basic air gap monitoring terminologies and standards

7/21/2019 BASIC AIR GAP MONITORING TERMINOLOGIES AND STANDARDS

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©VibroSystM 2008. All rights reserved

AIR GAP MONITORING

HYDRO-ELECTRIC GENERATORSCHAPTER I

Prepared by André Tétreault

Group leader

Technical support group




AIR GAP MONITORING

BASIC AIR GAP MONITORINGTERMINOLOGY AND STANDARDS




BASIC AIR GAP MONITORING

TERMINOLOGY

• NOMINAL AIR GAP

Designed air gap value at static-cold conditions.

• AIR GAP VARIATIONDifference between maximum inside radius of the stator andminimum outside radius of the rotor (maximum gap).

• AVERAGE AIR GAPAverage of all measured and calculated air gaps for all rotor poles.





TERMINOLOGY

• ROTOR CIRCULARITY

The difference between the maximum and minimum radii asmeasured, or measured and calculated, from the best center.

• ROTOR CONCENTRICITYDifference between best rotor center (geometric) and rotor rotation

axis (reference) calculated from the outside radius of each pole onthe same plane facing sensor #1.





TERMINOLOGY

• STATOR CIRCULARITY

The difference between the maximum and minimum radii asmeasured, or measured and calculated, from the best center.

• STATOR CONCENTRICITYDifference between best stator center (geometric) and rotor rotation

axis (reference) measured on the same plane and calculated fromthe reference pole.





TERMINOLOGY

Best center

Theoretical

center

d

Circularity = d

d Max

d Min

Roundness = d Max –

d Min


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TERMINOLOGY

Best center

Theoretical

center

c

Concentricity = c

Circularity and concentricity

definitions are identical for

both the rotor and stator.

Theoretical center is

identical for both rotor andstator.




STANDARDS (VSM)

PARAMETERS TOLERANCES

Assembly Acceptable Critical

Max. Air Gap Variations < 13% 13 to 30% > 30%

Stator Circularity < 7% 7 to 20% > 20%

Stator Concentricity < 5% 5 to 10% > 10%

Rotor Circularity < 6% 6 to 10% > 10%

Rotor Concentricity < 1.2% 1.2 to 4% > 4%

Minimum air gap > 85% 85% to 50% < 50%

* Dynamic conditions, unit running.Based on nominal air gap value.




STANDARDS (CEA)

PARAMETERS TOLERANCES

Assembly Intervention value Critical

Stator Circularity n/a>

20%* n/a

Stator Concentricity n/a > 5%* n/a

Rotor Circularity n/a > 12%* n/a

Rotor Concentricity n/a > 5%* n/a

Minimum air gap > 70% < 70% < 50%

* Static conditions, unit stopped.

Based on average air gap values.


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AIR GAP MONITORING

HYDRO-ELECTRIC GENERATORSCHAPTER I

Prepared by André Tétreault

Group leader

Technical support group

basic air gap monitoring terminologies and standards

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