Test procedure dir o c and def blocking during lop apply setting lop y1 to the relay make to get lop signal by applying va 60 100o volts and remove the voltage to zero in one shot apply current on phase a ia2 100o check that def didnt operate def converting to non dir e f apply setting lop y to the . Known the differential relay can easily be test ed by using procedures presented in this sect ion in o rder to facilitate understanding of these t esting procedures o ne application examples will. When setting a high impedance differential scheme the objective is to ensure stability under worst case through fault conditions setting a low z diff relay settings generically defined as follows i s1 s principles of differential relaying principles of differential relaying . Test engineer in a step by step procedure properties of the protection relay as such as settings it can be quite tricky to test a numerical transformer differential relay by secondary . 5 timing test procedures 246 6 tips and tricks to overcome common obstacles 246 chapter 12 simple percent differential 87 element testing 247 1 application 247 2 settings 257 3 restrained differential pickup testing 259 4 restrained differential timing test procedure 264 5 restrained differential slope testing 266 6