Problem In 11k/440v Transformer

Looks like the load Vy is shorted to ground to me. A measurement of the currents will tell a qualified electrician what is your problem. Hire a qualified electrician.

I agree with Redfred. What concerns me more is... based on the reading of the phase to the netural and to ground on the un-loaded secondary, the secondary star point (the neutral) is tied to ground (as it should be), so... why does your protection system (the fuses and the other overcurrent devices) not trip? You should never be able to see a load phase conductor shorted to ground as you do now.

Get someone in there fast.

Actually it's possible if we remove the assumption that the secondary neutral is grounded. The data as presented indicates it's a wye-delta transformer, not uncommon when continuity of service under first-fault conditions is the goal.

As we know in a delta connection there is no neutral, so the first solid ground fault pulls that phase to system ground and reads zero volts. The other two phases rise approximately to √3 times the prefault voltage with respect to ground, in this case it should be 1.73x230≈400 Volts. the readings were probably made with a DVM (Digital Volt Meter) which often gives erroneous readings on anything other than a balanced system due to things like stray capacitive pickup, induced voltages, and harmonics that an analog meter is insensitive to.

Most modern ungrounded systems have some form of unbalanced voltage monitoring to alarm on first fault conditions. Otherwise a much bigger problem arises when the second fault occurs, that's when PPE (Personnel Protective Equipment) and arc-flash calculations take over.

Message to OP, heed everyone's advice and get out of there now and let qualified personnel take over.

Agreed... if one of the phase conductors read a low voltage to ground at the load end, why does it not read the same low value at the supply end?

Can I ask you whether a SAT (site acceptance test) has been performed before on your Tx/Tr? For e.g one Vector-Group check/test...

In no load conditions, you are measuring a "ghost voltage" from Vy to grnd, most likely thru carbon deposits in a damaged connection, thats why it drops to 3V under loaded conditions without tripping the protections.

Warning: Stop trying now and get the transformer serviced, or a nasty arcflash will ruin the whole unit and cause a potentially deadly situation.

Regards

The problem seems to be a failure to de-energise the equipment and call in a qualified Electrician, Boss.

My guess, site unseen......

• The neutral is not grounded.
• The ground is connected to the Y phase.
• Until the neutral is grounded there will not be a short cct on Y phase, hence no protection is popping or unprotected conductors glowing.

Disconnect the ground wire from the Y phase, measure again (phase to earth will be wandering a lot as you now have an isolated trafo) and then deck the neutral and measure again.

I had to check this with a pencil and a bit of paper. Once you see it drawn the voltage readings listed are in accord with my guess.

Taking a stab in the dark here....your electrician was just a mechanical assembler with no real electrical knowledge and G/Y(ground) was connected to Y as it was the nearest colour match..... or yellow sheathed conductors are used for ground as well....

You get that.

Vy seems to be shorted to ground on load. need to check the same. Eliminate one by one load on Vy and check if the voltage is improved above 3 V. You neeed to see if the problem is on load side as well. Check one by one breakers by switching off and checking the voiltage.

Also check if some lighting load and other single phase load is taken in this Vy and some short circuit some where to the ground. This could be serious as the system is not tripping even when grounded some where. Looks like there is no protection circuit on this phase load side. Also seems mostly the load is on Vy only as there is no data as how much load is given and what is the distribution across pahses. dont see iny dip in voltage, seems there is no substantial laod or loading factor is very low. If the total load is on single/ two phase only. Thoroughly check the load pattern on Vy.

What is system earthing for Transformer. I guess IT (Insulated Earth)

In that case Your transformer is healthy. (Equal voltages on phases)

When load is connected one of the phase, which got earthed in load, pulls that phase voltage near to zero and other phase reads heigher.

Check Load....

when transformer is at load condition...according to your measurement..it shows y phase to ground voltage drops 3 volts and remaining phases are showing more voltages..it means you have a problem of y phase body leakage when it comes on load ...if the load has such problem... check that load's insulation phase to ground ...then transformer..then supply LT line's insulation..then you can find the problems.

1.I would confirm my readings first, if they are taken from a reliable spot.

2. Is the Y neutral point grounded well.

3.Is the frame grounded well.

4. Is the cable connections correctly done especially the neutrals and earths.

Everyone is saying Y-phase is grounded how it's possible

Can you ground a live phase to ground

Go and try it you might very severe fault even at the cost of life.

If live phase get grounded it leads to very high current and transformer protections will get tripped.

I guess they said Y neutral point is grounded. It means the star point of winding.