The effect of variable DC bearing current amplitude, bearing current polarity, mechanical force, rotation speed, bearing temperature, and number of the balls on the fluting in an axial ball bearing ...type 51208 is investigated under DC currents. The results are obtained from two different test setups with two different lubricants (mineral-oil-based grease and polyglycol oil). The speed varies between 100 rpm and 2000 rpm, the axial bearing force between 200 N and 2400 N, the DC current amplitude between 0.5 A and 20 A, the bearing temperature between 29 °C and 80 °C, the number of steel balls per bearing between 3 and 15, and the test duration between 6 h and 168 h. The results show that with a higher bearing current density and/or a higher bearing speed, a lower bearing force and/or a lower bearing temperature, a bigger number of roller elements, but also at a negative polarity of a DC electric bearing current, the occurring of fluting is more probable and occurs at an earlier stage of operation.
Electrical bearing currents may disturb the performance of the bearings via electro-corrosion if they surpass a limit of ca. 0.1 to 0.3 A/mm2. A continuous current flow, or, after a longer time span, ...an alternating current or a repeating impulse-like current, damages the raceway surface, leading in many cases to a fluting pattern on the raceway. Increased bearing vibration, audible noise, and decreased bearing lubrication as a result may demand a replacement of the bearings. Here, an electrically corroded axial ball bearing (type 51208) with fluting patterns is investigated. The bearing was lubricated with grease lubrication and was exposed to 4 A DC current flow. It is shown that the electric current flow causes higher concentrations of iron oxides and iron carbides on the bearing raceway surface together with increased surface roughness, leading to a mixed lubrication also at elevated bearing speeds up to 1500 rpm. The “electrically insulating” iron oxide layer and the “mechanically hard” iron carbide layer on the bearing steel are analysed by WLI, XPS, SEM, and EDS. White Light Interferometry (WLI) is used to provide an accurate measurement of the surface topography and roughness. X-ray Photoelectron Spectroscopy (XPS) measurements are conducted to analyze the chemical surface composition and oxidation states. Scanning Electron Microscopy (SEM) is applied for high-resolution imaging of the surface morphology, while the Focused Ion Beam (FIB) is used to cut a trench into the bearing surface to inspect the surface layers. With the Energy Dispersive X-ray spectrometry (EDS), the presence of composing elements is identified, determining their relative concentrations. The electrically-caused iron oxide and iron carbide may develop periodically along the raceway due to the perpendicular vibrations of the rolling ball on the raceway, leading gradually to the fluting pattern. Still, a simulation of this vibration-induced fluting-generation process from the start with the first surface craters—of the molten local contact spots—to the final fluting pattern is missing.
Bearing currents induced in electrical motors, driven with fast switching power electronic inverters, can lead to bearing surface damages on the raceway. In this paper the electrical contact in the ...bearing is studied. The influence of surface oxidation in the electric contact is described. The bearing voltage and the bearing current of the axial ball bearing, type 51208, are investigated under influence of injected DC bearing currents. The contact radius of the electric contact spots ( a- spots) are estimated based on the measured bearing resistance. Measured voltage-current characteristics of the bearing are presented for rotational speeds <inline-formula><tex-math notation="LaTeX">{\boldsymbol{n}} = 0, 100, 1000 \mathbf{mi}{\mathbf{n}}^{ - 1}</tex-math></inline-formula>, bearing forces <inline-formula><tex-math notation="LaTeX">{{\boldsymbol{F}}}_{\mathbf{b}} = 100 \mathbf{N}</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">1000 \mathbf{N}</tex-math></inline-formula>, DC bearing currents between <inline-formula><tex-math notation="LaTeX">{{\boldsymbol{I}}}_{\mathbf{b}} = 10 \mathbf{mA}</tex-math></inline-formula> and <inline-formula><tex-math notation="LaTeX">9.5 \mathbf{A}</tex-math></inline-formula>, without and with lubrication and without and with the oxide-cleaning agent, citric acid. This paper is for better understanding of the bearing electrical behavior.
In this paper, a comprehensive design procedure for the Brushless DC (BLDC) motors is proposed and the governing equations are derived from the motor flux linkage and are utilized in the flowchart ...presented for the BLDC motor design. The proposed algorithm is based on the weighted target functions optimization. This algorithm is developed for a surface-mounted permanent-magnet inner-rotor 2pole-3slot pattern BLCD motor. A 120 watt 8pole-12slot 4000 rpm BLDC motor is designed by means of the flowchart as a case study. The resulted parameters from the flowchart are used to make the 3-D model analysed by finite element analysis (FEA). Then, FEA results are compared with the flowchart results to verify the proposed design algorithm. Output parameters of a fabricated BLDC motor having the same physical properties are measured and presented to show the applicability of the algorithm.
This paper investigates the origins of common-mode voltage (CMV) noises in SiC MOSFET-based three-level T-type inverters (3LT 2 I), targeting adjustable speed drive (ASD) systems, and proposes ...methods for their mitigation. Although achieving zero common-mode voltage (ZCMV) is theoretically unattainable in a two-level voltage source inverter (2L-VSI), it can be realized in a 3LT 2 I by selecting specific switching states. However, the necessary simultaneous switching of two half-bridges in ZCMV methods generates significant CMV noises, which are due to the dead-time and differences in output voltage transition times. This work proposes a method to mitigate these CMV noises through precisely adjusting the timing of the transitions in the gate drive signals. This method can reduce electromagnetic interference (EMI) associated with CMV and minimize passive filter size. Lastly, the paper answers the critical question: Is full CMV suppression practically possible?
Electrical bearing currents, e.g. in inverted-fed electrical machines, may disturb the performance of the bearings. In this paper the steady-state temperature of the bearing surface at the electrical ...contact point between the balls and the raceway is derived in the mixed lubrication state. The thermal analysis is presented based on the Holm's electric contact model, namely the a-spot. The contact model of Andreason is presented as well for comparison. The results are extended to predict the instantaneous contact surface temperature in an axial bearing (type 51208) at 500 rpm with 1 A average bearing current and with an axial bearing force of 800 N. Moreover the average of the contact surface temperature is obtained for the same bearing in a range of operating points, i.e. a rotating speed from 0 rpm to 3000 rpm, a bearing average current from 0.25 A to 3 A, at an axial bearing force 800 N. The results can be utilized to predict the contact temperature on the bearing surface for any given bearing from the measured bearing voltage.
The influence of static rotor imbalance on the generation of bearing fluting due to bearing currents is experimentally investigated. For that six inverter-fed induction machines with the rated power ...of 1.5 kW and three with the rated power of 11 kW were tested with especially prepared bearings. The machines were operated with three different static rotor imbalances (U0, U1, U2) to test the imbalance influence on the fluting effect due to discharge and rotor-to-ground bearing currents. The damaging effect of inverter-induced bearing currents is influenced by the parameters "rotor speed", "bearing temperature", "bearing grease" and "grounding conditions" of the inverter-motor-system. The impact of a static rotor imbalance on the damaging process caused by the parasitic bearing currents is so far unknown. Therefore it shall be clarified, if the combination of static rotor imbalance and bearing currents may damage the bearing raceway surfaces much faster than without imbalance. As a concluding result our test procedures showed no acceleration of bearing deterioration due to static rotor imbalances.
Measuring of electrical currents, voltage and resistance of an axial bearing Safdarzadeh, Omid; Weicker, Martin; Binder, Andreas
2021 International Aegean Conference on Electrical Machines and Power Electronics (ACEMP) & 2021 International Conference on Optimization of Electrical and Electronic Equipment (OPTIM),
2021-Sept.-2
Conference Proceeding
Bearing currents induced in electrical motors driven with fast switching power electronic inverters lead to bearing surface damages on the raceway. This may be the case especially when the rotor is ...electrically connected to the earth potential of the system e.g. via the cogging wheels of a coupled gear. In this paper an axial bearing type 51208 is investigated at standstill and in rotation concerning the bearing resistance. The a-spot situations are estimated in standstill based on the measured signals. In rotation the bearing resistance is measured for a range of operating speeds from 0 rpm to 3000 rpm, a range of bearing currents from 0.5 A to 3 A, and two axial forces 180 N (rated condition), 800 N. A special test rig is designed to measure the bearing voltage and current signals without using mechanical brushes in the rotating system to eliminate the contact resistance of the brushes in the measured bearing signals. The results allow to predict the bearing electrical behavior at a bearing current flow through the ground.
To fully exploit the energy of photovotaic (PV) panels, a sub-module MPPT strategy (known as distributed maximum power point tracking) is extensively utilized in PV systems. This strategy is ...performed using the micro-inverters which serve as the interfaces of PV panels. Therefore, ac microgrids equipped with large scale PV panels, are expected to be dominated by micro-inverters. This paper investigates the parallel operation of a large number of micro-inverters in islanded microgrids. It is shown that stability of ac microgrids is jeopardized under a high penetration of micro-inverters. This is done using the impedance stability analysis and with the help of pole map of the whole ac microgrid. Moreover, a robust active damping approach is proposed. This approach improves the parallel operation of ac micro-invertes and prevents the instability of ac microgrids. Different simulation scenarios are provided to validate the findings and effectiveness of the proposed active damping approach.
