Schemes

Question 1

What is SEF?

Answer 1

Sensitive Earth Fault protection.

A relay measures differences between three phases; often an open-delta voltage check (0V).

Question 2

What is REF, and where is it used?

Answer 2

Restricted Earth Fault protection. Operates between CTs (unit protection). Used on transformers

Question 3

What is an O/C check?

Answer 3

Overcurrent check.

Used on CB fail schemes to check if CB has opened.