i think that ElectricPete nailed it Two second start? Two pole? Failing in the endturns after 6 months? Sounds like the long endturns are under braced. I would make sure that the endturns are tied, anchored, tied top to bottom in more than one location, looped connections and the windings...
It is not unheard of for manufacturers to place cold field resistance on the nameplate but utilize hot current as these are measured at different times. In this case, the 88 ohms resistance makes sense as the field resistance will increase as the fields warm up. An increase of between 20 to 25%...
I agree that the wedge material needs to be changed. I have had good results with G11 wedges. One caution with G11 though. This material is composed of layered glass sheets impregnated with epoxy. In milling the wedge angle to fit the slot I have found that matching the wedge groove angle is...
Pete
The reason that I believe it is aluminum is that 1. Aluminum is standard in this size 2. The bar tops are standard shape for aluminum bars but uncommon in copper bars which are normally rounded or square. 3. The welded end ring imperfections can be seen in the picture. In fact, the weld...
Rockman
This rotor is a standard design where the bars are extruded and include a sacrifice tab at the bottom of the bar that is milled off during the insertion process to insure a tight fit in the rotor slots. This prevents bar vibration which leads to cracked bars over time. The bars are...
Rockman
This is an aluminum bar, aluminum endring custom 8000 fabricated rotor of a design still being utilized by GEVISA in Campinas, Brazil. It appears to be about an 8411 or so frame. Much is known about the thermal performance and endurance of these machines. Unfortunately, much is not...
i guess that i have had too many bourbons and branch in my life because I remain confused. I missed the lock rotor time by 2 seconds and I am sorry. We are looking at curves for a 1250 hp which has had magic HP increasing serum dispensed by some unknown someone and now everyone forgets that...
What am I missing here. If you rewound the stator for a higher horsepower and wound up with a higher locked rotor amps and kept the same rotor, why would you be that interested in the original thermal curves? I would be surprised if the original thermal limit would have been more than 27...
This looks like a GE custom 8000 frame rotor. you say it is on a fan. how long does it take to get up to speed? Is there a chance that this machine is an extended start machine which could have been energized repeatedly? If it is a GE, the endring is not cast but milled and tig or mig welded...
One major US manufacturer uses a temperature of 115C for the switching temperature in an effort to limit armature heating to below the permanent damage point. I see no real use for it in cases where the motor is locked down by the driven load or the brake.
About 30 years ago, I performed a PI on a motor out of a salt mine which had wrapped and dipped coils; a pre VPI winding. The readings indicated a very high PI, on the order of 8 or so. The unit was washed and treated in a dip tank and returned to service. The megger and PI were excellent on...
I have a customer with a 4500 KW Toshiba that has suffered two failures in the ring assembly. The application is a cement finish mill, a TEWAC enclosure. I increased the creepage distance from the ring to rheostat buss by increasing the opening and enlarging the insulating feed through...
If the rapid wearing brush is nearest the riser and it only occurs at high loads, has anyone considered air flow? The inner brush is in the shadow of the solid riser on this machine if memory serves. How much current, exactly are we drawing? I think that the 752 was originally designed as a...
I know of at least 6 horizontal pump motors in the New York area running at 177 RPM so the design is there and as these motors are old units being converted to VFD, I would say that the design is proven. I,too, would expect a high line current.
My learning is that inrush is not related to load. If this motor were started at 460 volts, had a KVA code of F, it would draw 4000 amps or so on start. If the voltage were limited to half, the current would be half. If the voltage were 500 vac,then the current would be 5% higher. I can see...
http://www.plantengineering.com/article/CA144818.html
Take a look at this site. It appears to me to be slot bar marking related to the number of coils per slot. From the picture, it appears to be a darkening of every third bar which makes sense as you have three coils in each armature slot.
