Improved method of preventing injurious earthing currents in electrical nets

摘要

141,756. Akt.-Ges. Brown, Boveri, et Cie. April 17, 1919, [Convention date]. Protective arrangements.-In electric supply systems having capacity asymmetrically distributed over the different phases of the system, injurious earthing currents are prevented by connecting the earthing lead to the " capacity gravity point " of the system. To obtain this point for a three-phase system, a voltage diagram C1, C2, C3, Fig. 2, is drawn and masses are assumed at the angles proportionate to the part capacities of the phases. The centre of gravity S of this mass system gives the earthing point, and as shown applied to the main transformer p, q, r, Fig. 1, may be outside the windings thereof, suitable transformer windings being provided for the connexion. An induction coil D is connected in the lead and a voltage may be imposed thereon by a second auxiliary transformer. The two auxiliary transformers may be replaced by one. The inductance of the earthing coil and the superposed voltage are arranged to allow a slight amount of earthing current, to avoid possible resonance effects that might occur if they were arranged to balance exactly such current.