×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Contact US

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!

*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

Thermal protection devices fror stator windings
6

Thermal protection devices fror stator windings

Thermal protection devices fror stator windings

(OP)
Dear All,

I would like to receive your inputs about how calculate/select this types of devices (thermistors, RTDs,thermocouples, etc.) based on insulation class of the stator windings.

Thanks and Regards

Petronila

RE: Thermal protection devices fror stator windings

4
Thermistors - Used exclusively in mush windings (LV motors) since they are small and cheap. They only act as on/off switch for the particular temperature they are designed for (usually from 100 to 150 deg C). Can't be used to track winding temperatures and they fail often.

RTD's - Used exclusively in form wound windings. They are flat and rectangular fitted in between top and bottom layers of coils/bars. Can measure temperatures from 0 to 200 deg C and are normally connected to a temperature scanner+controller which can track the winding temperatures 24x7 with individual alarm and trip points. Failure rate is minimal and last the life of the windings. A minimum of 3 (one per phase) and up to 12 nos. are used based on the machine diameter. I have seen water cooled generator stator windings having RTD's for all slots to detect loss of water through the bars.

Thermocouples - Rarely used in electric machines since their normal range is over 200 Deg C.

RTD's are more accurate than thermocouple at temperatures less than 200 deg C, are more sensitive and react faster to any temperature change than thermocouples and have a smaller drift when compared to thermocouples. Hence, their wide spread use in electrical machines.


Muthu
www.edison.co.in

RE: Thermal protection devices fror stator windings

petronila: Your device has to satisfy two criteria - be able to protect the machine component (in this case, winding) based on its insulation rating AND be able to reliably differentiate temperature based on the application (note that some applications restrict allowable temperatures to well below the actual insulation class limit).

edison123 has listed the available devices, with their respective pros and cons quite clearly. I would add that there are a few basic resistance temperature detectors (RTDs) which have varying ranges and capabilities based on the base metal used. They are:
1) copper element which reads 10.0 ohms at 20 C. Works great for temperatures in the -10 C to + 50 C range.
2) platinum element which reads 100 ohm at 0 C. Works great for temperatures in the -50 C to +250 C range.
3) nickel element which reads 120 ohm at 0 C. Works great for temperatures in the -50 C to + 180 C range.

Thermistors and RTDs are not intended to be in direct contact with live conductors. Thermocouples can - and often are (provided the data acquisition is done with that in mind).

Converting energy to motion for more than half a century

RE: Thermal protection devices fror stator windings

Gr8blu,
Now I can see why Platinum RTDs are so popular. Thanks for sharing the info.

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! Already a Member? Login



News


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close