A general local powerline has implemented to mimic a lifelike powerline build around 1960s in thecountryside. Since reconstruction is needed a new projection is made of the area to improve the powerquality. The projection includes the old transmission lines will be replaced with underground powercables to make it weatherproof. The implication of underground power cables leads to smaller distancebetween the phases which generates greater capacitance. Due the increase will make the capacitivecurrents greater as well which affect the power quality for the costumers in the area. The projectionmust be adapted to the increase of earth fault currents which the capacitive currents contribute. The regeneration of the old and new power lines consists a sketch of terrain, merge of the powerconsumption, electrical fuses, line diagram, sizing transformers and right dimensions of cables. Calculations on capacitive fault current, voltage drop as well as neutral grounding reactor (a resistanceparallel with an inductor) was executed. Calculations of the powerline followed Swedish standard andthe neutral ground reactor after the norms of Swedish electrical industry. Regard to the projection, including underground cables, the capacitive fault currents increased with 46,75 times compared to transmission powerlines at 10 kV. Calculations of the neutral ground reactorresulted in 5,25 Henry for the inductor and 1154 Ohm for the resistor to compensate the gain. The conclusion is that weatherproofing the powerline at 10 kV leads to compensating otherwise the powerquality and selectivity will be affected. That result in a more expensive arrangement cost forunderground cables compared to transmission.

The rural power grid has traditionally mostly consisted of overhead power lines. In recent years the trend has been to replace the overhead lines with cables instead. The reason is that overhead lines are relatively vulnerable, strong winds and storms can cause trees and branches to fall over the power lines and cause a phase to ground fault. This will then trip the ground fault relays and disconnect the faulty power line. A cable grid is not vulnerable in the same way, and could be considered a solution to make the power grid more reliable. A cable grid does come whit other types of problems instead. It generates about 50 times more phase to ground capacitance compared with the same length of overhead lines. When a phase to ground fault occurs the capacitance in the healthy phases will generate a current to ground and then through the fault. On average a cable grid generates about 2 A per kilometer. Large cable grids can therefore cause very large capacitive currents to flow through the fault.  To counter this, a reactor is placed between the neutral point of the transformer and ground. When a phase to ground fault occurs, the reactor will generate an inductive current which is in the opposite phase compared to the capacitive current. This current will flow through the faulty line and cancel out the capacitive current. In a perfectly tuned power grid the only component left in the fault is a smaller resistive current. Large cable grids will require a large reactor to generate the large inductive current, which might need to flow over a great distance in the grid to reach the fault location. To reduce the inductive current from the central reactor, it is possible to install smaller local reactors in the grid. These will then in the event of a phase to ground fault generate a part of the inductive current, which will reduce the currents from the central reactor. This report will look at the factors related to grounding systems and how these factors affect the ground fault currents. The purpose of the report is to give recommendations to Umeå Energi on where in their grid they should install additional local reactors and also which factors they should consider when doing future expansions and rebuilds of their power grid.