When DC shunt motor is started with maximum field resistance the field current and hence the magnetic flux set up in the motor is minimum giving rise to increase in speed than normal value. The motor may try to race up causing protective devices to disconnect from the supply.
What is the effect of increasing the field winding current of DC shunt motor?
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. When the voltage applied to the armature is decreased, the armature current is decreased, and the motor again slows down.
How does field current affect DC motor?
The speed of a DC motor is changed by changing the current in the field or by changing the current in the armature. When the field current is decreased, the field flux is reduced, and the counter EMF decreases. This permits more armature current. Therefore, the motor speeds up.
What will happen if the field current of the DC shunt motor gets interrupted?
Answer: n d.c shunt motor if field winding supply is removed the motor back emf will drop to zero, hence the armature will draw more current to make up the emf. … In dc series motor the motor will go to infinite speed (theoretically) as flux is inversely proportional to the speed…
What will happen to a DC shunt motor running on full load and its field circuit gets open suddenly?
If the shunt field suddenly opens while the motor is being operated under full-load conditions, only a small voltage due to the residual magnetism of the pole pieces will be induced into the armature. Current will increase considerably. The magnitude of this current may be sufficient to burn out the motor.
What are the advantages of DC shunt motor?
Advantages of Dc shunt motor:
- The power supply of the DC motor is any way cheap.
- Shunt would motor able to runs at a predetermined speed.
- The speed of a dc shunt motor is sufficiently constant.
- Direct current machines can use for heavy industrial applications where the torque and speed wider range.
Why DC shunt motor is constant speed?
If the load on the motor increases armature speed reduces and thereby cause a reduction in the back emf. … Hence, a DC shunt motor always maintains a constant speed. Under no load condition, the back emf becomes nearly equal to the applied voltage.
What is field current in dc motor?
: the current supplied to the field windings of a generator or motor to establish the magnetic field for its operation.
How do you calculate field current in a DC motor?
Calculate the field current for the motor using the formula I = V/R where I is the field current. As an example, assume V is 40 volts and R is 500 ohms: I = 40/500 = 0.08 amps.
How do you control 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.
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.
Where is DC shunt motor used?
The applications of shunt DC motor include the following. These motors are used wherever stable speed is required. This kind of DC motor can be used in Centrifugal Pumps, Lifts, Weaving Machine, Lathe Machines, Blowers, Fans, Conveyors, Spinning machines, etc.
What will be the effect of opening of Field of DC shunt motor while motor is running?
What will be the effect of opening of field of a DC shunt motor while motor is running? Explanation: In a DC shunt motor if supply for the field winding is cut down, the speed would dangerously increase in order to maintain the back emf of the motor.
What will happen to the speed of the DC shunt motor when the flux is increased?
The speed will increase abruptly. The speed will remains almost constant. The speed will increase in proportion to reduction in load. In case of DC shunt motor, flux is practically constant as field is parallel to the armature.
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.
Why starter is used in DC shunt motor?
Starters are used to protect DC motors from damage that can be caused by very high current and torque during startup. They do this by providing external resistance to the motor, which is connected in series to the motor’s armature winding and restricts the current to an acceptable level.