Eet 360 Ch4

Front 1

What is synchronous speed?

Back 1

Front 2

What is the rotor speed of an induction motor?

Back 2

Front 3

How do you change the rotational direction of the rotor and magnetic field in a stator in a three phase induction motor?

Back 3

By swapping any two of the three lead wires

Front 4

Equation for calculating synchronous speed

Back 4

ns is synchronous speed and fs is the frequency of the 3-phase Supply

Front 5

How do you describe the difference between synchronous speed and rotor speed

Back 5

Slip speed

Front 6

Rotor slip equation

Back 6

Front 7

Better frequency equations

Back 7

Front 8

What is the term for when power is applied to an induction motor and the rotor is not turning

Back 8

This is called a blocked rotor or locked rotor and can cause overheating in the stators. This can happen during startup or during overloading conditions.

Front 9

Under blocked rotor or locked rotor conditions, what are the conditions of rotor speed, slip and rotor frequency?

Back 9

Rotor speed is zero, the slip is 1 and the rotor frequency is the same as the synchronous speed / 100%

Front 10

Equations for blocked rotor frequency and frequency of the signal in the rotor (fr)

Back 10

Front 11

Equations for inductive reactance in an induction motor

Back 11

Fr is the frequency of the rotor, LR is the inductance, S is the slip, fBR is the blocked rotor frequency, XBR is the blocked rotor reactance

Front 12

Equation for rotor impedance and equations similar to V = IR

Back 12

Front 13

Equations for rotor current and phase angle in an induction motor

Back 13

Front 14

Describe the relationships between apparent, real and reactive power in an induction motor

Back 14

Front 15

Rotor power equations for an induction motor

Back 15

Front 16

For the real power P gap..... What does it provide to the rotor over the air gap?

Back 16

It provide the mechanical power,,,,,,, P mech and the rotor copper loss P rcl

Front 17

Mechanical Power and developed torque equations (1)

Back 17

Front 18

Mechanical Power and developed torque equations (2)

Back 18

Front 19

Equation for induction motor relating mechanical Power in watts to horsepower

Back 19

Front 20

Equations relating mechanical Power and developed torque in an induction motor

Back 20

Hint 20

Front 21

What is the torque developed under blocked rotor conditions called?

Back 21

The locked rotor torque or starting toward

Front 22

Describe the conditions leading to break down torque in an induction motor

Back 22

as the motor begins to accelerate, the slip decreases and the developed torque increases. This continues until the speed reaches a point where the developed torque is at a maximum. This is called the breakdown torque.

Front 23

Describe the conditions leading to rotor and load equilibrium in an induction motor

Back 23

The speed will continue to increase until the developed torque matches the load torque. At this point, there will be some slip which will be sufficient to cause a rotor current needed to maintain the motor at its operating speed

Front 24

What's happens when an increased load demand is put on the rotor of an induction motor (applied while in equilibrium.

Back 24

First the rotor speed will decrease which will increase the slip. This will increase the electrical current frequency inside of the rotor which will in turn induce more current and produce the needed additional torque to run the increased load. Equilibrium is reached once again.

Front 25

What condition will cause an induction motor to stall?

Back 25

If too high of a load is put on the motor, the breakdown torque will be surpassed and the motor will stall.

Front 26

Induction motor power losses equation

Back 26

Names for variable are in the hint section

Hint 26

Front 27

Diagram with all motor losses

Back 27

Front 28

Equation for efficiency of an induction motor

Back 28

Front 29

Which type of applications are induction Motors not good for?

Back 29

Applications that involve high torque or find speed control

Front 30

What can be said about using induction Motors versus direct current Motors?

Back 30

Induction Motors are much more durable and much less expensive.

Front 31

Who invented the induction motor?

Back 31

Nikola Tesla in 1888

Front 32

What happens if you increase the frequency of the supply voltage and an induction motor?

Back 32

It will increase the frequency of the current in the stator coils, causing the flux to rotate at a proportionately higher speed which means the synchronous speed increases

Front 33

How can the synchronous speed of an induction motor operating from a fixed frequency be changed?

Back 33

By changing the number of poles in the stator which is done by using a frequency converter to change the frequency, or both.

Front 34

What methods can be used to change the synchronous speed of an induction motor?

Back 34

Separate windings within the motor can be turned on and off therefore changing the pole number and synchronous speed. When two separate windings are used, it's called a two-speed two-winding motor. Three separate windings is a 3 speed 2 winding motor and so on and so forth.

Front 35

Equation for the voltage induced in a rotor loop at any rotor speed

Back 35

Front 36

What does the power triangle look like for an induction motor?

Back 36

Front 37

Steinmetz Equivalent Circuit Equation

Back 37

Front 38

Which NEMA units are used electric motor parameters in regards to various speeds, torque and power?

Back 38

r/min, lb-ft, hp

Front 39

Equation for torque

Back 39

Front 40

Equations for shaft power output

Back 40

Front 41

Equation for efficiency for induction motor

Back 41

Front 42

Power Factor equation for an induction motor

Back 42

Front 43

Equation for power loss in an induction motor

Back 43

Also: P loss = P in - P out

Hint 43