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. It consists of a cylinder composed of multiple metal contact segments on the rotating armature of the machine. 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. The windings coils of wire on the armature are connected to the commutator segments.
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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. Among these motors, what do you think will happen if AC power is applied to a series motor?
Assume that when the motor is rotating in the condition shown in Fig. If the polarity of the electromagnet remains the same as shown in Fig. However, with a series motor, the polarity of the electromagnet is also reversed as shown in Fig. So the rotation direction remains unchanged. However, if you apply AC power to a series motor designed to be used with DC power, there occurs a problem. 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 current , generating a large amount of heat.
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. However, since these motors are mostly operated on AC in practical use, they are called AC commutator motors. Because of these characteristics, they are used for home appliances such as electric vacuum cleaners and tools such as electric drills Fig.
When an electromagnet is used for generating fields, the inductance of the field coil becomes larger than that of the armature. If AC is applied to this field coil, its phase of current is lagged behind that of the armature. 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.
In this case, sufficient motor torque is not available. Compared to this, such a phenomenon does not occur on the series coil since its field coil and armature coil are in series and the phase of current of the both is identical. That is why the series structure is employed for AC commutator motors. Basic Motor Information. Basic Motor Information Namely, this motor has a feature of being capable of continuing the rotation with AC power, too.
These motors are called universal motors since they are operable both on AC and DC. Is there a shunt AC commutator motor? A series commutator motor is operable on AC. Then, is a shunt motor usable with AC? Basic Motor Information Previous Next. What Is a Motor? Components of a Motor Classification of Motors DC Motor Brushless DC Motor AC Motor Switched Reluctance Motor Stepping Motor Ultrasonic Motor Basics Rotation Principles Rotating a Brushless DC Motor Characteristics of Brushless DC Motors Detecting the Rotor Rotation Principle of Induction Motor Characteristics of Induction Motors Motor Using Arago's Disc Structure and Operation of HB-type Motor Characteristics of Stepping Motors.
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A.C. Commutator Motors
The situation was so bad that motors could not be designed ahead of the actual construction. The success or failure of a motor design is not known until it is actually built and tested. He formulated the laws of magnetic hysteresis in finding a solution. Hysteresis is a lagging behind of the magnetic field strength as compared to the magnetizing force. This produces a loss not present in DC magnetics. Low hysteresis alloys and breaking the alloy into thin insulated laminations made it possible to accurately design AC commutator motors before building.