×
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

Amp draw from clamp on meter versus Power Logic meter

Amp draw from clamp on meter versus Power Logic meter

Amp draw from clamp on meter versus Power Logic meter

(OP)
While performing maintenance on a UPS we run our gens and do a wrap around feed to a distribution board. The power going through the bypass breaker and the power for the wrap around is coming from the same Emergency buss. When 1 of the 2 paralleled feeds is energized, current readings are approximately 40 amps per phase measured with a clamp on meter and by  the Power logic system. When both feeds are energized; because they are paralleled we would expect the load to be approximately 20 amps per phase, per feeder. What we see with a clamp on meter is 50 to 70 amps per phase on 1 feeder and 60 to 90 amps per phase on the other feeder; but Power Logic still reports 40 amps per phase. This is not a problem I am just trying to figure out what is happening to better understand this anomaly. Thanks  

RE: Amp draw from clamp on meter versus Power Logic meter

If your voltages don't match, you will have a lot of reactive current circulating between the systems.
Can you post a diagram?

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

RE: Amp draw from clamp on meter versus Power Logic meter

(OP)
The voltages are identical......they are both coming from the same emergency buss. I do not have any way to get a diagram uploaded. Secure facility doesn't allow uploads.

RE: Amp draw from clamp on meter versus Power Logic meter

Trublmkr,
The two supplies are coming from the same source but are the cables same size and cable lengths identical!!
As waross said the current you see in individual incoming circuits cannot be any thing but the circulating current. There needs to be some source to drive these currents.

RE: Amp draw from clamp on meter versus Power Logic meter

Can't be. They are different.

If they were bolted (identical), you wouldn't need the wrap.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Amp draw from clamp on meter versus Power Logic meter

(OP)
The cables are the same diameter but they are different lengths. The wrap around feeder is substantially longer than the primary feed.

RE: Amp draw from clamp on meter versus Power Logic meter

That would explain an unbalance. But not an increase in total current.

For that, you need a voltage difference that drives the circulating current.

 

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

RE: Amp draw from clamp on meter versus Power Logic meter

(OP)
Thanks to everyone that replied....I appreciate it. I will try to put together a diagram and get exact wire dimensions and voltage and amperage readings, when I come back to work Sunday night. Hopefully we can figure this out at that time. Thanks again.

RE: Amp draw from clamp on meter versus Power Logic meter

I think the difference is due to harmonics (generated by UPS).

 

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