When the speed of a DC motor increases back EMF?
If the speed of the DC motor increases, then the back e.m.f Eb = (PΦZN/60 A) also increases. It is clear from the above equation that the armature current (Ia) will decrease. Under Construction. It is clear that speed (N) of a DC motor is inversely proportional to flux per pole (Φ).
Why is the speed of DC shunt motor dependent on back EMF?
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. So the torque increases with the increase in current and accelerates the armature which maintains its speed with the additional load.
What will happen with increase in speed of dc motor?
Explanation: In case of DC motor, the speed is proportional to the back emf (Ea ∝ N). 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 will happen to torque if back EMF and speed of the DC motor is doubled?
What will happen to torque if back emf and speed of the DC motor is doubled? Explanation: Torque depends on armature current, so as long as armature current remains constant torque will not change. Speed depends directly with back emf thus, it will definitely become double when back emf is doubled.
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 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 DC shunt motor is constant speed?
Since torque is proportional to armature current, torque also increases. Finally, this increased torque allows the motor to increase its speed and compensate for the slowdown due to loading. Hence, a DC shunt motor is able to self-regulate its speed, and can be referred to as a constant speed motor.
What will happen if excitation of DC shunt motor is changed?
What will happen if excitation of DC shunt motor is changed? Explanation: The motor will accelerate the mechanical load connected during this period but no increase in the mechanical load as Pload = T1W1 = T2W2 where W2 >W1. So, at the higher speed there is less electrical torque for the same mechanical load / power.
Why is the DC motor preferred over AC motor?
DC motors have the advantage of: higher starting torque, quick starting and stopping, reversing, variable speeds with voltage input and they are easier and cheaper to control than AC. AC motor advantages include: lower power demand on start and minimal maintenance.
When the speed of DC motor is increased?
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.
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.
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. Which DC motor is used with flywheel for intermittent light and heavy loads?
What will happen if the back EMF in the DC motor absent?
If there is no back end then large current flows in starting of motors because initial speed is zero and back emf is zero thus winding gets damaged for this purpose only we use starters for all motors. motor will not start. when the motor runs,there has to be back emf.
What is back emf in dc motor?
A motor has coils turning inside magnetic fields, and a coil turning inside a magnetic field induces an emf. This emf, known as the back emf, acts against the applied voltage that’s causing the motor to spin in the first place, and reduces the current flowing through the coils of the motor.
Which motor has the poorest speed control?
1. 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.