National Power Grid comprises of large number of assets established across the country. Interconnectedness is a key feature of networked world and cyber opportunity and threat are part of it. For curbing the cyber threats over national power grid, multiple steps have been taken. For securing transmission assets of POWERGRID, communication from equipment of Substations to control centers are done over dedicated optical fiber network owned by POWERGRID without any connectivity to external networks. They are further protected through multiple Firewalls. These systems are kept isolated from office networks, to prevent any malicious online attack because of Internet connectivity.