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
Medium voltage drive for enhanced energy efficiency and process optimisation Schneider Electric South Africa
Motion Control & Drives
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...Powerful high-precision hexapod
Motion Control & Drives
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...Servicing the electric motor sector
Motion Control & Drives
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...Control system for deep antenna Rockwell Automation
Motion Control & Drives
When a major university in South Korea set out to build a 21-metre deep space antenna, the researchers needed a control system that could track celestial objects with pinpoint accuracy, a level of precision they thought was out of reach. By partnering with Rockwell Automation, they discovered that the right technology and support could turn their vision into reality.
Read more...Manufacturers should go PFAS-Free igus
Motion Control & Drives
igus continues to develop engineered plastics that are free of per- and polyfluoroalkyl substances (PFAS-free) in response to mounting evidence of severe environmental and health hazards caused by the chemicals.
Read more...South African paper producer partners with ABB
Motion Control & Drives
Neopak, a leading manufacturer of containerboard and paper products, has renewed its partnership with global technology company, ABB to upgrade the existing automation system at its Rosslyn Paper Mill in Pretoria.
Read more...Compact, powerful and green mini-picker
Motion Control & Drives
SkyJacks has introduced Jekko’s Mini Picker to the southern African market. This is a compact, highly versatile and environmentally friendly electric mini-picker that is set to redefine lifting capabilities across multiple industries.
Read more...Redefining industrial lifting
Motion Control & Drives
The Konecranes S-series hoist redefines industrial lifting through its integration of a ground-breaking synthetic rope with smart features, a lifting capacity of 20 tons, and the ability to adapt to diverse girder configurations.
Read more...Bühler drives innovation in agriculture and food processing
Motion Control & Drives
NAMPO 2025 is set to be one of the most significant agricultural events in southern Africa. It provides a unique platform for Bühler to showcase its advanced solutions that are designed to improve efficiency, sustainability and profitability in the agricultural sector.
printer friendly version