delta vs. star
delta vs. star
(OP)
this sort of question has appeared before on this site. if a delta/ parallel delta wound motor that has 12 leads and is wye start delta run was wired for low voltage wye or parallel star and ran on 240vac, what would the results be for hp output torque and so forth? the nameplate vac is 240/480vac at 60hz. parallel delta is 240vac and delta is 480vac. three phase of course. parallel star should be 415vac at flvac, but only 240vac is applied to this configuration which would 57.8% flvac. now the motor is 7.5hp when ran in delta at 480vac or parallel delta at 240 vac. so what if the motor were ran on 240 vac while in parallel wye, now what would be the expected horsepower output and current draw of that configuration please? any takers?





RE: delta vs. star
Bill
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"Why not the best?"
Jimmy Carter
RE: delta vs. star
Should that be it 230/460? (Just checking). I'll stick with 240/480 for now.
I think we can ignore the fact that it is a dual voltage motor, focus only on the parallel (low-voltage) winding configurations, and just compare the star vs delta connection (both parallel). We already know the nameplate current, horsepower and torque capability in delta/parallel with 240vac applied. Let's say for argument sake those ratings are 18A, 7.5hp, 250% of rated torque. When we reconnect that motor for star/parallel at that same terminal voltage, the voltage seen by the winding goes down by a factor of sqrt(3), so the peak torque capability goes down by 3 to approx 80% of rated torque. Likewise starting torque decrease by approx factor of 3.
Consider the steady state current limit (thermal). In delta the phase current was limited to 18A, which corresponded to 18/sqrt(3) ~ 10A in the winding. When we reconnect for wye, we should probably limit phase current to that same 10A (not taking any credit for reduced core loss).
What is the associated steady-state horsepower limit: we kept the phase voltage the same (240vac 3-phase) and reduced the current by a factor of sqrt(3), so I think the steady state horsepower limit associated with our current limit would be in the neighborhood 7.5 / sqrt(3) = 4.3hp = 57% of original nameplate. It may not be wise to load the motor that heavily since your peak torque would be only 80/57 = 140% of your load torque.
At least that's my first cut. Hopefully others will chime in if I have over looked something.
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(2B)+(2B)' ?
RE: delta vs. star
Along the lines of Bill's question: why would you want to do this?
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(2B)+(2B)' ?
RE: delta vs. star
RE: delta vs. star
RE: delta vs. star
Bill
--------------------
"Why not the best?"
Jimmy Carter