Patent GB-373120-A (GB)
Title: Improvements in or relating to means for indicating variation from a standard or predetermined frequency of an alternating current electrical supply system
IPC: H02J3/08
Filed: 1931-01-05
Abstract: 373,120. Speed governors. SHOTTER, G. F., 14, The Ridgeway, Friern Barnet, Middlesex, and ELLIOTT BROS. (LONDON), Ltd., Century Works, Lewisham, London. Jan. 5, 1931, No. 364. [Class 57.] A movement indicating any variation of the frequency of an alternating current supply system from a standard value is utilized for restoring automatically the standard value of the frequency, e.g. by a control of the speed of the generator of the supply station. The indicating apparatus comprises a pair of motor elements operatively connected to an indicating or like member, the one to drive it in one direction and the other to drive it in the opposite direction, the one motor element being such that as the frequency varies from the standard in one direction, e.g. increases, its speed or torque increases, and the other being such that as the frequency varies from the standard in the opposite direction, e.g. decreases, its speed or torque remains constant or increases, and the two elements being such that at the standard frequency the indicating or like member is stationary, and on any variation from this standard the member moves continuously. In one arrangement, Fig. 1, the indicating member 10 is connected through differential gearing to the shafts 7 of two discs 1 of conducting material driven in opposite directions by the two motor elements, each comprising a first electromagnet 2 connected across the supply mains 3 and a second electromagnet 4 also connected across the mains but with a reactance 5 and capacity 6, and preferably also a resistance 21, in circuit. The circuits of the magnets 4 have resonant frequencies the one below and the other above the standard value. At the standard frequency the discs 1 rotate at the same speed and the member 10 is stationary. Upon an increase in the frequency the speed of one disc increases and that of the other decreases and the member 10 moves continuously in one direction, while upon a decrease in the frequency it similarly moves continuously in the opposite direction. Damping magnets 12 may be provided and may be connected across the mains 3 to compensate for variations of the voltage. The associated magnets 2, 4 may, as shown, have a common magnetic circuit, their cores being in planes at right-angles, and a U-shaped member of soft iron is preferably arranged between the pole of each magnet 2 and the corresponding disc 1. Fig. 8 shows the connection of the shafts 7 through gearing 8 to spindles 25, 30 carrying gears 26, 29 driving crown wheels 27, 28 respectively of the differential gearing of which the intermediate wheel 31 operates the central spindle 32 connected through gearing to a fast movement pointer 34 and a slow movement pointer 10. In a modification, Fig. 2, a single disc 1 is controlled by the motor elements, one magnet 2 being common to each element. The shaft 7 in this case carries an indicating disc 40 and is also connected to the member 10 through reduction gearing. The reactance in the circuit of each magnet 4 may, as shown, be constituted by the energizing winding alone. In a further modification, Fig. 3, each motor element controls one of two sectors 14 of metal connected by an arm 16 centrally pivoted at 15 and carrying at right-angles thereto an arm 17 provided with a contact 18 arranged to move over contacts 19, 20 according as the frequency of the supply system varies in one or the other direction from the standard value. The closing of the contacts 18, 19 or 18, 20 may control apparatus for regulating automatically the frequency by adjusting the speed of the generator at the supply station.