A shearing-wave generator for operation in deep bore holes

An oscillation generator is developed for the German geological research project KTB (continental deep drilling). The purpose is to explore the structure of the lithosphere by shearing waves. Some technical demands are similar to the requirements of industrial servo drives: true running without cogging torques, run-up without rotor position sensor, and torque detection from the cable terminals. Supplying the machine and measuring the data through a thin and long cable impose additional problems that must be solved. The investigations show that a permanent-magnet synchronous machine is appropriate for producing shearing waves at the bottom of a deep bore hole. The restricted transmittable power makes a separate run-up motor necessary operating at a fifth of the generator frequency. The operation program, the sensorless run-up process, and the torque determination from the cable terminals are controlled by a microprocessor