I want to protect voltage transformer by fuse.
voltage transformer : 6.3kv/110v ac,10vA,cl 0.5+3p
i have a fuse with 3.15A ,12kV
as you see the voltage rating of both is different
is it possible that protect this fuse with voltage transformer?
A fuse blows on too many amperes and does not care about voltage.
Except that in a circuit with too high a voltage for the fuse rating, current can jump through air from one end or side of the fuse to the other (the official term is flashover) causing unpredictable and hazardous behavior.
So when you put it in the transformer primary circuit of 6300 volts (within the 12000 volt fuse rating), it will limit the primary current to 3.15 amps which will occur when the secondary current (110 volts) is about 180 amps.
But the transformer as you said is rated for 10 kva which is about 90 amps at 110 volts at the secondary (half of the preceding) so the fuse is too big for the transformer. You would need a 1.5 amp fuse in the transformer primary circuit.
(Using any component (switch, Romex cable, etc.) on a circuit with more voltage than the component's rating can result in similar hazardous results.)
Stop wasting time re-adjusting the pattern. Have several lawn sprinklers, one for each pattern.