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Part-Winding  Starters

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Part-Winding  Starters Figure 7-54.—Resistance reduced-voltage starter. Part-winding  starters  use  two  magnetic  starters  and operate like a resistance start controller. Figure 7-55 is a schematic  drawing  of  a  wye-connected,  three-phase motor. The control circuits for the S and R relays are the same as for a resistance reduced-voltage starter, and so they are not shown. The S relay is energized first, connecting voltage to only part of the winding. The motor starts to run but develops little torque. At a predetermined time, the R relay closes. This action parallels the windings in the motor, reducing their resistance and causing increased current flow and more torque. MOTOR MAINTENANCE, TESTING, AND REPAIR An electric motor must be checked, maintained, and repaired  just  like  any  other  piece  of  mechanical equipment.  With  proper  servicing,  a  motor  will  last longer and give more efficient service. Included in maintenance   services   are   cleaning,   lubrication, ventilation, and testing. Cleaning Inspect motors internally and externally for foreign materials, such as dust, dirt, corrosion, and paint. Open- frame motors may be blown out with compressed air. You should not apply too many coats of paint to motors. A thick coat of paint will interfere with heat dissipation. Figure 7-55.—Part-winding starter. 7-44



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