Motor Failure

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The motor overload setting if lower than FLC it can lead to tripping.To understand why it is happening continuosly monitor voltage and see variations.Is all motors are with class F insulation and temp rise limited to Class b.More than anything else Monitor temp rise.This will be temp recorderd on thermometer-10deg- ambient.If there ia a high rise then need to check why.Check Bearings of V.Pump whether any locking or friction.Most pumps have a impeller in good condition when new.Due to usage over a period of time the wear and ttear slightly results in lower eff of the pumps and hence more power demand from Motor.that is why in India there is a cut off for eff.value when evaluating in tenders.

Hello Sir, What is the Ambient temperature? <I guess since Overload relay has a delay time to trip, this delay is causing motor to overheat and bringing its life down>.....Heat (time) is your enemy. <as the days roll on pump …..take more load> As they wear in, they should draw less current, but pump effectiveness will be reduced. Are there strainers in the system? Are the seals cooled with water? What is the condition of the internal parts? Are they running dry and are they clogging? < pump has to be serviced very often, is it true. If so how ofter should be serviced?> How often service is needed, depends on operating conditions. Do you have a set gages that you can monitor?

Hi

I guess the load is becoming heavier as the vaccum is developed, thus increasing the current on the motor. If the time required for achieving the vaccum is not critical, probably you can use a gearbox ( maybe 2:1 ?) to increase the torque applied to the pump while decreasing the current drawn by the motor.

You would have the pumps running slower, so you need to find if it does affect your requirements.

Yahlasit

One simple solution may be to just replace the motors with ones a size or two larger the next time they burn out.

Far to often when I service commercial and industrial equipment I run across similar problems that only exist because some pin headed desk jockey engineer designed the system with no real world working overhead capacity so as things wore and efficiency dropped even a little there is no reserve overhead capacity left for the system work on.

On paper and on computer simulation it was theoretically good but unfortunately reality likes to add up all that little inconsequential aggregate of inefficiency that the Sim software ignores then beats you over the head with it with a high finical cost to you do to someone else learning curve not accepting that realty is not the same as his perfect theoretical model says is is.

Basically in theory the numbers say the load is 7 Hp and that a 7.5 HP electric motor will carry it. Unfortunately reality tossed a few extra tenths of hp losses in along the way and now that theoretical 7 Hp load now takes 7.8 Hp more often than not and eventually cooks the motor when everything is not in perfect or ideal working conditions.

In summary toss a 10 Hp motor on it, set the overloads at 8.5 Hp and life is good again.

I generally replace any of my motors that fail with one with a higher service factor. I personally like US Motors ( Emerson) as they offer a 1.25 sf - I would also monitor my amperage during a typical duty cycle and set my overloads accordingly. Also too many restarts per hour can really overheat your motor and eventually "cook "it Edmund

If the liquid (oil or water) is kept cool within recommended temperatures, and clean, the vacuum pump should be able to run continuously for long hours with minimal service.

Verify what the service factor is on the motors. Small service factor motors do not like heat or running near the HP limit.

Normally I do not like the idea of arbitrarily adding more HP because something on the driven side will usually become the weak link and break down. On the other hand, it might get you by.

I do not have 3 phase 220 in my shop. For years I've depended on Phase-O-Matic devices to "fool" my Bridgeport milling machine and my Boxford lathe into thinking they were getting real three phase. Aside from some power loss the machines have run well for 20 years.

A few years back I got an old Oliver jointer, a commercially made unit of considerable vintage. After a top down restoration I attempted to run it as I did the big machines, on phony 3 phase. It couldn't take it. It ran alright and planed hard wood very nicely but the motor ran hot as Hell. Within just a few minutes the housing got so hot, I could not touch it for fear of being burned.

I went and got my Westinghouse solid state single to three phase inverter and tried that. The machine not only runs cool and like a champ, the rpms can now be adjusted by raising or lowering output frquency. The Westinghouse unit even has a torque compensation algorithym and a soft start and stop option.

I've a high horsepower Mitsubishi inverter as well and use that to drive the twin motors on a high vacuum system for a composites bench.

All my 3 phase motors are well behaved and run cool.

I've taken time to convey all this so as to justify a suggestion that you do a careful assessment of the power supply. Some older 3 phase motors are fussy.

L.J.

"vacuum pumps initially draw nominal current, but as days roll on the pump starts taking more load."

That is true, more so for 'liquid ring vacuum pumps' than '(liquid alone handling) centrifugal pump'.

In liquid ring vacuum pumps there are great inter-actions between air and water. This leads to an accelerated wear and tear due to correction and erosion. Wetted areas in the rotor is (unlike pumps) not fully immersed in liquid. Oxygen contact leads to severe corrosion and turbulent (though undesirable) flow of water current, successive in and out of rotor cavities between vanes lead to severe erosion. Thereby the rotor internal volume gets enlarged sooner than later, unless they are protected otherwise.

Such enlarged rotor internal space takes more liquid and leads to draw more current as getting aged.

The solution for this problem includes: Check the orifice size (which maintain the quantity of circulating water), if such orifice exist. Check the rotor working areas for excess corrosion and erosion. Consider corrosion resistance merials like brass or SS etc. Maintain the ph of circulated liquid such that it is preferablly alcaline, around ph: 9/10.

Erosion or corrosion open up the clearances - leading to loss of performance. The rotor does not become larger in either case.

Buildup could cause additional load. Excess expansion due to overheating could close up clearances leading to additional load.

The suppliers are Nash & Siemens?

Contact the vacuum pump manufacturer for advice.

The firm has a reputation to protect!

what you mean of tripping? The RCCB or switch disconnector aka circuit breaker? Have you experience grounding when touching the machines? Are your electrical connection properly tight? How fast the tripping occurs?

check the grounding and the wire connections physically. Sometimes there are connections that when tested using multimeter shows good results, but during operation vibration takes place and the connection start to lossen and causes an intermittent single phasing.

Make sure that sorrounding temperature are tolerable. Make sure the suction filter (element) of vacuum pump is clean, have the required filter size and not damage.

otherwise you need to install a bigger motor or if your vacuum requirement is not reach replace a bigger capacity vacuum pump.

Likewise, check also the of vapour (air) temperature your machine is sucking if you have a direct coupled vacuum pump. maybe it is very hot and it transfer towards the motor during operation.

Make sure that you can rotate the pump manually if not you need to service it.

The reply from Yesyen (#9) is the nearest I can guess to be the Problem:

- The liquid ring vacuum pump is using the flow of liquid to draw air from the chamber and create the vacuum.

- Therefore, the same liquid is circulating from a reservoir tank and back to it (is this correct?).

- Because of the above, the liquid temperature will have a tendency to increase gradually over several days of continuous running (as you mentioned it is running for several days continuously before tripping).

- If the liquid temperature is increasing enough to heat the pump shaft and body, it will also input heat into the Motor's body (via the flanged setup), therefore, the cooling of the motor is going to be compromised! Also the mechanical parts including the bearings (especially the front bearing) --> increasing the mechanical load and the electric current --> tripping.

- Since the O/load trip is being reset, the motor etc temperature is going to be still increasing and will eventually damage the windings.

Suggestions: Check the liquid temperature increase during the days it is working without tripping. If necessary, the volume of the liquid could be increased and /Or must be cooled continuously to remove the heat generated during the pumping action...etc (Heat exchange if OIL or Spray cooling tower if water or any other means).

I hope this is usefull.

Agreed - this talk of changing motors rather than determining the problem is scary. If one of my electrical guys came to me with that I would have found them a new department to work in.

İf a system is correctly engineered then the problem is elsewhere. If the system is not correctly engineered then you also know who to get rid of.

If they could observe the liquid temp over a few cycles on a recorder it might show a lot.

One thing for sure - ıt ain't magic!

the vaccum pumps are supplied two very reputed manufactures, water ring pump by one vendor and oil ring by other vendor. we have problems with both pumps. I unable to comprehend the reasons.

I dont think there could be any problem in design, based on vendors background and nature of problem

May be connecting a recorder will give me the load current drawn by motor over a time period.

as far as cooling is concerned, oil ring pumps are air cooled there is not other cooling agent and it is found during operation motor is reaching high temperatures(ambient is about 40 deg max)

for water ring pumps, there is a dedicated cooling water line for pump casing to cool the pump, motor is again air cooled with cooling fan. even this is reaching high temperatures during operation

Your suggestion to record the current over the period is most usefull to see if the motor is getting overloaded after a certain period of time! then you will be able to find out why it is getting overloaded:

- Try to reduce the liquid (oil or water) going into the pump, therefore reducing the load on the pump: Maybe there is some cavitation (which is normal in vaccuum pump ) therefore the liquid is circulating within instead of flowing in/out. See if the flow of liquid is maintained all the time! Cooling this liquid is important if it is getting too hot due to being re-circulated over a long period.

- The Motor temperature should remain within the specs if the current is below the rated nameplate current. The air cooling fan of the motor will not be enough if heat if migrating from the fluid in the pump to the front Bearing area--> the bearing will expand if too nuch heat gets to it via the shaft... All depends on the level of Overheating that is going on.

also continuouly record the temperature.It is very important.if the temp. is within limits then there is some thing else.

The one question you need resolved is the Maintenance question. What kind of maintenance, how often is it done? Based on the manufacturers recommendations as a start.

Until you can eliminate this from the equation you won't get an accurate idea of what is going on.

Oil change outs, filter replacements. Until you have all your ducks in a row it is tough to ask for new equipment, when upper management will want to know 'Why' and your only answer is they get hot and wear out.