Construction Of Automatic Phase Changer

Fuses are typically employed inn the electrical utility industry to protet. Distribution transformers cables capacitor bank and other equipment from damaging over currents the fuse are arranged to disconnect the faulted aquiment or circuit promptly from its source of supply before damage can occur.
Fuses are used extensively in high voltage electrical net works from damage cause by surges through the system generally occasioned by short circuiys or over loads.
Fuses are used as necessary can be electrically connected in series with the semiconductor power element requirespecial installation space and the constraction expense the goes along with it. They add electrical series resistance which results incurrent depenent he heat loss.
Fuse are very important in protecting circuit from predetermined curreent level and are selected based upon safety specifications designated for a partcular circuit the susible element or fuse link is inbtended to melt away under the influence of a current which exeeds a particular length of time.
There are thermal fuses mechanical fuses spart gap surge arrestors, varistor and other similar devices each designated specifically as a solution to one or more extreme electeical event each device provide benefit in  particular situatin tat may be greatr than othar types of devices.
In general an electrical fuse combines both a sensing and interrupting element in one self contained device and is direct acting in that it respond onloy to a combination of magniture and duration of current flowing through it the fuse normally does not include anby provision for making or breaking the connection to an energized circuit but requires separate device to parform this function
A fuse is a single phase device such that only the fuse in the phase or phases subjected to over current wil respond to de energized the afected phase or phases of the circuit that fautty after having interrupted or over current it’s replaced to resfors service.
Currently two basic types of fuses are employed the expusion fuse and the current limiting fuse each type employs fusible element designed to melt when a current of a pretermined magnitude and duration passes through the element the deionizing action of gases that are liberated when the fusible element melts. An expulsion fuse typically employs a relatively short length of a fusible element contained within a tabular enclosure that is part of a larger assemly known as a fuse holder the enclosure used in the expulsion type fuse is lined with an organic materia interruption of an overcurrent take place within the fuse is lined with an organic material.
The operation of the expusion type fuse is characterized by; oud nopise and violent emission of gases flame and burning debris all of which pase a danger to persomel who may be in close proximity to the fuse which it operates because of its voilent mode of operation this type of fuse has generally been restricted to out door usage only.
The current limiting type interrupt overcurent when the are that established the melting of the fusible element is subject to the mechanical restriction and cooling action of a sand filler  that surrounds the fusible element a current limiting fuse typically consists of one length which are electrically connected at their end to a pair of electrical terminations.
The assembly is placed in a tabular housing that is made of a highly temperature resistant materials and the housing is than typically filed with high purity silica stqandard sealed electrical fuses have taken many form and ganarally compise fuses having a fusible link extending between a pair of terminal portions.
The fusible link May be provided either with notches cut in one or more sides of the fusible portion or with holes formed there through to create narrower and therefore weaker portionsa within the fusible portion.
One of the most common types of fuses is the thermal fuse (electro thermal fuse). In the thermal fuse eletrical current flowing through the fuse cause the fuse to heat.