×
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

Unbalance currents

Unbalance currents

Unbalance currents

(OP)
Can I consider Pt100 sensors at induction motor stator windings a good protection against overheating caused by unbalance currents (max unbalance voltage=5%).RTD has a relatively slow reaction time. Can it respond adequately to the heating process? Thanks

RE: Unbalance currents

In my opinion, yes, but the control equipment is more expensive. If you want to monitor all three phases you will require 3 x PT 100 controllers on a more expensive PT 300 controller. The latter will not allow you to discern which phase is over heating so it will be the same result from thermistors. Modern soft starters and VSDs have inputs for both.

What size is the motor and how many poles?

Watch for retro fitting them and running the probe conductors parallel the motor windings as mutual induction may blow the controllers.

RE: Unbalance currents

(OP)
Thanks Squeeky
The replaced (4P) motor is new, the Pt100 available. The problem is the voltage, 13,8kV, the low nominal current 45 Amps and the existing CTs ratio (too high to perform a good ANSI 46 protection.

RE: Unbalance currents

I would think the RTDs should provide adequate response for low magnitude negative sequence current heating. For gross problems (loss of phase), a negative sequence overcurrent function will improve your odds. This is generally going to be available in any microprocessor-based motor protection relay. You say the CT ratio is too high, but the newer relays are very sensitive.

RE: Unbalance currents

OK so it'its a large motor. At that size you should have a decent motor protection relay. These should have PT100 inputs. Which one do you have?

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