AC Motors Overview and Types

<p>They require an auxiliary method to start. (D)</p> Signup and view all the answers

<p>It operates at about seven times the speed. (C)</p> Signup and view all the answers

<p>Single phase synchronous motor (A)</p> Signup and view all the answers

<p>Mechanical wear from brushes and commutators. (B)</p> Signup and view all the answers

<p>Polyphase or single phase lines. (B)</p> Signup and view all the answers

<p>6,000 to 24,000 rpm (D)</p> Signup and view all the answers

<p>Stator (D)</p> Signup and view all the answers

<p>P = 120 × f / N (D)</p> Signup and view all the answers

<p>Three phase AC induction motor (B)</p> Signup and view all the answers

<p>No EMF is induced in the rotor. (A)</p> Signup and view all the answers

<p>Frequency and number of poles (A)</p> Signup and view all the answers

<p>Stator (D)</p> Signup and view all the answers

<p>Induced current in the rotor (D)</p> Signup and view all the answers

<p>Distributed windings (C)</p> Signup and view all the answers

<p>To ensure proper torque production. (B)</p> Signup and view all the answers

<p>Has longitudinal slots with heavy bars. (D)</p> Signup and view all the answers

<p>Physical dimensions (D)</p> Signup and view all the answers

<p>Arrangement of wire coils (B)</p> Signup and view all the answers

<p>By reversing two of the leads to the motor. (C)</p> Signup and view all the answers

<p>It will deliver only one-third of its rated power. (B)</p> Signup and view all the answers

<p>It operates at the same speed as the stator's magnetic field. (C)</p> Signup and view all the answers

<p>Their rotor is too heavy to reach synchronous speed from a standstill. (C)</p> Signup and view all the answers

<p>Using a separate AC motor to bring it close to synchronous speed. (B)</p> Signup and view all the answers

<p>The rotor will pull out of synchronization with the field. (A)</p> Signup and view all the answers

<p>Through DC supply via slip rings. (A)</p> Signup and view all the answers

<p>By reversing connections to the starting winding. (A)</p> Signup and view all the answers

<p>Direction of rotation cannot be reversed. (D)</p> Signup and view all the answers

<p>To vary rotor pole strength for load control. (A)</p> Signup and view all the answers

<p>Torque is independent and does not rely on rotor currents. (C)</p> Signup and view all the answers

<p>They are a type of single-phase motor. (B)</p> Signup and view all the answers

<p>To create a lag in the magnetic field, aiding rotor rotation (B)</p> Signup and view all the answers

<p>Weak, suitable for devices with low initial traction (A)</p> Signup and view all the answers

<p>Opposing currents in the rotor create a turning force (C)</p> Signup and view all the answers

<p>Through a phase shift between the starting and running windings (A)</p> Signup and view all the answers

<p>They offer a higher starting torque, suitable for heavy loads (A)</p> Signup and view all the answers

<p>It is automatically disconnected by a centrifugal switch (C)</p> Signup and view all the answers

<p>From the interaction between the waves from the shading coil and stator field (B)</p> Signup and view all the answers

<p>Shaded pole induction motor (C)</p> Signup and view all the answers

<p>To disconnect the starting winding at low speeds (A)</p> Signup and view all the answers

<p>Shaded pole induction motor (A)</p> Signup and view all the answers

<p>The difference in speed between the rotor and synchronous speed (B)</p> Signup and view all the answers

<p>The phase shift created by the capacitors (C)</p> Signup and view all the answers

<p>Simple construction and reliability (C)</p> Signup and view all the answers

<p>Small appliances like fans and refrigerators (A)</p> Signup and view all the answers

<p>Large eddy current and hysteresis losses (B)</p> Signup and view all the answers

<p>Laminate the field poles, frame, and armature (D)</p> Signup and view all the answers

<p>To neutralize the effect of armature magnetomotive force (C)</p> Signup and view all the answers

<p>In series with the armature (D)</p> Signup and view all the answers

<p>A knocking sound (A)</p> Signup and view all the answers

<p>Universal motor (A)</p> Signup and view all the answers

<p>By using high resistance leads (C)</p> Signup and view all the answers

<p>It is the only limiting operating factor (A)</p> Signup and view all the answers

<p>To minimize hysteresis losses (A)</p> Signup and view all the answers

<p>Inductively compensated winding (A)</p> Signup and view all the answers

<p>Imbalance in electrical supply (A)</p> Signup and view all the answers

<p>It establishes large currents that lead to short circuits (D)</p> Signup and view all the answers

<p>Humming evenly (D)</p> Signup and view all the answers

<p>Preventive leads (A)</p> Signup and view all the answers

<p>Coils' cleanliness and dryness (A)</p> Signup and view all the answers

AC motors are more affordable compared to DC motors with similar capabilities.

AC motors often operate without brushes and commutators, eliminating sparking issues.

AC motors generally require less maintenance than comparable DC motors due to their design.

AC motors, especially 3-phase types, are suited for various applications requiring significant power, such as aircraft systems.

The rotational speed of an AC motor is determined by the frequency of the power source and the number of poles in the motor.

Induction motors and synchronous motors are the two primary types of AC motors used in aircraft.

Three-phase induction motors are powerful and used in aircraft for high-power devices like landing gear and hydraulic pumps.

Single-phase induction motors are used in aircraft for low-power devices such as surface locks and oil shutoff valves.

The speed at which the magnetic field rotates in an induction motor, calculated by dividing 120 times the frequency by the number of poles.

The stationary part of an induction motor containing windings that create the rotating magnetic field.

The rotating part of an induction motor, consisting of a core with embedded copper or aluminum bars, forming a 'squirrel cage' structure.

The difference between the synchronous speed of the rotating magnetic field and the actual speed of the rotor.

The torque produced by an induction motor is proportional to the slip, meaning higher slip, more torque.

The speed at which the motor operates under load, slightly less than the synchronous speed due to slip.

The number of poles on a motor can be calculated using this formula: P = 120 * f / N, where P is the number of poles, f is the frequency, and N is the rated speed.

The current induced in the rotor bars creates its own magnetic field, which interacts with the rotating field, causing the rotor to turn.

The rotating magnetic field is created by applying three-phase voltages to coils wound on the stator, creating a rotating magnetic field.

A common name for a 3-phase induction motor, due to its rotor structure resembling a squirrel cage.

The magnetic field rotates once per cycle of the AC voltage, if the frequency is 60 Hz, the field makes 60 rotations per second.

Induction motors are categorized by their horsepower output, voltage, current, speed, phases, frequency, and operational mode (continuous or intermittent).

The principle of operation for both single-phase and three-phase induction motors relies on the creation of a rotating magnetic field.

The alternating current flowing through the coils creates a changing magnetic field, which rotates due to the phase differences in the three-phase voltage.

Induction motors are used in various applications requiring significant power, such as aircraft systems.

The difference between the synchronous speed and the actual speed of a rotor in an induction motor, expressed as percentage of synchronous speed.

A single-phase induction motor uses a single winding to generate a pulsating magnetic field instead of a rotating one.

This type of motor starts by using a shaded portion of a pole that induces a lagging magnetic field, creating a small rotating effect.

A shaded pole motor uses a copper band on a portion of the pole to create a delayed magnetic field, leading to a rotating effect.

The shaded pole motor has low starting torque and is best suited for applications that require small initial torque like fans.

A split phase motor uses separate starting and running windings, with different resistance values, to create a rotating magnetic field for starting.

The starting winding in a split phase motor gets disconnected once the motor reaches about 25% of the rated speed, using a centrifugal switch.

A capacitor start motor is a stronger variation of the split phase motor, using a capacitor in the starting winding to create a greater phase shift for better starting torque.

Capacitor start motors are often used in appliances like refrigerators due to their high initial torque, enabling them to handle heavy loads.

A centrifugal switch in capacitor start motors also disconnects the starting winding when the motor reaches around 25% of the rated speed.

Single-phase induction motors, though used for some applications, are more common in lower power ranges (1hp or less) compared to their polyphase counterparts.

Polyphase motors, especially 3-phase motors, are favored for high power applications due to their superior starting torque and overall performance.

A single-phase motor can be self-starting, meaning it can start rotating even when the rotor is not spinning, whereas DC motors require external help to start.

While single-phase motors find application in various devices, they are generally more common in low-power applications like fans, pumps, and other small tools.

The direction an AC motor rotates can be changed by switching the connection of two of the leads in a three-phase motor, or by reversing connections to one phase in a two-phase motor.

A single-phase AC motor uses a starting winding to help it get going. Reversing the connections to this starting winding will reverse the direction of rotation.

Shaded pole motors have a copper ring that determines the direction of rotation, and it can't be reversed.

If a three-phase AC motor loses one of its connections, it will continue to run but produce only 1/3 of its normal power. A two-phase motor will also keep running, but with half its normal power.

Synchronous AC motors rely on a rotating magnetic field to spin the rotor. This field is created by AC current in the stator windings.

The field winding on the stator of a synchronous motor produces a rotating magnetic field, which is matched by the rotor's field.

The rotor of a synchronous motor can be a permanent magnet for small applications or an electromagnet energized by DC for larger motors.

A synchronous motor requires a starter to reach synchronous speed before it can lock into the rotating magnetic field.

A synchronous motor is not self-starting. It needs to reach a high speed before it can lock onto the rotating magnetic field.

The rotor of a synchronous motor is designed to match the rotating field's speed, ensuring constant rotation.

If the load on a synchronous motor is too high, it will fall out of sync with the rotating magnetic field and stop rotating.

A rheostat controls the DC current to the rotor windings, allowing operators to adjust the motor's output power.

A three-phase winding produces a rotating magnetic field, which is the basis for creating synchronous motor operation.

An AC series motor is a distinctive single-phase motor that is neither an induction nor synchronous motor. It uses a series winding for both field and armature.

The AC series motor is a single-phase motor that uses a series winding, meaning the same current passes through both field and armature.

The direction of rotation of a DC series motor remains consistent regardless of the voltage polarity, provided the field and armature connections stay unchanged.

Large eddy currents and hysteresis losses occur in the unlaminated parts of the magnetic circuit, leading to excessive heating and reduced efficiency.

Laminating the field poles, frame, and armature helps to minimize eddy current losses in AC series motors.

Using high permeability, transformer-type, silicon steel laminations helps to reduce hysteresis losses in AC series motors.

Shallow pole pieces, fewer turns of wire, low frequency, low flux density, and low reluctance (short air gap) help to reduce the reactance of the field windings in AC series motors.

A compensating winding embedded in the pole pieces is used to reduce the reactance of the armature in AC series motors.

A compensating winding connected in series with the armature is called a conductively compensated armature.

A compensating winding designed to be inductively coupled with the armature is called an inductively compensated armature.

The axis of the compensating winding is displaced 90° from the main field axis, similar to compensating windings used in some DC motors and generators.

The shorted compensating winding acts as a secondary of a transformer, with the armature being the primary. The induced current in the compensating winding counteracts the armature reactance.

Preventive leads, such as those shown in Figure 18-10, are used to limit the induced current when coils are short-circuited by the brushes, reducing sparking.

Armature coils with a single turn and multipolar fields also contribute to reducing sparking at the commutator.

Fractional horsepower AC series motors without compensating windings or preventive leads are called universal motors.

AC motors generally require less maintenance compared to DC motors.

A knocking sound in a motor can indicate issues like a loose armature coil, a misaligned shaft, or worn bearings.