This includes fuses as well as MCB

1. FUSES AND ITS TYPE IN POWER
SYSTEM
GUIDED BY:- PRESENTATION BY:-
GURSIMRAN SINGH CHAWLA

2. CONTENT
 Introduction
 Basic Definitions
 Packages & Materials
 Fuse Element Materials
 Characteristic Parameter
 How Fuse Is Constructed ?
 How Fuse Works ?
 Types Of Fuses
 What Is MCB ?
 How MCB Is Constructed ?
 How MCB Works ?
 Advantages & Disadvantages Of Fuse

3. INTRODUCTION
 Electric power system is a network of electrical
components used to supply, transmit and use electric
power.
 Over current protection devices are essential in
electrical systems to limit threats to human life and
property damage.
 Fuse was patented by Thomas Edison in 1890.
 Fuse is the simplest & cheapest device used for interrupting
an electrical circuit under short circuit or excessive
overload.
 Its essential component is a metallic strip which melts as
excess current flows through it.

4. BASIC DEFINITIONS
 FUSE:-It is a current interrupting device which breaks
the circuit by fusing the element when current in the
circuit exceeds certain value.
 FUSE WIRE:- It is the part of fuse which melts due to
excessive current flowing through circuit.
 FUSE LINK:- Part of the fuse which needs replacement
when the fuse blows out.
 FUSING FACTOR:- Minimum fusing current (> 1)
Current rating of fusing element
 FUSE LINK OPERATION:- It is the process of pre-arcing
& arcing resulting in blowing of fuse link.

5. 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

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

7. Characteristic Parameters
 Rated voltage: Design of the fuse should be such that
rated voltage must be greater than the nominal operating
voltage of the circuit.
 Normal rated current: Maximum current that the fuse
can continuously conduct without interrupting the circuit.
 Speed/Time lag: It defines the time taken by the switch to
open and it depends upon the over current. Usually a time
lag is necessary to avoid nuisance blowing. Very fast
operating fuses are required where a momentary fault can
cause damage to sensitive electrical equipment.

8. CUT-OFF CURRENT
CHARACTERISTICS:
The maximum
instantaneous value,
which occurs due to a
short circuit current
limited by fuses, are
presented in graphs
called the cut-off
characteristic and can
be obtained from the
manufacturer.

9.  Prospective current: It is current which would have
flown in the circuits if fuse had been absent .
• Pre arcing time(Ts): 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) :T=Ts + Tl
 Breaking capacity: Maximum current that can be
safely interrupted by the fuse.
 Voltage drop: A voltage drop is provided by the fuse
and it changes with the change in temperature of the
fuse so, it should be taken into account.

10. Temperature derating:
Due to change in
temperature it may allow
more or less current than
the current at ambient
temperature
I2t value:
A measure of energy
required to blow the
fuse.

11. HOW FUSE IS CONSTRUCTED ?
A fuse consists of a metal
strip or wire fuse element, of
small cross-section compared to
the circuit conductors, mounted
between a pair of electrical
terminals, and enclosed by a
non-combustible housing.
The fuse element is made of
zinc, copper, silver, aluminum,
or alloys to provide stable and
predictable characteristics.

12. HOW FUSE WORKS ?
 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.

13. TYPES OF FUSES
TYPES OF
FUSES
LOW
VOLTAGE
FUSES
REWIREABLE
FUSES
CARTIDGE
TYPE FUSES
D-TYPE
CARTRIDGE
FUSES LINK TYPE CARTIDGE
OR
HIGH RUPTURING
CAPACITY(HRC) FUSES
DROP-OUT
FUSE
STRIKER
FUSE
SWITCH FUSE
HIGH
VOLTAGE
HRC FUSES
CARTTRIDGE
TYPE HV HRC
FUSE
LIQUID TYPE
HV HRC FUSE

14. LOW VOLTAGE FUSE
 REWIREABLE FUSES :-
The most commonly used fuse in ‘house wiring ’ and a small
current circuits is the semi-enclosed or rewirable fuse.
 Also known as KIT-KAT type fuse.
DISADVANTAGES:-
Unreliable Operation
Lack Of Discrimination
Small Time Lag
Low Rupturing Capacity
No-Current-Limiting Features
Slow Speed Of Operation
Risk Of Flame & Fire

15.  CARTRIDGE TYPE FUSES:-
The fuse element is enclosed in a totally enclosed container
and is provided with metal contacts on both sides.
(A.) D-Type Cartridge Fuses:-
It is a non-interchangeable fuse comprising a fuse base ,
adapter ring , cartridge and a fuse cap.
(B.) High Rupturing Capacity:-
Where large concentration of power are concerned , as in
the modern distribution systems , it is essential that fuses
should have a definite known breaking capacity and also
this breaking capacity should have a high value.

16.  DROP-OUT FUSE :-
The melting of fuse causes the element to drop under
gravity about its lower support – an additional isolation.
Such fuses are employed for protection of outdoor
transformers.
Drop-out fuse-isolator combination is usually pole
mounted.

17.  STRIKER FUSE :-
 It is a mechanical device having enough force and
displacement which can be used for closing
tripping/indicator circuits.
 SWITCH FUSE :-
It is a compact combination , generally metal enclosed of a
switch and a fuse and is widely used for low and medium
voltages.

18. HIGH VOLTAGE HRC FUSES
 CARTRIDGE TYPE HV HRC FUSE :-
Its construction is similar to low voltage type except
that some special design features are incorporated.
 LIQUID TYPE HV HRC FUSE :-
This fuses are filled with carbon tetra chloride & have
the widest range of applications in high voltage
circuits.
They are employed for voltage transformer protection
or for circuits up to about 400 A rating current on
systems up to 132KV or higher and may have breaking
capacity of 6,100 A at 33KV (350 MVA , 3-phase).

19. WHAT IS MCB ?
 MCB is Miniature Circuit Breaker .
 It is commonly used in low voltage electrical network
instead of fuse.
 It automatically switches off the electrical circuit
during abnormal condition of the network means in
over load condition as well as faulty condition.
 As the switch operating knob comes at its off position
during tripping, the faulty zone of the electrical circuit
can easily be identified.
 It is mostly costlier.

20. HOW MCB IS CONSTRUCTED ?
 Miniature circuit breaker construction is very simple, robust and
maintenance free.
 A miniature circuit breaker has normally three main constructional
parts. These are:
Frame of Miniature Circuit Breaker
The Frame of Miniature Circuit Breaker is a molded case.
This is a rigid, strong, insulated housing in which the other components
are mounted.
Operating Mechanism of Miniature Circuit Breaker
The Operating Mechanism of Miniature Circuit Breaker provides the
means of manual opening and closing operation of miniature circuit
breaker.
Trip Unit of Miniature Circuit Breaker
The Trip Unit is the main part, responsible for proper working of
miniature circuit breaker.

21. HOW MCB WORKS ?
 There are two
arrangement of
operation of miniature
circuit breaker.
 One due to thermal effect
of over current and other
due to electromagnetic
effect of over current.
 The thermal operation
of miniature circuit
breaker is achieved with a
bimetallic strip whenever
continuous over current
flows through MCB, the
bimetallic strip is heated
and deflects by bending.

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

23. DISADVANTAGES OF FUSE
 Considerable time is lost in rewiring or replacing a fuse
after operation.
 The current-time characteristics of a fuse cannot
always be correlated with that of the protected device.
 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.