3 phase motor wiring

[matt1e]

I'm not talking about ratings, I'm talking about what happens with a star delta starter when it starts up. Initially the motor is connected star which has 230v applied across each coil, phase to the star point (400 / root 3).
It then switches to delta and each coil is connected directly to two phases each which is 400v per coil.
All figures I quoted are RMS.

It's your description that's confusing spark123 (I'm not saying it's incorrect)
Yes if you were to measure between each phase and the star point you would get 230v hence the common motor rating of 230/400

Which is why the star rating of the motor becomes 690v with 400v rated windings
But at the end of the day you are still feeding the motor with 3ph 400v

The rating of each winding never changes and is always the delta figure given on the plate

Where does 680V come from??

I presume (but obviously may be wrong) that it's meant to be (400 x √ 3) (i.e. the between-phase voltage of a 400V phase-N 3-phase supply) - but that should be about 692.8V, not 680V.

Kind Regards, John
Edit: crucial missing bit added!

I think that is meant to be divided by, not multiplied by. For this very same reason your normal street 3 phase transformer gives out 400v between phases and 230v between each phase and neutral.

You are both correct,
Johns working out gives delta > star which he gave the correct answer to
Your working out is star > delta which also gave the correct answer
If you catch my drift

If one simply has a standard 230V/400V 3-phase supply, then, as has been said (amidst all the confusion!), the motor connection situation is incredibly simple. One starts with star connection, which gives 230V across each winding, and then switches to delta, which gives 400V across each winding. Full stop. All references to 680V/690V (or 400/690V 3-phase supplies) are then a completely irrelevant distraction, corresponding to nothing in the real world of a motor fed from a standard 230V/400V 3-phase supply.

Kind Regards, John

Not so John 400/690 rated motors are very relevant in the 230/400v real world as in every star/delta started motor you will come across and every large motor over 4 kw
Hardly a completely irrelevant distraction

3ph 690v supply's are used extensively offshore and in large industry too btw

Matt

 

[ban-all-sheds]

Once at speed the rotor will nearly be at the same speed as the stator

So the rotor will be nearly stationary?

 

[ricicle]

Once at speed the rotor will nearly be at the same speed as the stator

So the rotor will be nearly stationary?

Sorry - nearly at the same speed as the stator's rotating magnetic field.

 

[JohnW2]

If one simply has a standard 230V/400V 3-phase supply, then .... All references to 680V/690V (or 400/690V 3-phase supplies) are then a completely irrelevant distraction, corresponding to nothing in the real world of a motor fed from a standard 230V/400V 3-phase supply.

Not so John 400/690 rated motors are very relevant in the 230/400v real world as in every star/delta started motor you will come across and every large motor over 4 kw. Hardly a completely irrelevant distraction. 3ph 690v supply's are used extensively offshore and in large industry too btw

I still stick by what I said - that IF one has a standard 230V/400V supply, then all this talk about 690V is inappropriate and irrelevant. There is no way that you will get 690V between anything and anything else from such a supply.

If you are telling me that, offshore or wherever, there are 400V/690V supplies (i.e. each phase 400V to neutral, 690V between phases), then what you say would obviously be right in relation to that supply (i.e. delta connection of the motor to such a supply would put 690V across each winding) - but is there any likelihood that the OP has such a supply?

Kind Regards, John

 

[matt1e]

I still stick by what I said - that IF one has a standard 230V/400V supply, then all this talk about 690V is inappropriate and irrelevant. There is no way that you will get 690V between anything and anything else from such a supply.

Kind Regards, John

And I still beg to differ
The thread started off with a query concerning motor terminal configurations
There are many sparks who are unsure too due to lack of training/experience
So when I get a phone call asking for advice when swaping out motors this is what I tell them

Look at the voltage rating on the plate,Does it say
230/400 or thereabouts
Or
400/690 or thereabouts
If the first connect star if it is being supplied by 3ph 400v
Delta if it being supplied 3ph 230 (we almost never come across this but some on here may)
If the later then connect it delta if it is being supplied by 3ph 400v

If you think that the second number (690) is irrelevant on the plate John then so be it, you have not had much experience with motors I guess
e-mail the motor manufacturers if you don't agree how motor plates are marked up
Put it this way if I give you 400v as one of the voltage ratings on a motor but don't give you the other, then tell me how to configure the links Star or delta?

Matt

 

[JohnW2]

I still stick by what I said - that IF one has a standard 230V/400V supply, then all this talk about 690V is inappropriate and irrelevant. There is no way that you will get 690V between anything and anything else from such a supply.

And I still beg to differ

I'm getting very confused ....

The thread started off with a query concerning motor terminal configurations ... Look at the voltage rating on the plate,Does it say
230/400 or thereabouts Or 400/690 or thereabouts

Exactly. The plate we have been shown clearly indicated 240V/415V. In all of the pages of this discussion, you are the only person who has ever mentioned 680V or 690V.

If you think that the second number (690) is irrelevant on the plate John then so be it, you have not had much experience with motors I guess

If the 690V figure appeared on the motor plate, and if the OP had a 400V/693V supply, then it would obviously be very relevant. However, the plate doesn't mention 690V and I very much doubt that the OP has a 400V/690V supply. That's what I mean by 'irrelevant' (to this discussion).

Kind Regards, John

 

[matt1e]

you don't give up do you John?

The thread started off with a query concerning motor terminal configurations ... Look at the voltage rating on the plate,Does it say
230/400 or thereabouts Or 400/690 or thereabouts

Exactly. The plate we have been shown clearly indicated 240V/415V. In all of the pages of this discussion, you are the only person who has ever mentioned 680V or 690V.

Lets get a few things straight
The ops question was answered correctly for him on the first page fourth post by RF Lighting,
this was then followed by bickering/discussion until the third page where

ericmark made probably the best post in the entire thread which also contained this sentence BTW

It would seem there is some inexperience out there. Small motors normally would 230 volt delta and 400 volt star. (Allows use of inverters) Larger motors are 400 volt delta and 695 volt star although never designed to run star the configuration just helps starting.

but just for you I am going to concede that Eric said 695 whereas I said 680/690 so that makes you right and me wrong as it will save you mentioning it, happy?

If you think that the second number (690) is irrelevant on the plate John then so be it, you have not had much experience with motors I guess

If the 690V figure appeared on the motor plate, and if the OP had a 400V/693V supply, then it would obviously be very relevant. However, the plate doesn't mention 690V and I very much doubt that the OP has a 400V/690V supply. That's what I mean by 'irrelevant' (to this discussion).

well when you go back to page three to check out erics post look at the fifth post before his and you will find the op has asked another question

My brother has just purchased a large inverter to run a decent size lathe, we're struggling to identify L1, L2 & L3 at the moment and haven't attempted to connect it yet. I had no idea that he'd need to alter the motor's terminals to delta, is this usual practice?

how do you know what the plate says on that, because he hasn't posted any details on that, and as for the relevancy of my posts to the ops questions, I'd say they were more relevant than the mention of

Ohm's and Kirchoff's Laws

My A-Level Physics Course was 1964-1966

If, like me, one lives in Bucks,

Not quite. 400V RMS has a peak of (400 x √ 2), as you say about 566V, but the peak-to-peak would then be 1132V. However, we're not talking about either peak or peak-to-peak - all the figures being discussed are RMS.

What I'm talking about is the relationship between the RMS (or peak if you wanted) phase-neutral voltage and phase-phase voltage in a 3-phase supply. The latter is √ 3 times the former - hence,for example, the standard UK supply has a nominal voltage of 230V between each phase and neutral, but just under 400V (230 x √ 3) between any two phases. As I was saying, if there were 400V between each phase and neutral, the voltage between any two phases would then be (400 x √ 3), which is about 692.8V.

my younger daughter, who got 5 A-grade A-Levels, a First Class Hons degree and various higher degrees and qualifications

etc etc
Or are you saying it is ok for you to engage in conversation thats irrelevant to the topic

Matt

 

[JohnW2]

well when you go back to page three to check out erics post look at the fifth post before his and you will find the op has asked another question

Fair enough. Amidst all the 'bickering', I actually missed that 'another question' and therefore assumed that all the subsequent discussion (and further bickering) related to the 'original OP'. My apologies

Or are you saying it is ok for you to engage in conversation thats irrelevant to the topic

Personally speaking, I regard it as OK for anyone to engage in any sort of discussion they want, no matter how irrelevant to the topic - as you point out, with my history I could hardly say otherwise However, to be fair, I never said, or even implied, that there was anything wrong ('not OK') with your having introduced (what I, incorrectly, thought was) irrelevent material - I merely pointed out that I thought it was irrelevant. I know that some things which go on in these forums tend to make one a little defensive, but it isn't the case that every 'negative' comment constitutes some sort of 'attack' or criticism. If, in my working life, I felt 'attacked' every time someone disagreed with me, or felt that some point I had made was 'irrelevant', I would have become a nervous wreck decades ago!

Kind Regards, John

 

[bhm1712]

The new motor is not actually intended for 230/240 volt single phase as you have been lead to believe. It is a 3 phase motor like the old one. The data plate will tell you what voltage is required for star and for delta, and it will also state the current draw for each. With a star delta starter system there are no links between winding terminals, and there will be 6 cables at the motor.

The only way this can be used on a single phase supply is to do as already mentioned and use a single phase inverter drive /VFD/VSD whatever you want to call them.

Compare the data plates, and you will probably find that the links will need to be connected the same as your old motor to run on the 3 phase voltage you have.