Techno-economic analysis of single-phase, versus three-phase load dependant, dynamic set-point control in voltage regulating distribution transformers (VRDT) to increase hosting capacity of low voltage networks

The increased installation of distributed energy resources (DER), heat pumps and electric vehicle chargers forces distribution system operators (DSO) to increase the hosting capacity of their grids. Voltage regulating distribution transformers (VRDT) are a proven asset to tackle this goal. These on-load tap-changer (OLTC) equipped distribution transformers allow automatic voltage regulation at the low voltage bus bar. Thus, VRDTs decouple low voltage networks from the upstream medium voltage variations and allow a broader voltage band for both, generation, and load situation and therefore increasing hosting capacity. This contribution describes different voltage control algorithms, the implications to hosting capacity enhancement, networks planning aspects, and the decision process of the Dutch DSO Alliander’s decision to choose dynamic set-point control as their standard for VRDTs. The set-up of the technology used is a three-phase measurement unit. A techno economic project evaluation of a dynamic voltage regulation with single-phase measurement against the established three-phase arrangement is undertaken. As a result, the decision was made to develop and introduce single-phase dynamic set-point control in VRDTs, due to the advantage of reduced purchasing cost, reduced space requirements and usage of resources, minimised installation and commissioning effort, that outweigh the disadvantages caused by the reduced measurement set-up.