here's the setting...a large Iron foundry,
5 induction furnaces with capacities between 25 and 65 tons, each supplied by separate xfmrs and running 600V

the lids on these furnaces are opened and closed using hydraulics...

20hp driving pumps each capable of supplying 2100psi...with a total of nine pumps on four systems 2-2-3-2

the dist. panel is fed from another service and NOT from the furnace trannys.

there is a schedule for charging and other tasks that the dept.adheres to with very little deviation,
and they were having trouble with the bank of three pumps
tripping the OL's ...constantly......

the motors were being removed on a fairly regular basis, due to motor failure.
current readings showed all the motors drawing around 37A @ 480V under load.

So, after pulling three burned motors in one week, the decision was finally made to install a test motor that was rated for the amps the overloaded motors were pulling and lower the pressure to 1800psi

I suggested that trying to solve the problem by using a larger motor based on the overloaded motor amps was kinda crazy .....but being the new guy.......
whado I know!!!

So a 30hp motor / pump gets temped in,
the dataplate states 35A with a 1.15SF so MAX is going to be around 41-42A.....the motor,( with less pressure.)........is pulling 51A but is not tripping out, I also have no idea what heaters were used, since the big brains figured it all out !

but now the thinking is to install a 40hp, (can you believe this ) ... I told them the pipe, wire, feeders to and size of the dist. panel and wallspace for the bigger starters was inadequate....

Then I asked if anyone knew what the PF on the dist. service was and they looked at me like I had lobsters crawling outta my ears...It was only a question, but I felt the problem may be due in part to low PF.!

I don't think these blockheads will listen,
but I might not be there long enough to find out anyway

The power factor,if it was an issue, would tend to affect the feeder overcurrent and not the loads downstream. And this would be so if the power factor suddenly got worse, because your reactive current has increased on the feeder. But from the sounds of it, there is a problem in the hydraulic system with the three motors driving it. I am assuming you had a millwright have a look at that system also. From your description none of the other banks of motors are failing, so its probably not on the distribution.

Millwright??? no millwright.....

I failed to mention that the problem has been persistent since the pumps were installed, (8-10 years ago )and whomever commissioned the setup pointed their finger at the plant , so they have just been resetting OL's and changing out motors and fuses ever since.!

the three other systems use one pump for one furnace, plus a backup..... the problem pumps are used for two furnaces, with 2 backups.......

this latest idea of a larger motor is merely a guessing game between a vendor and a couple of the folks in the maint. dept.

I have no idea what I'm looking at while staring at the plumbing.....but the the overload on the larger pump sure has me scratching my watch...because

there is also a tendency at this place to simply use the largest fuses when equipment begins causing too many trouble calls...as a result the feeders are fused at 100A on #6 THWN.........and the existing starters at 60A

the temp 30hp is hooked into a size 5 starter that they found, with 100A fuses ......

I thought PF could have been the culprit, since the service has had more load placed on it since then, I can't be certain....the one line is in somebodys head ........ but around 40 additional motors are fed from it, including RTUs ,cranes, sand mixers, and cooling towers and there are no panel meters at the service itself

Let's see... less pressure, bigger motor, and you're still drawing lots more amps?

The only way I can see that happening is if both the RPM of the motor is too high, and the hoses are too small. And, while there is no "Natl Hydraulic Code" with a rule limiting the number of bends," bends DO matter, and affect the load.

In such situations, the resistance is in proportion to the cube of the flow rate... so again, it looks like they're trying to open the doors too fast. We're back to motor rpm.

There is such a thing as "inertia." It takes a bit to get those covers started in motion. This might be a place to try a "soft start" motor controller as well.

Oh- I just remembered.... there is sure to be a pressure regulator, that allows excess pressure to recirculate. This device prevents the pump from pushing against a closed circuit. That device might not be working properly.

`Hi reno.
I thought about the smooth-move/speed thing as well, but decided that since the system was installed by some outside outfit it definitely was engineered to work...Ok maybe that was a bit sarcastic, but the RPMs are the same,and this time the vendor is what used to be Berry Bearing....these folks have volunteered that the new setup is just a WAG.......

I further assume, that this system is identical to the other units that have no problems.
..perhaps my PFquestion is not applicable after all...!

I am further bewildered by their decision to simply pick a motor hp that matches the amps of an overloaded motor and now the overloaded amps on the bigger motor would indicate a more serious problem. at least to someone as dim as myself

but in spite of all the guessing and butt scratching, these folks want yet another, larger motor.
to run @ the higher amps the 40 is pulling..like a dog trying to catch his tail


perhaps Doofy will save the day

[This message has been edited by togol (edited 07-02-2006).]

forgot.....the piping kinda looks like that screensaver that constructs some pipework with different colors...

anyhow, someone explained the circuit to me and it does have recirculating, bypassed, regulated , "dyno-timed and analyzed " plumbing...so I suppose that means its OK?

Any chance that the circuit has been overloaded all along and you are getting a severe voltage drop at the motors? That would explain the overloading of even the larger motors, because they would have been drawing MORE current and causing even a greater voltage drop than the smaller ones. If that is the case, increasing the motor size is going to make the situation worse, not better! How are the motors fed, i.e. wire size and routing distance. Any junction boxes in between where a bad termination might be causing a voltage drop under load?

486-495V (running) on the T's at the starter for the temp. setup, which is fed from the same gear as the existing....

and they have always had problems...they finally are reaping the benefits of ignoring them. I would just like to eliminate the electrical from the equation

From the sound of things there, I figured that he was promoted to upper management... :-(


Seems that they should split the paired furnaces and use the "one pump per furnace" system. (unless I misunderstood something).

Maybe something got into the hydrolics plumbing and clogging it?

wa2ise,
your understanding is fine,
perhaps at some point those two furnaces had their own pump, while sharing the same 3rd pump as backup.....I don't know....it would make more sense to power each furnace independently,
but that would only allow them to think they are one pump short, instead of utilizing the two spares that are doing nothing.....I did suggest an alternator ....but they didn't respond to that

their intransigence has allowed an already overloaded pump to overheat some more, trip out , and then someone has to run over there , reset OLs and sometimes change fuses , and put the same pump back in service, and occasionally pull a burned motor out.....( Iwas involved with that .how dam stupid is this???

but they are so pleased with the new setup..even with that motor running overloaded...that they are talking about simply replacing three 20hp pumps with two 30 or 40hp..

...and no one will take the time to determine what the cause of the overload truly is !

It isn't at all crazy to size the new motors based upon the current drawn by the old motors. The current on the old motors is a very rough measure of the torque loading the old motors. So if you make the presumption that the old motors were simply mechanically overloaded, then going to new motors of the same output shaft speed but higher torque capability is probably a good solution.

However the _evidence_ is that after the motors were increased in capacity, they were _still_ overloaded. Togol, I totally agree with you; this strongly suggests some serious other problem.

'Power factor' cannot directly be an issue here. The motors will consume current that is slightly out of phase with the applied voltage, but external factors cannot change the _internal_ power factor of the motor. As long as the voltages at the motor terminals are correct and _balanced_ the over-all power factor on the feeder to the motor is not relevant.

Can you confirm that the motors were replaced 'like for like', eg. a 4 pole 1800 RPM motors with larger 4 pole 1800 RPM motors? Are the motors of similar class with similar slip versus load characteristics.

Were any shaft speed measurements taken on the old and new motors? What I am wondering is if there is some strange interaction between the pressure regulation, the pumps, and the motors, such that the motors _never_ get up to speed. The motors could be happily running along in a high slip, low efficiency condition, burning themselves up. Note that if the problem is the motors not actually getting up to speed, then a larger motor might be able to push past the 'hump' and function correctly, but this is not the real fix to the problem.

-Jon

Togal, based on a couple of your posts the question that comes to my mind is why are you working there?

Find a new place to work, this one sounds like a total disaster.

BTW listen to 'winnie' he knows a thing or two about motors.

Bob

You said the voltage at the motor starter terminals was correct. What about at the motors themselves? How far is the run to the motors?

This sounds more like a hydraulic problem than a motor problem.

winnie....
the speeds on the dataplates are identical.. 1750
.but I did not compare other relevant info...I will tonite.!..( I just got home )


Bob..
this job was meant as a stopgap due to the slowdown of big new construction around here...it is NOT my intention to overstay my visit.one minute longer than necessary........nosirree

JBD....
the pump was in service when I checked voltages so I could not open the peckerhead, but the the whip is about 5' and amps were close 51...49.5....49.8


to everyone.......

I had tried to avoid this whole fiasco .....but as more of the history of these pumps was revealed, the more skeptical I became of the fix, and naturally more inquisitive....

my only remark was more from the gut, but their reponse to the PF question was more like..
..what the hell is power factor ?
even though there are five rather large induction furnaces right behind the pump wall..!!!

this place is a nightmare I know, but after sitting for almost 11months, I needed some sort of income,

I have (almost always ) endeavored during my career to find answers to problems,...... if I didn't understand the solution, there would always be someone who could get it to stick to something inside my skull

So, while I am there I will keep notes on this circus for my own knowledge.
besides, the last time I held a maint. job Carter was president


the one plus in this, is discovering that I have absolutely no grasp of PF fundamentals and need to head down to the Technical area..... oboyoboy

but please don't stop posting your thoughts on this thread...OK ,

its bedtime for me....g'night johnboy

I can just imagine all the money being blown in terms of blown motors, time spent trying to "fix" this, and all the downtime costs caused by the inability to use the affected furnaces.

When I used to work for Intel, they had a rule of sorts that said "Copy exactly" a successful production facility. We had semiconductor integrated circuit (chip) fabrication facilities and once we had a successful and reasonably efficient operation we wanted to duplicate exactly that facility and not try to improve it. Or you'd risk it not working and thus not being able to make and ship more of a popular product before the competition hits the market with something better yet. We wanted to be able to sell more stuff and make more money

Seems this iron foundry ought to just "copy exactly" the working "one pump one furnace" systems and forget about using bigger motors. But management there would have to realize that nobody really understands what the trouble is. Even if it costs more than yet another bigger motor, it should get them running reliabily.

[This message has been edited by wa2ise (edited 07-04-2006).]