Patent GB-337863-A (GB)
Title: Improvements relating to maximum demand indicators for electric circuits
IPC: G01R11/56
Filed: 1929-08-21
Abstract: 337,863. Wall, G. Aug. 21, 1929. Special quantities, registering.- An energy meter operating a maximum demand indicator controls a meter for measuring the reactive component in such a way that its indication is changed only on the occurrence of a maximum demand or an increase in the maximum demand. The shaft 1 of an energy meter drives a shaft 8 through differential gearing of which one sun pinion 10 is normally held stationary by the engagement of a pawl 12 with a ratchetwheel 11. On the shaft 8 is mounted a disc 18 carrying an angle-piece 21 with two contacts 22, 23, insulated from the disc 18 but electrically connected to a slip-ring 45. The maximum-demand pointer 25 is carried by a shaft 26 in alignment with the shaft 8. A disc 27 is mounted on the shaft 26 and carries an angle-piece 29 insulated from the disc but electrically connected to a slip-ring 48. Loose on the shaft 26 is a sleeve 32 carrying a disc 31 and a ratchet-wheel 36. The disc 31 carries an angle-piece 34, insulated from the disc but electrically connected to a slip-ring 51. Friction washers 42, 43 engage the shaft 26 and the ratchet-wheel 36. An electromagnet 15 is momentarily energized by means of clock mechanism at intervals of half an hour, lifting the pawl 12 and permitting the return of the shaft 8 to its zero position under the action of a spring 16. The shaft 60 of a reactive kilo-voltampere meter drives a shaft 67 through a differential gear of which one sun pinion 70 is normally held stationery by the engagement of a pawl 72 with a ratchet-wheel 71, this pawl being lifted at half-hourly intervals by the energization of an electromagnet 75 thereby allowing the shaft 67 to return to its zero position urder the influence of a spring 77. The shaft 67 is connected to the shaft 80 carrying the pointer 82 by means of a spiral spring 86, of which one end is fastened to the shaft 67 and the other end to a drum 85 on the shaft 80. Rotation of the shaft 80 is normally prevented by the engagement of a brake shoe 88 with the drum 85. On the shaft 80 is also mounted a ratchet-wheel 100 normally engaged by a pawl 101 and permitting rotation of the shaft 80 in the forward direction only. At the beginning of a registration period the shaft 8 and the disc 18 are in the zero position, and the shaft 26 and its disc 27 are in the position reached at the end of the previous period. The disc 31 is in advance of this by a small angle, through which it was moved by the engagement of the pawl 37 with the teeth of the ratchet wheel 36. When the disc 18 has moved forwards to its previous maximum position the contact 22 engages the angle-piece 29 on the disc 27 so as to drive the disc and with it the shaft 26, at the same time closing the circuit of an electromagnet 91 through a battery 111. The brake shoes 88 is thereby lifted and rotation of the shaft 80 in the forward direction takes place if the rotation of the shaft 67 has been greater than in the preceding period. Further rotation of the shaft 8 through the small angle by which the disc 31 is in advance of the disc 27 causes the contact 23 to engage the angle-piece 34 on the disc and at the same time close a circuit through electromagnets 40, 104, causing the pawls 37, 101 to be lifted. The shaft 80 is thereby freed and moves in either direction to a position corresponding to that of the shaft 67. In place of the spring 86 a snail or heart cam or a magnetic or electromagnetic connection may be employed. The magnets 91, 40, 104 remain energized until the end of the registration period. On energization of the magnets 15, 75 at the end of this period, the shafts 8, 67 return to their zero positions, the contacts 22, 23 are carried away from the angle-pieces 29, 34, and the circuits of the electromagnets 40, 104, 91 are broken. The de-energization of the magnet 40 causes the ratchet-wheel 36 and the disc 31 to be moved forwards through a small angle by the engagement of the pawl 37 so that a circuit is not made at the contact 23 unless the existing maximum demand is subsequently exceeded by this amount.