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 for determining the electric strength of fibrous insulating materials.
| Identifier | ExFiles\Box 24\2\ Scan217 | |
| Date | 21th February 1922 guessed | |
| X1109 794 DIRECTIONS FOR DETERMINING THE ELECTRIC STRENGTH OF own trade, all trade, rests is in a feeling of confidence and security, and above all the removal of grandmotherly Government interference. One of the first elements of such a foundation is that sentiment which enables men of different views and abilities to work together for a common end. Let a group of men decide to accomplish an end and they will accomplish it; that spirit brought us through the war. We have now a common end and I see every reason why schemes such as the South Lancashire scheme and the South Wales scheme should be the success that all desire. It is to be hoped that the Government will help. The only real help they can give at the present time is to reduce taxation. We hear much about improving efficiency, the more economical use of coal and all sorts of remedies which engineers alone can apply, views often expressed by men who do not know what the words mean. Engineers are always at work on these jobs and after thought and hard toil effect some small percentage savings representing hundreds of pounds. Meanwhile rates and taxes account for thousands of pounds and not only the savings but also portions of the profits are many times wiped out. Seldom are savings made until real necessity drives, and I hope the Government and local authorities will voluntarily and boldly reduce taxes and rates and then fit their expenditure to their reduced income as most individuals have been obliged to do. If this be done I see every reason why with good will trade should slowly be restored to a state of prosperity. --- DIRECTIONS FOR DETERMINING THE ELECTRIC STRENGTH OF FIBROUS INSULATING MATERIALS. (REPORT RECEIVED FROM THE BRITISH ELECTRICAL AND ALLIED INDUSTRIES RESEARCH ASSOCIATION.) CONTENTS. Page Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 794 PART I: RESEARCH TESTS ON ELECTRIC STRENGTH 795 1. General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 2. Preparation of Material Previous to Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 3. Conditioning of Material Previous to Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 795 4. Tests in Air or Oil . . . . . . . . . . . . . . . . . . . 795 5. Method of Expressing Electric Strength 795 6. Time-voltage Curves . . . . . . . . . . . . . . . . . 796 7. Temperature-voltage Curves . . . . . . . . . . 796 8. Thickness-voltage Curves . . . . . . . . . . . 797 9. Calculation of Electric Strength . . . . . . . 797 10. Test Equipment . . . . . . . . . . . . . . . . . . . . . 797 11. Electrodes . . . . . . . . . . . . . . . . . . . . . . . . . 798 12. Longitudinal Breakdown . . . . . . . . . . . . . . 798 13. Tests at High Frequencies . . . . . . . . . . . 799 PART II: ABRIDGED TESTS ON ELECTRIC STRENGTH . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 799 Appendix I: Standard Conditions . . . . . . . . . 800 Appendix II: Long Application of A.C. Stress. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 800 PREFACE. In the past there has not been, either in this country or abroad, any recognized standard method of carrying out electric strength tests on insulating materials. Amongst the factors which influence the result of these tests are the following:— (a) The condition of the material at the time of the test, (b) The time during which the voltage stress is applied, (c) The temperature of the material, (d) The thickness of the material, (e) The electrodes employed, and (f) The test equipment used. These factors are of particular importance in dealing with the large class of insulating materials having a fibrous base, and this group has been given special consideration. From what has been said it is evident that the practice of giving a single figure for the electric strength of an insulating material is of no value, unless the various factors which influence the results are either stated or clearly understood. The suggestions contained in this report have been arrived at after very careful consideration of the various methods which have been used in the past. The adoption of the methods of test given herein is strongly commended to manufacturers and to users of fibrous insulating materials, so that a uniform practice in tests of this nature may be established. The tests contained in the first part of the report are essentially of a thorough research nature, whilst the abridged tests in the second part of the report are intended for use when a complete investigation of the electric strength is not required. The clauses in the report are not intended as "acceptance" tests in the purchase of insulating materials, although developments of some of them eventually may be capable of adoption for this purpose. A method of studying the characteristics of fibrous insulating materials subjected to prolonged electric stress under conditions approximating to those existing in the high-tension windings of electrical machinery has been developed in a research on varnished fabrics. This method is described in Appendix II, and is the subject of further research. Special attention is called to the recommendation that in considering the electric strength of these materials attention should be given to the results obtained when the material is hot and under long continued stress. In the past the electric strength has often been determined at air temperature; it is sug- | ||