BCIT Electrical LEVEL 2 > Motor Control > Flashcards

Motor Control Flashcards

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1
Q

One characteristic of AC induction motors is that they draw large, momentary ___________ when they are switched on

A

In rush current

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2
Q

The __________ starter is a snap-action switch, giving simple on-off control.

A

toggle switch

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3
Q

What is the rating of the toggle switch ?

A

1 HP, 230V

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4
Q

what does manual motor- starting switch has that regular light switch doesn’t?

A

H.P rating

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5
Q

what does is mean if the switches have horsepower rating?

A

it can safely interrupt the in-rush current or locked-rotor current of the motor

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6
Q

___________ is a rotary-action selector switch

A

Drum Switch

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7
Q

what is drum switch commonly use for?

A

Manually control speed, change in (forward/reverse)directon of the motor.

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8
Q

What manual motor starting switch that does not have a overload protection?

A

Drum Switch

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9
Q

drum switch requires overload protection?
True or False

A

True

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10
Q

What is the rating of the drum-switch

A

3HP, 240V or 1.5HP 120V

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11
Q

The motor automatically restarts when power returns is referred to as ______________.

A

Low voltage release or under voltage release

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12
Q

An equipment such as saws, lathes, and machinery that might harm the operator during an unexpected start-up. These application require ______________.

A

Low-voltage protection (LVP) or under voltage protection (UVP)

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13
Q

Manual starters provides low-voltage protection?
True or False

A

False, manual starters do not provide low-voltage protection

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14
Q

The three significant electrical ratings for manual motor starters are………

A

Voltage (V), Ampacity (A) and Horsepower(H.P)

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15
Q

To guard against overload currents, motor starters use protective devices called ______________.

A

overload relays

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16
Q

What are the two most common types of thermal overload protection?

A

Melting-alloy relays (solder pot relay) and bimetallic strip

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17
Q

The heater element and the n.c. contacts are wired in ____________ with the line to the motor

A

series

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18
Q

How does melting alloy relay work?

A

The current drawn by the motor is conducted through the heater element of the relay.
If the current is unusually high for too long, then the element heats up, causing the alloy in the solder pot to liquefy. When the solder melts, the ratchet wheel, which is normally held under spring tension, spins free. This causes the line contacts to trip open and interrupt current flow to the motor.

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19
Q

What process needs to be done right after when overload occurs?

A

allow a cooling-down period, then reset the contacts:
* On a toggle starter, the handle automatically moves to the centre position during overload.
* To reset, move the handle to the full OFF position.

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20
Q

____________ means that the motor is started with full line voltage.

A

Across-the-line

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21
Q

What is the fundamental purpose of any motor starters?

A

To safely start and stop the motor, and provide running protection (overload) for the motor

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22
Q

What are the two types of contactors?

A

the clapper type and the vertical type

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23
Q

A basic magnetic starter has two fundamental parts are……

A

contactor and an overload relay

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24
Q

What provides running protection for the motor

A

Overload relay

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25
How does start-stop action of the motor is controlled when energizing or de-energizing?
- When it is energized, the coil attracts a movable iron piece called the armature. - The movement of the armature closes a set of normally-open contacts (by pushing a set of movable contacts against stationary ones). - When the coil is de-energized, the armature is released, opening the contacts again.
26
If the motor starter has tripped because of overload, you must do the following:
* Determine the cause of the overload. * Wait for the OLR to cool down. * Reset the OLR.
27
The three-phase AC magnetic starter consists of two circuits:
- Power circuit - control circuit
28
What does power circuit of magnetic motor starter usually consists of?
disconnect switch over current protection hp-rated contacts OLR heaters
29
Isolation switch is rated in HP? True of False
False, isolation switch is not HP rated
30
Two-wire circuits provide under voltage release? True or False
True
31
In the three-wire circuit, which button is a normally-closed use for?
Stop button
32
In the three-wire circuit, which button is a normally-open use for?
Start button
33
what is the term when the auxiliary contact is in parallel with the start button?
seal-in contact or holding contact or maintaining contact.
34
contact will opens or closes when___________
energizing or de-energizing action of the electromagnetic coil
35
If there is a power failure during normal operation, the magnetic starter coil becomes de-energized and all starter contacts open. When power is restored, the control circuit must be manually restarted. This is known as
Low Voltage Protection
36
The most common controllers for three phase motors is the _______________.
across-the-line magnetic starter
37
A basic magnetic starter has TWO fundamental parts:
Contactor and Overload relay
38
Low Voltage starters typically range from Size 00 (2 hp maximum) to Size 8 (900 hp maximum) True or False
True
39
What kind of circuit provide under voltage protection?
three wire circuits
40
what does shading coil do?
reduce chatter
41
What is the difference between manual motor starter and magnetic motor starter?
Magnetic Motor Starter- whose contacts are open & closed electromagnetically. Manual Motor Starter- contacts open or closed manually
42
The fundamentally difference between three-wire and two-wire circuits?
Normally open contacts on the magnetic starter is added in the three- wire circuit.
43
what is the purpose of a pilot light?
to indicate operation status of the motor in a remote location.
44
_______ and ________ are control terms that mean momentarily operating a motor to allow small movements of the driven machine.
Jogging, Inching
45
The continuous jogging causes the motor to draw repetitive inrush currents. True or False
True, if you press it like so fast in millisecond repetitively, excessive high current occurs
46
What kind of diagrams is frequently used in motor control work?
schematic diagram also known as ladder diagrams or elementary diagram.
47
what kind of diagrams is used in motor control installation?
Wiring diagram, also know as connection diagrams.
48
Before energizing a motor, it is advised first to test electrically with a __________.
meggar
49
How can one protect ones face and eyes from arcs and flashes when closing a motor switch?
Turn your head away when energizing a motor switch
50
what is a fundamental difference between a magnetic contactor and a magnetic motor starter?
A magnetic motor starter consists of a magnetic contactor plus overload relay protection
51
How control relays are used?
Control relays are used as auxiliary devices in motor-control circuits to switch low-level currents
52
contact of the control relay is called a ______
pole
53
The three different current ratings of the control relay contacts are:
- inrush or make contact rating - Normal or continuous rating - Opening or break contact rating
54
What is a latching type relay?
A special kind of relay. A latching relay is a control relay that is activated electrically but held mechanically. The coil needs only to be energized momentarily for picking up or dropping out the relay.
55
what are the main disadvantage of a manual starter compared to a magnetic motor starter?
manual starter do not provide low voltage protection
56
How does a "magnetic type" of overload relay differ form a thermal type.
Magnetic - uses solenoid action to activate contacts Thermal- uses heating- action to activate contacts
57
identify the five parts of the basic contactor contruction:
1. stationary 2. moving contact 3. coil 4. armature 5. laminated iron core
58
what is meant by the terms "normally-closed" and "normally-open"
Condition or operational state of contacts when circuit is de-energized
59
why are combination starters provided with a "door (cover) mechanical interlock"?
so the door cannot be open when starter is energized
60
what is meant by the term "across-the-line" starting
starting a motor with "Full line voltage"
61
Would a motor starter rated at 10HP/600V be suitable replacement for a 20 HP/240V motor starter? Yes or No? Explain why?
No- 600V would have a lower current rating for contacts 10hp/600V draws 10amps (FLA) 20hp/240V draws 25amps (FLA) *contactors need to be replace for appropriate/correct amp rating contacts
62
If a three-phase motor is energized from an AC supply. Notice that the motor is rotating in the wrong direction. How would fix this?
Simply interchange any two of the three line leads feeding the motor
63
How many three-pole contactors in reversing magnetic starters
There are TWO x three poles
64
A relay is designed to activate or __________at approximately _______ of its rated voltage.
pick up, 85%
65
Relay Coils are generally available in standard AC or DC voltage ratings from ___ to ___.
24V to 600V
66
List 8 common pilot device:
Pressure switches Mechanical limit switches Flow switches Float switches Temperature switches Remote-bulb switches Proximity switches Photoelectric switches
67
Three components of the control circuit for a motor starter are the:
Magnetic coil, start button, and maintaining contacts
68
When working on a motor, the electrician must ensure the motor cannot be started:
by locking the motor disconnect in the open position
69
MULTIPLE CHOICES If a magnetic starter picks up when the Start button is pressed, but then immediately drops out when the button is released; the problem is most likely that: a. the start button is welded closed b. the coil has an open c. the control circuit voltage is too low d. the maintaining contact circuit is faulty
d. the maintaining contact circuit is faulty
70
MULTIPLE CHOICE Three components of the Control Circuit for a motor Starter are the: a. magnetic coil, overload heaters, and stop button b. start button, magnetic coil, and overload heaters c. start button, magnetic coil and safety switch d. magnetic coil, start button, and maintaining contacts
d. magnetic coil, start button, and maintaining contacts
71
MULTIPLE CHOICE To simplify connections, and assist in troubleshooting, most relay cabinets contain: a. voltmeters and ammeters b. all the two-wire control devices c. all the three-wire control devices d. terminal strips
d. terminal strips
72
MULTIPLE CHOICE The main advantage that a schematic diagram has over a wiring diagram is that it: a. is easier to identify circuit operation b. is easier to determine the physical location of devices c. is easier to trace the physical wiring d. all of the above
a. is easier to identify circuit operation
73
what the three common types of pressure sensor?
Bourdon tube, bellows and diaphragm
74
When dealing with pressure controls, what is the term refers to the pressure of the system when the switch closes: this normally applies to decreasing pressure?
Cut-in
75
The term ________ refers to the pressure of the system when the switch opens; this normally applies to increasing pressure.
Cut-out
76
what kind of switches that are used to primarily in pump-motor applications to respond to changes in liquid level
Float switches
77
what kind of switches are commonly used to prevent over-travel?
Mechanical limit switch
78
What is a time-delay relay?
Time-delay relay is a control relay with contacts that operate after a preset time interval.
79
What is the difference between Anti-plugging or Plugging?
Plugging is a method used to stop a motor very quickly or reverse its direction by reversing the motor leads while the motor is still spinning. Anti-plugging is protection that stops you from reversing the motor while it’s still moving.
80
what are the two basic types of Manually operated switches.
continuous contact and momentary contacts
81
what are the two basic types of Proximity Switch
Inductive proximity can detect the presence of both ferrous and non ferrous metals Capacitive proximity can detect the presence of almost any material.
82
What is a Proximity switch?
is a type of limit switch which relies on a sensor to detect mechanical in motion
83
BCIT Electrical LEVEL 2
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