SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: Sheila Prather
Organization:Northrop Grumman Corp
Date posted: Thu Dec 6 9:40:53 US/Eastern 2001
Subject: ESS of Rotating Devices, e.g., motors, resolvers, synchros
Is there a recommended ESS regimen for these type devices? Is ESS feasible?
Subject: Rotating Device Screening
Reply Posted by: B.W.Dudley
Organization: Reliability Analysis Center
Date Posted: Thu Dec 6 13:43:24 US/Eastern 2001
All devices can be screen tested, the problem is defining the parameters that will be effective and not cause permanent damage or great loss of life. Rotating devices such as motors and resolves have three general failure modes, worn bearing, open or shorted winding and mechanical failure. The relative frequency of these failure modes is approximately the same, that is, 30 to 35%.
The primary failure causes for the bearings are poor lubrication, contamination or overloading. Screen testing for these conditions is very difficult, as the test would have to be an overload stress test. This test condition could cause damage to “good” units.
Winding failures are generally caused by high temperature resulting in the wire or the insulation to short or open. By performing high temperature testing, this failure mode can be detected. This test should be performed with the motor operating to accelerate hot spot failures. High temperature testing should not cause damage or extensive loss of life of the motor.
Mechanical failure cause can include cracked housings, worn brushes, sheared armature shaft or cracked rotor laminations. Cracked housing failure usually can be identified with a visual inspection, A short test with a maximum load applied can be used to identify worn or misarranged brushes. Sheared shafts will also be identified with this type of testing.
Cracked rotor laminations are more difficult to find. Vibration analysis could be considered, but the use of use of a low voltage, high frequency signal to measure the inductance reading for each of the stator windings seems to be the best approach.