3 Phase LV motor failure 2

[raj2488]

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

 

[TugboatEng]

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.

 

[edison123]

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

http://www.edison.co.in

 

[raj2488]

@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

 

[edison123]

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

Muthu

http://www.edison.co.in

 

[raj2488]

@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?

 

[raj2488]

@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.

 

[edison123]

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

http://www.edison.co.in

 

[raj2488]

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?

 

[edison123]

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

http://www.edison.co.in

 

[waross]

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!

 

[TugboatEng]

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.

 

[RRaghunath]

"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).

 

[itsmoked]

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

Keith Cress
kcress -

http://www.flaminsystems.com

 

[panter]

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

 

[jraef]

"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

 

[FacEngrPE]

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)

 

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

 

[waross]

Welcome to Eng-Tips, Jessica.

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!

 

[electricpete]

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.

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

Top 4 Causes Of Electric Motor Failure (by 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.

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

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