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Motor Control > Motor Control > Flashcards

Motor Control Flashcards

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
Q

What is 3 wire control
What is 2 wire control

A

Low voltage protection (3wire)
Low voltage release (2 wire)

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26
Q

What are connect in parallel with start button in 3 wire circuit

A

Seal in contact ( holding contact/maintaining contact)

Closes and opens with energising/de energising action from electromagnetic coil

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27
Q

Two types of magnetic starters

A

Clapper/ front closing
Plunger/Vertical lift

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28
Q

Difference between contactor and magnetic starter

A

Magnetic starter is a contactor WITH OVERLOAD RELAY

Contactor have NO overload relays

29
Q

What is jogging/inching

A

Momentarily operates a motor to allow small movements of the driven machine

30
Q

What protects jogging from being dangerous circuit

A

circuit breaker/fuse- use selector switch or control normally open contact relay

31
Q

Motor with jogging button has to have a hp rating higher than motor serves, why?

A

Jogging causes repetitive inrush currents. Motor starter must be rated higher HP then motor serves

32
Q

What is a float switch used for.

A

Float switch also called (liquid level switch)
- used in pump motor applications to respond to changes in water levels

33
Q

Another name for seal in contact

A

Seal-in
Maintaining
Holding

34
Q

When are seal-in contacts used for

A

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
Q

Two wire circuit difference from 3 wire

A

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
Q

Low voltage protection

A

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
Q

Relay coils designed to activate at what percent of rated voltage

A

85% of rated voltage
Can operate at 10% over rated voltage without damage to coil

38
Q

Advantage of latching relay (two things)

A

Quieter operation and energy saving

39
Q

Stop button and start button wired in series/parallel

A

Stop = series
Start = parallel

40
Q

What two components are horsepower rated in control circuit

A

1- disconnect
2: contacts (normally open)

41
Q

What components are current rated in control cct

A

1: fuse
2: overload relays (O-L)

42
Q

Difference between overload protection and overcurrent protection

A

Overload= protects normal current path with overload protection relays (solder pots/bimetallic strip)

Over current= fuse/circuit breaker= protects outside normal current path

43
Q

How do you switch direction of motor

A

Switch any two of the three load leads supplying motor

44
Q

Three ways to jog a circuit

A

1: control relay
2: selector switch
2: double contact jog button

45
Q

Difference between maintain button and momentary button

A

Momentary returns to original off position when not being pushed

Maintain: if you let go of button it stays on

46
Q

Stop push buttons are momentary contact type t/f

A

True normally closed momentary contact

47
Q

Limit switches limit what

A

Limit over travel

48
Q

Contactor and magnetic starter difference

A

Contractor doesn’t contain overload protection and is 2 wire cct

Magnetic starter contains overload protection and is 3 wire cct

49
Q

What is a 3 main causes of chattering on motor

A

1- broken shading coil
2- poor contact in contact circuit
3- low voltage

50
Q

5 causes of over heating in a motor

A

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
Q

Welding and freezing main causes

A

1- abnormal Inrush current
2- rapid jogging
3- insufficient tip pressure
4-short cct
5-foreign matter preventing contact close

52
Q

Three names for a pressure switch

A

1-bourbon
2-bellows
3-diaphragm

53
Q

Is a control relay HP rated?

A

NO! Only power contactor and disconnect switch are hp rated

54
Q

What is proximity switch 3 facts-

A

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
Q

Explain photoelectric switch 3 facts

A

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
Q

What 3 ratings do control relays have

A

1- Inrush or ( make contact)
2- normal or ( continuous rating)
3- opening or ( break contact rating)

57
Q

Explain a control contact

A

Magnetic device used remotely to switch loads and circuits

Made from epoxy coating to reduce moisture and improve protection

58
Q

What is the purpose of shading coils

A

To prevent chattering noise in contactor

59
Q

Cross cross method tests what

A

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
Q

Another name for zero speed switch?

A

Plugging switch

61
Q

Which switch is not hp rated

A

Isolating switch

62
Q

Why are contacts hp rated

A

So that they can handle inrush current

63
Q

What is a combination starter

A

Magnetic starter with overload protector and a fused switch that is manually operated.

64
Q

A dotted line in schematic indicates what?

A

Mechanically connected

65
Q

Difference between mechanically and electrically held contactors

A

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
Q

Are isolation switches hp rated and where about in power are they located?

A

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
Q

Three types of overloads (2 thermal/1 elec)

A

Bimetallic strip
Melting alloy relay(solder pot)
Electronic

68
Q

Another name for plugging switch

A

Zero speed- plugging switch is used when you need to instantly stop a motor

69
Q

What does FLA stand for/mean

A

Full load amperes- used to select appropriate motor

Motor Control (1 decks)

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