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Motor Control Flashcards

(69 cards)

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1
Q

Three manual motor starters

A

-Toggle switch
-push button starter
-Drum switch

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2
Q

Three ratings found on motor starters

A

-Voltage
-Ampacity
-Horsepower

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3
Q

Two thermal overload protections

A

1-Melting alloy relay
2-Bimetallic strip relay

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4
Q

Explain low voltage protection

A

Will not restart machinery if power outage and power returns. (Think of a saw, would be dangerous if it automatically turned on when power returns) three wire circuits

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5
Q

Explain low voltage release

A

Will Automatically restart after power outage once power returns (two wire circuit)

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6
Q

Explain toggle switch

A

1hp @230v toggle switch is like a normal switch on/off

To reset- move toggle handle to full/Off position then flick up to on to turn on

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7
Q

Explain push button starter

A

5h@230v

Stop start button, once pressed stays engaged in the in position until opposite button pressed.

To reset- push off button all the way in to the “off” position

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8
Q

What are three enclosure functions and what do they protect against.

A

1-Shield (shields live buttons from accidental pressing)
2-protect( protects starter from dust/moisture
3-prevent (prevent explosions when starter in hazardous locations

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9
Q

Two main parts of magnetic starter

A

1-the contractor ( starts and stops motor)

2- the overload relay ( provides running protection for the motor)

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10
Q

Explain drum switch

A

3hp @ 240hp/ 1.5hp @120v

Rotary switch turning a central shaft. used to control SPEED and DIRECTION.

Does NOT provide overload protection

Overload protection required in the circuit

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11
Q

Most common magnetic three phase motors

A

Across the line magnetic starter

(Electromagnet used to operate contacts)
(Across the line = motor is started with FULL line voltage)

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12
Q

What is a con

A

Controls the circuit by connecting or disconnecting the load from supply (acts like a switch)

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13
Q

Three steps in overload trip resetting

A

1: determine cause of overload
2: wait for the overload relay to cool down
3: reset the overload relay

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14
Q

Isolation switch explain

A

Provides a local disconnect without disconnecting full circuit NOT HP RATED

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15
Q

How is heat element wired in circuit series/parallel

A

1:Has a heat element connected in series with the motor.

2: normally closed auxiliary contact in series with the coil of the magnetic contact.

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16
Q

What does overload relay do

A

Will trip and close circuit when:
1: motor overheats prevent motor burning out/fire hazard
2: when dangerous current being ran to motor it will also trip

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17
Q

How does melting alloy work

A

Uses a solder wheel (normally closed contact)

When current too high, alloy will melt and make wheel spin freely tripping circuit.

Once cooled solder solidifies and wheel resets to close contact again

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18
Q

Are overload relays wired in series or parallel

A

Series

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19
Q

How do bimetallic strip overloads work

A

-Placed close to heater element

-once heater element overheats it will melt the bimetallic strip bending it down until it presses onto the tripping relay which opens a normally closed switch tripping the circuit

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20
Q

What two things determine heater selection for a manual starter

A

FLA (full load table)
Heater selector table

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21
Q

Why does drum switch have 240v motor have two power contacts

A

To open both ungrounded conductors to the motor (120v each line)

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22
Q

What is hp ratings for all three switches

A

Toggle = 1HP 230v
Push = 5HP 230v
Drum = 1.5HP 120v / 3HP 240v

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23
Q

What two things is a drum switch used for

A

Controlling speed manually
Control direction

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24
Q

What are three things that happen if overload occurs

A

LINE current INCREASES
Heater element WARMS up
Excess heat causes overload to trip

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25
What is 3 wire control What is 2 wire control
Low voltage protection (3wire) Low voltage release (2 wire)
26
What are connect in parallel with start button in 3 wire circuit
Seal in contact ( holding contact/maintaining contact) Closes and opens with energising/de energising action from electromagnetic coil
27
Two types of magnetic starters
Clapper/ front closing Plunger/Vertical lift
28
Difference between contactor and magnetic starter
Magnetic starter is a contactor WITH OVERLOAD RELAY Contactor have NO overload relays
29
What is jogging/inching
Momentarily operates a motor to allow small movements of the driven machine
30
What protects jogging from being dangerous circuit
circuit breaker/fuse- use selector switch or control normally open contact relay
31
Motor with jogging button has to have a hp rating higher than motor serves, why?
Jogging causes repetitive inrush currents. Motor starter must be rated higher HP then motor serves
32
What is a float switch used for.
Float switch also called (liquid level switch) - used in pump motor applications to respond to changes in water levels
33
Another name for seal in contact
Seal-in Maintaining Holding
34
When are seal-in contacts used for
Used in 3 wire circuits to prevent machine/motor turning on voluntarily after a power outage. Places in parallel to start button and is a n/o contact
35
Two wire circuit difference from 3 wire
Uses a on off switch and will restart automatically if power outage if left in “on” position. ( Low voltage release ) the on/off switch easily replaced with float/pressure switch
36
Low voltage protection
Three wire circuit. When power outage and power returns machine/motor will automatically switch off and will have to be restarted to turn on
37
Relay coils designed to activate at what percent of rated voltage
85% of rated voltage Can operate at 10% over rated voltage without damage to coil
38
Advantage of latching relay (two things)
Quieter operation and energy saving
39
Stop button and start button wired in series/parallel
Stop = series Start = parallel
40
What two components are horsepower rated in control circuit
1- disconnect 2: contacts (normally open)
41
What components are current rated in control cct
1: fuse 2: overload relays (O-L)
42
Difference between overload protection and overcurrent protection
Overload= protects normal current path with overload protection relays (solder pots/bimetallic strip) Over current= fuse/circuit breaker= protects outside normal current path
43
How do you switch direction of motor
Switch any two of the three load leads supplying motor
44
Three ways to jog a circuit
1: control relay 2: selector switch 2: double contact jog button
45
Difference between maintain button and momentary button
Momentary returns to original off position when not being pushed Maintain: if you let go of button it stays on
46
Stop push buttons are momentary contact type t/f
True normally closed momentary contact
47
Limit switches limit what
Limit over travel
48
Contactor and magnetic starter difference
Contractor doesn’t contain overload protection and is 2 wire cct Magnetic starter contains overload protection and is 3 wire cct
49
What is a 3 main causes of chattering on motor
1- broken shading coil 2- poor contact in contact circuit 3- low voltage
50
5 causes of over heating in a motor
1- over voltage or high ambient temp 2- dirt or rust on pole faces 3- shorted turns from corrosion 4- under voltage 5: incorrect coil
51
Welding and freezing main causes
1- abnormal Inrush current 2- rapid jogging 3- insufficient tip pressure 4-short cct 5-foreign matter preventing contact close
52
Three names for a pressure switch
1-bourbon 2-bellows 3-diaphragm
53
Is a control relay HP rated?
NO! Only power contactor and disconnect switch are hp rated
54
What is proximity switch 3 facts-
1- solid state device/no moving parts 2-non contact they active when in proximity to an object 3- inductive type= attracted to metals Capacitive type = any material (Works like a sensor in door or window to close)
55
Explain photoelectric switch 3 facts
1- works using light beam and light sensor. Two parts a led emitter and a light sensor 2- 3 types (through beam/retro/diffuse)
56
What 3 ratings do control relays have
1- Inrush or ( make contact) 2- normal or ( continuous rating) 3- opening or ( break contact rating)
57
Explain a control contact
Magnetic device used remotely to switch loads and circuits Made from epoxy coating to reduce moisture and improve protection
58
What is the purpose of shading coils
To prevent chattering noise in contactor
59
Cross cross method tests what
Fuse- source volts mean fuse good. 0 volts = blow fuse One lead behind fuse (source line) other lead in front of other fuse (line)
60
Another name for zero speed switch?
Plugging switch
61
Which switch is not hp rated
Isolating switch
62
Why are contacts hp rated
So that they can handle inrush current
63
What is a combination starter
Magnetic starter with overload protector and a fused switch that is manually operated.
64
A dotted line in schematic indicates what?
Mechanically connected
65
Difference between mechanically and electrically held contactors
Electrically held = once electrical power supply cut of the contact will go back to original state Mechanically held (latching) once a contactor is closed and power cut off it will remain closed or (latched)
66
Are isolation switches hp rated and where about in power are they located?
NOT HP rated Located : just before motor and after the overload relays. They switch off the motor but not from the main supply (disconnect switch)
67
Three types of overloads (2 thermal/1 elec)
Bimetallic strip Melting alloy relay(solder pot) Electronic
68
Another name for plugging switch
Zero speed- plugging switch is used when you need to instantly stop a motor
69
What does FLA stand for/mean
Full load amperes- used to select appropriate motor

Motor Control (1 decks)

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