induction machines Flashcards

1
Q

typical effiecncy

A

> 90%

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2
Q

key components

A

soft iron core,
3 phase winding,
soft iron rotor
squirrel cage

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3
Q

setup of staor winding

A

iron stator core in which a three-phase stator winding is incorporated into a series of slots in the core

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4
Q

airgap field produced by phase A

A
Ba = magnetic flux density in the airgap
K = a constant which relates to the dimensions of the iron circuit in the machine
N×Ia = phase Ampere-turn
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5
Q

current in each coil a,b ,c

A

Ia=isin(wt)
Ia=isin(wt-120)
Ia=isin(wt-240)

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6
Q

synchronous speed

A

Ns=f*60/pole pairs

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7
Q

induction speed in comparison to synchronous speed

A

an induction machine runs at a speed which is close to, but always
slightly lower than the synchronous speed

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8
Q

equivalent cicuit for one phase

A

a resisistor and inductor then in parallel an inductor/resistor/back emf

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9
Q

what does each element of the equivalent cicuit represent

A

R1- stator winding resistance per phase
X1- stator leakage resistance
Rm- eddy cuurent and hysteress(iron losses)

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10
Q

Vp and Ip when star connected

A

Vp=Vl/sqrt(3)

Ip=Il

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11
Q

Vp and Ip when delta connected

A

Ip=Il/sqrt(3)

Vp=Vl

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12
Q

slip

A

S=(Ns-N)/Ns

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13
Q

what happens when the speed reaches synchronous speed

A

The rotor and stator field move at the same speed. No change in flux linkage, no induced voltage , zero current and therefore zero torque

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14
Q

Power delivered by the stator

A

Ps=(2piNs/60)*T

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15
Q

Mechanical output from the rotor

A

Pr=(2piN/60)*T

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16
Q

rotor loss

A

the difference between stator power and power from the rotor

17
Q

rotor loss in teerms of power delivered by stator and slip

A

stator power*slip

18
Q

rotor equivalent circuit

A

An inductor and a resistor in series

19
Q

what do the resistor and inductor represent

A

R-rotor resistance

L- rotor leakage and inductance (fields that do not couple to the stator)

20
Q

impedance of the inductor

21
Q

torque and power

22
Q

referring voltage uses

A

E’2=(N1/N2)*E2

turns ratio

23
Q

referring current and voltage

A

I’^2R’=I^2R

24
Q

for referring current

A

I’2=(N2/N1)*I2

25
for referring resistance and inductance
R'2=(N1/N2)^2*R2
26
what is the referred circuit multiplied by
f1/f2
27
aswell as the referred components what is in equivalent circuit
in parralel and and in parralel to eachother and inductor and resistor
28
what is the star connected phase voltage
Va=V/sqrt(3)
29
what side of pull out torque is a machine normally operated
Above the pull out torque
30
what speed is when current at a maximum and why can't this be maintained
at 0 speed - it will overheat
31
slip is an indicator of
rotor thermal losses
32
what is lagging/power factor
power with a phasor | cos(theta)=x lagging
33
copper loss equation
I^2*R
34
output power using torque
P=Tw
35
f1 to f2 using slip
f1=s*f2
36
how does a reluctance stepper motor work
the rotor alligns with energised teeth
37
how can the number of steps in a reluctance stepper be increased
half stepper mode
38
what is 2 benefits of half stepper mode
the overshoot of the rotor is lower and greater resolution of load positioning
39
At a high step rate what happens to pul out torque
it goes down