Electric Motor Reliability Model
CONTENTS :
1.0 Introduction
2.0 Summary
3.0 Discussion
3.1 Data Bank Analysis
3.2 Bearing Reliability Model
3.2.1 Literature Review of Bearings
3.2.2 Development of Bearing Life Prediction Model
3.3 Motor Winding Reliability Model
3.3.1 Literature Review of Electrical Failures
3.3.2 Regression Analysis of Winding Failures
3.3.3 Influence of Altitude on Bearing and Winding Temperature
3.4 FHP Motor Failure Model
3.4.1 Failure Rates of FHP Motors
3.4.2 Use of FHP Motor Failure Models
4.0 Conclusions
5.0 References
6.0 List of Symbols
Appendix A
Multiple Linear Regression Analysis Techniques and Examples
A.l Regression Analysis
A.2 Use of Regression Analysis
A.3 Correlation Coefficients
A.4 Correlation Matrix
A.5 Correlation Coefficients of Transformed Data.
A.6 Selecting an “Optimum Set” of Explaining Parameters
A.7 A Large Number of Independent Variables
A.8 Regression Tables Explained
A.9 Examples of Data Analysis Reduction
Appendix B Recommended Replacement of Reliability Model for Electronic Cooling Devices and FHP Motors
Motor Reliability Prediction Model
Predicting Failure Rate Without Utilizing Tables
B.2.1 Bearing Characteristic Life Resulting
from Thermal Cycling 105
B.3 Winding Characteristic Life Resulting from Thermal
Cycling
B.4 Examples of Motor Failure Rate Prediction 103
LIST OF FIGURES
1 Fractional Horsepower Motor Reliability Data Life 22
Versus Temperature
2 Motor Temperature Rise Distribution 27
3 Bearing Life at Low Temperature 35
4 Bearing Life over Temperature Range 37
5 Bearing Test Data — All Greases 39
6 Winding Life Versus Ambient Temperature. . 48
7 Winding Life Versus Bearing Life at 100 C Ambient 50
8 Influence of Altitude on Life 55
9 Temperature Rise Characteristics Internally Fan Cooled and
Non-Fan Cooled Totally Enclosed Motors Versus Altitude
A-l Schematic Plots Depicting Various Amounts of Scatter, as Well as Correlation Coefficient (R) between Variable X
and Response Y
A-2 Correlation Matrix for over 1000 FHP Motor Failures
A-3 Schematic Data Plot Showing Observed Data Points (X., Y.),
Best Fit Points (X., Y.), Average x = X /N, Y = Y./N
Error Values (Y.-Y.), and Residuals (Y.-Y) 90
A-4 Three Criteria for Testing the Relative “Best Fit” of a
Combination of Variables in a Hypothetical Regression Model 91
A-5 Regression Table Description
A-6 Regression Table for Bearing Temperature
A-7 Regression Table for Ambient Temperature
A-8 Correlation Matrix for over 1000 FHP Motor Failures.
A-9 Correlation Matrix Winding Failures 96
B-l Thermal Cycle
LIST OF TABLES
1 Life Test Summary Grease 1 9
2 Life Test Summary Grease 2 J.1
3 Life Test Summary Grease 3 12
4 Life Test Summary Winding Failures 14
5 Typical Output from 45 Test Populations 15
6 Test of Bearing Failure Data versus Predictive Equations
for .35 Standard Deviation 25
7 Grease Constant K 24
8 Typical Motor Temperature Rise Data 28
9 Bearing Size Vs. Motor Input Power 30
10 Bearing Life Test Summary Cyclic Temperature Tests 31
11 Thermal Cycling Tests Duty Cycles 32
12 Low Temperature Bearing Life 33
13 Literature Review of Temperature Influence on Life 41
14 Motor Winding Failures 45
15 Winding Failure Weibull Slope Mean Values 47
16 (Reference 21)
Influence of Altitude on Motor Life for Fan-Cooled Motors . 57
17 FHP Motor Life Prediction 59
A Motor Failure Rate Table 99
