If the load on the motor increases armature speed reduces and thereby cause a reduction in the back emf. Hence, when back emf decreases the armature current increases. … Hence, a DC shunt motor always maintains a constant speed. Under no load condition, the back emf becomes nearly equal to the applied voltage.
Which motor should be used where constant speed is required Why?
Both ac and dc motors are suitable for constant speed applications. DC motors provide full torque at zero speed and have a large installed base. AC motors are also a good choice because they have a high power factor and require little maintenance.
What is the effect on motor speed if the field current is increased?
Therefore, the motor speeds up. When the field current is increased, the field flux is increased. More counter emf is developed, which opposes the armature current. The armature current then decreases, and the motor slows down.
What is the reason for reduction in speed of DC shunt motor from no load to full load?
As the load increases, to maintain the voltage at a constant value, current decreases, due to which the strength of magnetic field produced by the Internal Winding of DC motor decreases. This results in a decreased interaction of the two magnetic fields and thus Decrease in Speed of motor is observed.
Why the armature current of a shunt motor decreases as the motor accelerates?
The generator voltage opposes the driving voltage. With a lower overall voltage across motor’s internal resistance as the motor turns faster, the current flowing into the motor decreases. The faster the motor spins the less current it draws.
Which motor is constant speed?
This motor combines a power on activated type clutch and brake with an induction motor. It is ideal for high-frequency starting and stopping. Suitable for applications where the motor is operated starting, stopping and reversing repeatedly and the motor is operated at synchronous speed regardless of load torque.
Which motor is used for constant speed?
Hence, a DC shunt motor is able to self-regulate its speed, and can be referred to as a constant speed motor.
How do you reduce current in a field?
With weak, pole field flux, torque produced will be less, the back EMF also, should reduced, and as applied voltage is same(V=Eb+IaRa), but Eb should increased, as (Ia) cannot increased above rated, or speed (Eb=OZNP/60A) must increased to increase Eb, to balanced the motor equation, a stage will come, after which …
Which motor has the poorest speed control?
Which of the following DC motor has the poorest speed control? Explanation: DC series motor at no load condition gives infinite speed ideally. Practically it will damage all the armature circuit.
What happens to speed when you increase torque?
If you increase the torque you increase the speed UNLESS you increase the load. The important thing to remember is that with electric motors there is a back-EMF (a motor is a generator too) which increases with speed and that limits the effective voltage and thereby the current and thereby the torque.
Why DC shunt motor is started on no load?
For DC shunt motor the field resistance is high and armature resistance is low so the variation of flux is very less when rated voltage is applied to the motor and motor speed does not exceeds rated speed at no load. So we can start the DC shunt motor with no load.
What is the principle of DC shunt motor?
Construction and Working Principle
The working principle of a DC Shunt Motor is, whenever a DC motor is turned ON, then DC flows throughout stator as well as the rotor. This current flow will generate two fields namely pole as well as the armature.
What are the factors affecting the speed of a DC shunt motor?
The above equation shows that the speed depends upon the supply voltage V, the armature circuit resistance Ra, and the field flux Ф, which is produced by the field current. In practice, the variation of these three factors is used for speed control.
What will happen if the motor is highly loaded above its full load capacity?
If the induction motor is overloaded beyond its capacity, it draws more current than its rated value, hence there is a danger of burning up of both stator and rotor winding. Another case is, if you keep on increasing the load, the slip keeps on increasing at a particular point, it will halt.
How does load increase current?
In an electric motor, almost all types, the current is proportional to the torque. If the load increases, in other words, the torque increases and the current will increase. The magnetic field in a motor are related to the voltages. The rotor produces a field that turns at the same speed as the supply.
What will happen with the increase in speed of a DC motor?
What will happen, with the increase in speed of a DC motor? a) Back emf increase but line current falls. … So, with the increase in speed, the back emf also increases. Therefore, armature current is also decreased, in case of series motor, armature current is equal to the line or load current.