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yorgi (Electrical) (OP)
30 Nov 12 10:38
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 (Structural)
30 Nov 12 11:38
Surely the vendor should know something??!!
Helpful Member!  jraef (Electrical)
30 Nov 12 12:05
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."
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John2025 (Industrial)
30 Nov 12 12:55
@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 (Electrical)
30 Nov 12 16:36
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 (Electrical)
1 Dec 12 0:29
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 (Electrical)
1 Dec 12 1:59
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 (Electrical)
1 Dec 12 7:21
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 (Electrical)
3 Dec 12 9:11
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 (Electrical)
3 Dec 12 13:01
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.

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

Helpful Member!  jraef (Electrical)
3 Dec 12 19:29
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.

Quote (Weg data sheets)

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)

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yorgi (Electrical) (OP)
4 Dec 12 8:00
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 (Electrical) (OP)
4 Dec 12 8:07
Cable length only 30m from drive to motor Dv/Dt filter fitted. Sorry for leaving this detail out of the original post.
LionelHutz (Electrical)
4 Dec 12 8:10
So this turn to turn short - start and end of the coil against each other?


Quote:

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 (Electrical) (OP)
4 Dec 12 9:48
No shorted turns on one phase winding effectively giving us an out of balance on the motor
Helpful Member!(2)  jraef (Electrical)
4 Dec 12 10:04
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)

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electricpete (Electrical)
4 Dec 12 12:53
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.

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

electricpete (Electrical)
4 Dec 12 12:55
Jeff - by the way, good discussion of power supply requirements in Weg's motor specs. I didn't realize the specs were that detailed.

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

Helpful Member!  LionelHutz (Electrical)
4 Dec 12 16:17
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 (Electrical)
4 Dec 12 23:35
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?
gattie (Electrical)
5 Dec 12 4:45
There could be a quality issue regarding the winding wire insulation - I've had cases where inferior low cost materials were used in manufacturing particularly, where copper varnish coated winding wire was involved.
The Random or 'Mush' method of winding & installation of motor stator coils is an ancient
proven method for low voltage motors.
Any starting & speed control devices (eg:vacuum contactor or VSD) that generate abnormal voltage spikes will find a weak spot in conductor insulation.

ScottyUK (Electrical)
5 Dec 12 12:23
Is there some direct relationship between temperature class (F v's H) and suitability for VFD operation, for example is Class F better than B, but worse than H? Or are the synthetic materials used in Class H insulation systems also better able to withstand impulse voltages? The latter sounds more plausible to me.
ozmosis (Electrical)
5 Dec 12 16:09
It is worth noting that the VFD used is an AFE (active front end) and they operate on a higher DC link voltage than a 'standard' 6 pulse rectifier pwm drive. This means the output peak-peak voltage will be somewhat higher than normal, I'm not sure of the exact figure but around 10-15% higher.
Normally, this would not pose too much an issue on a cable length of 30m and the fact yorgi has advised that there is also a dv/dt filter fitted but if there was some problem with the WEG motor to start, there is a possibility the higher p-p volts could find out this weakness quickly.
Yorgi, your opening question related to how others see WEG motors regarding reliability. I think the responses from most highlight a similar theme that 'generally' the product is ok but as this post has developed then it is clear that the issue is quite different and it seems that the local service and support is very questionable. This is a different issue but probably more important; you can have the best product in the world but if the local support is poor it will mean this will always be the common denominator.
yorgi (Electrical) (OP)
16 Jan 13 4:03
As a final update on this problem we have now changed out the remaining 2 failed motors. The same fault has been found on inspection of the failed WEG motors. We retrofitted ABB motors and have had no further failures to date. So as a summary we have had a 75% failure rate on the 4 WEG pump motors supplied as original eqyuipment by LOWARA. The remaining WEG motor is still in operation but we have an equivelant ABB as a spare incase of failure. When I contacted LOWARA they told me that they fit WEG because they are the cheapest motors ( chinese brands excluded) on the market and if they quoted with a major manufacturers motor fitted they would be less competitive. They further added that they would fit ABB, Siemens, Leroy Sommer etc if requested at an additional charge and further added that this was quite common for supply into the major utility companies who wont touch WEG. On purchasing the ABB motors we noticed that there is a price differential of about 25%. Maybe we were unlucky but to exhibit this level of failure has determined that we will fit Siemens Leroy Sommer or ABB on all our future schemes and also as replacements and retrofits. In fairness to WEG they immediatly and repeatedly offered free of charge replacements. However for us it is not so much the cost of the replacement its the down time. Many thanks to all posters for your observations and welcomed advice.
jraef (Electrical)
16 Jan 13 14:17
Thank you for the feedback.

I had very similar experiences (2 decades ago) with Weg motors on rock crushers. Over 50% infancy failures, great customer service in that they supplied immediate replacements via air freight at their cost, but the cost to me was well beyond the cost of the replacement motors. I lost an OEM customer over it because of the delays involved.


"Will work for salami"

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