This standard specifies the functional requirements of directional relays and power relays with two input power quantities. These relays form a subfamily of measuring relays with various input power quantities, defined in the UNE 21-136/6 standard: "Measuring relays with various input power quantities", and whose characteristic values must be declared by the manufacturer. It also specifies the modes of representation of the functional characteristics and their values. This standard includes impedance relays and specifically deals with:
——Phase angle measurement relays (directional relays). - Power measurement relays. The requirements of this standard relating to phase angle may be associated with requirements relating to other characteristic quantities (for example, intensity) specified in other parts of the standards such as "current relay". For particular cases, complementary prescriptions may be agreed between the user and the manufacturer or specified in national standards. All tests in this standard are type tests. This standard only applies to relays in new condition.