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simulation to recreate measured wiggle in P.F. during DOL start

simulation to recreate measured wiggle in P.F. during DOL start

simulation to recreate measured wiggle in P.F. during DOL start

(OP)
I had previously posted a thread which showed an unusual wiggle in motor starting power factor: thread238-227811: motor starting power factor profile reasonable? starts at pf ~ 0.33

I have also posted a thread which included discussion of various strange behaviors predicted by the inducation motor trasnient model, including overshoot of sync speed: thread237-248895: quiz - can a DOL-start unloaded induction motor "overshoot" sync speed

I have done some analysis (attached powerpoint) using Krause's transient model to figure out whether the wiggle in power factor represents an overshoot of sync speed.  My conclusion is that it probably represents an overshoot of the final steady-state speed (rather than the sync speed).  But that is still something not predicted by typical quasi-static analysis representing motor and pump by their torque-speed characteristics (since there is no accelerating torque available when we reach the speed where these curves cross).

A summary of the slides as follows:
SLIDE 1 Measured data from motor start, including wiggle in power factor [SAME AS IN THE LINKED THREAD]
SLIDE 2 Motor Data Sheet
SLIDE 3 Motor Curves.
SLIDE 4 My Fitted Model Parameters. (used data sheet as target)
SLIDE 5 Performance of Model Parameters against target (S.I. units)
SLIDE 6 Model Output using steady state equivalent circuit calcs.
SLIDE 7 Simulation output when driving high inertia load (10 kg*m^2) to verify the transient simulation conforms to the equivalent circuit model.
SLIDE 8 Simulated start 100% Load.
SLIDE 9 Simulated start 75% Load.
SLIDE 10 Simulated start 50% Load.
SLIDE 11 Simulated start 25% Load.
SLIDE 12 Simulated start No-Load.
SLIDE 13 Miscellaneous notes (conclusions in red)

You can see comparing slide 1 to slides 9 and 10, they match fairly closely (certainly not exactly but the same general shape).

A few other miscellaneous comments and discussion on slide 13.

Just for info, but interested if any comments.  

=====================================
(2B)+(2B)'  ?

RE: simulation to recreate measured wiggle in P.F. during DOL start

(OP)
One thing I didn't do was adjust the torque-speed curve for voltage - I assumed nameplate voltage at motor terminals throughout.  In actuality I'm sure it was lower.  That affects how I adjusted the inertia (to match the starting time).  Oh well, not perfect.

=====================================
(2B)+(2B)'  ?

RE: simulation to recreate measured wiggle in P.F. during DOL start

(OP)
Also I forgot to say I assumed a torque~speed^2 load profile. "75% load" means it started at 0 torque at 0 speed and reaches 75% of FLT at full speed.

=====================================
(2B)+(2B)'  ?

RE: simulation to recreate measured wiggle in P.F. during DOL start

(OP)
If I reduce the total inertia to 0.4 kg*m^2 and keep the load torque at 75% (varying with speed squared), the power factor curve now looks almost identical to our measurement (attached slides 1 and 2).  Now the simulated motor accelerates faster than the measured motor, but it may be a result of the actual drooping voltage (there is 400 to 500' of cable between mcc and motor), which was not modeled (assumed nameplate voltage throughout).

By the way, I intended to post this as an information item (light-bulb item) rather than question (question mark icon).  I have red-flagged and asked the site admins to fix that if they can.

=====================================
(2B)+(2B)'  ?

RE: simulation to recreate measured wiggle in P.F. during DOL start

(OP)
Actually, I have been reading the time scale on the measured start wrong all along... it doesn't start at time zero... it starts at 0.4 seconds.  So the latest simulation ends up matching the whole waveform pretty closely.  I can't guarantee I have the right total inertia or right voltage, but at least with this combo it matches well.  

=====================================
(2B)+(2B)'  ?

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