In Chapter 1, you have read about electromagnet-based DC motors. You have seen various connection methods there such as shunt, series, and separate field. Sep 22, AC commutator motors, like comparable DC motors, have higher starting torque and higher speed than AC induction motors. The series motor operates well. If a d.c. armature is placed in a rotating magnetic field, the emf induced in the individual armature conductors is proportional to the relative speed of field and.

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Refillable dovetailed commutators are the most common construction of larger industrial type commutators, but refillable commutators may also be constructed using external bands made of fiberglass glass banded construction or forged steel rings external steel shrink ring type construction and internal steel shrink ring type construction. However, since these motors are mostly aa.c.commutator on AC in practical use, they are called AC commutator motors.

Eventually the brush wears small and thin enough motprs steady contact is no longer possible or it is no longer securely held in the brush holder, and so the brush must be replaced.

Typically the brush is wide enough to span 2. Fine copper wire mesh or gauze provided better surface contact with less segment wear, but gauze brushes were more expensive than strip or wire copper brushes. However, these hard metal brushes tended to scratch and groove the smooth commutator segments, eventually requiring resurfacing of the commutator.

You May Also Like: In small appliance and tool motors the segments are typically crimped permanently in place and cannot be removed. Compensated series motor The arcing and sparking is mitigated by placing a compensating winding the stator in series with the armature positioned so that its magnetomotive force mmf cancels out the armature AC mmf.


Two or more fixed brushes connect to the external circuit, either a source of current for a motor or a load for a generator. During operation, it was necessary to adjust the position of the brush ring to adjust the commutation to minimise the sparking at the brushes. Coilgun Railgun Superconducting machine.

On large industrial equipment, the commutator may be re-surfaced with abrasives, or the rotor may be removed from the frame, mounted in a large metal latheand the commutator resurfaced by cutting it down to a smaller diameter. As the copper brushes wore away, the motos and pieces of the brush could wedge between commutator segments, shorting them and reducing the efficiency of the device. Then, is a shunt motor usable with AC?

This produces a loss not present in DC magnetics. Spurious resistance is an apparent increase in the resistance in the armature winding, which is proportional to the speed of the armature, and is due to the lagging of the current. The resulting motor is only practical in the smallest sizes.

Structure And Characteristics Of AC Commutator Motors | Nidec Corporation

Motors and generators suffer from a phenomenon known as ‘armature reaction’, one of the effects of which is to change the position at which the current reversal through the windings should ideally take place as the loading varies.

This opposing field helps to reverse the lagging self-inducting current in the stator. To minimize sparking at the brushes due to this short-circuiting, the brushes are advanced a few degrees further yet, beyond the advance for field distortions. The effect can be considered to be analogous to timing advance in an internal combustion engine.

Commutator segments are connected to the coils of the armature, with the number of coils and commutator segments depending on the speed and voltage of the machine. As the brush and commutator wear down, w.c.commutator spring steadily pushes the .ac.commutator downwards towards the commutator.

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A.c.commutatod commutator motors are not as maintenance free as induction motors, due to brush and commutator wear. By reversing the current direction in the rotating windings each half turn, a steady rotating force torque is produced.

Commutator (electric)

Timeline of the electric motor Ball bearing motor Barlow’s wheel Lynch motor Mendocino motor Mouse mill motor. Motors as large as those employed in a kitchen mixer, or larger, use compensated stator windings.

Instead, the rotation of the rotor induces field effects which drag and distort the magnetic lines of the a.c.cmmutator non-rotating stator. Small line operated appliances, such as drills, vacuum cleaners, and mixers, requiring to 10, rpm use universal motors.

Alternating-current commutator motor

Improving Gain Sensitivity and Bandwidth Having introduced the general negative feedback structure, we will now demonstrate that negative feedback has a beneficial effect on two Each conducting segment of the commutator is insulated from adjacent segments. Commutators were used as simple forward-off-reverse switches for electrical experiments in physics laboratories.

On large industrial machines say, from several kilowatts to thousands of kilowatts in rating it is economical to replace individual damaged segments, and so the end-wedge can be unscrewed and individual segments removed and replaced.

A commutator consists of a set of copper segments, fixed around the part of the circumference of the rotating machine, or the rotor, and a set of spring-loaded brushes fixed to the stationary frame of the machine.

The introduction of the carbon brush had convenient side effects.

If the polarity of the electromagnet remains the same as shown in Fig. While such a motor will rotate, operation a.c.commutato marginal. AC commutator motors The single phase series motor is an attempt to build a motor like a DC commutator motor.