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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Commutation and the Commutator, p.

A spring is typically used with the brush, to maintain constant contact with the commutator. Early machines had the brushes mounted on a ring that was provided with a handle. On the other hand, AC commutator motors have the following disadvantages: The AC line is directly connected to the stator of a repulsion a.c.comnutator with the commutator shorted by the brushes.

AC Commutator Motors | AC Motors | Electronics Textbook

Disposable, molded type commutators commonly found in smaller DC motors are becoming increasingly more common in larger electric motors. In small appliance and tool motors the segments are typically crimped permanently in place and cannot be removed. In this case, sufficient motor torque is not available. By using this site, you agree to the Terms of Use and Privacy Policy.

In addition to the commonly used heat, torque, and tonnage methods of seasoning commutators, some high performance commutator applications require a more expensive, specific “spin seasoning” process or over-speed spin-testing to guarantee stability of the individual segments and prevent premature wear of the carbon brushes.

Assume that when the motor is rotating in the condition shown in Fig. He formulated the laws of magnetic hysteresis in finding a solution.

If AC is applied to this field coil, its phase of current is lagged behind that of the armature. A commutator consists of a set of contact bars fixed to the rotating shaft of a machine, and connected to the armature windings. For a single armature winding, when the shaft has made one-half complete turn, the winding is now connected so that current flows through it in the opposite of the initial direction.


Commutator (electric) – Wikipedia

Therefore, just like with a.c.cokmutator induction motor, a silicon steel-based insulation lamination structure is employed in the core of a commutator motor a.c.commufator operates on AC. Later articles will extend to negative impedances and some When a commutated motor or generator uses more power than a single brush is capable of conducting, an assembly of several brush holders is mounted a.v.commutator parallel across the surface of the very large commutator.

In other projects Wikimedia Commons. Hysteresis is a lagging behind of the magnetic field strength as compared to the magnetizing force. Large motors may have hundreds of segments. Typically the a.c.clmmutator is wide enough to span 2. While such a motor will rotate, operation is marginal. Thus, the magnetic flux density becomes low when the current is conducted to the armature, and when it becomes high, the current to the armature is stopped.

This is known as a universal motor. When an induction motor drives a hard starting load like a compressor, the high starting torque of the repulsion motor may be put to use. 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.

There are two well-known historical types: While starting, armature windings connected to commutator segments shorted by the brushes look like shorted transformer turns to a.c.commutator field.

Alternating-current commutator motor

Early machines used brushes made from strands of copper wire to contact the surface of the commutator. If AC power is applied when cast metal or soft steel is used for the stator core, current is generated due to electromagnetic induction this current is called eddy currentgenerating a large amount of heat. When using the social button, e-mail, and printing function, you must enable JavaScript. As the brush and commutator wear down, the spring steadily pushes the brush downwards towards the commutator.


When an electromagnet is used for generating fields, the inductance of the field coil becomes larger than that of the armature. If the polarity of the electromagnet remains the same as shown in Fig.

There is less sparking with carbon as compared to copper, and as the carbon wears away, the higher resistance of carbon results in fewer problems from the motord collecting on the commutator segments.

What Are Motors?

That is why the series structure is employed for AC commutator motors. So even for mootrs rotor which is at rest and initially requires no compensation for spinning field distortions, the brushes should still be advanced beyond the perfect degree angle as taught in so many beginners textbooks, to compensate for self-induction.

These effects can be mitigated by a Compensation winding in the face of the field pole that carries armature current.

Insulating wedges around the perimeter of each segment are pressed so that the commutator maintains its mechanical stability throughout its normal operating range. The contact point where a brush touches the commutator is referred to as the commutating plane. So the rotation direction remains unchanged.

The windings coils of wire on the armature are connected to the commutator segments. A commutator consists of a set of copper segments, fixed around the part of the circumference of a.c.commutqtor rotating machine, or the rotor, and a set of spring-loaded brushes fixed to the stationary frame of the machine.