When it comes to supplying a reliable service to a customer how much faith should I put in the results from typical motor testing programs? We have multilins to shut off the motor before too much damage occurs and we do surge tests, circuit analysis and megger tests at least once a year. What are the chances that a motor will fail without any warning? Is it good practice to have spares no matter how diligent the maintenance department is at testing the motors?
Answer:
Annual testing is not frequent enough for PdM. Your multilin will shut off equipment after a fault occurs, providing only a little more protection than an overload. Equipment of this type is meant to be circuit and load protection, not motor protection. Predictive maintenance, on the other hand, is meant to be a series of repeatable measurements that can trend a fault over time. The more frequent the readings, the more accurate the program. Annual testing provides no more than a spot-check. Therefore, if you are only testing annually, then, yes, you must have a large number of reactive spares. Once test results are trended more frequently, and corrections are made to correct the root-cause of faults, then you can decrease your spare inventory.
Sincerely,
Howard W Penrose, Ph.D. General Manager
ALL-TEST Pro BJM Corp
123 Spencer Plains Rd
Old Saybrook, CT 06475
Ph: 860 399-5937
Fax: 860 399-7784
www.alltestpro.com
Can you please tell me the probable causes for 2 X line frequency in motors.
We had a problem of high vibration in one of our motors. Main contributor to vibration is 2 x line freq.. When we opened motor we found all things okay.
Can you tell me reasons for 2 x line frequency.
Answer:
The number one reason for any 2FL (twice line frequency) signature is electrical. Now, the type of electrical problem will be the question:
1) Stator eccentricity, shorted laminations, loose iron and a loose stator core will cause a high 2FL frequency, normally without sidebands.
This will also occur with unbalanced voltage incoming voltage.
2) Some 3600 RPM, and to a limited extent, some 1800 RPM, low voltage concentric-wound motors will show 2FL just because of the placement of the coils in relation to the stator core and rotor. This signature is more pronounced when the motor is connected for Delta.
3)Pole pass frequency (or twice slip frequency) sidebands around running speed and the 2FL peak indicate eccentric rotor conditions (usually dynamic eccentricity).
4) Broken rotor bars will show as multiples of running speed with pole pass frequency sidebands and may also show as rotor bar pass frequency
(RBPF) harmonics. 2FL sidebands around RBPF harmonics indicate looseness in the rotor bars.
5) Loose connections will appear as sidebands around a 2FL peak as 1/3 FL peaks with harmonic sidebands.
The good news is that motor current signature analysis is designed to quickly detect these issues using the motor current instead of mechanical vibration (the two technologies complement each other tremendously).
Please visit our site: www.alltestpro.com for more information on motor current signature analysis (MCSA).
Howard W. Penrose, Ph.D.
General Manager, ALL-TEST Pro
A Division of BJM Corp
123 Spencer Plains Rd
Old Saybrook, CT 06475
Ph: 860 399-5937
Fax: 860 399-3180
www.alltestpro.com
What are the best practices for lubrication of electrical motors? We have moved away from using spike energy to detect higher levels of energy and are now using a time based program depending upon rpm and voltage level of the motor. Spike energy was not repeatable from technician to technician, pressure exerted on the accelerometer and placement of such are both critical to the reading.
We have charted our bearings and fill capacity for each and have installed grease relief on the motors that can be pulled to allow excess lubricant to exit the motor.
I have read a few articles on the usage of ultrasonics to detect lubrication needs, is this the way that reliability based maintenance is going?
We have purchased Assalub greasing equipment which will provide us with an accurate fill count.
Any input into building a world class motor lubrication program would be appreciated, thank you.
Could someone tell me once in for all what if any kind of signature you should see on a good arrestor and what on a bad one. I was under the assumption that there would be no heating on a good arrestor. I have 18KV MOV arrestors and I've measure anywhere from 2C to 20C. I always try to scan these on cooler damp days. The signature covers the whole arrestor but not connections to ground or input just the insulator body of the arrestor.
What is the best plan to predict standby to operating movement of a system?
I would receive information about low speed vibration on rolls bearings < 100 rpm
We are looking for a characteristic value of the shape parameter in a Weibull distribution describing the wrong signal failure mode for the
following instruments: 1.vibration magnetic sensor; 2.temperature switch; 3.pressure switch; 4.temperature resistance; 5.pressure transmitter. Could you help us?
We have a centrifugal compressor driven by a motor. It has lube oil system consisting of pumps, coolers, filters, overhead tank, rundown tank etc. During the last Shutdown we analyzed the oil in the oil reservoir for moisture content and found to be 0.4 % w/w.
Our concern is...
1. How much moisture, in percentage or ppm, is acceptable in lube oil?
2. Is there any standard/code or reference available in this regard?
I was debating the characteristics of a DC Shunt Motor with come coworkers and would just like some clarification. A DC Shunt motor can be thought of as a "constant-speed" motor, right? This means that as the torqued load on the motor increases, a DC drive will increase the armature current required to drive the motor at the same speed. But as the load changes, so does the output (HP) of the motor, even if the DC drive is inputting the maximum power (Watts). This is where an efficiency map of the motor would be a useful item. This came about because we were trying to spec out a gearbox and I wasn't sure that the contracted engineer knew the workings of a DC motor. Am I correct in what I have said?
We have several hydraulic systems through out the plant, some low pressure and some high pressure servo systems. We are looking into establishing a cleanliness level of 14-12-10 for all systems. Is this feasible? If this level is achievable what warning levels should we use, ie. caution level 16-14-12 and warning level 17-15-13 or should the caution and warining levels be lower? Any advice will be greatly appreciated.
I know that statistics are kept on failed equipment but how do you come up with an accurate figure on equipment and money saved through the implementation of an infrared program.
How can misalignment be recognised using frequency analyses?
I've recently been assigned an area of responsibility concerning vibration monitoring of rotating equipment. We used velocity probes (Wilcoxson 973v). As I review our collection specifications (Entek - Emonitor/Enshare) I noticed that the vendor specifies 100mV/ips whereas the collection specification calls out 100mV/g. This doesn't seem consistent or correct to me, but I'm told it makes no difference either way???? Additionally, manufacturer accuracy specification is +- 10% yet when I review the calibration acceptance criteria it states +- 3dB from reference. Again this doesn't seem to be consistent.
Can you provide some insight?
We are currently working on a system that has a 10 yr storage requirement on it. There is also a requirement that the system must able to work after 10 yrs of storage and achieve an operational MTBF of 233Hrs min from 1200 hours of powered transit in a Jet Fighter environment. How would you recommend that I carry out such a prediction on an electro mechnaical system with no redundancy
Can you tell me the electrical relationship between a VFD and a motor, particularly what I am looking for is how to match VFD's and motors. Thank you.
Joe Balkind, Maintenance Supervisor with Cargill Salt. 916 South Riverside Avenue, St. Clair, MI, 48079, US. WorkPhone: (810) 326-5140. Email: joe_balkind@cargill.com.
Click on the comments tab for an answer and use this link for a VFD paper (pdf)
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What is the relationship of oil, acid number and corrossion? Can oil cause corrossion on a metal substrate?
I am looking to find a "Best Industry Practice" for exercising an emergency standby generator with an automatic transfer switch. Our current mode of exercising the generators is on a weekly cycle running for one hour with the transfer switch transferring the load to the generator. I want to convince management that the transferring of the load should be done only several times a year rather than every week. Doing the load transfer every week causes too much wear on the mechanical linkages and could possibly fail to transfer when it is actually needed. We have 80 of the Onan 15KW generators installed at ou locations through out the state. Walter Rieble, Maintenance Engineer with CAP. email wrieble@cap-az.com. address: CAP, PO Box 43020, Phoenix, AZ, 85080, USA.
If you find the signs of broken/loose rotor bars in your FFT and have no MCE equipment available how do you suggest determining the severity of the problem. Side bands around running speed @ slip freq*# of poles. Any advise would be appreciated
Is it true the cleanliness code for particle count has been wrong and it is not 2-5-15 but that it is 4-6-16 or something close to that. I heard this and was wanting to know for sure.
Do any case studies exist on the detrimental effects of soft foot on machinery? In almost every article or report that I read, it
explains how important it is to eliminate soft foot, but there is no explanation as to why. I have found that most maintenance people do not understand how a soft foot condition actually effects the internal components of a machine with moving parts. I have also discovered that only a very few "Alignment Experts" understand that soft foot can exist other places than just on the feet of machine.
Overall readings were taken on a motor running uncoupled. Readings were .176 ips vertical,.199 ips axial, and .034 ips horizontal. The motor was
replaced with a new one. Overall readings taken on the new one were .124 ips vertical, .141 ips axial, and .018 ips horizontal. Not knowing any
more than this, I suspect that there is nothing wrong with the motors, that the problem must be related to the method of support for the
motors. Motors are supported by flexible metal beams. Any help help would be appreciated. What further data, such as full spectrum readings,
should I ask for?
What approach consider best practice regarding pump duty rotation? (Methodical duty change at XXXX intervals? Random? Continuous run between unit outages?)
Suppose load requirement is 1.5 KW and contractor has provided 3 KW motor.What will be the minus and plus points?and considering all pros and cons should I acceept this?
I have tested various oil samples from parts requested by the client to the
contract standard. The current standard requested is ISO 4406 _12/10. The
recomended oils in some cases are specified _/15/12 and that this would be
out of the contractual requirement. The other oils are specified by the manufacturers under ISO VG 150 and ISO VG 46. With the first sample
specified as _/15/12 and a viscosity of ISO VG 32, can I relate the viscosity value to the purity and would this mean that the recomended oils would be lower grades than required by the contract.
Can you recommend a source for vibration standards? More specifically we're looking to compare paper mill vibration levels. Hopefully one for overall "mill wide" and separate levels by mill areas.
Your assistance and/or direction will be most appreciated.
Jerry