suspected faulty 6.6kva transformer

[Knobhead]

If it was anything to do with me it wouldn’t be made live until it was sorted out.

I’ve lost the N→E link on a 500KVA transformer before. It caused total mayhem.

 

[Lucien Nunes]

Agreed. Your entire system is floating free, get two faults at the same time and two people get fried. Even the normal leakage current returning via a single fault could be enough to do harm. Pull the power and look for that missing link.

 

[Besoeker]

Agreed. Your entire system is floating free, get two faults at the same time and two people get fried.

And it could be floating at any voltage WRT earth.
Not good.

 

[Clive P]

Hi,

I may be totally off track here, but scanning through the posts I was just wondering; is the Transformer an Isolation transformer using the rods for a TT system. The reason I am saying this is at the moment the N/E connection has not yet been verified as to its existence, only earthing from the TX casing to the MET and other extraneous pipework. Like I say , I may be totally off course with this, but the rods got me thinking.

Regards.

 

[Knobhead]

For a private network TT is highly unlikely. TN-S is usual for a ∆Y transformer.

Until we hear from the OP we may as well give up on this.

 

[Lucien Nunes]

TT uses the mass of earth to connect the consumer's installation MET to the earthed neutral at the transformer, so it requires the same N-E connection at the transformer end. In any case unless I've misread it the TX is in the same location as the installation, so TT would not be a useful configuration. ??Oops post crossed with Tony's... strange, it wasn't there a minute ago and I only just opened the page??

 

[Clive P]

Hi,

Yes, with a delta/star configuration you are probably right. I have read the post again.

Regards.

 

[Danspark]

For a private network TT is highly unlikely. TN-S is usual for a ∆Y transformer.

Until we hear from the OP we may as well give up on this.

Please excuse me, i attempted a reply and lost it some where after hitting the post button... hey-ho...

Whilst the premises were empty and the industrial unit non operational the fault was not present. During my half hour window I investigated connections and setup at the isolator and busbar arrangement immediately after the transformer. Although I felt it unlikely that it would be a TT system I remain puzzled. The 2 earth rods and what I believe to be an earth plate are connected to the casing of my isolation switch and subsequently the busbar For now i will assume this is my main earth terminal. From here there is a connection to the multiple earthing point adjacent, from here this is connected to the usual extraneous conductive parts including the casing of the transformer. There are a couple of earth cables that come out the ground that i am unsure of where they come from, perhaps they come from the utility companies transformer outside providing a TN-S system... or may be they don't and i have a TT system. I can tell you that with the power off I took a Zs reading (Zs because I left all the earths in situ) The reading was higher than I would have expected; of the three phases the highest was 0.21 ohms.

I'm not convinced any more that i have a faulty transformer but something within the industrial unit. I have left an energy logger recording data and will go back to investigate tomorrow.

Thanks for your thoughts chaps; keep them coming

Dan

 

[Knobhead]

So have you tracked down the N→E link?

From your description that’s where I think the problem lies.

Out of interest who’s doing the switching operations?

 

[Besoeker]

So have you tracked down the N→E link?

Or the absence of it.
You'd think it couldn't be that complicated.

 

[Bobster]

I think from the sounds of it your slightly out of your depth and confusing things.

Who's the site SAP?

 

[Danspark]

So have you tracked down the N→E link?

can confirm there is no link. it is believed to have been removed past.

 

[Clive P]

Hi,

The plot thickens, I am awaiting further updates.

Regards.

 

[Bobster]

can confirm there is no link. it is believed to have been removed past.

Are you being serious?

Is this a wind up?

 

[Lucien Nunes]

Well unless there's some extreme subtlety here that I'm missing, whoever did that has some odd ideas about electrical safety! I'd turn the whole thing off now before somebody gets hurt, do the obvious tests to make sure the breaker isn't going to come flying out, and restore the link to its proper place. Or maybe, like the HMV102...

 

[Besoeker]

can confirm there is no link. it is believed to have been removed past.

Believed by whom?

 

[Knobhead]

Is this system still live?

For gods sake get someone that knows what they are doing before you kill someone!

Both RoB and I asked about the sites SAP, you haven’t answered that. Someone has to be legally responsible for it. MV/LV isn’t something for the uninitiated to play with, it has a bad habit of biting or killing the innocent.

Where are you?

 

[Knobhead]

The DNO will charge for any switching operation for a small MV off take.
Having the transformer MV connection switched in to circuit earth isn’t an unnecessary expense, it’s a requirement! Only they can perform switching as it is on their system.

Stop being an annoying fool and accept advise, before you kill someone!

 

[Megavolt]

What is a site SAP ?

 

[Clive P]

Hi,

AP- Authorised Person

SAP- Senior Authorised Person

Regards.