Experience with synchronous motor driven chipper drives with power factor regulation

It is pointed out that most existing and new installations could use the inherent characteristics of synchronous chipper motors to far better advantage with the proper field regulation and control. The various control methods which are being implemented are discussed, and the deficiencies of many of these schemes are noted. The control of the synchronous motor field by power factor regulation is recommended, and field test results are discussed. It is concluded that power factor regulation has been found to be useful in chipper applications where the motors are subjected to high-level transient impact loads. The power factor regulator senses the power factor dip that occurs when the motor is loaded and causes the motor to respond with a boosted output. As a result, the pull-out torque of the synchronous motor is increased for the duration of the transient load, thus reducing the probability of pole slippage. This automatic boosting of field current is called field forcing. Thus, the power factor regulator provides automatic boosting when field forcing is required, and economical low-field operation when the motor is idling