×
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

Line to Line/earth fault evaluation

Line to Line/earth fault evaluation

Line to Line/earth fault evaluation

(OP)
What are the things or calculation you would consider to determine if your motor could operate under fault conditions (e.g line-to-line or earth fault)?

I am assuming that if a phase fault happen, you would get higher negative sequence current as a result of unbalance 3-phase motor. Therefore the motor would vibrate even more, and losses would be higher.

Where would the current go for each of the fault conditions?? It is correct to assume that the motor current will be flowing towards the fault area, and if the two phase lines are normal, current will flow towards the motor?

How would you know how long will your motor will be able to operate under such fault?

RE: Line to Line/earth fault evaluation

The motor will probably fail completely. It may fail faster than I can answer your question in detail.

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

RE: Line to Line/earth fault evaluation

(OP)
What is the mechanism that would make it fail?

RE: Line to Line/earth fault evaluation

Melted windings?

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

RE: Line to Line/earth fault evaluation

Are you talking about a fault inside the motor or an external fault?

RE: Line to Line/earth fault evaluation

(OP)
I am more interest in an external fault.

RE: Line to Line/earth fault evaluation

Normally an external fault is going to result in the the interruption of power to the motor, so motor damage is not an issue. For a sustained ground fault that is not cleared, the motor will fairly quickly overheat due to loss of phase voltage that results in high negative sequence currents. The bigger risk to the motor is loss of a phase due to a blown fuse, downed line, etc. This is not generally cleared quickly and can cause significant motor damage.

RE: Line to Line/earth fault evaluation

OK external fault. The motor acts as a generator due to the back EMF. The motor generates a back EMF with equal voltages, just a little below normal line voltage and at equal angles. It wants to see balanced voltages and equal phase angles. If, due to an external fault, the voltages and/or phase angles are not equal, there will be a difference between the line and the motor back EMF. This difference in voltages and/or phase angles will cause heavy currents to flow in the motor windings.

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

RE: Line to Line/earth fault evaluation

(OP)
Typically, how much current is expected to be drawn to or flow from the motor?

RE: Line to Line/earth fault evaluation

The current unbalance may be 10 times the voltage unbalance.

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