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Electrical Or Mechanical Problem

01/28/2012 11:08 AM

I have a kiln with 8 fans(don't know if that matters). Anyway motor 1 keeps trping out, I've done everything I can think of to make sure its not an electrical problem,I.e. wires, balanced voltages ,balanced current, checked wiring, checked for bleed off. If there s any other electrical thing I can do let me know. I have advised the management in this department to check bearings and pitch of fan and they say its all good. So if there is anything I can check for that end let me know please. Thanks

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#1

Re: electrical or mechanical problem

01/28/2012 11:14 AM

Use a clamp on amp meter to check the current draw of each motor, motors do go bad eventually. A shorted winding may be causing excessive current draw, internal heating and thermal shut off. Also, check the thermal overload device on the motor, it might be bad.

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#2

Re: electrical or mechanical problem

01/28/2012 12:16 PM

Does the odd fan have a damper that could be closed slightly? This would decrease the amp draw on the motor, but the total air flow would also go down some.

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#3
In reply to #2

Re: electrical or mechanical problem

01/28/2012 12:57 PM

Yeah all that has been done its even a new motor. Im just confused and need smarter help than myself

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#4

Re: Electrical Or Mechanical Problem

01/28/2012 1:03 PM

Certainly sounds mechanical. Can you not check the fan drive yourself? I have an inbuilt distrust of fitters checking drives. The ones I've worked with would say anything to avoid changing a motor / fan assembly.

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#5
In reply to #4

Re: Electrical Or Mechanical Problem

01/28/2012 1:42 PM

Yeah I think the mechanism just don't want to work

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#6

Re: Electrical Or Mechanical Problem

01/28/2012 1:58 PM

Do you have the motor FLA and the actual running amps?

If the motor overload relay is at a higher ambient temperature than the motor, it may be possible to go to the next higher heater rating, thereby eliminating nuisance trips. (If that is what is really happening. In the absence of full info, this may be only a wild guess.)

You might also "shoot" the motor with an infrared gun to see if it is really running too hot.

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#7

Re: Electrical Or Mechanical Problem

01/28/2012 2:39 PM

Also, if each motor is on a separate breaker, that could be the culprit.

Was any wiring changed? Smaller wiring may cause the motor to trip.

I like the "shoot the motor" idea as well. If none of these suggestions work, I would use a shotgun.

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#8
In reply to #7

Re: Electrical Or Mechanical Problem

01/28/2012 7:50 PM

Each motor is on a separate breaker but its the overload relay tripping out not the breaker. I would check the fan pitch but I have no idea what it needs to be and they aren't to quick to share info. But hey I do believe my cr4 buddies would know and tell me :)

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#9
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Re: Electrical Or Mechanical Problem

01/28/2012 8:38 PM

You might just need to get a bit subversive...

Can you surreptitiously reduce the pitch of the problem fan? Just a smidge might do.

(I would still like to know the FLA versus actual A of this motor, as well as the overload settings.)

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#10
In reply to #9

Re: Electrical Or Mechanical Problem

01/28/2012 8:56 PM

Fla 34 - o/l 32

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#11
In reply to #10

Re: Electrical Or Mechanical Problem

01/28/2012 9:05 PM

How about actual amps? The OL32 vs. FLA34 looks like a nuisance trip just waiting to happen.

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#12
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Re: Electrical Or Mechanical Problem

01/28/2012 9:28 PM

Well running amps is 30. I set my overload to that because why should I push my motor to the ragged edge all because mechanical techs don't wanna do the preventive maintenance

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#13
In reply to #12

Re: Electrical Or Mechanical Problem

01/28/2012 9:36 PM

Hmm, it sounds as though you may have some weird jurisdictional issues in your plant. On the basis of info so far, I would probably bump the motor overload heaters up one or two steps; but also monitor the motor for overtemperature.

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#14
In reply to #13

Re: Electrical Or Mechanical Problem

01/28/2012 10:02 PM

Well it is a family ran mill were the older u are the more clout u have regardless of how wrong u are. Us know you the good old boys way of thinking. Hahaha

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#17
In reply to #9

Re: Electrical Or Mechanical Problem

01/29/2012 12:49 AM

Reducing the resistance to flow for an axial (propeller) fan will indeed reduce the load on the motor, as will reducing the pitch of the blades or the speed of rotation. If this is a centrifugal (squirrel-cage) fan, just the opposite will occur. As airflow increases, so does the load on the motor. You should use a tachometer to compare the motor's rotational speed with the speed on its nameplate. If the speed is somewhat low because of excessive load the motor may overheat and activate the thermal protection device even if the increased current draw is not enough to trip the breaker. You should then check for air leaks in the ducting that conveys air from the blower to the kiln.

You may have noticed that when you block the hose of a tank-type or canister-type vacuum cleaner (which use a centrifugal fan) the motor speeds up. It isn't "straining" as people say, but running at above its design speed because of the reduced load, hence the higher-pitched sound. Likewise, if you open the blower compartment of a warm-air furnace while it is running so that outside air as well as return air are admitted to the blower intake, the blower motor will be overloaded, and may overheat and even burn up.

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#22
In reply to #8

Re: Electrical Or Mechanical Problem

01/29/2012 11:47 AM

Swap the blade with another motor. If the problem moves wallah !

If the problem does not move, swap the entire assembly with another. You will now know if it's the motor or the service feed.

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#15

Re: Electrical Or Mechanical Problem

01/28/2012 11:00 PM

Can you pls provide a rough schematic diagram of air circulation system in the kiln.

This will definitely help. As I undesrstand you have tried almost everything. But some weird looking solution may still be possible.

Best

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#16

Re: Electrical Or Mechanical Problem

01/29/2012 12:44 AM

Has somebody "stolen" the feed to the motor to power something else? A meter, computer or even a small personal device such as a fan.

If not try swapping over the thermal overload device to another motor. It may be faulty.

Are there RCD's on the same line? They can cause nuisance tripping.

If you decide to try to adjust the pitch of the fan blade make sure you can get each blade the same. You will need to be able to measure the distance between a flat surface ( that is perpendicular to the axis of the fan ) and the leading edge of each blade. Once they are all the same measure the trailing edge down to the flat surface. Obviously if each blade has the same pitch the measurement will be the same. If they overlap you won't be able to do this, you can either make a special test rig or take the blade to a fan or propellor manufacturer.

Sorry, on second thought you may be able to turn the fan over on your test table to measure the trailing edge, just more painfull.

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#18

Re: Electrical Or Mechanical Problem

01/29/2012 5:34 AM

This is on a kiln. Have you checked if the air blowing through this fan is hotter than the air blowing through the other fans. Maybe this fan intake is grabbing air from another fan output. It is Fan No1, so it is likely to be at the end, where the ambient conditions could be different. The solution might be as easy as installing a baffle.

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#19

Re: Electrical Or Mechanical Problem

01/29/2012 9:21 AM

Is the motor controller located in a hot area,more so than the others? I am suspecting the ambient or radiant heat may be the culprit.If available, use an infrared scanner of camera to detect hot spots, loose connections.

I have also seen cases where the pawl that holds the trip mechanisms in has lost tension, causing premature tripping.

On some thermal overloads(heaters) the contact is held in place(once manually reset) by a very low-melt metal alloy, or a precisely engineered wax that will melt at a specific temperature.The spring tension encountered when resetting it is held in abeyance by the pawl latch until the element has melted, then the spring opens the holding contact.

Other types use a bi-metal mechanism for trip, but still use a latching pawl.

If the pawl,which holds it in place is bent or worn, it could cause a premature trip situation.

If it is truly a overload trip, and all other tests are good, then change the motor starter (controller).

If it is a matter of unexplained stops, then check the stop circuit wiring for intermittent connections or bad splices.

Good luck...(ol' sparky)

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#20

Re: Electrical Or Mechanical Problem

01/29/2012 9:46 AM

Heat & electricity are a bad combination

you never really said when the trip happens, both compared to the motor start & the kiln start

Assuming everything is the same between the different fans

bad overloads, bad connections or bad wire

the connection could be a wirenut or terminal block that is assumed to be good

or even the contacts on the starter

there could be some heat leaking out from the kiln, hitting a conduit in a hidden area

as a last resort pull in new wire, an inspection of the old wire, may tell a story

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#21

Re: Electrical Or Mechanical Problem

01/29/2012 10:45 AM

Is the fan located that can be classified as forced or induced?

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#23

Re: Electrical Or Mechanical Problem

01/29/2012 12:37 PM

There's new starter new o/l and new wire and new motor. Previously the motor went bad due to the contacts were welded together due to the supervisor in this area turned the old o/l too high with out contacting me on why this motor was tripping out. And I do believe there are baffles but the condition is uncertain. Its hard to say because the newest boiler we have is from 75 and is in terrible shape.

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#24
In reply to #23

Re: Electrical Or Mechanical Problem

01/29/2012 12:57 PM

well, to answer the original question

if you've replace everything electrical & checked or replaced the wiring feeding this circuit

mechanical

what type blower/fan?

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#25

Re: Electrical Or Mechanical Problem

01/29/2012 4:12 PM

Matt,

This sounds like you are running propellor fans in a lumber dry kiln, with exterior fan motors?

If so, the fans will draw more current when moving cooler air when the kiln is heating up, since the cold air is denser and harder to move. If the offending motor is at one end of the kiln or the other, it will stay moving colder air longer than the others since each end of the kiln takes more energy to heat up.

You are running the fan on the ragged edge of the motor power, so little differences as compared to the others will be the culprit.

Your prop fan blade angle settings are the first place I would look. These are set with U-bolts so if you can "borrow" the fan angle guage I'd back off the prop pitch just a little.

Another place to check is the motor drive--I'm guessing you have a V-belt or toothed belt drive from the motor to the fan shaft. Is the ratio a little different on this one than the others? Probably not likely, but worth checking.

Baffling on the fan discharge isn't usually an issue-if you block the flow of these fans the hp draw will drop off, not increase. However, if these fans are on the end of the kiln charge, the lumber sometimes doesn't fill right to the end of the kiln, allowing air to short-circuit past the ends of the lumber which will ADD to the fan load.

And then, you may not even be in the lumber business, so my assumptions may be 'WAY off!

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#26

Re: Electrical Or Mechanical Problem

01/29/2012 6:54 PM

OK,everything checks out when you are there,so install an event recorder on all three phases of the motor.When it trips, you will have a record of the event,amp draw,exact time of the event,voltage,etc. Worth renting if your company does not have one. Are Door seals good?

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#27
In reply to #26

Re: Electrical Or Mechanical Problem

01/29/2012 9:25 PM

Hitek that is a negative its also full of leaks. Ah I might as well just jack up the o/l block and let it be. I buy all my own test equipment anyways.

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#29
In reply to #27

Re: Electrical Or Mechanical Problem

01/30/2012 9:35 AM

What is the service factor of the motor? This is a multiplier to determine actual full load,including heater(OL) size.

A S.F of 1.25 (Typical) allows the motor to be overloaded by 25% without damage.Did you take this into consideration when calculating your OL size?

What brand and size is the motor starter? A size 3 or 4 is appropriate for 30 HP.

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#28

Re: Electrical Or Mechanical Problem

01/29/2012 11:19 PM

You have said the current readings are ok it has been replaced with a new motor & the problem is the same Then you say its the overload relay tripping out, have you tried swapping the overload relay with 1 of the others to me it sounds like the overload is faulty. or set too close to the current that is being drawn through it.

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#30

Re: Electrical Or Mechanical Problem

01/30/2012 2:01 PM

Alright I just got a look at the fan and drive bearings. They do look alright free spin feels good. Fan pitch is set to match the other ones. Also checked the shelves and they are minute worn, belt tension is ok. So I suppose ill turn the o/l up a tad invade its a bad door seal letting thefan draw in cooler air. And yes I am in the lumber business -export rough cut- no domestic. Thanks for the in put people.

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#31

Re: Electrical Or Mechanical Problem

01/30/2012 6:23 PM

No need to try to protect the motor by having the OL set below FLA. In fact, you are adding stress to the motor by tripping it off and having to restart it needlessly. Most off-the-shelf motors will have a 1.15 Service Factor, meaning you can run them at 115% continuously if you have to, but THAT is where you start shortening their expected life.

Running a motor overloaded would not have welded the contacts on the contactor. They are either undersized, or they were subjected to rapid starts and stops, or "chattering" from something not working correctly in the control circuit. I would start looking for what that may have been.

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#32

Re: Electrical Or Mechanical Problem

01/31/2012 2:00 PM

You state in a previous message "Well running amps is 30. I set my overload to that because why should I push my motor to the ragged edge all because mechanical techs don't wanna do the preventive maintenance" Could you actually give us the size of the motor & what the current rating is on the ID plate on the motor, that is what is important when setting the overload not what current it draws in use

I agree with JRaef it is quite comon practice to set the overloads at 15% to 20% over the rated current of the motor ID plate that allows for the extra current on start up & any extra loads for what ever reason might happen as on conveyor belts carrying gravel they can have no load & maximum load in a short period of time

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#33

Re: Electrical Or Mechanical Problem

05/16/2012 1:14 AM

one of your motor is gounded my friend !!!! pls check diconnect the other motor then start one by one then you will see the problem fam motor trippin problem mostly the bearing the stator are not in lignment pls do this advice to resolve your problem

NOTE: disconnect all fan then one by one start !!!

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