Page 152 - Electrical Equipment Handbook _ Troubleshooting and Maintenance
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MAINTENANCE OF MOTORS

                                   MAINTENANCE OF MOTORS                   8.7

            results in a reduction in the operating and maintenance costs and an increase in efficiency
            and reliability.
              The philosophy behind predictive maintenance is to anticipate impending equipment
            failures by using modern technologies, and to eliminate the root cause before it can result
            in catastrophic failure. The benefits of predictive maintenance are as follows:
            1. Repetitive problems are identified and eliminated.
            2. Equipment installation is performed to precise standards.
            3. Performance verification ensures that new and rebuilt equipment is free of defects.
            Predictive maintenance technologies include

            1. Vibration spectrum analysis for rotating equipment
            2. Oil and wear analysis
            3. Thermography for all electrical equipment


            MOTOR TROUBLESHOOTING

            Figure 8.2 illustrates a troubleshooting flowchart which provides logical, step-by-step
            methods for identifying and correcting motor problems.
              Warning: The internal parts of a motor could be at line potential even when it is not
            rotating. Disconnect all power to the motor before performing any maintenance which
            could require contacting internal parts.
              This is the key for Fig. 8.2 on troubleshooting ac motors.
            A. Motor would not start or accelerates too slowly.
            B. Motor runs noisy.
            C. Motor overheats.
            D. Motor bearings run hot or noisy.


            DIAGNOSTIC TESTING FOR MOTORS

            The following factors affect the insulation systems in motors:
            ● High temperature
            ● Environment
            ● Mechanical effects such as thermal expansion and contraction, vibration, electromag-
             netic bar forces, and motor start-up forces in the end turns
            ● Voltage stresses during operating and transient conditions

            All these factors contribute to loss of insulation integrity and reliability.
              These aging factors interact frequently to reinforce one another’s effects. For example,
            high-temperature operation could deteriorate the insulation of a stator winding, loosen the
            winding bracing system, and increase vibration and erosion. At some point, high-temperature
            operation could lead to delamination of the core and internal discharge. This accelerates the
            rate of electrical aging and could lead to a winding failure. Nondestructive diagnostic tests
            are used to determine the condition of the insulation and the rate of electrical aging. The
            description of the recommended diagnostic tests for the insulation system of motors and the
            conditions they are designed to detect are discussed below.


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