switchboard voltages 270/127V ?

[sahkotekniikka]

Can anybody explain backround for voltages used in a Mexican power plant:

Auxiliary transformer 480/270V Dyn (secondary winding star point solidly grounded)

Switchboard has voltage ratings: 270/127V

I could understand voltages 240/120V as used in US influenced countries but 270/127V? It cannot be printing mistake because 127V is nominal voltage for the country.

att

 

[busbar]

Is it possible the transformer-secondary and switchboard voltage are 220Y/127 volts?

460V - 220Y/127V is one standard transformer rating for Latin-American applications.

 

[sahkotekniikka]

Thank you "busbar" for your early reply.

I would assume that the switchboard nominal voltage is 220/127V instead of 270/127V. Then all other busbar voltages applied make sense.
The transformer ratio 480/270V might have misled the drawer? I just wonder why such ratio has originally been selected - to compensate high internal voltage drop? Or is that value wrong as well?

Thanks anyway.

att

 

[busbar]

North of Mexico, a standard system voltage is 480Y/277 volts, and does not represent a primary-to-secondary transformer rating. It designated nominal phase-to-phase and phase-to-neutral magnitudes {in this case--likely that of a 4-wire system serving the subject transformer primary.}

Presumably, the same logic applies in Mexico and “270” is in error. Another site visit may be in order, for accuracy’s sake.

A “slash” is typically reserved to separate ø-ø and ø-n labeled voltage ratings of a single wye-connected transformer winding.

A “dash” is the conventional means used on a label to separate transformer primary and secondary voltages.