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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Commutator segments are connected to the coils of the armature, with a.c.commutatof number of coils and commutator segments depending on the speed and voltage of the machine. The windings coils of wire on the armature are connected to the commutator segments.

While such a motor will rotate, operation is marginal.

To conduct sufficient current to or from the commutator, the brush contact area is not a thin line a.c.commutatod instead a rectangular patch across the segments. Therefore, just like with an induction motor, a silicon steel-based insulation lamination structure is employed in the core of a commutator motor that operates on AC.

Commutator (electric)

There are two well-known historical types: 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 commutator on small motors say, less than a kilowatt rating is not designed to be repaired through the life of the device. It is therefore difficult to build an efficient reversible commutated dynamo, since for highest field strength it is necessary to move the brushes to the opposite side of the normal neutral plane.

Self-induction — The magnetic fields in each coil of wire join and compound together to create a magnetic field that resists changes in the current, which can be likened to the current having inertia. 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.



Commutator (electric) – Wikipedia

A commutator is a rotary electrical switch in certain types of electric motors and electrical generators that periodically reverses the current direction between the rotor and the external circuit. Mica was used on early machines and is still used on large machines.

The single-phase AC version suffers a double line frequency torque pulsation, not present in poly-phase motor. A.c.commuutator starting current produces high starting torque. In both the motor and generator case, the commutator periodically reverses the direction of current flow through the winding so that current flow in the circuit external to the machine continues in only one direction.

Though, the development of solid state rectifiers and inexpensive permanent magnets is making the DC permanent magnet motor a viable alternative.

This article is about the electrical component. It was usually constructed of brass and ivory later ebonite. Such requirements are a.c.dommutator with traction, military, aerospace, nuclear, mining, and high speed applications where premature failure can motros to serious negative consequences.

Instead, the rotation of the rotor induces field effects which drag and distort the magnetic lines of the outer non-rotating stator. However commutator motors are not as maintenance free as induction motors, due to brush and commutator wear. When an electromagnet is used for generating fields, the inductance of the field coil becomes larger than that of the armature. Two or more electrical contacts called ” brushes ” made of a soft conductive material like carbon press against the commutator, making sliding contact with successive segments of the commutator as it rotates.

Very small universal motors may be uncompensated. As the shaft rotates, the commutator reverses the flow of current in a winding. Practical commutators have at least three contact segments, to prevent a “dead” spot where two brushes simultaneously bridge only two commutator segments.

These field effects are reversed when the direction of spin is reversed. It is common for a flexible power cable to be directly attached to the brush, because current flowing through the support spring would cause heating, which may lead to a loss of metal temper and a loss of the spring tension.


The ratio of copper to carbon can be changed for a particular purpose. If the polarity of the electromagnet remains the same as shown in Fig. This motor has superior commutation below synchronous speed, inferior commutation above synchronous speed. With the wide availability of alternating current, DC motors have been replaced by more efficient AC synchronous or induction motors.

Speed can a.c.commmutator controlled by rotating the brushes with respect to the field axis. 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 currenta.c.cokmutator a large amount of heat. 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 in parallel across the surface of the very large commutator.

These effects can be mitigated by a Compensation winding in the face of the field pole that carries armature current. Operating life of a.ccommutator machines is much longer, limited mainly by a.c.commurator wear. Therefore, commutated machines are declining in use, being replaced by alternating current AC machines, and in recent years by brushless DC motors which use semiconductor switches.

This moves the rotor winding undergoing commutation slightly forward into the stator field which has magnetic lines in the opposite direction and which oppose the field in the stator.

Similarly the segment coming into contact with the brush has a similar ramping up of the current.