×
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

6600V Wye Synchronous Motor 4160V delta connected?

6600V Wye Synchronous Motor 4160V delta connected?

6600V Wye Synchronous Motor 4160V delta connected?

(OP)
Gentlemen,

I have GE 1070 HP synchronous motor that is wye wound for 6600V and FLA of 98A and PF of 0.8.  It has six leads to the stator and will turn at 257 rpm when synchronized driving a high inertial load.  This motor does not have part-windings.
It has been proposed to connect the motor in delta using 4160V from a generator set.  Can anyone answer the following:
1) Will the motor run properly at 4160V delta connected even though the data sheet says it is wye wound?
2) If the motor will run at 4160V delta connected, will there be a reduction in torque or horsepower resulting from this configuration?
 

RE: 6600V Wye Synchronous Motor 4160V delta connected?

I've never heard of it done, but my two uninformed cents are as follows: I don't see any showstoppers which require major derating.  There is possible increased 3rd time harmonic (zero sequence) exciting current circulating in the delta configuration which is suppressed in wye which might require minor derating.   Exactly why it is that wye winding is so universal among large motors, I'm not sure.

Best bet is to check with manufacturer.
 

=====================================
Eng-tips forums: The best place on the web for engineering discussions.

RE: 6600V Wye Synchronous Motor 4160V delta connected?

For this size motor, I would check with the mfr. (GE) first. Having said that:

1) 4160 is about 9% higher than the winding's rated voltage of 6600/1.732 or 3180V. For this alone you may want to check with GE if this would be acceptable. It is possible that the motor is rated to work on up to 7.2kV.

2)In this particular case, since the voltage is 9% higher, the torque will  in fact be 19% higher. This may or may not be acceptable mechanically. So again check with the mfr.
Horsepower would also be slightly more, HP=T*rpm, but you should not exceed the rated current or rated HP by controlling the load.


Its late in the day so, I may have overlooked something. Hope the motor experts in this forum will chime in.
 

Rafiq Bulsara
http://www.srengineersct.com

RE: 6600V Wye Synchronous Motor 4160V delta connected?

What is the 6.6 KV frequency ? 6.6 KV is normally 50 Hz zone but a synch speed of 257 RPM indicates 60 Hz (28 pole) machine.

Just because the winding has six leads coming out does not automatically mean that three leads are phase and other three leads are neutral. It could be an internally connected wye with six leads coming out for handling the current. One way to check this is to test for continuity between the six leads. If the winding is internally connected wye, you'll have continuity between all the six leads and you cannot reconect the motor in delta externally. If it is an external wye, then only pairs of leads will have continuity and then you can reconnect for delat externally.

Assuming it is an externally connected wye, then you have to identify the starts and ends of individual phases (like U1, U2, V1, V2, W1, W2), if they are not already tagged.

After all the above checks, you can run the motor at 4160 V, delta but the starting current (what is the starting method for this synch motor ?), the no-load current and the core losses will be higher due to the over-voltage as Rafiq says. This would mean a derating but by how much depends on the original design data.
 

Muthu
www.edison.co.in

RE: 6600V Wye Synchronous Motor 4160V delta connected?

I would connect in delta and drop the generator voltage to 3810V.
If this causes issues with other equipment, consider splitting the difference and dropping the voltage 5%, (to 3950V).
The nominal torque will be higher if the motor is started on a higher voltage. At 9% over voltage there may be mechanical issues with the greater starting torque and faster acceleration if started on the utility. However, you will be starting on a generator and unless the generator is more than an order of magnitude larger in capacity than the motor, I expect that the block loading caused by the starting current will drop the voltage enough so that in the real world the actual starting voltage and torque may even be lower than during a utility start.
In the IEC world motors are commonly built with six leads and connected in either star or delta to match the available supply voltage.

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