3 phase and single phase...

[thomaskennedy]

Hi all,

Could someone please explain what these mean??

I have seen some tools on ebay and they are single and 3 phase...

I am predicting that a 3 phase would not work with the standard plug sockets, but does single phase work?

Ta

Tom

 

[Anonymous]

OK

I'm afraid that this is rather a complicated area - hope the following is not too over-the-top

Electricity in England is generated as 3-phase. Each phase changes its voltage amplitude in time in a sinewave pattern and the amplitude at a given time can be described by the following equation

V*Sin(omega * t) + phi where omega is 2 *pi*f (f= frequency = 50Hz), t is time and phi is the phase angle

A single waveform will curve up from zero V to fully positive V, down to zero V again and then down to fully negative V and up again to zero V in a given time and this is defind as one cycle

Mains electricity in UK has 50 cycles per second (Hz)). Each cycle is defined as a rotation of 2*pi radians which is 360 degrees.

For three phase, we generate 3 of these sinewave voltages at 120 degrees apart, thus, for example, the first (red phase) will pass through zero V at 0 degrees, the second sinewave (blue phase) will pass through zero for the first time at 120 degrees and the third sinewave (yellow phase) will pass through zero V at 240 degrees.

Three phase waveforms looks like this:
(any one of these plus a neutral is the the supply you get in your house) E is the voltage amplitude and for English distribution system would be 586.81 V peak (415V RMS)

All three phases are sent out to the sub stations. What the electricity board do is take a different (single) phase (Red, Blue or Yellow) + a neutral to each street and then to each house in that street. Phases are generally not mixed in a street and so all will be on red or all on yellow etc.

The 240 V you know and love is the RMS voltage between a single phase and Neutral

(RMS = Root Mean Squared = SQRT((Peak V * Peak V)/2)

Between ANY two phases we get an RMS voltage of 415V. When all three phases are joined at the power station, the mid point = ZERO V and is the Neutral that you use in your house.

3-phase has a higher voltage and can deliver more power to a machine (there are other advantages, particularly for motor design but that's enough for now)

I will try to post some pictures tonight to clarify a little

 

[Alf]

Now look what you've done, Tom. You've set him off again... :roll:

Only kidding Tony, something I've never been very clear on myself. That's what comes of having a chemist teaching you Physics

Cheers, Alf

 

[Bone]

Thomas,

Single Phase (1 ph) is the normal domestic supply in the UK, where you have one Live wire, one Neutral wire and an Earth.

Three Phase (3 ph) is a commercial electricity supply where there are three live wires (Red, Yellow, Blue), one neutral and an Earth.

The phases refer to the windings of the electricity suppliers generator. The windings on the generator are wound so that the electricity is produced out of phase in each winding, (120 degrees offset between windings).

In laymans terms, a domestic installation will have a single phase supply, which supplies the normal 13A sockets and light fittings in your home. A 3PH motor will not run off of this supply, hence the talk of 3 Phase converters and motor changing etc.
to allow commercial machinery to be used in a domestic situation.

Hope this is of some help, I have tried to make this fairly simple, there are lots more dull details that could be ventured into.

Bone

 

[Philly]

Is this still the Star Trek thread??????????? :lol: :lol: :lol:
Some great info there guys-cheers!
A humbled Philly

 

[Anonymous]

Hope this is of some help, I have tried to make this fairly simple, there are lots more dull details that could be ventured into.

Bone

DULL!! How can mathematics be dull? :shock: :shock: :wink:

 

[thomaskennedy]

riiiggghhhhtt..................

So simply i can use a single phase on the average plug socket!

Tony-If i can only understand a word of that :? :lol: i kind of got the drift though....

Bone-Thanks for er.. essentially... dumming it down for the "Non-Sparky"

Thanks again people!

Tom

 

[Midnight]

Tom...

simply put.... everything you're using right now is single phase. Industrial rated machines benefit from 3 phase simply because it gives more bang for yer buck, at the cost of needing bulky and moderately expencive switch gear and power distribution.

 

[Anonymous]

I have added an image to illustrate the description - might help but probably not


I can only apologise. I thought I had provided a basic and useful guide to a very complex subject but clearly misunderstood what was required.
Sorry, occupational hazzard I guess. I am usually expected to go into some great depth

Please post add 'Tony don't answer this' to questions of this nature in the future :wink:

 

[Midnight]

Tony..

now THAT'S better...

been working witht he stuffff for over 20 years an you had me wayyyyy confised too.... no idea what you were sayin.... but I knew whatchya meant..

:wink: