AC Machines

How can the direction of mechanical rotation in a three-phase induction machine be reversed?

What is the synchronous speed in rpm for a six-pole three-phase induction motor operating from a 60-Hz source?

What is the construction of a squirrel-cage rotor in a three-phase induction machine?

A 60-Hz, four-pole, three-phase induction motor runs at a full-load speed of 1750 rpm. What is the slip under these conditions?

For a 60-Hz, four-pole induction motor running with a slip of 0.02778, what is the frequency of the rotor currents, also known as the slip frequency?

For a typical three-phase induction motor, how is the developed torque related to the slip for small values of slip?

What is a primary purpose of connecting external variable resistances to the terminals of a wound-rotor induction machine?

What is the typical starting current of a three-phase induction motor when started with rated voltage, compared to its full-load running current?

In the power-flow diagram for an induction motor, the developed power (Pdev) is the power that is converted to what form?

For a three-phase induction motor with a wye-connected winding, what is the relationship between the phase voltage (Vs) and the line-to-line voltage (Vline)?

A certain 30-hp, four-pole, 60-Hz, three-phase, delta-connected induction motor operates at 1746 rpm. Calculate the slip.

A 30-hp, four-pole, 440-V-rms, 60-Hz delta-connected induction motor has a total input impedance of 20.28 ohms at an angle of 27.59 degrees. What is its power factor?

A delta-connected induction motor has a phase current (Is) of 21.70 A. What is the magnitude of the line current (Iline)?

The equivalent circuit for one phase of an induction motor shows that the power converted to mechanical form is dissipated in a resistance of 19.4 Ohms. If the reflected rotor current (I'r) through this resistance is 19.88 A, what is the total developed power (Pdev) for the three-phase motor?

A delta-connected induction motor has a starting phase current of 132.8 A. What is the magnitude of the starting line current?

The total power crossing the air gap (Pag) of a four-pole, 60-Hz induction motor during startup is 30.75 kW. What is the starting torque?

What is the primary speed characteristic of a synchronous motor operating from a constant-frequency AC source?

What is the typical construction of the rotor in a synchronous machine with field windings?

In synchronous machine construction, what is the typical application difference between salient-pole and cylindrical-rotor machines?

In an automobile alternator, how is the output DC voltage regulated to approximately 14 V despite varying engine speeds?

What does the torque angle (delta) in a synchronous motor represent?

In the per-phase equivalent circuit for a synchronous motor, what does the voltage source Er represent?

How can a synchronous motor be used to improve the power factor of an industrial plant?

What is a synchronous capacitor?

At what torque angle (delta) does a synchronous motor produce its maximum or pull-out torque?

Which of the following is a described method for starting a synchronous motor?

Besides being used for starting, what is another purpose of damper (amortisseur) conductors in a synchronous motor?

What is the speed in rpm of a 200-hp, 60-Hz, eight-pole, delta-connected synchronous motor operating with a developed power of 50 hp?

A 480-V-rms, delta-connected synchronous motor develops 50 hp of power at a 90 percent leading power factor. What is the magnitude of the armature phase current (Ia)? Note that 1 hp = 746 W.

A synchronous motor has an applied phase voltage Va of 480 at an angle of 0 degrees and a synchronous reactance Xs of 1.4 Ohms. If the armature current Ia is 28.78 at an angle of 25.84 degrees, what is the induced voltage Er?

A synchronous motor is operating with a developed power of 50 hp at a torque angle (delta1) of 4.168 degrees. If the load is increased so the developed power becomes 100 hp, and assuming constant excitation, what is the new torque angle (delta2)?

The 'V curves' for a synchronous motor are plots of which quantity against which other quantity, for a constant load?

A 480-V synchronous motor develops 200 hp (149200 W) at an 85 percent lagging power factor, drawing 121.9 A of phase current. If the field current is adjusted to achieve 100 percent power factor (unity) while the power remains constant, what will be the new phase current?

What is the net starting torque of a basic single-phase induction motor with only a main winding?

The pulsating magnetic flux produced by the main winding of a single-phase induction motor can be resolved into what components?

How does a split-phase induction motor create the necessary phase shift between the main and auxiliary winding currents to produce starting torque?

What is the function of the centrifugal switch found in many single-phase induction motors like the split-phase motor?

What is a major advantage of using a capacitor-start motor compared to a standard split-phase motor?

How does a shaded-pole single-phase motor produce starting torque?

For which of the following applications are stepper motors particularly well-suited?

A variable-reluctance stepper motor has eight salient stator poles and six salient rotor poles. What is the angular rotation of the shaft for each step?

How is the direction of rotation of a variable-reluctance stepper motor reversed?

What key feature distinguishes a brushless DC motor from a basic permanent-magnet stepper motor?

According to the discussion on single-phase motors, what is a significant disadvantage of universal motors when compared to induction motors?

What is the effect of interchanging any two of the three connections to a three-phase source on an induction motor?

What is the operating speed of a six-pole synchronous motor connected to a 60 Hz power source?

In the per-phase equivalent circuit for an induction motor, the impedance of the rotor branch is given by R'r/s + jX'r. The resistance term R'r/s is often conceptually split into R'r and [(1-s)/s]R'r. What do these two split resistance terms represent?

What is the relationship between the developed power (Pdev) and the power crossing the air gap (Pag) in an induction motor with a slip of 's'?

When an unloaded synchronous motor is 'underexcited,' what is its electrical characteristic as seen by the AC source?

As the field current of a synchronous motor operating with a constant load is increased from a very low value, what happens to the magnitude of the armature current?