Operation of DC and AC drives of rotary table in unstable rotation mode of drill bit

This article continues the study into operation of rotary table drives in unstable rotation of drill bits. Uneven and unsteady rotation of drill bit, with locking, sliding and even reverse rotation, called the Stick–Slip Effect, can lead to auto oscillations accompanied by higher losses, decreased input power, resonances and vibrations of drilling pillar and, finally, by accelerated depreciation of drilling equipment. The problem of unstable rotation of drill bits is particularly acute in case of polycrystalline diamond compact (PDC) bits which have found wider application in recent decades. Many studies address various aspects of torsional behavior and unstable rotation of drill bits during operation. This article analyzes operation of DC/AC drives of rotary tables, compares their modes and reveals the stick–slip effect in the drives. In MATLAB Simulink environment, a generalized model is constructed for an automatic motor of rotary table with DC and AC drives, including the system of subordinate speed and current control. The mechanical part of the drives, including the drill tool, is represented by a three-mass model with regard to phenomena of elastic deformation and viscous friction in drill string. The numerical modeling is accomplished, and the regular patterns of speeds, moments and currents of DC and AC drives are found. The signs and the assessment criterion of the stick–slip effect are determined from the nature of the current oscillations in DC and AC drives in unstable rotation mode of drill bits.

Ershov M. S., Komkov A. N., Feoktistov E. A. Operation of DC and AC drives of rotary table in unstable rotation mode of drill bit. MIAB. Mining Inf. Anal. Bull. 2021;(6):153167. [In Russ]. DOI: 10.25018/0236_1493_2021_6_0_153.

M.S. Ershov¹, Dr. Sci. (Eng.), Professor, e-mail: msershov@yandex.ru,
A.N. Komkov¹, Cand. Sci. (Eng.), Assistant Professor, e-mail: komkov.a@gubkin.ru,
E.A. Feoktistov, Student, e-mail: Eugene.Feoktistov@yandex.ru, Moscow Institute of Physics and Technology (National Research University),
¹ Gubkin Russian State University of Oil and Gas (National Research University), 119991, Moscow, Russia.

M.S. Ershov, e-mail: msershov@yandex.ru.

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