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Voltage

Voltage

(OP)
Hi,

I'm actually on a site which is driving me nut.The site is powered from a nearby power station which provides 3 Phase 400V 50 Hz supply.This supply comes from a high impedance grounding source.The measurements taken on site are L1L2 350 V, L1L3 363 V, L2L3 356 V, L1E 306 V, L2E 433 V, L3E 136V.The earthing E is the earthing on site.I'm suspecting a ground fault from the source but the 433 V is really suspecting.I have verified the measurements using many diffrent measuring devices and they are correct.

Guardiano

RE: Voltage

Yes, this would drive me crazy, too.

Your line-line voltages compute. They form a nice triangle with close to 60 degrees in the corners. But your earth potential seems to be outside the triangle. That is why you have a higher voltage (433 V) L2-E.

I could expect that if you have lots of capacitance in the grid.

The voltages are very low. Regardless of grid configuration, you should have more than 350 - 360 V. Where is this? a 400 V IT grid is not very common. Are you sure it shouldn't be a TN grid?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Voltage

(OP)
Thanks Skogsgurra for your comments.The line voltages are very low as they are struggled to provide power to the site.Yes, the supply is a high impedance neutral grounding one.

Guardiano.

RE: Voltage

Is this in Africa?

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Voltage

(OP)
Yes, you're right.Nigeria.

Guardiano

RE: Voltage

Not the nicest place. Sorry, can't help you. Do they expect you to do something about it without actually doing anything?

Or is there a specific problem that needs to be solved? Magnetic stabilizers can do wonders in some cases.  

Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

RE: Voltage

Guardino,

As you suspected, yes there is a high impedance earth fault.Since the source is weak,there is no much earth fault current to trip the overcurrent device.If there was a residual current operated circuit breaker (RCCB or ELCB with 30/300 mA)then definitely it would have been tripped.Isolate the line and check every thing to locate and clear the high impedance earth fault.   

RE: Voltage

Is it possible to take similar readings at the power plant?
Look at your voltages with a 'scope. You may have a discontinuous or arcing ground fault which is interacting with the system capacity to developing high frequencies.  
If so, that will direct our efforts at a solution.

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

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