GB736523A - Electric lowering arrangement for rotary deep drilling work - Google Patents

Abstract

736,523. Automatic tension control systems. SCHULZE, W., and SCHWEDLER, U. Dec. 24, 1952 [Dec. 28, 1951], No. 32713/52. Class 38 (4). [Also in Groups XXI and XXXVIII] In a system for automatically maintaining a constant pressure on the boring tool during the rotary boring of deep wells, the speed and rotational direction of a motor provided in addition to the main driving arrangements of the hoisting gear drums and serving to lower the drill pipes as boring proceeds and which is made continuously regulable in speed from standstill to maximum is controlled by means responsive to the tool pressure. The control may be obtained from the variations in the power input to the rotary table which revolves the drill, for example by measuring deviations in armature current where the table is driven by a direct-current shunt-wound motor, or it may be obtained from a dynamometer which measures variations in tension in the drill suspension tackle. The drawings show a system utilizing the latter method. Fig. 4 shows the electro-mechanical dynamometer from which is suspended the length of drill pipe. It consists of a sleeve 24 serving as an elongation measuring member to the upper end of which are rigidly connected two pairs of induction coils 27, 28 mounted on U-magnet frames 29, 30. An armature 31, rigidly con. nected to the other end of the sleeve, is mounted between the pole shoes so that any length variation of the sleeve gives a corresponding variation in inductance of the coils. The dynamometer may also be constructed to convert tension variations into resistance or capacitance variations. The coils, shown as 27a, 28a in Fig. 5, are arranged in an A.C. bridge circuit with another pair of coils 34, 35 between which is mounted a pivotable armature 36 by means of which the bridge voltage can be adjusted to zero to correspond to the desired boring pressure. Any out-of-balance current caused by variation in this pressure is amplified at 37 and drives a servomotor 38 which rotates a disc 45 (Fig. 6). This movement is transmitted by a rack 46 and wheel 47 to an arm 43 which selects a corresponding A.C. voltage from a transformer 42 supplying current to a selenium rectifier 44, the output from which passes, via half rings 51, 52, to the armature 40 of the lowering motor which has a separately excited shunt winding 41. In operation, an increasing boring pressure causes a reduction in the voltage applied to the armature until the motor speed reaches zero. If the pressure still increases the brushes 49, 50 connecting the half rings reverse the polarity of the applied voltage so that the motor eventually begins to lift the drill pipes from the well.