Model SEL-3021 Serial Encrypting Transceiver safeguards existing and new communications links between power control centers, electrical substations, and generating plants. Stops malicious physical and cyber attacks on key infrastructure tied into electrical power grid. Stops attackers from secretly monitoring sensitive information on data links, sending messages to operate equipment or change settings, stealing data that identifies customers and usage patterns, or pinpointing physical targets. Also prevents unauthorized individuals from controlling operation of breakers, machines, gates, or valves. Uses encryption and session authentication to lock out unauthorized control.