few quick questions

[andy]

1: 3 phase supplies to pylons are from a delta transformer. so where does the earth come from? am i missing something?

2: if i do some minor works, and its not against part P (i.e add a second socket in a bedroom), is there anything to stop me puttin my name/address on a minor works cert? (obviously, work will be done to BS7671)

 

[mapj1]

1)
The HV network is not usually earthed explicitly along its length, only at the generator end by the apparatus that detects a fault.

2)No, you can put your adress, my adress, even "Micky Mouse, Disneyland " whatever.
If you are doing the testing, then your adress seems most logical.
For recording results of DIY testing, I suggest the IEE forms free for download here.
http://www.iee.org/Publish/WireRegs/forms.cfm as these are 'neutral' in terms of bias, and make it clear that it is the IEE regs that are being tested to, not Nics roll your own or whatever.

 

[andy]

1)
The HV network is not usually earthed explicitly along its length, only at the generator end by the apparatus that detects a fault.

2)No, you can put your adress, my adress, even "Micky Mouse, Disneyland " whatever.
If you are doing the testing, then your adress seems most logical.
For recording results of DIY testing, I suggest the IEE forms free for download here.
http://www.iee.org/Publish/WireRegs/forms.cfm as these are 'neutral' in terms of bias, and make it clear that it is the IEE regs that are being tested to, not Nics roll your own or whatever.

1: i should have explained my first question a bit better. if you touch a HV line with a large pole etc etc you get a shock. but if it comes from a delta transformer, with no earth, then how do you complete the path?

2: thanx. i have already got some forms ive printed, just wasnt sure about it.

 

[felix]

In any circuit there are components that don't appear on the diagram. In your (hopefully hypothetical) case the important ones are capacitors. These are scattered all over the place, eg from each overhead (or underground) wire to earth and from the transformer windings to the core. If you draw all these in you'll see why touching that HV line would be a really bad idea.

 

[andy]

In any circuit there are components that don't appear on the diagram. In your (hopefully hypothetical) case the important ones are capacitors. These are scattered all over the place, eg from each overhead (or underground) wire to earth and from the transformer windings to the core. If you draw all these in you'll see why touching that HV line would be a really bad idea.

where are the capacitors connected?

(i havent done much HV stuff and was just thinkin, if there is no earth then how do you get a shock)

 

[mapj1]

I dont think Felix means there is a specific component with a lead at each end deliberately fitted so you get a shock, but there is a distributed capacitance of all the cables and transformer windings and stuff to ground of a few 10s to hundreds of pf/m that will complete the path for you, but additionally, there are lost wire detectors that have a definite (small) current to ground from each phase as part of their normal operation.
Between these two effects there is more than enough to finish you off.

 

[andy]

I dont think Felix means there is a specific component with a lead at each end deliberately fitted so you get a shock, but there is a distributed capacitance of all the cables and transformer windings and stuff to ground of a few 10s to hundreds of pf/m that will complete the path for you, but additionally, there are lost wire detectors that have a definite (small) current to ground from each phase as part of their normal operation.
Between these two effects there is more than enough to finish you off.

i (kinda) understand now. thanx

 

[BJS_Spark]

3 phase supplies to pylons are from a delta transformer. so where does the earth come from? am i missing something?

A three phase generator has a star arrangement where the three phases of live are generated with respect to a neutral point. This neutral point is grounded at the source as the return path, and then the three phases distributed around the grid. The earth (as in the planet) is a good conductor and as so is used as the fourth wire of the grids transmission system.

i should have explained my first question a bit better. if you touch a HV line with a large pole etc etc you get a shock. but if it comes from a delta transformer, with no earth, then how do you complete the path?

What you are possibly missing is that the grid is normally stepped down via a transformer wired delta on the HV side and star on the LV side giving a local neutral/earth. If you touch the HV side your path is complete through ground to the generator end not the substation.

Clear as mud? (Or as conductive at least??)