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Dc series motor starter

by noreldaim
Tags: motor, series, starter
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noreldaim
#1
May11-12, 11:11 AM
P: 29
we have an air comprissor screw type driven by dc serise motor direct start it use in locomotive the control circut inclode pressure switch and tempratue switch but alway we have problem in it many times the motor burnt.
The motor is from simo company
Rated volt 110
Rated current 210
Rated speed 1500
Starting mode direct start

Please help me to protect it

There is no circuit breaker in the power circit but fuse of 350 ampere and always the motor damage and the fuse still ok

at last is it better to direct start or use starter?
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noreldaim
#2
May11-12, 11:46 AM
P: 29
the air screw is L2.4/10 SCREW AIR COMPRESSOR
jim hardy
#3
May11-12, 12:28 PM
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fuse of 350 ampere and always the motor damage and the fuse still ok
If i found correct links
that's an 18.5 hp compressor with a 30 hp motor.
And you aren't blowing fuses?
At first glance it sounds more like a compressor overload problem than a motor starting problem.

Have you watched this thing start? Does the motor struggle or smoke?
Is it equipped with an ammeter?
Are there a flow gage and a pressure gage on compressor discharge?

noreldaim
#4
May13-12, 05:33 AM
P: 29
Dc series motor starter

thank you jim

Yes it is 18.5kw motor and didnt blowing fuse
they used 350ampere for staring purpse and when the overload happen it damage the motor
so i am thinking about softstarter to prevent overload

The system consist of to air compressor in locomotive for breaking purpose
The control circuit consist of :
Pressure switch and temperatuer switch and these two NC piont connected with dc contactor coil
The power circuit:
just only the main contactor contac

So le us begin to improve and develop these two circuit

Than you Mr jim
NascentOxygen
#5
May13-12, 10:08 AM
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Is the motor consistently burning out during starting? Or just at any random time during operation?

When the motor "burns out" are you having it repaired each time, or replaced? If repaired, what is the repair involved, precisely?
noreldaim
#6
May13-12, 12:17 PM
P: 29
No it doesnt burn during starting but it burn at any random time 
And we just replace it by new one we replace 12th motor!!
sometimes it just only damage not burn
Bcuz the screw blocked and broken then as it is serise dc motor running without load its speed increase rapidly and brocken the bearing and fan ventilator
noreldaim
#7
May13-12, 12:18 PM
P: 29
No it doesnt burn during starting but it burn at any random time
And we just replace it by new one we replace 12th motor!!
sometimes it just only damage not burn
Bcuz the screw blocked and broken then as it is serise dc motor running without load its speed increase rapidly and broken the bearing and fan ventilator
jim hardy
#8
May13-12, 09:44 PM
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Well now it's getting interesting ! Troubleshooting !

I assume braking air is mighty important. Are there redundant compressors on the locomotive? Or are all the locomotives on a train connected by the brake air line?

serise dc motor running without load its speed increase rapidly and brocken the bearing and fan ventilator
Yes, a series motor that loses its load will speed up and destroy itself by centrifugal force. That's why you NEVER use one in a belt drive application.
Series motors draw horriific starting current and you probably have ample current available on a locomotive.

Bussman's site was down this morning, i wanted to direct you to their "Fuseology" .
Here's their motor protection guide
http://www.cooperindustries.com/cont...ion_Tables.pdf

Looking at last page, 159, for heavy start DC motors in your 210 amps current range , they indeed suggest the 300 amp fuse as "optimum", 350 maximum.
Can you look and see if your locomotive has one of these types,
Bussman LPJ, LPN, FRS ? That'd indicate somebody knowledgeable selected them.

Looking at their datasheets they all have pretty good let-through current for motor starting, and that's what they are designed for.

First thing i'd try is a fuse that's closer to motor's full load amp rating. A 200 amp FRS fuse will pass 1000 amps for about fifteen seconds, is that long enough time to start the motor?

If so i'd try a Bussman LPS or FRS 250 amp and see if the motor starts.
That smaller fuse will give the motor better overload protection.
That 350 amp is sized more to protect the branch circuit against short circiuts than to protect the motor against overloads.

Study these fuse datasheets:
http://www.cooperindustries.com/cont...R(65-600)A.pdf

http://www.cooperindustries.com/cont...R(70-600A).pdf

http://www.cooperindustries.com/cont...RK_70-600A.pdf

in particular the time-current graphs. As you see a fuse designed to protect motor windings will tolerate surprising overloads. But so will a motor.
That's unlike a fuse designed to protect semiconductors, which have a reputation for being pretty effective fuse protectors..


That 350 amp recommendation for branch circuit assumes there's another overload protector between it and the motor, which is not your case.
Let's see if we can improve your overload protection first off.

Then figure out why the motor is being overloaded.
Does the pressure switch shut off the compressor at correct pressure?
Is there an ammeter for that motor?

old jim
jim hardy
#9
May13-12, 09:46 PM
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PS those headlamps on the front of locomotives - where would i buy a few?

They'd make great off-road lights.

old jim
NascentOxygen
#10
May14-12, 02:39 AM
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Quote Quote by noreldaim View Post
sometimes it just only damage not burn
Bcuz the screw blocked and broken then as it is serise dc motor running without load its speed increase rapidly and broken the bearing and fan ventilator
For how many minutes does the motor typically operate once it has started, before it switches off? How long can it be expected to then stay off before it restarts?

So the source of the problem is fundamentally that the compressor seizes and/or disintegrates, precipitating the motor into major overspeed?
noreldaim
#11
May14-12, 06:48 AM
P: 29
thanx old jim
noreldaim
#12
May14-12, 07:42 AM
P: 29
Run .. stop and restart:

Mr oxygen ur quest is so inprtant like ur name
:)
thanx for direct our attention to zis point
Here is the air system procedure:

Two typical air screw comporessor
Used to deliver the air to two main resirvoir their capacity 900Mpa
The 1st one starting and after five second followed by the other
And when the air decreased to about 750Mpa the system start again
But always the air doesn't stable at 900MPa even we dont use the handle brake!! Bcuz we have air leakage in the wagons' air tubes
So our two motors have no rest
And always when the train leave the workshop we keep our fingers cross hopping the locomotive reaching its gaol safely!!
noreldaim
#13
May15-12, 06:54 AM
P: 29
Is it useful to connect shunt free wheeling diode to series dc motor?
NascentOxygen
#14
May15-12, 07:54 AM
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Quote Quote by NascentOxygen View Post
So the source of the problem is fundamentally that the compressor seizes and/or disintegrates, precipitating the motor into major overspeed?
Is this correct?

When you replace the motor, do you also need to replace the compressor or part of the drive to the compressor?
noreldaim
#15
May15-12, 10:36 PM
P: 29
almost we maintenance the mechanical screw part and use it again but even we replace the whole system by new one the problem still exist!!

Hot sick motor!!
noreldaim
#16
May15-12, 11:31 PM
P: 29
I guess i found the source of the problem as there is a leakage in the air system
The motor work, the resirvoir pressure become 900Mpa , and the pressure switch open the circuit
But as there is leakage in the air system , the air in the resirvoir decrease , when the air became 750Mpa the pressure switch close and the motor start again , so this procedure make the motor always works with huge starting current , thus the motor's coils became more hot and burn ,

there is another reason , the two air resirvoirs are standing near front of the system, take into account the air drier system not working, and when you drain them the humidity increase and affect the performance of the motor,

Am i true?

The question now is there any method to monitor the motor's coil temperature?

Note:

We have tempratue sensor but it been inserted in side the lubricating oil of the male and female screw not the motor's coils
jim hardy
#17
May16-12, 07:34 AM
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there is another reason , the two air resirvoirs are standing near front of the system, take into account the air drier system not working, and when you drain them the humidity increase and affect the performance of the motor,
it's a fact compressors prefer to compress cool dry air.
Do you drain your reservoirs too, or just the dryers?

When the reservoir gets a substantial amount of water in it , it is effectively a smaller reservoir for air. Its capacity is reduced by however much water is in it so the compressor cycles more often giving you more frequent starts hence more starting duty. I don't know if you are in a dry desert country or a tropical rain forest. Open the drain on a reservoir and see how much water comes out.
On my home ar compressor i leave the drain open just a teeny bit in the humid summertime and it makes a puddle, but in dry wintertime just drain it at end of the day and get almost no water.

You are in the shop so don't see these in operation?
Perhaps the train crew would help you by observing how often the compressor runs and for how long.

The question now is there any method to monitor the motor's coil temperature?
There's electronic non-contact thermometers, perhaps you could open a cover and look at the winding with one of these


but a little magnetic dial thermometer on the motor casing near coils would be almost as good i'd think.



EDIT PS - screw compressors have tight clearances inside so will be very sensitive to ingested dirt and sand.
Make sure your air filters and intake piping are in good shape.
Grit on the screws will increase friction overloading your motor.
Ever take apart a modern automobile fuel pump? The tiniest piece of grit will lock one up tight(and strand you alongside highway). That's because they too require very close clearances inside.
The automobile fuel pump motor is purposely made too weak to catch fire for obvoius reasons , but your air brake motor is probably designed to sacrifice itself to stop the train. That's pretty noble of it, and we ought to take good care of that unselfish creature.

old jim
NascentOxygen
#18
May17-12, 07:21 AM
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Even were it possible to monitor the motor's temperature, it can't be an ideal solution. Disconnecting power to the compressor's motor will mean the loco is brought to a halt while the motor cools: an inconvenience that invites an exasperated crew to look for a way to defeat that lockout.

It should be feasible to monitor the shaft's RPM and disconnect power in the event the revs exceed some level, but that's still not solving the underlying problem.


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