An explanation of Phases?

[Floody]

Ok so I hear quite a lot the term 'single phase'. & '3 phase'.

Can anyone elaborate on what this means and possibly give some examples?

Thanks

 

[Baker1988]

hi ya floody you will go over this in depth at college but ill just give you a quick explanation

basically single phase means 1 line conductor (would of said 1 live conductor but they class neutral as a live conductor now) which is 230v between live and earth this is used most in domestic houses as lights and every thing are single phase.

then there is 3 phase this basically means there are 3 line conductors which will 400v if you measure between the 3 phases but each individual phase still has 230v this is most commonly used in industrial and commercial for huge machines and motors.

electric is generated at the power station at 3 phases through induction of the generator moving 3 coils(the 3 phases) through a magnetic field which creates the electric (this is only basic could go into more detail but had a few beers) useually generated at 25kv then it the voltage is upped through a step up transformer to either 400kv or 235kv and is distributed to your area then stepped down and your house is connected to one of the phases and if it went to a industrial it would get all 3 phases.

there is 2 different type formations of 3 phase there is star and delta star you would gives you a neutral and delta is used as it does not need a neutral cos of the formation.

sorry if that makes no sence as i said i had a few beers and didnt proof read it haha hope it helps

 

[Floody]

Cheers Baker, I get a better picture now =) I could have never wrote that after a few beers. Thats worth a definate Thanks

 

[not_today]

so single phase carries less current than 3 phase?

 

[Baker1988]

Your welcome pal its only a basic explination

so single phase carries less current than 3 phase?

No mate it doesnt really meen that obviously 3 phase circuits usually use more current but voltage is basically pressure it pushes the current so single phase and 3 phase could carry the same ammout think of it like water current is the electric and voltage is the pressure that pushes the water around and resistance is a kink in the water pipe

 

[trev]

so single phase carries less current than 3 phase?

Usually, yes but as with everything there are exceptions. Baker you're a star mate, you saved me a load of typing

 

[Happy Jack]

Having a bit of a night of it tonight, I do apologise. Quite a simple observation has left me wondering.

If we consider a 45A single-phase load and a balanced 45A three-phase load, star, assuming both with a purely resistive load, does the maths resolve as follows?

45A SP -
kVA
= (UI x PF) / 1000
= (230 x 45 x cos 1) / 1000
= 10.35kVA

45A TP -
kVA
= (√3 x Ul x Il x PF) / 1000
= (√3 x 400 x 45 x cos 1) / 1000
= 31.17kVA

So via the TP load Il for each phase is 45A? So rearranging for Il and solving for a TP load with the same VA rating as the SP load, 10.35kVA we get -

Il
= kVA / (√3 x Vl x PF)
= (10.35 / (√3 x 400 x cos)) x 1000
= 14.9A

So the TP load here is 14.9A for each phase?