Neutral to ground voltage high? 1

[mannumss]

we have 600 KVA tr 3.3KV/440 V, its 400 V secondary using for various loads like lightings, LT motors ETC. One of recently load connected to Iron XRF ( X-RAY ) machine. which is very sensitive machine to analize Iron properties.this machine supply coming through UPS. as per Service engineer of this machine Neutral to earth voltage should be < 1 volt. but checking time found that voltage is more 2,2.5,4 volt in different places of tr. secondary load side and incoming of UPS side.. how to solve this problem? is there any earthing problem? one thing that this transformer having more lightings load already before and its starpoint neutral is grounded via resistance.
thanks in advance .
can any device to be use to reduce the earth to neutral voltage?

 

[Kiribanda]

mannumss,
If the N conductor is grounded more than at the star point, then unusual N-E voltages are possible.
Check your N conductor for any possible multiple grounding.
Also uploading a SLD of your distribution is helpful for the forum to contribute more thoughts.

 

[waross]

"one thing that this transformer having more lightings load already before and its starpoint neutral is grounded via resistance."
The codes that many of us are familiar with prohibit resistance grounding when there are line to neutral loads or any devices (except monitoring devices) are connected that require a neutral connection.
Option #1: Do an engineering study of any possible implications of using a solidly grounded system, and if feasible, change to a solidly grounded system.
Option #2: Use a delta wye isolating transformer to feed the X-ray machine and solidly ground the secondary wye point.
If you have any loads connected from line to neutral, option #1 is mandatory in North America.

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

 

[rbulsara]

This is another confusion propagated by 'electronics' engineers with little knowledge about codes and system grounding.

Where and when is the measurement made? How far is the measuring point from the point of source N grounding?
Is there a dedicated neutral for this machine circuit?

For a properly grounded systems (N grounding at source or service equipment only), at no-load, there would not be a voltage measured between N and G. A dedicated neutral for this circuit would help in this regard.

If there is a return load current through the neutral you will obviously measure the voltage drop=IR, where I is the current in neutral and R is resistance of the neutral conductor from point of measurement to the grounded point. And this would be normal.

Also as Kiribanda indicated verify that there is no current flowing in ground conductor in normal conditions.

Also check the meter on a dead open circuit conductors, to verify it does not read false non-zero volts anyway. (Check for calibration)



Rafiq Bulsara

http://www.srengineersct.com

 

[davidbeach]

On the other hand, no properly constructed equipment would know or care what the neutral-ground voltage might be.