MAJOR problem with supply...

[dlt27]

Sorry title was a bit dramatic, but wanted to get as much knowledge as possible.
I was working at a biomass factory today after they had a fire. Extension leads were apparently the cause.
When doing a test at the db I noticed that L1 phase was at 272v to earth. L2 phase was 222v to earth and L3 phase was 240v to earth. Any phase to neutral was 240v. I then carried out a high loop test on all phases and got between 76 and 80 Ohms.(TNC's/PME).
Due to these readings I went to 11kv transformer that is in the building and done the same test a lv side of panel and was still getting same results. I then took a feed out to earth rods/ earth mat of transformer, but was still getting the same figures. I have got past test results that said ze was 0.2 Ohms a couple of weeks ago.
I also noticed when any circuit is turned off you get 30v from earth to neutral and earth to live. Also rcd's are failing to trip on push buttons.
Just wondered if anyone had an explanation for these findings and if so could you please explain in simpletons terms.
Much appreciated in advance
(I'm guessing a problem with neutral at star point of transformer).

 

[snowhead]

Any phase to neutral was 240v.
(I'm guessing a problem with neutral at star point of transformer).

Earth bar Test link left loose by whoever did the recent test.

 

[Clive P]

Hi,

Probably best to wait for Tony or one of the other lads with experience in this field. They'll know the answer before they've finished reading the thread.

Regards.

 

[dlt27]

Ok Thanks. I have tested at every earth point in building and still got same readings. Even at earth mat for transformer.
Another funny thing is that western power said they had an issue with one of their transformers the same time the fire started. However they will not look at this one as it is a private transformer . What the issue was I don't know. He also hasn't got any surge protection on building so wondering if there was a transient voltage or something that has caused some damage!

 

[UKMeterman]

Ok Thanks. I have tested at every earth point in building and still got same readings. Even at earth mat for transformer.
Another funny thing is that western power said they had an issue with one of their transformers the same time the fire started. However they will not look at this one as it is a private transformer . What the issue was I don't know. He also hasn't got any surge protection on building so wondering if there was a transient voltage or something that has caused some damage!

Ask WPD to spill the details of the issue that they had... Also try measuring the voltage between N and true earth ( the brown stuff outside.

 

[Silly Sausage]

Out of my league, but some company I worked with a while back, one of their lads burnt somewhere down by leaving some gear powered overnight off an unrolled extension lead!

 

[dlt27]

The guys who installed the transformer are supposed to be coming out tomorrow with a SPECIAL tester , what ever that means. However I wanted to see if you guys knew a possible cause.

 

[JD6400]

I have got a trapped nerve in my back at the moment , so having a job to concentrate .
But it sounds to me like a failing neutral on the incomer

 

[dlt27]

Sorry about your back. Is there any way you could explain how this could cause these readings. Thanks.

 

[JD6400]

I will try but my head is just not with it tonight !
If you you have a failing neutral joint on the incomer before the meter , it will give a poor return . On three phase it can find a alternative path through any 3 phase connected equipment . I have seen the variations you have described several times , and each time it was a failing supply neutral .
I have not explained it very well , but I am afraid it is the best you will get out of me tonight

 

[Silly Sausage]

dlt27, I suspect JD is referring to floating star points, get googling.

 

[Guest55]

dlt27, I suspect JD is referring to floating star points, get googling.

all kneel before the mighty instr. tech. !

;-)

 

[dlt27]

Ok Thanks very much. It's a shot in the dark, but are there any books that explain these sort of things.

 

[dlt27]

Just out of interest could western powers problems have caused this and would it be possible in any way for this to contribute to the fire.
JUST STARTING TO GOOGLE.

 

[Silly Sausage]

all kneel before the mighty instr. tech. !

;-)

Finally, some acknowledgement of my mightiness!!!

Instuments, just one of my many skills

 

[Guest55]

and i bet that avatar pic really is you as well , your holyness !

 

[Guest111]

Put simply if you lose the connection to the star point then you lose the neutral,so on a 3 phase system imagine you had a socket fed off red phase and neutral and another from yellow phase to neutral if you lost the main neutral then the neutral bar in the dis board effectively links the sockets on red and yellow phases,so instead of each socket getting 230v they end up getting 415v and bang goes anything thats connected to them.which is why when working on a 3 phase system you should NEVER remove a neutral link with the supply energized.

 

[dlt27]

I understand that but any phase to neutral is 240v So neutral isn't broken, but possibly failing.

 

[Knobhead]

If the OP wants to PM me I’ll go through the testing required. I’m not going in to it in open forum or until I’m satisfied he will be safe.

 

[GEOFF S]

Thos sound like a fault on one of the phases to earth, the fault being a high impedance earth fault. This in effect drops a voltage accross Rb of the Tx. Test to true earth with a large screwdriver.