FUSES MRIDUL SADAWARTI
INTRODUCTION This presentation discuses about fuses, how it works, its design and how it will effects the electric circuits around us .
What is fuse? In electrical and electronics engineering a fuse is a type of sacrificial overcurrent protection device. Its essential component is a metallic strip which melts as excess current flows through it.
PACKAGES AND MATERIAL Fuse consist of two main parts: Fuse casing Fuse elements Fuse casing may be made up of: Ceramics Glass Plastic Molded mica laminates
Fuse element is made up of: Tin Lead Zinc Silver Copper Aluminium
FUSE- WORKING A fuse has a metallic strip of small cross section area , mounted between a pair of electrical terminal. The fuse is connected in series with the circuit through which all the current will pass. In case of heavy current, fuse will melt. This will break the circuits and protect the electrical appliance.
CHARACTERISTIC PARAMETER Rated current Maximum current that a fuse can bear without interrupting the circuit . Speed speed at which fuse blows depends on the amount of current passing through it . Based on speed blow can be of 3 types Normal blow Fast blow Slow blow
I2t value A measure of energy required to blow the fuse. Voltage drop Resistance changes as the fuse temperature varies , this will lead to voltage drop . temperature derating With change of temperature , there’s a change in the nature of fuse .
Cut off characteristic
Prospective current It is current which would have flown in the circuits if fuse had been absent . Pre arcing time(Ts) Time taken from the instant of increase to the instant of cut off and arc initiation. Arcing time(Tl) Time from the instant of cut off to the instant of arc being extinguished. Total operating time T=Ts+Tl been absebt
Types of fuses Rewirable type Open type Semi closed type Following are two main type of fuses: Rewirable type Cartridge type Rewirable type Open type Semi closed type Cartridge type D type cartridge fuse High rupturing capacity cartridge fuse
FUSE MARKINGS Most fuses are marked on the body or on the end caps , with marking representing their rated value. Fuse marking will convey the following information: Ampere rating Voltage rating Breaking capacity Time current characteristic Approval by international standard agencies
Coordination of fuses in series All fuses are connected in series at various level of power distribution system. It will blow the fuse nearest to the fault. In this case only faulty circuit is interrupted with minimal disturbance to the other circuits.