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