The xatron - a variable speed electronic drive for process control

The trend today is the use of electronic variable speed drives in applications which normally would have been filled by rotating conversion units. Physically, electronic drives have a space and weight advantage over rotating equipment. Electrically, they lend themselves to precise control and rapid response to error signals. Small drives using thyratrons to supply and control d-c. motors are quite common. Large Ignitron and Excitron drives have been in successful use for many years. An electronic drive, the Xatron, using a grid controlled rectifier has been marketed in the 30 to 100 horsepower range. It is believed that this drive will capture the mass market for packaged drives within five to ten years. Chief use will be in the machine tool industry and for process control. Many varieties of electric variable-speed drives have been built and used in the past seventy-five years. The common feature in most of them has been the prime mover itself, the d-c. motor. Compared to the induction motor, the d-c. motor is an expensive device to produce, chiefly due to necessity for a commutator and brushes. In spite of this factor the d-c. motor today remains the foundation upon which the commercial wide range variable speed drive is based. Today between 80 and 90% of the electric drives built consist of a motor driven d-c. generator providing a variable armature voltage for a d-c. motor. Until 10 years ago an additional d-c. generator was used to supply excitation for the motor field.