Line protection: Redundancy, reliability, and affordability

In this paper, we apply fault tree analysis to compare the dependability and security of line protection schemes with different degrees of redundancy. We also compare the scheme costs. For each scheme, we use a basic protection scheme as the reference. We then evaluate schemes with double redundancy and two-out-of-three voting schemes. We also evaluate the effect of comprehensive commissioning testing, hidden failures, and common-mode failures, as well as using relays from the same or different manufacturers in redundant schemes.