Electrical bearing failures in electric vehicles

In modern electric equipment, especially electric vehicles, inverter control systems can lead to complex shaft voltages and bearing currents. Within an electric motor, many parts have electrical failure problems, and among which bearings are the most sensitive and vulnerable components. In recent years, electrical failures in bearing have been frequently reported in electric vehicles, and the electrical failure of bearings has become a key issue that restricts the lifetime of all-electric motor-based power systems in a broader sense. The purpose of this review is to provide a comprehensive overview of the bearing premature failure in the mechanical systems exposed in an electrical environment represented by electric vehicles. The electrical environments in which bearing works including the different components and the origins of the shaft voltages and bearing currents, as well as the typical modes of electrical bearing failure including various topographical damages and lubrication failures, have been discussed. The fundamental influence mechanisms of voltage/current on the friction/lubrication properties have been summarized and analyzed, and corresponding countermeasures have been proposed. Finally, a brief introduction to the key technical flaws in the current researches will be made and the future outlook of frontier directions will be discussed. Document type: Articl

Electrical Bearing Damage, A Problem in the Nano- and Macro-Range

Rolling bearings face different damaging effects: Besides mechanical effects, current-induced bearing damage occurs in electrical drive systems. Therefore, it is of increasing interest to understand the differences leading to known electrical damage patterns. It is of utmost importance not to consider the harmful current passage in the machine element as an isolated phenomenon but to take into account the whole drive system consisting of the machine elements, the electric motor and the connected power electronics. This publication works toward providing an overview of the state-of-the-art of research regarding electrical bearing currents

Bearing Wear In Electric Motors and Rotating Equipment Under the Aspect of VSD Converter Operation

Lectur

Laakerivirtojen ja -jännitteiden mallintaminen taajuusmuuttajaohjatuissa sähkömoottoreissa

The possible bearing damages in inverter-fed AC motors are nowadays an important issue in the industrial scope. These motors are known to experience bearing voltages and currents. The root causes for the bearing voltages and currents are common-mode voltages produced by the inverter. However, no cost-effective solution for large AC motors, especially in Azipod systems, has been found to mitigate these problematic voltages and currents. The existing solution is to insulate the non-drive end bearing shield, which takes a large amount of space, is expensive and challenging to manufacture. In addition, no high-frequency model of large AC motors has been created for the purpose of the analysis of bearing voltages and currents. The work presented in this thesis identifies the common factors that lead to these harmful voltages and currents, and from a consideration of these factors, a high-frequency model of the AC motor is created. This model is then adapted to the Azipod system. Simulations are carried out showing the interdependence of different components in the system. In order to complete the simulations, extraction of model parameters that involves analytical calculations and measurements are shown in detail. The model presented in this work can be connected to an appropriate electric drive in order to predict the bearing voltages and currents with a simulator such as OrCAD. The results of the simulations show that the present mitigation techniques can be simplified, with certain precautions, without increasing the bearing voltages and currents to dangerous levels.Mahdolliset laakerivauriot taajuusmuuttajasyötetyissä vaihtovirtamoottoreissa ovat merkittävä haaste teollisuudessa. Kyseisten moottorien tiedetään altistuvan laakerijännitteille ja -virroille, joiden on havaittu aiheutuvan taajusmuuttajan tuottamasta yhteismuotoisesta jännitteestä. Toistaiseksi ei ole löydetty kustannustehokasta ratkaisua pienentämään näitä ongelmallisia jännitteitä ja sähkövirtoja suurissa vaihtovirtamoottoreissa, varsinkaan Azipod-järjestelmissä. Nykyinen ratkaisu on trustipään laakerikilven eristäminen, mikä vie paljon tilaa ja on kallista sekä haastavaa toteuttaa. Toistaiseksi ei ole kehitetty suurtaajuusmallia isoille vaihtovirtamoottoreille laakerijännitteiden ja –virtojen analysointia varten. Tässä työssä on esitetty yleiset tunnistetut tekijät, jotka johtavat näihin haitallisiin jännitteisiin ja virtoihin vaihtovirtamoottoreissa. Työssä on luotu nämä tekijät huomioon ottaen suurtaajuusmalli vaihtovirtamoottoreille. Mallia on kehitetty niin, että sitä voidaan käyttää Azipod-järjestelmässä. Simulaatioiden perusteella voidaan osoittaa eri komponenttien keskinäiset riippuvuudet järjestelmässä. Simulaatioiden suorittamiseksi työssä on esitetty yksityiskohtaisesti mallin parametrien ekstraktoiminen, mikä sisältää analyyttista tarkastelua ja mittauksia. Työssä esitetyn mallin voi yhdistää sopivaan sähkökäyttöön, jolloin laakerijännite ja –virta ovat ennustettavissa piirisimulaattorilla, kuten OrCAD:lla. Työn simuloinnit osoittavat, että nykyisiä käytettyjä laakerivirtojen lieventämistekniikoita voidaan yksinkertaistaa tietyllä varauksella ilman laakerivirtojen ja -jännitteiden nousua vaarallisille tasoille

Wind Turbine Generator Reliability: An Exploration of the Root Causes of Generator Bearing Failures

Increasing the availability of multi-megawatt wind turbines (WT) is necessary if the cost of energy generated by wind is to be reduced. Reliability surveys have shown that WT generator bearings have a relatively high failure rate, with failures happening too early to be due to classical rolling contact fatigue. It has been the purpose of the present work to demonstrate the value of models which may help to explain some of the failure modes of wind turbine generators (and their root causes). The work has considered two potential root causes of wind turbine generator failure. Firstly, gearbox-generator misalignment caused by deflection of the compliant drivetrain under loading. Secondly, electrical discharge machining (EDM) of the generator bearings due to the common-mode voltage caused by pulse width modulation (PWM) of the power electronics. Numerical simulations have been used to investigate these potential failure modes and to show how they bring about premature failure. It has been shown that there exists a mechanism by which gearbox-generator misalignment can exacerbate EDM. This demonstrates the importance of holistic analyses of WTs, which are complex electromechanical systems with non-trivial interactions between sub-assemblies. The need for further research has been shown

Electrical Characterisations of Bearings

Mechanical bearings are an integral part of industry, and are used in various places in order to reduce friction between two interacting surfaces and are used to transmit power and loads. Mechanical bearings are one of the most extensively used components within the wind industry, but on the other hand they are also one of the most dominantly failing failed components. In order to increase the feasibility of wind energy, and to make the wind power more sustainable, a reduction in operation and maintenance cost of wind energy is important. The failures in bearings in the wind energy sector and other industries increased after the introduction of switched power electronic switches (Insulated Gate Bipolar Transistors, or IGBT) within the power converters. The reasons of early failures have been linked to the presence of a common mode voltage at the neutral of the converter and its coupling on the shaft, where the bearings are located. The system is also vulnerable to different types of bearing currents, which are discussed in this report. A small voltage in range of 10\u27s of volts could lead to large electric-field stress of 30 to 40 V/\ub5m in a bearing depending on nominal film thickness at the operating point. The build-up of large electric field stresses in the bearing leads to ohmic electrical conduction through the bearing. Presently, the mitigation techniques mainly discharge the voltage across the bearing by providing a low resistance path for the flowing current using different methods, such as carbon brushes, \ua0or shaft rings, but damages due to bearing current activity and early failures still exist. Another way to mitigate bearing currents is to use filters in the electrical connections, to obstruct or to reduce the amplitude of the bearing currents, but they fail to completely eliminate them. The use of insulating coating on surfaces of the bearing and ceramic rolling elements helps to provide a high resistive path for the current in case of DC voltage, but act capacitively and let the current pass through the bearing when high frequency circulating type bearing currents flow in the system. Nevertheless, to device a successful mitigation technique, it is important to fully understand the electrical breakdown and discharge activity within the bearing’s insulation (i.e., the lubricating film) along with electrical properties of the bearing during running conditions. In our research, we have focused on understanding the electrical properties of the mechanical bearing at different operating conditions and elaborating it through an electrical circuit model. The components of this electrical circuit model are found out experimentally through different laboratory tests. The mechanical bearing is sometimes found to behave as an insulator of electricity and is hence characterizecharacterised by an impedance during the ‘Insulating state’ of the bearing in the model. The impedance in this insulating state is further categorized as a parallel combination of a resistor and a capacitor (parallel RC branch), which corresponds to the ‘real’ and ‘imaginary’ part of the measured bearing impedance. Furthermore, when the bearing enters in into a partial breakdown state, the voltage across the bearing is ‘discharged’, resulting in flow of current through the bearing until the voltage across the bearing again recovers. The Electrical electrical characterization characterisation of bearing lubricants has been performed in order to find out the relevant electrical properties, such as relative permittivity, electrical conductivity and electric breakdown strength at rather short gaps. The electrical behaviorbehaviour of the mechanical bearing at different operating conditions such as rotational speed, mechanical load along with magnitude, frequency and shape of applied voltage has been found out experimentally in order to understand and elucidate the electrical properties of a mechanical bearing in operation

Embedded Sensors and Controls to Improve Component Performance and Reliability Conceptual Design Report

The objective of this project is to demonstrate improved reliability and increased performance made possible by deeply embedding instrumentation and controls (I&C) in nuclear power plant (NPP) components and systems. The project is employing a highly instrumented canned rotor, magnetic bearing, fluoride salt pump as its I&C technology demonstration platform. I&C is intimately part of the basic millisecond-by-millisecond functioning of the system; treating I&C as an integral part of the system design is innovative and will allow significant improvement in capabilities and performance. As systems become more complex and greater performance is required, traditional I&C design techniques become inadequate and more advanced I&C needs to be applied. New I&C techniques enable optimal and reliable performance and tolerance of noise and uncertainties in the system rather than merely monitoring quasistable performance. Traditionally, I&C has been incorporated in NPP components after the design is nearly complete; adequate performance was obtained through over-design. By incorporating I&C at the beginning of the design phase, the control system can provide superior performance and reliability and enable designs that are otherwise impossible. This report describes the progress and status of the project and provides a conceptual design overview for the platform to demonstrate the performance and reliability improvements enabled by advanced embedded I&C

Electrical Bearing Damage, A Problem in the Nano- and Macro-Range

Rolling bearings face different damaging effects: Besides mechanical effects, current-induced bearing damage occurs in electrical drive systems. Therefore, it is of increasing interest to understand the differences leading to known electrical damage patterns. It is of utmost importance not to consider the harmful current passage in the machine element as an isolated phenomenon but to take into account the whole drive system consisting of the machine elements, the electric motor and the connected power electronics. This publication works toward providing an overview of the state-of-the-art of research regarding electrical bearing currents

Bearing Wear In Electric Motors and Rotating Equipment Under the Aspect of VSD Converter Operation

Lectur

An assessment of flywheel storage for efficient provision of reliable power for residential premises in islanded operation

Energy storage systems (ESS) are key devices for improving power quality, electrical system stability and system efficiency by contributing to the balance of supply and demand. They can enhance the flexibility of electrical systems by mitigating supply intermittency, which has recently become problematic due to the increased penetration of renewable generation. The subject of this thesis is flywheel energy storage system (FESS), a technology that is gathering great interest due to benefits offered over alternative energy storage solutions, including high cycle life, long calendar life, high round‐trip efficiency, high power density, operation at high ambient temperatures and low negative environmental impact. This thesis describes the modelling and assessment of small scale energy system incorporating FESS with solar photovoltaic (PV) and a diesel generator for use in islanded residential premises with highly intermittent or non‐existent grid infrastructure. In this application, incorporation of FESS is shown to be beneficial in comparison to a system without storage or one with the alternative storage technology, Li‐Ion batteries. The thesis begins with a description of flywheel storage systems configured for electrical storage which comprises of a mechanical part; flywheel rotor, bearings and containment, and an electric drive part; motor‐generator and associated power electronics. Each of these components is described in the thesis along with the equations and modelling, itself carried out in the MATLAB/Simulink environment. Finally, the flywheel model is combined with a model of an islanded residential power system incorporating a solar PV system with a diesel generator. Such a system would be particularly useful for offgrid applications or those with weak grids as occurs in developing countries