and is the most concerning disadvantage of these motors.
Why is a series wound DC shunt motor useless?
Because if its run for too long, the high series current might burn out the series field coils thus leaving the motor useless. Unlike in the case of a DC shunt motor, the DC series motor has very poor speed regulation. i.e. the series motor is unable to maintain its speed on addition of external load to the shaft. Let us see why?
Which is the series resistance of a DC motor?
R se is the series coil resistance and R a is the armature resistance. This is the basic voltage equation of a series wound DC motor. Another interesting fact about the DC series motor worth noting is that, the field flux like in the case of any other DC motor is proportional to field current.