Hello,
What you mentioned it is not exactally correct, as kWh is energy , so as you mentioned :
“Now the formula,which you know, KWH = Line Current * Line Voltage * Power factor can be applied.
The only unknown value ‘current’ can be calculated.”
You must not use de time, as P= dW/dt, the correct is kW = Line Current * 1,73*Line Voltage * Power factor * efficiency.