How do you identify step up or step down transformer from phasor diagram?

Answer 1

Number of turns

Answer

I assume that you have a phasor diagram of a transformer, and wish to identify the primary phasors and the secondary phasors?

For a three-phase transformer, this is fairly straightforward, provided the usual procedure for drawing a phasor diagram has been followed. Whenever you start to draw anysort of phasor diagram, you usually start by selecting a phasor of reference and draw that in the horizontal positive direction. For a three-phase transformer, the phasor of reference is usually the primary phase voltage A (or however else it is identified: R, red, or whatever). The remainder of the primary phase voltages are then drawn, enabling the primary line voltages to be constructed (which, in the case of a primary delta are the same as the primary phase voltages!). So if you can identify the phasor of reference, then you have identified the primary-winding phasor diagram. As the primary and secondary voltages are not usually drawn to scale, relative to each other, you can't assume a turns ratio from the phasor diagram. The labelling might also help, as high-voltage phase and line voltages are identified by upper-case letters, while low-voltage phase and line voltages are identified using lower-case letters -but, remember, these identify high- and low-voltages, not which is primary and which is secondary (primary winding is connected to supply/secondary winding is connected to load).

For single-phase transformer, the phasor of reference is the flux set up in the magnetic circuit, and voltages/current phasors are drawn relative to this. In this case, the primary line and induced voltages are usually identified as V1 and E1, and the secondary induced voltage as E2 (sometimes, the Es and Vs are interchanged). Again, the lengths of the primary and secondary voltages are not necessarily to scale relative to each other.