Ensuring That Your Electric Motor Repairs Are Complete
EP Editorial Staff | February 20, 2013
Cascade Machinery Vibration Solutions points out that there’s an easy way to measure motor condition and reliability—with an emphasis on “easy.”
It’s referring to the Easy-Laser® E-Series system that lets a motor shop record a unit’s condition before and after repair, as well as provide full documentation that indicates changes throughout the life of the motor.
Full documentation without extensive setup
Until recently, most motor stators could only be measured in repair shops after extensive setup. Moreover, that type of difficult setup meant most 2-pole electric motors would just get measured when a vibration issue was reported. The Easy-Laser E-Series system has changed this equation: As shown in the accompanying photos, crucial measurements can now be made on the shop floor with NO special setup. But that’s not the only benefit for motor shops and end-users:
- The Easy-Laser E-Series system gives the end-user a new parameter by which to measure motor condition and reliability. Measuring parallelism of the stator centerline compared to the feet has been simplified with this package. Through such measurement, the client is able to verify that all repairs have been completed and within allowable tolerances. When the motor is tested in the shop and recorded, there will be fewer questions as to what was repaired (and how).
- A large motor can be in service for 20 years or more—with a repair scheduled every seven years on average. Depending on the unit’s type of service, it could be started many times within a year. This generates uneven heat and distortion typically not measured until a real problem arises. With the Easy-Laser E-Series system, the motor could be checked at each repair interval, over the life of the motor.
- The Easy-Laser E-Series system has the ability to document the ovality of the stator. There are tolerances for ovality (out of round) of a motor stator before it must be corrected. Until now, this has been manually measured and documented.
Think of the Easy-Laser® E-Series system as extra insurance—and peace of mind—when it comes to your large, expensive motors. As Cascade notes, in the past, there was no simple solution for ensuring the complete repair of these types of motors. Now there is. MT
About Cascade Machinery Vibration Solutions (MVS)
Cascade MVS (part of Cascade Analytic, LLC) is the U.S. Master Distributor for Easy-Laser®, “the total alignment solution.” The company offers a wide range of machinery-health products and services backed up by a “No Cure No Pay” policy. For more details, visit www.cascademvs.com.
Cascade Analytic, LLC USA
Alignment Tips From
Cascade Machinery Vibration Solutions (MVS)
When a motor is installed in the field, the four points of contact (motor feet) need to be co-planar and parallel to the stator center line. This evaluation has typically been performed on a test bed at the motor shop. Using feeler gauges, the technician will check contact to the test plate at each motor foot. Most shops will accept up to .002” total across all feet.
The magnetic field of a 2-pole motor is not strong enough to hold the rotor in the center should the motor not be mounted level. This will cause the rotor to shift in the axial direction. With large motors, there is as much as .500” float within the motor and when using flexible element couplings, this can cause a preload on the elements.
Before performing an alignment, the motor should be set on the magnetic center. The DBSE (distance between shaft ends) should be set correctly when using flexible element couplings, typically with .010”-.015” of pre-stretch, not compression. (Consult the coupling manufacturer.)
When the motor feet are not all in the same plane, it can cause the motor frame to distort and misalign the rotor and stator center lines. This causes a vibration at twice the frequency of the incoming supply power, 2x Line Frequency or 120Hz. This sometimes can be heard when standing near the motor as a beat frequency.
It’s important to verify that the rotor and stator are centered. This is typically verified once the rotor is installed. Feeler gauges are used to check radial clearances around both ends of the rotor/stator.