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- This paper describes a percentage current differential relaying algorithm for bus protection blocked by a CT saturation detection algorithm. The detection algorithm blocks the output of a current differential relay only if a differential current is caused by CT saturation in the case of an external fault. Moreover, if a current differential relay operates faster than the detection algorithm, the blocking signal is not ignited. On the other hand, if the detection algorithm operates faster than a current differential relay, the output of the relay is blocked. The results of the simulation show that the proposed algorithm can discriminate internal faults from external faults even when a CT is saturated in both cases. This paper concludes by implementing the algorithm into the TMS320C6701 digital signal processor. The results of hardware implementation are also satisfactory. The algorithm can not only increase the sensitivity of the current differential relay but improve the stability of the relay for an external faults.