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Is This Motor Failure Due to Protection Failure?

08/27/2017 8:51 AM

Dear All,

One of our plant motor has recently Burnt. It was newly installed and within 8-months even not being in continuous operation (Operating in duty cycle on/off).

Motor rating: 400Vac 50Hz 36A 18.5KW 1465rpm Cos phi 0.84

The operating conditions for this motor were same as of original existing motors that is balanced three phase power supply without any harmonics, no overloading (electrical or mechanical), ambient temperature less than mentioned on motor data sheet and name plate(+50°C).

Our Maintenance department has the following assessment:

1. Motor quality was not as the existing original motors.

2. The original motor Insulation class is F/F. While the burnt motor Insulation class is F/B. That is Insulation class F but limited to temperature rise of class B. (Motor data sheet).

3. The Type of newly supplied motor is D5C while the existing motor has type D4C. Same difference exists in their serial nos. (Manf. Confirmed motor is same but with new series).

4. The motor was supplied without any QA/QC, test certificates, performance curves, and conformities.

5. No factory acceptance test or third party inspection was made/involved.

6. Considering new motor from factory no tests were conducted by our maintenance department and motor was directly installed.

7. The RTDs in the motor were not connected to any PTC relay. As in original motor starter this option is not available. (Motor Starter Wiring Diagram).

8. The newly supplied motor had insulation failure specially the place of embedded RTDs. Two phase winding were shorted.

9. Protection system worked, the only short circuit by the MCCB found tripped and earth fault relay found tripped.

Could you please identify the true cause of stator winding flashover, and recommendation shall be highly appreciated.

Please feel free to ask any further details you may require.

Best Regards

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#1

Re: Is This Motor Failure Due to Protection Failure?

08/27/2017 10:08 AM

thumbnail pictures are not suitable for us to view. You need to link the original documents.

In addition, it sounds like the purchasing department bought a cheap Chinese motor that was badly made and did not endure - which is what the maintenance men stated.

Replace the purchasing agent, get the new person to buy the correct motor

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#2
In reply to #1

Re: Is This Motor Failure Due to Protection Failure?

08/27/2017 12:06 PM

Yes it could be the reason. But we have its starter with protection. the circuit breaker NS80H - MA, Thermal overload relay LRD33 are perfectly coordinated. Residual current relay. we found them tripped but stator winding phase to phase were already burnt. Seems protection worked even winding damage occurred. This motor is DOL start. Its RTDs we did not connect to any protection. As in original design there is no thermistor relay. As the motor was not thermally protected, might be damaged for this reason. I am not sure.

I am looking the way to link the documents, could you please guide me to link original documents.

Thanks in advance

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#6
In reply to #2

Re: Is This Motor Failure Due to Protection Failure?

08/27/2017 6:37 PM

Get a free account at https://imgur.com/

upload the pix, then place the links here. imgur provides the links

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#3

Re: Is This Motor Failure Due to Protection Failure?

08/27/2017 1:06 PM

Did you send these photos to mfg?

Who wrote the engineering performance/purchasing specification?

Cost should not be the deciding factor in choosing motors, unless the mfg will certify the performance if each.

Simply placing an order and trusting the mfg will not normally result in the best outcome.

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#4

Re: Is This Motor Failure Due to Protection Failure?

08/27/2017 3:24 PM

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#5

Re: Is This Motor Failure Due to Protection Failure?

08/27/2017 3:38 PM

What was the ambient temperature at the motor when the failure occurred?

What was the typical amperage drawn by the motor when in use?

What are the approximate on/off times. How many starts per hour?

Next time, you might add an RTD-actuated relay to the circuit.

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#7

Re: Is This Motor Failure Due to Protection Failure?

08/27/2017 10:13 PM

To me it sounds like your protection circuitry worked exactly as designed. When this inferior motor failed you did not get an uncontrolled fire in your plant.

Usually one shouldn't blame their seat belts for the accident that ruined the family car. One should praise the seat belts for saving the family.

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#8

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 12:31 AM

In my opinion, since the damaged part it is in open position- not in a slot -it is not likely to be an overloading the cause. However, if it was not high-potential tested I don't think the overvoltage was the problem- as the rated voltage seems to be low.

I think the winding was damaged mechanically while in assemble process and withstand it-damaged-for a while.

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#9
In reply to #8

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 6:04 AM

Some more details:

It is fan cooler motor belt driven. It is being used to cool inlet gas from compressor.

A pitch controller is the only load varying factor. The operator monitors the inlet gas temp. and accordingly set a command…. motor to run and adjust the fan blades to some angle via a pitch controller to get maximum cooling. If he set fan blades angle 100% then motor runs at its rated amp 36A or bit more 37. The burnt motor was operating on 36/37 Amp as the fan blades runs at max. efficiency 100% max blade pitch angle.

For similar motors whose fan blade pitch angle is set at 75% runs at max. 22 AMP.

Hence swap of these motors depends on gas temp. In summer they run all and in winter some off. Their operation start/stop is manual by control room operators.

The original motor had a rotor run out that is slight rotor bend. Due to a high tension belt and long idle condition. It was rubbing against Bearing inner cap. Thereby violating the clearance. As these motor are used in hazardous area Zone -0, So we replaced it by new motor. The old motor worked for 15-years with normal PM and routine overhauling.

These motors are Ex Proof, and are designed for harsh environment like ours (Gas Plant) in desert. Some of these days temp reached 48°C. In extreme winter its goes to -5°C. Humidity max reaches to 89.

Similar other motors are working under same condition for the last 15-years.

All the rest winding are clear, no sign of overheating there. Only the spot shown is affected. It was like huge spark which melted the broken conductors, blackened the drive end cover, rotor side etc. Short like welding arc.

We have our own Gas turbine generators, with very stable, balanced and clean power supply. I am sure any kind of transient phenomenon does not exist in normal operating conditions.

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#17
In reply to #9

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 3:03 AM

The only electrical thing that should be installed in <...hazardous area Zone -0...> is EEx ia installations.

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#22
In reply to #9

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 7:17 AM
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#50
In reply to #9

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:00 PM

I may be incorrect but the pictures do not look like an EXPLOSION PROOF motor. I don't see any seals and the motor body looks a bit THIN!

I worked in the wastewater field where we had several EX-PROOF motors installed and they were SIGNIFICANTLY thicker and heavier that what is in the pictures!

However, The pictures are a bit small to get an accurate assessment.

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#10
In reply to #8

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 6:44 AM

7anoter4, I agree with you to suspect mechanical damage during manufacturing. If that motor was meg- gered before installation it might have failed.

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#47
In reply to #8

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 3:25 PM

I was about to say that there was probably damage to the windings as a result of improper / aggressive motor assembly!

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#11

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 10:54 AM

In my opinion this is an insulation protection due to motor's vibration (weak insulation design).

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#12

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 12:14 PM

Why was the replacement motor with F/B insulation class authorized for purchase, and who authorized it. That guy needs to pay for this somehow.

The theory about damage during assembly is also completely reasonable, and you could have ended up with a faulty product from the time it was received.

Who is responsible for going over products as received, and who checks them out?

Megger is indispensible tool in this business. Learn how to use, and keep one around.

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#13

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 12:40 PM

DISPOSITION:

Update insulation system to prevent premature failure. Or, do not damage insulation during assembling (if this was the way the insulation was damaged).

Plan A): Replace damaged coils if these can be removed.

Plan B): Strip unit and re-wind it.

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#14

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 1:16 PM

8. The newly supplied motor had insulation failure specially the place of embedded RTDs. Two phase winding were shorted.

In my opinion given this little tidbit of information, someone damaged or compromised the winding installation in the process of embedding the RTD, then the lack of QA/QC, testing, documentation and acceptance testing at your end allowed this defective motor to be placed into service.

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#15
In reply to #14

Re: Is This Motor Failure Due to Protection Failure?

08/28/2017 5:08 PM

Why did they put the RTD's in wrong, mess up the insulation, and then not even bother to connect RTD's to read out the over temperature conditions?

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#16
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Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 1:40 AM

The issue of this motor was totally handled by maintenance department. Engineering was not requested to provide any kind of assistance. And due to lack of technical knowledge, they could not know about insulation class. As F was mentioned there. Similarly just considering new motor they installed it directly without any testing.

We are oil and gas plant fully equipped with latest test equipment’s. In my final report I will put this condition, MR can be issued by respective department. But purchase requisition must be approved by engineering dept. prior to the issue of PO.

As I explained these motors are used in Zone -0, very sensitive (Hazardous), we can not replace coil or rewind the motor. As the issue of EX-Proof re validation certificate holds.

We did not connect the RTDs as in original design of motor starter this option was not available.

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#19
In reply to #16

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 3:33 AM

NKA, you actually thought you had an EX proof certified motor. It may be that it failed that rating already in the manufacturers factory. You could have had more than a blown motor. Purchasers are people that must chase and source the exact equipment as classified/certified by the Engineer and it must not be up to the maintanance staff to ensure the correctness. The data sheet for this motor already failed the test even before the order was placed. The purchase department at your facility think they are the qualified people and will still cost you because they report to the financial officer. (Just my gutt feeling) you can correct me.

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#18

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 3:07 AM

Why bother to buy a motor with embedded RTDs if these are not to be connected to a thermal protection trip circuit (rhetorical question - NNTR)?

No mention has been made about the setting of the motor overload trip device.

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#20
In reply to #18

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 6:17 AM

Dear All,

Last night we had similar accident, stator winding burnt of a 37KW motor. I will shortly upload all details. Now I am sure the issue is not particular the motor itself or its quality. I believe its indeed the protection failure. I will upload all protection details. and I would request all of the analysts to see this failure from protection point of view.

Thanks for every one.

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#21
In reply to #20

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 7:13 AM

<...protection point of view...> How about "all equipment failures stem from inadequate protection"?

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#24
In reply to #20

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 8:05 AM

No.

Protection systems do not protect motors from failing. Protection systems protect people, buildings, and product from further damage from a failing motor. A maintenance system can reduce the rate of failure but every moving part will eventually wear away without proper maintenance. A Quality Assurance (QA) system may detect a partial failure of a system before a catastrophic failure happens. However, since all QA measurements indirectly measure the machine producing product this is an inexact indicator of the product producing machine.

I believe the root cause of these three failures is one of two possible scenarios.

First, management's cost cutting practices have finally resulted in repeated failures.

Second, normal wear and tear have happened to produce a coincident failures at two motors.

It's time to get your engineering department to investigate. CR4 is not your engineering department. We cannot review your design paperwork, maintenance logs, purchase orders or inspection documents. Your engineering department should have access to all of these to make a report. CR4 can translate the report for you.

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#26
In reply to #20

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 9:52 AM

did it become a lost production accident, or a lost time accident?

This reminds one of a ticking time bomb, especially if this is a processing or refining operation.

How do you know this is not the direct result of sabotage? Do you have any way of knowing? Surveillance?

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#23

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 7:21 AM

A 3-phase motor connected in delta doesn't care about the state of balance of the incoming supply, as it is irrelevant.

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#25

Re: Is This Motor Failure Due to Protection Failure?

08/29/2017 9:32 AM

Where is this motor located?

Who is the manufacturer?

Does this motor use VFD?

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#27
In reply to #25

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:08 AM

Dear All,

Thanks to all of you for your valuable analysis. I understood now the protection system for LV motor without being connected with RTDs does not see the wear and tear in the motors, insulation degradation, heating due to bearing problems, inercaps rubbing, greecing etc. Motor draws still rated amperes or even bit low, till insulation failure and overheating of winding lead it to short circuited and earthed.

Both of these two motors 18.5kw and 37kw were connected in star. Direct on line starting not VFD. they were from renounced manufacturer Marrelli Motori Italia.

18.5 KW motor was new but 37KW motor served for ten years almost in continuous operation.

The 18.5KW motor was belt driven, had insulation failure due to manufacturer defect.

37KW motor had mechanical overheating. It tripped two weeks b4 on overloading. Maint. Dept found everything Ok as they could not guess that problems are mechanical. They reset the overload and put back motor in service. two weeks later it burnt. Electrical protection could not detect and once winding overheated, two phase short circuited and earthed. it tripped all its protection along with main feeder, thereby tripping the whole MCC. I found the contractor was stuck (pressed inside), one contact was quite sparked and the bottom iron core was broken.

In conclusion LV Motor protection simply with thermal OL, residual Current Relay and MCCB (For Motors) can not detect moderate mechanical overloading/overheating, heat and losses due to wear and tear, bearing and inner caop rubbings etc.

In this case RTDs have to be connected with some PTC relay to trip the MCCB. or probably the new electronic thermal OL relays with TESYS starter might be effective.

We started monitoring the amperes of each fan cooler motors from yesterday.

For your ref i am sending you all photos of 37kw motor and motors operation.

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#28
In reply to #27

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:10 AM
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#29
In reply to #27

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:12 AM

That doesn't look like a <...zone -0...> hazardous area, i.e. in the vapour space immediately above the surface of a stored flammable liquid?

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#31
In reply to #29

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:26 AM

These are zone-0, the 18.5 KW motor is for compressed in let gas, and 37KW motor is or regeneration gas Compressor on discharge sections. The compress gas has very high temp. A tiny spark can ignite fire in the whole gas train.

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#32
In reply to #31

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:28 AM

Only EEx ia installation is allowed in zone 0! Therefore either the motor must lie outside zone 0 or the hazardous area designation is wrong.

No-one would put 18.5kW of electricity into an area where a flammable gas/air mixture were more or less continuously present as a normal circumstance.

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#51
In reply to #32

Re: Is This Motor Failure Due to Protection Failure?

08/31/2017 1:33 AM

PLEASE SEE THIS NAME PLATE PHOTO

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#52
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Re: Is This Motor Failure Due to Protection Failure?

08/31/2017 1:19 PM

So you are in fact attempting to run a 50 Hz designed motor on 60 Hz service?

That might void the warranty... just sayin'

Somebody must have glossed over a few details...

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#30
In reply to #27

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:17 AM

<...reset the overload...> The overload device is there to protect the motor from <...overheated...> by tripping were the motor to be running above its nameplate maximum current. No mention is made of the setting of this device. No mention is made of the device having been adjusted to a higher setting to avoid "nuisance trips".

The <...MCCB...> is there to protect the cable.

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#33
In reply to #30

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:32 AM

I have mentioned all setting on the photos. Photos themselves show clear setting. Any way 37KW at 400V 50 HZ, is 67AMP, the thermal overload is set at 67AMP exactly.

This overload could not detect the heating effect of bearing problem and bearing inner cap rubbing. please see the photos, you can easily see the rubbing of end cap on the rotor shaft. As the amp were still in range, so it did not trip. But heating action was in continuous progression.

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#34
In reply to #33

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:40 AM

No electrical protection arrangements would prevent it recurring, then. It's merely down to misfortune following insufficient bearing maintenance.

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#35
In reply to #34

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 4:49 AM

I issue is with engineering department now. Deep investigations and recommendations shall be given by them. We do 36 Month overhauling, greecing on its schedule. For motors running for many years, i think good to reduce overhauling periods. Like 24 Months instead of 36Months. Monitoring amperes and temp by technicians time to time will improve the condition.

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#36
In reply to #35

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 9:09 AM

Further clarification, I come to know now that the MCCB in the starter panel did not trip, Contactor was stuck so main feeder breaker in power center was tripped.

I would appreciate your comments on my conclusion drawn. Or any recommendation to improve the efficiency of the protection.

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#38
In reply to #36

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 10:33 AM

When was the last time your site had a full inspection/evaluation of the electrical controls? Are the required arc flash energies clearly posted as labels on the control enclosures?

If you are having issues with the starter contacts welding together, then you have some real EE issues that need to be sorted out, and pronto.

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#43
In reply to #38

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 12:24 PM

This plant was commissioned in 2003. Since then as it is. No inspection/evaluation of control was done. only routine PMs. No arc flash energies posted as labels on the control enclosures?

For in operation since 2003, i am sure these contactors need replacement. Will be one recommendation from my side.

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#46
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Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 1:34 PM

There are various organizations that will consult with you, and help with the labeling, such as NVO - for a fee.

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#39
In reply to #36

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 10:43 AM

NKA,

I can see what happen with your motor but I don't want to go in discussion anymore. If your motor fail again, take into account that we can manufacture your motor. I have done R&D on insulation systems, I perform root cause of failures as well.

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#40
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Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 12:07 PM

Great I would like some one to perform root cause of failures /failure analyst. I do not know how to proceed with you. As we are bound by forum regulation neither to send e-mail address nor phone nos.

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#41
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Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 12:15 PM

Send the e-mail and phone nos information via private messaging.

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#44
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Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 1:32 PM

NKA,

Where is located your motor?

I am located in Minneapolis MN.

From the Rules: Do not post phone numbers or email addresses. The Admin will delete all phone numbers and email addresses posted in threads or comments. You can share this information via the forum's internal messaging system.

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#48
In reply to #44

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 3:34 PM

Why in the world are you using a 50 HZ motor in 60 HZ power grid Minneapolis unless there actually was a VFD somewhere?

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#49
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Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 3:36 PM

Another excellent question, and should have been glaring at all of us, I even thought about it, then wrote it off, because 2 was not being combined with 2 at the time, I kept getting three.

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#45
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Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 1:32 PM

send him a private message.

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#37
In reply to #35

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 10:28 AM

Seriously? Do these technicians actually make their inspection and logging rounds as they were originally required to?

You need some serious instrumentation help - get those bearing temperatures up and running, and with electronic data logging. Someone having integrity and responsibility needs to be reviewing the data on a frequent basis to look for signs of trouble, since the "average" technician may not know that they don't know what they are looking at, or why they are looking, if they are looking, and also actually caring about what they are looking at. Those who don't know, often do not know what they don't know, or care.

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#42
In reply to #37

Re: Is This Motor Failure Due to Protection Failure?

08/30/2017 12:16 PM

I agree with you. Nice!!! All our Medium Voltage Motors 6.6KV are linked to ECS/DCS system. They are being continuously monitored. SEPAM Relays well do thermal modelling for these motors. But all LV Motors are out of ECS/DCS system. What maximum we can do to take a clamp meter and infra red thermo meter do condition monitoring of these fan cooler motors at some regular intervals. They are not so many.

We have asked production, all motors subjected to cooler blade pitch angle, set pitch controller setting not more than 85%. Motors operate in lower amperage at lower blade pitch angle.

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#53
In reply to #42

Re: Is This Motor Failure Due to Protection Failure?

09/02/2017 1:41 AM

Dear All,

I have two suspects here.

I found 37-KW motor Non Drive End Bearing was not free;y moving, as if some of its ball is damaged. it had a big friction at one place while rolling with hand. seems bearing damaged. It might have caused sudden high current melting of one cobtactor contact causing single phasing.

Thermal overload was tripped but contactor did not go off. It was slightly stuck/pressed inside.

Or it is the contactor Failure causing single phasing. We have tested the motor. One winding is okay. The other two winding are burnt and earthed.

So, I am still confused is this damage is caused by the bearing high friction. Or it is contactor failure.

Please if you could confirm, if it is a single phasing, the result is a damage of two winding only.

Thank you in advance.

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#54
In reply to #53

Re: Is This Motor Failure Due to Protection Failure?

09/02/2017 11:09 AM

Today our motor specialist open bearing upon my request. He removed the seal cover. He found small particles. flashed from winding and overheated greece. It was causing bearing hard. He cleaned the bearing and it become like a new.
So it is confirmed, it was single phase failure. Only one thing I am surprised as one phase was missing, why the residual current relay did not trip. It is the only protection causing MCCB to trip.

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#55
In reply to #54

Re: Is This Motor Failure Due to Protection Failure?

10/04/2017 9:34 AM

One phase failure: so this is due to turn to turn failure. Failure occurred in the weakest spot. Your relay was not set up to protect this type of failure.

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#56
In reply to #55

Re: Is This Motor Failure Due to Protection Failure?

10/04/2017 11:02 AM

Dear Jose,

Yes we agree it is single phasing, on testing two winding were short and grounded.

So turn to turn fault between two coils/phases.

Also my concept is clear now the residual current relay can not detect such fault.

Thanks any way for all the participants and their outstanding expertise. Highly appreciated.

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