Capacitor

In this method, large capacitors are connected with the motor so that the capacitors supply much of the current during the start cycle. Careful sizing and switching of the starting capacitors is required to insure that the capacitor current is not all placed on the line at once, and that the capacitors are not left connected with the motor after acceleration is accomplished.

Capacitors are switching on before motor, and off when motor is up to speed.

Capacitor Starting

Starting Characteristics:

  1. Capacitors are sized to supply some portion of the reactive motor current during acceleration. The amount of current drawn from the line depends on the capacitor sizing.
  2. Starting torque is the same as for across the line starting.

Applications:

Usually with very large motors with normal load torque during acceleration. Cost is very high for the capacitors, additional switch-gear, sensors and protective relaying.