parametres of equivalent circuit for three phases induction motor
parametres of equivalent circuit for three phases induction motor
(OP)
hello
I have an 3 phases IM 5.5kv ,2450kw , 291 amps, Id/In=4.5, Td/Tn=0.3 , 50Hz, 2983tr/min
when I calculate the current in full load with equivalent circuit(see attachment file ) i can't found 291 amps
if i do a mistake? I don't know, can anyone give helpregards
I have an 3 phases IM 5.5kv ,2450kw , 291 amps, Id/In=4.5, Td/Tn=0.3 , 50Hz, 2983tr/min
when I calculate the current in full load with equivalent circuit(see attachment file ) i can't found 291 amps
if i do a mistake? I don't know, can anyone give helpregards





RE: parametres of equivalent circuit for three phases induction motor
Bill
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"Why not the best?"
Jimmy Carter
RE: parametres of equivalent circuit for three phases induction motor
For X2, R2, I believe the higher-R, lower X at bottom of table corresponds to starting and lower-R higher X at top of the table corresponds to running (deep bar effect). But there is no deep bar effect for stator....why two values?
Interesting that the French word for torque seems to be"couple".
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
the document in attachment is an official document from ABB the motor type is : AMDT 500-700 with directive atex ,
if we compare between this document and other induction machine guide books there is a named difference for the resistance and reactance stator and rotor example: in the theorie books there is : R1 , X1 for stator R2 ,X2 rotor for no load test and R2' , X2' for blocked rotor test however in this attachement there is a data about the temperature , and when i have done a current and torque calculation (i take for 50° a blocked rotor and 120° a full load value the outcome is wrong.
what is the solution?
regards
RE: parametres of equivalent circuit for three phases induction motor
Two values each for R2,X2 are expected (running and locked rotor).
Two values each for R1, X1 are not.
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
R_1 0.0704000
X_1 1.9801000
R_2 0.0653000
X_2 1.1985000
X_M 98.5000000
R_NL 2950.0000000
RPM = 2981.3 (lower than your 2983, but5 this is the value required to produce rated output by this model).
Using the equivalent circuit with above (i.e. FullLoadSlip = 0.0062333), it generates:
FullLoadAmps 288.9717651
FullLoadEff 0.9829193
FullLoadPF 0.9241550
FullLoadPower 2,500,583.81693
FullLoadTorque 8009.5315818
Full Load Slip 0.0062333
This seems to match the data sheet reasonably well.
Note my equivalent circuit is slightly different in that my R_NL (which plays the role of your Rfe) is on the supply side of the primary impedance, rather than in parallel with magnetizing reactance. The expected difference from this change is small.
To recalculate, the spreadsheet requires the "analysis toolpak" for excel.
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
Another run of the same spreadheet, using the same model
R_1 0.0704000
X_1 1.9801000
R_2 0.0653000
X_2 1.1985000
X_M 98.5000000
R_NL 2950.0000000
But this time set RPM a few tenths higher at RPM = 2981.75 (Full Load Slip 0.0060833)
This results in calculated
FullLoadAmps 282.7061375
FullLoadEff 0.9831461
FullLoadPF 0.9256792
FullLoadPower 2,450,965.01628
FullLoadTorque 7849.4145590
The number of decimal places is not intended to convey the precision... just didn't spend time cleaning it up.
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
but what means by changing speed ,is the machine manufacturer make mistake about speed measured?
regards
RE: parametres of equivalent circuit for three phases induction motor
A few random thoughts:
1 - small errors in speed measurement cause big errors in slip
2 - the resistances are dependent upon temperature. All resistances affect efficiency. Rotor resistance also affects slip for a given power pretty dramatically. We don't really know if all of these numbers represent the same temperature.
3 - per NEMA standards the accuracy requirement for nameplate speed is pretty loose. I don't know about other standards.
4 - small error due to position of that R_NL vs Rfe as discssed above.
5 - I never did figure out the significance of the extra value R1 and X1
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
regards
RE: parametres of equivalent circuit for three phases induction motor
One problem as we've stumbled onto is that there are various ways to determine performance and equivalent circuit and there may be some assumptions that need to be known about what is being presented. Ideally the definition of each term if not standard, and how was it determined, and what temperature is assumed,
IEEE112 section 5.9.2 presents three standard test / calculation methods to develop equivalent circuit model. It might be a useful reference for NEMA motors. Probably not much used in the IEC world.
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
best regards
RE: parametres of equivalent circuit for three phases induction motor
Part 1 recreates the calculation reported above (7 May 13 9:13).
s:=0.006083 is required to make P = 2450 and results in FLA = 282.7
Part 2 adjusts the parameters based on slip. Result is not much different.
s:=s:=0.006125 is required to make P = 2450 and results in FLA = 282.
282 is around 3% away from 291. So a combined error of 3% in pf*eff compared to the value reported (pretty big error).
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(2B)+(2B)' ?
RE: parametres of equivalent circuit for three phases induction motor
1) transforming from [parallel] Rfe||jXm in Ro+jXo [in series].
2)transforming Zeq= Z1+Zo||Z'2 where Zo=Ro+jXo Z1=R1+jX1 Z2=R'2/s+jX'2 I=UN/sqrt(3)/Zeq and for 2981.15 rpm I got 291 A.
As electricpete said: the result is very sensitive to the rpm changes[namely to slip].
For instance if rpm=2980 I=306 A and for 2983 I=265 A.
I get, approximately, same result if I neglect Rfe and Xm [264 A]for 2983 rpm.