Why DC Series Motor should not be Started at No Load The DC series motor attains dangerously high speed when we run it on no load. The main reason of over speeding is that at no load the flux produced by the field winding is very less and the reduced flux cause over speeding of the motor.
What happens when a DC series motor is operated at no load?
At no load, the armature current of the DC series motor is very low. If the motor is operated at no load, the motor will attain the enormously high speed that can physically damage the rocker arm assembly and the motor parts. This is like the same case when the separately excited DC motor is started without switching on the filed supply.
Why DC series motor should not be used for belt drives?
This is the reason why DC series motor should never be started or Operated on light loads or No load conditions. For this reason, it is not selected for belt drives as breaking or slipping of belt causes to throw the entire load off on the motor and made to run motor with no load which is very dangerous.
Can a DC shunt motor start without a 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 ? is constant, and the speed, N ∝ Eb where Eb is the back emf. Why should a series motor always start with a load?
What is the load of a motor at no load?
At no-load, the load is actually whatever friction is in the motor such as from bearings, brushes, and air resistance. This friction mostly heats the motor. The motor will speed up to its no-load speed, which may damage the motor.
Which DC motor should not be started on no load?
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 should a dc series motor always be started with load?
When the motor is connected across the supply mains without load, it draws small current from the supply mains. This current will flow through the series field and armature, the speed tends to increase so that back emf may approach the applied voltage in magnitude.
Why a DC series motor Cannot be started on no load explain your answer with the help of basic speed torque equation and necessary diagrams?
It is because when no load is connected on motor, torque requirement will be low. Now as torque requirement is low, speed will be higher as speed is inversely proportional to main flux and torque is directly proportional to main flux.
Why series motor should not be started unloaded?
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 is series always started with load?
A. at no load, it will rotate at dangerously high speed.
Why a DC series motor should not be started with no load condition Mcq?
Run at dangerously high speed. Not develop starting torque. Draw more current without producing sufficient torque. On no load the series motor would attain tremendoushly high speed and the motor may get damaged due to heavy centrifugal force set up in rotating part.
Can a series motor be operated on no load?
This can be seen from the speed-armature current and the speed-torque characteristics that on low armature current and low torque condition motor shows a tendency to rotate with dangerously high speed. This is the reason why series motor should never be started on light loads or no load conditions.
Why should a universal motor always be connected to a load?
Theorerically 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.
Why is DC series motor always on load condition?
So if current is small, flux in the motor is also small, and speed of motor is high and result is that due to high speed it can damage the rotor of motor. So, DC series motor is always run on load condition. When load is connected to motor so current taken by armat. Continue Reading.
Why should a DC series motor not be switched on without a load on its shaft?
When a motor runs on no load, it draws a very low armature current. As field current is same as armature current in series motor, the field current and therefore magnetic field too reduces to a very low value.
What happens when armature current is low?
that is why as armature current is low, the speed of will rotate in dangerous speed. So it will break the construction of the DC motor.
How does flux develop in series motors?
In series motor same current flows through field winding and armature winding. Flux developed in motor is directly proportional to the current flowing through the winding. When we increase load on any motor the current drawn by that motor increases. But speed of motor is inversely proportional to the flux.
What is the magnetic flux produced by the field winding of a DC series motor?
Magnetic Flux produced by the Field winding of DC Series Motor is directly proportional to the Armature current. where K is constant. The name DC Series motor itself says that he field winding is in series with the Armature winding in DC Series motor.
Why is a series motor always started without load?
So a series motor has very high starting torque, If it is stared with out load it may throw out it's armature and shaft and it could also burn itself due to high inrush starting currents. So a series motor is never started without load.
What happens to the speed of a series motor when the load decreases?
The speed equation of a series motor shows that when the load decreases, the speed increases. So, at the no - load condition, there is a possibility of dangerously high speeds, which may damage the series DC motor, due to centrifugal forces, which will be large in this case.
Why should a series motor never be started on light loads or no load conditions?
In any DC motor the speed depends inversely on the flux and directly proportional to emf, N ~E/flux. At no load the armature current is very less and so is the flux, since the series winding has less number of turns. Click to see full answer.
What happens to a DC series motor when its load is removed?
The motor can be damaged by overspeed. Similarly, what will happen to a dc series motor when its load is removed? The motor will speed up to its no-load speed, which may damage the motor . At no-load, the load is actually whatever friction is in the motor such as from bearings, brushes, and air resistance. This friction mostly heats the motor.
What happens when a series motor is not mechanically loaded?
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.
Can you start a DC shunt motor without a load?
You can start a DC shunt motor without a load, but never start a DC shu nt 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.
Why should a series motor never be started on light loads?
This is the reason why series motor should never be started on light loads or no load conditions. When the motor is connected across the supply mains without load, then it will draw a small current from supply mains.
Why is torque requirement low?
It is because when no load is connected on motor, torque requirement will be low. Now as torque requirement is low, speed will be higher as speed is inversely proportional to main flux and torque is directly proportional to main flux.
