From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Directions and diagrams for determining the electric strength of materials in tube, cylinder, and sheet form.
| Identifier | ExFiles\Box 24\2\ Scan222 | |
| Date | 21th February 1922 guessed | |
| 798 DIRECTIONS FOR DETERMINING THE ELECTRIC STRENGTH OF but the radius at the edge must not exceed 1/32 in. (see Fig. 4). (b) For Small Tubes (up to about 3 in. diameter). The outside electrode shall consist of a band of sheet metal 1 in. wide. The inside electrode shall consist of a cylinder with the ends rounded to a radius of 1/8 in., or when a cylinder with rounded ends cannot conveniently be obtained, a sheet metal cylinder sprung into place may be employed. The length of the inside electrode shall be not less than 1 in. plus three times the thickness of the wall of the tube (see Fig. 5). Fig. 5.—Electrodes for small tubes. (c) For Large Tubes (often called Cylinders). The outside electrode shall consist of a strip of sheet metal 3 in. wide. The inside electrode shall consist of a disc 1½ in. diameter of sheet metal sufficiently flexible to conform to the curvature of the cylinder; this disc of sheet metal to be pressed against the inside of the cylinder so as to make good contact over the whole of the area of the disc (see Fig. 6). Fig. 6.—Electrodes for cylinders. (d) Suggestions for obtaining good Contact. Sheet zinc about 1/32 in. thick has been found convenient for springing into tubes for forming the inside electrode. Soft aluminium foil from 2 to 5 mils thick has been found convenient for use as the outside electrode on tubes. When the surface of the specimen is irregular or any difficulty is experienced in obtaining good contact, it is recommended that tinfoil should be interposed between the electrode and the dielectric. 12. LONGITUDINAL BREAKDOWN. Materials which are composed of a number of superimposed layers generally have a different electric strength in the direction parallel to the laminæ from that in the direction at right angles to the laminæ. All such material should, therefore, be subjected to a longitudinal breakdown test carried out as follows :— (a) Tubes. Cut out a complete cylinder from the tube, or in the case of tubes of large diameter, a portion of a cylinder, with a cross-sectional area of about 1 sq. in., if possible. Clamp hand-tight between parallel metal plates, immerse in oil at 90° C., apply voltage between the metal plates, and ascertain the voltage required to produce breakdown in one minute [for method, see Part II (c), p. 799]. The length to be tested to be 1 in. and also 2 in. (see Fig. 7). (b) Sheet Material. Cut strips of 1 in. and also of 2 in. wide respectively, and of any convenient length. Test singly in a manner similar to Tubes (a) above. (c) Alternative Method for Tubes and Plate. If it is found by the above tests, or it is previously known, that the longitudinal breakdown of the material is greater than the breakdown of an equal length of oil, the material should be tested by the following method :— Drill two holes, using a 5/64 in. twist drill, in the same | ||