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electrical Flashcards

1
Q

In a capacitor-start Induction run motor, which set of windings have a lower resistance, the run winding or start windings?

A

Run winding.

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2
Q

What are the minimal number of terminal leads required for a single-phase motor?

A

2 leads

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3
Q

Which single phase motor has a commutator and brushes?

A

Universal motor

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4
Q

which single phase motor is the cheapest?

A

shaded coil motor

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5
Q

Calculate the synchronous speed of a 10-pole motor operating at 60 hertz.

A

Synchronous speed = F x 120/P

= 60 x 120/10

=720 rpm

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6
Q

Calculate slip% of an 8-pole motor rotating(rotor) at 860rpm operating at 60 hertz?

A

Slip % = Sync speed – rotor speed /Sync speed x 100

= (900 – 860/900) x 100

= 4.44%

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7
Q

What is the minimum number of stator leads for a dual voltage, reversible split phase motor?

A

6 leads

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8
Q

A single phase, 4 pole split phase motor has a 3% slip at 60 hertz. Calculate the rotor speed.

A

Synchronous speed = F x 120/Poles

= 60 x 120/ 4 = 1800rpm

Rotor speed = 1800 x 3% = 54 RPM

Rotor speed = 1800 – 54 = 1746 RPM

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9
Q

Are the starting torque characteristics of a Capacitor-Start Induction-Run motor greater or less than a resistive start motor?

A

greater

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10
Q

When current flows through a conductor a magnetic field is produced around the conductor, what is this principle called?

A

magnetic induction

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11
Q

Anytime a conductor cuts through a magnetic field a voltage is induced into that conductor. What is this principle called?

A

electromagnetic induction

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12
Q

What is the rotational force produced by a motor called?

A

interaction of 2 magnetic fields

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13
Q

A single voltage, reversible split phase motor has 4 terminal conductors at a junction box. Which two terminals are interchanged to reverse the motor?

A

Leads T5 and T8.

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14
Q

What type of disconnecting means for a split phase motor functions as both a starting relay and overload relay?

A

hot wire relay

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15
Q

Which split phase motor has their windings energized all the time?

A

Capacitor-Stat Capacitor Run.

Permanent split motor.

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16
Q

What type of single-phase motor does not have a squirrel cage assembly?

A

Universal Motor.

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17
Q

Why are pole pieces laminated?

A

to prevent eddy currents

18
Q

When creating a magnetic field are the lines of flux in the direction of north to south across an air gap?

A

YES.

19
Q

What is the typical phase displacement in a shaded pole motor?

A

10 degrees

20
Q

What is the typical phase displacement between currents in the run and start windings in a resistive start induction motor?

A

90 degrees

21
Q

The nameplate of a 4-pole motor has a Full load rotational speed of 1705rpm. Under no load its speed increases to 1750 rpm.

A

Speed regulation = no load – full load / full load x 100

= (1750 – 1705)/1705 x 100

= 2.63%

22
Q

What approximate percentage of rotor speed does a centrifugal switch open it?

A

75 to 80%

23
Q

what is the resistance to magnetism?

A

reluctance

24
Q

If a Centrifugal switch fails to open what can happen to the start windings?

A

overload and over heat

25
Q

Which single pole motor is non-reversible?

A

shaded pole

26
Q

What type of AC machine converts electrical input into mechanical input?

A

motors

27
Q

Does an increase in current through a single conductor result in a increase of magnetic field around the conductor?

A

YES

28
Q

What is the amount of magnetism left in a material after the magnetizing force has stopped called?

A

Residual magnetism

29
Q

How are hysteresis currents reduced in core materials?

A

sillicon steel alloys

30
Q

hat components support the shaft and allow the rotor to rotate freely?

A

Bearings

31
Q

What happens to a load in a universal motor when a load is increased?

A

Rpm decreases

32
Q

In a universal motor, are the armature windings and field windings connected in parallel or series, or a combination of both?

A

Dc series

33
Q

Does a shaded coil motor rotate towards the shaded coil or away from the shaded coil?

A

towards

34
Q

A motor has a full load nameplate speed of 3450 rpm at 60 hertz. Calculate the number of poles and slip percent.

A

Number of poles

Sync speed = F x 120 / P

= 3450 rpm = 60 x 120 / p

P = (60 x 120) / 3450rpm

P = 2

Slip percent

Slip % = sync speed – rotor speed / sync speed x 100

= (3600 – 3450) / 3600 x 100

4.17%

35
Q

what is the rotational force profuced by a motor?

A

torque

36
Q

what compoonent forms the axis for rotation of the rotor assembly in a ac machine?

A

shaft

37
Q

2 types of capacitors

A

electrolytic capicitor
oilfilled capacitor

38
Q

what are the minimum number of stator leads required for a single voltage reversible split phase induction motor

A

4 lead

39
Q

in a capacitance start induction run split phase motor, start field windings are wound with more turns of smaller wire

A

more and small

40
Q

does a current relay use N/O or N/C contacts

A

N/O

41
Q

whih relay is the cheapest?

A

Centrifugal switch

42
Q

which switch is used externally to disconnect the start capacitor in a capstart cap runmotor?

A

potential relay

construction electrician (1 decks)

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