This standard specifies the performance requirements of electrically biased (percentage differential relays). These relays constitute a particular sub-family of measuring relays with more than one input energizing quantity as defined in I E C Publication 255-6, Electrical Relays, Part 6: Measuring Relays with More than One Input Energizing Quantity, and the parameters whose values are to be declared by the manufacturer of such relays. It also .specifies methods of presentation of the characteristics and performance of these relays .This standard applies to relays designed for the detection of faults particularly in a.c generators, motors and transformers. It does not apply to relays designed for busbar protection, nor does it apply to current differential (e.g. pilot wire) relays used for the protection of transrhission lines. This standard covers the majority of biased (percentage differential relays) and also, for example, those where the restraint percentage increases as the through-current increases. For particular cases, supplementary requirements may be stated in .national standards .All tests in this standard are type tests .This standard applies only to relays in a new condition