Induction motors are commonly used in numerous industrial applications. To maintain a reliable operation of the motor, it is important to identify the potential faults that may cause the motor to fail. Bearing failures are one of the main causes of motor breakdown. The causes of bearing damage have been studied in detail for a long time. In some cases, bearing failed due to the current passing through them. In this thesis, bearing currents in an inverter driven five-phase induction motor are studied and a new solution is proposed. First, theory of shaft voltage and bearing current are presented. The causes are identified and current solutions are discussed. Then, new switching patterns are proposed for the five-phase induction motor. The new schemes apply a modified algorithm for the space vector pulse-width-modulation (SVPWM). The system is simulated and the results of the new switching patterns are compared with the conventional switching pattern. Finally, the new schemes are experimentally tested using a digital signal processor (DSP) to drive the five-phase IGBT inverter. The experimental results verified that the new switching pattern could reduce shaft voltages and bearing current without affecting the performance.

This thesis project was executed at ABB AB. The purpose of the thesis was to formulate aselection of ionic liquids with different thickeners as greases and experimentally understand thetribological characteristics and electrical properties. The performance of four ionic liquids, 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (IL6), 1-Butyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide (IL2), 1-Hexyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide (IL3), and 1-Hexyl-1-methylpyrrolidiniumbis(trifluoromethylsulfonyl)imide (IL4) and two thickeners, polytetrafluoroethylene (PTFE)powder and lithium stearate were evaluated for tribological and electrical properties. Two ionicliquids, 1-Ethyl-3-methylimidazolium dicyanamide, 1-Butyl-3-methylimidazolium dicyanamidefailed to form stable greases due to poor miscibility with the thickeners. Frictional tests for all thecomposed grease were performed and afterwards analyzed with a light optical microscope forassessment of the wear tracks. Electrical conductivity was measured with a contact resistancetest setup. Moreover, the dropping point for the greases was measured to ensure theformulations were qualified as lubricant greases. Ionic liquid greases containing PTFE as athickener show better thermal stability than those containing lithium stearate. In regards to antiwearand friction reduction, the results indicate better tribological properties for the IL3 and IL4with the 25 wt% of PTFE and lithium stearate. The electrical conductivities were similar for allthe ionic liquid grease formulations which were higher than the general purpose grease as thereference. The work has paved the way for further investigation of ionic liquid based greaseswhich show potential in mitigation of bearing current in electric machines.

This diploma thesis deals with the issue of EMC of tram vehicles and traction system. The first chapter defines the issues that are then dealt with in the thesis. The next chapter lists the objectives of the work. Subsequent chapters analyze the issues described in chapter 2. In the last chapter, a flow chart is proposed, which should serve as a tool to estimate the hazards of the traction drive due to induced bearing currents.

Klimatutmaningar, lagändringar och ett ökat miljötänk har tvingat transportsektorn att ställa om till eldrift. Batterier och elmotorer har utvecklats kraftigt och är nu ett alternativ även för tunga fordon. Ett vanligt förekommande problem med elmotorer i fordon är lagerströmmar, här kallat gnista eller blixthändelser. Dessa uppstår på grund av oönskade urladdningar i motorn och förorsakar skador på lagren i motorn. Syftet med motorlager är att avlasta och minska friktionen kring motoraxeln. För att förebygga problemet och se förbättringar eller försämringar av olika åtgärder som görs krävs att lagerströmmar kan identifieras utifrån mätdata. Detta examensarbete analyserar relevant forskning inom området för att sedan introducera en metod och en algoritm för att identifiera lagerströmmar i samarbete med Scania CV. Algoritmen består av tre olika parametrar som påverkar identifieringen av de oönskade strömmarna på olika sätt. Verktyget lyckades identifierade lagerströmmar i olika mätdata, och hittade skillnader i antalet blixthändelser mellan olika körningar av provobjektet. Dock krävs vidare utveckling av verktyget och möjligheten att bearbeta annan typ av data som exempelvis spänningar i motorn för atthitta bättre samband. / A changing climate, changing laws and an increased environmental consciousnesshas forced the transport sector to transition to electric power. Batteries and electric motors have seen a quick and powerful development which means that they are now an alternative even for heavy vehicles. A common problem with electric motors forvehicles is bearing currents. The bearing currents occur as a result of electrical discharges in the motor and can damage the bearings inside the motor. The purpose of motor bearings is to offload and reduce friction for the motor shaft. To prevent the issue and to see improvements or deteriorations from different preventativemeasures it is critical to be able to identify bearing currents from data. This thesis analyzes relevant research in the area before introducing a method and an algorithm for detecting bearing currents in cooperation with Scania CV. The algorithm is composed of three different parameters which affects the identification in different ways. The tool was able to identify bearing currents from various data and found differences between the number of bearing currents between different test runs of the motor. However, more development of the tool and the possibility to process different kinds of data like voltages inside the motor is needed to be able to find better patterns in the data.