Main 1 and Main 2 Protection - Same or Different?

Redundant functionally equivalent protection systems (FEPS, sometimes known as main 1 and main 2) are usually applied for transmission line protection.
What are the relative advantages and disadvantages of using different types of systems for FEPS? This article discusses this question.
Most utilities provide redundant FEPS on the Bulk electric System to maximize the dependability of these schemes to clear short circuits.More