GB454292A - Improvements in protective cut-out systems for alternating electric networks - Google Patents

Abstract

454,292. Protective cut-out arrangements. TASSERON, W. H., 24, Conradkade, The Hague. Oct. 22, 1935, No. 29089. Convention date, Nov. 7, 1934. [Class 38 (v)] A cut-out apparatus for protecting metallic parts of A.C. plants against high voltages utilizes the decrease in voltage resulting upon a failure between one of the phases and earth to effect the switching-off of the phase in question. The supply 1 has its star point 2 earthed at 4 over a resistance 3, and supplies consuming circuits 7, 8 over the phase lines 5 and neutral 6. The circuits 7, 8 are controlled by mercury switches 9, 10 which are retained closed by coils 11, 12 connected between the phase line and earth 15, 16 in series with resistances or lamps 13, 14. If a phase line comes in contact with a machine casing or with, as shown, a piece 18 of earthed iron structural work, the resultant volt-decrease on the coil 11 or 12 is inadequate to hold the switch closed. The service to the faulty consumer cannot be restored until the failure is removed, but the other consumers can switch on again at once. When service is being restored after a severe shut-down, immediate disconnection of supply due to the initial current-rush is prevented by employing switches with differing time-lags or glow lamps 13, 14 of different ohmic values. In Fig. 2, the parts are enclosed in a casing 20 having an earthing terminal 22 and line terminals 21, 23, and a switch 24 is provided to restore service after switching-off due to breakdown. The resistance 3 is so chosen that with a complete short-circuit the parts becoming live will only attain a potential of, for example, 24 volts to earth.