Single- or Three-Phase Supply to Homes : Advantages and Disadvantages compared between Single-phase and Three-phase domestic electricity

Sammanfattning

A three-phase power supply is a de facto standard when selecting a power supply to homes in Sweden, regardless of whether it is flat with low energy consumption or a house with electric heating. This project aims to determine the advantages and disadvantages of using a three-phase supply compared to a single-phase supply to homes. This thesis starts with a historical literature review to find answers to why a three-phase supply is a de facto standard in Sweden. Single-phase and threephase supplies to homes were compared by creating an electrical circuit model that used actual household load profiles. The load profiles were taken from a study that measured the power consumption in 400 Swedish homes. Two houses and four flats from that study was selected as input data to the circuit model. Each house was modelled as both single-phase and three-phase. The power losses in the supply conductors from the power meter to the homes distribution panel was calculated. The selectivity between the main fuses and Miniature Circuit Breakers (MCB) was also investigated by comparing the let-through energy of MCBs and pre-arcing energy of fuses. The results from the historical review indicate that one of the reasons that three-phase supplies became the de facto standard is that Sweden implemented a new tariff system. All the customers with low power consumption were placed in the 16 A main fuse category, and the network fee was the same for single-phase and threephase the previous system had a higher price for three-phase. The power losses in single-phase supplies and three-phase supplies with a similar total conductor area were compared. The results that a three-phase supply had lower losses in all the cases, even though the loads were mostly 230 V loads and not perfectly balanced between the phases. A three-phase supply is preferable over a single-phase supply if the home has high energy consumption. However, a single-phase supply might be a good option if the home has a low to moderate energy consumption. The reason for this is that the losses are only slightly higher in absolute terms, and a single-phase supply enables a higher main fuse rating for the supplies total cross-section, and it is, therefore, easier to coordinate the downstream protective devices