No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
Effects of modified modulation strategies on bearing currents and operational characteristics of AC induction machines
Abstract
Newest investigations have shown that bearing currents can be lowered by using modified pulse pattern generation methods. One suggestion for such a solution is the principle of sequentially positioned pulses. Hereby, a modified space vector modulation is used, in order to reduce both the amplitude of and the number of potential alterations in the common mode voltage. This voltage is the reason for EDM and dv/dt currents which are mostly responsible for severe bearing damages in modem inverter fed drive applications. The paper will show the fundamental basics concerning this principle and its characteristic influences on the operational behaviour of an inverter fed AC induction machine.
... A high percentage of process disruptions are due to bearing failures. In the meantime a substantial number of mitigation techniques have been developed [1,[7][8][9][10][11][12]. However, the industrial user searching the literature for an immediate solution encountering a concrete bearing current problem in an existing plant configuration finds itself abandoned since most of the mitigation techniques are not feasible without enormous changes of the electrical plant configuration. ...
The effect of bearing currents in inverter driven induction motors has been investigated and reported for about ten years. Mitigation techniques have been developed and approved by experiments. In this paper, the special situation of troubleshooting in a given configuration such as existing large plants is discussed. The determination of the actual bearing current phenomenon and the development of the appropriate mitigation technique under given circumstances are shown. A new equivalent circuit diagram for the bearing currents in large drives has been developed and used for evaluation of mitigation techniques. Experiences applying the mitigation techniques to a drive suffering premature damages due to rotor ground bearing current are presented and discussed using experimental results
The converter switching in variable-frequency drives can generate high frequency common mode voltage between the machine winding and the converter ground, leading to high frequency parasitic currents which can flow through the machine bearings unless precautions are taken in design and installation. These parasitic and unintended currents in the bearings cause deterioration of the lubrication film and surface damage to the rolling elements of the bearings. These problems will be exacerbated as wide-bandgap semiconductors with faster switching rise times start becoming more widespread in variable-frequency drives. This paper reviews the modelling and mitigation techniques of high frequency bearing currents in inverter fed AC drives. It aims to provide a solid base for the research community to further understanding the bearing currents phenomenon and helping to find novel improved technique for their mitigation and measurement.
Bearing currents cause a reduction of ball bearing's lifetime in electronically commutated permanent magnet motors. To compensate the lifetime decreasing factors, a tradeoff between special bearings and additional changes in the machine design have to be found. Stator grounding, for example, keeps the bearing voltage low and thus guarantees a long fan system's lifetime, however, results in a higher input filter effort. On the other hand, instead of reducing the bearing voltage, hybrid bearings could be deployed, which feature a high dielectric strength. The major disadvantage is that hybrid bearings are much more expensive than conventional metal bearings, thus the extra cost for the hybrid bearings has to be weighed up against the higher filter effort needed with stator grounding. In this paper bearing damage mechanisms are analyzed and the impact of stator grounding to avoid bearing currents in low power singlephase motors is presented. Based on the presented filter design procedure, the additional filter effort for stator grounded motors is determined, which shows that hybrid bearing are undesirable in mass application.
Drive manufacturer migration to insulated gate bipolar transistor
(IGBT) output devices demands a more careful selection of motors and
load cables. IGBT drives have faster output voltage risetimes which have
increased the dielectric voltage stress placed on the motor.
Semiconductor risetime now has a greater influence on motor transient
voltages, emphasizing the need to understand the reflected wave
phenomenon and its system effects on both motors and cables. Issues and
solutions relative to motor selection, cable selection, and installation
are outlined and discussed. Potential problems and solutions not
commonly known even among experienced drive users are presented
This paper examines AC motor shaft voltages and resulting bearing
currents when operated under pulse width modulation (PWM) voltage source
inverters. The paper reviews the electrical characteristics of bearings
and motors that cause shaft voltages and bearing currents. A brief
review of previous work is presented, including a system model for
electrical analysis of bearing currents. Relying on the work of a
companion paper, the propensity for electric discharge machining (EDM)
is determined by a design equation that is a function of system
components. Pertinent machine parameters and their formulas are
presented and values calculated for machines from 5 to 1000 HP. The
effects of system elements on shaft voltages and bearing currents are
evaluated experimentally and the results compared to theory. Finally,
the paper presents quantitative results for one solution to the shaft
voltage and bearing current problem
Shaft Voltages and Bearing Currents - New Phenomena in Inverter Driven Induction Machines
- H.-J Conraths
Reduction of Bearing Currents by using Asymmetric, Space-Vector-Based Switching Patterns
- J Zitzelsberger
- W Hofmann
Balcells; Improvement possibilities of PWM voltage inverter EMI effects using different modulation methods
- D Gonzalez
- A Llaquet
- D Arias
- J L Bedford