Split phase

[ElectroChem]

I’ve been avoiding posting any of my drawings here.

I knew I hadn't quite grasped the point of distinction Tony. The two live wires are IN PHASE (they are driven by the same winding and reach their maximum values simultaneously) but of OPPOSITE POLARITY (the center tap means that relative to earth one will be +ve and the other -ve). Have I got it?

 

[GEOFF S]

I knew I hadn't quite grasped the point of distinction Tony. The two live wires are IN PHASE (they are driven by the same winding and reach their maximum values simultaneously) but of OPPOSITE POLARITY (the center tap means that relative to earth one will be +ve and the other -ve). Have I got it?

Yes you have it, two sine waves, both pass through 0 at the same time, the polarity is 180 degrees out of phase.

If you look on a oscillascope you would see the positive of one sine reach its maximum at teh same time as the other meets its negative max. The two sine ways give you the voltage. If they were in phase the two sine ways would be superimposed, the area of the sine would not change.

Cheers

 

[GEOFF S]

Read up on transformer phase and vector angles and then tell me I'm wrong.

Do we need to consider the HV/LV displacement of a Tx to understand what voltage and current will exist in a LV polyphase system?


Cheers

 

[GEOFF S]

I knew I hadn't quite grasped the point of distinction Tony. The two live wires are IN PHASE (they are driven by the same winding and reach their maximum values simultaneously) but of OPPOSITE POLARITY (the center tap means that relative to earth one will be +ve and the other -ve). Have I got it?

Yes that is correct, if you looked on a oscillascope you would see the two sinewaves, the positive of one meets its maximum at the same time the other sine meets its maximum negative.

Cheers

 

[Knobhead]

Do we need to consider the HV/LV displacement of a Tx to understand what voltage and current will exist in a LV polyphase system?


Cheers

Yes, the primary makes a difference to phase shift for poly phase transformers. I’ve written an article about all kinds of transformers on another site.

The commonest type of 3 phase unit is vector group Dyn11 where the secondary leads the primary by 30°. The 11 comes from the clock position.
Vector groups are based on the physical angle not the output waveform. Hence the centre tapped being 0°.

 

[GEOFF S]

Yes, the primary makes a difference to phase shift for poly phase transformers. I’ve written an article about all kinds of transformers on another site.

The commonest type of 3 phase unit is vector group Dyn11 where the secondary leads the primary by 30°. The 11 comes from the clock position.
Vector groups are based on the physical angle not the output waveform. Hence the centre tapped being 0°.

Hi Tony

Out of intrest, your diagram uses kirchoffs cxurrent law to determine the neutral current, im not aware of the having to condider the primary/secondary winding connections, equally when calculating voltages within the LV system i have never taken winding displacments into account.

Could you explain how you take into account the phase displacment in your calculations.

Paralell Tx require phasing(circulating currents), and 30 degree phase shift nulifies third harmonics, im interested into how your calculations include primary/secondary phase displacement.

Cheers

 

[Knobhead]

PM sent

 

[Knobhead]

Yes you have it, two sine waves, both pass through 0 at the same time, the polarity is 180 degrees out of phase.

If you look on a oscillascope you would see the positive of one sine reach its maximum at teh same time as the other meets its negative max. The two sine ways give you the voltage. If they were in phase the two sine ways would be superimposed, the area of the sine would not change.

Cheers

To play devils advocate, what do you get if you place the oscilloscope on L[SUB]1[/SUB]→L[SUB]2[/SUB]?

 

[Barry White]

 

[GEOFF S]

Thats exactly what you will see.

Cheers

 

[Silly Sausage]

Thats exactly what you will see.

Cheers

On two channels.
I think Tony means L1 & L2 on ONE channel!

 

[Knobhead]

Thats exactly what you will see.

Cheers

Wrong!

Stop playing the smart arse. Learn about transformer phase and vector diagrams.

 

[davesparks]

Well isn't that pretty! I think it's going to peak at a bit more than 240V though.
You could easily create that trace on an oscilloscope screen, but it's not an accurate representation of what is going on.

 

[Knobhead]

I think √2 comes in to it somewhere doesn’t it Dave?

I don’t think we’re wrong, but you never know.

240V RMS = 339.41V peak→base line.

 

[ElectroChem]

240V RMS = 339.41V peak→peak.

Wouldn't the peak-to-peak be twice that Tony?

 

[Barry White]

Well isn't that pretty! I think it's going to peak at a bit more than 240V though.
You could easily create that trace on an oscilloscope screen, but it's not an accurate representation of what is going on.

was a rough representation so I used RMS voltages it was my representation of what I thought I would see would you like to draw it please

 

[Knobhead]

Wouldn't the peak-to-peak be twice that Tony?

I was altering it while you posted

 

[Knobhead]

was a rough representation so I used RMS voltages it was my representation of what I thought I would see would you like to draw it please

You used peak→base line which would give 169V RMS.

I did the drawing years ago and it's on photobucket for use elsewhere.

 

[ElectroChem]

I was altering it while you posted

Gotta be quick around here, there's always some smart-arse apprentice looking to score a point off the boss!

 

[Knobhead]

Gotta be quick around here, there's always some smart-arse apprentice looking to score a point off the boss!

True, many years ago I was the apprentice. I also got my arse kicked when I got things wrong.

I worked with some real old barstewards, learnt a lot from them though.
Up until about ten years ago I still phoned my old foreman for a chat. At 85+ he told me where to look for a fault in a 2000HP motor he’d never even seen. He was spot on the mark.

Can’t phone him now, R.I.P. Ted