VI balance grades 12 2006

Balance Grades: Electric Motor Experience Vibration Institute Piedmont Chapter 14 12/01/2006 Clay Boyd, PE CBM Analyst 704-382-3608 chboyd@duke-energy.com References Schenck Trebel Corporation 535 Acorn Street Deer Park, NY 11729 Toll Free: 1-800-873-2352 http://www.schenck-usa.com http://www.mpta.org/MPTABalancingPrimer.pdf http://www.irdbalancing.com/downloads/TechPaper1BalQualityReqmts.pdf Motor Repairs  Motor Repair Specification  Balance Grades  Initial Balance with Shop Balance Machine  Final Balance with Motor Assembled Motor Repair Specification  Work to be performed  Acceptable Repair Practices  Required Reporting  Acceptance Criteria, including BALANCE GRADE Balance Grades  Balance Grades are used to specify the allowable residual imbalance for rotating machinery  The ISO 1940 standard defines balance grades for different classes of machinery (Rigid Rotors Only*)  Example: Balance Grade “G2.5” is recommended for Steam Turbines, Machine Tools and Small Electric Armatures * ISO 11342 defines the balance quality requirements for rotors in a flexible state Permissible Residual unbalance per unit rotor weight (g*mm/g*1000) or Permissible cg displacement (mm*1000) Balance Grades: Sample Chart Service Speed (rpm) http://www.plant-maintenance.com/articles/balancingqualitylimits.pdf Balance Grades  A rotor balanced to G2.5 will vibrate at 2.5 mm/sec (Velocity) if freely suspended while rotating at service speed (2.5 mm/sec = 0.10 IPS) V(mm/sec) = 2pe(mm)*RPM 60sec/min e(mm) = Residual Imbalance (g-mm) Rotor weight(g) Balance Grades  Balance Grade is a function of  Rotor Mass (lbm, Kg, g)  Service speed (rpm)  Residual imbalance (g-in, oz-in, lb-in, g-mm…) Initial Balance with Shop Balance Machine It is difficult if not impossible to achieve Balance Grades G1.0 or G0.4 in a balance machine only Balance Grades G1.0 and G0.4 have special requirements  G1.0  The rotor must be mounted in its own service bearings  No end drive (for balance machines)  G0.4  The rotor must be mounted in its own housing and bearings  Must be run under normal service conditions: Load, Temperature  Self driven Initial Balance with Shop Balance Machine : Roller Size “…the roller diameter should differ from the journal diameter by at least 10%, and the roller speed should never differ less than 60 rpm from the journal speed… “ p.54 Fundamentals of Balancing, 2nd Ed 03/1983; Schenk Trebel Final Balance with Motor Assembled  Motor Setup  Flexible or Rigid Rotor – Large 2-pole motors  Effect of startup heating  Interference of 60 Hz electrical vibration on unloaded 2pole Motor phase readings Final Balance with Motor Assembled Motor Setup  Motor on Solid Base  Elevate on shims at base bolt locations  Shim to eliminate soft foot  Secure with bolts or clamps  Lubricate bearings  Monitor vibration from the first start Flexible or Rigid Rotor – Large 2-pole motors In test runs at service speed, moving two test masses from the end planes to the center plane, results in a vibration change of less than 20% pp.21-22 Fundamentals of Balancing, 2nd Ed 03/1983; Schenk Trebel Graphic: http://www.schenck-usa.com/lib_101_types_unbal.asp Effect of startup heating 60 Hz Trial (1:25 PM) Trial 2, 3, 4, … (9:00 PM) 1X Vibration BC 2C CBPM mils pk-pk 5 1 2 Run1(ODE) Run2(ODE) Run3(ODE) Run4(ODE) Run5(ODE) Run6(ODE) Run1(DE) Run2(DE) Run3(DE) Run4(DE) Run5(DE) Run6(DE) As low as reasonably achievable Before and After MOV Spectrum Year Overall Trend Questions? Balance Grades: Electric Motor Experience Clay Boyd, PE CBM Analyst ... Criteria, including BALANCE GRADE Balance Grades  Balance Grades are used to specify the allowable residual imbalance for rotating machinery  The ISO 1940 standard defines balance grades for different... Residual Imbalance (g-mm) Rotor weight(g) Balance Grades  Balance Grade is a function of  Rotor Mass (lbm, Kg, g)  Service speed (rpm)  Residual imbalance (g-in, oz-in, lb-in, g-mm…) Initial Balance. .. lb-in, g-mm…) Initial Balance with Shop Balance Machine It is difficult if not impossible to achieve Balance Grades G1.0 or G0.4 in a balance machine only Balance Grades G1.0 and G0.4 have special