Patent GB-173606-A (GB)
Title: Improvements in electric inductance apparatus
IPC: H01F27/36
Filed: 1920-10-04
Abstract: 173,606. British Thomson - Houston. Co., Ltd., (General Electric Co.). Oct. 4, 1920. Transformers; polyphase transformers. - In order to prevent the production of excessive transient voltages within an electric winding, such as a high-voltage transformer winding or a reactance coil, means are provided for imposing electrostatically upon the winding a substantially uniform distribution of voltage, the voltage distribution due to capacity in the winding being made substantially coincident with that due to inductance. In the arrangement shown in Fig. 7, the winding comprises a number of disc coils 30 connected in series between terminals a, b, the terminal b being earthed. Condensers 32 are connected in series with each other and in parallel with the individual coils as shown, the capacities of the condensers being such as to ensure a uniform potential gradient through the winding. If the end of the winding is not earthed, the added condensers are of equal size and of sufficient capacity to neutralize the inherent capacity of the winding. In other arrangements the terminals of the winding are connected to the plates of a condenser, and the turns of the winding progress at a substantially uniform rate in the dielectric between the plates so that the potential existing at any point of the winding due to its position in the dielectric is substantially the same as the potential due to inductance. One example of this arrangement is shown in Fig. 11, in which the individual coils of the winding are of conical form connected in series between flat condenser plates 48, 49. In a modification the condenser plates are conical and the coils flat. In the arrangement shown in Fig. 13, flat disc coils 62 are wound between cylindrical condenser plates 60, 61. The plates may be of tapering form in order to permit the use of coils of the same diameter. The invention may be applied to windings formed of cylindrical layers, the crossover connections between the layers being preferably brought outside the condenser cylinders, as shown in Fig. 18. The ground capacity of these shown in Fig. 18. The ground capacity of these connections may be eliminated by arranging them between auxiliary condenser plates 90 connected to the main condenser plates. The connections between the layers may be eliminated altogether by the use of alternate inverted conical layers as shown in Fig. 22. The application of the invention to a shell-type transformer is shown in Fig. 24. The high-voltage winding of the transformer comprises a number of cylindrical layers 124 supported on insulating-cylinders 125 separated by spacing strips 126. The inner and outer cylinders are covered with layers of conducting material 127 such as tin or aluminium foil, which form the plates of the protecting condenser. The crossover connections between the various layers are carried outside the transformer through tubular bushing structures 134. A method of winding a multi-layer coil which reduces the capacity between the layers is shown in Fig. 28. The initial turns 151 - - 160 are wound in pyramid fashion until a desired depth is reached and succeeding turns are wound against the side of the pyramid in the successive grooves formed by the laying of the preceding turn. In applying the invention to a single-phase core-type transformer, Fig. 29, low-voltage windings 201 and high-voltage windings 203 protected by condenser cylinders 204, 205 are mounted on each leg 202 of the core. The terminals a, b are connected to the outer cylinders of each condenser, the inner cylinders being connected together by a conductor 206 which is preferably earthed at d. Ordinary lightning arresters L may be placed across the individual windings. The invention can also be applied to polyphase transformers.