Abstract
AN article by E. A. Beavis (Eng. Supp. Siemens Magazine, Nos. 202 and 203, March and April, 1942) considers the various factors contributing to cable failures in the sphere of dielectric heating. For any type of high-voltage cable installation there is a definite limit to the heat which can be dissipated, and above which the condition of the cable insulation becomes thermally unstable. The chief factor governing instability is the dielectric loss, which has a certain critical value dependent partly upon the thermal constants of the cable but chiefly upon the external thermal conditions. When this value is exceeded, cable breakdown becomes inevitable in course of time, provided such conditions continue unchanged. This maximum value of dielectric loss, which denotes the commencement of instability, remains constant for a given set of thermal values, and the higher the applied voltage the lower is the critical temperature at which this loss occurs, since it increases as the square of the voltage. For the same conditions, therefore, the higher the voltage the shorter the time required for thermal breakdown to occur. Failure will normally take place when the temperature of the insulation has reached the point at which the existing potential gradient exceeds the dielectric strength, and in most cases will occur shortly after passing the critical value.
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THERMAL BREAKDOWN IN SUPER-TENSION CABLES. Nature 149, 737 (1942). https://doi.org/10.1038/149737a0
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DOI: https://doi.org/10.1038/149737a0