Power Quality

Publications

We provide a brief discussion of one or two timely PQ topics. More information on the topics will be provided as a document that can be viewed and/or printed as an Adobe (pdf) file for your use.

Current Topic

Testing of Plug-In Transient Voltage Surge Suppressors (TVSS) 

Upcoming Topic

Harmonic Filter for Personal Computers -font Part 2: Passive, Series-Connected Parallel-Resonant

Past Topics Description
Harmonic Filter for Personal Computers Part 1: Passive, Parallel-Connected Series Resonant Part 1 of a 2-part series that deals with using filters to reduce harmonic current distortion caused by personal computers on a common branch circuit.
Everything You Wanted To Know About Harmonics (But Were Afraid To Ask) Part 1: A Few Basics Part 1 of a 2-part series that deals with the significant issue of harmonics in power quality and how they affect electronic equipment.
Everything You Wanted To Know About Harmonics (But Were Afraid To Ask) Part 2: Advanced Topics Part 2 of a 2-part series that deals with the significant issue of harmonics in power quality and how they affect electronic equipment.
Motor Bearing Currents and Adjustable Speed Drives A technical brief on bearing currents and how it may lead to preventable mechanical failure for motors in adjustable speed drive applications.
Line Reactors and Adjustable Speed Drives A technical brief on using line reactors to reduce harmonics and transient voltages on the line side of adjustable speed drives.

Motor Bearing Currents Information

Adjustable Speed Drives (ASDs) are widely used in HVAC and process applications for precise load control and energy efficiency. As the technology advances, faster switching frequencies are used to precisely modulate the speed of motor shaft rotation.

Bearing pitting or failure is a potential problem, however, associated with ASDs using fast-switching semi-conductors to pulse-width modulate motors. The high switching frequency results in a steep change in voltage at the output of the ASD inverter. If conditions are right, a charge builds up on the rotor casing, ultimately resulting in a current arc to the bearings. The arc can cause a pit to form on the bearing surface and grooves to form in the bearing race over time. In extreme cases, "frosting" will develop on the bearings that will finally cause the bearing to fail completely.

Read more about this topic and possible solutions by viewing:
Bearing Currents: A Major Source of Mechanical Failure for Motors in Adjustable Speed Drive Applications (210 KB)

Read an actual case study of bearing current problems encountered at a Honolulu facility:
Motor Bearing Failure Case Study (4.24 MB)

Need more information? View this easy to read paper with application tips on diagnosing and mitigating the problem:
Preventing Premature Failure of Bearings in Motors Driven by PWM ASDs (852 KB)

Need even more information? Here's a link to ABBs site with more in-depth technical information on the subject:
ABB Bearing Currents Tech Guide 5 (370 KB)