Current balance percentages.
Current balance percentages.
(OP)
Hi, when placing a clamp meter across each phase and measuring the current, what is the permissible difference expected between the phases, 2%, 5%, 10%?
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Current balance percentages.
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RE: Current balance percentages.
Two percent is probably not to worry about. Especially if your grid shows a simmilarly bad symmetry.
If your grid is perfectly symmetrical, a two percent difference between line currents can be an indication that something is wrong. Especially in larger machines. But probably OK.
Usually two percent is within normal tolerances. Make sure that you keep the clamp centered around the conductor or you may get an additional reading error of one or two percents.
RE: Current balance percentages.
jeff
www.motors-direct.co.uk
RE: Current balance percentages.
RE: Current balance percentages.
There has been much discussion in electrical topics at this site. Search on “current imbalance” and “current unbalance.”
RE: Current balance percentages.
Thank you all. I just needed a refresher for this and other things that I haven't done in quite a while.
RE: Current balance percentages.
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RE: Current balance percentages.
max deviation from average/average * 100% = unbalance (uses three numbers).
Percent difference (used on only two numbers) is (#1-#2)/#2.
Maybe this is already understood and the terminology was just used wrong.
RE: Current balance percentages.
I have seen higher unbalances at low load than at high load.
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RE: Current balance percentages.
But for current 9-10 % is the limit. For motors 1 % voltage unbalance will normally result in 9-10 % current unbalance.
System voltage and winding resistances of motor should be further checked to see the root cause. System voltage can be brought within limits by readjusting / balancing single phase loads in the system.
RE: Current balance percentages.
Good point sahab to clarify those numbers are voltage unbalances.
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RE: Current balance percentages.
ANSI Standard C84.1-1995 Annex D — Field surveys and statistics indicate that:
(1) Each motor rating is associated with a unique optimal range of voltage unbalance
(2) These ranges vary from 0–2.5 percent to 0–4.0 percent voltage unbalance with the average at approximately 0–3.0 percent
(3) Approximately 98 percent of the electric supply systems surveyed are within the 0–3.0 percent voltage-unbalance range, with 66 percent at 0–1.0 percent or less
Electric supply systems should be designed and operated to limit the maximum voltage unbalance to 3 percent when measured at the electric-utility revenue meter under no-load conditions.
For 3ø induction motors, current imbalance with respect to voltage imbalance is proportional to:
Motor Locked-Rotor Current / Motor Full-Load Current [a factor of roughly 4-7]