Section 6(18)(i) in Tamil Nadu Electricity Grid Code, 2005
(i)Every element of the power system shall be protected by a standard protection system having the required reliability, selectivity, speed, discrimination and sensitivity. Where failure of a protective relay in the system of one entity has substantial impact on the system from which power is drawn by it, it shall connect an additional protection as standby. The entity supplying power to another entity shall provide back-up protection to the system which receives power.