The speed of a dc motor is inversely proportional to the flux per pole. Therefore, if you decrease flux you can increase speed. Resistance is added in series to the windings to control the flux. The more resistance, the more speed as this will reduce the flux.
What is the relation between speed and flux?
It is already explained above that the speed of a dc motor is inversely proportional to the flux per pole. Thus by decreasing the flux, speed can be increased and vice versa. To control the flux, a rheostat is added in series with the field winding, as shown in the circuit diagram.
What is relationship between speed with back EMF and flux of DC motor?
Back EMF is directly related to speed, so when the speed decreases, so does the induced back EMF. From the equation above, we can see that if there is less back EMF, the voltage (and, therefore, current) across the motor will increase.
Why does speed of DC motor increases when flux is reduced?
1 Answer. The instant flux is reduced, the back emf reduces and this causes the armature to increase current. More current means a higher driving torque and this accelerates the armature to run at a higher speed until the speed equation is in balance again.
What is flux in DC motor?
When both the armature and the field windings are excited by a DC supply, current flows through the windings and a magnetic flux proportional to the current is produced. When the flux from the field interacts with the flux from the armature, it results in motion of the rotor.
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.
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.
Why back EMF is used in DC motor?
The presence of back emf makes the d.c. motor a self-regulating machine i.e., it makes the motor to draw as much armature current as is just sufficient to develop the torque required by the load. When the motor is running on no load, small torque is required to overcome the friction and windage losses.
What is the EMF equation of a DC motor?
As the armature rotates, a voltage is generated in its coils. In the case of a generator, the emf of rotation is called the Generated emf or Armature emf and is denoted as Er = Eg. In the case of a motor, the emf of rotation is known as Back emf or Counter emf and represented as Er = Eb.
What will happen if the back EMF of a DC motor vanishes suddenly?
Explanation: If back emf vanishes suddenly, motor circuit will try to retain back emf by drawing more current from supply. … 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.
What is flux speed?
The block takes the measured rotor speed and issues the flux linkage command. It is evident that if the speed is less than or equal to rated, the flux is kept at its rated value. However, for speeds higher than rated, the flux should be reduced to run the machine in a constant-power mode by field weakening.
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.
Why is it necessary to control the speed of a DC motor?
DC Motors plays an important role in energy conversion process. It is a machine which converts electrical energy into mechanical energy. In mechanical system, speed varies with number of task so speed control is necessary to do mechanical work in a proper way. It makes motor to operate easily.
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.
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.
Why starters are required in a DC motor?
1. Why starters are required in a DC motor? … Explanation: Starting resistance of a DC shunt motor and DC compound motor is low. Well, that’s the reason why we use starters in a DC motors, in order to limit the armature current flowing through the armature and to protect machine circuitry.