CHAMELI DEVI SCHOOL OF ENGINEERING

FUSES AND ITS TYPE IN POWER SYSTEM

GUIDED BY:- PRESENTATION BY:-GURSIMRAN SINGH CHAWLA

CONTENTIntroductionBasic DefinitionsPackages & MaterialsFuse Element MaterialsCharacteristic ParameterHow Fuse Is Constructed ?How Fuse Works ?Types Of FusesWhat Is MCB ?How MCB Is Constructed ?How MCB Works ?Advantages & Disadvantages Of Fuse

INTRODUCTIONElectric 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.

BASIC DEFINITIONSFUSE:-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 elementFUSE LINK OPERATION:- It is the process of pre-

arcing & arcing resulting in blowing of fuse link.

PACKAGES AND MATERIALFuse consist of two main parts:• Fuse casing• Fuse elementsFuse casing may be made up of:• Ceramics• Glass• Plastic• Molded mica laminates

FUSE ELEMENT MATERIALSThe 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

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.

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.

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 + TlBreaking 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.

Temperature derating: Due to change in temperature it may allow more or less current than the current at ambient temperatureI2t value:A measure of energy required to blow the fuse.

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.

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.

TYPES OF FUSESTYPES OF FUSES

LOW VOLTAGE

FUSES

REWIREABLE

FUSES

CARTIDGE TYP

E FUSES

D-TYPE CARTRIDGE FUSES

LINK TYPE CARTIDGE OR HIGH RUPTURING CAPACITY(HRC) FUSES

DROP-OUT FUSE

STRIKER FUSE

SWITCH FUSE

HIGH VOLTAGE

HRC FUSESCARTTRIDG

E TYP

E HV

HRC FUS

E

LIQUID TYP

E HV

HRC FUS

E

LOW VOLTAGE FUSEREWIREABLE 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 OperationLack Of DiscriminationSmall Time LagLow Rupturing CapacityNo-Current-Limiting FeaturesSlow Speed Of OperationRisk Of Flame & Fire

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.

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.

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.

HIGH VOLTAGE HRC FUSESCARTRIDGE 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).

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.

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.

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.

ADVANTAGES OF FUSEIt 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.

DISADVANTAGES OF FUSEConsiderable 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.