Motors: Theory and Application
A polyphase synchronous motor has three stator windings that are
120 apart
The power factor of an induction motor at no-load conditions can be as low as
15%
The synchronous speed at which a four-pole, 60Hz induction motor operates is
1800 rpm
Several motors are permitted to be supplied by a single branch circuit as long as each motor is no larger than
1hp
A three-phase induction motor may have
2 poles
Horsepower is used to rate the
output capacity of a motor
The speed of a three-phase squirrel cage induction motor is controlled by the frequency of the applied voltage and
the number of poles
The most common service factor appearing on a motor's nameplate is
1.15
In a DC series motor, how much of its full-load torque is developed at starting?
500%
Any exposed live parts must be guarded if they are operating at
50V or more between terminals
In a split-phase motor, how much greater is the starting current when compared to the full-load current?
6 to 8 times
A medium-size motor has a frame number of 284T. The D dimension of this motor is
7"
A delta-connected motor has
9 leads
Which of the following motors is used when the required starting torque is high and speed control is desirable?
Compound
Which of the following is most likely to use dynamic braking?
Forklift
For a given number of poles, which of the following determines the speed of an AC motor?
Frequency
Which of the following motors is the best installation choice for an application requiring adjustable speeds?
Shunt DC
Which of the following motors provides constant speed from no-load conditions to full-load conditions?
Synchronous
According to NEMA definitions, which of the following is a type of totally enclosed motor?
Water-cooled
According to NEMA definitions, which of the following is a type of open motor?
Weather-protected
Which motor should be used for applications that require frequent starts without overheating the motor?
Wound rotor induction motor
The primary method of varying the speed on a DC shunt motor is to adjust the voltage and current on the field winding or the
armature
A typical constant-torque load would be a
conveyor
The stationary magnet of a DC motor is represented by the
field poles
The capacitor-start motor is the single-phase motor type that has the
highest starting torque
For a constant-torque load, the horsepower increases and decreases
in direct proportion to the speed
The value indicated in rpm on the nameplate is the
rated full-load speed
DC injection braking is used on
the stationary windings of AC motors
The terminals of a motor can be identified using a battery and a(n)
voltmeter
The NEC® requires motor disconnecting means be
within sight of the controller location