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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(More)
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(More)
The occurrence of high-frequency discharge bearing currents (also called "electric discharge machining (EDM) currents") that can occur in machines of inverter-based drive systems depends strongly on the value of the capacitive voltage divider "bearing voltage ratio" (BVR) of the machine. This paper presents a straightforward approach to calculate the(More)
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(More)
An eddy-current model can describe the high frequency circulating bearing current that may occur in machines of inverter-based drive systems. 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(More)
—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(More)
Carbon brushes using electrically conductive carbon graphite have been used for shaft-grounding and current-conduction purposes for a long time. We present an alternative brush concept made from millions of conductive microfibers. If properly designed, such brushes can meet all the demands on carbon brushes but exclude the problems of excessive and(More)
Ocean energy conversion has been of interest for many years. Recent developments such as concern over global warming have renewed interest in the topic. This paper gives a systematic and comprehensive overview of wave energy converters (WEC) as opposed to ocean current energy converters. The point absorber and oscillating water column WEC devices are(More)
Ocean energy conversion systems have recently seen renewed interest, stimulated mostly by today's increasing energy discussions. In addition to ocean current energy converters, several commercial ocean wave energy projects have already been undertaken; however, no clear economic model exists for developers to follow. Therefore, this paper focuses on U.S.(More)
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(More)