For a constant load (torque), speed is directly proportional to potential difference across the armature. Thus greater resistance in armature circuit, greater the fall in speed. This method is used for obtaining speeds below rated speed.
Which speed control method offers below normal speed in DC shunt motor?
Shunt motor is a special type of DC motor which runs at a constant speed. But using field and armature rheostat control method we can make it more versatile. Field rheostat provides above normal speed and armature rheostat provides wide range of below normal speed.
Which method is used to control the speed of DC shunt motor?
Field Rheostat Controlled DC Shunt Motor
In this method, speed variation is accomplished by means of a variable resistance inserted in series with the shunt field. An increase in controlling resistances reduces the field current with a reduction in flux and an increase in speed.
Which method used to control the speed below the rated speed?
In armature circuit resistance method armature resistance is increased. As a result the back emf decreases. As the speed is directly proportional to back emf speed will also decrease. Therefore this method is only used for below rated speed.
How is the speed of a DC motor controlled below base speed?
Speeds above the motor base (nameplate) speed are obtained by weakening the motor shunt field with a rheostat or electronically. Speeds below the motor base speed are obtained by weakening the generator field. This, in turn, lowers the generator voltage supplying the DC motor armature.
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 will happen if excitation of DC shunt motor is changed?
2. What will happen if excitation of DC shunt motor is changed? … Explanation: Speed of the DC motor obtained from speed equation is inversely proportional to flux produced by the field. So, reducing the field current flux produced by armature will decrease, and speed will increase.
What are the 3 types of DC motors?
Main Types of DC Motors
- Permanent Magnet DC Motors. The permanent magnet motor uses a permanent magnet to create field flux. …
- Series DC Motors. In a series DC motor, the field is wound with a few turns of a large wire carrying the full armature current. …
- Shunt DC Motors. …
- Compound DC Motors.
How do you increase 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.
What is the speed of dc motor?
DC controls adjust speed by varying the voltage sent to the motor (this differs from AC motor controls which adjust the line frequency to the motor). Typical no load or synchronous speeds for an AC fractional horsepower motor are 1800 or 3600 rpm, and 1000-5000 rpm for DC fractional hp motors.
Which is not a method of speed control of a dc motor?
Which of the following is not the method of speed control in DC series motor? Explanation: Diverter means adding a variable resistance in parallel with field winding. Tapped field control is the method where field ampere turns are adjusted in steps by varying the number of turns included in the circuit.
How can you reduce the speed of a DC motor?
If you want to reduce rpm without compromising speed regulation then use a voltage regulator or PWM controller to lower the motor voltage. If you also want higher torque then use a gearbox (which increases torque by the same proportion as it reduces shaft rpm).
How do you calculate the speed of a DC motor?
Speed of a DC Motor
A = number of parallel paths. Z = total no. conductors in armature. Hence, speed of a DC motor is directly proportional to emf of rotation (E) and inversely proportional to flux per pole (φ).
How do you increase motor speed?
Increasing the speed can be achieved by increasing the supply frequency as the speed and frequency are directly proportional; however, there are two constraints. The first is the saturation of the magnetic circuit, but this issue can be significantly avoided by keeping the V/f ratio constant.
What is base speed of DC shunt motor?
Base speed is Hz multiplied by 60 then divides the result by half the number of poles. Rated speed is the base speed minus the slip at full rated load. An induction motor slows as it is loaded. 60 x 60 x 2 = 7,200 no-load rpm Ã· number of poles.