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Unread November 11th, 2019, 11:40 PM   #1
rejoe.koshy
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Issue with clamp meters

Hey guys,
I am facing an issue with clamp meters, to resolve which I need a little bit of assistance.
I had installed a 30 KW motor which belongs to air compressor and post its installation when I checked its current on all three phases (on load) I was surprised since it showed huge imbalance (72, 84, 75) and was seen to be on the higher side.I checked mechanical side but everything seemed to be fine.

Moreover , the motor wasnt getting hot and nor was the overload relay getting actuated. This got me thinking as to whether the motor is actually drawing such high imbalance currents.

I replaced my meter with another one but showed the same results...Now I am confused as to what to conclude.

Could this be a meter issue or a wrong measurement technique?

Pls help

Last edited by rejoe.koshy; November 11th, 2019 at 11:45 PM.
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Unread November 12th, 2019, 12:59 AM   #2
SwedeFill
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Motor voltage & connection

Check the motor connection maybe its in delta connection and it should be in star
read the motor name plate and make sure the right voltage and frequency is connected
Good luck
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Unread November 12th, 2019, 01:25 AM   #3
rejoe.koshy
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The motor is run via star-delta starter. The frequency and voltage is as per its rated value and the current is measured post its switch over to delta connection.
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Unread November 12th, 2019, 01:42 AM   #4
SwedeFill
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Low power factor like 0.6
And low motor efficiency
Could have such values
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Unread November 12th, 2019, 02:10 AM   #5
lfe
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Clamp meters are basically inaccurate and the measurement can be altered by other inductive fields apart from the cable you measure.
Measure de current in another cable passage, maybe you will read different values.
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Unread November 12th, 2019, 02:28 AM   #6
rejoe.koshy
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Can the current measurement on one phase be affected by the magnetic field of the current on the other phase?

If so, what are the chances...because since the motor does not get too hot and nor does its overload relay trip I am not really convinced that the motor is actually drawing such high currents.
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Unread November 12th, 2019, 09:44 AM   #7
OkiePC
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How does the current imbalance compare with the voltage imbalance? If you find the voltage to be more consistent, then the current imbalance is probably due to physical differences in the motor. You are showing a current imbalance of over 10%. I generally worry about anything greater than 5%.
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Unread November 12th, 2019, 01:15 PM   #8
cookie_cookie
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Hi

Check the incoming/outgoing voltage, motor winding resistance also star/delta/main contractor pole resistances. One of these may point to the issue.
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Unread November 13th, 2019, 09:55 AM   #9
rejoe.koshy
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Quote:
Originally Posted by OkiePC View Post
How does the current imbalance compare with the voltage imbalance? If you find the voltage to be more consistent, then the current imbalance is probably due to physical differences in the motor. You are showing a current imbalance of over 10%. I generally worry about anything greater than 5%.
The voltage was observed to be consistent(1 % variation).In any case should nt the overload relay trip , which is set at 34 A (installed on the phases)?
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Unread November 19th, 2019, 04:38 PM   #10
mass89
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I wouldn't concern over 1% voltage variance (that's good) and definitely wouldn't cause current imbalance of 10%.
Easiest thing to try is winding resistance test when motor is at a stand still, if they're not balanced then thats your problem.

Regarding meter not reading right or being influenced, I've never seen a reading vary (notably anyway) when in a noisy environment or even with the outside of the clamp resting against another phase, even if this does happen it wouldn't cause a 12A/10% difference IMO. If it was your meter then it would consistently read the same amount out roughly on all phases or repeating the test would give different results.
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Unread November 20th, 2019, 06:18 PM   #11
alive15
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Are you using any kind of filter ?
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