110v vs 240v on building sites.

[westie101]

Basically the whole of the system, apart from some LV stuff in rural areas, is interconnectable and should have the same phase rotation!
If we get it wrong it can lead to a no tea, no biccies interview
This is used as far as possible to maintain supply following a fault or during maintenance and we generally refer to it as an open ring.
There are some areas where there are closed rings but these do increase the PFC so have to be managed carefully.

The top wire on a pylon is just an earth wire that is provided to ensure some degree of lightning protection and prevent potential differences between adjacent points during works

 

[SimonH2]

The top wire on a pylon is just an earth wire ...

Plus, on many, fibre optic data cable as well.

 

[westie101]

Plus, on many, fibre optic data cable as well.

Yep most of those round the county!

 

[AdrianUK]

Simon,

The are loops in the 415V network. If you look at the pavement you will often find access holes labelled 'electricity supply'. Often these are link boxes - where the two extreme ends of radials from two different distribution transformers meet. In normal operation the neutrals of the two systems are joined but the phase links are left open. The idea is that in the event of a fault it may be possible to remove the fuses from the LV side of one substation & insert links into a link box to backfeed both networks from a single substation hence quickly restoring supply while the problem is sorted.

If the outage is planned then the links maybe inserted with both feeds live. Obviously for this to happen both supplies must be in phase. Normally one would test for voltage R-R, Y-Y & B-B before inserting the links. Once the links are inserted the two transformers are operating in parallel temporarily until one is taken off line. The Customer, meanwhile, sees no interuption in supply.

In certain major cities such as London distribution transformers are often run in parallel feeding a grid network in order to cope with the high demand. Obviously for this to be possible, all the LV secondary sides must be in phase.

The network is generally all run in phase. Care is taken to ensure that the phase shift introduced by, say a Dy1 step up transformer would be cancelled out by using a Yd11 step down transformer but this is not always possible. Sometimes phase shifting transformers are deliberatly introduced to correct phase alignmnet so that parallel operation of parts of the network is possible, even if only in an emergency scenario.

Adrian

EDIT: Too slow typing! Beaten to it by Westie!

 

[JBR]

Now consider you connect three heater elements, each between a different phase and neutral. One will have a current that looks like the black line, one a current that looks like the red line, and the third a current that looks like the blue line. If you look at the left of the graph, the black line is at 0, the blue line at about 0.86, and the red line at about -.086 - so all the currents sum to zero.

So if I'm on red phase and my two next door neighbours are on yellow and blue phase, and we each switch on a single-bar electric fire, we'd collectively be drawing no current and therefore not be charged any money!

Please ignore me; I'm being flippant!

A very clear explanation, by the way.

 

[EFLImpudence]

You'd all be drawing lots and sending none back so should be charged more.

 

[bernardgreen]

I am staying neutral

 

[SimonH2]

Puns like that should draw a charge of mental battery, but at least in modern prisons they should find you a dry cell.

OK, I'll get my coat.

 

[dhutch]

I'm not sure but I think 55-0-55V predates the widespread use of RCDs.

I think that is a large part of it. That and the tools not being kicked quite so much, giving a reason for it to stay.

So then, how come 240v is not ....120 - 0 - 120 ??
Would that not be safer in our homes???

I my mind the two reasons are: Firstly, 120 is enough to kill you anyway, unlike 55 which typically wont. Two, with the advent of RCDs its not a major issue. With the issue of increased current being the reason for 240v supply.

Also, it works...!

Daniel

 

[ban-all-sheds]

This topic has been transformed.

 

[bernardgreen]

This topic has been transformed.

No it is just a wind up !

 

[winston1]

Just to be clear the US supply is 120v not 110v. It is sometimes quoted as 117v, as it is assumed there will be a 3v drop between the transformer and the consumer.

 

[OwainDIYer]

So if I'm on red phase and my two next door neighbours are on yellow and blue phase, and we each switch on a single-bar electric fire, we'd collectively be drawing no current and therefore not be charged any money!

You'd be drawing current on the phase wires, but little or no current on the neutral.

In many cases a reduced size neutral can be used in 3 phase wiring for this reason. (Saves cable costs)

 

[ban-all-sheds]

So if I'm on red phase and my two next door neighbours are on yellow and blue phase, and we each switch on a single-bar electric fire, we'd collectively be drawing no current and therefore not be charged any money!

You'd think so, wouldn't you.

But you underestimate the devious cunning of electricity companies who sell us electricity, even though they actually get it back almost immediately and then sell it to us again, or to somebody else.

3:58 onwards.

 

[JBR]

So if I'm on red phase and my two next door neighbours are on yellow and blue phase, and we each switch on a single-bar electric fire, we'd collectively be drawing no current and therefore not be charged any money!

You'd think so, wouldn't you.

But you underestimate the devious cunning of electricity companies who sell us electricity, even though they actually get it back almost immediately and then sell it to us again, or to somebody else.

3:58 onwards.

Ah, but I can be devious and cunning too!

I've a good mind to disconnect my neutral cables and then they won't get any back from me!

Or I could put my own meter on the neutral and charge them for what they take back!