motor failure 2

[humbleuser]

I don't hang out in this forum anywhere near enough as I should. This is great technical site. However, I do have a question that I'm hoping some of the more experienced mebers can answer. Keep in mind that I'm not a trained electrician; I'm more of general maintenace type of guy

I have 25 HP G.E. motor (230/460 3-phase) attached to an injection molding machine. I saw this machine running and making parts prior to me buying it. The place where it came from had it wired for 460. I brought it and rewired it for 230. The motor ran for about 5 minutes, somewhat noisy, before it started smoking and tripped the breaker. The shop that is rewiring it told me that I had the proper wire connections to the motro. I asked him what caused it to burn out? He's not sure. He says the bearings aren't in bad shape. he thinks that some of the 'varnish coating' on the windings may have worn out. It's possible that some condensation on the worn area may have caused the motor to short out. Is this possible? Thanks in advance.

 

[davidbeach]

Check motor rotation and general operation BEFORE mating it to the pump.

 

[powerjunx]

humbleuser,

With such incident, im pretty sure you never did wrong upon wiring it on 230V (it's simple).

The issue here is the "reliable solution" of the culprit that was the repair center ambigiuos diagnose of failure, as i agree to stardelta.

When we repair such machine, before we strip out the winding or dismatle it, we conduct a pre-diagnostic survey or query as why is the unit needs for repair? Consequenlty, we conduct diagnotic testing, visual inspection and check up. Thereby, we acquire our own assestment of " root cause failure analysis " and reported to our client, since we offer a repair warranty.

in your case, The best thing you'll have to undertake is to run the machine without load to ensure the unit is good. Eventually, try to investigate your load if it really fits your motor capability.

 

[stardelta]

The ability of the repair agent to provide an accurate root cause analysis is vital. High-end clients expect reliable repairs and value for money in todays market. They tend to ask 3 questions regarding motor repairs. The Accounts dept ask how much is it going to cost? The Production dept ask when will it be back? And the Engineers ask what caused it? Its accepted that if the Engineers dont get a quick and accurate answer first, accounts and production could be asking the same question again in a few days time if the motor fails again owing to the possibilty of an undiagnosed fault on the driven side or with the supply. Accounts wont like the additional repair bill and Production wont like the additional downtime. This is why customers insist on accurate root cause failure diagnosis and if a repair company cannot provide it they will find someone else who can and the buisness will go with them. We in this forum can offer advice and point you in the right direction but its my view that the full answer to your question lies with the motor and the state of the failed winding and it can only really be fully determined by careful inspection, examination and testing by competent individuals. At the very least insist with the repair co` that you are present when the final motor test is conducted. Ask for an explanation of their test procedures. As a mechanical issue is suspected ensure they conduct a locked rotor test which can highlight rotor faults, check they conduct a shaft run-out test and that vibration is within the limits for the relevent construction and manufacturing standards. Idealy they also need to check and record the G/S/E figures for each bearing and ensure they are satisfactory for the sise and speed. If the motor fails again your repair company can easily say "It was ok when it left here" and refuse to accept any warranty on their behalf but if you are present at the test it works both ways, they will ensure everything is done correctly and you will be satisfied they have done a thorough job. Reputable firms welcome witness tests for these reasons.
There is a worldwide repair trade organsisation known as EASA and members operate within a code of practise. The EASA website offers a PDF download in the `Industry Info` section that explains minimum requirements relating to repairs and testing which I am sure you will find useful.

http://www.easa.com/

 

[macmil]

I would suggest that you ask the rewind shop for the old bearings so you ( and others ) can examine them. As mentioned previously, if they were the problem there will be some wear/ damage. If there's no damage, they probably were not the problem. And make sure you check the bearing numbers to ensure they were the correct bearing in the first place.

 

[powerjunx]

macmill, repair center should simply depicts or somewhat report the probable cause of the unit as to assist " root cause failure analysis" report, with these... you will have the confident to prevent the damage from happening again...
Reliable Solution as what EASA had advocated.

 

[moira]

Hi again, Humble:: You have said something about the motor sitting around for about a month. I hope that it was protected , if outdoor in bad weather? Was the motor always together as the same pump motor set? Should mention that it is always good practice to check the insulation resistance of each winding against ground and the internal connection continuity. Always want to have resistance readings towards infinity. Should be done ,at least, with a 500 volt MEGGA. A good MEGGA is a MUST have tool for any work on motors! These checks should be made at rewire/hook-up. If they can be recorded; they provide some type of motor health history. Direction check is CRITICAL; should be done ( uncoupled) at site! Should be easy change back at breaker/starter, if necessary. RECHECK AFTER CHANGE!!! Your comment that STRANGE noise was present might indicate some type of mechanical binding in the impeller housing: corrosion build up during storage; impeller being loosened from wrong directon. 3 phase direction can be different at different locations. If using a VFD for speed controll; you must check the actual final VFD output for proper direction. With start up of new pump/motor set take running load readings. Make sure you are within and understand NEC motor running load rateings. Being conservative; start around 115% of FLA, increase to 140% of FLA if loading dictates. A higher running amperage will eventually affect the long life of your motor. A last thought is that you may have a motor speed issue. Maybe you had a 3600 RPM motor, correctly o/l protected. You'll have to think about it! Recheck the o/l devices application to the starter. Hope this is help; at least, for the future! MOIRA

 

[humbleuser]

The repair shop called me today and informed me that I indeed have the motor hooked up incorrectly; the motor is a delta not star. that explains why I burnt it out. Please keep in mind that there's no info on the face plate. next time I will do a continuity check. Expensive lesson on my part.

Now I have another question. I just noticed that the motor did not come back with two small wires that it had before. One of the wires was marked "PC". I'm guessing that it's for the PLC control on the injection moldinvg machine. What signal it provides is beyond me. Can someone confirm that these 2 leads are for the PLC and do I really need them? Thanks.

 

[itsmoked]

Next time use an ammeter to check the running motor currents.

Those are/were temperature leads. Sad if you don't have them and need them..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[humbleuser]

I assume these leads are connected to thermocouple. Where would the thermocouple be mounted?

 

[itsmoked]

Inside the windings.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[humbleuser]

Could you please post a link to where I may be able to get a thermocouple for a motor applaication? Thank you.

 

[moira]

Hi, HUMBLEU: The two small wires in your motor originally were most probably the high heat/thermal protector. They are normally closed switches that are calibrated to go open when an abnormally high temperature is sensed in the motor. They are inbedded in one of the motor windings. You will have to check w/ GE, etc. to know what their set temperature is. There is quite a variety. They could be wired into your controll circuit to provide a motor stop/alarm. Their intent is some degree of fire protection. Although not to be an actual motor control device; they can in an emergency supply a world of good. They do not reset until normal temperature ( what that is?) is obtained. A lot of damage can be done to a motor relying on a high heat device to open in controlling a motor! No matter what exact type of motor control circuit you have, your first concern should be to STOP that motor before any harm is done. Where they originally wired to your PLC system? I'm believing them to be this, as described, normally closed switch. This could have been used ,if wired, to provide a digital input to your PLC signifing that motor temperature was OK. I think it to be unlikely that they are the ends of a thermocouple or even an RTD. Did your original 25HP, 230 volt motor have a certain two small wires wired to your (its) PLC? When you rewired this purchased 25 HP, 460 volt motor for 230 volts; I'm understanding that it had a certain two wires, did you connect them to any two wires you may have originally disconnected? Basically, if you had them in the beginning , you need them now! If the original motor had these two wires connected to the PLC; then you possibly need them. You must understand your motor controll circuit!!!! Again!!! If these certain two wires were originally connected , to the PLC, you need them. Let me ask you another way; the first time you saw these wires, what were they connected too? MOIRA

 

[humbleuser]

I haven't traced the wires yet, but one of the wires coming out of the motor was labeled "PC". The two wires from the control panel are labeled but I'm having a hell of a time finding their reference in the machine schematics. If it is a connection for a thermocouple then I can do with out it. If it's an overload protection device that is normally closed then, and correct me if I'm wrong, I'll tie the two wires together to close the circuit. I know, I know this is jury rigging but I need to get this machine back up and running. If anyone knows definetavely what those leads are for please let me know. A link to a replacement part would be truly appreciated.

Thanks everyone for your help!

 

[waross]

Thewires most likely were from some type of temperature monitoring device. There are several types. Some connect to a dedicated module that monitors the temperature and opens the motor control circuit if/when the motor temperature is too high.
If it was working when you aquired the machine it would have most likely saved the motor. If you had a good quality motor overload relay, it would have likely saved the motor.
The temperature detector is usually imbedded in the motor windings as the motor is being wound or rewound.
Do what most people do with older motors with inoperative thermal sensing. Forget it. It's too late now in any event.
This is an added level of protection which most motors don't have, and was apparently out of service on your motor anyway.
BUT DO use a good quality motor overload relay (often a part of a magnetic motor starter).
respectfully

 

[moira]

Hi, again, HUMBLE.: I'm not positive that they are thermal o/l switch. I'm pretty sure they are (were). If they were just a straight digital open/close verify for OK temp. of the motor then you can temp. get away with a jumper to keep this part of the PLC as seeing a good, closed issue. I pretty sure that they weren't a thermocouple (to create an analogue voltage input) ,or an RTD ( to create an analogue current input) to Your PLC Does your PLC have analogue current or voltage inputs?? Can you see the digital input rack when you jumper ( splice together the two wires?? Hopefully you have led indicators for each input??? Check and find the ACTUAL motor starting relay for your 25HP motor. I think you will find thermal/mechanical o/ls. One for each phase. Each heater element should be able to operate a common , normally closed overload switch. This is what you want! This is your motor running overload; which will stop your motor if their is a problem! You probably have some assortment of switches; hand or automatic to turm the motor on/off under normal r un conditions. Should be a size 2 starter. I'm hoping again that you can find all this in one box/ compartment. Then again the motor starter is probably in the MCC. Ask G.E., give them all your motor name plate, serial # , data Getting holp of your PLC's ladder logic print and the elemental electrical schematic will be big help. Do you have colligues in an IT department; contact them! MOIRA

 

[moira]

H Humble:::: If you have other similar machines, check them! Check with operating personnel, sometimes these folks can be a tremendous asset. Your pump supplier may be able to help. MOIRA

 

[stardelta]

I concurr with Waross and will elaborate. The leads will have been Thermistors which are temperature sensetive resistors. Usualy there are 3 of them in series with one buried in a coil from each phase during manufacture/rewind. The `PC` means they have a positive temeperature coefficient, i.e the resistance increases as temperature increases. They connect to a control module that monitors any increase in resistance then flags an alarm or shuts down the supply as the temperature of the winding increases. By burying them in a coil from each phase circuit the whole winding is monitored. The operating temperatures for the Thermistor are indicated by the colour of its leads. Its all in the link.

http://www.aev.co.uk/

Here in Europe larger motors usualy have 2 sets of thermistors, a lower value set to flag a warning, usualy about 120 deg, then a higher value set to trip usualy about 160 deg. I have never seen Klixon type cut-outs or thermal trips fitted in a standard motor of this size. Most machines are fitted with thermistors as standard but they are not always employed by the end-user which may explain why you cant find any reference in the machine schematic.
Your rewind company should have replaced them as a matter of course, they cost nothing and the fact they didnt means I have even less confidence in them now. I would be demanding to know why they were not, at the very least they should have checked with you if they were vital.

 

[jraef]

startdelta,
Just FYI, here in the US thermistors are not as automatic as they are elsewhere in the world, you pretty much have to special order them. In fact a lot of people here have no idea what they are or what to do with them when they see them in IEC motors. Many rewind shops frequently leave them out because they are used to customers having no clue or even putting power on them thinking they are Klixons and causing problems when they reconnect the motor. I'm not saying that's the right thing to do, it just happens a lot. I still agree that the rewinder should have asked.

http:/

http://www.jraef.com

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[humbleuser]

Thank you everyone. A technician from the repair shop is installing one right now as I type. They admitted that it was their fault for not installing one. I hope to have this motor back in the machine and connected by the end of the day. Again, thanks everybody.

 

[humbleuser]

I installed the motor back in the machine and connected the power to motor...correctly!!! After pump ran for a few minutes and all of the air was bled from the hydraulic system the motor/pump combo run nice and smooth. The thermistor (165C rating) is connected to the PLC and that should take care of that.

Thanks a million to everyone that made suggestions. This is the most useful/helpful forum that I belong to. Keep up the good work, forum members.