ELECTRIC LOCO SHEDn.c.r. KANPUR(an unit of indian government)

2016

Project Report on FAILURE OF FUSE & MCB

SUBMITTED BY:MR SACHIN SINGH

SUBMITTED TO:Mr. Md. Israr (SSE)

a project report onFAILURE OF FUSE & MINIATURE CIRCUIT BREAKER

Submitted by:

Mr. SACHIN SINGH

in partial fulfillment for the award of the degree

of

Bachelor Of TechnologyIN

electrical Engineering

At

Maharana pratap engineering collegeKothi MANDHANA, KANPUR

2013-2016

Certificate

This is certify that Mr. SACHIN SINGH a student of Electrical Engineering,3rd year from Maharana Pratap Engineering College Kothi Mandhana, Kanpur, has done their semester project at Electric Loco Shed Anwarganj, Kanpur from june25,2016 to July23,2016.

The project work entitled “FAILURE OF FUSE & MINIATURE CIRCUIT BREAKER” embodies the original work done by them during their above full semester project training period.

This is also certify that this project has been prepared and submitted under my guidance.

During the training period they were regular and completed their training sincerely and successfully. Their overall performance was satisfactory. I wish them good luck and success in future.

(Signature of Guide)

DATE: …………………… MR. M.P. SINGH

PLACE: …………………. Senior Section Engineer

E-2 Section

4

Acknowledgement:Summer project is a golden opportunity for learning and self-development. We consider our self

very lucky and honored to have so many wonderful people lead us through in completion of this project.

Our grateful thanks to Mr. M.P. SINGH, SSE of E-2 Section and All the Staff Members who inspite of being extraordinarily busy with his duties, took time out to hear, guide and keep me on the correct path. We do not know where I would have been without them. A humble thank you Sir.

I also wish to express my gratitude to the officials and other staff members of “ELECTRIC LOCO SHED (ELS), KANPUR” who rendered their help during the period of my project work. My

special thanks to Sir Mr. M.P. SINGH, SSE of the industry for their kind co-operation to the completion of

my project work.

Last but not least I wish to avail myself of this opportunity, express a sense of gratitude and love to my friends and my beloved parents for their manual support, strength, and help and for everything

Mr. SACHIN SINGH

Mr. VINAY SINGH

Mr. ANIL KUSHAWAHA

PrefaceThe importance of fuse is well defined in railways engines WAG for various purposes such as

protection of traction motor, protection of blower motor, protection of various devices such as arno

converter transformer, rectifiers, vacuum circuit breaker etc. but some time it is failed and creates problem.

The project report is structured to cover the key aspects, importance and remedies of failure of relay.

The project report uses plain, lucid language and related figures to explain fundamental of this topic.

The project report provides logical method of explaining various complicated concepts and stepwise method

to explain the important parts. All related topics in this project report are arranged in a proper sequence that

permits each related topics to build upon earlier studies. This makes the understanding of this topic clearer

and makes it more interesting.

I have many goals in writing this topic but the overriding one is to provide instructors with a tool. In this project report also explain about relay and which types of failure creates? And also explain the remedies of these failures by suitable and scientific methods.

Mr. SACHIN SINGH

Declaration

I hereby declare that the work which is being presented in the project entitled“Failure of fuse& miniature circuit breaker” in partial fulfillment of the requirement for the award of the

degree of B.TECH submitted in the department of Electrical Engineering, Maharana Pratap

Engineering College Kothi Mandhana, Kanpur is in authentic record of my own work carried out during

the period from june25, 2016 to july23, 2016 under the supervision and guidance of Mr. “M.P. SINGH”

Sir. The matter embodied in this project work has not been submitted for the award of any other degree or

diploma.

Name of guide: Name of Students:

Mr. M.P. SINGH Mr. Sachin Singh

Senior Section Engineer

E-2 section

Place: Kanpur

Date:

CONTENTS

S.NO. PARAGRAPH/HEADING PAGE NO1- Introduction to electrical loco shed 82- What is train 92.1- Electric locomotive 102.2- History of locomotive 102.3- Classification of locos 12

2.4- locomotive manufactures 1

32.5- Bharat earth mover limited (BEML) 14

2.6- Working principle of electric train

15 3- Fuse 184- Different types of fuse 19

5- Protection from short circuit damage

236- Circuit breaker 257- Miniature circuit breaker 277.1- construction of mcb 287.2- Miniature circuit breaker working principle 28

7.3- Operating mechanism of mcb 2

9

7.4- Characteristics 2

9

8- Fuse in electric loco 30

9- Use of fuse in electric loco 3110- Failure of fuse in loco 3311- Indication of failure of fuse in loco 3312- Maintenance of fuse in loco 33

13- References 34

1.Introduction to Electric Loco Shed

The Electric Loco Shed, Kanpur was established in 1965 with the electrification of

Mughalsarai-Kanpur section. The shed started functioning with a meager holding of 11 imported WAM-1

type locomotives for Passenger services. Present holding of the shed is 169 locomotives (40-WAP-4, 126-

WAG-7 & 3-WAM-4).

A view of CNB electric loco shed with the freight yard in the foreground. CNB is the largest

locomotive shed on NR homing 2 classes of locos - the WAP4 & WAG7.

Established in April 1965. Shed recovered area- 9989 sqmt.

Passenger service (WAM-1) - 11 locos in 1967.

Freight service WAG-4(CLW) – 22 locos in 1967.

WAG-5A (CLW) - 04 locos in 1988.

WAG-5HB (BHEL) - 10 locos in 1995.

WAG-7(CLW) - 20 locos in 1996.

2.WHAT IS TRAIN?

The work 'train' comes from the Old French trahiner, itself from the Latin trahere 'pull,

draw'.

A train is a connected series of vehicles that move along a track (permanent way) to transport freight or

passengers from one place to another. The track usually consists of two rails, but might also be a monorail

or maglev guide way. Propulsion for the train is provided by a separate locomotive, or from individual

motors in self-propelled multiple units. Most modern trains are powered by diesel locomotives or by

electricity supplied by overhead wires or additional rails, although historically (from the early 19th century

to the mid-20th century) the steam locomotive was the dominant form of locomotive power. Other sources

of power (such as horses, rope or wire, gravity, pneumatics, and gas turbines) are possible.

2.1.Electric locomotive:

An electric locomotive is a locomotive powered by electricity from an external source. Sources include overhead lines, third rail, or an on-board electricity storage device such as a battery or flywheel system.

Electric traction offers a lower cost per mile of train operation but at a higher initial cost, which

can only be justified on high traffic lines. Since the cost per mile of construction is much higher, electric traction is

less favored on long-distance lines with the exception of long-distance high speed lines. Electric trains receive their

current via overhead lines or through a third rail electric system.

Electrically propelled locomotives with on-board fueled prime movers, such as diesel engines or gas turbines, are classed as diesel-electric or gas turbine electric locomotives because the electric generator/motor combination only serves as a power transmission system.

2.2.HISTROY OF ELECTRIC LOCOMOTIVE:

The Chicago, Milwaukee, St. Paul and Pa AC locomotive in Valtellina (1898-1902). Power supply: 3-phase 15 Hz AC, 3000 V. Designed by KálmánKandó in Ganz Works, Hungary.

A steel cab electric locomotiveA Milwaukee Road class ES-2

The first known electric locomotive was built in 1837 by chemist Robert Davidson of Aberdeen. It was

powered by galvanic cells ('batteries'). Davidson later built a larger locomotive named Galvani which was

exhibited at the Royal Scottish Society of Arts Exhibition in 1841. The seven-ton vehicle had two direct-

driver motors, with fixed electromagnets acting on iron bars attached to a wooden cylinder mounted on each

axle, and simple. It hauled a load of six tons at four miles per hour for a distance of one and a half miles. The

machine was tested on the Edinburgh and Glasgow Railway in September of the following year, but the

limited electric power available from batteries prevented its general use. It was destroyed by railway

workers, who saw it as a threat to their security of employment. The first electric passenger train was

presented by Werner von Siemens at Berlin in 1879. The locomotive was driven by a 2.2 kW, series-wound

motor, and the train, consisting of the locomotive and three cars, reached a maximum speed of 13 km/h.

During four months, the train carried 90,000 passengers on a 300-metre-long circular track. The electricity

(150 V DC) was supplied through a third, insulated rail situated between the tracks. A contact roller was

used to collect the electricity from the third rail. The world's first electric tram line opened in near Berlin,

Germany, in 1881. It was built by Werner von Siemens (Britain, Volk's electric railway was opened in 1883

in Brighton (see Volk's Electric Railway). Also in 1883, Tramwas opened near Vienna in Austria. It was

the first tram and railway in the world in regular service that was run with electricity served by an overhead

line. Five years later, in the US electric trolleys were pioneered in 1888 on the Richmond Union Passenger

Railway, using equipment Sprague's invention of multiple-unit train control in 1897Surface and elevated

rapid transit systems generally used steam until forced to convert by ordinance.

The first use of electrification on a mainline was on a four-mile stretch of the Baltimore Belt Line of the

Baltimore and Ohio Railroad (B&O) in 1895. This track connected the main portion of the B&O to the

newly built line to New York and it required a series of tunnels around the edges of Baltimore's downtown.

Parallel tracks on the Pennsylvania Railroad had shown that coal smoke from steam locomotives would be

a major operating issue, as well as a public nuisance. Three Bo+Bo units were initially used, at the south

end of the electrified section; they coupled onto the entire train, locomotive and all and pulled it through the

tunnels. Railroad entrances to New York City required similar tunnels and the smoke problems were more

acute there. A collision in the Park Avenue tunnel in 1902 led the New York State legislature to outlaw the

use of smoke-generating locomotives south of the Harlem River after 1 July 1908. In response, electric

locomotives began operation in 1904 on the New York Central Railroad. In the 1930s, the Pennsylvania

Railroad, which also had introduced electric locomotives because of the NYC regulation, electrified its

entire territory east of Harrisburg, Pennsylvania.

2.3.Classification of Locos:

Early locomotives in India had a bewildering variety of classification schemes. Regional railways had their

own classification schemes too. For more details on this, refer to reference works such as Hugh Hughes'

classic 4-volume work on Indian locomotives. The first BESA standard classes appeared in 1903. The HPS,

SPS, HGS, and SGS steam loco classes were quite popular. HP = Heavy Passenger, SP = Standard

Passenger, HG = Heavy Goods, SG = Standard Goods. In these, the suffix 'S' stands for 'superheated'. An

alternative suffix 'C' indicates a conversion to superheating, e.g. SGC. A suffix 'M' was sometimes used to

mean 'modified', for variant designs. However, these classification codes were by no means universally

adopted, and various railways had their own schemes.

In 1924, when IR decided to classify engines, the initial notation was:

X for broad-gauge

Y for meter-gauge

Z for 2' 6" narrow-gauge

Q for 2' 0" narrow-gauge

The IRS (Indian Railway Standard) classes XA, XB, XC, XD, XE, and others in the 'X' series for BG; YA, YB, YC, YD, and YE for MG; and ZA, ZB, ZC, ZD, ZE, ZF for 2'6" NG; and QA, QB, QC for 2' NG, were all adopted as standards by the Locomotive Standards Committee by 1925 or soon thereafter.

In fact the Q classes were never built, and of the Z classes, only ZB and ZE (and a modified version of ZF to

agree with existing locos) classes were built. Not all locos of a given class were built by the same

manufacturer. Some of these class designations were re-used later (e.g., ZD). In 1945, 'IRS' became 'IGR'

(Indian Government Railway Standard), although the class notations remained the same.

'W' was used for broad-gauge instead of 'X' soon after World War II, with the introduction of the WP and

WG locomotives. 'Q' was also replaced by the 'N' code. Some early electrics had codes beginning with 'E'

(EF, EM, EG, etc.), but after about 1945, when diesel and electric locos were included in the scheme, the

codes for motive power were added (D, A, C, CA, B), which have remained unchanged.

2.4.Locomotive Manufacturers:

Early locos (late 19th century) were almost all imported. The first steam locomotive was built in India in 1895 at the Ajmer workshops.

Details of some of the more important manufacturers are to be found in the section on production units and workshops.

CLW: Large-scale loco production in India did not begin until the establishment of the Chittaranjan Locomotive Works (CLW) in 1950.

DLW: The Diesel Loco Works set up at Varanasi began producing diesel locos in 1967, and has since then produced a large number of mainline and shunter diesels. Variants of various classes in the WDS and WDG series are supplied to industrial concerns as well.

BHEL: Bharat Heavy Electricals Ltd. (BHEL) supplied some WAG-5 and three NBM-1 units in the '80s,

and more recently has supplied WCAM-2's, WCAM-3's, WAG-8's, and NDM-6's. BHEL also makes

electrical transmission components, traction motors, alternators, and other components for both three-phase

and tap-changer locomotives. The locomotives are made at BHEL's facilities at Bhopal and Jhansi. Recently

[2008] BHEL has entered an agreement with IR to supply several dozen high-horsepower locomotives. As

its expertise extends currently only to 6,000hp diesel locos, BHEL is exploring foreign partnerships with

GE, Toshiba, and others for production of 10,000hp locomotives.

DCW: Diesel Components Works, Patiala - now renamed the Diesel Modernization Works or DMW, supplies components for some locomotives to DLW. It also works on rebuilding and upgrading locos (e.g., older WDM-2's being converted to WDM-3A locos).

NGEF and Crompton Greaves are other domestic suppliers of traction motors, alternators, etc.

TELCO: Tata Electrical and Locomotive Co. (TELCO) supplied some YP and YG units in the 50's and 60's.

Cummins India makes the diesel engines for DMU's, HPDMU's, and some MG locos.

Suri and Nayar (SAN), located in Bangalore, have supplied some shunters and other locos, and parts such

as transmissions.

Ovis Loco, based in Hyderabad supplies some shunting locos (mainly for industrial customers).

Venkateshwara Transmissions (Ventra) of Medak (Andhra Pradesh) is another manufacturer who supplied some locomotives and locomotive parts to IR.

ICF: Integral Coach Factory has been making EMUs for suburban systems (e.g., the YAU-1 MG 4-car

EMU) since 1966. It also makes some self-propelled special-purpose units, such as the diesel Medical

Relief Van and diesel-electric tower cars.

2.5. Bharat Earth Movers Limited (BEML):

Formerly a state owned enterprise, Bangalore-based BEML manufactures heavy engineering products, including a wide variety of Railway vehicles made at its Bangalore and Mysore facilities. BEML makes coaches based on the standard ICF type design

Bombardier Transportation makes train-sets for the Delhi Metro at its plant in Vadodara, Gujarat.

The Jamalpur Workshop of ER manufactures diesel self-propelled units such as cranes for clearing wreckage and construction work.

The izzatnagar Works manufactures railbuses and railcars using Ashok Leyland Iveco engines, and Hindustan Motors or Kirloskar Pneumatics converters and transmissions.

2.6.Working principle of electric train :

The overhead lines that are running over the electric train are containing 25 kv

electric current. The catenary of the pantograph contacts the wire, this 25 kV AC current is collected in the

bow collector of the pantograph. From the bow collector the current then goes to the step down transformer

through the porcelain insulators where the current is stepped down. This stepped down AC current is then

passed through the rectifier where it is converted into DC. This current then goes to the stator of the traction

motor where a magnetic field is produced due to this current. A current is induced in the rotor by the

commutator and due to the magnetic field produced by the stator and induced current a force acts on the

rotor and the rotor starts rotating. A wheel is mounted on the axle and finally the wheel starts moving.

25 kV

↓

Pantograph

↓

Insulator

↓

Step-down transfers

↓

To selenium rectifiers

↓

DC motors

↓

Stator

↓

Rotor

↓

Axle

↓

Pinion

↓

Wheel

Railways generally tend to prefer overhead lines, often called "catenaries" after the

support system used to hold the wire parallel to the ground.

3. FUSE

A fuse is one type of over current device that is designed to be a sacrificial element in an electrical power system. Fuses are designed to open circuits when excessive currents are present due to overloads or faults and to prevent further damage to the system that might result if the fuse were not present. The subject matter of this paper is the outcome of a bird‟s eye view on the concept and working of the different types of fuses. Also this paper highlights the significant role played by the fuses in providing protection from short-circuit damages. This review study may be useful to the electrical engineering graduates to put good efforts to further develop protective fuse concept, since one of the most common and potentially serious problem is a short circuit .

A short can occur whenever a loose wire, dropped tool, flood of seawater, or other circumstance provides electricity with a shortcut around all or part of the regular load. Since the load normally limits the amount of current allowed to flow from the battery or other source, a short can cause a huge surge in current. This surge can quickly heat wires or other components red-hot and start a fire. A short can also bring higher voltage parts of a circuit into direct electrical contact with parts that are normally at lower voltages, so in high-voltage circuits, a short can present a dangerous electrocution hazard. Fuses are therefore selected to allow passage of normal current plus a marginal percentage and to allow excessive current only for short periods.

Slow blow fuses are designed to allow higher currents for a modest amount of time longer, and such considerations are and were commonly necessary when electronics devices or systems had electronic tube tech. The most common device in use for over current protection in high-current circuits today is the circuit breaker. Circuit breakers are specially designed switches that automatically open to stop current in the event of an over current condition. Small circuit breakers, such as those used in residential, commercial and light industrial service are thermally operated. They contain a bimetallic strip (a thin strip of two metals bonded back-to-back) carrying circuit current, which bends when heated.

When enough force is generated by the bimetallic strip (due to over current heating of the strip), the trip mechanism is actuated and the breaker will open. Larger circuit breakers are automatically actuated by the strength of the magnetic field produced by current-carrying conductors within the breaker, or can be triggered to trip by external devices monitoring the circuit current (those devices being called protective relays).Fuses are rated in terms of their voltage capacity as well as the current level at which they will blow. Some large industrial fuses have replaceable wire elements, to reduce the expense.

The body of the fuse is an opaque, reusable cartridge, shielding the fuse wire from exposure and shielding surrounding objects from the fuse wire. Over current devices primarily protect the conductors of a circuit from over temperature damage (and the fire hazards associated with overly hot conductors), and secondarily protect specific pieces of equipment such as loads and generators (some fast-acting fuses are designed to protect electronic devices particularly susceptible to current surges).

The basic purpose of the fuse is to protect and is composed of an alloy which has a low melting point. A strip of this fuse is placed in series with the circuit. The working principle is that if the current is in excess then the strip would melt and break the circuit. There are different variants of fuse boxes available with different types of circuit breaking. For instance, in the case of slow blow fuses, a small overload is carried for some period without the circuit been broken. Other fuse boxes are designed to break the circuit rapidly.

The selection is based upon the kind of device and also the fluctuation level of the current. Today, semiconductor devices are being manufactured with maximum continuous current ratings up to 4kA and peak inverse voltages of 6kV, . Unfortunately, these devices still have poor overload capacities and continue to need sensitive and fast-acting protection.

4. Different types of fuses

A brief idea of the different types of fuses and their working is given here. The main components of a standard fuse unit consist of the items: Metal fuse element, Set of contacts, Support body. The major two categories of fuses included are (1) Low Voltage Fuses, (2) High Voltage Fuses. In order to understand Low voltage fuses better, and can further classified into: Semi Enclosed or Rewireable Type, Totally enclosed or Cartridge Type.

A. Rewireable Fuses

This kind of fuse is most commonly used in the case of domestic wiring and small scale usage. Another name for this type is the Kit-Kat type fuse. The main composition is of a porcelain base which holds the wires. The fuse element is located inside a carrier that is also made out of porcelain. It is possible to remove the fuse carrier without any risk of electrical shock. Normally what happens is that when the fuse blows, it can be replaced without having to change the complete thing.

The main metals or alloys used in making fuse wire include lead, tinned copper, aluminum or tin lead alloy. When there is an over surge that causes the fuse element to blow off, it can be replaced. A new fuse carrier is inserted in the base. The main advantage of this type of fuse is that it is easy to install and also replace without risking any electrical injury. Totally Enclosed or Cartridge Type In this type of fuse has a completely closed container and there are contacts (metal) on either side. The level of sub division in this case includes, D type, Link Type.

D Type Cartridge Fuses: This cannot be interchanged and comes with the following main components: fuse base and cap, adapter ring and the cartridge. The fuse base has the cap screwed to it and the cartridge is pushed into it. The circuit becomes complete when the tip of the cartridge is in contact with the conductor. In this case, the main advantage is that of reliability.

Link Type Cartridge fuses: In Link type, further a knife blade type and bolted types are available. The Knife Blade Type HRC Fuse is easily replaceable in the circuit without any load. For this purpose, special insulated fuse pullers are used. In the Bolted Type HRC Link Fuse, the conducting plates are bolted to the base of the fuse. There is also a presence of a switch through which the fuse can be removed without getting an electrical shock. In HRC fuse or High Rupturing Capacity Fuse, the fuse wire or element can carry short circuit heavy current for a known time period.

During this time if the fault is removed, then it does not blow off otherwise it blows off or melts. The enclosure of HRC fuse is either of glass or some other chemical compound. This enclosure is fully air tight to avoid the effect of atmosphere on the fuse materials. The ceramic enclosure having metal end cap at both heads, to which fusible silver wire is welded. The space within the enclosure, surrounding the fuse wire or fuse element is completely packed with a filling powder.

This type of fuse is reliable and has inverse time characteristic, that means if the fault current is high then rupture time is less and if fault current is not so high then rupture time is long. The Operation of HRC fuse clearly shows that when the over rated current flows through the fuse element of High Rupturing Capacity Fuse the element is melted and vaporized. The filling powder is of such a quantity that the chemical reaction between the silver vapor and the filling powder forms a high resistance substance which very much helps in quenching the arc.

B. ANL/ANE fuses

ANL kind of fuses is mostly used in cars for the audio systems. They are available in various sizes. As opposed to others, this one has no wire terminal block. How to check the fuses? In order to check the fuse, a probe is used with readings from the terminals. The correct functioning would be when the value is 0V DC. The fuse should be checked with the voltage being supplied. In cases, the value getting is higher than 0V DC, this means than there is a need to remove it.

In this category all fuses up to 1.5 kV can be included. But the most typical voltage levels for low voltage fuses are 500 V, 690 V and 750 V.LV HRC fuses are used for installation systems in non-residential, commercial and industrial buildings, as well as in the switchboards of power supply companies. They therefore protect essential building parts and installations. LV HRC fuse links are available in the following operational classes: gG (previously gL) for cable and line protection, aM for the short-circuit protection of switching devices in motor circuits, gR or aR for the protection of power semiconductors, gS operational class combines cable and line protection with semiconductor protection.

C. High Voltage Fuses

All fuses used on power systems from 1.5 kV up to 138 kV are categorized as high voltage fuses. High voltage fuses are used to protect instrument transformers used for electricity metering, or for small power transformers where the expense of a circuit breaker is not warranted. Large power fuses use fusible elementsmade of silver, copper or tin to provide stable and predictable performance. High voltage expulsion fuses surround the fusible link with gas evolving substances, such as boric acid. When the fuse blows, heat from the arc causes the boric acid to evolve large volumes of gases.

The associated high pressure (often greater than 100 atmospheres) and cooling gases rapidly quench the resulting arc. The hot gases are then explosively expelled out of the end of the fuse. Such fuses can only be used outdoors. The most frequent application is in transformer circuits, with further uses in motor circuits and capacitor banks. These types of fuses may have an impact pin to operate a switch mechanism, so that all

three phases are interrupted if any one fuse blows. High-power fuse means that these fuses can interrupt several kilo amperes. Some manufacturers have tested their fuses for up to 63 kA cut-off current.

D. Coordination of Fuses in Series

Where several fuses are connected in series at the various levels of a power distribution system, it is desirable to blow (clear) only the fuse (or other over current device) electrically closest to the fault.

This process is called "coordination" or "discrimination" and may require the time-current characteristics of two fuses to be plotted on a common current basis. Fuses are selected so that the minor, branch, fuse disconnects its circuit well before the supplying, major, fuse starts to melt.

In this way, only the faulty circuit is interrupted with minimal disturbance to other circuits fed by a common supplying fuse. Where the fuses in a system are of similar types, simple rule-of-thumb ratios between ratings of the fuse closest to the load and the next fuse towards the source can be used. E. Resettable Fuses

So-called self-resetting fuses use a thermoplastic conductive element known as a Polymeric Positive Temperature Coefficient (or PPTC) thermistor that impedes the circuit during an over current condition (by increasing device resistance). The PPTC thermistor is self-resetting in that when current is removed, the device will cool and revert to low resistance. These devices are often used in aerospace/nuclear applications where replacement is difficult, or on a computer motherboard so that a shorted mouse or keyboard does not cause motherboard damage.

F. Thermal Fuses

These single operation devices work primarily as a temperature sensitive fuse. Due to their compact size and low cost they can be used as a primary protection device in applications where there is little thermal inertia experienced during normal operation conditions. Thermal fuses are also valuable as a cost effective added safety back-up to a primary operating control. The construction of the most common form of thermal fuses basically uses a contact spring encapsulated into a wax pellet. The pellet is formulated to melt at a predetermined maximum temperature. As the wax melts the spring stretches until it breaks the circuit in the process. Other types of thermal fuses incorporate the use of a specially formulated solder that effectively melts when exposed to given maximum temperature.

These devices are non-resettable and react primarily to changes in temperature. There is some self heating effect for these devices under higher current loads which may cause the operating characteristics to change over time. Thermal fuses are also referred to as thermal links, thermal cutouts (TCO's), or one shot. A thermal fuse is often found in consumer equipment such as coffee makers, hair dryers or transformers powering small consumer electronics devices. They contain a fusible, temperature-sensitive alloy which holds a spring contact mechanism normally closed.

When the surrounding temperature gets too high, the alloy melts and allows the spring contact mechanism to break the circuit. The device can be used to prevent a fire in a hair dryer for example, by cutting off the power supply to the heater elements when the air flow is interrupted (e.g., the blower motor stops or the air intake becomes accidentally blocked). Thermal fuses are a 'one shot', non-resettable device which must be replaced once they have been activated (blown).

G. Surface-Mount Fuses

Fast-Acting Chip Fuses: Our fast-acting chip fuses help protect equipment from damage caused by over current conditions when relative quick clear or open times are required in DC power applications. They reduce fuse aging, improve product reliability and resilience, and enhance high-temperature performance.

High-Current Rated Fuse: Our high-current chip fuses support surface-mount applications where space is critical and high current is required. The high reliability and strong arc suppression characteristics help make them suitable for over current protection in power supplies servers, communication equipment and more.

Slow-Blow Chip Fuses: Our slow-blow chip fuses help provide protection from damage caused by over current events on systems that experience large and frequent current surges as part of their normal operation.

5. Protection from Short Circuit Damages

Fuse selection and device plays a predominant role in providing protection from short-circuit and other damages. It also works as a safety device in protecting human life and property. Safety by low voltage fuses and high voltage fuses in case of over currents, over loads, and short-circuits is also examined here.

A. Safety in Low Voltage Fuses

In case of low voltage fuses both in rewirible and cartridge type of fuses suitable fuse construction is made. The rewirible fuse (KIT-KAT), when blows, it can be replaced without having to complete thing. Safety fusers like cylindrical type, enclosed or cartridge type or high power rupturing capacity fuses(HRC),knife blade fuse, bolted fuse like types are providing more safety limiting the over currents and short-circuit dangerous and damages.

B. Safety in High Voltage Fuses

High power fuses can interrupt several kilo Amperes. Different types of high voltage fuses are in use to protect from overloading current and short-circuit damages. Such high voltages fuses are used to protect transformers used for electricity metering. These high power fuses are made with protective switching devices.

C. Over Currents

A fuse can provide protection in the event of over currents. An over current is either an overload current or a short-circuit current. The overload current is an excessive current relative to normal operating current but one which is confined to the normal conductive paths provided by the conductors and other components and loads of the distribution system. As the name implies, a short-circuit current is one which flows outside the normal conducting paths. D. Overloads

A fuse can provide protection to circuits from overloads. Overloads are most often between one and six times the normal current level. Usually, they are caused by harmless temporary surge currents that occur when motors are started-up or transformers are energized. Such overload currents or transients are normal occurrences. Since they are of brief duration, any temperature rise is trivial and has no harmful effect on the circuit components. (It is important that protective devices do not react to them.) Continuous overloads can result from defective motors (such as worn motor bearings), overloaded equipment, or too many loads on onecircuit.

Such sustained overloads are destructive and must be cut-off by protective devices before they damage the distribution system or system loads. However, since they are of relatively low magnitude compared to short-circuit currents, removal of the overload current within a few seconds will generally prevent equipment damage. A sustained overload current results in overheating of conductors arid other components and will cause deterioration of insulation which may eventually result in severe damage and short-circuits if not interrupted.

E. Short – Circuits

A fuse can offer protection to circuits from short-circuits. Whereas overload currents occur at rather modest levels, the short-circuit or fault current can be many hundreds of times larger than the normal operating current. A high level fault may be 50,000 Amps (or larger). If not cut off within a matter of a few thousands of a second, damage and destruction can become rampant-there can be severe insulation damage, melting of conductors, vaporization of metal, ionization of gases, arcing, and fires. Simultaneously, high level short-circuit currents can develop huge magnetic-field stresses. The magnetic forces between bus bars and other conductors can be many hundreds of pounds per lineal foot; even heavy bracing may not be adequate to keep them from being warped or distorted beyond repair.

F. The concept of Controllable Fusing

With the aim to improve the fuse features, a new concept of controllable fusing has been patented. The controllable fusing means the possibility of fuse to operate at certain time moments when an external command is activated. The key element of the controllable fusing is an electrode which is placed on the fuse link element. The electrode is made from graphite and is pressed on the copper strip of the fuse element. The electrode terminal is made from brass in order to allow a good contact with the supply conductor. With the aim to supplythis electrode, a detachable contact, or a plug device is used in the case of more parallel fuse link elements. Thus, when an over current occurs within an electric circuit where a high breaking capacity fuse is mounted to protect a device against over currents, especially short-circuits, some transducers which are sensitive at current value, di/dt, temperature, etc., will provide a command signal for a power switch. This switch will supply with the necessary power the electrode, which finally will interrupt the fuse element, through an auxiliary electric arc. Therefore, the fuse will turn off the main electric circuit.

6. CIRCUIT BREAKER

A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload or short circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow.

As name indicates that circuit breaker means device which breaks (Open) the circuit under abnormal condition and protect the system from hazards. The function of a circuit breaker is to isolate the faulty point of the power system in case of abnormal conditions such as faults. Another important device

which is protective relay detects abnormal conditions and sends a tripping signal to the circuit breaker after receiving tripping command from the relay, the circuit breaker isolates the faulty part from the power system. For opening and closing the circuit the contacts are presents.

These contacts are placed in the closed chamber containing a fluid containing medium (either liquid or gas) which quenches the arc formed between the contacts.

Under normal conditions these are at closed position but when the circuit breaker requires to isolate the faulty part, the moving contacts moves to interrupt the circuit onseparation arc is formed and until this arc is quenched the current continues to flow the circuit is isolated when the arcis quenched.

7. MINIATURE CIRCUIT BREAKERThe MCB is an automatic, electrically operated switching device that was designed to automatically protect an electric circuit from overload currents and short circuit currents. It is a complicated construction made up of almost 100 individual parts [3]. It has the ability to respond within milliseconds when a fault has been detected. Westinghouse Electric introduced the World’s first MCB and it initially had a porcelain base and cover mounted in a metal housing. . It automatically switches off the electrical circuit during abnormal condition of the network means in over load condition as well as faulty condition. The fuse does not sense but Miniature Circuit Breaker does it in more reliable way. MCB is much more sensitive to over current than fuse.Another advantage is, as the switch operating knob comes at its off position during tripping, the faulty zone of the electrical circuit can easily be identified. But in case of fuse, fuse wire should be checked by opening fuse grip or cutout from fuse base, for confirming the blow of fuse wire.

Quick restoration of supply can not be possible in case of fuse as because fuses have to be rewirable or replaced for restoring the supply. But in the case of MCB, quick restoration is possible by just switching on operation.

Handling MCB is more electrically safe than fuse. Because of to many advantages of MCB over fuse units, in modern low voltage electrical network, Miniature Circuit Breaker is mostly used instead of backdated fuse unit.

7.1. Miniature Circuit Breaker Working Principle

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. This deflection of bimetallic strip releases mechanical latch.

As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts. But during short circuit condition, sudden rising of electric current, causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts. This was a simple explanation of miniature circuit breaker working principle.

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. This deflection of bimetallic strip releases mechanical latch. As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts. But during short circuit condition, sudden rising of electric current, causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts. This was a simple explanation of miniature circuit breaker working principle.

7.2. Construction of mcbMiniature circuit breaker construction is very simple, robust and maintenance free. Generally an MCB is not repaired or maintained, it just replaced by new one when required. A miniature circuit breaker has normally three main constructional parts.

7.3. OPERATING MECHANISM OF MCB

The Operating Mechanism of Miniature Circuit Breaker provides the means of manual opening and closing operation of miniature circuit breaker. It has three-positions "ON," "OFF," and "TRIPPED". The external switching latch can be in the "TRIPPED" position, if the MCB is tripped due to over-current. When manually switch off the MCB, the switching latch will be in "OFF" position. In close condition of MCB, the switch is positioned at "ON". By observing the positions of the switching latch one can determine the condition of MCB whether it is closed, tripped or manually switched off.

When the the moving contact separated from fixed contact, there may be a high chance of arc. This arc then goes up through the arc runner and enters into arc splitters and is finally quenched. When we switch on an MCB, we actually reset the displaced operating latch to its previous on position and make the MCB ready for another switch off or trip operation.

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7.4. CHARACTERSTICS-:1. Rated current not more than 100A.2. Trip characteristics normally not adjustable.3. Thermal or thermal magnetic operation.8. FUSE IN ELECTRIC LOCO

Fuse used in electric locos are different types such as shown in figure. they are different from conventional fuse. they are bigger in size heavier in weight as compared to normal fuse. the construction of fuse is also different such as they are made up by molding the winding or made up by ceramics. the fuse have very high rating. they can survive for high voltage and high current. the rating of fuse shown in figure is 1000V/1000A. the resistance of fuse are very small such as in milliohm. the resistance of fuse shown in figure is 0.0949mΩ/210C.

NH fuses are types of electrical resistors used as sacrificial devices to protect electrical circuits in industrial related plants as well as in public mains electricity related production and distributions. NH fuses are easily identified by their square or oblong bodies combined with blade style terminals. Due to their larger body size they have higher ratings comprising of up to 1.25kA in sum total.

9. Use Of Fuse In Electric Loco.

The loco have six dc motor to run these motor the dc supply is required. The loco have a pantograph which takes supply from the main line which is generally a 25Kv line. A circuit breaker are connected in pantograph called DJ Circuit breaker. it opens up when a fault or short circuit occurs in electric loco. The pantograph receives the supply from main line this supply is supply so we have need to convert this AC supply into DC supply to run the DC series motor.

A transformer is connected After the pantograph to step down the supply to probably 1000V. A bridge rectifier is connected in the secondary side of the transformer. the rectifier is used to convert the stepped down AC supply of main line into DC supply which gives to the DC series motor to drive the loco. The bridge rectifier used diode to rectify the supply.

The maximum number of diode used in rectifier is 28 & the minimum number of diode used is12. Basically a bridge rectifier have four arms in which diode are connected. For the maximum number of diode 7 diode are connected in parallel in a single arm & for the minimum number of diode 3 diodes are connected parallel to each other in a single arm.

The given figure shows the diode which is used to rectify the AC supply into DC supply. It is also different from conventional diode. They are circular in size & heavy in weight. The anode & cathode are mentioned in the diode. They are not directly connected to the secondary side of transformer. It is connected with the help of iron metallic box.

The fuse are connected in parallel in each of diode to protect it from damage. If a high voltage supply comes above the rating of diode or a short circuit may occurs in the transformers which may cause to flow of very heavy current then diode may damage or fired. To protect diode from this fuse are used. They are connected in parallel of each diode. When a fault current occurs it diverted it due to its small resistance.

The anode & cathode are mentioned in the box. It is divided into two parts & diode is settled in between of the parts. The diode is works as a bridge in between them. The terminal of anode & cathode is as a blade type. The parts of box are made of iron plates. the current I travels from one parts plates & then diode, the diode is rectify it & then it goes to another parts. After rectifying the supply it is given to the traction motor which are basically a DC series motor.

10. FAILURE OF FUSE

When the current due to fault is very heavier & crosses the rating of fuse then the fuse’s contact is opened up. Due to which supply is cutoff so the equipments of loco are safe. The fuse winding are in a box so a mentor is unable to see the fuse whether it us damage or not. So a indicator is holded upon the surface of fuse it is near the blade type terminals. When the fuse is blown out the red pin comes up which means the fuse is damaged. When the fuse is in use that pin is inside the surface of fuse but when the fuse is blown out the pin is comes upon the surface which indicates the person that the fuse will not under the use & you have to maintain it to drive the loco safely. The indicator is shown in the red circle of the given figure.

11. MAINTENANCE OF FUSE

When fuse is blown out the indicator indicates that by pin mounted on the surface of fuse. The pin comes outside the surface of fuse that means the fuse not more usable. So for the safe drive of train that’s the equipments will not be damaged it has to replace by some another fuse. So maintenance of fuse is done by replacing it by another fuse. The damaged fuse will not rectified again so that we can not use it again means when a fuse is damaged it can not be repaired by anyhow. So the only thing which is possible is replacing that fuse by another new fuse.

12. Reference

http:// www.google.co m http://www.wordwebonline.com/en/Fitment of Relay http://www.construction-dictionary.com/definition/ lubricating pin.htm l http://sites.google.com/site/downloadfreeprojects/fitment of Relay-failure

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