A series motor should never be 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.
Why are series motors never started on no load?
It is seen earlier that motor armature current is decided by the load. On light load or no load, the armature current drawn by the motor is very small. on no load as Ia is small hence flux produced is also very small. … This is the reason why series motor should never be started on light loads or no load conditions.
Why a series motor must always be started on load?
at no load, it will rotate at dangerously high speed. it will fail to start. it will not develop high starting torque.
Can we operate dc series motor at no load condition?
Hence based on above discussion it is advised that DC Series motor should not operate at no load condition.
Which motor should not be started at no load?
Since speed is constant and torque (τ) is proportional to armature current (Ia). So that, starting a shunt motor at a heavy load requires a high starting current. In order to avoid this high starting current, shunt motors are not started at heavy loads and they should be started without any load.
Why does Series motor tend to race at no load and light loads?
As from Speed Equation Speed is inversely proportional to flux and for no load or less load the flux produced is also less hence the rotor rotates at very high speed which can damage the motor mechanically. This is the reason why series motor should never be started on light loads or no load conditions.
Can we start the DC shunt motor and series motor without load?
You can start a DC shunt motor without a load, but never start a DC shunt motor with heavy load because, The change in field flux is very less due to the load, so we can assume the flux to be constant. So flux ɸ is constant, and the speed, N ∝ Eb where Eb is the back emf.
Which of the following can be started on no load Unlike DC series motor?
Unlike DC series motor, DC compound motor can be started on no-load. Explanation: Cumulative motor takes best from shunt motor and series motor as well. Due to shunt field flux component, DC cumulative motor can be started on no load.
Why Series motor produces high torque and speed initially without load?
Explanation: At no load, armature current tends to zero, flux φ tends to zero, where speed is inversely proportional to the flux, speed will tend to infinity. Thus, no load speed of DC series motor is highest. … Explanation: A conveyor requires high torque with steady speed, which provided by DC series motor.
Which motor is start with load?
Since series motors has this property it is used in trains to pull high load.
When a DC motor has no load what will happen to the back emf?
At no load condition,( i.e when there is no mechanical load connected to armature end) small torque is required to overcome the friction and windage losses. Since torque is directly proportional to armature current Ia ,therefore the armature current Ia is small so the back emf is nearly equal to the applied voltage.
Which of the DC motor should not be run at no load?
Hence DC series motor are never operated without load. Because the speed is inversely proportional the flux. And flux is directly proportional to the armature current in series motor. In no load ,ideally armature current is zero that’s why flux is also zero.
Where is series motor used?
A series motor has very high starting torque and is commonly used for starting high inertia loads, such as trains, elevators or hoists. This speed/torque characteristic is useful in applications such as dragline excavators, where the digging tool moves rapidly when unloaded but slowly when carrying a heavy load.
Why Swinburne’s test is not conducted for series motor?
The Swinburne test is only applicable for motors where flux is virtually constant, which includes DC shunt and compound motors. The test does not work for series motors because they cannot be run at light loads, and because speed and flux vary significantly in series motors.