The subject of dissertation is to address the problem of reactive power in public buildings. These objects are nowadays a very specific type of electricity consumers. This is due to the fact that they are equipped with advanced technical devices, including building management systems (BMS), access control, ventilation and air conditioning. The components of these technologies are e.g. asynchronous engines in air handling units, or drives of escalators, electrically powered and controlled valve actuators, countless electronic components. All of these devices need electricity to work in order to ensure the comfort of users. More and more public utility buildings are reaching the capacity ordered at the level of several MW. Investors more and more often decide to invest in LED lighting. Choosing the cheapest solutions, in the first contact they define them as the best, but with time it turns out that they fall into the trap of reactive power. This paper also deals with the problem of lack of understanding on the part of investors about reactive power. On the pages of this paper the author presents examples of measurements recorded in one of the office buildings. They are analyzed and discussed and then the solution of reactive power compensation is selected according to the results of the analysis. After the selection activities, the economic calculation of the investment is presented. The aim of the work is to raise awareness of the problem of reactive power
in public buildings. The diploma dissertation is motivated by the author's own experiences concerning the condition of objects with which he works on a daily basis.