Hardware and software for measuring and monitoring the unbalance factor of the three-phase voltage system is developed. The shortcomings of the existing technical and software solutions for calculating the unbalance factor, as well as problems of applying the methods used for analog control systems to digital systems are described. The block diagram of the microprocessor system for measuring the voltage unbalance factor in the ship three-phase network with the effective values of phase voltages is used. The analysis of the analytical expressions to calculate the unbalance factor allowed minimizing the utilization of system hardware necessary for the formation of all necessary signals. The optimized structure of the digital filter to calculate the effective value of the deterministic periodic signal at the optimum speed of a discrete system is proposed. An increase in the sampling rate in the optimized filter structure does not lead to an increase in the number of arithmetic operations of addition and multiplication, which is an advantage of the proposed system in comparison with similar ones. This allows monitoring of instantaneous changes in the unbalance factor of three-phase voltage and enables the system to operate in real time. The developed hardware and software can be integrated into the automated control system of the power plant and used in voltage control systems, as well as for the timely detection of voltage unbalance to protect equipment and prevent violation of normal operation.