DID YOU KNOW THAT THERE IS AN EASY WAY TO MEASURE MOTOR CONDITION AND RELIABILITY? WITH THE EASY-LASER® E-SERIES SYSTEM, MOTOR SHOPS CAN NOW RECORD THE ELECTRIC MOTOR BEFORE AND AFTER REPAIR AND PROVIDE FULL DOCUMENTATION TO INDICATE CHANGES THROUGHOUT THE LIFE OF THE MOTOR.
THE IMPORTANCE OF THE ROTOR AND STATOR PLACED AT THE SAME LEVEL
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 test 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 prior to aligning. The DBSE (distance between shaft ends) should be set correctly when using a flexible element couplings, typically with .010‘ – .015” of pre-stretch, not compression. (Consult 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, 2xLine 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.
FULL DOCUMENTATION WITHOUT AN EXTENSIVE SETUP
Until now, most motor stators were measured in the repair shops and required extensive setup to make this measurement. Due to the difficult setup, most 2-pole electric motors are only measured when a vibration issue was reported. With the Easy-Laser® E-Series system, the ability to make these measurements are made simple. Now, these measurements can be made on the repair shop floor and no special setup is required as before. The motor shops can now record a motor before and after repair with full documentation for the client.
THE BENEFITS OF USING THE EASY-LASER® E-SERIES SYSTEM
- The Easy-Laser® E-series system gives the end-user a new parameter in which to measure motor condition and reliability. The ability to measure parallelism of the stator centerline compared to the feet is made easy with this package. Through this measurement, the client would be able to verify that all repairs were completed and within allowable tolerances. When the motor is tested in the shop and recorded, there would be fewer questions as to what and how the motor was repaired.
- These motors are usually in service for 20 or more years with a repair scheduled every 7 years on average. Due to each motor’s service, they could be started many times within one year. This generates uneven heat and distortion typically not measured until a real problem arises. With this system, the motor could be checked at each repair interval, for the longevity 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. This has been manually measured and documented until now.
- The Easy-Laser® E-series system is simply one extra insurance and peace of mind for large, expensive motor repair. Previously, this kind of measurement was not a simple solution – now it is!
Want to know more about the Easy-Laser® E-series systems? Learn more here!
By Troy Broussard, President& CEO Cascade MVS