Line Current in a 2 phase transformer

[anoor]

I am a graduate engineer and have been set a small task to work out the current (primary side) in a 2 phase 30kVA 415:650 transformer. The 2 phases have been utilized from a 3 phase source and are hence 120 degrees out of phase.

I understand had it been a 3 phase 30kVA transformer I could calculate my current by 30kVA / 415 / route*3 = 42A.

If it was a single phase then simply 30kVA / 415 = 73A.

However if I am only using 2 phases from a 3 phase source yet still need to produce 30kVA of power, how do I calculate the line current?

Thanks in advance.

 

[Windadct]

Hello Anoor and Welcom :

I think we will need a little more info -- you are describing a 30KVA trans but the Voltage is 415:650? And by 2 phase - is the secondary like an Open delta - or some other arrangement? Best bet is to post a diagram of the nameplate info.

Lastly -It is not clear if you are actually working on this physically? In the USA you would not be a " qualified person" - working on this is extremely dangerous, does your University have a qualified electrician that you can work with?.

 

[anoor]

I am not working on it physically its just in theory.

Maybe its my poor explanation ill try again!

If I have a standard 230/400V switchboard and want to connect a transformer it would normally be a 3 phase (400V) or single phase-neutral (230V). However if I wanted to connect a transformer to phases L1 & L2, instead of the neutral (giving me 400V). What would my line current be on the primary and how would I calculate it? I apologise if my ignorance doesn't allow me to adequately suscribe the situation! I have attached a pdf showing an extract of the schematic, I hope this helps!

Thanks again.

 

[Windadct]

OK the diagram help a little. If you think of the "phase" as between the lines, as in L2-L3 - this is really a single phase question - IN the USA we refer to this as Line to Line. In this case there is no phase angle - so the Line current is KVA/V - also the transformer input or out put is only a 2 wire device - right?

The lines L2 and L3 are only out of phase 120Deg relative to the neutral

 

[alphy]

I would approach this problem by first understanding the basics of a 2 phase transformer. A 2 phase transformer is a type of transformer that has two separate primary and secondary windings, each receiving a different phase of the input power. The two phases are typically 90 degrees out of phase with each other.

To calculate the line current in a 2 phase transformer, we can use the formula:

Line Current = kVA / (2 x Voltage x Power Factor)

In this case, we have a 30kVA transformer with a primary voltage of 415V and a secondary voltage of 650V. Assuming a power factor of 1 (which is ideal), the calculation would be:

Line Current = 30kVA / (2 x 415V x 1) = 36.14A

This means that the total line current on the primary side of the transformer would be 36.14A, which is lower than the 42A calculated for a 3 phase transformer with the same kVA rating.

It is important to note that the 120 degree phase difference between the two phases does not affect the calculation of line current in a 2 phase transformer. This is because the two phases are still contributing to the total power output of the transformer.

In summary, to calculate the line current in a 2 phase transformer, we use the formula kVA / (2 x Voltage x Power Factor) and take into account the voltage and power factor of the transformer.