A fuse is a short piece of metal, inserted in the circuit, which melts when excessive current flows through it and thus breaks the circuit. The fuse element is generally made of materials having low melting point, high conductivity and least deterioration due to oxidation e.g., silver, copper etc. It is inserted in series with the circuit to be protected. Under normal operating conditions, the fuse element is at a temperature below its melting point. Therefore, it carries the normal current without overheating. However, when a short-circuit or overload occurs, the current through the fuse increases beyond its rated value. This raises the temperature and fuse element melts (or blows out), disconnecting the circuit protected by it. In this way, a fuse protects the machines and equipment from damage due to excessive currents.

2. FUSES
(The power system protection)
PRESENTATION BY:-
1.152-33-2629
2.152-33-2607
3.152-33-2632
4.152-33-2665
5.132-33-1542
PRESENTATION TO:
MAHZUBA ISLAM

3. Introduction
Basic Definitions
Fuse Casing Materials
Fuse Element Materials
Characteristics
How Fuse Is Constructed
How Fuse Works
Types Of Fuses
Advantages & Disadvantages Of Fuses
CONTENT

4. INTRODUCTION
o Electric power system is a network.
o Over current protection.
o Fuse is the simplest & cheapest device.
o Essential component of fuse is metallic
strip.
o Fuse was presented by Thomas Edison
in 1890.

5. BASIC DEFINITIONS
o FUSE:-It is a current interrupting device
which breaks the circuit by fusing the
elementwhen current in the circuit
exceeds certain value.
o FUSE WIRE:- It is the part of fuse which
melts due to excessive current flowing
through circuit.
o FUSE is connected in series in circuit.

6. FUSE CASING MATERIALS
Fuse casing:
o Ceramics
o Glass
o Plastic
o Molded mica
laminates

7. FUSE ELEMENT MATERIALS
METAL
MELTING
POINT IN
°C
SPECIFIC
RESISTANE
IN µΩ-mm
VALUEOF
FUSE
CONSTANT K
FOR d in m
(I = kd3/2)
SILVER 980 16 -
TIN 240 112 12.8
ZINC 419 60 -
LEAD 328 210 10.8
COPPER 1090 17 80
ALUMINIUM 665 28 59
The materials used for fuse elements must be of low melting
point, low ohmic loss, high conductivity,low cost & free from
deterioration.

8. CHARACTERISTICS
o Rated voltage
o Normal rated current
o Fusing current(I = kd3/2)
o Cut-off current
o Pre arcing time
o Arcing time
o Total operating time

9. HOW FUSE IS CONSTRUCTED
The fuse element is
made of zinc,
copper, silver,
aluminum, or
alloys to provide
stable and
predictable
characteristics.
Onetypeoffuse

10. HOW FUSE WORKS
o The fuse is connected in
series with the circuit
through which all the
current willpass.
o In case of heavy current,
fuse will melt. This will
break the circuits and
protect the electrical
appliance.

11. TYPES OF FUSES
Two types of fuses:-
 Low Voltage Fuses
 High voltage Fuses
Low Voltage Fuses:-
Rewireable fuses
Cartridge fuses
High Voltage Fuses:-
Cartridge type hv hrc fuses
Liquid type hv hrc fuses
Low Voltage Fuses

12. HIGH VOLTAGE FUSES
Cartridge type hv hrc fuses liquid type hv hrc fuses

13. ADVANTAGES OF FUSE
1.It is the cheapest form of protection available.
2.It needs no maintenance.
3.It interrupts enormous short circuit currents
without noise , flame , gas or smoke.
4.The minimum time of operation can be made
much smaller than that with the circuit
breakers.
5.The smaller size of fuse element imposes a
current limiting effect under short circuit.
6.Its inverse time-current characteristics enables
its use for overload protection.

14. DISADVANTAGES OF FUSE
1. Considerable time is lost in rewiring or
replacing a fuse after operation.
2. The current-time characteristics of a fuse
cannot always be correlated with that of the
protected device.
3. On heavy short circuit , discrimination
between fuses in series cannot be obtained
unless there is considerable differences in
the relative sizes of the fuses concerned.