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:
Magma X100 delivers AMB systems for wide range of industrial machinery
Electrical switching & drive systems & components
SpinDrive launches Magma X100 controller, bringing active magnetic bearing technology to a new generation of industrial applications. The Magma X100 expands SpinDrive’s oil-free, frictionless AMB technology to applications below 150 kW, unlocking new addressable markets.
Read more...
Mammoet completes major bridge replacement at Amsterdam Centraal Station
Electrical switching & drive systems & components
Mammoet completes the second of five major bridge replacements at Amsterdam Centraal Station, transporting steel deck sections by water to keep the station open throughout the works.
Read more...
Compressorless hydrogen turbine generates electricity using detonation waves
Electrical switching & drive systems & components
Researchers at the Karlsruhe Institute of Technology (KIT) have demonstrated a hydrogen gas turbine that generates electricity without a mechanical compressor.
Read more...
Why lubrication fails in mining and what to do about it
Editor's Choice Electrical switching & drive systems & components
Lubrication Engineers explains the recurring failure points behind mining lubrication problems and how the right product, storage and application practices can improve equipment reliability.
Read more...
Echain protects cables in cleanrooms
igus
Electrical switching & drive systems & components
Advanced polymer manufacturer igus has developed a new cleanroom energy chain with an innovative guide system that allows for abrasion-resistant travel over distances of up to 30 metres.
Read more...
PowerFlex drives cut energy use by up to 30% amid rising costs
Electrical switching & drive systems & components
Rockwell Automation’s PowerFlex 755TS variable frequency drives are delivering energy reductions of 10 to 30% in Africa’s industrial operations, with adaptive control and predictive maintenance features that cut downtime by up to 50%.
Read more...
Next-generation oil-free motor systems with active magnetic bearings
Electrical switching & drive systems & components
WEG and SpinDrive are collaborating to integrate SpinDrive’s AMBs and built-in IoT condition monitoring into WEG’s market-leading electric motor offering, creating an oil-free, maintenance-free drive solution.
Read more...
Direct drive with integrated control
Vepac Electronics
Electrical switching & drive systems & components
The PSD 40 direct drive is a mechatronic system with integrated control, bus interface and absolute measuring system, with no battery required.
Read more...
AI-powered on-premises analytics for industrial drives
Siemens South Africa
Electrical switching & drive systems & components
Siemens is introducing a new on-premises analytics solution for industrial drive systems. The software enables users to evaluate drive data entirely within their own infrastructure and meet stringent data-sovereignty requirements.
Read more...
Hydrostatic machine base for ultra-precision grinding centre
Electrical switching & drive systems & components
Hyprostatik Schönfeld has developed a high-precision hydrostatic machine base for a new ultra-precision grinding centre for Optotech. The machine platform enables a previously unattainable combination of dimensional accuracy, dynamics and surface quality in the ultra-precision grinding of optical surfaces.
Read more...
printer friendly version