Construction Of Welding Machine

The relationship between winding turns and input and output voltage and current are as follows:
            N1 = V1 = L2  / V2N2L1
Where N1 is the number of turns on the primary winding of the transformer,N2 is the number of turns on the secondary winding. V1 is the input voltage, V2 is the output voltage, L1 is the input current and l2 is the output (load) current.
    It will be seen that the magnetic flux forms the connecting link between the primary and secondary circuits and that any variation of the flux and therefore of the e.m.f. induced in the primary, there  by enabling the primary current to vary approximately proportionally to the secondary current.  This balance of primary and secondary ampere turns is an important relationship where-ever transformer actions occur.
5.3    USEFUL AND LEAKAGE FLUXES IN A TRANSFORMER
    When the secondary winding of a transformer is a an open circuit, the current taken by the primary winding is responsible for setting up the magnetic fluxes and providing a very small power component to supply the loss in the core.
    Fig  5.2 (b) show all the flux set up by the primary winding passing through the secondary winding.  There is a small amount of flux returning through the air space around the primary winding.  This is negligible compared with that through the secondary.  It follows that the e.m.f. is induced in the primary applied voltage V1 is equal and opposite to the e.m.f. E1 induced in the primary.