In recent years, more and more distributed sources have been connected to the electric power distribution network, whose powers are becoming comparable to the power of consumers in the network, and in some cases even exceeding them. In such circumstances, it is necessary to introduce new methods of planning the distribution network and revise the existing criteria for connecting new distributed sources so that they do not adversely affect the stability of the distribution network and other network users. Technical problems that can be caused by distributed sources in the distribution network include problems with the thermal ratings of existing equipment, with voltage regulation in the network, excessive short-circuit currents, voltage quality in the network, problems with reverse power flows, islanding in parts of the network, and problems with the operation of the protection systems in the network. The most significant problem faced by distribution system operators is the problem of voltage regulation in the network, that is, large voltage fluctuations during frequent changes in the amount of power injected into the network, such as occur with intermittent sources (sun, wind). The paper describes interventions that can be made in the network in order to alleviate the mentioned problems and to increase the capacity of the network to accept distributed production. In addition, the criteria for connecting distributed sources to the network in the Republic of Croatia and several foreign countries are presented. On the specific example of a medium-voltage line with a high integration of distributed sources, which no longer allows the acceptance of new distributed sources, the transition of the line from the operating voltage of 10 kV to 20 kV was proposed in order to rehabilitate the voltage conditions and enable the connection of new sources. In addition to the savings due to the reduction of losses after the transition to a higher voltage level, it is necessary to consider the producer's connection fee in order to make this investment profitable for the distribution system operator. The maximum capacity of the transmission line for the connection of new distributed sources was calculated and the fee for the connection of the producer was optimized.