This guide specifies the basic norms for protection and control equipment of High-Voltage Direct Current (HVDC) transmission systems that have the voltage range up to and including 800kV. It also defines and specifies requirements for control and protection equipment used in the design, manufacturing, research and testing of HVDC control and protection equipment. These guidelines apply to the control and protection equipment for monopolar and bipolar and two-terminal LCC (line commutated converter) HVDC systems with the main circuit structure of one 12-pulse converter or two series 12-pulse converters per station pole. This guidance can also be used as reference for HVDC applications with other topologies like back-to-back links, parallel converter systems, and multi-terminal/multi-circuit HVDC transmissions .