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3 Phase LV motor failure
2

3 Phase LV motor failure

3 Phase LV motor failure

(OP)
Hi,

I have a situation. We recently installed two brand new motors(name plate details are attached) to pump units and both failed. They are identical to previous old units which were sent for servicing. One of the new units tripped and the rotor found in jammed state. the second one has one of the phases in open loop(burnt). trying to find root cause of the failure as they were both brand new. the operating current is 5.6amps and rated current is 5 for 415V supply. What is the service factor for 3hp motor or allowed over current percentage? Appreciate expert advise.

Best regards,
Raj

RE: 3 Phase LV motor failure

With no service factor listed I would assume 1.0 which you have exceeded. Your overload protection should have prevented damage. Why did the previous motors require service? These small motors are usually run to failure as they're not economical to repair.

RE: 3 Phase LV motor failure

What do you mean by rotor found in jammed state? Photos of the failures would be more helpful than just a nameplate. Were the previous motors running with same 5.6 A, which is 12% more than rated? What kind of OL protection do you have?

Muthu
www.edison.co.in

RE: 3 Phase LV motor failure

(OP)
@edison123 the rotor could not be hand turned. havent opened the end covers to inspect as its still under manufacturer warranty so not sure of the root cause

RE: 3 Phase LV motor failure

If the rotor cannot be turned, most likely seized/broken bearing(s). What about other questions?

Muthu
www.edison.co.in

RE: 3 Phase LV motor failure

(OP)
@edison thanks. since its a brand new motor and manufacturer strongly arguing it could not be bearing failure, im just trying to see if there could be any other possibilities like melted resin between stator and rotor or etc while waiting for their assessment report. though this can be easily answered once its opened for inspection, just checking for experience of fellow forum users here for similar experience. to avoid similar failure, how do i pick/design the correct motor ratin/ correct sizing?

RE: 3 Phase LV motor failure

(OP)
@tugboateng the previous motors failed too. as im still new to this department, i am just starting to collect some data to study this further. apparently the previous motors have worked well for many years before failing recently. at the moment,i am trying to get some details on the OL proctection type, past data of current, any modification done on pump and etc to conclude why the failures are happening. to start with, just wanted to know how much more current is really too much for this motor as no service factor is mentioned to know if the motor is undersized.

RE: 3 Phase LV motor failure

The OEM either has to let you open the motor or move their ass to your site. Till then, it's a Schrödinger's cat situation reg bearings.

Muthu
www.edison.co.in

RE: 3 Phase LV motor failure

(OP)
agreed,where can i study on selecting correct motor rating based on the full load current data that we have? can shed some lights on this please?

RE: 3 Phase LV motor failure

Yours is an S1 duty motor. So there is not much margin on OL current and duration. If your load current is 5.6 A always, then look for a motor with that current / HP rating. Having said that, if the brand new motors could not handle overloads for a short term and fail prematurely, then most likely they are poorly made.

Muthu
www.edison.co.in

RE: 3 Phase LV motor failure

Restrict the pump discharges slightly, until the current comes down to or below rated current. This wouldn't be the first pump motor destroyed because someone opened the discharge valve all the way.
Is the jammed motor disconnected from the pump?
A jammed bearing will often turn the opposite direction for a quarter turn or a half turn before jamming again.
And I once had a heated argument with the mechanical guys over a jammed bearing o a shaft mounted brake.
Despite the bearing being visibly damaged (the bearing spacer had broken and fallen away. The balls piled up together and jammed.
"The bearing is shot."
"NO it can't be the bearing."
"Why not/"
"It's brand new."
"Look at it. It is jammed and you can wobble the brake assembly on the shaft."
"No it"s not the bearing. The bearing is new."
The argument and the denial continued for some time until they finally changed the busted bearing.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: 3 Phase LV motor failure

Raj, thank you for letting us know about the previous motors. In your case they are clearly undersized. Hopefully, you can find a 5hp motor in the same frame size so you won't need to make any modifications to your system. Otherwise, as waross stated, you can throttle the pump to control the amps if your system permits.

RE: 3 Phase LV motor failure

"One of the new units tripped and the rotor found in jammed state. the second one has one of the phases in open loop(burnt).."
I am suspecting single phasing. This explains rotor damage, higher current drawal. You mentioned 'one of the phases in open loop' and this supports my suspicion.
If true, considering the old motors had no rating issue and the new ones are identical in all respects to the old ones, the new motors are also good enough for the duty (no rating issue).

RE: 3 Phase LV motor failure

Toshibas are good motors. Depending on the overload types single phasing can easily toast motors.

Keith Cress
kcress - http://www.flaminsystems.com

RE: 3 Phase LV motor failure

Raj,
Additionally the voltage of these motors should be checked. Higher , lower voltages or asymmetry can be a good reason for increased motor current

RE: 3 Phase LV motor failure

"Toshibas are good motors."
No argument there, but these are "Toshiba Dalian Co. Ltd.", a Chinese manufacturer (Dalian Lvsang Industry Corporation Ltd.) who licenses the Toshiba name. Not the same "Toshiba" motors we are used to seeing. When Toshiba started getting into financial trouble a decade or so ago, they began selling their name off to other manufacturers. According to Toshiba people I spoke to here, Toshiba Dalian was supposedly chartered to sell them in China only, but they ended up on a lot of OEM machinery that went elsewhere. When they end up here in the US, Toshiba here will not support them under warranty issues (which is how I learned all of this). They are (IMHO) poor quality motors prone to premature failure.

raj2488, are these being driven by inverters? Bearing and winding failures in motors not designed for use on inverters are not uncommon.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

RE: 3 Phase LV motor failure

It is easier to see the effect of single phasing with a clamp amp than a volt meter. Check all three phase leads, they should be close to equal. If there is a large difference look for things like a bad contactor or a loose connection upstream.

Yes I know, this does not work with a motor that is already toast, make it part of your startup with the next new motor. As indicated above, if amps are greater than label plate, close the pump discharge valve. Pump power increases faster with flowrate than with pressure (pump affinity laws)

RE: 3 Phase LV motor failure

Single phasing, a voltage unbalance that causes a three-phase motor to only run on two phases, can also result in motor failure. Often hard to detect, single phasing can cause a motor to burn out. ... According to Purcell, A VFD will protect the life of a motor and help simplify speed control, starting, and stopping.

RE: 3 Phase LV motor failure

Welcome to Eng-Tips, Jessica.

Quote (Purcell)

According to Purcell, A VFD will protect the life of a motor and help simplify speed control, starting, and stopping.
The problem is transferred from the motor to the VFD. Most VFDs will run on a single phase input but at a reduced capacity.
Standard motor overload protection provides a lot of protection against single phasing.
If the VFD does not have overload protection on the input circuit, it may fail in a voltage unbalance circumstance that would cause a motor to trip off line with no immediate damage.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: 3 Phase LV motor failure

Quote (Jessica Walliams)

Single phasing, a voltage unbalance that causes a three-phase motor to only run on two phases, can also result in motor failure. Often hard to detect, single phasing can cause a motor to burn out.

Quote (Jessica Walliams)

According to Purcell, A VFD will protect the life of a motor and help simplify speed control, starting, and stopping.

It seems you could have provided a link rather than copying word for word

Top 4 Causes Of Electric Motor Failure (by IBT)

Quote (IBT)

Single phasing, a voltage unbalance that causes a three-phase motor to only run on two phases, can also result in motor failure. Often hard to detect, single phasing can cause a motor to burn out.

Quote (IBT)

According to Purcell, A VFD will protect the life of a motor and help simplify speed control, starting, and stopping


=====================================
(2B)+(2B)' ?

RE: 3 Phase LV motor failure

Quote (Raj2488)

@edison thanks. since its a brand new motor and manufacturer strongly arguing it could not be bearing failure
If the motor name plate attached are from the "new" motor it says it is manufactured in 2013.
There is a strong possibility that if the motor has been stored and the rotor not turned during that time.
That the grease has ended up in the lower part of the bearing and that the topp part has rusted, so when you start it the bearing brakes in no time.
Especially if it has been stored in a hot and humid environment.



Quote:

ALTERNATIVE DESIGNATIONS:
These designations mean the same as that the bearing is open.
6206 ZZ
6206-ZZ
6206-2Z

Quote:

This 6206 2Z SKF ball bearing with the dimensions 30x62x16 is a single-row groove ball bearing with protective plates on both sides.
Advantages of sheet metal sealing are that you get low friction and that the bearing can handle higher speeds.
It protects against shocks and larger particles from eg metal shavings, stones etc.
But less good at excluding dust and retaining grease in the bearing compared to a rubber-tight bearing.

The same goes for 6304ZZ.

Ones we got a motor back from renovation and they hade forgotten to fill the bearings with grease or they forgot to tell us they didn't.
It didn't work for long. sad

Best Regards A

RE: 3 Phase LV motor failure

@redsnake

The grease is not a liquid to settle down. If anything, the grease becomes more solid if the motor was idle for a long time. Caking of grease can result in loss of its lubrication properties and lead to premature bearing failure.

Muthu
www.edison.co.in

RE: 3 Phase LV motor failure

smile No if it hade been a liquid it hade been oil.
Caking meaning. ponder

Quote (ABB)

The shoulders should be rotated regularly (once a quarter) for hand so that the grease film in the bearings does not penetrate.
Stationary heating, if installed, recommended to avoid condensation in the engine.
The motor must not be exposed to external vibrations stationary, as this can damage the bearings.

Quote (WEG)

1 Greased layer
We recommend that you rotate the motor shaft at least once a month (by hand, at least five turns, and stop
the shaft in a different position from the original).
If the engine is equipped with a shaft locking device, you must remove it before rotating the shaft and reinstalling it before performing any handling procedures.
Vertical motors can be stored in vertical or horizontal position.
If engines with open bearings are stored longer than six months, the bearings must be lubricated before the engine is used.
If the engine is stored for more than 2 years, bearings must be replaced or removed, washed, inspected and lubricated

It might be the opposite if you leave the motor in store without turning it all the weight from the rotor will be on the balls at the lower point of the bearing so eventually the grease will be pushed aside and it will only be iron against iron.

"the grease film in the bearings does not penetrate"



Best Regards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

RE: 3 Phase LV motor failure

Quote (Edited: An old anecdote)

My mechanic later became a tribolog, at one time he was greasing some bearings through a nipple and since he didn't clean up properly on the outside afterwards the end result was grease dollops on my electrical drawings, that was lying beneath the nipples, so he got the evil eye. evil
The conclusion is that Newton certainly can have a attraction on grease. winky smile
At least to me it is a proven fact.

Putting to much grease in a bearing can also break it, everything needs place to expand when getting hot.
In this case I would not consider it being a problem since it wasn't a tightly sealed bearing.

What I would like to know is what kind of pump it is?
And what is it pumping?
A displacement / screw pump, water / oil / dirt.ponder
I think someone asked what kind of motor protection device it hade too?

Best Reagards A

“Logic will get you from A to Z; imagination will get you everywhere.“
Albert Einstein

RE: 3 Phase LV motor failure

Great tips on motor failure analysis. Have you considered the load. What has changed with the pumps. Do we have impeller restrictions, material buildup causing blockages, pump bearing wear or failure, viscosity changes in fluids being discharged from the pumps. What kind of liquids or materials are going through these pumps. If your pumping molasses and the environment changed to cold temps you can be in overload. Good motors usually have a SF or service factor of 1.2 with some additional unpublished safety factor which has been exceeded. Is there a controller driving a VFD at half speed minimizing torque causing overload.

I'd start with the pump as two sets of motors have failed. Put on a clamp on ammeter and check the current draw when you reinstall the refurbished motors out for service and that should tell you what you are up against. If your underpowered upgrade the motors to a non-Chinese name brand. Down time is too expensive to screw around with cheap motors or pumps.

RE: 3 Phase LV motor failure

Welcome to Eng-Tips TFinstad.

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!

RE: 3 Phase LV motor failure

raj2488,
You have mentioned that the first motor was taking 5.2A while running in contrast to the name plate FLA=5A.
1) The O/L relay in the starter should be either Class 10 or 20. In that case, if the O/L is set to FLA=5A,
then it will trip only after 2Hrs of operation for 1.2xFLA.
2) In IEC motors there is no service factor given like in NEMA motors. IEC motors should show the range of rated output.
3) Your motor has no other rated outputs given for the rated voltage 415V. Therefore, your motor has to be
overload protected by Class 10 or 20 setting its setting as 5A.
4) Even though it is new, looks like it has got some jamming and continued to run and tripped by O/L relay in the starter.

RE: 3 Phase LV motor failure

Oddball question here, but I notice that the 220V supply is supposed to be Delta and the 380/415 as star. Would it make a difference if they got that the wrong way around?. i.e. wire 415V to the delta connections?

Or are these just sh1te motors?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

RE: 3 Phase LV motor failure

Raj seems to have vanished.
May be, he is not happy with the advice he got in this forum!!

RE: 3 Phase LV motor failure

Well he was trying to get the OK to run a motor at 112% of its rated max value and when we said don't think so clearly hasn't logged in since....

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

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