What is brush shifting in DC machines?

Brush Shift A natural solution to the problem appears to shift the brushes along the direction of rotation in generator action and against the direction of rotation in motor action, this would result into a reduction in air gap flux.

Can you change the position of brushes?

Yes, if you move both brushes far enough, then the motor can be reversed. However, if you move the brushes only a small distance around the commutator, then the speed of the motor will change.

What is the effect of reversing the field polarity on the direction of the rotation of the motor?

Reversing the polarity of the supply to the coils has no effect on the direction of rotation of the motor, since both the current in the armature and the field coils are reversed.

How does brush shifting affect the sparking problem in DC machines?

“Due to armature reaction, the natural direction of the magnetic field of the poles is distorted. Thus the neutral plane is also altered. Therefore, the armature conductors are not at zero potential when they come in contact with the brushes. This leads to sparking across the brushes and loss of power.”

What is back emf in motor?

back EMF in Electrical Engineering Back EMF is the system in the coil of an electric motor that opposes the current flowing through the coil, when the armature rotates. When the speed varies, the winding characteristics may fluctuate, resulting in variation of back EMF.

What is the neutral brush position in a DC motor?

zero
Leave the brushes at the position where the induced voltage is zero. This is the neutral point of your DC Motor/Generator. Each time you use the DC Motor/Generator the brushes should be set at the neutral position.

What happens if shunt field connection is reversed in the generator?

What will happen if the the supply terminals are reversed in case of a DC shunt motor? The motor will run in reverse direction. The motor will run at its normal speed in the same direction as before. The motor will stop.

What will be the effect if any of reversing both the battery terminals and the polarity of the magnet on the rotation *?

It is the same as if you reverse 2 magnets. Where they once attracted try now repel so the rotation is now in the other direction. If the motor has field windings. Reversing the polarity will not cause a change in direction, because you are changing other polarities.

Why brushes are kept at magnetic neutral axis?

It turns out that, these points lie along the Magnetic Neutral Axis (MNA), as the name suggests has magnetic neutrality along that axis. As net magnetic field along MNA is zero, hence no emf will be induced. So that’s where one must position the brushes.

What is armature reaction in a dc machine?

3.10 Armature reaction in d.c. generators. Armature reaction is the effect on the main field flux of that flux set up by the currents in the armature winding. The effect is the same for both lap- and wave-wound machines.

What would happen if the brushes of an electric motor were shifted?

If the brushes were shifted slightly in the direction of rotation, some of the interpole flux would enter the armature back of the conductors under commutation.

How do you change the speed of a brushed DC motor?

Brushed DC motors can be varied in speed by changing the operating voltage or the strength of the magnetic field. Depending on the connections of the field to the power supply, the speed and torque characteristics of a brushed motor can be altered to provide steady speed or speed inversely proportional to the mechanical load.

Why do DC motors have less arcing at the brushes?

Since current changes are half those of a comparable two-pole motor, arcing at the brushes is consequently less. If the shaft of a DC motor is turned by an external force, the motor will act like a generator and produce an Electromotive force (EMF).

Is the brushed DC motor still used today?

• The Brushed DC motor is not as widely used today as in the past, but it is still being used, especially at the low-power level. • Focus is on topics of interest to the mechatronics engineer