In FDLF method, B' corresponds to susceptance of unknown of PQ and PV bus Order of B' matrix is = (n -1)*(n - 1) Where n is total no. of buses. Order of B'' = (n - m - 1)*(n - m - 1)
Intern turn winding fault can be easily detect by differential protection relay. Also detect by buchholz relay (gas operated relay), cause buchholz relay is used to detect the internal fault of transformer.