Weird Voltage to Earth Readings

[Minetsky]

I will refer a weird voltage readings on my mate's workplace.. A newly installed transformer delta-wye, 440/380V will supply a TT power system. He measured 380V per phase on the secondary and 220V L-N.. But when he measured L3 to earth he measured 0V. L1 and L2 to earth is 380V and Neutral to earth is 220V.. I said that cant be and obviously L3 was mistakenly wired as neutral and earthed and the real neutral was put to L3. But he was sure that it is 380V per phase and the korean who installed the tx dont know whats causing the phenomenon hehe.. Is there anyone who have experienced this? I never really saw the installation but its really confusing if its really true.. Thanks in advance.

 

[Clive P]

Hi,

Quite common to use Delta/Wye for a Three Phase TT System. First thing I would do is switch it off and make some checks. L1/L2/L3 to the three primary windings. On the Secondary side L1/L2/L3 to the three Secondary windings and the Neutral bonded to Earth for your starpoint and connection to your Earth Bed. If this looks to be good, then do your continuity tests and IR tests on the windings. Anyhow you will need to check your Primary and Secondary voltage readings. Some of these Transformers will have tappings for the Secondary voltage, usually+/_ 5%.

Regards.

 

[Minetsky]

 

[Minetsky]

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As per him, white cable is the neutral..and solidly earthed.. L-L voltage is 380V,but L and N to earth are the only evidence he has.. How come that voltage to earth is 380V? and L3 to earth is zero? when he said that neutral is solidly earthed and measured L-L voltage is 380V...
Confusing!
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[Clive P]

Hi,

First,
If that switch is live I would be using GS38 leads and a good calibrated Instrument.
Secondly, I would be testing the input with the switch off, difficult to see what is connected to the output.

Regards.

 

[Clive P]

Hi,

When you carry out the continuity tests on the windings, one thing to check is the configuration. On one I checked some time ago which was faulty the windings had been mixed up by the installer. Each *Phase* winding consisted of two internal windings and the ends had been disconnected, then re-connected in the wrong sequence. In other words, part of one winding was mixed with a part of another winding. You will need to carry out continuity checks to ensure all of your windings are correctly identified and terminated.

Regards.

 

[Minetsky]

Is it possible that the blue wire will induce current to earth cable..And explains the voltage measurements?

 

[Engineer54]

I wonder how long it's going to be, before those cable ties stretch and those cables are going to embed themselves on those ultra long connection bolts?? Expect a big bang in the not too distant future!! Something doesn't look quite right with the cable connections to these bushing studs either, the directions just don't tally up. Are their loops in some of these parallel cables that we can't see??

Anyway, this isn't an installation that i would accept!!

 

[gnuuser]

clive may be right
a mis wired and mis labeled terminals can throw a wrench in the works so to speak.
first thing i would do is disconnect everything from it and do a continuity test on all terminals both primary and secondary, as well as continuity test between terminals to ground
if you have the specifications and other documentation on the xformer this can be of great help