GB1161841A - Improvements relating to Control Systems for D.C. Electric Motors. - Google Patents

Abstract

1,161,841. Control of D.C. motors. CONTACTOR SWITCHGEAR Ltd. 22 Sept., 1966 [27 Nov., 1965], No. 50487/65. Heading H2J. The armature of a crane motor is connected to the field circuit through two branches which are alternately rendered conductive or non-conductive automatically depending on whether the motor is driving or regenerating. On moving a master switch to the lowering notches, motor field winding SF, brake coil SB, and one or more resistance sections are connected across supply-lines L1<SP>1</SP>, L2<SP>1</SP>, whilst motor armature A<SP>1</SP> is connected, at one side, through resistor Ra, and selectively through resistor sections Rx, Ry, Rz, to the line L2<SP>1</SP>. The other side of the motor armature is connected through rectifiers T1, T2, across the windings SF, SB. When the load is being driven downwardly, current passes through rectifier T2 so that the armature and field winding are series-connected. As the load overhauls the motor, the armature current reverses for regenerative operation, the rectifier T1 conducting to feed armature current through the field circuit and back to the supply. In the " off " position of the master switch, a dynamic braking loop is established through resistor Rdb. The resistance network Rx, Ry, Rz is set to provide one effective value for determining the total series resistance common to both field and armature (on the first three lowering notches) or two other independent values for modifying the total field resistance (on the higher lowering notches). The rectifier T1 may be replaced by a contactor or silicon controlled rectifier. A safety relay VR is provided.