Level 2 Module 2 Motors: Theory and Application
A three-phase induction motor may have ___.
2 poles
How many motor designs does NEMA designate?
5
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
Which of the is located on a motor's nameplate?
FLA Rating
The stationary magnetic of a DC motor is represented by the ___?
Field poles
The wound rotor induction motor is used ___.
For speed control and to limit starting current
Which of the following are most likely to use dynamic braking ___?
Forklifts
For a given number of poles, which of the following determines the speed of an AC motor?
Frequency
The capacitor-start motor is the single-phase motor type that has the ___.
Highest starting torque
Which of the following motors operate on the principle of the rotating magnetic field?
Induction motors
Horsepower is used to rate the ___.
Output capacity of a motor
Due to the absence of any moving electrical contacts, which type of motor should be used where the motor is exposed to flammable dust or gas?
Squirl cage induction motor
Which of the following motors provides constant speed from no-load conditions to full-load conditions?
Synchronous
Slip is best defined as ____.
The difference between the synchronous speed and the speed of the rotor in an induction 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
DC injection breaking is used on ___.
The stationary windings of AC motors
Which of the following is true of the shaded-pole motors?
They have a low starting torque, a low efficiency, and a high noice level.
Which type of motor can be easily reversed by switching two of the leads?
Three phase induction motor
According to NEMA definitions, which of the following is a type of totally enclosed motor?
Water-cooled
A motor enclosure that minimizes the entrance of rain and airborne particles to the electrical parts is consider ___.
Weather-protected
According to NEMA definition, 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 router induction motor
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
NEC article 430 covers ___. the application and installation of motors ?
the application and installation of motors
The NEC requires motor disconnecting means be ___.
within sight of the controller location
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
The synchronous speed at which a four pole,60Hz induction motor operates is ____.
1,800 rpm
The most common service factor appearing on a motor's nameplate is ___?
1.5
A three-phase synchronous motor has three-stator windings that are ___.
120° apart
In a split-phase motor, how much greater is the starting current when compared to the full-load current?
6 to 8 times
Which of the following motors is used where the required starting torque is high and speed control is desirable ?
Compound
A wound rotor motor has been recently put back into service but is now rotating in the wrong direction. After examining the motor, you find the lead L1 is connected to T2, L2 to T3, and L3 to T1. To correct the rotation, you should:
Connect L1 to T1, L2 to T3, L2 to T2.
Which of the following motors is the best installation choice for an application requiring adjustable speeds?
DC