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Millwright Level 4 > Electrical > Flashcards

Electrical Flashcards

1
Q

What are Atoms made up of?

A

Protons +
Neutrons (Neutral)
Electrons -

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2
Q

What holds electrons in orbit?

A

Force of attraction between opposite electric charges

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3
Q

Atoms contain equal numbers of _____ and _____

A

Protons and electrons (electrically neutral)

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4
Q

Free electrons forced to drift in the same general direction is called _____ ______

A

Electric Current

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5
Q

Elements that make available a large number of free-electrons allow relatively large currents to flow

A

Conductors

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6
Q

Elements that make available relatively few free-electrons allow only incredibly small currents to flow

A

Insulators

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7
Q

What three things does electric current produce?

A

Heat, magnetic, chemical

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8
Q

If molecule in a metal can be aligned so that their individual magnetic fields all act in the same direction what does it become

A

A magnet (ferrous metals)

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9
Q

What makes a good temporary magnet?

A

Iron, silicon steel (used in larger motors, relays, solenoids)

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10
Q

What makes a good permanent magnet?

A

Steel, steel alloys w/ nickel and cobalt (simple electric motors, energy meters)

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11
Q

Law of magnetism

A

Like poles repel, and unlike poles attract

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12
Q

How can you increase a magnetic field?

A

Iron core inserted into the conductor coil

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13
Q

What behaves like a strong bar magnet that can be turned on or off?

A

Electromagnetism

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14
Q

The path which an electric current takes is called?

A

A circuit

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15
Q

What is current flow measured in?

A

Amps

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16
Q

What is potential energy measured in?

A

Volts (energy source)

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17
Q

What is resistance measured in?

A

Ohms

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18
Q

This uses electrical energy to do useful work

A

Load (motor, lights, heaters etc.)

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19
Q

These function as a remote controlled switches within control circuits

A

Relay

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20
Q

Types of circuits

A

Series: Same current through each load

Parallel: Same potential difference (voltage) across each load (most common)

Series Parallel: Combination of both

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21
Q

At a given temperature, the current flowing through a conductor is directly proportional to the voltage across that conductor

A

Ohm’s Law (Increasing the voltage across a conductor increases the current flowing through it)

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22
Q

The resistance of a conductor is independent of _____ and ______

A

Current and Voltage

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23
Q

An objects electrical resistance depends on what?

A

The resistivity of the material it is made from

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24
Q

As the temperature of a conductor increases, the value of resistivity _____

A

increases

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25
Q

As the temperature of insulators increase, resistivity ______

A

decreases

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26
Q

Power is measured in _____

A

watts

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27
Q

Electric Current in one direction only

A

DC (battery)

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28
Q

Electric Current back and forth continuously

A

AC (generators)

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29
Q

Transformers cannot work with this

A

DC

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30
Q

These increase and decrease alternating voltages with very little energy loss

A

Transformers (distribute electricity on a large scale)

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31
Q

If a secondary winding has fewer turns than the primary winding

A

Step-down transformer

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32
Q

If the secondary winding has more turn than the primary winding

A

Step-up transformer

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33
Q

What do homes and small workshops use

A

Single-phase AC 240V and 120V supply

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34
Q

Larger building and factories use

A

Three-phase AC (three separate armature windings displaced by 120 degrees)

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35
Q

Three phase windings are connected in a ___

A

wye (or star)
Star point most common
Delta/Mesh also used

36
Q

Advantages of three phase induction motors

A

Smaller, simpler

37
Q

Three phase induction motors are also called

A

Squirrel cage motors

38
Q

What does interchanging two of the three lines to the motor do

A

Change direction of rotation

39
Q

What are circuit protection devices connected in series with a load

A

Fuses (element made of an alloy such as silver-tin)

40
Q

The greater the value of a fault current, the faster the fuse operates. What is this called?

A

Inverse time characteristic

41
Q

What can high-voltage fuses do?

A

extinguish arcs using sand-filled cylinders or spring loaded elements

42
Q

These are switching devices that can interrupt fault currents

A

Circuit breakers

43
Q

Name the two types of Circuit breakers

A

Oil circuit breakers

Air-blast circuit breakers

44
Q

A heavy duty, electromagnetically controlled switch (contactor) which opens and closes the circuit to the motor

A

Motor controller

45
Q

These monitor the load current

A

Temperature sensors (built into motor controller)

46
Q

What electrical charges don’t move what is it called

A

Static electricity

47
Q

The interactive relationship between electric charge and magnetic flux

A

Electromagnetism

48
Q

The ease which a material can be magnetized by a solenoid is a measure of it’s ______

A

permeability

49
Q

A material that is neither a good conductor nor a good insulator

A

Semiconductor (germanium and silicon most common)

50
Q

This is similar to pressure in hydraulic

A

Voltage

51
Q

This is the rate of flow of electrons (current flow)

A

Amps

52
Q

1 horsepower =

A

746 watts

53
Q

This is similar to a flow restriction in hydraulics

A

Resistance

54
Q

If the area of a conductor is doubled, the resistance is ______

A

Halved

55
Q

If the length of a conductor is doubled, the resistance ______

A

Doubles

56
Q

Standard power line frequency

A

60 hertz

57
Q

Math Formulas

A 
E = I x R
P = E x I
58
Q

Series circuit rules

A

Total resistance (ohms) is equal sum of each individual resistance (Rt = R1 + R2 + R3). More loads added means resistance increases.

Current flow (Amps) is the same throughout

59
Q

Parallel circuit rules

A

Total resistance (ohms) is always less than the smallest resistor in the circuit.
Total current flow (amps) is equal to the sum of the current flow through each load.
Total Resistance is Rt = 1/((1/R1)+(1/R2)+(1/R3)
Volts is the same throughout circuit

60
Q

Which switch does not provide overload protection

A

Drum switch

61
Q

List two manual motor starters

A 
Toggle switch (max 1hp @230V)
Push button starter (5hp at 230V)
62
Q

These can safely interrupt the in-rush current or locked-rotor current of an electric motor

A

Horsepower rated contacts

63
Q

Types of switches

A 
SPST - Single Pole Single Throw
SPDT - Single Pole Double Throw
DPST - Double Pole Single Throw
DPDT - Double Pole Double Throw
Any more than 2 would be 3PST etc.
64
Q

What guards against overloads motor starters use these protective devices

A

Overload relays (Low melting alloy and bimetallic)

65
Q

This is often called a solder pot relay

A

Low melting alloy relay (normally closed)

66
Q

How do you reset a Bimetallic strip relay

A

Allow it to cool, reset by turning handle to the off position
(Push button type push to the off position)

67
Q

What do you need to prevent automatic startup after a power failure

A

Low voltage protection (manual starters do NOT provide this)

68
Q

An overload relay has 2 basic parts

A

A heater element

A normally closed auxiliary contact

69
Q

Who requires that each line of a three phase motor has OLR protection?

A

Canadian Electrical code (CEC)

70
Q

Steps for resetting an OLR

A

Determine the cause of the overload
Wait for the OLR to cool down
Reset the OLR

71
Q

3 types of rectification

A 
Half wave (cuts bottom of AC wave)
Full Wave (inverts bottom AC wave to top, output still spikes)
Rectification with filters (Flattens out spikes, nearly flat wave)
72
Q

When an area of lighting suddenly dims and stays that way it is called

A

Brown-out (could be plant wide low voltage)

73
Q

A Typical two-wire plus ground circuit has the following colour coding

A

Hot wire is Black
Neutral is White
Ground wire is natural copper or green

74
Q

How far should you be from power lines until you know the voltage?

A

22ft (7m)

75
Q

Electric arc temps typically reach

A

3500 C

76
Q

Switches over this horsepower are most vulnerable to arcing

A

50hp

77
Q

Hot energized connections to a disconnect switch or circuit breaker are called

A

Line Lugs

78
Q

These prevent electrical equipment from operating out of sequence

A

Electrical interlocks

79
Q

Max AC volt range on a Multimeter

A

750 V

80
Q

These are used to test insulation of motor windings

A

Megohmmeter (meggar) Don’t test low voltage circuits

81
Q

This is the allowable current carrying capacity of a wire or cable assembly

A

Ampacity

82
Q

Wire sizes smallest to biggest

A

40 gauge (smallest), 0000 (biggest)

83
Q

The magnetic field around a magnet is called

A

magnetic flux

84
Q

The number of cycles an alternating current generates per second is called _______

A

Frequency

85
Q

This is similar to a hydraulic accumulator

A

Capacitance

86
Q

A phase on the sine wave is measured in

A

degrees of rotation

Millwright Level 4 (5 decks)

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