11000/433 tx

Back in the dark ages, when Her Majesty's Volts came at a pressure of 240 nominal, the transformer end of the street was often set to the 250V tap, so that the folk at the far end never got less than 220, even in winter.

 
However, as far as I know, no-ne ever called that 433, though of course within rounding, it was. Other figures, 440, 420 and 415 were common, and since harmonization, 400.

All but the smallest of Tx have taps, typically in steps of 2.5%,  anyway, as the 11kV side is not that constant across the country either !

There is a 'roots of 3; trend on LV, so 230/400/690/1k3 are all LV side standards. but the HV (does anyone say MV?) stuff was not so simple  3.3/ 6.7/ 11/33

I agree it seems an odd choice, 

Mike,

Yes 433V will be the nominal voltage and the transformer will likely have a 'De-energised Tap Changer' (DETC), a mechanism that once the transformer is de-energised and isolated, can be used adjust the voltage by changing the selected tap. The details of the number of taps and tap voltages will also normally be included on the nameplate. 

433V is a no-load nameplate rating chosen to allow for on-load regulation drop-back to ~400-415V, not a live system voltage, and not inconsistent with 400/415V DNO practice, it's the same system, described from a different point (transformer design rating vs. network operating voltage).