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RustyCas

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Reply with quote  #1 
As a mechanical guy, motors are just a necessary evil (and 2-pole motors are a special kind of evil), so I don't claim to know much about them, electrically.

I see a fair number of WEG motors in the larger sizes (I'm guessing because they are relatively cheap compared to better brands) and in my experience they don't hold up all that well.

Had one on an air compressor that lost an inboard bearing, and the rebuild on restart was running a little hot.  In discussing it with the maint supv I asked how it was set up in terms of "loading" and he said that when it's "in the lead" it's programmed to run at max amps, so it's using all of the 1.15 Service Factor.  He said that's the way Ingersoll says to do it.  I suggested that given what I've seen with WEG motors, I'd never run one into the SF.  He said today that he was having them reprogrammed to only use a SF of 1.1

My question for you motor experts:  is it normal to use 'all' of the SF in applications where it's possible to control for this? (these are Centacs, so amps can be controlled closely using the inlet and bypass valves).  I always thought service factor was somewhat of a "safety factor" but apparently that's not the case?

Enlighten me.







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John from PA

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Reply with quote  #2 
http://ecmweb.com/motors/understanding-induction-motor-nameplate-information is pretty clear with regards to SF.

Service factor
 — Service factor (SF) is an indication of how much overload a motor can withstand when operating normally within the correct voltage tolerances. For example, the standard SF for open drip-proof (ODP) motors is 1.15. This means that a 10-hp motor with a 1.15 SF could provide 11.5 hp when required for short-term use. Some fractional horsepower motors have higher service factors, such as 1.25, 1.35, and even 1.50. In general, it's not a good practice to size motors to operate continuously above rated load in the service factor area. Motors may not provide adequate starting and pull-out torques, and incorrect starter/overload sizing is possible.
MarkL

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As an aside Rusty, I am  surprised you don't Rate WEG much, they are seen as a premium product in the Irish Market, in fact about only company still making all theyre own stuff, ABB siemens etc are all subbing out manufacture to china and worse. But I guess the Markets differ in the States? 
RustyCas

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John, that's exactly the way I've always understood it.  Just curious as to how closely this is followed, or if running into the service factor is normal.

Mark, the WEGs that we get here are manufactured in Brazil.  I doubt they are ever used because they are "better" -- I suspect they're considerably cheaper than a motor made in the U.S. (many still are).  I don't know that I've seen one from China here, but I haven't looked that closely.  Perhaps I don't like the larger WEGs because on the outboard bearing housing, there is nowhere to mount my accel for the radial readings - they only extend about 1/2" from the endbell.  Maybe it's a subconscious thing.

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MarkL

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WEG are Brazillian Rusty and as far as I know everything is Made in Brazil. They're huge in Mining applications and Vale in Brazil is one of the biggest Iron Ore concerns worldwide, and I have seen some serious WEG stuff on Applications in Vale mines. 

I haven't worked on anything bigger than 300kw from them, and they were all sterling motors reliability and build quality wise.

Service factors of 1.5 were always what we strived for the minimum when spec'ing gearboxes, but I am sure that with motors it's the same case.
RustyCas

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Reply with quote  #6 
Mark, maybe they keep the good ones for themselves and send us the rejects.  When I get time, I'll go back through my records on the air compressor motors and see if I can tell if the WEGs really fail more often.
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HuskerTim

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Reply with quote  #7 
In my short time in a repair facility so far(almost 5 years) I have witnessed a 1,250HP 2P compressor (IR brand comp I believe) motor,  that was continuously run at 110% of FLA and the aluminum rotor had degraded/failed.  This has happened two times in 9 years on this particular motor.  After the complete rebuild last winter (rewind/rebar due to heat stresses) I was onsite to witness start up and had several conversations with everyone in the Boiler Room to lower the load to relieve stress on the motor, good guys I think they listened.

I have recently installed and witness startup of a 250HP 2P on an NH3 Compressor (refrig) that until the valve settings were re-cal'd was running at 120% of FLA.  This particular brand of motor is neither robust nor overly reliable especially when running at such a high service factor.

Below is a pic of the 1,250 rotor.  The first picture demonstrates an arcing pattern down the long axis of the rotor bar on the external surface of the rotor iron.  The second is an overall pic.DSC08581.JPG  DSC08576.JPG 

HuskerTim

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Reply with quote  #8 
Rusty,

The Weg motors are more economical then some other brands.  At this repair facility we see many Weg motors of all sizes.  The largest being a 2,000HP 8P Synchronous fresh water pump motor.  They seem to be as reliable as most other brands in the presence of abuse and lack of proper maintenance. 
OLi

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ABB have a fully automatic plant in Sweden for small motors and the larger like 38MW are made in another plant that I visit frequently and that have a similar sister shop in Italy. I have not so far seen branded Asian parts here but who knows. WEG are also common and claim to be worlds largest manufacturer and part from being delivered with the winding cables just hanging out not lugged and in the connection box in some order they behave about the same as other.
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Danny Harvey

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Reply with quote  #10 
Keep in mind that I have not designed any equipment since the middle 90's, but we would never use the SF in motor sizing when designing our conveyor drives-even the big ones.

We sold motors. At first we had Allis Chalmers, the it was Siemens-Allis, then Siemens. Then we took on more competitive brands like Leeson and finally WEG.  

We sold WEG but we installed Siemens on our equipment because we felt it was a better quality motor.
RustyCas

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Reply with quote  #11 
I suppose we could evaluate the quality and reliability of motors based on their use in ideal or "as recommended" conditions, but how realistic is that?

On a tangential note, utility-grade (mowers, pressure washers, etc) Honda gasoline engines are regarded (in the US at least) as "the best" by (perhaps) a majority of folks.  They do seem to be well made, are reliable, start easily.  One of the first jobs I had 20+ years ago was to evaluate several brands of gasoline engines that were used on walk-behind concrete finishing trowels.  The Honda engines in particular were failing at a high rate.  Took data on several sizes of Onans, Kohlers, and Hondas as instructed.  All were about the same.  Finally talked to a field rep and he asked if I had opened the throttle screw wide open, "cause that's the first thing they do in the field, so they can finish faster."  So I repeated the tests with the throttle adjustment screws wide open.  The Onans and Kohlers were marginally rougher.... the Hondas were horrible!

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Sinski

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Reply with quote  #12 
Quote:
Originally Posted by MarkL
As an aside Rusty, I am  surprised you don't Rate WEG much, they are seen as a premium product in the Irish Market, in fact about only company still making all theyre own stuff, ABB siemens etc are all subbing out manufacture to china and worse. But I guess the Markets differ in the States? 


From what I have seen in Australia, mainly paper industry, WEG's seem to be the common cheap motor that everyone buys for standard stock pumps etc. When larger sizes are used they tend to be more Siemens or ABB motors.
VibGuy~5

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Reply with quote  #13 

I heard through the grapevine that WEG are now making motors in China. I guess market forces eventually caught up with them.

I normally like them because they always have the bearings on the nameplate and there’s usually a nice flat surface for my sensor-maybe they’re sending the crap ones over to you Rusty!! I wouldn’t normally class them as cheap, more mid-range.

They are also doing a cheaper version of large(ish) motors for running with VFDs. Instead of having insulated bearings they have insulated shields-I’ll let you know how I get on with those.

OLi

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Reply with quote  #14 
I have once experienced isolated shields on a mid size motor it was done using aluminium oxide I think. It did last 3 years then it was worn thru and problems returned. Maybe it can be done to last these days some way.
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MarkL

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Reply with quote  #15 
Quote:
Originally Posted by VibGuy~5

I heard through the grapevine that WEG are now making motors in China. I guess market forces eventually caught up with them.

I normally like them because they always have the bearings on the nameplate and there’s usually a nice flat surface for my sensor-maybe they’re sending the crap ones over to you Rusty!! I wouldn’t normally class them as cheap, more mid-range.

They are also doing a cheaper version of large(ish) motors for running with VFDs. Instead of having insulated bearings they have insulated shields-I’ll let you know how I get on with those.



The Bearings on nameplates and the nice flat surfaces for taking readings from are also a quality I admire in them.
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