Delta Wye Connection in Transformer

Can U please explain me from where u get the factor 1/sqroot3 as a reducing factor.Also I am mot clear if phase A is broken and its voltage become 0 in such case how we get the close delta phasee diagrame.Why not open delta ? Waiting for reply.

1/sqrt(3) is the ratio: (red)AC/(black)AC. If you draw a vertical line through Black A, red A, to the base you have two triangles with the same base. The ratios of the hypotenuses is cos(60)/cos(30) = 1/sqrt(3).

If phase A were open there would only be current between B and C, so on the output only one phase would be present, phase BC. Phases AB and CA would be zero.

If phase A were open there would only be current between B and C, so on the output only one phase would be present, phase BC. Phases AB and CA would be zero.
Corrrection: The BC voltage would also go through the CA and AB windings. So the outputs CA and AB would be 1/2 magnitude and opposite in phase with the BC.

1/sqrt(3) is the ratio: (red)CA/(black)CA, or (red)AB/(black)AB. If you draw a vertical line (blue) as shown, you have two triangles with the same base with angles at C of 30 and 60 degrees. The ratios of the hypotenuses is cos(60)/cos(30) = 1/sqrt(3). (cosine = adjacent/hypotenuse)

I like yr explaination it will be very helpful to me.

Thanks & Regards

Transformers main functionality is based solely on the winding "Turn Ratio" and "number of electromagnetic flux induced then cut or interrupted by its windings, while its rated capacity will mainly depend on the (AWG) size of magnet wire used and corresponding core size.

Therefore when one of the primary connections is broken, the net effect will be directly and proportionately reflected to the corresponding secondary winding(s).

Only 2 secondary phases, a and c, remain. The single-phase apparatus supplied from aN and cN will be supplied as usual. The bN supplied installation will be blackout.

Three-phase motor will not start but if it already started the current in phases a and c will be 73% more and the power produced by motor will be only 70% than when was three phases supplied [due to copper losses].See[also]:

IEEE Std 242-2001 ch. 10.3.3.2 Single phasing.

Is that before or after the appropriate circuit protective device has disconnected it?