Patent GB-190417813-A (GB)
Title: Improvements in Systems of Electric Motor Control
Filed: 1904-08-16
Granted: 1905-07-13
Abstract: 17,813. British Thomson-Houston Co., [General Electric Co.]. Aug. 16. Motors, controlling.-A motor driving an aircompressor &c. is controlled by an auxiliary motor which cuts out resistance, and by a governor adapted to reverse the auxiliary motor. As shown, Figs. 1 and 2, a small pilot motor m raises or lowers a crosshead d by rotating the screw n. The core of a solenoid A is provided with a number of bridging-pieces which engage the contacts a' to a<8>. The solenoid C is provided with a bridging-piece, and acts to prevent the motor m from cutting out resistance too rapidly. The core of the third solenoid B engages the lever G, which is connected to a relief valve by means of which the load may be removed from the piston of the air-compressor at starting. The governor F consists of a double diaphragm, each diaphragm carrying a point pressing against parts h<1>, h<3> of a lever system fixed at hand arranged to give the arm h<5> a quick motion from the contact f<2> to the contact f<3> when the pressure rises in the governor. The armature of the motor m, Fig. 1, is not in alignment with the field. The motor shaft carries a friction disc o, which rests on a fixed disc o<1> and acts as a brake to stop the motor when its circuit is broken. When the current flows, the armature is raised by the field flux, and the discs o, o<1> are separated, allowing the armature to turn. Fig. 3 shows the connections for the main motor. When all the switches s, s<1>, s<2>, s<3> are closed, two circuits are completed, one from the line L through the switch s<2>, circuit-closer A, and contacts d<3>, d<1>, f<2> f<1> to earth E, and the other from the line L through the switch s<3>, relief valve coil B, and contacts b<1>, d<6>, d<7>,f<2>, f<1>, to earth E. The coils A, B both draw up their armatures, the coil B thereby opening the valve on the air-compressor. Circuits are then closed up from the line L through the switch s', armature of the motor m, half of the field of the motor m, and contacts controlled by the coil C, contacts a', a<3>, contacts controlled by the coil B, and contacts d<6>, d<7>, f<2>,f<1> to earth E. The motor m starts and rotates the screw n, thereby raising the crosshead d, which makes contact with the lowest contacts of the switch D. putting the armature of the main motor M in series with all the resistance R. As the crosshead d rises, the resistance R is cut out of the circuit, but, if the current rises above a predetermined value, the coil C draws up its core, breaking the circuit of the pilot motor m, until the main motor M speeds up and diminishes the current, when the core falls again. When the crosshead d reaches the top of the screw n, it opens the circuit of the pilot motor m at d<6>, d', and also of the coil B, thus closing the relief valve. The motor then compresses air until the pressure in the governor F moves the lever h<5> on to the contact f <3>. The circuit of the pilot motor m is again closed, and it rotates to lower the crosshead d, inserting resistance R in series with the armature of the motor M, until the crosshead engages the contacts d<1>, d', opening the circuit of the motor M and pilot motor m. The circuits are then ready to be closed to start the motors when the air pressure falls sufficiently to shift the governor contact again. When the apparatus is applied to liquid storage reservoirs, the governor F is replaced by a float switch.