RATIO-DIFFERENTIAL RELAY

PURPOSE:To allow a device easily and surely to select optimum ratio characteristics different according to objects to be protected by connecting variable impedances respectively to the 1st and 2nd suppression circuits in parallel. CONSTITUTION:There provided are an object 1 to be protected, the 1st and 2nd CT 21 and 22 provided at both ends of it, a ratio differential relay 3, the 1st and 2nd suppression circuits 41 and 42 provided in a ratio differential relay 3 connected in parallel through a connection circuit 412 mutually equal in suppressive force and an operation circuit provided in the ratio differential relay 3. In particular, variable impedances 61 and 62 are connected in parallel to the 1st and 2nd suppression circuits 41 and 42 respectively. By changing the values of the 1st and 2nd variable impedances 61 and 62, the capacity of current flowing to the 1st and 2nd suppression circuit 41 and 42 are controlled. An optimum characteristic can thereby be selected to ensure proper protection.