Trying to understand 3 phase

[assegayer]

Hello everyone,
I am currently training in college and its my second year, we have just started on 3 phase topics.

I just wanted to ask what is 3 phase actually?
is it just a bigger consumer unit that can power more normal single phase circuits like 6 amp lighting etc and 32 amp rings?

and what are these 3 phase motors and all that talk

sorry if this sounds stupid but a friend recommended me these forums while he was training aswell.

 

[Marvo]

3-phase refers to the type of supply. There's 3 lives that are at voltages that are not in sync (120 degrees apart) which make up a 3-phase supply. There may or may not be a neutral as well.

If you have a 3-phase incoming supply and you want it to distribute it as single phase final circuits then you use any one of the lives and the neutral.

For the basics maybe start by reading the wikipedia article on 3-phase.

 

[trev]

Get this one a free pass into the trainee forum Andy please.

 

[trev]

Everybody breathe before replying and read his first sentence up to the first comma again.

 

[Marvo]

Get this one a free pass into the trainee forum Andy please.

We have a free trainee forum which I can give you access to if you're currently on a training course. Check out this thread and do the necessary then myself or the other Admin can give you access.

 

[assegayer]

Thank you guys for the replys. that would be very nice to go on the training forum i am just new to the forums and getting used to things

 

[trev]

Follow the link that Marvo provided, give the necessary information and you shall reach the trainee forum

 

[assegayer]

will do, thanks again

 

[ImpededLoop]

3-phase refers to the type of supply. There's 3 lives that are at voltages that are not in sync (120 degrees apart) which make up a 3-phase supply. There may or may not be a neutral as well.

If you have a 3-phase incoming supply and you want it to distribute it as single phase final circuits then you use any one of the lives and the neutral.

For the basics maybe start by reading the wikipedia article on 3-phase.

It's probably easiest explained by your tutor as putting it in writing could lead you to misunderstand how it works.

At the moment, you'll be used to 230V single phase AC electrical supplies. If you measure the potential difference (voltage) between the line (live) and neutral, you should get about 230V to 250V.

Electricity is produced from a generator which in simple terms consists of a magnet rotating past electrical coils. In a 3 phase generator the coils are located equally around the generator, so as Marvo says they are 120 degrees apart (3x 120 degrees = 360 degrees which is a full circle).

For 3 phase you have 3 line (live) conductors and sometimes a neutral, so 3 or 4 cables. If you measure the potential difference from any of the line conductors to neutral, the voltage will be 230V-250V - which is the same as single phase. If you then measure the potential difference between any two of the line conductors the voltage will be 400V-415V.

Three phase is used a lot and in your street 1/3 of the houses will be on each phase - ie 3 phases and neutral are run along the street but only one phase and the neutral is brought into your house.

This explanation is not very precise and the terminology is not perfect, but hopefully it gives you an idea of how it works.

 

[davesparks]

Why is this not taught at secondary school any more?

 

[assegayer]

impeed loop that was an excellent explanation truly..i actuallly understanded so much from that...i always seem to hear people saying it can be an unbalanced load or something like that when you split the 3 phases into seperate ones...whats that all about?

 

[ImpededLoop]

Why is this not taught at secondary school any more?

I did my work experience in 1993 and returned to school full of enthusiasm. I asked my physics teacher about 3 phase and he said we wouldn't need to know that for GCSE.......

 

[trev]

Why is this not taught at secondary school any more?

I never knew anything about phases, whether it be single or poly until I got into my apprenticeship.
O level physics didn't go into it

 

[baldsparkies]

Look at this link,
Three-phase electric power - Wikipedia, the free encyclopedia
Read it, and the many others you will find by internet searches.
Keep at it until the penny drops and you grasp the concept, ask your tutor at college for any reading he can give you, and remember the more you put in to your training the more you will get out.
Before you know it you will be telling us what 3 phase is.
Above all enjoy your learning because its a trade you will be learning for the rest of your life.

 

[ImpededLoop]

impeed loop that was an excellent explanation truly..i actuallly understanded so much from that...i always seem to hear people saying it can be an unbalanced load or something like that when you split the 3 phases into seperate ones...whats that all about?

OK, so think of the 3 phases as three single phase supplies to three houses (with neutral too).

House 1 (brown phase) is on holiday and is using 5 Amps of electricity.
House 2 (black phase) has the lights on and is watching TV and is using 20A of electricity.
House 3 (grey phase) is using the cooker, immersion heater and electric shower and is using 45A of electricity.

If everyone used exactly the same, the phases would be balanced, but they are not, so the phases would be described a inbalanced.

 

[trev]

I don't think we'll do anything but puggle his heed if we get into balanced loads now mate

 

[davesparks]

Blimey!
I did my GCSEs in 2003 and my physics teacher taught us AC theory from Faraday's first demonstrations up to single phase including the calculation of root-mean-square values and a basic explanation of three phase.

 

[ImpededLoop]

I don't think we'll do anything but puggle his heed if we get into balanced loads now mate

Yes, that's enough for now!

 

[assegayer]

OK, so think of the 3 phases as three single phase supplies to three houses (with neutral too).

House 1 (brown phase) is on holiday and is using 5 Amps of electricity.
House 2 (black phase) has the lights on and is watching TV and is using 20A of electricity.
House 3 (grey phase) is using the cooker, immersion heater and electric shower and is using 45A of electricity.

If everyone used exactly the same, the phases would be balanced, but they are not, so the phases would be described a inbalanced.

so is it bad to be inbalanced? by the way guys i really love learning this trade i find it so interesting for some reason, and i continuously thanks everyone on forums like this who help us new guys out,, Thank you to everyone

 

[ImpededLoop]

Blimey!
I did my GCSEs in 2003 and my physics teacher taught us AC theory from Faraday's first demonstrations up to single phase including the calculation of root-mean-square values and a basic explanation of three phase.

I should of gone to your school... I'd have lapped that up as I was fascinated with electricity! (still am)

 

[trev]

Blimey!
I did my GCSEs in 2003 and my physics teacher taught us AC theory from Faraday's first demonstrations up to single phase including the calculation of root-mean-square values and a basic explanation of three phase.

I did my school exams (CSEs and O#Levels) (google them, they were different ) quite a while before 2003 mate

 

[ImpededLoop]

so is it bad to be inbalanced? by the way guys i really love learning this trade i find it so interesting for some reason, and i continuously thanks everyone on forums like this who help us new guys out,, Thank you to everyone

My last post for tonight... Yes, if you think of the generator like a wheel, it spins well when the weight is balanced. If you strap a huge lead weight to one side of your bike wheel, it won't spin equally. That is similar to loading one coil (phase) more than the others.

Do a bit of research on the internet as there should be some diagrams that help to explain it more clearly than I can in words.

If you're as interested as you say, you'll make a very good electrician. Good luck

 

[assegayer]

My last post for tonight... Yes, if you think of the generator like a wheel, it spins well when the weight is balanced. If you strap a huge lead weight to one side of your bike wheel, it won't spin equally. That is similar to loading one coil (phase) more than the others.

Do a bit of research on the internet as there should be some diagrams that help to explain it more clearly than I can in words.

If you're as interested as you say, you'll make a very good electrician. Good luck

Thank you mate have a good night, i literally love electrics with no exaggeration especially when that moment comes and u fully understand a topic

 

[trev]

Thank you mate have a good night, i literally love electrics with no exaggeration especially when that moment comes and u fully understand a topic

Don't get too wrapped up in it though. There's these things called "girls" (or "boys" (depending on which way the land lies and thats got nowt to do with me, nor will I judge you either way)) and "beer"
Both things can be fun. Never neglect the fun side of life.

 

[assegayer]

Don't get too wrapped up in it though. There's these things called "girls" (or "boys" (depending on which way the land lies and thats got nowt to do with me, nor will I judge you either way)) and "beer"
Both things can be fun. Never neglect the fun side of life.

hahahahaha, believe me girls are not something unoticed and can be real fun as you said

 

[PEG]

Blimey!
I did my GCSEs in 2003 and my physics teacher taught us AC theory from Faraday's first demonstrations up to single phase including the calculation of root-mean-square values and a basic explanation of three phase.

I did my "O" level in Physics,a good few years before,and we covered all those areas,including making up Cells,rectifiers and generating rigs. Some teachers encouraged deviating from what was probably the standard curriculum...including allowing me to bring in the jacobs ladder spark generator i made,from an industrial pressure washer burner ignition transformer...plugged straight in the desk socket outlet...risk assess THAT today! :bobby:

 

[Engineer54]

I did my school exams (CSEs and O#Levels) (google them, they were different ) quite a while before 2003 mate

Did you mean GCE's?? Because that's all that was around in my day. And Yes they were different, and they didn't keep having to change the goal posts every year to boost political pass rates!!

 

[davesparks]

so is it bad to be inbalanced?

It can be in some situations.

I often work with generator supplies for festivals/outdoor events etc. In this situation the general rule is to never let a generator's load be more than 30% out of balance. I have seen sites where people have not followed this rule and damaged some rather expensive generators and spoiled the events somewhat.

However for a regular grid fed supply then a complete imbalance won't even be noticed at the level of the national grid.

 

[davesparks]

Did you mean GCE's?? Because that's all that was around in my day. And Yes they were different, and they didn't keep having to change the goal posts every year to boost political pass rates!!

I thought GCE was A-level? At least that's what it says on my A-level certificates.

 

[trev]

Did you mean GCE's?? Because that's all that was around in my day. And Yes they were different, and they didn't keep having to change the goal posts every year to boost political pass rates!!

No, CSEs were the lower ones and GCE O Levels were the higher level ones. After that you had A levels if you were staying on for 6th form but I left and got my apprenticeship so went down the C&G route.