Fuses - Principles of design and operation

1. Fuses - Principles of design and operation A fuse consists of a replaceable part (the fuse) and a fuse holder. Examples of fuse holders are The simplest fuse link is a length of It is mounted by screwing in support which partially encloses it. When an overcurrent or short circuit current is passed, the wire begins to melt and an arc begins at various places along with it. The arc voltage causes the current to drop and once it drops to zero the arcs are extinguished. The larger wire the cross-section, the greater the current that the fuse-link will carry without operating. In the UK, fuses of this type are specified for use with voltages up to 250 V and currents up to 100 A. They are known as semi-closed or rechargeable fuses. The most popular type of cartridge. This consists of a barrel (usually ceramic) containing one or more elements which are connected at each end to caps attached to the ends of the barrel. The arrangement is shown in Figures 2 and 3. If a high current breaking capacity is required, the cartridge is filled with sand of high chemical purity and controlled grain size. The entire fuse link is replaced after the fuse has worked and a fault

2. has been disconnected. Cartridge fuses are used for a much wider range of voltages and currents than semi-closed fuses. Merges can be divided into current-limited and non-current-limited types. A tapered cartridge filled with sand is of the current limiting type; when it works it limits the peak current to a value that is significantly lower than the prospective current. A non-current limiting fuse, such as a semi-closed fuse, does not significantly limit current. The element shown in Figure 2 is a notched strip. Fusion first occurs at the notches when an overcurrent flows and results in a number of arcs controlled in series. The voltage across each arc contributes to the total voltage across the fuse and this total voltage has the effect of reducing the current to zero. As the number of arcs is limited, the fuse voltage should not be high enough to cause damage elsewhere in the circuit. The characteristic development of current and voltage during the operation of a fuse is The function of the sand is to absorb the energy of the arcs and to help extinguish them; when a high current is disconnected, the sand around the arcs is melted. The element is usually silver because of its resistance to oxidation. Oxidation of the element in service would affect the current which could be carried without melting, as the cross-section of the element is changed. Silver-plated copper elements are also used. Many elements include an m-effect blob, which can be deposited on wire or notched tape. The drop is a solder-type alloy that has a much lower melting point than the element. If a sufficiently large current only melts the drop-off effect m, the solder diffuses into the silver. This creates a higher local resistance in the element and the fuse operates at a lower current than it would have been in the absence of the drop. Other types include the expulsion fuse which is used at high voltage and the universal modular fuse (UMF) which is used on printed circuit boards (PCB). Fuses offer long life without deteriorating characteristics or performance, and cartridge fuses have the particular advantage of completely containing arcing products.

3. BurraqEngineering Solutions is the best training institute in Lahore which is providing practical training of Electrical Automation and Short Electrical Courses including PLC course, SOLAR SYSTEM Installation, and DESIGN COURSE, ETAP course, DIALUX course, Panel FABRICATION course, VFD course, ADVANCED control Panel, SWITCHERGEAR design course, Building Electrical design course and all electrical diploma courses. Both online and physical classes available. We introduce a platform Lyskills from where you can get lifetime access to your desire courses at a very reasonable price.