Converting motor performance data into Eq Ckt parameters
Converting motor performance data into Eq Ckt parameters
(OP)
I see there are a few people on the forum who do motor simulations on the forum. ijl, zolka... maybe more. This forum seems to be a good place to discuss simulations (I don't know of any other forums where it is discussed ... does anyone?). Also there was mention of a free software ATP to do simulations.
Unfortunately, a prerequisite for doing a simulation is determining the equivalent circuit parameters R1, R2, X1, X2, Xm.
I don't see a lot of discussion of this topic in textbooks. The approach will vary depending on the available performance info that you are trying to match. I tend to think it's easy to match a small number of performance data points (we can throw in assumptions like X1=X2 if the problem is underspecified), but the results are not too accurate. As we try to match more and more performance data, it gets tougher, but the results are more accurate I believe.
Attached I have tried to do a match of data which iainuts posted 16 Jul 09 9:49 in thread237-249262: Low power factor, recip pump
That data sheet is included in tab "data sheet" of attached excel file.
In the attached excel file I have used the excel "solver" tool to find the equivalent circuit parameters which match the targets best (minimize the sum of the square of the errrors between model calculation and target).
I tried to make the spreadsheet self-documenting and self-explanatory. The calcualtions are in the "main" tab. I have provided an overview in the discussion tab along with discussion of results.
I will post the results here in the thread text, since I am not sure whether you guys will see any calculated values if you don't have the analysis tookpack loaded into excel.
The solution of the circuit parameters was:
R_1 0.0298
X_1 0.1831
R_2 0.0326
X_2 0.1760
X_M 7.09
R_M 1.2116
FullLoadSlip 0.0125
Performance of equivalent circuit using these parameters is:
Performance Measure || Calculated Value || Units || Target Value
FullLoadAmps || 111.12 || Amps || 113.00
FullLoadEff || 0.97 || none || 0.95
FullLoadPF || 0.90 || none || 0.87
FullLoadPower || 73203.09 || watts || 74600.00
HLEfficiency || 0.96 || none || 0.96
HLPowerFactor || 0.81 || none || 0.82
LRC || 737.40 || Amps || 675.00
LRT || 268.38 || N-m || 328.22
NoLoadCurrent || 36.00 || Amps || 28.00
As stated in discussion tab, since deep bar effect is excluded we expect R2 to be higher during locked rotor than running conditions. This is not included in the model and I have "weighted" the locked rotor performance parameters low, so that the resulting equivalent circuit parameters better reflect running conditions than locked rotor conditions. (I intend to use the parameters for simulation of transients during running conditions).
I am interested if anyone has any comments on this approach... suggested improvements... other suggested references or approaches for tackling the problem of converting motor performance data into equivalent circuit parameters.
Unfortunately, a prerequisite for doing a simulation is determining the equivalent circuit parameters R1, R2, X1, X2, Xm.
I don't see a lot of discussion of this topic in textbooks. The approach will vary depending on the available performance info that you are trying to match. I tend to think it's easy to match a small number of performance data points (we can throw in assumptions like X1=X2 if the problem is underspecified), but the results are not too accurate. As we try to match more and more performance data, it gets tougher, but the results are more accurate I believe.
Attached I have tried to do a match of data which iainuts posted 16 Jul 09 9:49 in thread237-249262: Low power factor, recip pump
That data sheet is included in tab "data sheet" of attached excel file.
In the attached excel file I have used the excel "solver" tool to find the equivalent circuit parameters which match the targets best (minimize the sum of the square of the errrors between model calculation and target).
I tried to make the spreadsheet self-documenting and self-explanatory. The calcualtions are in the "main" tab. I have provided an overview in the discussion tab along with discussion of results.
I will post the results here in the thread text, since I am not sure whether you guys will see any calculated values if you don't have the analysis tookpack loaded into excel.
The solution of the circuit parameters was:
R_1 0.0298
X_1 0.1831
R_2 0.0326
X_2 0.1760
X_M 7.09
R_M 1.2116
FullLoadSlip 0.0125
Performance of equivalent circuit using these parameters is:
Performance Measure || Calculated Value || Units || Target Value
FullLoadAmps || 111.12 || Amps || 113.00
FullLoadEff || 0.97 || none || 0.95
FullLoadPF || 0.90 || none || 0.87
FullLoadPower || 73203.09 || watts || 74600.00
HLEfficiency || 0.96 || none || 0.96
HLPowerFactor || 0.81 || none || 0.82
LRC || 737.40 || Amps || 675.00
LRT || 268.38 || N-m || 328.22
NoLoadCurrent || 36.00 || Amps || 28.00
As stated in discussion tab, since deep bar effect is excluded we expect R2 to be higher during locked rotor than running conditions. This is not included in the model and I have "weighted" the locked rotor performance parameters low, so that the resulting equivalent circuit parameters better reflect running conditions than locked rotor conditions. (I intend to use the parameters for simulation of transients during running conditions).
I am interested if anyone has any comments on this approach... suggested improvements... other suggested references or approaches for tackling the problem of converting motor performance data into equivalent circuit parameters.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.





RE: Converting motor performance data into Eq Ckt parameters
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
1 - use Thevinin approach to streamline the caluclation.
2 - fixed the torque target erro
3 - fixed an error in the half load calculation
4 - added breakdown torque.
This is still an error in there. If I look just at the full power results, they are not self-consistent as suggested in the check on rows 28-31. Still working on it. If anyone sees the cause of that discrepancy let me know.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
The circuit parameters:
R_1 0.024621
X_1 0.297346
R_2 0.029392
X_2 0.287261
X_M 7.668602
R_M 1.849573
Slip 0.011928
One calculations gives Pout ~73000watts and the other gives Pout~78,000 watts. There has got to be an error in there somewhere.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
There is now very good agreement for the performance data near full and half load. I think I am done with it.
... unless there are comments/suggestions on the approach.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Converting motor performance data into Eq Ckt parameters
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Converting motor performance data into Eq Ckt parameters
My apologies if the forum was inconvenienced. The bumps occurred over a relatively short time on a slow time (weekend) when there were not many other active threads, and I assumed most people would not re-open the thread if they had initially determined the subject matter was not of interest to them.
Next time I will keep the number of posts lower.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
TTFN
FAQ731-376: Eng-Tips.com Forum Policies
RE: Converting motor performance data into Eq Ckt parameters
I will mention this estimation of equivalent circuit parameters has a variety of other uses beyond simulation.... Over the weekend we had a small fan motor that tripped on instantaneous when it was stopped and restarted after an unknown period of time around 1 second or less. The question was asked how long is the minimum off time before restart. NEMG MG-1 provides an answer that the motor should be off for at least > 1.5 times the open circuit time constant (slow/transfer reclose) to allow the residual voltage to decay. As it turns out based on troubleshooting over the weekend we had captured data including voltage decay recording on load-side of contactor after disconnect for this particular motor which allowed to determine the open circuit time constant very well. But if we didn't have this data available, we could have estimated the open circuit time constant from the equivalent circuit parameters (Tau_oc = [L2+LM]/R2), which in turn could be roughly estimated from nameplate info and torque-speed/current-speed if available.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
I have used a little program motdatpr (see http://pp.kpnet.fi/ijl/prog.htm) for my simple simulations. It calculates the parameters of the equivalent circuit from the values at full power, plus the locked rotor current ratio. ATP, or actually the drawing program ATPDraw includes a utility, WindSyn for the same task.
RE: Converting motor performance data into Eq Ckt parameters
I looked at motdatpr
The problem is underspecified from a standpoint of unknowns and equations.
There are 5 unknowns: L1, L2, LM, R1, R2
There are 4 equations: 1 - power at full-load slip, 2 - power factor at full-load slip, 3 - efficiency at full load slip, 4- current at slip=1 (locked rotor).
Their resolution was to arbitrarily declare X1=X2 to get the last equation which seems a fairly common assumption.
I was able to use my spreadsheet and get very close to the same results as motdatpr by assigning a weight to thumbrule X1=X2. At least it's a double check there don't seem to be any large errors in my calculations related to LRC and to full load power, power factor, efficiency (compared to motordapr).
I think I need to work on the interface a little bit. I should have just the inputs and outputs (no calcs) on one sheet. Should have a button to trigger a macro to set up solver. Should put voltage and synchronous speed in more obvious place. Should put slip range in a more obvious place. If was really energetic I would add torque speed curve points perhaps at slip 0.25, 0.5, 0.75, 1. Same thing for currents. Any parameters which are not available to match or not desired to match can be turned off by setting the weight to 0.
=====================================
Eng-tips forums: The best place on the web for engineering discussions.
RE: Converting motor performance data into Eq Ckt parameters
pete - look forward to your modelling. your math skills are impressive. good luck.