Operating and electrical characteristics of "Written-Pole" machines

Written-Pole synchronous motors and generators have unique characteristics. This paper discusses some of the electrical and operating parameters. The basic design in Written-Pole machines allows the magnetic field on the rotor to be changed as the machine rotates. This effectively allows machines to operate in which the speed and the frequency are independent of each other because the number of poles can be a controlled variable. Poles are changed by a “writing” coil that can change the polarity of a normally “permanent” magnetic material