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 a series motor must always be started on load?
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 will happen to a dc series motor when its load is removed?
If the mechanical load is removed entirely, the speed increases without limit and destruction of the armature through centrifugal force is certain to occur. For this reason, series motors are always permanently connected to their load.
Which motor should not start on no load?
Speed of DC Series Motor ωm = Very high, which is also clear from the Speed Current Characteristics of DC Series Motor as shown in figure above. Therefore if the DC Series Motor is started at No Load then the speed of DC Series Motor will become dangerously high which will definitely damage the DC Series Motor.
Why do series wound DC motors have a high no load speed?
in series dc motor speed is inversely proportional to flux thus at no load very small current flows . this small current produces small amount of flux. as flux is less motor attends very high speed at no load as back emf is almost constant. that’s series dc motor can not be started at no load.
Which motor is always started with load?
At no load, it will rotate at dangerously high speed 2. It will fail to start 3. It will not develop high starting torque 4.
What are the advantages of DC series motor?
Advantages of DC Series Motor
- Dc series motor have good accelerating torque.
- Dc series motor have a relatively huge starting torques.
- Dc series motor delivers high torque during an overload.
- The dc series motor draws less current and power from the source compared to a shunt or compound motor.
Can DC motor start without load?
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.
Which DC motor has maximum self loading property?
Which DC motor has got maximum self-loading property? Explanation: A differentially compound DC motor, flux reduces so sharply at small increase in load at higher values of load.
When load is removed motor will run at the highest speed?
1 Answer. When load is removed, series motor will run at the highest speed.
Can we start the DC shunt motor and series motor without load?
We can operate a shunt motor with no load because their torque is not that high as series motors. They are moreover constant speed motors and tend to operate at stable speeds. Series motors cannot be started without load, as they tend to overspeed and get damaged. Motor armature current is decided by the load.
What controls the speed of a DC motor?
Thus, the speed of a DC motor can be controlled in three ways: By varying the supply voltage. By varying the flux, and by varying the current through the field winding. By varying the armature voltage, and by varying the armature resistance.
Which DC motor is preferred for constant speed?
Explanation: Rotary compressor generally demand constant speed operation throughout the load. Sometimes, DC machines are not able to produce constant speed throughout the process hence, synchronous machine is used. 4.
When DC motor is not running back EMF is?
The coil of a DC motor is represented as a resistor in this schematic. The back emf is represented as a variable emf that opposes the one driving the motor. Back emf is zero when the motor is not turning, and it increases proportionally to the motor’s angular velocity.
Which braking is not possible in series motor?
Regenerative braking is not possible in a series motor. Explanation: In regenerative braking, the motor acts as a generator. The back emf is more than the terminal voltage in case of regenerative braking.
Which starter is used for starting DC shunt motor?
Three point starter is used in shunt wound DC motor or compound wound DC motor. To start the motor, the starter arm is moved to stud 1 in the clockwise direction ie) whole of the resistance is added to the armature winding of the dc motor.