WEG motor reliability 5

[yorgi]

We have just fitted four lowara pumps that came with WEG motors (37kW 400V 2 pole) . These motors are controlled by ABB acs 800 active front end drives. Within a week we had lost Three of the four Motors, motors taking very large currents and tripping on overcurrent before they got anywhere near rated speed . pumps free motors even ran uncoupled and still failing. Has anyone else experienced these issues and level of failure with WEG motors , We have now fitted ABB motors to the same drives and pumps and have run for the last 3 weeks non stop.

 

[MiketheEngineer]

Surely the vendor should know something??!!

 

[jraef]

If I had to guess, I'd say that someone connected the motors incorrectly, i.e. they used the high voltage (Star) connections and for those motors, but 400V was actually the LOW voltage connection (Delta), because they are 690/400V motors.

I've run into that with Weg before. In Brazil where Weg is made, they use a lot of 690V in the minimg industry, so instead of making 400/230V motors, they make 690/400V motors and 400V users are expected to read the installation manuals and connect them in Delta. Happens here in the US as well, we are used to dula voltage motors being 460/230V with the connections for 460V being shown as "High" voltage. But some Weg motors that arrive are actually 720/460V motors (it's actually the same motor as 690/400V, just for 60Hz applications). Everywhere else in the world beside Brazil, installers are used to connecting 400V (or 460V) to the "High" voltage pattern and never read the manuals for the motors, because they have connected hundreds or thousands of motors.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[John2025]

@jraef: That's an interesting possibility. I've got a WEG that we installed on a compressor a couple years ago. It's fine so obviously we got it right, but it would be really easy to screw that up. How long do you suppose a motor would last like that? seconds? minutes?
John

 

[Marke]

Hi Jraef

It is not just in Brazil that they supply 400/690 volt motors, but much of the 50Hz world they supply motors above 4KW that are designed for star/delta starting. This is historical as in many areas, above 5KW or simiar, you had to use a star/delta starter (wye/delta starter).
Here in New Zealand, it is the norm for motors to be delta connected for 400V for motors 4KW and above and the exception for them to be star connected for 400V.

I agree with your proposal of the motor being incorrectly configured for the voltage. Makes perfect sense.

Best regards,
Mark

Mark Empson
Advanced Motor Control Ltd

 

[ozmosis]

I'm quite sure the ABB motors will also be 400/690v too, so if the WEG motors were wired incorrectly, what changed to ensure the ABB motors were wired correctly? Wouldn't the installer have suspected something when they opened the motor terminal lid and seen the straps in a different configuration?

Regarding WEG motors. I find them good quality motors generally. I wouldn't have thought the motors were the cause.

 

[itsmoked]

I wouldn't think they're the problem either. Never had any problems with ANY WEG devices. I've thrashed some too, with the expectation they'd fail - they never have.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

How long are the leads from the drives to the motors? Do you have output filters on the drives?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[LionelHutz]

We're run into a few cases where motors were failing on VFD's and replacements just kept failing. In most cases, a different motor or a rewind instead of a replacement fixes the issue.

Basically, the problem is the motors are machine wound with the windings just mashed into the stator. There is nothing else but some insulation in the slots and insulation over the lead connections. In some cases, this leads to the start and end of a winding being against each other or even the winding near the ends of the coils on different phases being against each other. Despite the claims that the wire insulation can handle the high voltage levels this creates between these touching winding, it doesn't and it fails.

This isn't isolated to WEG motors. I've seen the same thing from a number of manufacturers. It seems to be a numbers game. The manufacturers push the limits of the materials to build the motor as cheap as possible since the extra warranty claims cost less then the amount saved in manufacturing.

The only real fixes are to buy more expensive motors where the manufacturer will show you how they keep this from happening or get the motor rewound at a good shop where they take care to avoid placing too much voltage across the wire insulation. You can also just hope the coil placement has shifted in the next batch of motors and you eventually get ones that don't fail.

 

[electricpete]

Good points all around. The phase separators would be required by EPRI low voltage motor rewind spec, even for non-vfd motors.

It brings to mind another thought: Does WEG consider these motors "inverter duty" ?
Part 31 of NEMA Standard MG1 gives requirements for such motors, including withstanding "voltage spikes" with peak voltage of Vp = 3.1*VLLrms and with rise time as short as 0.1 microsecond.


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(2B)+(2B)' ?

 

[jraef]

Looks as though Lowara uses a High Efficieny motor for their pumps, the Weg W22 Series. Although the Weg literature SAYS the W22 is suitable for variable speed operation, a review of their motor data sheet reveals that they were probably not really designed primarily as "Inverter Duty", so they have a lot of qualifiers tagged on in the section describing their capabilities WRT VFDs.

Some of this was in table form so it is less than clear here, but the salient points are there and I've highlighted a few.

12. Variable speed drive application
12.1 Consideration regarding rated voltage
The stator windings of W22 motors are wound with class F insulation (class H optional) and are suitable for either DOL
starting or via a variable speed drive. They incorporate the WEG exclusive insulation system - WISE® (WEG Insulation
System Evolution) – which ensures superior electrical insulation characteristics.
The stator winding is suitable for variable speed drive application, taking into account the limits shown in table 18.

Table 18 – Limit conditions for variable frequency drive operation without application of a load reactor
Motor rated voltage | Peak voltage on motor terminals | dV/dt on motor terminals | Rise time | Time between pulses
Vn ≤ 460 V ≤ 1600 V ≤ 5200 V/μs ≥0.1 μs ≥ 6 μs
460 V < Vn ≤ 575 V ≤ 1800 V ≤ 6500 V/μs ≥ 0.1 μs ≥ 6 μs
575 V < Vn ≤ 690 V ≤ 2200 V ≤ 7800 V/μs 0.1 μs ≥ 6 μs

Notes:
1 – For the three cases above the maximum recommended
switching frequency is limited at 5 kHz. I believe that the factory default Carrier Frequency of an ACS800 drive is higher than that.
2 – If one or more of the above conditions is not followed accordingly (including the switching frequency), an output
filter (load reactor) must be installed on the output of the VSD.
3 – General purpose motors with rated voltage up to 460V may be operated by a frequency inverter respecting the
limits shown in table 18.
4 – General purpose motors which at the time of purchase did not have any indication of operation with a frequency
inverter, and with nominal voltage greater than 460 V, require special insulation to support the limits indicated in
table 18. Otherwise, the limits of the first line of the table (for nominal voltage up to 460 V) must be considered or a
load reactor at the output of the VSD must be installed.
5 – General purpose motors which at the time of purchase did not have any indication of operation with a frequency
inverter and which are the dual voltage type, for example 380/660 V and 400/690 V, may only operate driven by a
frequency inverter in the higher voltage with the installation of load reactor or otherwise respecting the
limits of the first line of the table (for nominal voltage up to 460 V).

A 1600V peak voltage and a .1 μs rise time is not what most "Inverter Duty" motors are designed for, it's more like 2000V and .025 μs now. This is better than the old 1200V ratings, but not the best in class by any stretch. Most likely these motors should have had reactors on them at the very least, if not some decent motor lead filters.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[yorgi]

Motor connected up in Delta as per nameplate first thing we checked. ABB machines also connected up in Delta now running a month. Had one of the failures independently inspected and found to have shorted turns on one phase also loose rotor bars. WEG contacted and a poor response recieved. suggested to retrofit their drives with the motors, Not really practical. Dont think we will accept weg motors on site again.

 

[yorgi]

Cable length only 30m from drive to motor Dv/Dt filter fitted. Sorry for leaving this detail out of the original post.

 

[LionelHutz]

So this turn to turn short - start and end of the coil against each other?

It brings to mind another thought: Does WEG consider these motors "inverter duty" ?

Here, if you want an "inverter duty" motor the supplier drills 2 holes in the case and pins a "inverter duty" tag on the motor.

 

[yorgi]

No shorted turns on one phase winding effectively giving us an out of balance on the motor

 

[jraef]

I think what Lionel was asking is the actual location of the short on the winding. "First turn" shorting is a very common indication of damage caused by high voltage pulses as a result of standing wave generation, ie the motor was not well designed for inverter applications.

If that is the case, I fail to see how using one brand of drive over another would make much of a difference. It's not as though ABB are newcomers to this issue, in fact I would venture to say that WEG are the neophytes by comparison of the two companies.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
For the best use of Eng-Tips, please click here -> faq731-376

 

[electricpete]

So WEG's recommendation was not to explore installation details or filtering options.
Instead they recommended to tear out the old drives and put in WEG drives.

Sounds perfectly logical to me. But only on 12/04.



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(2B)+(2B)' ?

 

[electricpete]

Jeff - by the way, good discussion of power supply requirements in Weg's motor specs. I didn't realize the specs were that detailed.

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(2B)+(2B)' ?

 

[LionelHutz]

Yes, that's what I asked. Was the coil of the phase wound so that the wires at the start and end of the coil were against each other?

Typically, a re-wind shop will attempt to wind the coils so the start is on one side and the end is on the other side. They also watch the voltage per coil so that even with the start and end of the coil against each other the coil doesn't fail. The contact we talk to every now and then attempts to use 50V/coil based on their past experience. They also use phase-phase paper and are careful where the windings in the end bells all land. Compared to that, we have seen motors inside motors which were factory wound at 200V/coil or higher these days without any phase windings and without much concern about seperating phases.

 

[zlatkodo]

Very useful posts from jraef and LionelHutz.
Yes, very often happens that a manufacturer or rewind shop uses the maximum number of parallel circuits, without taking into account the "volts / coil" ratio (at random wound coils).
Also, there is often a lack of insulation between the phases.
BTW, is there any other requirements or recommendations for materials and working procedure when rewinding standard to an inverter duty motor?