Which earthing system?

[Hayeso32]

Guys, I'm currently working on a national grid site and have been tasked with checking over some NIC sheets of the subbie. However access to the dno kiosk is not available quickly and the drawings aren't to hand. I have been told that the supply is tnc-s that then goes through a isolating transformer which is tt. So my question is what earthing system would I put on the test sheets?

Thanks in advance for any replies!!

 

[Plonker 3]

Meh....

 

[trev]

Talking cack as per.

 

[Hayeso32]

Typical condescending spark!!!

 

[Clive P]

Hi,
Having worked on dozens of National Grid sites, I would record the Earthing System as TT. All of your testing and circuitry reverts back to the secondary of the 1:1 Transformer, this as you will be aware is where you will get your Ze reading. You can measure the Ze on the primary side to check your TNCS supply to ensure it meets the relevant criteria, but as said TT.
.
Regards.

 

[Amp David]

I'd opt for TNS

 

[Engineer54]

Might be an idea to tell us what this isolating transformer is being used for and what is it supplying?? You say this is a National Grid site your working on and then say, you can't gain access to to a DNO kiosk, so again what is this kiosk supplying??


The Secondary side Neutral at the TX, will be earthed as a matter of course, it's what happens after this connection as to what earthing system is eventually used. It could be any TNC-S, TN-S, or TT!!

 

[Outspoken]

Guys, I'm currently working on a national grid site and have been tasked with checking over some NIC sheets of the subbie. However access to the dno kiosk is not available quickly and the drawings aren't to hand. I have been told that the supply is tnc-s that then goes through a isolating transformer which is tt. So my question is what earthing system would I put on the test sheets?

Thanks in advance for any replies!!

What is this transformer doing, that's a helpful start..

At first look if the secondary side is TT'ed then it should have an earth stake, thus it is TT!! Now there is rocket science for you..

 

[trev]

Typical condescending spark!!!

Don't know who that was directed at but if you look at the reasons for editing both Dillb and I had valid reasons for withdrawing our comments. Mine of "talking cack as per" was actually a criticism of myself.

 

[telectrix]

criticism or praise, trev? :6:

 

[MDJ]

Typical condescending spark!!!

Really? well racists and idiots tar everyone with the same brush due to lack of brain cells, are you suggesting sparks are typically condescending? Now if you would suggest Plumbers are condescending idiots I would agree LOL

 

[Outspoken]

Really? well racists and idiots tar everyone with the same brush due to lack of brain cells, are you suggesting sparks are typically condescending? Now if you would suggest Plumbers are condescending idiots I would agree LOL

Isn't that Tradism?

 

[Engineer54]

What is this transformer doing, that's a helpful start..

At first look if the secondary side is TT'ed then it should have an earth stake, thus it is TT!! Now there is rocket science for you..

Errrr, all TX secondary neutral points are earthed via a TT system, especially at a sub-station or in this case, National Grid site. It depends from that point onward, as to what the actual system earthing is. As i stated it could be any of three usual systems, could even be an IT system!! Without knowing what this TX is doing, it's anyone's guess!!

 

[Hayeso32]

Thanks for all replies so far, to clarify the site is a gas agi and is being worked on as part of the CNI project. The site is unmanned and so falls under the sco1+2 permit to work procedure thus making it difficult to gain access. The isolating transformer supplies all of the essential equipment to do with the gas pumping as far as I am aware.

 

[Outspoken]

Errrr, all TX secondary neutral points are earthed via a TT system, especially at a sub-station or in this case, National Grid site. It depends from that point onward, as to what the actual system earthing is. As i stated it could be any of three usual systems, could even be an IT system!! Without knowing what this TX is doing, it's anyone's guess!!

E54, couple of points, my first comment did actually ask what the Tx was doing..and secondly, IT systems are illegal to install in the UK and have been since the mid 1960's. Tate and Lyle had the last such operational system in the UK, located in what was the Industrial part of London Docklands. That was decommissioned and demolished in the late 1980's and the British Sugar (Formerly Tate and Lyle) site in Bury St Edmunds has it's own 132kV dual feeders incoming and all systems on site are TN-C.

So there is no way the Tx would be IT. It is obvious to anyone in the know that all generator sets and Tx's on the distribution grid are effectively TT systems, as such the enclosure they are in should be treated as such...well according to National Grid anyway..

 

[Engineer54]

Think you had better tell the mining industry and every hospital/medical centre in the UK, (and a few other area's i can think of) that they are using ''Illegal Supply'' systems!! lol!! IT systems are used where security of supply is recognised as a critical criteria, and are to be maintained, even in the event of a fault!!!

Now i don't happen to know how critical the security of the power supply is for an unmanned natural gas pumping station. I also don't partially know what sort of safety shut down features these pumping stations incorporate. But an Isolating Transformer is usually a prerequisite for an IT earthing system, where the supply is being brought in with it's own TN earthing arrangement!!

I simply have no experience with such sudo petro-chem gas pumping stations, so i'm not going to make any wild guess statements.

 

[Outspoken]

Think you had better tell the mining industry and every hospital/medical centre in the UK, (and a few other area's i can think of) that they are using ''Illegal Supply'' systems!! lol!! IT systems are used where security of supply is recognised as a critical criteria, and are to be maintained, even in the event of a fault!!!

Now i don't happen to know how critical the security of the power supply is for an unmanned natural gas pumping station. I also don't partially know what sort of safety shut down features these pumping stations incorporate. But an Isolating Transformer is usually a prerequisite for an IT earthing system, where the supply is being brought in with it's own TN earthing arrangement!!

I simply have no experience with such sudo petro-chem gas pumping stations, so i'm not going to make any wild guess statements.

I think you need to stop digging a hole here ET, I already mentioned I have worked in the NHS, and whilst some individual items of equipment may be connected up as an IT system via an Isolating Tx (Such as Medical Scanners - Nuclear Medicine) the overwhelming systems in a Hospital are either TN-S or TN-C-S depending on the age of the building and the services. I have worked in mining situations and my Brother-In-Law was a mining Engineer for 39 years and I can assure you that they are NOT IT systems and have not been for many decades (Just spoke to Steve on the phone to confirm as he now works as a Mining Consultant). Perhaps outside of the UK this is different. He explained that sub-surface electrical systems are fed via 1:1 Isolating Tx's, but they are most certainly not IT, the subsurface systems are TT and have been since at least the early 1970's..these days they are TT'ed with RCD's on everything.

What the hell are you going on about pumping stations for? No-one has mentioned a Transco Pumping station (Because in the UK it would be Transco) and i also happen to know that many of these are PME because they are connected to the local grid...but what relevance they have to this discussion I am unsure...Tate and Lyle make Sugar if that has confused you?

 

[Engineer54]

Digging a hole, ...lol!! Perhaps you should have taken more notice of the operating suites in the hospital you were working in, or you would have known that these areas all operate on an IT supplied monitored system!!
Now having been involved in the building of several Hospitals now (including my present project), ranging from small 150 bed, to 600 bed, and on what was the largest medical city project in the world at 1550 beds, i doubt very much, if you could tell me anything about hospitals there services and hospital supplies!!!


As for the mining situations, maybe your right about the UK, or maybe not, as according to our Mechanical Engineer here, who spent a good many years with the National Coal Board (or whatever they called it) on the coal mines in Wales, tends to think otherwise from many of his past stories/experiences that he's passed on to me...
But have no fear, i WILL definitely confirm or otherwise with him tomorrow!! Now just thinking logically about what you have posted, i would have thought, the very last thing they would want below ground, on what may be life support systems, is bloody RCD's tripping out!!

I'm only going by what the OP has stated in his post #17 eg, ....

Thanks for all replies so far, to clarify the site is a gas agi... (whatever a gas agi is)/ ... The isolating transformer supplies all of the essential equipment to do with the gas pumping as far as I am aware.

Sounds pretty much like a gas pumping station to me, ...What do you think?? lol!!

What Tate & Lyle and sugar has to do with any of this, i haven't a clue!! lol!!

 

[Engineer54]

Ok, i've had a bit of a chat on the phone with our Mechanical Engineer (Forgot he was off on a factory materials inspection to Changsha Saturday), and gather that the low voltage supplies for the coal mines he was involved with, had high impedance neutral earthing (aka a form of IT) in which the TX neutral point, is connected to earth through a resistor of a value sufficient to limit earth fault current to a few amperes, generally no more than 25 A and normally much less!! Reasons given, to limit earth fault currents and arc flash, which is/was the largest cause of electrical injuries in mines!! As with an un-earthed system, an earth fault to an energised phase will not operate an OCPD, so supplemental ground-fault detection is required to outgoing circuits and overall leakage/tripping monitoring at the supply source....

I'll be having a more in-depth chat with him when he returns to site, maybe tomorrow or Tuesday... I personally have no experience or knowledge of mine electrical systems, and very limited Quarry experience. But it sounds very much like NER IT earthing is used in mine situations, and for what sounds like, very good and sound reasons...