Patent GB-725453-A (GB)
Title: Improvements in or relating to electrically-driven earth-boring apparatus
IPC: E21B44/00
Filed: 1953-03-27
Abstract: 725,453. Automatic current/tension control systems. PINTSCH BAMAG AKT.-GES. March 27, 1953 [March 31, 1952], No. 8577/53. Class 38 (4). [Also in Group XXXVII] Earth-boring equipment comprises similar separately-excited D.C. motors M1, M2, for driving lifting mechanism H and pumps P1, P2, as well as a motor M3 for driving the rotary drilling table D. The motor armatures are supplied from three phase mains L through rectifier units S1, S2, S3, whilst a common grid-controlled rectifier S4 provides the field excitation. The motors M1, M2 drive the hoist drum through two-speed gearing and selective clutches, Fig. 2 (not shown), whilst further clutches connect the drive to the scavenging pumps. The torque of the motor driving the drill may be limited by means of a carbon pile regulator having opposing control coils energized respectively in accordance with the motor current and with a reference quantity. The motor has constant excitation and the armature current is prevented from exceeding its rated value since the carbon regulator operates to reduce the grid voltage of the rectifier when there is an overload, Fig. 3 (not shown). The hoist motors may be controlled to prevent excessive hook tension by having an end of the lifting cable coupled to adjusting means for a carbon pile regulator. When the cable tension overcomes the force of a spring the pressure on the carbon pile is reduced and the grid voltage of the rectifier is regulated to prevent the armature current from exceeding a value corresponding to a desired limiting value for the hook tension, Fig. 4 (not shown). The arrange. ments illustrated in Figs. 3 and 4 may be combined so that the grid voltage of the rectifier is regulated when there is either excessive armature current or excessive hook tension. The field winding of a hoist motor may be supplied through a grid-controlled rectifier which has a carbon pile regulator in its grid circuit, Fig. 5 (not shown). When the motor armature current reaches its rated value the rectifier operates to increase the field excitation. In addition, the armature current may be controlled to limit the hook tension. Reference is also made to arrangements in which the armature current of a motor is kept constant and the field excitation controlled in accordance with the armature voltage to limit the torque. The hoist motors are allowed to operate with increased current when lifting or lowering an empty hook. When lowering a heavy load regenerative or rheostatic braking is provided, together with mechanical braking. A wide range of speed for the drill is provided by a tapped transformer, which supplies the drive motor through a rectifier. In this case, grid control of the rectifier is only required for fine adjustment. The motors driving the scavenging pumps may be controlled in accordance with liquid pressure in order to prevent the armature current from exceeding a value corresponding to the limiting pressure. The control devices for the motors are mounted on a switchboard B which is protected against explosion, the motors being totally enclosed and connected by hosepipes to a fan assembly. The motors may be supplied from diesel-electric sets, and these sets together with the rectifiers, transformers, fan units, and switches may be mounted in a common portable housing which has runners at its base and lugs for lifting.