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Advanced Rotorbar Analysis – False Negatives: Dual Cage Rotors

advance rotobar-20022 Ernesto J. Wiedenbrug, Ph.D., SM IEEE
Introduction
Some squirrel-cage motors designed for high start-up torque may get weaker over time, needing longer startup times and may perhaps even trip during line-start – but never show big problems in vibration or MCSA. This paper explains what gives high startup torque motors their special capabilities, describes a common failure mode making it nearly impossible to find the issue using MCSA or vibration, and diagnostic alternatives for these problems.

To continue reading the full case study, with images, please download the free PDF file here. http://csaanalysis.com/PDFS/Advanced%20Rotorbar%20Analysis%20-%20False%20Negatives%20-%20Dual%20Cage%20Rotors.pdf
To contact Whitelegg direct please visit http://www.whitelegg.com

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Advanced Rotorbar Analysis – False Negatives: Dual Cage Rotors

whitelegg pic 2 Ernesto J. Wiedenbrug, Ph.D., SM IEEE
Introduction
Some squirrel-cage motors designed for high start-up torque may get weaker over time, needing longer startup times and may perhaps even trip during line-start – but never show big problems in vibration or MCSA. This paper explains what gives high startup torque motors their special capabilities, describes a common failure mode making it nearly impossible to find the issue using MCSA or vibration, and diagnostic alternatives for these problems.

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FAQ – Issues of High Distortion Surrounding VFDs

whitelegg pic 4 by Ernesto Wiedenbrug, Ph.D.
Variable Frequency Drives (VFDs) can introduce power quality problems to line-operated motors on the same buss, and also to the motors being driven by VFDs. This FAQ shows typical voltage and current waveforms for such systems, and touches upon some of the potential power quality problems.
To continue reading the full case study, with images, please download the free PDF file here.
http://csaanalysis.com/PDFS/FAQ%20-%20Issues%20of%20High%20Distortion%20surrounding%20VFDs.pdf
To contact Whitelegg direct please visit http://www.whitelegg.com

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Startup Transients – Two Case Studies of Reduced-Voltage Starters

whiteleggpic6 by Dave Olinger and Ernesto Wiedenbrug, Ph.D.
This paper discusses how voltage and current captures of motors starting at line frequency can be used to diagnose high resistance contact problems, and even detect whether these problems are up-stream or down-stream from where the measurements were taken [1-2]. These concepts are applied on startup transient captures of two 8-pole 100hp motors which are started via 80% reduced-voltage autotransformers (Fig. 1) [3]. One motor shows a high resistance contact below the point of measurement, and the other transient capture was used to diagnose a problem in the autotransformer, which has been verified to be shorts in the transformer.
To continue reading the full case study, with images, please download the free PDF file here.
http://csaanalysis.com/PDFS/Startup%20Transients%20for%20Reduced%20Voltage%20Starts.pdf
To contact Whitelegg direct please visit http://www.whitelegg.com

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New,Specialist Website OffersAffordable Range of World-Class Motors, Drives and Inverters, with Fully Trained, on-Line Support

Industry OEMs and plant managers now have a new online, direct source of AC motors and inverters at some of the best prices available online in the UK.

Rewinds & J Windsor (RJW’s) new website,www.motorsandinverters.co.ukoffers a vast, online range of high quality but affordable brands and specifications, combined with free delivery and the backup ofa fully manufacturer-trained technical helpline.

Whitelegg Supports Anstee & Ware in Winning new Rail Traction Motor Contract

For over 60 years The Anstee & Ware Group have provided electrical and mechanical engineering services to UK industry. From their 7 sites they are well placed to service the needs of industries as diverse as steel, aerospace, oil and gas, utilities, paper and quarrying.
In addition, the company identified an important market opportunity to become leaders in the servicing and repair of traction motors for the expanding rail and mass transit industry.

The Company agreed to commit £300,000 to the latest technology to enable rapid and high quality repairs to traction motors, with the focus of the investment to be at their Castle Donnington site adjacent to the famous motor racing circuit.

Advanced Rotorbar Analysis – False Positives: Spiders / Axial Cooling Vents

whitelegg pic 3 Ernesto Wiedenbrug, Ph.D., SM IEEE,
Virtually all rotors of motors above 100kW are designed with axial cooling vents, potentially causing false positives for both prevalent diagnostic technologies, vibration and MCSA. Fig 1 shows the rotor with 8 spider-legs of a 2.4MW 6.6kV motor that was pulled out of service due to such a vibration and MCSA false positive.
This paper explains how to recognize problematic motors, the reason for these false positives, how these motors react, and how to deal with them.
To continue reading the full case study, with images, please download the free PDF file here. http://csaanalysis.com/PDFS/Advanced%20Rotorbar%20Analysis%20-%20False%20Positives%20-%20Spiders%20-%20Axial%20Cooling%20Vents.pdf
To contact Whitelegg direct please visit http://www.whitelegg.com

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FAQ: Output voltage of a VFD has ‘flat’ spots – is it a problem?

whitelegg pic 5 Ernesto Wiedenbrug, Ph.D.
Description:
The voltage waveform to the left in Fig 1 looks normal, but at another point in time it looks like the waveform to the right of Fig. 1; where the waveform stays constant on the top and the bottom. What is going on? Is this a problem?
Fact:
VFDs don’t only change the frequency of the voltage, but also the voltage level in proportion with the frequency.
Comparing the frequencies:
Both plots show two complete cycles for the voltage waveforms; the one to the left takes 46.1ms for two cycles – which means 43.4Hz, and the one to the right takes only 41.7ms, which means that the VFD is running at 48Hz. According to the Volts per Hertz control technique [1], this means that the VFD output voltage needs to be almost 10% higher for the waveform to the right.
To continue reading the full case study, with images, please download the free PDF file here.
http://csaanalysis.com/PDFS/FAQ%20-%20what%20does%20it%20mean%20if%20the%20voltage%20waveform%20generated%20by%20a%20VFD%20has%20'flat%20spots'.pdf
To contact Whitelegg direct please visit http://www.whitelegg.com