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Flashcards in Motors Deck (75)
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1

What happens to slip speed as load is added

The slip speed increases

2

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

Lower speed regulation %

3

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

Higher efficiency

4

Which rotor parameter stays constant

Resistance

5

Which rotor parameter is proportional to rotor speed?

Power factor of the rotor
Pf(r)

6

Which five rotor parameters increase with slip speed?

EZfIX
Voltage
Impedance
Frequency
Current
Reactance

7

What is the formula to find voltage of the rotor

Er = Ebr x s

8

Which rotor parameters are directly proportional to slip speed

Frequency, reactance and voltage

9

What does I r(R) represent

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

10

What is breakdown or pullout torque

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

11

State the formulas to find breakdown torque

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

12

If mechanical load is reduced slip speed will do what

Decrease

13

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

Increase

14

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

Rotor speed decreases

15

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

Z(r) increases

16

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

Torque increases

17

As load is decreased what will happen to rotor voltage

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

18

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

Rotor reactance will increase

19

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

Power factor will increase

20

As load is increased what will happen to rotor resistance

It will stay the same because it is conctant

21

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

Increase

22

As load increase, motor current will do what

Increase

23

Is motor current directly proportional to power and torque?

No, but it will increase with them

24

Is torque directly proportional to slip?

Yes

25

Is mechanical power output directly proportional to slip

Yes

26

What causes torque in a motor

The interaction of the rotor in the stator fields

27

What is another name for breakdown torque?

Pullout torque

28

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

75-80%

29

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

Slip rings

30

The rotor current of a WRM is carried through what?

Brushes to external resistors