Andreas Binder

Calculation of Circulating Bearing Currents in Machines of Inverter-Based Drive Systems

The high-frequency circulating bearing current that may occur in machines of inverter-based drive systems can be described by an eddy-current model. The parameters of an equivalent circuit are derived from the model. The ratio between bearing current and common-mode current amplitudes for different machines is calculated. The theoretical maximum ratio is about 0.35. Copper loops applied for bearing current measurement may decrease the circulating bearing currents up to almost 40%

Practical Rules for Assessment of Inverter-Induced Bearing Currents in Inverter-Fed AC Motors up to 500 kW

The influence of different parameters of a variable-speed drive system on the phenomena of inverter-induced bearing currents has been studied under exactly the same conditions on inverter-operated alternating current motors from 1 to 500 kW. Detailed modeling may not always be applicable with practical applications in the field, where many parameters might be unknown. Therefore, the most important correlations are summarized in the form of a flowchart that is based on the physical cause-and-effect chains. This flowchart can serve as a tool for engineers to estimate the endangerment of a drive system due to inverter-induced bearing currents and select an appropriate mitigation technique if necessary, where detailed knowledge of the different design parameters is not available

Permanent magnet synchronous generators for regenerative energy conversion - a survey

A survey on recently installed or developed permanent magnet (PM) synchronous generators for energy conversion in regenerative and alternative power supply systems is given. Its focus is for low speed machines on geared and gearless PM generator systems for wind power plants and small PM hydro generators in gearless coupling. For distributed co-generation of heat and electrical power by micro gas turbines specially designed PM generators for high speed are necessary. Design example for both low speed wind and hydro generators and high speed generators are given along with application examples

Don't lose your bearings

22 HE EFFECTS OF PARASITIC BEARING currents in variable-speed drive systems caused by fast-switching insulated gate bipolar transistor (IGBT) inverters have been reported during the past several years [1]–[24]. In the past, research has focused on physical explanations of the bearing currents for a given drive system at a particular power level. The results presented are based on specific investigations with either small or large motors with respective power ratings of Pr = 1 . . . 15 kW and Pr ≥ 150 kW. One research lab reported on investigations done on motors with power ratings of Pr = 30 . . . 70 kW and Pr = 355 kW [20]–[22]. Different mitigation techniques to eliminate inverterinduced bearing currents have also been proposed. The studies reported were done using varied measurement techniques and test setups, rendering forthright comparison of the qualitative and quantitative results difficult. Thus, quantification of the relative weights of the different parameters on the phenomena still requires additional clarification. Such clarification is the goal of this article. A systematic analysis of the qualitative and quantitative influence of different parameters on a variable-speed drive system was carried out. The investigations were conducted under identical conditions on motors rated from 11 to 500 kW T

Scaling Effects of Inverter-Induced Bearing Currents in AC Machines

In this survey paper, we show by straightforward mathematical scaling considerations that small inverter-fed ac motors of up to typical 20 kW at 1500/min are likely to suffer from discharge (electric discharge machining) bearing currents, whereas larger motors are likely to be subjected to high-frequency (HF) circulating bearing currents. When comparing motors that operate at the same voltage level, the resulting bearing-current density is high for very small and very large motors. Smaller values occur in between these two extremes with medium size motors in the range of 10-100 kW. Therefore, electric bearing insulation is useful for larger motors to interrupt the HF circulating bearing-current path, whereas small motors need rotor shielding, common-mode voltage filters, or hybrid bearings.

Analytical Calculations of Induced Eddy Currents Losses in the Magnets of Surface Mounted PM Machines With Consideration of Circumferential and Axial Segmentation Effects

This paper presents a method for the calculation of eddy current losses in the permanent magnets, which takes into account the reaction of induced eddy currents. The developed quasi-3-D analytical method considers the effects of axial and circumferential segmentation of magnets. The 2-D time-stepping finite element method and 3-D time harmonic finite element method are used to evaluate the accuracy of the analytical method. A high speed surface-mounted permanent magnet motor with Samarium Cobalt magnets is used for detailed simulations. High-frequency time harmonics of the inverter are considered for analysis of magnet eddy current losses. The novelty of the proposed analytical method is the direct consideration of the reaction of induced eddy currents in the magnets due to travelling and pulsating field waves.

High-speed inverter-fed AC drives

High speed drives offer advantages such as small size, low noise, integrated and thus compact design for many industrial applications due to the fact, that as direct drives they avoid the mechanical gear. Inverter supply provides variable speed, which allows high efficient operation for compressors and pumps. A wide speed and power range from 0.1 kW up to 80 MW is covered with circumference speeds of 100 ... 250 m/s. Recent progress is discussed and details of the design of high speed electric machinery are addressed, such as electromagnetic utilization, loss components, types of motors, bearing aspects and inverter-motor interaction.

Techniques for Measurement of Parameters Related to Inverter-Induced Bearing Currents

Inverter-induced high frequency bearing currents are a parasitic effect that can occur in variable-speed drive systems. While the physical cause-and-effect chains are understood, little has been known on appropriate quantitative assessment of the phenomena. This paper discusses reliable techniques for the measurement of the different parameters of importance for the bearing damage assessment, including their effects on the phenomena and measured quantities. A good understanding of these correlations allows custom-design, cost-effective handling of the matter.

Calculation of influence of insulated bearings and insulated inner bearing seats on circulating bearing currents in machines of inverter-based drive systems

The high-frequency (HF) circulating bearing current that may occur in the machines of the inverter-based drive systems can be reduced or even completely suppressed by the use of the electrically insulated bearings or the insulated inner bearing seats. This paper proposes a method to calculate the influence of the thickness of the insulating coat on the obtained current reduction as a function of the several machine-design parameters. The parameters of the equivalent circuit are derived from an eddy-current model. The calculation considers the transient nature of the current flow. For the standard fan-cooled motors with up to 500-kW rated power, a minimum thickness of the insulating coat of 250 mum is required to reduce the circulating bearing currents to values where the apparent bearing-current density is less than 0.1 A/mm2, which is commonly taken as the threshold to the bearing failure

What can bearings bear

This paper studies the series of 22 test runs performance for bearing damage assessment due to inverter-induced bearing currents. The influence of bearing current amplitude and type, calculated apparent bearing current density, time of operation, and inverter switching frequency on bearing damage was investigated. The degree of electrical bearing stress W was introduced. The degree of melting of the bearing race surface and the grade of reduction of the carboxylic acid bound in the grease, which is an indicator for the deterioration of the grease, depend on W