Amp draw from clamp on meter versus Power Logic meter

[Trublmkr]

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

 

[waross]

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

 

[Trublmkr]

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.

 

[RRaghunath]

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.

 

[Skogsgurra]

Can't be. They are different.

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

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Trublmkr]

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

 

[Skogsgurra]

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

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[Trublmkr]

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.

 

[mastergate]

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