×
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

Capacitances of various coil sizes for AC hipoting

Capacitances of various coil sizes for AC hipoting

Capacitances of various coil sizes for AC hipoting

(OP)
I realize that with an infinite number of coil geometries, wire sizes, designs, voltages, etc that it is impossible to know the capacitance of a coil to estimate the AC voltage charging current necessary to hipot it, but, does anyone have any rough rules of thumb that might define even a dozen typical sizes of coils, probably stators mostly? Possibly someone has worked out a few examples of motor or generator coils based on voltage rating, MWs, HP, diameter, # of turns, etc for a few voltage sizes: 2400V, 4160V, 13.8 kV, etc. Also, do many motor shops perform power factor testing on rewinds? Thanks.

RE: Capacitances of various coil sizes for AC hipoting

"I realize that with an infinite number of coil geometries, wire sizes, designs, voltages, etc that it is impossible to know the capacitance of a coil to estimate the AC voltage charging current necessary to hipot it"
Energize the coil through a high value resistor with a fairly low DC voltage. Measure the time constant and from that calculate the capacitance. Don't forget the discharge diode.

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

RE: Capacitances of various coil sizes for AC hipoting

(OP)
Let me think about that and how it would correlate to the 50/60 Hz charging current. Thanks.

RE: Capacitances of various coil sizes for AC hipoting

For formwound stators, the insulation absorption current (vs simple capacitive current) is going to complicate things compared to an R-C circuit model. Of course we already knew the model isn't perfect, maybe good enough..I'm not sure.

Another thought would be to test with low voltage power frequency ac if that is readily available.

Rough estimate can be made using parallel plate capacitor model C = epsilon * A / d
Area is the total area of all core slots.
d is ground insulation thickness
epsilon between 2 and 4 times epsilon0. I think epoxy mica vpi insulation system would be towards 4.

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

RE: Capacitances of various coil sizes for AC hipoting

Doble have, or at least had, a fairly large database of machine data. You might be able to extract the data you want from there. They will almost certainly charge for access to it.

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