Capacitor-Start Induction-Run Motors
Capacitor-start induction-run motors are very similar to resistance-start induction-run motors. The design of the stator winding is basically the same. The main difference is that a capacitor is connected in series with the start winding, as shown in Figure 11–11. Inductive loads cause the current to lag the applied voltage. Capacitors, however, cause the current to lead the applied voltage. If the starting capacitor is sized correctly, the start winding current will lead the applied voltage by an amount that will result in a 90-degree phase shift between the run winding current and the start winding current, producing an increase in the amount of starting torque, as shown in Figure 11–12. If the capacitance of the start capacitor is too great, it will cause the start winding current to shift more than 90 degrees out-of-phase with the run winding current and starting torque will be reduced. When replacing the start capacitor for this type of motor, the micro-farad rating recommended by the manufacturer should be followed. It is permissible to use a capacitor with a higher voltage rating, but never install a capacitor with a lower voltage rating. A capacitor-start induction-run motor is shown in Figure 11–13. A typical starting capacitor is shown in Figure 11–14.
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