what is % impedance of transformer? how we calculate %impedence of transformer,
what is purpose of % impedence?
Dear Mr. Jatin ;
In some case called the impedance of transformer that is given in ” % “, but the sientific name is ” Usc or Ucc ” that means the percentage of primary voltage ( HV ) that should be applied to have the nimonal current ” In ” on short circuited secondary.
Normally, each transformer hase a Resistance ” Rtr ” and an Inductance ” Xtr “, where we can calculate by the following formula :
– Ztr = Usc x U²/Sn
– Rtr = Ptr / 3 x In²
– Xtr² = Ztr² – Rtr²
Noting that :
– Ztr : the impedance of transformer
– Usc : the voltage in percentage of transformer
– U : the voltage between 2 phases
– In : the nominal current for the transformer's secondary
– Ptr : the total loss at full load
As desiegner, we should calculate the ” Rtr & Xtr ” to the transformer ten add themm to the values ” R & X ” of cables to calculate the different values of short circuit currents.