Split phase

[JD6400]

Hi Tony , it was not so much it being an s-type ( although prudent for discrimination ) , it was more the fact that it being a dairy unit he will need an upfront rcd of 300mA or less to protect the whole installation .
And as it will almost undoubtedly need to be TT ( as I have never yet come across a holding that has had the designed considerations for it not to be ) , I would expect to see it double as a point of main isolation as well .

Sorry I should have explained myself better the first time

 

[GEOFF S]

This is quite simple, its classed as a single phase three wire system. In effect two phases 180 degree apart, the neutral point being at the center between the two phases.

They cant be in phase, draw out two vectors with the same direction and magnitude.

Cheers

 

[Knobhead]

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

 

[GEOFF S]

There are 2 sine waves, The positive of teh first sine is in phase with the negative of the second sine.

Cheers

 

[Knobhead]

This is quite simple, its classed as a single phase three wire system. In effect two phases 180 degree apart, the neutral point being at the center between the two phases.

They cant be in phase, draw out two vectors with the same direction and magnitude.

Cheers

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

 

[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