Dala Energi Elnät is a smaller grid company with network operations consisting of the distri-bution and measurement of electricity. The company is interested in acquiring greater know-ledge of the error detection equipment that can in a early stage detect errors in the medium-voltage network. Which hopefully results in faster fault location and cost savings for the company.The purpose of this study is to investigate the fault-detection equipment that would fit into the Dala Energys medium voltage grid and what experiences others electricity companies have with fault-detection equipment. Fault detection equipment used in the study has been limited to equipment from the companies Protrol AB and dLaboratory AB. Structure and function of the equipment are investigated and empirical experience obtained through a telephone interview and a visit on the electricity network companies Kraftringen respectively Falu Elnät AB.Protrols fault-detection equipment consists of error detectors that measure only the current for detecting ground faults and over currents and mainly used in substations. Communication to the control center can be made by fiber, Ethernet or signal cable. The simplest detectors have no communication link without signals with LED indicator on the substation if the fault current passed. Configuration, settings, and registered error events must be downloaded by USB connection on site.dLaboratorys concept is that the industrial PC installed in a distribution substation, where the current and voltage are measured in each output tray, to detect ground faults and overcurrents. Relay Protection functions are available on the PC, which means that both fault detection and protection equipment available. Information from the measurements sent to dLaboratorys serves for analysis and transmitted to power grid owner. On dLaboratorys website the information can then be reviewed with a convenient interface.Selection of fault-detection equipment is affected by electricity network design with radial or meshed networks, existing grid equipment, relay protection, geographical distance and communication facilities etc. Where a comprehensive solution from a longer term perspective should be taken into account. Recording options in error-detection equipment can be used to better understand the reasons why a protection relay trips, where the events before and after the fault can be analyzed. A financial investment in fault-detection equipment do not always pay for itself, but also provides greater customer benefits and opportunities to identify weak points in the grid. Benefiting from successful experience of other grid companies have had with fault-detection equipment.For the fault-detection equipment included in the study, recommended Protrols equipment to be used on radial parts of the network, where the error detectors are not placed in each substation but strategically where geographical distances are great to reduce troubleshooting time substantially.dLaboratorys fault detection equipment is best suited to distribution stations with many exhausting tray and where it is possible that if sectioning out the fault with remote-controlled switch or circuit breaker. dLaboratory relay protection has worked well in conducted tests on the other hand it remains to be seen how it manages in normal operation. / <p>Validerat; 20160617 (global_studentproject_submitter)</p>

The grid in the northern part of Sweden is characterized by long radial lines with just a few customers. To secure electricity supply it is necessary to have a redundant feeding alternative. A loop structured grid which is used in the more populated urban area is a poor solution in the rural areas both regarding economy and technology due to the long distances. To feed the northern grid in Sweden a battery energy storage system (BESS) is therefore a solution that could secure the power delivery. An important aspect to investigate is how the electric power quality changes with the new feeder, but more importantly to secure disconnection of supply at fault occurrence.   This thesis investigates how a battery storage system installed at the end of a mid-voltage line affects the electric power quality and the protection system compared to a reference case which represents the line today. The mid-voltage line is an existing line in the northern grid and is a good representation of the general northern grid.     The results obtained from this study show that the loop impedance does not necessarily have to deteriorate with the new feeder, which means that the voltage quality in this aspect does not change. This is only true for this particular grid when the impedance contribution from the mid-voltage grid is small and the contribution from the low-voltage grid is large because of long and weak distribution low-voltage lines.     The inverter is the limiting factor for the short circuit currents, and the short circuit power and current decrease with the new feeder. At fault occurrence in the low voltage grid the short circuit current does not affect the fuse blow. However the inverter will disconnect for all fault occurrences in the mid-voltage grid, and for faults with high short circuit power in the low voltage grid. This means that the selectivity will decrease, but the system will have a high security level.   For this particular grid the results show that the transformer can be isolated from the ground. A residual overvoltage relay is enough for disconnection of grounding faults. Directional ground fault protection is not necessary for this line with this particular characteristics. If the sensitivity for the disconnection of grounding faults with high transition impedances is adjusted according to ground fault currents in island operation, the sensitivity then decreases at the event of a fault during normal operations when the battery storage system is charging. The sensitivity might also be tuned according to normal operation, which then results in a higher sensitivity than necessary during island operation.