Bearing currents in converter operation

Figure 4 is an example of common-mode voltage. This new neutral voltage has a frequency equal to the switching frequency of the inverter and can yield high-frequency currents in the bearing with limited amplitude and duration.

Motors and drives with proper low-impedance grounding rarely exhibit bearing currents. Often, bearing currents will occur because of specific installation conditions. Many methods for preventing bearing currents exist. Depending on the cause, some are better options than others. Different options include:. These options are highlighted in Figure 5. The red arrow displays shaft to ground currents. The green arrow displays circulating currents, and the yellow arrow displays currents from the shaft through the load and to the ground.

A large grain elevator in North Dakota had a horsepower motor and variable frequency drive VFD installed on top of it. While both the motor and VFD were grounded, the length of cable to the ground was more than 1, feet. Loud squealing and noises began coming from the motor bearings. This indicated fluting in the bearing race caused by bearing currents. A motor grounding brush was installed upon startup as a preventive measure.

As a result, a large flow of current moved through the grounding brush, which did not remove the difference in voltage potential between the motor shaft and ground. As a result, the motor shaft voltage increased with time and was then arcing through the bearing. Two measures were taken to resolve the situation. First, insulated motor bearings were installed. This prevented current from flowing through the bearings.

The second was to replace the installed grounding cable with stranded grounding cables. This allowed for more current to flow through the grounding wires by eliminating the problem of skin effect. Skin effect occurs when high frequency currents pass through a conductor of a certain size. Because of the high frequency, current will only flow through the outer portion of a conductor and not through the inside similar to glazing only being able to stick to the outside of a doughnut and not to the center.

By using stranded cable with high frequency currents, the current is forced to flow through each strand, which reduces resistance of the grounding cable. This removed the large difference in voltage between the motor shaft and ground. These solutions are all viable options, depending on the source of the problem. No solution is a cure all for bearing currents because they can have several causes.

If an operator suspects that a system is experiencing bearing currents, consulting an engineering service with the proper measurement tools is the best way to identify the source of the problem.

He performed electric machine and transformer research using advanced high frequency magnetic materials under a grant from the U. Advanced Research Project Agency — Energy. Scioscia is senior application engineer at Eaton. Subscribe Now and Get: In-depth articles on pump industry issues Expert insights into important topics in the field Keep up with trends, basics, and more.

Breadcrumbs You are here: Home. How to Find a Solution for Bearing Currents. The best option for preventing bearing currents depends on the source of the problem. Bearing currents occur in specific motor and drive installations and can lead to motor fatigue and failure. What Are Bearing Currents? These shaft voltages will do one of the following: Cause the current to flow directly from the shaft, through a bearing, and through the motor or load frame into the ground see Figure 1 Cause the current to circulate from one side of the shaft, through a bearing, through the motor frame, back into the opposite bearing, and back into the shaft see Figure 2.

Figure 1. Current flow from shaft to ground. Figure 2. Tischmacher , S. In order to obtain an integrated overview of the situation, it is decisive that the main points of investigation that are discussed are combined and viewed holistically. Results from the parameter test area and their link with the overall situation are shown. A higher-level systematic to simulate electric currents flowing through a… Expand.

View on IEEE. Save to Library Save. Create Alert Alert. Share This Paper. Background Citations. Methods Citations. Results Citations. Figures from this paper. Citation Type. Has PDF. Publication Type. More Filters. Bearing wear caused by converter-induced bearing currents. In order to obtain an integrated … Expand. View 4 excerpts, cites methods and background. Investigations on bearing currents in converter-fed electrical motors.

As shown in [6], the issue of current flowing through a motor bearing is a system-related topic. Different aspects have to be taken into account to identify countermeasures to avoid or dampen the … Expand. Influence of bearing currents on the bearing lifetime for converter driven machines. The possibility to calculate motor bearing currents from motor geometry and the mechanisms that lead to these currents are known today [1], [2].

The precise mechanical and electrical procedures which … Expand. Prediction of motor bearing currents for converter operation.

The mechanisms that lead to bearing currents have been known for several years. Empirical results have been collected for a few combinations comprising converter, motor and motor feeder cable. Probability model for discharge activities in bearings of converter-fed electric motors. Voltage source inverters in electrical drive systems are the main sources of possible mechanical degeneration inside the anti-friction bearings of downstream drive train components. In order to find … Expand.

View 2 excerpts, cites background. 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 … Expand. This paper deals with the bearing wear and the early detection of possible damages in bearings of variable-speed, converter-fed electrical motors.