Two competing failure modes were found to dominate motor life; i.e., bearing failures and winding failures. All bearings in the failure bank were of the grease-packed ball bearing type. Separation of failure by failure mode indicated that both failure modes could be described by a Weibull Commulative Distribution. A mathematical model for each failure mode, with dominant variables was developed and a competing risk failure model established.
An existing data failure bank consisting of over 2000 actual fractional horsepower (FHP) motor failures was upgraded and utilized to develop a failure model for FHP motors. Motor failures were dominated by two failure modes: i.w. , winding failures and bearing failures.
A literature survey of bearing failures and winding failures was conducted to verify failure modes and dependent failure variables. The following sections of this report describe the data failure bank, failure modes, literature review and development of the mathematical prediction models.
CONTENTS:
Data Bank Analysis
Bearing Reliability Model
Literature Review of Bearings
Development of Bearing Life Prediction Model
Motor Winding Reliability Model
Literature Review of Electrical Failures
Regression Analysis of Winding Failures
Influence of Altitude on Bearing and Winding Temperature
FHP Motor Failure Model
Failure Rates of FHP Motors
Use of FHP Motor Failure Models
Appendix A
Multiple Linear Regression Analysis Techniques and Examples
Regression Analysis
Use of Regression Analysis
Correlation Coefficients
Correlation Matrix
Correlation Coefficients of Transformed Data
Selecting an “Optimum Set” of Explaining Parameters
A Large Number of Independent Variables
Regression Tables Explained
Examples of Data Analysis Reduction
Appendix B
Recommended Replacement of Reliability Model for Electronic Cooling Devices and FHP Motors for MIL-HDBK-217B
Motor Reliability Prediction Model
Predicting Failure Rate Without Utilizing Tables
Bearing Characteristic Life Resulting from Thermal Cycling
Winding Characteristic Life Resulting from Thermal Cycling
Examples of Motor Failure Rate Prediction
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