Any Electricians ?

[Skywave]

Thanks Lawrence - but the drawings there confuse me even more!
On p.6, there are 3 configuration drawings shown. One drawing shows 3-phase and no neutral feed to the load, the other two drawings show 3-phase and a neutral feed to the load. Can't have both!
The Wiki. drawing shows no N feed to the load: hence my previous remark.

Al.

[pwdrive]

Thanks Lawrence - but the drawings there confuse me even more!
On p.6, there are 3 configuration drawings shown. One drawing shows 3-phase and no neutral feed to the load, the other two drawings show 3-phase and a neutral feed to the load. Can't have both!
The Wiki. drawing shows no N feed to the load: hence my previous remark.

Al.

Guilty as charged, I didn't actually read much of the document, I found the document because my old mate has worked for Schniders for years and I preussumed they knew what they were talking about.
PS I know zilch about three phase.

Lawrence.

[Skywave]

Lawrence: thanks for that link.

Three-phase: the fundamentals of 3-phase are actually quite easy to grasp: anyone who has had some experience with oscillators, understands sine-waves, has a good grasp of basic d.c. theory and knows some fundamental algebra and trigonometry can easily get to grips with the basics of 3-phase: you shouldn't find it that difficult to pick up. But when you go beyond the basics of 3-phase, then things do indeed get complicated - especially in the mathematics.
When I was studying Electrical and Electronic Engineering at college, the early years were all about low-frequency single, and then, later, 3-phase. The stuff I was interested in - electronics - came a lot later. Although I found that early stuff pretty boring, I do now appreciate that it did provide the grounding for the advanced stuff that followed later in the Electronic and Communications Engineering courses that I studied in the final two years.

Al.

[pwdrive]

Hi Al, I guess my lack of knowledge on three phase is due to the fact that during my working life I have never been involved with it much, the only time was when I was sawmilling and I had an old three phase mortice machine but only a single phase supply, my solution for that was to buy a second hand phase converter which seemed to do the job.

Lawrence.

[Skywave]

Getting back on topic: I found provides a clear description, especially as it uses coloured circuit diagrams . . .

http://www.google.co.uk/url?sa=t&rct=j&q=electrical%20earthing%20systems&source=web&cd=4&ved=0CEcQFjAD&url=http%3A%2F%2Felectrical.theiet.org%2Fwiring-matters%2F16%2Fearthing-questions.cfm%3Ftype%3Dpdf&ei=kvd3UJmiN4Wa0QXo0oDoDw&usg=AFQjCNGgVmZa42MaWWheFH0je93n2TQVdg&cad=rja

Al. / Oct. 13, 2012 //

[pwdrive]

Getting back on topic: I found provides a clear description, especially as it uses coloured circuit diagrams . . .

http://www.google.co.uk/url?sa=t&rct=j&q=electrical%20earthing%20systems&source=web&cd=4&ved=0CEcQFjAD&url=http%3A%2F%2Felectrical.theiet.org%2Fwiring-matters%2F16%2Fearthing-questions.cfm%3Ftype%3Dpdf&ei=kvd3UJmiN4Wa0QXo0oDoDw&usg=AFQjCNGgVmZa42MaWWheFH0je93n2TQVdg&cad=rja

Al. / Oct. 13, 2012 //

Hi Al, that's the one I posted in post No. 17.

Lawrence.

[Mark Hennessy]

Thanks Lawrence - but the drawings there confuse me even more!
On p.6, there are 3 configuration drawings shown. One drawing shows 3-phase and no neutral feed to the load, the other two drawings show 3-phase and a neutral feed to the load. Can't have both!
The Wiki. drawing shows no N feed to the load: hence my previous remark.

With 3-phase, it's entirely possible to have no neutral.

Without the neutral, you have a Delta system. This is used for distribution - obviously it saves copper.

When you do have a neutral, this is a Star system. To convert between Star and Delta, you use special transformers: http://en.wikipedia.org/wiki/Delta-wye_transformer

These are typically what you find in sub-stations. Incoming 11kV is stepped sown to 415V 3-phase star with 230V between neutral and each phase, which is very convenient for distributing to a mix of houses and small businesses (that require just a single phase supply), and slightly larger premises that might need 3-phase.

This looks like quite a good article: http://www.epemag.net/electricity-generation6.html

Cheers,

Mark

[Skywave]

Getting back on topic: I found provides a clear description, especially as it uses coloured circuit diagrams . . .

http://www.google.co.uk/url?sa=t&rct=j&q=electrical%20earthing%20systems&source=web&cd=4&ved=0CEcQFjAD&url=http%3A%2F%2Felectrical.theiet.org%2Fwiring-matters%2F16%2Fearthing-questions.cfm%3Ftype%3Dpdf&ei=kvd3UJmiN4Wa0QXo0oDoDw&usg=AFQjCNGgVmZa42MaWWheFH0je93n2TQVdg&cad=rja

Al. / Oct. 13, 2012 //

Hi Al, that's the one I posted in post No. 17.
Lawrence.

Whoops! So it is! Sorry: I'm getting a bit carried away with all this - but there is quite a lot here that I'm learning and you know what enthusiasm can do . . .

Al.

[Skywave]

Hi Mark,
Re: your post #37: thanks. I read all of that and, yes, it is in agreement with my understanding of 3-phase electrical power distribution networks. So presumably, the IT network is used solely for such distribution networks: e.g. a sub-station transformer with delta-connected primaries and star-connected secondaries. In which case, the Wiki. drawing is confusing, since it shows the 3-wire delta feed to a box labelled 'consumer'. In an electrical power distribution network, to me, a 'consumer' is the 'end user': factory or domestic, not an network distribution transformer. I suppose that one could argue that the use of the word 'consumer' here includes a customer-owned delta-star transformer situated on the consumer's premises - such as a factory requiring 230-v. and 415-v. feeds. In which case, I am of the opinion that the Wiki. drawing should make that clear, at least in text, ideally in a supplementary drawing.

As I mentioned in an earlier post, I studied 3-phase electrical systems in depth many years ago at college, but no reference to earthing systems featured in those studies. Consequently, modern earthing systems are of interest to me and I am learning a lot of useful stuff here via this thread. Your contributions - and those of others here - are of value to me.

Cheers,
Al.

[Mark Hennessy]

Hi Al,

Thanks

I agree that Wikipedia article could be clearer - perhaps we should update it . I think I'd be happier with the IT diagram if the source was drawn in Delta configuration, but I guess they were trying to keep things simple as earthing was the main point they were trying to get across.

But yes, it's quite common to take one or more 11kV feeds and step them down on site - we do routinely.

All the best,

Mark