<p>The background to this work is the introduction of the RCC Ground Fault Neutralizer in countries that earlier have used solidly earthed medium voltage networks. The RCC Ground Fault Neutralizer is a protection system that is capable of handling earth faults without disconnecting the feeder. Since some equipment, that cannot be immediately replaced, only can withstand the full voltage for a limited time, the operating time of the system needs to be limited. This is also true during the commissioning when calibrating the system means that the voltage against earth needs to be increased.</p><p>The primary purpose with this work is to create a possibility to automatically calibrate the settings for the inverter that are used when reacting to an earth fault. A goal with the new automatic calibration is that it should be faster than a preset time per phase. A second goal is to create a more user friendly control of the neutral voltage using the inverter. The purpose of this is to prepare the system for the possibility that PD measurement in combination with the control of the neutral voltage offers. This way isolation defects could be found and possibly also delayed.</p><p>The solution that was chosen was as simple as possible and is a combination of setting the inverter to a calculated value and proportional control. This was implemented in the service software which is normally used for commissioning, surveillance and manual control.</p><p>The solution was proven to be good enough to clear the goal that was set up for this work. The first tests were performed against a net model. After the solution had proven to be successful in the net model more test where performed on a system installed in a real substation. Also the PD control software was tested but only in the net model and because higher voltages is needed to test PD activity no real test with PD was performed. Hopefully this new software can be used to further develop this idea in the future.</p>

The background to this work is the introduction of the RCC Ground Fault Neutralizer in countries that earlier have used solidly earthed medium voltage networks. The RCC Ground Fault Neutralizer is a protection system that is capable of handling earth faults without disconnecting the feeder. Since some equipment, that cannot be immediately replaced, only can withstand the full voltage for a limited time, the operating time of the system needs to be limited. This is also true during the commissioning when calibrating the system means that the voltage against earth needs to be increased. The primary purpose with this work is to create a possibility to automatically calibrate the settings for the inverter that are used when reacting to an earth fault. A goal with the new automatic calibration is that it should be faster than a preset time per phase. A second goal is to create a more user friendly control of the neutral voltage using the inverter. The purpose of this is to prepare the system for the possibility that PD measurement in combination with the control of the neutral voltage offers. This way isolation defects could be found and possibly also delayed. The solution that was chosen was as simple as possible and is a combination of setting the inverter to a calculated value and proportional control. This was implemented in the service software which is normally used for commissioning, surveillance and manual control. The solution was proven to be good enough to clear the goal that was set up for this work. The first tests were performed against a net model. After the solution had proven to be successful in the net model more test where performed on a system installed in a real substation. Also the PD control software was tested but only in the net model and because higher voltages is needed to test PD activity no real test with PD was performed. Hopefully this new software can be used to further develop this idea in the future.

Insulation in rotating machines is a common cause for failure. Therefore, research in the area is large and is important to further increase the knowledge of the phenomena related to insulation degradation. This thesis is a case study on 20 stator bars obtained from a generator that had been showing signs of insulation degradation while in operation. The insulation was investigated using a range of measurements to be able to evaluate the degradation of these bars. The measurements performed were electrical partial discharge measurements, acoustic partial discharge measurements, dielectric response measurements, and breakdown testing. Furthermore, a more scientific approach to the commonly used tap test in the industry was conducted, which has not been done before and the purpose was to validate this commonly used test method. It was concluded that the bars have a significant amount of partial discharges within them, and that the stress grading is likely to be blamed in many of the worst cases. Furthermore, the dielectric response measurements provided good information on the thermal stability of the insulation. The set-up of the tap test did not provide reasonable results, and the method approach as well as the experimental set-up was to blame for this. In future work, investigating this specific area could be beneficial. The electrical partial discharge measurements and the breakdown test provided unexpected results when compared, where the former indicated much degradation while the latter proved that the bars can withstand very high voltage levels. / Isolering i roterande maskiner är en vanlig orsak till fel. Forskningen på området är därför omfattande och viktig för att ytterligare öka kunskapen om fenomen som rör isoleringsnedbrytning. Denna avhandling är en fallstudie på 20 statorstänger som erhållits från en generator som hade visat tecken på isoleringsnedbrytning under drift. Isoleringen undersöktes med hjälp av en rad olika mätningar för att kunna utvärdera nedbrytningen av dessa stänger. De mätningar som utfördes var mätningar av elektriska partiella urladdningar, akustiska partiella urladdningar, mätningar av dielektrisk respons och genombrottstester. Dessutom genomfördes ett mer vetenskapligt tillvägagångssätt för det allmänt använda tapptestet i branschen, vilket inte har gjorts tidigare och syftet var att validera denna allmänt använda testmetod. Slutsatsen blev att stängerna har en betydande mängd partiella urladdningar i sig, och att spänningsgraderingen sannolikt får skulden i många av de värsta fallen. Dessutom gav mätningarna av den dielektriska responsen god information om isoleringens termiska stabilitet. Upplägget för tapptestet gav inte rimliga resultat, och detta berodde både på metodiken och på försöksupplägget. I framtida arbete kan det vara bra att undersöka detta specifika område. Mätningarna av den elektriska partiella urladdningen och genombrottstestet gav oväntade resultat när de jämfördes, där de förstnämnda visade på mycket försämring medan de sistnämnda bevisade att stängerna kan motstå mycket höga spänningsnivåer.