400 kV and 765 kV are not the muliple of 11 kV . Hence it
is not true that the transmission voltage must be a muliple
of 11 kV.
It is the traditional voltage at which the electrical
equipments are designed and the switchgear manufacturing
companies are not doing any R&D work. They are
manufacturing the switchgear at the same standard voltage
levels as many of the clients( PGCIL,NTPC and all state
electricity boards etc.)do copy-paste in the tender
specification and they dont want to do the hectic work to
produce the new specification.
That is the only reason that transmission is done at the
predecide voltage levels. The new voltage levels will not
be the exact multiple of 11 kV as 765 kV and 400 kV are
There isn't really any electrical principle for that.
Originally Commercial Electric distribution was first done
by Edison and his Manhattan DC lighting system was opened
in September,1882.Edison took 100V as the voltage for his
incandescent lamps.( Why 100 V?Round number,safe electrical
voltgae to handle,but high enough to save copper in
conductors)But it soon became clear that at the fag end of
street the lamps were not burning well due to voltgae drop
in line.Edison had to raise the generator voltage to 110 V
( there by distribution voltage became 110V!)to take care
of the voltgae drop in line.thus it became a std in US.
N PPL, THERE IS NOTHING TO DO WITH FORM FACTOR AS U THINK.
the ans is form factor (FF). The form factor is 1.11 for
sine wave . while we are calculating the voltage produced by
the generator we are using form factor for the same. so all
standard voltage ratings in world are of multiples o 1.11
Transformer induced voltage equation contains 4.44 factor, i.e. E= 4.44*f*T*Phi
E= induced emf/phase
T= no. of turns
Phi= maximum flux/ pole
Since, E is proportional to 4.44 and it is in turn multiple of 11. So always transmission and distribution voltage are multiple of 11.
becoz as power is transmitted, losses does occur. so we are
providing a margine of 10% to account for this drop. i.e. if
the transmitted power is 110 units then we are receving 100
units at least.if the drop is more we are to take corrective
methods.but if the losses are well in this 10% range nothing