I was wondering if anyone could help on a problem we have on our site regarding earth leakage current.

On all our HV transformers on site we have earth leakage meters, which measure current feed back on the earth path from all equipment coming off the LV side of the transformers.

We have found that the production equipment is giving us high leakage currents which measure between 30A-65A, I require your assistance on a method of attempting to reduce this current.

Using ammeters we can see which earth wire from the various busducts are feeding back a particular value of current back to the transformer earth,

Would the situation where the buildings material which is steel have an impact on the high currents we are measuring?

many thanks

Please indicate LV voltage and configuration of neutral earthing.

You can trace the earthing current if you know how the cables are laid out and the earthing arrangement.

Regards
Chris Chew

11000V/433V

DO you mean the earthing arrangements on the LV side at production level?

For example 2 out of the 3 phases are connected to LV transformers...usually 415V/230V or 415V/110V

those transformers have an earth wire on the primary side

collectively all those earths feed back to the HV transformers to then they go to a main earth

Is the neutral solidly earthed? Is the neutral earthing connected to main earthing arrangement?

Are you using only 2 phases to supply 415/230V and 415/110V transformers? If so what is the arrangement on the 230V and 110V side? Is any of the 230V and 110V terminal earthed? What kind of equipment is used on the 230V and 110V side?

Regards
Chris Chew

A few answers to your questions more to follow:

LV Tx's are supplied by only 2 phases...mainly Red and Blue

most of the equipment is control units for production equipment, inverter type equipment

It will be useful if you can measure or read the current values on the 433V LV side. Currents consumed on the equipment to be measured as well. Hopefully we will be able to see a clearer picture on the high earth leakage currents.

Regards
Chris Chew

Do some research on your inverter drives, many leak current to Earth.

Regards.

Our site has an earth nest underneath the ground and all neutral points of the HV tx's are connected to this earth nest

It appears that the earth leakage currents are inherent characteristics of the production equipment. One of the possible reasons the equipment need to pass so many amperes to earth is it can comply with the EMC directives. If this is the case, it is not advisable to try to eliminate or reduce the earth leakage (but healthy) current at source (the production equipment). In order to function properly, it needs to pass this current through the cpc to return to the source of energy.

One possible way to prevent a cumulation of these earth leakage current at the HV/LV Tx is to provide an isolation Tx (with an earthed secondary) for each of the leakage equipment. This way the leakage current circuit will be confined to the output side per isolation Tx / equipment. The advantage of this arrangement is you can use Section 543.7 to ensure the safety of operators and maintenance staff. The neutral earth connection of your HV/LV Tx should have a reduced leakage earth current then.

The other way is pretty obvious that if the equipment is replaced with new ones with lower or nil earth leakage characteristics you will have a lower overall leakage current. Clearly you must have considered this and it was a 'no go'.

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Tony Sung