Purpose

Purpose of this documentation is to understand –

Deciding backup relay settings for EHV lines: By using formulae how to design proper backup protection system for EHV lines.

There are many great text books available about the subject. Also there are good reference books for power system protection. This documentation is neither a text book nor the reference book it can be considered as practice book where protection engineer working in a transmission system shall get the knowledge for deciding settings of backup protection for EHV lines which is generally sufficient for routine work.

Thus first we will go through examples of deciding settings of backup protection for EHV lines and then we will discuss theory behind formulae and setting calculation method. After going through the theory part you will do the same calculations and by same way but with better insight. Hence it is highly recommended to go through theory part also.

Note: - Readers are requested to go through text books and reference books for more details and during un-common situations.