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Flashcards in Unit 20 Deck (36)
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1

Dual-voltage ac motors are made with two field windings, each rated for the ____ of two possible operating voltages

Lower

2

In a motor, the stationary field winding of a motor is mounted on the _____, which is the part of the motor that does not turn

Stator

3

What are the three main characteristics of a series-wound dc motor?

Poor speed control
Slow down considerably when a load is applied
Run at very high rpm's without a load

4

The actual current drawn by the motor is dependent upon what two things?

Load on the motor and actual operating voltage at the motor terminals

5

Universal motors are ______ horsepower motors that operate equally well on ac and dc

Fractional

6

The most prevalent type of ac motor is the ______ motor

Induction

7

This type of motor has no physical connection between its rotating member (the rotor) and the stationary member (the stator)

Squirrel-Cage Induction Motor

8

How would you reverse the rotation of a three-phase ac motor?

Swap any two of the three line conductors

9

In a dual-voltage ac motor the field windings are connected in _______ for low-voltage operation and in ____ for high-voltage operation.

Parallel ; Series

10

If a motor is ______, or it operates at a _____ below its rating, the operating current can increase to a value above the motor FLA rating.

Overloaded ; voltage

11

The rotating part of the motor is referred to as either the ____ or the _____

Rotor ; Armature

12

If the rotating part of the motor winding is jammed so that it cannot rotate, no CEMF will be produced in the motor winding, which will cause the motor to what? And what is the main reason for it?

Operate at locked-rotor current (LRC) ; Low impedance on the conductor

13

The FLA rating is the current rating in amperes that the motor _____ while carrying its rated horsepower load at its rated voltage

Draws

14

One of the great advantages of the shunt-wound dc motor is its ability to to what?

Maintain a constant speed under load

15

How many watts are there in one horsepower?

746

16

When voltage is first applied to the field winding of an induction motor, what is the only thing opposing the flow of current through the motor winding?

Conductor resistance

17

When voltage is first applied to the field winding of an induction motor it will have a very large inrush of current, how much current will there be?

A minimum of six times the FLA rating.

18

DC motors use brushes with springs to hold them in contact with a _______

Commutator

19

A motor must have ______ opposing magnetic fields in order to rotate

Two

20

When a motor is operating at LRC, it is at least ____ times the running current value

Six

21

In a synchronous motor, the _____ is locked in step with the rotating _____ field and is dragged along at the synchronous speed of the rotating magnetic field

Rotor ; Stator

22

What is the formula for calculating the Full-Load Ampere rating of a three-phase motor?

FLA = (Motor HP x 746) / (E x 1.732 x Eff x PF)

23

In a Shunt-Wound dc motor, the armature and field are in ______

Parallel

24

The NEC requires standard overload protection devices to be sized at ____ to _____ percent of the motor FLA rating.

115 ; 125

25

What is the formula for calculating the Full-Load Ampere rating of a single-phase motor?

FLA = (Motor HP x 746W) / (E x Eff x PF)

26

According to the NEC, electrical components must be sized in accordance with what as listed in the NEC Tables?

Full-Load Current Rating

27

(T/F) Induction-type ac motors depend on commutation for operation

False

28

The output mechanical work of a motor is measured or rated in what?

Horsepower

29

Wound-rotor induction motors only operate on what type of power?

Three-phase ac power

30

What does FLA stand for?

Motor Full-Load Ampere