Industrial Electronics Chapter 6 [AC Motors]

The magnetic field that protrudes out of the end of the main pole of a shaded-pole motor is the greatest when the current through the coil is _____

Increasing

In a synchronous motor, a large amount of excitation current will cause there to be a power factor that goes in the _____ direction

Leading

When a wound rotor induction motor is running at full speed, the variable external resistors are set to a ____________________ (low, high) resistance, and the slip is ____________________ (low, high)

Low, low

When a WRIM is started, the ohm setting of the resistor network is ____________________, and the torque is maximum because ____________________

Maximum, the rotor and stator flux field are in phase with each other

A wound rotor motor will not start if _____

A stator winding is open

A synchronous motor does not have a good starting torque without _____

Amortisseur

After running at normal speed, a wound rotor motor will stall if a rotor winding is opened (T/F)

False

If a split-phase motor hums and does not turn after power is applied, the most likely problem is _____ A. a short exists B. the start winding is open C. the motor shaft is stuck D. the motor is overloaded

B

Which type of single-phase induction motor is used for hard-starting applications, such as for compressors?

Capacitor start

The ____________________ induction-run motor has the highest starting torque because ____________________

Capacitor-start, the phase difference between the start and run coils is nearly 90 degrees apart

Which of the following types of motors are capable of being stalled without being permanently damaged? A. split-phase B. capacitor-start C. synchronous D. wound rotor E. universal

D

Which of the following factors determine the synchronous speed of an AC motor? A. inductance of the rotor windings B. the frequency of the applied voltage C. the number of field poles per phase D. the physical load driven by the motor E. both b and c

E

Which of the following types of AC motors use slip rings and brushes? A. split-phase B. capacitor-start C. wound rotor D. synchronous E. both c and d

E

The direction of rotation by the shaft of a universal motor can be changed by reversing the AC power leads (T/F)

False

The direction of the wound rotor induction motor can be reversed by interchanging two of the three rotor terminals (T/F)

False

When a polyphase motor encounters a single-phase condition, only one of the three-phase leads is supplying power (T/F)

False

To change the direction of a capacitor-start AC induction motor, _____

Reverse either the main winding or auxiliary winding

The direction of rotation of a three-phase motor can be reversed by _____

Reversing any two of the three line connections

The auxiliary winding in a split-phase AC motor helps create a(n) ____________________ field, and the run winding produces a(n) ____________________ field

Rotating, alternating

The poles in a synchronous motor that project outward are called _____ poles

Salient

The rotor of an induction motor can be compared to the _____ of a transformer

Secondary

The capacitor-start AC motor has a capacitor in _____ with the _____ winding

Series, auxiliary

A ____________________ motor is also called a condenser motor

Synchronous

Motor slip is not required in a ____________________type motor

Synchronous

The rate at which the magnetic field in the stator rotates is called the ____________________

Synchronous speed

A synchronous motor has the same number of stator windings and rotor poles (T/F)

True

The number of wound rotor poles must be the same as the number of stator poles

True

The shaded-pole motor is a form of induction motor (T/F)

True

The speed of a synchronous motor can be varied within a given range by adjusting the resistance of the starting resistor connected to the rotor (T/F)

True

There is no current flow in the rotor of a squirrel-cage motor if it is turning at the same speed as the stator's synchronous field (T/F)

True

A lagging power factor is caused by _____

Underexcitation

Motors that operate by using AC or DC power are called ____________________ motors

Universal

The slip of a synchronous motor is ____________________ percent at full speed

Zero