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In order that the supply of electric power remain stable and sustainable, a certain level of power quality must be maintained while securing energy resources and resolving environmental issues. The distributed generation (DG) has become an essential and indispensable element of such distribution systems from both an environmental and an energy security perspective. However, the installation of DGs in distribution systems may cause variations of voltage on distribution feeder because the DG power outputs may change randomly and dramatically. Generally, the sending voltage at substation in distribution systems can be regulated by an under load tap changer (ULTC) designed to maintain customers' receiving voltages within a predetermined range. Voltage regulation performed by ULTC calls for two parameters: the equivalent impedance and the load center voltage. Therefore, in distribution networks with DG interconnections, these parameters should be designed with attention not only to load variations but also to DG outputs. This paper proposes a method for designing ULTC parameters with reference to variations in DG output. The proposed algorithm is tested with IEEE 13-node system and Korean model network. The results demonstrate the validity of the proposed design method for varying DG distribution. [ABSTRACT FROM AUTHOR]