Motor bearing current phenomenon
3rd Quarter 2011
Electrical switching & drive systems & components
Yaskawa application note.
Introduction
Since the introduction of PWM inverters, it has been recognised that PWM inverters introduce motor shaft voltages and bearing currents. The bearing damage in inverter-driven motors is mainly caused by the shaft voltage and bearing currents created by the common-mode voltage and its sharp edges. All inverters generate common-mode voltages relative to the power source ground that cause coupling currents through the parasitic capacitances inside the motor. The main source of bearing currents is the capacitance-coupling currents that return via the motor bearings back to ground.
This paper discusses the relationship among common-mode voltage, motor shaft voltage and bearing currents using parasitic capacitances and its mathematical representation inside the motor.
Common-mode voltage in inverter-driven AC machines
In a three-phase AC system, the common-mode voltage can be defined as the voltage difference between the power source ground and the neutral point of a three-phase load. If the load is an AC motor, the neutral point of the load means the stator neutral of the motor. It is important to define the common-mode voltage in mathematical terms in order to compare its characteristics among different types of source and load combinations.
In three-phase AC loads, the phase to ground voltages can be written as the sum of the voltage from phase to the neutral point of the load and the neutral point of the load to the system ground. As per the definition, the common-mode voltage is the voltage across the neutral point of the load and the system ground.
Readers interested in a full mathematical analysis of the subject together with some recommended approaches to prevent bearing current damage in AC machines can find the complete application note at http://instrumentation.co.za/+C15396
Further reading:
Control without complexity
Axiom Hydraulics
Electrical switching & drive systems & components
In an era where precision, performance and smart control define industrial success, the right driver can make all the difference. At Axiom Hydraulics, we’ve seen firsthand how the Sun Hydraulics XMD series transforms hydraulic systems, from mining and construction to agriculture and automation.
Read more...
Planetary gear units for high torque requirements
SEW-EURODRIVE
Editor's Choice Electrical switching & drive systems & components
Packing a compact design, along with high torque and low-speed outputs, the new SEW PPK and SEW P2.e planetary gear units from SEW-EURODRIVE offer new capabilities in continuous heavy-duty applications where space is at a premium.
Read more...
Medium voltage drive for enhanced energy efficiency and process optimisation
Schneider Electric South Africa
Electrical switching & drive systems & components
Schneider Electric South Africa has unveiled its cutting-edge Altivar Process ATV6100 medium voltage (MV) drive range, designed to enhance energy efficiency and operational reliability across various industries.
Read more...
Servicing the electric motor sector
Editor's Choice Electrical switching & drive systems & components
Hexagon Electrical has expanded its manufacturing and service capabilities to meet the growing demand for customised, high-performance specialised electric motors in heavy engineering, and hazardous industrial and mining applications.
Read more...
Powerful high-precision hexapod
Electrical switching & drive systems & components
With the HEX150-125HL, Aerotech is launching the latest generation of its hexapod technology. The compact six-axis positioner combines precise movements with high load capacity and simple integration.
Read more...
Why turbomachinery should break free from vendor lock-in
Schneider Electric South Africa
Electrical switching & drive systems & components
Today’s modern turbomachinery control systems form an important of operational efficiency, be it in heavy industries, traditional power generation or renewables such as hydroelectric facilities. Independence is the name of the game, and turbomachinery stands to gain lot from this newfound freedom.
Read more...
Industrial gear units for mixing and agitating processes
Bearing Man Group T/A BMG
Electrical switching & drive systems & components
Nord Drive Systems encompass modular drive configurations that ensure optimum performance of mechanical speed control for specific applications in almost every industry.
Read more...
PC-based control for a food capsule and pod packaging machine
Beckhoff Automation
Editor's Choice Electrical switching & drive systems & components
For TME, a machine builder specialising in the packaging of powdered foods, Beckhoff’s PC-based control technology offers unlimited opportunities when it comes to performance and innovative capacity in terms of flexibility, scalability and openness.
Read more...
New torque sensors for fastening applications
Electrical switching & drive systems & components
Sensor Technology, a global leader in innovative torque and load measurement solutions, has launched its latest advancement in torque sensing technology.
Read more...
Miniature position sensor for precision motion control applications
Electrical switching & drive systems & components
The ILPS-13Z Series miniature linear variable inductive transducer position sensor is designed to deliver exceptional performance and reliability for a wide range of industrial and laboratory applications, including automotive R&D, motorsports, motion control, medical, military and aerospace.
Read more...
printer friendly version