Transformer differential function testing I vector correction I zero sequence filtering

Describe about testing procedure of Transformer protection relay, relay connection, CT secondary Current flow at full loaded condition, internal fault condition, external fault condition , vector correction, Amplitude correction ,zero sequence current filtering ( No zero sequence current to conventional relay) in Numerical relay. . For learner, it will be useful to test differential protection of conventional transformer protection relay and to understand about numerical transformer protection relay’s differential function .