Generator circuits set special requirements for circuit-breakers, therefore the circuitbreakers of distribution circuits are neither designed nor tested to meet these requirements. The circuits of large and small generators experience unique phenomena such as: a short-circuit at two characteristic points, a high rate of rise of recovery voltage and out-of-phase switching. These phenomena are described in the second chapter of the master thesis. Further on, the connection diagrams and the configuration of generator circuits are elaborated. A short review of the historical development of generator circuit-breakers is presented in the second chapter as well. The standard ‘IEC 62271-100, High-voltage alternating-current circuit breakers’ refers to the high-voltage circuit-breakers and the third chapter of the paper is according to the standard. Rated characteristics of generator circuit-breakers are sorted out as well as instructions that should be followed when selecting a generator circuit-breaker. The right selection of the circuit-breaker rated characteristics is the first condition of an efficient and reliable plant. The characteristic diagrams showing the oscillogram during the duty cycle of the circuit-breaker and make-and-break operations are also given. When considering the replacement of the present breaker or during the implementation of a new one into the system, all life cycle costs of the circuit-breaker should be taken into account and are explained in the fourth chapter of the thesis. As breakers are mechanical devices capable of working for many years, the inflation rate should be considered, and these values should be calculated into the present inflation rate. The fifth chapter of the thesis covers the calculation of three phase short-circuit current according to the standard ‘HRN EN 60909-0:2016 − Struje kratkog spoja u trofaznim izmjeničnim sustavima - 0. dio: Proračun struja (IEC 60909-0:2016; EN 60909-0:2016)‘ and the generator circuit-breaker has been selected for the hydropower plant Kraljevac. This chapter explains the replacement reasons, the current state and the design operating state of the hydropower plant Kraljevac. Then, the control and quality assurance programs as well as the equipment maintenance one are described in order to satisfy the designed life cycle, according to the detailed electrotechnical design ‘Zamjena 35 kV prekidača ABM-a‘