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).
Technical specification page detailing testing procedures for fibrous insulating materials.
| Identifier | ExFiles\Box 24\2\ Scan221 | |
| Date | 21th February 1922 guessed | |
| FIBROUS INSULATING MATERIALS. 797 For a selected number of time values on the time-voltage curves a temperature-voltage curve should be drawn similar to Fig. 2. 8. THICKNESS-VOLTAGE CURVES. (a) When the material is supplied in more than one thickness it is further desirable that sufficient of the foregoing temperature-voltage curves (Fig. 2) should be obtained to enable the thickness-voltage curve to be plotted for definite time and temperature conditions, as in Fig. 3. (b) One of the thickness-voltage curves should be plotted from the one-minute values and another from the values obtained when the breakdown voltage is sufficiently independent of the time during which the voltage is applied (see curves in Fig. 3). For both the above curves the recognized standard temperatures are 90° C. for B.E.S.A. Class A insulation and 150° C. for B.E.S.A. Class B insulation. NOTE.—In plotting thickness-voltage curves, the values on the vertical axis should be in terms of volts per mil, and not in terms of breakdown voltages. 9. CALCULATION OF ELECTRIC STRENGTH. (a) Diagrams. For drawing the time-voltage curves sufficient tests shall be made to enable fair curves to be drawn over the time range under investigation. In order that some idea may be formed of the uniformity of the material, all the experimental values are to be indicated, and when considerable variation is found, this fact should be specially mentioned. As the temperature-voltage curves are taken from the mean curves drawn through the values obtained on the time-voltage tests, the experimental points cannot be indicated on these or on the thickness-voltage curve. (b) Measurement of Thickness. The thickness of the dielectric shall be measured by means of a micrometer or other suitable method. 10. TEST EQUIPMENT. (a) Output of Testing Set. The output of the testing set shall be sufficient to maintain on the sample under test the necessary voltage for the maximum period required. (b) Frequency, etc. The frequency of the supply voltage shall be approximately 50 cycles, and if its value shall be noted. The wave shape shall be as near sinusoidal as possible, and the conditions of the test such as to prevent any high-frequency oscillations. NOTE.—In carrying out electric strength tests the voltage should be increased smoothly, preferably by means of a suitable resistance in series with the field of the alternator. When the voltage is varied by means of a resistance in series with the primary of the testing transformer the wave-shape is liable to be distorted. If the wave-shape is not known to be satisfactory, it should be checked whilst a sample is under test, and near the point of breakdown, by means of (i) a spark gap or (ii) a crest voltmeter. 11. ELECTRODES. (a) For Sheet Material. The bottom electrode shall consist of a flat disc of brass 3 in. diameter by ¼ in. thick. Image 1 (Graph): Volts per Mil Temperature — 90°C. for class A Insulation " -150°C " " B " Time = 1min. Time — such that electric strength is independent of duration of application of voltage THICKNESS Fig. 3.—Curves showing variation of electric strength with thickness. Image 2 (Diagram): Brass Sample Brass Dimensions: 1½", 1½", ¼", 3" Not to scale Fig. 4.—Electrodes for sheet material. The top electrode shall consist of a solid cylinder of brass 1½ in. diameter by 1½ in. high. The sharp edges shall be removed from the electrodes. | ||