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IEEE Std C37.48-2020 pdf free download
IEEE Std C37.48-2020 pdf free download.IEEE Guide and Tutorial for the Application of High-Voltage (> 1000 V) Fuses and Accessories.
220.127.116.11.1 Temperature considerations
In the case of low fault currents, say up to around five times the fuse rated current, the fuse elements reach melting temperature gradually over a period of many seconds or minutes (or, for full-range fuses, even hours). Thc melting tcmpcraturc of silver is approximately 960 °C, that of copper, approximately 1080 °C. If the melting time of a fuse is more than a few seconds (or for some types a few minutes), and the fuse as a whole had to reach such a high temperature during operation, damage to the fuse itself or its associated equipment could result. Various means are therefore employed to overcome this problem. Some fuse designs include a spot of low-melting-point alloy on the fuse element, to produce an iii -e/Jeci (after its discoverer Prof. Metcalf) as shown in Figure 4. If a typical tin alloy is used for the M-effect. at about 230 °C the alloy melts and the base fuse element material diffuses into it. This causes the fuse clement to melt open at a lower temperature than its normal melting temperature, and initiate the process of current interruption. Where M-etTect is not employed, other techniques include the incorporation of a low-melting-point section in series with a fuse element (common in sonic types of lull-range fuse), the formation of a hot spot on the fuse clement by creating a long narrow neck in the strip, or by enclosing part of the fuse element in thermal insulating material. The object. again, is to produce fuse element melting without the strip as a whole having to reach an excessively high temperature.
An alternative solution, employed where the fuse is mounted in a striker-tripped switching device, is to use a thermal striker which is designed to operate and trip the associated switching device, when the temperature of the fuse reaches a pre-determined value. In this particular case, it is the switching device, and not the fuse, which performs the current interruption.
18.104.22.168.2 Low current interruption
In the case of low fault currents or overloads, with tuses having more than one fuse element, the parallel luse elements do not melt and arc simultaneously, as with high fault currents, but instead melt randomly in turn. usually at one location on each element, until the last one melts. For fuses that employ fuse elements having a plain strip with restrictions, and that operate at more than a few thousand volts, more than one series break is necessary to interrupt current. The last fuse element to melt therefore has to see sufficient current to achieve multiple melting during the arcing that then occurs. IEEE Std C37.48-2020 pdf free download.
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