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This paper proposes a full adaptive technique for setting all overcurrent (OC) relays in HV substations. This technique can be used online and there is no need to employ a telecommunication infrastructure. It is based on an appropriate equivalent circuit of the power grid in the substation, online estimation of the equivalent circuit parameters, and application of the equivalent circuit to estimate the required short-circuit currents. This full adaptive technique is used in setting the OC relays of a typical 230/20-kV substation connected to a sample 9-bus grid. Significant advantages of the proposed technique over the usual setting method are shown by comparing the corresponding results. Furthermore, the technique is improved to resolve problems due to penetration of distributed generation. Developing this adaptive setting technique is a step toward introducing self-adjustment OC relays.