Patent GB-468558-A (GB)
Title: Improvements in or relating to electric motor starters employing starting resistances
IPC: H02P1/34
Filed: 1936-04-14
Abstract: 468,558. Actuating controllers ; variable resistances. BROOKHURST SWITCHGEAR, Ltd., and HEATON, F. April 14, 1936, No. 11482/35. [Class 38 (iii)] [Also in Group XXXVI] Disposition of resistances.-A starter comprises a resistance 2, Fig. 4, composed of metal wound into a helix or zigzag having bare metal portions arranged in line so that a brush 15 moved from end to end makes direct contact with bare portions in succession, a carrier for the brush movable from a starting to an on position, hand or power operated means for moving the carrier, an electromagnetically controlled main switch 38 having a control circuit which must be energized for the switch to be closed, and an interconnecting switch 33 in the control circuit closed only when the carrier is in its starting position, the interconnecting switch being short-circuited by an auxiliary switch 39 closed with the main switch. Resistances 2, Fig. 1, are formed of bare wire wound into a helix so that the outer surfaces are cylindrical in shape and in line with a cylindrical copper portion 4 to which one end of the resistance coil is connected, the other end being clamped at 5. The resistances, which are three in number for a three-phase motor, are carried by frames 6 and 7 in an oil filled tank 1, and a three-armed brush carrier 14 is arranged so that brushes 15 contact with the resistance coils and are displaceable longitudinally by an endless chain 18 wound over sprockets 19, 201, the sprocket 19 being carried by a shaft 20 rotated by a handle 25 pivoted at 261. An auxiliary switch 28, 29 is arranged to be closed by operation of a shaft 26 effected by applying pressure to the handle 25, and this switch is retained closed when the pressure on the handle is released and the brush carrier is in its resistance cut-out position by means of an element 47 which engages a button 27 on the shaft 26. The chain 18 carries a pin which closes the switch 33 when the brush carrier is in its lowest position and all resistance is inserted. Blades or scoops 35 fitted to the brush carrier 14 circulate the oil in the tank 1. With the resistance all in circuit and the handle pressed in, switches 33, 29 are closed so that a low voltage coil 40, Fig. 4, is energized and the circuit-breaker 38 may be closed by hand; auxiliary contacts 39 on the circuit-breaker maintaining the circuit independently of the switch 33. The handle is then operated to raise the brush carrier and exclude the resistances 2. A switch 42 is operated by a thermal device when the temperature of the oil in the tank is excessive and effects de-energization of the coil 40 and disconnection of the motor. In a modification, Fig. 6, the brush carrier is operated by a cord 71 supporting a weight 72, the cord being wound on a drum 79 rotated by a control motor 73 through gearing. The drum is moved axially while it is rotated, by means of a fixed nut 81 engaging a threaded portion 80 of the drum so that the cord is kept in line with an opening 82. The brushes 65 are mounted on levers 66 which are rotated to bring the brushes into engagement with the resistance coil when tension is applied to the cord 71. The speed of the control motor is controlled by a brake consisting of a disc 90 rotating in the field of a magnet 92 energized by the motor current, and the starter is held in the on position by a pawl engaging a ratchet 83 on the drum 79 until an electromagnet is de-energized to release the pawl. The switch 33 in this embodiment is closed by the weight 72, and a switch 93 is operated when all resistance is cut out and stops the control motor. The main circuit-breaker may be under the control of press-button start and stop switches, and may have an auxiliary switch which in the closed position short-circuits the start switch and the switch 33. The retaining pawl and ratchet may be replaced by a worm and wormwheel between the control motor and the raising drum, the worm-wheel being mounted on a shaft coupled to the drum through a flexible coupling so that it can be moved into and out of engagement with the worm by the energization and de-energization of an electromagnet. Suitable arrangements of the resistance elements and their contact brushes for direct-current and alternating-current systems, where the number of elements varies from two to six are described with reference to Figs. 13-16 (not shown). The resistance helices may be wound on a cylindrical metal tube enamelled on the outer surface and split longitudinally, the resilience of the tube maintaining the wire taut in spite of expansion and contraction. For large motors the helices may be wound of wire of such cross-section that they maintain their own shape. The Specification describes, with reference to Fig. 17 (not shown), a cross-section of wire which results in a true cylindrical surface of the helix. The wire may be wound in a groove of variable pitch. The surfaces of the helices may have flattened portions for the brushes to engage, or the section of the element may be polygonal. The resistances may be formed from sheet-metal slotted from opposite sides as shown in Fig. 22, the zigzag element so produced being folded on a carrier 74<1>, Fig. 23, so that the ends 74 of the zigzag are close together.