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In DC Series Motors the field is in series with Armature. When the motor starts at
no load, the armature current is very low and so is the field current. As the speed
of DC Motor is inversely proportional to field current, the motor will try to shoot up
to very high speed at no load and it can be dangerous for the motor itself and for
this reason, any DC Motor should always be started on load.
Jameson Hauck
Wiki User
∙ 10y agoIn a series motor the same current flows through the armature and the field winding. The torque is therefore proportional to the square of the current. The current is set by the supply voltage and the back-emf generated in the armature.
At zero speed there is no back-emf therefore the current is limited only by resistance, so the current and torque are high.
This type of motor is commonly used for transport because it can provide a lot of torque for starting, and the driver (e.g. in a tram) controls the starting process with a handle that places a variable resistance in series to limit the current while starting.
Wiki User
∙ 12y agoA DC series motor provides high torque when it is fully loaded.
It is mainly used as a starting motor as it provides high torque , but it is operational only for a few minutes.
This is because the field winding and the armature winding are connected serially.
Hence current will flow through the field winding, so the field winding is made up of a high gauge copper wire.
Because the field winding is thick there will be less number of turns.
And since the winding being big will have very low resistance and heavy current will be drawn from the source. As a result strong magnetic field will be set up causing the armature shaft to rotate with maximum torque.
Wiki User
∙ 14y agotry wikipedia page
http://en.wikipedia.org/wiki/Shunt_generator
Wiki User
∙ 11y agospeed is directly proportional to the negative of torque in dc series motor..
Wiki User
∙ 9y agoThe starting current is high because when the motor is not rotating no back-emf is generated, leaving the starting current to be determined by the armature resistance, which should be low.
Wiki User
∙ 7y agoBecause it has much higher torque at low speeds than other types of motor.
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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 can we start a shunt motor under no load but why can't a series motor?
The torque on a series motor is determined by the square of the armature current and, so, is very large -much larger than that of a shunt motor. Consequently, on starting, with no back-emf being generated, the torque on a series motor can be dangerously high if the machine has no mechanical load.
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 a dc series motor should never run at no load condition?
if you run the unloaded motor at max rpm the centrifugal forces will cause the motor to be totally destroyed so it is advisable to not to run it at max rpm it should be okay to run it till 50% of max rpm without loading it
What is Ratio between starting and running current of 3 phase ac motor?
The start up current should be listed on the motor nameplate as FLA , full load amps.
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.
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 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 the series motor is started with some minimum load?
In series motor, At no Load Condition the flow of Armature Current is low, then the Flux is also low. Flux is inversely proportional to speed. If flux is decrease the speed is rapidly increase it spoil the rotor parts...... so SERIES MOTOR is start with LOAD.....
Why can we start a shunt motor under no load but why can't a series motor?
The torque on a series motor is determined by the square of the armature current and, so, is very large -much larger than that of a shunt motor. Consequently, on starting, with no back-emf being generated, the torque on a series motor can be dangerously high if the machine has no mechanical load.
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.
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 series motor should have a load?
when the load is removed the field is weakened then the speed is limited only by mechanical restraints ... (bearings, vibration, power available)
Can DC series generator start on no load?
yes.it is possible to start dc series generator on no load condition
Can a 7.5 HP DC series motor pull a load of 1000 kilograms?
There is not enough information in the question to answer it. Any motor can pull any load through an appropriate pulley system. The question should include how fast that load needs to be moved.
Can induction motor start at no load?
yes
