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.
Why should a DC series motor not be operated under no-load?
Hence a DC series motor should never be run on no load. At high loads due to saturation the flux becomes constant, consequently, the speed will become constant. Originally Answered: Why DC series motor should not be operated under no-load? Well flux is directly proportional to the armature current.
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.
Why is a series motor always started with the load?
Speed is inversely proportional to flux and therefore to field current. At no load the current is very low. This results in a weak field which leads to very high speed, which may damage the motor. Hence the series motor is always started with the load.
What is the armature current of a DC series motor?
In case of DC Series motor armature current is decided by the load. On light load or NO load, the armature current drawn by the motor is very small. Φ α Ia (or) Flux ( Φ) is directly proportional to armature Current ( Ia). On No load as Ia is small hence flux produced is also very small. N α 1/Φ as Eb is almost constant.
Why is a DC series motor never started on 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.
Can we operate DC series motor in no load condition?
At no load condition, load on the motor is zero hence armature current(Ia) is also zero. From equation (i) (If=Ia) hence field current(If) will also=0 at no load condition. Hence based on above discussion it is advised that DC Series motor should not operate at no load condition.
Why should DC series motor 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.
Can a series motor may be operated with no load connected?
Counter-electromotive force (CEMF) and back-EMF are names for the voltage induced into the armature of a DC motor. A series motor may be operated with no load connected.
Why no load test is not performed on series motor?
At no load the armature current is less . From the emf equation we know speed varies inversely with the flux and in series motor flux varies directly with armature current . So at no load the flux is less and speed is enormoualy high and could mechanically damage the machine .
What occurs if the load is removed from an operating Series DC motor?
What occurs if the load is removed from an operating series DC motor? (D). It will accelerate until it falls apart.
What is the ideal no load speed for a series DC motor?
infiniteThe speed of the DC series motor is directly proportional to back EMF and inversely proportional to armature current. As Ia is zero and Ea is a constant value, so the speed of a DC series motor at no-load conditions will be infinite.
Should not run DC series motor without load why Mcq?
It is advised not to run dc series motor with no load. Why? Explanation: If the torque is zero in dc series motor then the speed will be infinite causing the damage of the machine permanently.
What is the back EMF?
The voltage of the opposite polarity to applied voltage (V) is induced in the armature to impede the armature current. The voltage induced in the armature is known as the back EMF (Eb).
Why should a DC motor not be started at no load?
Why DC Series Motor should not be Started at No Load. In DC series motor, the field and armature winding is connected in the series and , both winding carries the same amount of current.The field winding has to carry the full rated armature current, therefore the field coil has few turns of thicker wire. The speed of the DC motor is proportional ...
What happens if a DC motor is operated at no load?
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.
What is the sum of all the voltage around any closed loop in a circuit?
According to the Kirchoff’s current law, the algebraic sum of all the voltage around any closed loop in a circuit is zero.
Is the speed of a motor inversely proportional to the armature current?
From equation (5) it is clear that the speed of the motor is inversely proportional to the armature current.
Is the speed of a DC motor proportional to the back EMF?
The speed of the DC motor is proportional to the back EMF (Eb) and inversely proportional to the flux. The flux is proportional to the field current. In the DC series motor the field current and the armature current is same. Therefore, the flux in the motor is proportional to the armature current (Ia).
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 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.
How does main flux affect speed?
So now as low current will flow through the field winding as well as armature winding ( as it is series motor) so main flux produced will be lesser, as before saturation point current is directly proportional to flux. So as main flux is lower, speed will tend to increase. As speed increases, back ems also increases and thus current drawn from the supply will become more and more lower and thus main flux will also become more and more lower and thus speed will tend to increase more and more and this continues till armature of motor has attained speed which is so high that due to centrifugal forces set up in the rotating parts damages armature.
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. So as speed will be higher, back emf will be higher i.e higher opposition to the flow of current from supply to motor and thus current will be less on no load condition.
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 determines the armature current of a motor?
Motor armature current is decided by the load. On light load or no load, the armature current drawn by the motor is very small.
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.
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.
How much load should a series motor be on?
Therefore as a thumb rule we never run series motor on less than 15% of full load. If accidentally it occurs then quickly disconnect the motor from the supply.
Is flux proportional to current?
Flux is Directly proportional to Armature current. and on no load as Ia is small hence flux produced is also very small. According to speed equation, Speed is Inversely proportional to Flux i.e ( N α 1/Φ) as Eb is almost constant.
Is Eb constant or variable?
as Eb is almost constant. 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.
What does torque mean when there is no load?
At no load I=0 which means torque=0 and torque is inversely proportional to speed means speed increases rapidly and machine rotates fast enough to damage itself.
Why can't a series motor start without load?
Series motor cannot be started without load because of high starting torque. Also at no load the current passing through the field is minimum. and almost zero ,so the flux at the field will be alsoalmost zero and we know that the speed is inverslyperpotional to the flux in the field so due to almost zeroflux the speed will be maximum ...
What happens if you start a DC series motor without load?
if we start Dc series motor without load then it shout more and may get damage itself ............ so in simply words we can say if applied load its get quit ...........
Why should DC motors never be operated at load?
The high forces, associated with high speeds, cause the rotor to fly apart, often with disastrous results to people and property nearby. And hence the DC series motor should never be operated at no load.