ac series motor construction and working pdf Saturday, December 19, 2020 6:52:12 AM

Ac Series Motor Construction And Working Pdf

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A series motor can be run from either dc or ac single-phase supply provided that both stator and rotor cores are laminated to limit the iron-loss. Figure

AC Motors: Principle of Operation

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.

AC commutator motors, like comparable DC motors, have higher starting torque and higher speed than AC induction motors. The series motor operates well above the synchronous speed of a conventional AC motor. AC commutator motors may be either single-phase or poly-phase. The single-phase AC version suffers a double line frequency torque pulsation, not present in the polyphase motor. Since a commutator motor can operate at a much higher speed than an induction motor, it can output more power than a similar size induction motor.

However, commutator motors are not as maintenance-free as induction motors, due to brush and commutator wear. If a DC series motor equipped with a laminated field is connected to AC, the lagging reactance of the field coil will considerably reduce the field current. While such a motor will rotate, the operation is marginal. While starting, armature windings connected to commutator segments shorted by the brushes look like shorted transformer turns to the field.

This results in considerable arcing and sparking at the brushes as the armature begins to turn. This is less of a problem as speed increases, which shares the arcing and sparking between commutator segments The lagging reactance and arcing brushes are only tolerable in very small uncompensated series AC motors operated at high speed. Series AC motors smaller than hand drills and kitchen mixers may be uncompensated. Figure below. 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.

A smaller motor air gap and fewer field turns reduce lagging reactance in series with the armature improving the power factor.

All but very small AC commutator motors employ compensating windings. Motors as large as those employed in a kitchen mixer, or larger, use compensated stator windings. It is possible to design small under watts universal motors which run from either DC or AC.

Very small universal motors may be uncompensated. Larger higher speed universal motors use a compensating winding. Thus, the offsetting effects result in a nearly constant speed from DC to 60 Hz.

The small line operated appliances, such as drills, vacuum cleaners, and mixers, requiring to 10, rpm use universal motors. Though, the development of solid-state rectifiers and inexpensive permanent magnets is making the DC permanent magnet motor a viable alternative.

The field induces a current flow into the shorted armature whose magnetic field opposes that of the field coils. Speed can be controlled by rotating the brushes with respect to the field axis. This motor has superior commutation below synchronous speed, inferior commutation above synchronous speed. The low starting current produces high starting torque.

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. The induction motor rotor windings are brought out to commutator segments for starting by a pair of shorted brushes. At near running speed, a centrifugal switch shorts out all commutator segments, giving the effect of a squirrel cage rotor. The brushes may also be lifted to prolong brush life.

Don't have an AAC account? Create one now. Forgot your password? Click here. Latest Projects Education. Textbook AC Commutator Motors. Home Textbook Vol. Single Phase Series Motor If a DC series motor equipped with a laminated field is connected to AC, the lagging reactance of the field coil will considerably reduce the field current. The resulting motor is only practical in the smallest sizes. The addition of a compensating winding yields the compensated series motor , overcoming excessive commutator sparking.

Most AC commutator motors are this type. At high speed, this motor provides more power than a same-size induction motor but is not maintenance-free. It is possible to produce small appliance motors powered by either AC or DC. This is known as a universal motor.

The AC line is directly connected to the stator of a repulsion motor with the commutator shorted by the brushes. Retractable shorted brushes may start a wound rotor induction motor. This is known as a repulsion start induction motor. Published under the terms and conditions of the Design Science License. Log in to comment. Load more comments. You May Also Like. Sign In Stay logged in Or sign in with.

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Universal Motor - construction, working and characteristics

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The universal motor is a type of electric motor that can operate on either AC or DC power and uses an electromagnet as its stator to create its magnetic field. It is often referred to as an AC series motor. The universal motor is very similar to a DC series motor in construction, but is modified slightly to allow the motor to operate properly on AC power. This type of electric motor can operate well on AC because the current in both the field coils and the armature and the resultant magnetic fields will alternate reverse polarity synchronously with the supply. Hence the resulting mechanical force will occur in a consistent direction of rotation, independent of the direction of applied voltage, but determined by the commutator and polarity of the field coils.

A universal motor is a special type of motor which is designed to run either on DC or single phase AC supply. A universal motor has a high starting torque and variable speed characteristics. Such motor runs at dangerously high speeds during no load. A standard DC series motor has very poor characteristics when operated on AC, mainly due to two reasons:. To insure satisfactory operation of the universal motor from an AC power source, some modifications are necessary. The reactance of the series field and armature windings must be reduced as much as practicable. The reactance of the series field winding can be somewhat reduced by using fewer turns of heavier wire.

Universal Motor - construction, working and characteristics

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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.

The motors which can be used with a single phase AC source as well as a DC source of supply and voltages are called as Universal Motor. It is also known as Single Phase Series Motor. A universal motor is a commutation type motor.

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Single Phase Series Motor. The single-phase series motor is a commutator-type motor. If the polarity of the line terminals of a dc series motor is reversed, the motor will continue to run in the same direction. Thus, it might be expected that a dc series motor would operate on alternating current also. Let a dc series motor be connected across a single-phase ac supply. Since the same current flows through the field winding and the armature, it follows that ac reversals from positive to negative, or from negative to positive, will simultaneously affect both the field flux polarity and the current direction through the armature.

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