Let Vsc is the voltage required to circulate rated current on short circuit, θsc is the power factor angle on short circuit, and θ2 is the load power factor angle and E2 is the secondary rated voltage. The Per unit voltage regulation of a transformer is given by
1
\(\frac{{{V_{sc}}}}{{{E_2}}}\tan \left( {{\theta _{sc}} - {\theta _2}} \right)\)
2
\(\frac{{{V_{sc}}}}{{{E_2}}}{\rm{cos\;}}\left( {{\theta _{sc}} + {\theta _2}} \right)\)
3
\(\frac{{{V_{sc}}}}{{{E_2}}}\cos \left( {{\theta _{sc}} - {\theta _2}} \right)\)
4
\(\frac{{{V_{sc}}}}{{{E_2}}}\tan \left( {{\theta _{sc}} + {\theta _2}} \right)\)