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  1. roryrobb

    3X Predominant Vibration Peak in 2 Pole Large AC motors

    Thanks guys for your responses. This continues to be a problem for us on motors we are rebuilding with new babbits and proper clearances to shaft and housings. Mostly split endbell types with no way to ensure proper bore alignment to one another other than checking air gaps at each end. TIR...
  2. roryrobb

    3X Predominant Vibration Peak in 2 Pole Large AC motors

    We continue to experience higher than acceptable overall vibration levels in large, say 900 to 1250 hp two pole, Babbitt bearing electric motors. The predominant peak vibration energy is usually 3X in either the vertical or axial plane. Current Example: outboard vertical reading 1.3 ips...
  3. roryrobb

    Bearing Defect Detection

    Pete you've been doing this a long time and your opinion is most valuable. Thanks for the response! I agree except that .0049 is a bit tighter than .01 ips. It is acheivable, sometimes costing multiple sets of bearings and assemblies. Handling prior to our plant is out of our control, and...
  4. roryrobb

    IEEE 429 Immersion testing

    I can understand the desire for this test on a new winding designed to pass such a test, but have never been able to get a winding to pass once it has been in service, even after a second VPI and cure. Is it practical to expect an original immersion winding to pass the IEEE 429 after being in...
  5. roryrobb

    Bearing Defect Detection

    Customer refuses validity of acceleration envelope readings to detect rolling element defect frequencies in newly installed bearings. Specifies no more than 3 peaks in a single spectrum in alignment with a bearing element frequency with an amplitude greater than .0049 i/s. does this seem...
  6. roryrobb

    Locomotive Traction Motor Pinion Installation

    David Your probably right, the highway sign going along the tracks says 5 to 6% grades, the tracks are probably not that steep...sorry for the misconception, I stand corrected.
  7. roryrobb

    Shaft replacement in small motor

    Pete; 4140 is great material but machinability as far as internal stresses goes is sometimes a problem (the stuff moves all over the place). For this size of motor, it would be tough to have to stress relieve the material prior to finish machining the journals and extensions. Be careful with...
  8. roryrobb

    Locomotive Traction Motor Pinion Installation

    GE specifies a hot advance of their locomotive traction motor pinions of .085" to .100". GM and MKO specifies only .055" hot advance and the taper is basically identical in angle, length and diameter. We are actually going to about .070". Of about 80 of these motors done, where pinion...
  9. roryrobb

    Acoustical Vibration

    Can someone define acoustical vibration in layman terms?
  10. roryrobb

    Maximum Speed for AC Induction Motors

    100 hp Reliance IEEE 841 design 1200 rpm (6 pole) motor. Running on PWM VFD. Is there a standard for frequencies over 60 hz. or a maximum speed rating for motors. I know on larger motors peripheral speeds should not exceed 10000 ft/min but what about a guestimated 13" rotor core diameter?
  11. roryrobb

    PAM Motor Basics

    Can anyone explain the basic theory behind pole amplitude modulation in an electric motor. I have a 6500 hp with 9 leads connected 2 par star on high speed (894) and series delta on low speed (710). Motor has 120 slots/coils. I can see no change in poles when reconnecting from 2 wye to 1 delta...
  12. roryrobb

    WHAT IS A SALENT POLE

    First of all, the spelling is "salient". The answers provided thus far are correct. However if your new to the electric motor repair industry, a basic understanding of what a salient pole motor (or generator) does. In a 3 phase AC induction motor, when voltage is applied to the...
  13. roryrobb

    VFD application to standard duty motor

    Customer has 3 each 75 hp Reliance standard duty motors, 4 pole, 460 vac, tefc that run from ROM stacks of coal for train loading. They need to start blending these stacks and want to slow down the feed on the belts based upon sulphur content etc. The worst scenario the engineers can see is...
  14. roryrobb

    Can DC Motor Bearings have Fluting from Shaft Current?

    A customer reports finding first high freq vibration in the 130 to 180kcpm range, with one of the high peaks at 2BSF. He suspected fluting and then discovered it upon disassembly. I am somewhat familiar with shaft currents in AC Induction motors, but haven't encountered it in DC. This is a...

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