estimation of induction motor operating power factor
TRANSCRIPT
Estimation of Induction Motor
Operating Power Factor From
Measured Current and
Manufacturer Data
Sl
NoTittle Page
No
1 Introduction 02
2 Background Information 04
3 Current βOnly, Pf Estimation 06
4 Power Factor: From Voltage, Current ZC 11
5 Power Factor: From Instantaneous Power 14
6 Discussion Of Results 16
7 Conclusion 20
8 References 21
index
Estimation of IM Operating PF From Measured Current and Manufacturer Data
1
Estimation of IM Operating PF From Measured Current and Manufacturer Data
introduction
β THREE-PHASE induction motors (IM) are industrial work-
horses, responsible for consumption of 40β50% of generated
electrical power. β
2
Estimation of IM Operating PF From Measured Current and Manufacturer Data
Recently there has been a lot of focus on IM
protection at LV, &MV levels.
These protection devices typically monitor the
motor current and/or voltage to provide the motor
protection functionalities
One of the interesting parameters to monitor is the
operating power factor (PF)
Traditionally, to monitor the operating PF of the IM,
one would require both the voltage and the current
A low cost method of determining the operating PF
of the IM using only the measured current and the
manufacturer data is developed.
3
BACKGROUND INFORMATION
IM equivalent circuit.
v1
r1 X1
I1
rC Xm
I1β
X2β
r2βs
I1 = Im +I1 β Load
componentExciting
component
Im
core-loss
resistance magnetizing
reactance
Leakage reactance sta
tor
Roto
r
Estimation of IM Operating PF From Measured Current and Manufacturer Data
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π½π in the range 75 β85
ie, stator PF at no load may
be as low as 0.1β0.3.
Typically, stator PF of
about 0.8β0.9 at 80β100% of
the full-load
I1β N1= I2β N2
Power Factor and Motor Load
Estimation of IM Operating PF From Measured Current and Manufacturer Data
5
Estimation of IM Operating PF From Measured Current and Manufacturer Data
CURRENT βONLY, PF ESTIMATION
Estimation of IM Operating PF From Measured Current and Manufacturer Data
Total input electrical apparent power , π· = ππ½π°
Active power, for supplying the load ,π· = ππ½π° cos β
PF =π·
π·= cos β Eqn 1
I= π°πππππππ + π°ππππππππ
π
π°ππππππ = I cos β , π°ππππππππ= I sin β π°ππππππππ=I sin cosβπ(π·π) Eqn 2
PF = πππ β = 1 β π ππβ 2 = 1 β (πΌπππππ‘ππ£π
πΌ)2 Eqn 3
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Estimation of IM Operating PF From Measured Current and Manufacturer Data
π°ππππππππ remains constant, it can be estimated from
nameplate data using π°ππππππππ= I sin cosβπ(π·π)
At no-load condition, there is no active current flow.
So, at no-load, I= π°ππππππππ PF = 0 (
PF= 1 β (πΌπππππ‘ππ£π
πΌ)2 )
As motor load increases the PF will increase toward
unity. Motor
load
increases
Total
motor I
increase
π°ππππππππremains
constant
(π°ππππππππ
π°)π
Decreases
Physically, at no-load, there is not much mechanical
resistance, so the whole circuit is mostly inductive due to
the stator coils, causing low PF.
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Estimate the π°ππππππππ from the nominal PF out of
the nameplate data. ( π°ππππππππ=I sin cosβπ(π·π)) Estimate the operating PF from measured motor
current & constant π°ππππππππ
β It would not require synchronized voltage and current measurement like in the displacement PF measurement principle.β
Basic Algorithm
Estimation of IM Operating PF From Measured Current and Manufacturer Data
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experimental setup
Estimation of IM Operating PF From Measured Current and Manufacturer Data
Load
supply
Motor
supply
ABB
Lv drive
IM 3 ph
Load
Motor
(7.5kw)
Test Motor
(2.2 kw)
two pole
pairs IM,
M2AA LA4
Motor
current
measureme
nt
Main supply (50 Hz)
IM 3 ph
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NOMINAL VOLTAGE 400V
NOMINAL CURRENT 4.9A
RATED POWER 2.2KW
RATED PF 0.81
RATED SPEED 1430 RPM
NAME PLATE RATING OF THE
TEST MOTOR TYPE ABB M2AALA4.
Estimation of IM Operating PF From Measured Current and Manufacturer Data
π°ππππππππ=I sin cosβπ(π·π)= 4.9* Sin (cosβ1 0.81)
=2.87
Measured
CURRENT
I(A)
I/π°πππππππ (%) PF
3.01 61.43 .30
3.23 65.92 .46
4.37 89.18 .75
5.21 106.33 .83
6.21 126.73 .89
MEASURED I,CALCULATED PF
FROM
CURRENT-ONLY METHOD AT
DIFFERENT LOAD
PF= 1 β (πΌπππππ‘ππ£π
πΌ)2=
1 β (2.87
3.01)2 = 0.3
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Estimation of IM Operating PF From Measured Current and Manufacturer Data
Power Factor: From Voltage, Current ZC
Basic Algorithm
Synchronized measurement of the supply voltage and
the motor current are done.
Displacements in the ZC timings between the voltage
(taken as reference) and the current signals are
estimated.
Estimate the PF using the equation Β±x ms : Deviation between the current
ZC w.r.t. the voltage ZC,
ππ βΆ πupply frequency.
PF=πππ(π
(π
ππ)
X ππππ)
The current ZC deviation is positive or negative w.r.t.
The voltage would decide whether the PF is lagging
or leading.
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experimental setup
Estimation of IM Operating PF From Measured Current and Manufacturer Data
Load
supply
Motor
supply
ABB
Lv drive
IM 3 ph
Load
Motor
(7.5kw)
Test Motor
(2.2 kw)
two pole pairs IM,
M2AA LA4
Tektronix Voltage probe
Current hall-sensor probe
Main supply (50 Hz)
oscilloscope
Agilent
IM 3 ph
12
Β±x ms : 3.4 ms ,ππ =ππ
Pf =πππ(π
(π
ππ)
X ππππ)
=cos(3.4
20πΏ ππππ) =
0.48
PF MEASUREMENT USING
DISPLACEMENT IN THE ZC OF THE
SYNCHRONIZED SUPPLY VOLTAGE
AND MOTOR CURRENT AT 66%
CURRENT LOAD.
Estimation of IM Operating PF From Measured Current and Manufacturer Data
RMS
current
I(A)
ZC time
difference
(ms)
PF
2.97 4.6 0.12
3.00 3.4 0.48
3.54 2.8 0.64
4.24 2.1 0.79
5.23 1.6 0.87
RMS CURRENT,TIME DEVIATION
BETWEEN ZC OF VOLTAGE
&CURRENT, PF FROM
DISPLACEMENT METHOD AT
DIFFERENT LOAD
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Power Factor: From Instantaneous Power
Estimation of IM Operating PF From Measured Current and Manufacturer Data
Basic Algorithm
Estimate instantaneous power per phase (i.e., point-
by-point multiplication of the two waveforms) from
the synchronized supply voltage and the motor
current
Average power ( π ) per phase from the
measurement in the scope.
Estimate the PF using the equation : PF = π
ππΌ
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Power factor measurement using
instantaneous power from the measured
synchronized supply voltage and the
motor current at 66% current load.
π=328.525 V=230 I=3
PF = π
ππΌ=
328.525
230 π 3= 0.476
RMS
current
(A)
RMS
voltage
(v)
Instantaneou
s power(w)
PF
2.97 230 72.86 0.1
1
3.00 230 328.53 0.4
8
3.54 230 547.48 0.6
7
4.24 230 774.67 0.7
9
5.23 230 1014.32 0.8
4
RMS CURRENT,RMS VOLTAGE ,
INSTANTANEOUS POWER ,POWER
FACTOR AT DIFFERENT LOAD
Estimation of IM Operating PF From Measured Current and Manufacturer Data
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Estimation of IM Operating PF From Measured Current and Manufacturer Data
METHOD I(A) PF I(A) PF
From Measured Current 3.00 0.221 4.24 0.71
From Voltage, Current ZC 3.00 0.48 4.24 0.79
From Instantaneous
Power
3.00 0.48 4.24 0.79
DISCUSSION OF RESULTS
βThe PF estimation error using the current-only method is about +0.04 , except at the no-load condition, where it is aboutβ0.18 . This could be because, the sensitivity of the motor current measurement module might not be very perfect at no-load condition.β
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Estimation of IM Operating PF From Measured Current and Manufacturer Data
The proposed method relies on the fact that the inductance of the total circuit remains constant.
This rule might be violated if the motor is supplied via a variable speed drive.
Most modern drive systems usually measure both voltage and current and can provide PF measurement . Hence, no need for cheaper calculation of PF.
it is assumed that manufacturers comply with the relevant IM manufacturing standards, providing rated values with acceptable accuracy.
Estimation of IM operating PF could be used for PF compensation
17
Estimation of IM Operating PF From Measured Current and Manufacturer Data
For bigger IMs with low I(noβload)/I(rated) ratio, the assumption to use I reactive = constant for light loads might lead to high errors in the PF estimation.
Higher power machines usually come with MV or LV drives already provided with the PF computation.
Under no-load condition, the referred reactance of the rotorX2β would be absent.
The no-load current would comprise of the magnetizing current only. ie the no-load current would not be a good representative of the total reactive current
So, the reactive current estimated from the rated condition, would not miss any inductive elements.
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Estimation of IM Operating PF From Measured Current and Manufacturer Data
Measure
d c
urr
ent
(A)
Measured current (A)
πππππππ ππ’πππππ‘ (π΄)
Pow
er
facto
r
Measured current (A)
πππππππ ππ’πππππ‘ (π΄)
Underload protection using motor current & power factor
At low loads the nonlinear curve of the PF provides better resolution
It challenging to accurately measure the low current change from small load change at low loading.
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Estimation of IM Operating PF From Measured Current and Manufacturer Data
CONCLUSION
Low cost method of determining the operating PF
of the IM using only the measured current and the
manufacturer data typically available from the
nameplate and/or datasheet.
This would provide a cheaper solution to under
load protection, e.g., in pump applications, using
the operating PF, without requiring the voltage
sensors.
Operational PF can also be used for PF
compensation to improve the power quality.
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REFERENCE
P.S.Bimbhra, electrical machinery. New delhi, india:
khanna publishers,,
βIdentification of induction motor equivalent circuit
parameters
using the single-phase test,β IEEE trans. Energy
convers.
Abb. (2009). Manual for low voltage motor.
Http://www.Abb.Com/motors.
Abb. (2010). LV drives, model ACS800.
Www.Abb.Com/drives
D. Sharon, βpower factor definitions and power
transfer quality in no sinusoidal situations,βieee trans.
Instrum.
βPower-factor compensation of electrical circuits,β
IEEE control syst.
Estimation of IM Operating PF From Measured Current and Manufacturer Data
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Thank you!
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ANY
QUESTION
S?
Estimation of IM Operating PF From Measured Current and Manufacturer Data
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