×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

delta vs. star

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

Is this a theoretical study question? Do you actually have a twelve lead motor? Do you at least have a spec sheet for a twelve lead motor?
 

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: delta vs. star

Attached is an example connection drawing for 12-lead motor at our plant.  I assume most 12-lead single-speed motors are similar.

Quote:

the nameplate vac is 240/480vac at 60hz.
Should that be it 230/460? (Just checking).  I'll stick with 240/480 for now.

Quote:

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?
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.
 

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

RE: delta vs. star

Needless to say, asking the OEM is your best bet if you actually intend to do this.

Along the lines of Bill's question: why would you want to do this?

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

RE: delta vs. star

(OP)
okay thanks for the replies. the motor is a teco westinghouse motor and is 2 pole ac induction 3450 rpm 230/460 vac 60 hz 3 phase. it is delta wound i think and wye start delta run with 12 leads. i was going to test it with a vfd in the parallel wye connection and adjust the vfd for slip. and run it on 230vac. my thoughts were that it would only safely produce 2.5hp and the input kw would 4330 watts of single phase to the vfd or the sqrt3 more than what is required for 2.5hp or it would produce 4.33hp at 4330 watts of single phase or it would produce 4.33hp at 2500w of single phase or it would produce 2.5hp at 1443watts of single phase input or even 4.33hp at 7500 watts single phase input. in other words some strange unexpected result but totally explainable and leads to more clearer undersatnding of how all this stuff really works anyway. this kind of question is only for those who want to become thorough technicians rather just average electrician. i do appreciate your feedback i take it as a sign that you care.

RE: delta vs. star

With that smashed together blurb I have a very hard time knowing what are you asking. However, as an engineer or technician, you should know that for a system the input power = the output power + the losses. Having a 1-phase or 3-phase system doesn't change the basic rules.
 

RE: delta vs. star

4.33 HP @ 746 Watts/HP = 3230 Watts. Add some Watts to cover losses and expect 3500 Watts to 4000 Watts input power.  

Bill
--------------------
"Why not the best?"
Jimmy Carter

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources