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No load speed is the speed that the motor run when it has no load, i.e., the motor is separated from the engine, that speed is than greater than the rated speed, because the rated speed is the speed whwn the motor are linked to the load and it is the full load.
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Why no load-speed of a dc series motor is very high?
high torque
Why dc series motor cannot be start without any load?
If a DC series motor is started without load, the armature winding (winding that doesn't spin) current will be at a minimum, resulting in the motor going to maximum speed / runaway, which can cause things to fly apart. As Armature current increases, the speed of the motor will decrease. The armature current will be forced to increase / speed of the motor will be forced to decrease as more and more load is applied.
Why a DC series motor should never be stared without load?
since torque is proportional to flux and armature current . Flux for dc shunt is constant . torque is proportional to armature current only. And initially armature current is very low hence it cannot be started at load .
Why will an unloaded series-wound motor overspeed?
The Torque Speed characteristics of a series connected dc motor is such that at zero load the speed is "infinite"! ie it over runs and can burn out/explode! The characteristics are quite easy to derive from the basic equations of a dc motor but you can see them in most text books on electrical machines.
What happens when load is removed from an operating series DC motor?
The speed will increase possibly to the point that it throws out the coils from the armature & self destructs.
Why no load-speed of a dc series motor is very high?
high torque
Why dc series motor cannot be start without any load?
If a DC series motor is started without load, the armature winding (winding that doesn't spin) current will be at a minimum, resulting in the motor going to maximum speed / runaway, which can cause things to fly apart. As Armature current increases, the speed of the motor will decrease. The armature current will be forced to increase / speed of the motor will be forced to decrease as more and more load is applied.
Why dc series motor is always runs at loads?
At no load, the flux is only due to the residual flux, which is very small. the no load speed of dc series motor is very high. so the rotating part of the motor are damaged. hince dc series motor should never be run without motor.
Is Swinburne test applicable for dc series machine?
No.it is not applicable for dc series motor at no load..at no load armature current is too small in dc series motor and we know that speed is inversly proportional to the armature current(speed=v/kI-Ir/k).Hence speed is dangerously high which is not efficient for Swimburne's test...
Why the series motor is started with some initial load?
In dc motors Speed is directly proportional to back emf and inversely proportional to flux i.e N∝(Eb/φ) In series motor back emf is practically constant. So if we start motor without any load Flux will be small and so speed will be very high. if we start motor without any load it will gain very high speed and may get damaged due to centrifugal forces. Series motor have very high starting torque and used where high starting torque is required.
Why dc series motor is never started on light load?
the speed N is inversely proportional to armature current I. At light loads this current is very small. Hence motor will run at very high speed when started on no load/light load.........
What motor must be never run without a load connected to them?
DC Series motor should never run without load connected to it because starting torque for DC series motor is infinite and running it on no load will damage the motor due to overspeeding.
Why flywheel is used in dc series motor?
because starting torque is high and without any load, speed becomes infinite.
Can a DC series motor with speed control be connected on AC supply?
A dc series motor with speed control can be connected on ac supply because dc machines are totally reversible.
Why a DC series motor should never be stared without load?
since torque is proportional to flux and armature current . Flux for dc shunt is constant . torque is proportional to armature current only. And initially armature current is very low hence it cannot be started at load .
Why will an unloaded series-wound motor overspeed?
The Torque Speed characteristics of a series connected dc motor is such that at zero load the speed is "infinite"! ie it over runs and can burn out/explode! The characteristics are quite easy to derive from the basic equations of a dc motor but you can see them in most text books on electrical machines.
Why should a series motor always start with a load?
In any DC motor the speed depends inversely on the flux. Consider when starting a series motor the current flowing will be high, but the flux that the motor produces will be moderate since the series winding has less number of turns. If u start the motor without load the speed will increase. as speed increases the back emf increases. this decreases the current through the series winding and hence flux decreases and the speed further increases. Theoretically speaking the speed becomes infinite. But practically the motor will accelerate to very high speed , which will damage the motor. But if you start the motor with the load, you are actually reducing the starting speed hence the motor runs safely. Since series motors has this property it is used in trains to pull high load.
