3 Phase presentation

[Iain123]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]HiForum[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Thisall came about as I am looking to use a 3 phase motor with variablefrequency drive/VFD and started to get confused with 3 phasevoltage.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]MyVFD uses one phase and neutral on the input and presents 3 phases onthe output in Delta (no neutral). At first I though I could simulate400V 3 phase star with my VFD.[/FONT]

W[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]henI though of 3 phase I always though of a cupboard with a 400Vwarning.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Iam used to domestic 230V single phase and neutral so the 3 phase Starpresentation is just another 2 phases from the DNO and would lead tothe 400V warning (star).[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]HoweverI have found most motors run in delta (balanced load) so at 230V perphase its still 230V overall so only a 230V warning would be requiredon the cupboard, not what I expected for 3 phases![/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Foundsome 3 phase motors have 230V/400V name plate so looks good for myVFD in the Delta 230V rather than the star 400V presentation which myVFD cannot produce.[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Howeveralso found a lot of motors marked up as 400V/690V. So that's 400V perphase not the 230V I expected?[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]400Vin Delta and 690V in Star now that does not match with my idea of 3phase Star being 400V all these years?[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Irealise 3 phase input VFD are common and would allow 3 phase 400VDelta or 690V Star (after more reading).[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Sothough out of interest I thought would look at a DNO form to order a new 3phase supply, from what I had found above I though the DNO would askwhat Voltage I wanted 230V/400V/690V and if I wanted it presented inStar 400V/690V or Delta 230V/400V, but they only seemed interested inthe load current.[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Somy question how does a DNO present 3 phases at low voltage is itStar/Delta 240V, 400V or 690V or all of the former.[/FONT]
[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Orare transformers used on site to convert the DNO Star 400V input toget the required presentation?[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Alsoif the supply is in Delta then RCD type devices would not work asthere's no neutral to monitor?[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Thanksfor taking the time to read my long post[/FONT]

[FONT=Verdana, Arial, Tahoma, Calibri, Geneva, sans-serif]Iain[/FONT]

 

[telectrix]

don't get confused between line voltage and phase voltage. if you have a 400V 3 phase supply, the line volts are 400, but the phase volts are 230. oase.elta, so thast the voltage across each winding is 230V in either c you run in star, on 230V you run ib d

 

[Darkwood]

You are trying to look at too many area's here at once and getting yourself confused.

The 400v/690v motor is commonly known as a star/delta motor and can be useful in relation to using a star/delta starter to limit inrush current on start-up where you have it configured in star (690v) but input 400v to get the motor turning then automatically change over to delta (400v) at a calculated changover time, this means larger motors can be started without massive current surges.

The 400v/230v motors are commonly known as duel voltage motors and more than likely what you will be given if you bought a standard inductive motor, they are ideal if you lack 3phase supplies as you can feed an inverter with 1ph and get 230v 3ph out thus running a 3ph motor in delta in this case on a single phase supply, the star config allows the same motor to run on 3ph 400v.

If you ask for a supply from the DNO be it new or an upgrade then the vast majority of the time it is assumed and you will get either sngle phase 230v or polyphase 400v dependent on your requirements. Only very large industries with massive energy needs will see other voltages used and not something your average spark will ever come across.

 

[Iain123]

Hi Darkwood

Thanks for your comments, things are not as complicated as I thought they might be.

I now remember reading about the star delta starter, but did not realise the Star (690v) was actually the normal 400V 3ph.

"The 400v/690v motor is commonly known as a star/delta motor and can be useful in relation to using a star/delta starter to limit inrush current on start-up where you have it configured in star (690v) but input 400v to get the motor turning then automatically change over to delta (400v)"

But how do you get Delta 400V from a star 400V 3ph supply (230V between line and neutral and 400V between phases) a star delta transformer?

thanks
Iain

 

[Darkwood]

You are confusing yourself... its the motor winding configuration which changes not the supply, when we say a motor is connected in star or delta it has nothing to do with the supply source its how the windings are arranged inside the motor, the 6 terminals and the arrangement of the shorting links defines how the motor is connected, if you have a star/delta starter on a 400/690 motor then no links are connected and instead 6wires are run to the starter which automatically changes the arrangement from a star to delta when it is started.

 

[Iain123]

Hi Darkwood

I think a lot of my confusion has come after looking at VFD and other converters. At first I though a single ph input VFD could produce a 400v delta or star output.

Got a bit more understanding of single ph input VFD and their 230v delta output, big error I then transferred this to 3ph supplies (and 3ph input VFD) and they also only became 230V in delta and 400V in star output rather than the correct 400v for both star and delta.

Not having really having worked with 3ph or 3ph motors has not helped, so thanks to everone for their help.

iain

 

[snowhead]

Got a bit more understanding of single ph input VFD and their 230v delta output,

At first I though a single ph input VFD could produce a 400v delta or star output.

The VFD output becomes a supply, the same as it would be from the DNO , so it doesn't produce Star or Delta, that's specific to the load connections.

You choose whether to connect the VFD to the load in Star or Delta.

 

[Darkwood]

Hi Darkwood

I think a lot of my confusion has come after looking at VFD and other converters. At first I though a single ph input VFD could produce a 400v delta or star output.

Got a bit more understanding of single ph input VFD and their 230v delta output, big error I then transferred this to 3ph supplies (and 3ph input VFD) and they also only became 230V in delta and 400V in star output rather than the correct 400v for both star and delta.

Not having really having worked with 3ph or 3ph motors has not helped, so thanks to everone for their help.

iain

The shouldn't think of the output of a drive as star or delta, it is commonly at full speed either 3ph 400v output or 3ph 230v output, motor ratings vary with regards to input voltage and thus winding arrangements so where one motor may require 3ph 400 with its windings arranged in delta another motor may require the same voltage but with the windings arranged in star.

You need to forget about the supply to the motor as a star or delta and treat the arrangements of the windings of the motor as the key factor for what voltage can be connected.

Take a duel voltage motor - 230v Delta / 400v star.

If your VSD outputs 230v 3ph then you arrange the motor windings in a delta formation by using the shorting links in a certain arrangement on the motor terminals.
If your VSD outputs 400v 3ph then you arrange the motor windings in a star formation again by using the shorting links in a different arrangement.

It is wrong to think or say the drive is outputing star or delta just because its voltage may be common to a certain motor winding arrangments so try forget the supply source be it a drive or DOL as been what classes it as star or delta and start thinking on the lines of the load connections itself that determine whether you call it connected in star or delta.

 

[Iain123]

I think it was the lack of a neutral out of the VFD that lead me to believe it was Delta only supply.
I now realise a two shorting links between w2 u2 and v2 on the motor can be used to adjust the motor windings to be driven in the Star arrangement.

 

[Darkwood]

I think it was the lack of a neutral out of the VFD that lead me to believe it was Delta only supply.
I now realise a two shorting links between w2 u2 and v2 on the motor can be used to adjust the motor windings to be driven in the Star arrangement.

Whether the motor is star or delta arranged you don't have a neutral....