Substation Earthing Arrangment

[QuestionableSpark]

Hi All,
I have a question trying to understand earthing arrangments

SO,
We have a DNO Substation, 4 Core armoured Feeding the Distribution Board Fed from an Auxillary Transformer (Clients)

The DNO Substation has an Earthtape around the substation, which connects to the earthmat of the entire substation.

The Transformer, which supplies the Substation, Has a N-E Link, This Earth link goes directly to the Earth Mat.

The Main earth for the DB is supplied from the earth tape around the substation.

I would guess, this is a TT System,
However, The company i work for, says it is classed as a TNS System, As there is a separate Earth.
As it comes into the DB as a L1,L2,L3,N from the armoured - Then A Separate Earth To The DB (Via Tape/Earth Mat

Im just confused, and would like clarification

 

[davesparks]

TNS because your earth connects back to the N-E link by a seperate conductor.

What makes you think it would be a TT?

 

[Lister1987]

Hi All,
I have a question trying to understand earthing arrangments

SO,
We have a DNO Substation, 4 Core armoured Feeding the Distribution Board Fed from an Auxillary Transformer (Clients)

The DNO Substation has an Earthtape around the substation, which connects to the earthmat of the entire substation.

The Transformer, which supplies the Substation, Has a N-E Link, This Earth link goes directly to the Earth Mat.

The Main earth for the DB is supplied from the earth tape around the substation.

I would guess, this is a TT System,
However, The company i work for, says it is classed as a TNS System, As there is a separate Earth.
As it comes into the DB as a L1,L2,L3,N from the armoured - Then A Separate Earth To The DB (Via Tape/Earth Mat

Im just confused, and would like clarification

Who is the local DNO/DSO, most have publically available technicial documents relating to things like substation design, earthing and the like.

 

[QuestionableSpark]

TNS because your earth connects back to the N-E link by a seperate conductor.

What makes you think it would be a TT?

My thinking is it goes to an earth electrode on the ground (Earth Mat)

 

[davesparks]

My thinking is it goes to an earth electrode on the ground (Earth Mat)

Yes but that's the substation N-E link, so provides the first T in the earthing system. If it was TT then the installation would be connected to another, completely separate, earth electrode.

In this case you have a N-E link referenced to earth via the earth mat and then a seperate earth conductor from there to the installation so it is TNS

 

[QuestionableSpark]

I understand I think,
if that transformer was connected to 1 earth mat, and the DNO Substation was connected to its own earth mat
Then the DNO would be on a TT System

 

[davesparks]

I understand I think,
if that transformer was connected to 1 earth mat, and the DNO Substation was connected to its own earth mat
Then the DNO would be on a TT System

No that sounds like a potentially dangerous situation (assuming the 2 transformers are in close proximity)

A TT system has the transformer N-E link referenced to earth via an earth electrode and then the installation has a completely separate earth electrode with the only connection between them being via the mass of the earth.

 

[QuestionableSpark]

Sorry there isnt 2 Transformers.

1 Transformer, N-E Link to Earth Mat 1
Transformer Feeds Substation with 4 Core SWA (B,Bl,Gr,N)
Substation Main Earth Connects to Separate Earth Mat

Is that then a TT System?

Thankyou for your help, I know it probably seems simple to you, I'm just trying to get my head around things

 

[davesparks]

Sorry there isnt 2 Transformers.

1 Transformer, N-E Link to Earth Mat 1
Transformer Feeds Substation with 4 Core SWA (B,Bl,Gr,N)
Substation Main Earth Connects to Separate Earth Mat

OK I'm a little confused now, isn't the transformer one of the main components of the substation?

I'm not 100% up on correct terminology as far as that goes.

Unless the transformer is a long way away from the substation so that the earth electrodes don't interfere with each other I don't see how that could be anything other than a potentially dangerous situation.

 

[Lister1987]

Dunno if this document will help at all, might give a bit of clarity/insight.

Also look for 'ENA TS 41-24' and BS EN 50522, of which the former is based on.

 

[QuestionableSpark]

OK I'm a little confused now, isn't the transformer one of the main components of the substation?

I'm not 100% up on correct terminology as far as that goes.

Unless the transformer is a long way away from the substation so that the earth electrodes don't interfere with each other I don't see how that could be anything other than a potentially dangerous situation.

So the set up of this site in particular

1 HV transformer
This feeds 2 Auxillary Transformers

Aux TX 1 has a Neutral earth link directly to an earth mat
This in turn feeds the DNO Substation with a 4Core SWA. Powers the substation dB.

Aux TX 2 feeds the customer substation main LVAC Board. This TX Has an earth to the earth mat, just not from the neutral bar.
This LVAC board has the N-E link done within the panel rather than the transformer. (earth directly to earth Mat which


My question is,
1) if the DNO has a separate earth Matt, to that of the customer earth mat, would that make the DNO a TT System and the Clients a TNS System ?

2) why would it be dangerous if they are both adequately earthed?

 

[QuestionableSpark]

Thanks, I will have a read of this across the weekend!

 

[QuestionableSpark]

Dunno if this document will help at all, might give a bit of clarity/insight.

Also look for 'ENA TS 41-24' and BS EN 50522, of which the former is based on.

Thanks I will have a read over the weekend