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Motors > Motors > Flashcards

Motors Flashcards

1
Q

What happens to slip speed as load is added

A

The slip speed increases

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2
Q

Do motors with higher full load rotor speeds have higher or lower percent speed regulation?

A

Lower speed regulation %

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3
Q

Do motors with higher full load rotor speeds have higher or lower percent efficiency?

A

Higher efficiency

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4
Q

Which rotor parameter stays constant

A

Resistance

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5
Q

Which rotor parameter is proportional to rotor speed?

A

Power factor of the rotor

Pf(r)

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6
Q

Which five rotor parameters increase with slip speed?

A 
EZfIX
Voltage
Impedance
Frequency
Current
Reactance
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7
Q

What is the formula to find voltage of the rotor

A

Er = Ebr x s

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8
Q

Which rotor parameters are directly proportional to slip speed

A

Frequency, reactance and voltage

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9
Q

What does I r(R) represent

A

Active, in phase, horizontal or resistive current in the rotor

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10
Q

What is breakdown or pullout torque

A

The point at which max torque is reached and any added load causes the motor to stall.

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11
Q

State the formulas to find breakdown torque

A 
Rr = Xr 
Ir(R) = Ir(x)
pf(r) = .707 or cos45*
0theta(r) = 45*
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12
Q

If mechanical load is reduced slip speed will do what

A

Decrease

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13
Q

If mechanical load is increased then what will happen to %slip?

A

Increase

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14
Q

As slip speed increases, what will happen to rotor speed?

A

Rotor speed decreases

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15
Q

If mechanical load is increased what will happen to the impedance of the rotor (Zr)?

A

Z(r) increases

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16
Q

Within normal range, as load is increased, what will happen to rotor torque

A

Torque increases

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17
Q

As load is decreased what will happen to rotor voltage

A

Deceases

Slip goes does down as load decreases, voltage is proportional to slip

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18
Q

As load is increased what will happen to reactance of the rotor

A

Rotor reactance will increase

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19
Q

As slip is decreased what will happen to the power factor of the rotor?

A

Power factor will increase

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20
Q

As load is increased what will happen to rotor resistance

A

It will stay the same because it is conctant

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21
Q

As load is increased from no load to full load, the stator current will do what

A

Increase

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22
Q

As load increase, motor current will do what

A

Increase

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23
Q

Is motor current directly proportional to power and torque?

A

No, but it will increase with them

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24
Q

Is torque directly proportional to slip?

A

Yes

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25
Q

Is mechanical power output directly proportional to slip

A

Yes

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26
Q

What causes torque in a motor

A

The interaction of the rotor in the stator fields

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27
Q

What is another name for breakdown torque?

A

Pullout torque

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28
Q

Both nema A and B design rotors produce a max torque of what percent of sync speed?

A

75-80%

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29
Q

The rotor winding ms of a WRM are brought out and connected to what?

A

Slip rings

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30
Q

The rotor current of a WRM is carried through what?

A

Brushes to external resistors

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31
Q

Is the resistance of the WRM rotor circuit high or low at start ?

A

High

32
Q

What happens to the external resistors of a WRM once it has started?

A

They are bypassed so that the rotor runs with a low resistance at full load speed.

33
Q

What are the best starting characteristics for a motor?

A

High resistance (R) and low inductance(L)

34
Q

What are the best running chracteristics for a motor?

A

Low resistance (R) and low inductance(L)

35
Q

Can you change the speed of a WRM by adjusting the resistance of the rotor? Explain

A

Yes, the greater the resistance the lower the speed

36
Q

At what speed range can a WRM be used for speed control?

A

Half load to full load… torque is unstable at lower speeds

37
Q

Which rotor produces the best starting torque with the lowest starting current

A

Wound Rotor Induction Motor

38
Q

What are some disadvantages to a WRM?

A

Higher cost
Larger frame size
More maintenance
Additional equipment ( resistors and controller)

39
Q

Define synchronous speed

A

The speed of rotating magnetic field in the stator

Nsync = 120f/N

40
Q

Define slip speed

A

The difference between rotor speed and sync speed

Ns = nsync - nr

41
Q

Define slip

A

The ratio of slip speed to sync speed

s = ns /nsync

42
Q

When is stator frequency the same as the rotor frequency?

A

At the instant of start

Blocked rotor

43
Q

When is rotor reactance at max?

A

At the instant of start (blocked rotor)

Xr = rotor

44
Q

When is rotor impedance at max?

A

When rotor reaches slip speed

45
Q

What is proportional to the rotor power factor?

A

Rotor speed is proportional to Pf

46
Q

What is proportional to active rotor current?

A

Torque

Ir(R) = active rotor current
Ir(R) = Ir x Pfr
47
Q

When does breakdown torque (max torque) occur?

A

When the active current equals the reactive current.

48
Q

List four disadvantages of WRIM?

A

Higher cost
Larger frame
Requires aux equipment
Extra maintenance

49
Q

Lost four losses that contribute to inefficiency in a SCIM?

A

Hysteresis
Eddy currents
Windage
Friction

50
Q

What are the iec names for t1 T2v and t3?

A

U1, V1,W1

51
Q

How many leads does a dual voltage motor have ?

A

12 leads in total, but only 9 at the terminal box

52
Q

Which terminals are T1,T4, and T7 typically associated with ?

A

Phase A

53
Q

How many leads does a 9 lead motor have?

A

12 leads. But only 9 at the terminal box

54
Q

True or false

The high voltage dual voltage delta motor is connected in parallel

A

False

Dual voltage delta is connected in series

55
Q

Is the high voltage wye connection of a dual voltage motor wired in series or parallel?

A

Series

56
Q

How many groups of windings in a 3 lead motor

A

Three groups

57
Q

How many groups of leads are in a 6 lead wye delta motor?

A

3 groups of 2

58
Q

Is name plate data of a wye delta motor for the wye or delta connection ?

A

It’s is for the delta connection
Based on running condition
This motor starts in wye and runs in delta

59
Q

True or false

A part winding motor has two or more sets of 3 phase windings

A

True.

Once started all winding are connected in parallel for running operation

60
Q

Which motor has one group of 3 leads and 3 groups of two leads?

A

Dual voltage 9 lead wye motor

61
Q

True or false

A 9 lead delta connected motor had 3 groups of 2 leads

A

False

A 9 lead delta connected motor has 3 groups of 3 leads

62
Q

True or false

A delta connected 9 lead motor is wired in series for a high voltage connection.

A

True

63
Q

Rotor resistance can be increased by (increasing/decreasing) the thickness of the rotor bars

A

Decreasing

64
Q

Rotor inductance can be (increased/decreased) by imbedding the rotor bars in the rotor

A

Increased

65
Q

Which rotor design is the most efficient?

A

NEMA A

66
Q

Which rotor design produces the highest starting current

A

NEMA A

67
Q

Which rotor design is the most common

A

NEMA B

68
Q

Which rotor design produces the lowest starting current

A

NEMA D

69
Q

Which rotor design is the least efficient

A

NEMA D

70
Q

Which rotor designs produces a breakdown torque of 200% of full load

A

NEMA A And B

71
Q

Which rotor designs produces starting torque 150% of full load

A

NEMA A And B

72
Q

Which rotor design is made of a double squirrel cage

A

NEMA C

73
Q

Which rotor produces the maximum starting torque

A

NEMA D

74
Q

When do NEMA D motors produce breakdown torque?

A

At start

75
Q

Which rotor design produces the lowest full load slip

A

NEMA A

Motors (3 decks)

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