Three phase power

[nikkicallaghan]

I'm sure this will sound very basic to some but,

Could someone explain 3 phase power and its use in dimmers etc as all the stuff I've googled just goes on about motors

Please out this in language an idiot can understand as I have no knowledge of it and it's uses

[Whiskers]

Simple explanation DIMMERS USER SINGLE PHASE

 

When a three phase supply includes a neutral it is very easy to use one of the phases and neutral

 

BUT it is a can of worms, there are all sorts of iffs and buts and you really DO need an electrician.

 

When the supply has no neutral (AKA delta) then forget it!

 

 

Hard Explanation Start at

 

https://en.wikipedia.org/wiki/Three-phase_electric_power

[sleah]

Simple explanation DIMMERS USER SINGLE PHASE

Of course the OP may have heard about 3 phase feeds being used for dimmers such as the Betapack range.

 

Put simply, if a 6ch dimmer such as a Betapack has a 3 phase feed in to it (3L + N + E) it is internally configured in to 3 pairs of single phase dimmers, so each dimmer channel with in a dimmer pack is still single phase, as Whiskers states.

[J Pearce]

Hi Nikki, good to see you on here, been a while since I saw you at Derby Playhouse! Hope all is well?

AC power is a sine wave, single phase is one sine wave. 3 phase is 3 different lives, all sine waves, offset by a third of a cycle. (Think about 3 coils placed at thirds around the generator).The beauty of this is that the sum of all the lives is zero, so if you have a load that is the same on all three lives you don't need a neutral as it all cancels out.Dimmers use 3 phase because the suppliers want their consumption to average out to no neutral so want us heavy users to balance our loads across all 3 phases.

If you looked at the maths you'd find that between any two lives you get 415V and between any live and the neutral you get 230V. (This is why we have 415V warning signs and red connectors on 3 phase outlets.)

I hope I have not introduced further confusion?

Jon

[musht]

Alternator works by whirling a magnet round inside coils of wire, CHANGING magnetic field induces a current in the wire. Or whirling the coils inside a fixed magnet , magnetic field has to be changing for anything to happen.

 

If just used one wire in multiple coils around generator, wire would end up very thick to cope with all the current passing through all the wire.

 

Divide the wire into 3 groups of coils around the spinning magnet and wire can be much thinner, it`s only taking 1/3 total output.

 

The output power is ideal for motors because they can act like a generator in reverse with the energised coils repelling magnets.

 

Delivered to your dimmers will probably have 3 phase, neutral and earth. Between any single phase and neutral a meter would measure 230/240V typical wall socket volts.

 

Between any 2 phases, meter will register nearer 415V. Dimmers are connected between phase and neutral and distributed between the phases either internally or via power distribution.

 

A meter suitable for doing the measurement isn`t just the cheapest one to hand:

 

http://ecmweb.com/arc-flash/case-deadly-arc-flash

 

Motors often dont use a neutral and run on the 415V available between phases.

 

Single phase equipment presented with a lost neutral could see the voltage rise up to a possible 415V with not good consequences.

Ensuring the neutral has a good connection is as important as not leaving a phase conductor dangling about.

[nikkicallaghan]

1438640014[/url]' post='525659']

Hi Nikki, good to see you on here, been a while since I saw you at Derby Playhouse! Hope all is well?

AC power is a sine wave, single phase is one sine wave. 3 phase is 3 different lives, all sine waves, offset by a third of a cycle. (Think about 3 coils placed at thirds around the generator).The beauty of this is that the sum of all the lives is zero, so if you have a load that is the same on all three lives you don't need a neutral as it all cancels out.Dimmers use 3 phase because the suppliers want their consumption to average out to no neutral so want us heavy users to balance our loads across all 3 phases.

If you looked at the maths you'd find that between any two lives you get 415V and between any live and the neutral you get 230V. (This is why we have 415V warning signs and red connectors on 3 phase outlets.)

I hope I have not introduced further confusion?

Jon

 

Hi Jon yeah it's been a while hope you're ok.

 

 

Thanks for all the input.

I've never used 3 phase and probably never will but it's useful to know these things just in case

 

 

[paulears]

You probably have used three phases, you're just not normally aware of it because the primary reason for having it is to get more overall power in one place. In a home there's no real need for lots of electricity, even though the cable passes your house is three phase. You just tap into it and use one. If next door is a macdonalds, they need more power for the kitchen stuff, so they bring in all three. Some of the gear in the kitchen is designed to spread it's load across all three phases, and is connected via one of those red connectors. In America, they have two phase power in many homes, and therefore two different voltages available.

 

As electricity is produced by spinning things, three phase is a nice common way of distributing it to other spinning things, and with transformers they can give the end users any form they like.

 

Cable sizes go up as current increases, so a three phase dimmer pack might only need a 32a connector, when a single phase wired one needs 63a.

 

For people who work in theatre and events, it's just two colours and four sizes of connectors, so pretty hard to make yourself look daft.

[adam2]

Virtually all electricity supplies start as 3 phase.

 

For example a house or small business usually has a single phase supply, but this is obtained from a main cable in the street that carries 3 phase. The first house would be connected to one phase, the second house to the next phase, the third house to the remaining phase, and the fourth house to the first phase. This is repeated along the road such that about one third of the houses are connected to each phase.

 

Larger premises, including most theatres, have a 3 phase supply. Single phase loads such as dimmers are connected between one phase and neutral. To best utilise the three phase supply, it is usual to connect about one third of the dimmers to each phase. This may be done in 2 ways. If the dimmer rack is designed for single phase input, then several racks are used with roughly equal numbers on each phase. If the dimmer racks are intended for 3 phase supply, then they are wired internally so that roughly equal numbers of dimmers are on each phase.

 

A single phase dimmer rack or other loads will normally have 3 input connections, live, neutral and earth.

 

A 3 phase dimmer rack should have 5 input connections, 3 live connections, neutral and earth.

 

Other types of 3 phase load will have either 3, or 4, or 5 connections. 3 live connections, probably an earth, (though double insulated 3 phase equipment that needs no earth does exist) and maybe a neutral depending on whether or not the load needs a neutral.

 

A single phase load may easily be powered from a 3 phase supply provided that a neutral is available, this is not complex but actually making the connections can NOT BE RECOMENDED for the novice, consult an electrician.

 

If no neutral is available then there is no simple way of powering a standard single phase load.

 

In the UK, a standard 3 phase supply will be nominally 230 volts from any phase to neutral and 400 volts from any phase to any other. The actual voltage tends to be a bit higher at about 240/415 in most places.

 

Most of Europe uses a similar system but the voltage tends to be slightly lower at about 220/380 volts, despite having a nominal voltage of 230/400.

 

A variety of "weird and wonderfull" systems still exist overseas and detailed advice should be taken before use of any such.

 

 

 

 

 

 

 

 

[Jivemaster]

Three phase is essential for things that move. Many motors (especially BIG ones run much better on three phase that they could on single phase)

 

For most stage and entertainments use three phase ins't needed (very little rotates) but the advantage of three phase is the saving on the neutral conductor. Three single phases will need six full size conductors (plus earths) but a three phase supply will usually only need four wires plus earth, over all the country that's LOT of copper(ie cost) saved. However in dimmer city there may be need to increase the neutral conductor as some of the efficiencies of steady loads don't apply to dimmed circuits.