Motors / Transformers

Question 1

Which type of breaking is used to bring a motor to a quick stop by phase reversal

Answer 1

Plugging

Question 2

What does a rectifier do in a circuit

Answer 2

Converts Ac to Dc

Question 3

What type of waveform is produced by half- wave rectifier

Answer 3

Pulsating DC

Question 4

What would be done prior to opening the primary disconnect switch of a high voltage distribution transformer

Answer 4

Unload the secondary

Question 5

How does a Triac dim an incandescent lamp?

Answer 5

Changing the circuit impedance

Question 6

Which AC motor would be installed, if a motor with good variable speed qualities is required?

Answer 6

Wound rotor

Question 7

How must a synchronous motor be started?

Answer 7

As an induction motor

Question 8

Which device serves the same function as a synchronous condenser?

Answer 8

A bank of capacitors

Question 9

Which device is used to test for short circuited coils in a motor?

Answer 9

Ohmmeter (key word test)

Question 10

When does the blower fan operate during normal heating operation of a forced air gas furnace?

Answer 10

The fan comes on last and shuts off last

Question 11

What best describes the comparison between a split phase resistance start motor and a capacitor start motor of the same size?

Answer 11

Different starting torque and the same running torque

Question 12

What type of DC motor would be used for an application requiring extremely high starting torque if good speed regulation was not important?

Answer 12

Series

Question 13

What is the function of a an automatic compensator used with a 3 phase motor?

Answer 13

Lowers the starting current

Question 14

What is the function of the grease in the bearings of an electric motor?

Answer 14

Reduce heat from the mechanical friction

Question 15

What type of single phase motor is used with domestic refrigerators?

Answer 15

Capacitor start

Question 16

What is another term for Root mean square?

Answer 16

Effective value

Question 17

What is the phase relationship between current and voltage in pure capacitive circuit?

Answer 17

Voltage lags current by 90 degrees

Question 18

When an AC installation requires a motor having variable speed characteristics, what type of motor should be used?

Answer 18

Wound rotor induction motor

Question 19

What conditions would cause a motor to burn out?

Answer 19

Excessive heat due to an overload

Question 20

What is the main reason for lubricating bearings in a motor?

Answer 20

Reduce heating

Question 21

What is the proper procedure to follow when energizing an oil filled transformer for the first time?

Answer 21

Open the secondary and energize the primary

Question 22

What would you use to clean DC motor brushes?

Answer 22

Fine sandpaper

Question 23

What does a megohmmeter measure?

Answer 23

Resistance

Question 24

How is the primary of a current transformer connected?

Answer 24

Series with the load

Question 25

What is a plugging switch?

Answer 25

Zero speed switch

Question 26

What function do electrical interlocks provide for a reversing starter?

Answer 26

Prevent more than one coil from energizing at the same time

Question 27

What is required for a single phase motor to operate on two voltages?

Answer 27

Two run windings

Question 28

How does motor current compare, when dual voltage AC motor is operated on the higher voltage?

Answer 28

Decreases from lower voltage

Question 29

What part of an AC to DC power supply keeps the output voltage constant with changing load?

Answer 29

Voltage regulator

Question 30

Which switch type can only be used to separate the circuit from its source of supply but neither establish nor interrupt the flow of current

Answer 30

Isolating switch

Question 31

Where are the overload relays for a size 1 magnetic starter physically placed?

Answer 31

At the contractor

Question 32

Which of the following motor control circuits would provide low voltage release?

Answer 32

Two wire circuit with switch connected in series with the coil

Question 33

What must be done when removing the meter from a metering circuit that uses a current transformer?

Answer 33

Short the secondary winding

Question 34

What test instrument is used to determine the speed of rotating equipment?

Answer 34

Tachometer

Question 35

How would an ammeter indicate that a motor had shorted coils in one phase?

Answer 35

Higher then normal current in one phase

Question 36

How would an ammeter indicate that a motor had an overloaded condition

Answer 36

Higher than normal current in all three phases

Question 37

An ungrounded 3 phase system has a ground detection lights installed. How would the ground detection lights indicate that none of the phases are grounded?

Answer 37

All three lights are on

Question 38

What is the standard direction of rotation of a DC motor

Answer 38

Counterclockwise from the commutator end

Question 39

Which DC motor should be directly coupled to its load

Answer 39

Series

Question 40

How is the direction of any DC motor reversed?

Answer 40

Reverse polarity of armature field

Question 41

Which DC motor must contain field loss protection?

Answer 41

Shunt

Question 42

What is the maximum speed that the rotor of an induction motor will turn?

Answer 42

Rotates at synchronous speed minus slip

Question 43

How do you reverse a shaded pole motor?

Answer 43

Take the motor apart and rotate the rotor shaft end from end

Question 44

When asked to bump the motor what will the test indicate?

Answer 44

The direction of rotation

Question 45

Which of the following is one disadvantage of an auto transformer?

Answer 45

There is no primary - secondary electrical isolation

Question 46

What is the main purpose of bonding a motor frame to ground?

Answer 46

Limit the Voltage to ground

Question 47

Which of the following factors influences the voltage regulation of an AC alternator?

Answer 47

Load and power factor

Question 48

What is the term mechanical degrees referring to in a generator?

Answer 48

The revolution of the armature conductor

Question 49

What is the purpose of reduced voltage starting for a motor?

Answer 49

Reduce the inrush current

Question 50

What are the purpose of the auxiliary contacts on a motor starter?

Answer 50

They seal the coil in the energized state when the start button is pressed

Question 51

Which of the following pairs of motor data determines the nema size starter for a motor?

Answer 51

Horse power and voltage

Question 52

What does a VFD insert into the stator of an AC induction motor in order to achieve electric frictionless braking?

Answer 52

Direct current

Question 53

What is the purpose of overload protection in a motor control circuit?

Answer 53

Protect the windings of the motor

Question 54

Where should the overload protection device be installed in a motor branch circuit?

Answer 54

Between the motor control contractor and the motor

Question 55

How is the direction of a single phase AC capacitor start induction - run motor reversed?

Answer 55

Reverse the connection of the start windings

Question 56

When connecting two generators in parallel to supply an electrical system, what items must be synchronized?

Answer 56

Voltage and frequency

Question 57

A DC motor obtains its supply from a bridge rectifier and a solid state starter. If one diode of the bridge rectifier opens, what happens to the motor if running under full load?

Answer 57

Motor would stall

Question 58

What is the speed of the rotating magnetic field of an induction motor?

Answer 58

Synchronous speed

Question 59

How would the shunt field windings of a cumulative compound motor be described?

Answer 59

Many turns of small wire

Question 60

What can be used to correct armature reaction in a DC motor with varying load

Answer 60

Using interposes of the same polarity connected in series with the armature

Question 61

The load requirements of a DC motor is do an extremely high starting torque. If speed regulation is not important, what type of motor should be used?

Answer 61

Series motor

Question 62

Which device is used to test for unbalanced current in a feeder installation?

Answer 62

Ammeter

Question 63

Which device is used to test for unbalanced current in a feeder installation?

Answer 63

Ammeter

Question 64

What device is used to help prevent tracking and flashover in high voltage cables?

Answer 64

Skirts

Question 65

How is the range of an analog ammeter increased?

Answer 65

Install a shunt in parallel

Question 66

How is the range of an analog ammeter increased?

Answer 66

Install a shunt in parallel

Question 67

What is the speed of the rotating magnetic field of an induction motor?

Answer 67

Synchronous speed

Question 68

What two conditions could cause higher than normal nameplate full load current in a squirrel cage induction motor?

Answer 68

Low system voltage and excessive mechanical load

Question 69

How will moisture in the oil of a liquid filled transformer affect it?

Answer 69

Bad dielectric

Question 70

Which of the following DC motors would not be used for belt drive applications?

Answer 70

Series

Question 71

What is the purpose of the shading coil in AC contractors?

Answer 71

Prevent chatter and AC hum

Question 72

How are magnetic blow out coils connected in large DC starters?

Answer 72

In series with the load

Question 73

How do you safely dry out a damp air cooled transformer?

Answer 73

Apply a small amount of voltage to primary under no load

Question 74

What is the condition of a capacitor that has a reading of zero when tested with an ohmmeter?

Answer 74

Short circuited

Question 75

What condition is indicated by an ohmmeter that registers infinity when testing across an overload heater?

Answer 75

Open

Question 76

Which diagram shows the complete electrical distribution layout?

Answer 76

Single line diagram

Question 77

What is the purpose of the shunt field relay in the DC motor control circuit?

Answer 77

Prevent dangerous acceleration

Question 78

What will be the result if the contacts of the centrifugal switch in a single phase motor do not close due to malfunction of accumulation of dirt?

Answer 78

The run winding will be energized but the motor will not start

Question 79

Which type of voltage are generally indicated by AC voltmeters?

Answer 79

RMS

Question 80

Which of the following is not a common method of starting a polyphase squirrel cage induction motor?

Answer 80

Capacitive starting

Question 81

Which of the following characteristics best describes a wound rotor motor?

Answer 81

High stating torque and low starting current

Question 82

How is the range of a voltmeter increased?

Answer 82

Connecting a multiplier in series

Question 83

What type of motor is considered a general purpose 3 phase AC motor?

Answer 83

Squirrel Cage