With series compensation of the line reactance, the problem of its protection against overcurrents arises regarding relay protection. The greater the degree of compensation, the greater the problem. When compensating for more than 50% of the reactance of the line, the protection of power transmission lines becomes practically impossible due to the failure or false operation of all existing kinds and types of protection [1, 2]. Therefore, as for now, the compensation of the line reactance usually is no more than 50% [3, 4], which does not allow to reveal the full potential of the line in terms of its transmission capacity. The goal of this research was to study the processes occurring in emergency modes on power lines equipped with a series capacitor bank, the understanding of which would help to produce algorithms that can protect power lines with SCB with a degree of the longitudinal resistance compensation of the line of more than 50%.