Nonlinear Resistor

#Channel1

Before we proceed, We should have clear view about linearity.
What is linearity?
A graph which holds linear graphical picture i.e how current changes due to voltage, Its linearity.
Then what is linear resistor?
When output is propotional to Input, i.e linear condition. When a resistance resists current to flow in presence of a electrical potential force, we call it a kind of electric circuit. Here input is voltage and output is current.
Now, If we get linear graphical picture of V-I curve, then we say, that element is linear resistance.

Those elements whose V-I curves are not straight lines are called nonlinear elements because their resistance are nonlinear resistance e.g. incandescent lamp, varistors , thermistors and diodes etc.

Incandescent lamps :
Let me explain with an example. The cold resistance of a 100 w incandescent lamp is about 9.5 ohms. If that resistance stayed same with 120 V potential applied, according [like us on facebook]to ohm's law, the bulb would draw about 12.5 amp with 1500 watt(power dissipation). But hot resistance of tungsten becomes 144 ohms(15 times the cold resistance). The resulting current is 0.83 amps with 100 watt(power dissipation). So here we come to the conclusion that when tenperature is increased, resistance increases highly.

Varistors :
A varistors is an electronic component with an electrical resistance that varies with the applied voltage. It is a voltage dependent metal-oxide material whose resistance decreases sharply with increasing voltage. There is a corresponding rapid decrease in resistance when the current increases. So it is used to provide over voltage protection.
The zinc-oxide based varistors are primarily used for protecting solid-state power supplies from low and medium surge voltage in the line. And silicon-carbide varistors provide protection against high-voltage surge.

Thermistors:
   A thermistors is a type of resistors whose resistance is dependent on temperature, more so than in standard resistors. Thermistor is made of metallic oxides in a suitable binder and has a large negative coefficient of resistance i.e its resistance decreases with increase in tempt.

Diodes:
    In electronics, a diodes is a two-terminal electronic component that conducts primarily in one direction, It has low resistance to the current in one direction and high resistance in the other. It has also a non-linear graph. When voltage continue increases, current increases high suddenly.
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Basic Idea of Temperature Coefficient and increase/decrease in resistance due to Temperature

#Channel1

A resistor's  tempt. coefficient of resistance tells you how much its value changes as its temperature changes.
unit = ohm /ohm°C

                   #Check_Fig_here.

R(0) = Resistance of the material at 0°C
R(t) = Resistance of the material at t°C

Increase in Resistance depends upon
¡) initial resistance
¡¡) rise in tempt.
¡¡¡) on thr nature of the material.

#Alpha signs denotes temperature co-efficient of resistance normally.

wiki source :
Alpha (uppercase Α , lowercase α; Ancient Greek :
άλφα, álpha , modern pronunciation álfa ) is the
first letter of the Greek alphabet . In the system
of Greek numerals it has a value of 1. [dont forget to like, follow and support facebook.com/thecurrentblogelectrical for more]

α=[ dR/ R(0) ]x t
where dR = R(t) - R(0)

Theoretically, at -t tempt., the resistance should be vanished, but in actual at-234.5°C (easy to remember,look again), it never meet zero, it departs from a straight line at very low tempt.
see figure.
So The second part now.

Question is, Why does electrical resistance increase as tempt. increases?
- Resistance of the conductor changes with change in size of the conductor as well as temperature.

Some says, as tempt. increases, the dimension of the conductor will expands or contracts and that is the reason behind change of resistance in material. It is actually misconception.
lets read! Those material,about which, we are talking in this post are classified into two groups
1. Resistance increases with increase in temperature.
2. Resistance decreases with increase in tempt.
Most of the metals are belongs to the the first one and insulators are from second.
The reasons for these changes can be explained by considering the flow of current(actually electron) through that material. Electron are negatively charged particles and will be attracted by positive atoms and repelled by negative charged electrons. So when a electric potential is applied, the free electrons tends to flow into the material and start to flow in time. Now Temperature is increased.
The effect of increase in temperature in material is to make the atoms vibrate and vibrate violently as tempt increases more. In a conductor which already has large amount of electron will make collision between electrons and vibrated atom. As a result, some kinetic energy of electron may fall and that vibration [ dont forget to like and follow and support us facebook.com/thecurrentblogelectrical for more] increases the resistance of that metal body.
Whereas, in insulators free electrons are quietly less than metal. Almost all the electrons are tightly bound within their particular atom. Increase in tempt. sufficiently vibrates the atoms and enough to actually shake some of the their captive electrons free.
So the resistance of Insulator material falls due to increase in tempt.
I have a question for you here.
What happen to electrolyte when tempt. increase? tell us in comment section.
P.S.
In a material where the resistance increases with an increase in tempt., the material is said to have a POSITIVE TEMPERATURE COEFFICIENT( e.g. Copper Cu).
When resistance decreases with an increase in tempt., the material is said to have a NEGATIVE TEMPERATURE COEFFICIENT(e.g. Semi-Conductors).

Important Resistor Materials

#channel1

Tungsten
W-wolfram Atomic Number-74

1. Hard Metal

2. It can be drawn into very thin wires.

3. Melting point 3422°C

4. Used as filaments in incandescent lamps, and in electron tubes and also in heater.

Carbon
C atm no 6
Graphite 90% of carbon coal coke charcoal etc

1. High resistivity about 4600 micro ohm.cm

2. Negative tempt. Coefficient of resistance.

3. Pressure sensitive resistance material and has low surface friction.

4. This oxidised at about 300°C and is very weak.

5. Used as brush in electrical machines.

6. As components in electronics and communication equipments.

Nichrome
Nickel 75-78% chromium 20-30% manganese 1.5% and iron(balance)

1. Its resistivity is high.

2. Temperature coefficient of resistance is low.

3. Withstands high tempt for a long time.

4. Used as electric iron coil, furnace and heating elements.

Manganin
Copper 80% manganese17-18% nickel 1.5-2%

1. Resistivity 0.49 to 0.50 micro ohms.m

2. Low tempt. Coefficient of resistance(0.00015)

3. Melting point is 1020°C

4. Specific gravity is 8.19

5. Used for instruments shunts and for standard resistance.

Constantan
Copper 60% nickel 40%

1. It does not rust or corrode due to air , heat and moisture.

2. Resistivity is 49 micro ohm.cm

3. Specific gravity is 1.9

4. Melting point is 1300°C

5. Used for different types of rheostats, resistance wires, resistance boxes, arc lamps, motor starters, supporting wires for electric filaments.

Platinum
Pt atm no 78

1. It is non corroding.

2. Resistant to most chemicals.

3. Can be drawn into thin wires and strips.

4. Melting point 1775°C

5. Resistivity 10.5 micro ohm.cm

6. No oxidation.

7. Used for heating element in laboratory ovens and furnaces.

8. Used for platinum-rhodium thermocouples measurement of upto 1600°C.

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What will happen if DC is provided to primary of transformer?

Basically, transformer windings
are designed with specified value of impedence
that they have, now most part of the impedence
is contributed by inductance. In case of DC we
dont have capacitive and inductive effect in
concern anymore, the only opposition to the flow
is made by resistance which is small. Now high
currents will flow through the primary windings
and windings will burn out. They do so because
they are designed for ac specification in case of
dc they can't handle such high currents due to
less resistance offered.

Why lower order harmonics are more hazardous than higher order harmonics in a power system?

Let me explain. Actually, when we
talk harmonics we talk about a signal that is
multiple of fundamental frequency. As frequency
increases the inductive reactance also increases
as it is given by Xl=2πfl. As harmonic multiples
increase the overall opposition to them also
increases due to reason stated earlier. Harmonics
having frequency multiple close to fundamental
frequency are more dangrous as they get less
inductive reactance to their flow and produce
greater magnitude than higher order hamonics.

Asked by #ameer

How can we distinguish between Current & Potential transformer physically?

if it already connected then ct is always in series
and pt is always in parallel , a wire cnnectd
towards earth i think.
Potential has high resistance with
it, so if it not connected we can measure it by it.
CT has either phase or nuetral
through it or in series and there is no ground
connection. In case og PT the ptential difference
is concern so is connected in parallel with phase
and ground.

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Answered by #aMeer.

What is cogging phenomenon in induction motor, what are the causes of cogging and how to eliminate this bug?

locking of induction rotor due to tooth harmonics
(caused by specific relation between no. of stator
and rotor tooths). due to this motor fails to
rotate and can be avoided by skewing of rotors in
cage type rotors ( not a phenomonen in slipring
induction motor)
If rotor and stator slots are equal
then cogging is likely to happen.
Harmonics is the 2nd reason, you
are right.
Lastly, if rotor slots are exactly
parallel to the rotor shaft axis then also it cause
cogging. These slots or copper bars inserted in
them are angled or skewed to let the fields cut
each other. Hence torque is produced there.

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Why Asian countries transmit power at 50 Hz but Europe and America are doing so at 60 Hz?

It can be explained in terms of
these three factors 1)Cost factor 2)Temperature
rise and 3)Device design.
The distributed capacitance and inductance are directly
proportional to frequency along the length of
transmission line. Losses increase when
frequency increases, asian countries are not that
strong economically to let these losses happen or
cost factor to increase. Next asian countries have
hot weather conditions and frequency increase
will cause tepmreature rise and global warming
can occur so higher frequency is avoided. West
mostly experiences winter season so they keep
frequency a bit higher to nuetralize the effect.
Thirdly it is upto the devices and appliances
design that matters.

Answered by #ameer
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Why did earth pin larger than other pins ?

It depends upon R=ρL/A where area (A) is
inversely proportional to resistance (R), so if
area (A) increases, R decreases & if R is less
the leakage current will take low resistance path
so the earth pin should be thicker.
It is longer because the The First to make the connection
and last to disconnect should be earth Pin. This
assures Safety for the person who uses the
electrical instrument.

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Index

Index

#Channel1
- Maximum Power Transfer Theorem
- Millman's Theorem
- Superposition Theorem
- KCL & KVL
- Independent source and dependent source.
- Circuit's Word( bilateral,linear,loop, mesh, node etc.)
- Current Divider Rule and Voltage divider Rule
- Nonlinear Resistor
- Basic idea of temperature coefficient and increase/decrease in resistance due to temperature
- Important Resistor Materials
- Resistors
- Ohm's Law
- Conductors (Cu,Al,Ni etc.)

#Channel2

- Current Limiting Reactors
- Fuse Part 5
- Fuse Part 4
- Fuse Part 3
- Fuse Part 2
- Fuse Part 1

#MindOfMorning

1. What is danerous voltage or Current? (D.C circuit)

2. Why domestic appliances are connected in parallel? (D.C circuit)

3. What will happen if dc is provided to primary of transformer? ( Transformer)

4. Why lower order harmonics are more hazardous than higher order harmonics in a power system? (Harmonics)

5. How can we distinguish between Current Transformer and Potential Transf. physically?( Instrument Transformer)

6. What is Cogging phenomenon in induction motor? What are the causes of Cogging? And how to eliminate Cogging? (Induction Motor)

7. Why Asian countries transmit power at 50 Hz but Europe and America are doing so at 60 Hz.?( Transmission and Distribution)

8. Why did Earth pin larger than other pins? (House Wiring)

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Current Limiting Reactors

#Channel2

#Old name : Current Limiting  Coil.
#Inventor : Vern E. Alden

Current limiting reactors or series reactors. Actually it is a large inductive reactance(X part) + small resistance (R part)
Current limiting reactors are series connected to the transmission/distribution line or to the feeder in order to limit the short circuit power on the load side of the reactor. The reactor limits the short circuit currents to a level which can be handled by the components installed in the electrical system( e.g. breakers,fuse,switches).
Due to linear inductance characteristics over the current range the full reactor impeadance is also maintained during system fault conditions.
Current limiting reactors is limited to large power station. Their cost is comperatively more for small power station than a suitable circuit breaker.
Its fully clear that, the short circuit current are reduced by an increase of the percentage reactance(%x) of the system.
[  percentage reactance %x = (Ix/V)*100  ]

#Why_we_need_a_reactor?

In large interconnected system, total rating of the alternators are high. When short circuit occurs, oviously short circuit current starts to flow at a high rate. For this current, suitable circuit breaker is also expensive. So we want to limit the fault current to a lower value to use a low rating circuit breaker.
So we use current limiting reactors.

#Advantage¶¶
protect apparatus from excessive mechanical stress, and overheating.

#Disadvantage¶¶
Inductive reactance becomes more. So more lag happens. Thus regulation becomes poor.

Reactors Rating:
• Continuous rated current(Irms, can      carry continuous without any   problem)
•• Rated short time current
••• Rated voltage

#design Features of Current limiting reactors:

When current reaches a high value, its reactance should not decrease on account of saturation under short circuit conditions. When fault current is so high the iron core should have large cross sectional area and it makes the reactors costly and heavy. In this place, we can use air core reactors or iron core with air gap.

#Types_of_reactors

• Shielded- designed for indoor and outdoor service, high thermal capacity, laminated iron shields or copper shields for support,oil cooled.
•• Unshielded- designed for outdoor service, upto 33 kv, concrete are used for mechanical support, air cooled.

Position Wise Classification
° Generator reactor
°° Feeder reactor
°°° Busbar reactor

#Difference between shunt and series reactors
Shunt Reactors helps us to reduce the receiving end voltage which attained a high value for ferranti effect. Series Reactors limits the short circuit value.

#Reactors_measured_in_KVA_or_MVA.
From this rating we get maximum power rating, the device can handle without burning.
Same goes with the shunt capacitor banks.
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Read about Fuse.

Resistors

#channel1

Type of resistors :

a) Carbon Composition-
^^^^^^^^^^^^^^^^^^^^^^^^^
          It is a combination of carbon particles and a binding resin with different proportions for providing desired resistance.
They are available in power ratings of 1/8, 1/4, 1/2 ,1 and 2 W.
and their voltage ratings are of 250, 350 and 500 V.
This kind of resistors have a tendency to produce electrical noise due to the current passing from one particle to another.

b) Deposited Carbon-
^^^^^^^^^^^^^^^^^^^^^^

           It consists of ceramic rods which have a carbon film deposited on them. They have a ceramic rod in a mithane filled flask which is heated until a carbon film is deposited on them.

    
c) High-Voltage Ink film-
   ^^^^^^^^^^^^^^^^^^^^^^^
   range : 1 kiloohm to 100000 Megaohm with voltage range upto 1000 kv.
It consists of a ceramic base on which a special resistive ink is laid down in a helical band.

d) Metal film-
^^^^^^^^^^^^^
    made by depositing vaporized metal in vacuum on a ceramic rod. Suitable for high grade applications.

e) Metal Glaze-
^^^^^^^^^^^^^^
   consists of a metal glass mixture which is applied as a thick film and then fired to form a film.
range : 1 ohm to Megaohm

f) Wire-wound -
^^^^^^^^^^^^^^^
       high stability and highest power rating.
Because of their bulk, high-power ratings and high cost, they are not suitable for low cost or high density, limited-space applications.

g) Cermet(ceramic metal)-
^^^^^^^^^^^^^^^^^^^^^^^^^^^
       made by firing certain metals added with ceramic sub-strate.
Resistance value depends on the type of mix and how thick it is. Those are usually used in PCB(printed circuit board).

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Ohms law

#Channel1

It deals with Voltage and Current in an ideal conductor(called ohmic or linear). This relationship states that the potential difference across an ideal conductor is propotional to the current through it. i.e when potential is applied , a current will be there and it comes in propotional rate.
Ohm's law is given by, V=I.R
R = Resistance (constant of propotionality)
for some work, if g is the conductance of a material
g=1/R, In this form, I=g.V
#ohmic or #linear- material that obeys ohm's law is called ohmic or linear because potential difference across it varies linearly with current.
V=W/q
(In a circuit there is 1 volt difference from a to b i.e. equal to a gain of 1 joule for 1 coulomb of charge moved from a to b)

I= is the flow of electrical charge and is a way to count the charge that cross a section every second.
I=dq/dt,
So,now, ohm's law states that if R is small than is like going in vacation following a large highway. A lot of charge will move very fast even if energy gain is little. In the other hand, If resistance is big than is like going in vacation following a small road, not many charge will move not very fast even if the energy gain is constant.

Conductors (Cu, Al, Ni etc)

#Channel1

COPPER (Cu-Atomic no.29)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
• Highly sensitive to impurities.
• Malleable and ductile with very               high thermal and electrical conductivity.
• Resistivity =1.72 x 10 to the pwr -8 Ω·m
• Electrical Conductivity =59.6 x 10^6 s/m
• Specific gravity  8.9
• Melting point 1084° C
• Magnetic ordering : diamagnetic
• The maximum permissible current density of copper in open air is app. 3.1 x 10^6 A/sq.m of cross sectional area, above which it begins to heat excessively.

Aluminium(Al, third most abundant element after oxygen and silicon, atm. no. 13)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
• Resistivity 2.6 x 10^-8 Ω·m
• Melting point 658°C
• Specific Gravity 2.7
• Cheif ore Bauxite
• Magnetic Ordering - Paramagnetic
• Low density and its ability to resist corrosion through the phenomenon of passivation, It is remarkable for those two reasons. • A thin surface layer of Aluminium oxide forms when it is exposed to air, prevention further oxidation.
• Soft, Durable, Light Weight, Ductile, and Malleable.

Brass(Cu-60 Zn 40)
^^^^^^^^^^^^^^^^^^^^^^^
• High tensile strength, lower conductivity, ductile, high resistance to corrosion.
• Relatively low melting point 900 to 940°C
• Specific gravity 3.3
• Resistivity 7.5 x 10^-8 Ω·m
• Melting Point 840°C

Bronze(Cu88%+tin12%)
^^^^^^^^^^^^^^^^^^^^^^^^^^
• Hard and brittle
• Corrosion Resistance is better than Brass.
• Alpha bronze alloys of 4-5% tin,  are used to make turbines, blades etc
• Plastic bronze _ bronze with #lead content which makes far improved plasticity.

Mercury( Hg, atm no 80)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
• Expands and contracts in Regular degree.
• Resistivity 95.8 x 10^-8 Ω·m
• Oxidation takes place at tempt. more than 300° C
• Melting Point =  -38°C
• Specific gravity: 13.5
• Magnetic ordering diamagnetic.

Silver(Ag, Atm no. 47)
^^^^^^^^^^^^^^^^^^^^^^^^
• Not affected to weather change.
• Used for HRC fuse element, radio frequency conducting bodies
• Resistivity 1.65x 10^-8 Ω·m
• Melting Point 961°C
• Magnetic Ordering diamagnetic.

Zinc(Zn, atm no 30)
^^^^^^^^^^^^^^^^^^^^^^^
• Resistivity 59.0 nΩ·m(at 20°C)
• Magnetic Ordering diamagnetic

Nickel(Ni, atm no 28)
^^^^^^^^^^^^^^^^^^^^^^^
• Hard and brittle
• Melting point 1455°C
• Electrical Resistivity 69.3 nΩ·m(at 20°C)
• Magnetic Ordering Ferromagnetic

Tin(Sn, atm no 50)
^^^^^^^^^^^^^^^^^^^^^
• Melting point 231°C
• Electrical resistivity 115 nΩ·m at 0°C
•• Magnetic ordering -
               • gray : diamagnetic
               • white : Paramagnetic

Molybodenum(Mo, atm no 42)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
• Melting point 2623°C
• Specific gravity 10.28
• Electrical Resistivity 53.4 nΩ·m(at 20°C)
• Magnetic ordering :  Paramagnetic

Why domestic appliances are connected in parallel?

The whole matter is analogus to driving on a road. If you are driving a car on road and suddenly you find it closed due to some maintenance stuff. You will be blocked. It is same as series circuit. A single fault in series circuit may collapsed the whole.
        In a house, if a appliances is turned on or off, it should not affect the other. This is only possible if all appliances were connected individually to the supply i.e. Parallel Circuit. When appliances are connected in series, each of them can not be put on and off independently. Also, theoratically, If appliances were wired in series, the potential difference across each of them would vary depending on the resistances or impedances.

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Fuse part 5

#Channel2

Previous part1 part2 part3 part4
Fuse Characteristics
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The action of fuse is based upon the heating effect of current. Larger the current, the more rapidly the fuse will blow and save their circuit and equipment from unnecessary problem. It has #Inverse_time_characteristics (When large current flows, It takes less time to melt than for a small Current). This characteristics helps it to use in overload purpose.

#Selection_of_fuse: • For Short circuit protection, the fuse elements must be with a good margin for temporary overloads.
• Speed of operation- It depends upon how much current flows through it and depends upon the material of fuse element.
The operating time is not fixed, but decreases as current increases(Inverse Time Characteristics)
• SemiConductor devices need a fast blow or ultra fast blow fuse because a small excessive current can damage the device easily. Normally fast blow fuses are the most general purpose fuses.
•  Time delay fuse can continue with a small high current for a while. (It is used in motor)
• The fuse element must not be damaged by minor harmless surges of current and must not oxidise or change its behaviours after use for several years.
• It should withstand the transient surge due to switching in and out.

#Difference_between_fuse_and_CircuitBreaker
¡) fuse - fast operation. (0.001 or 0.002 sec)
   CB - comperatively slow. (0.1 to 0.2 sec)

¡¡) fuse - when it melts, you must change it
    CB- you can reset it, when fault clears totally.

¡¡¡) fuse is cheap and possibly of failure is Nil.
      CB is expensive and a small defect in trip mechanism can damage it fully.
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Fuse Part 4

#channel2

[to read previous parts part1 part2 part3]
#Terms related to fuse

#Rated_Current : It is the maximum current which the fuse can carry without any heating or melting. It depends upon fuse element material,temperature rise and deterioration of the fuse by oxidation.
#Fusing_Current : It is the maximum current at which the fuse elements melts and disconnects the circuit. It is more than the rated current. If rated current is 5A, then 5A can easily flow through the fuse without heating but fusing current will be more than 5A.
if fusing current = I
k = constant depends upon metal of wire
d= diameter of fuse element
then, I = k.  d to the power (3/2)

#Fusing_factor: Ratio of fusing current to rated current.
for rewirable fuse it is 2 for copper.

#Prospective_Current: r.m.s value of the first loop of the fault current is called prospective current.

#Cut_off_Current: value of current reached before the fuse melts. Depends upon ¡) prospective current
¡¡) current rating of the fuse.

#pre_arcing_time: It is the time between time of fault occurs and instant of fuse melts.( 0.001 sec)

#arcing_time: it is the time taken from the instant of arc started to the instant of arc extinguished.

#BreakingCapacity_or_RupturingCapacity: It is the maximum current that can safely be interrupted by the fuse. This should be higher than the prospective current. Fuses for high voltage equipment, upto 115000 volts, are rated by the total apparent power(MVA) of the fault level in the circuit.

#Melting_ i square t
- is propotional to the total energy required to begin melting the fuse element.
#Clearing_ i square t
- is propotional to the total energy let through by the fuse when clearing a fault.
#Rated voltage- Rated voltage should be higher than the maximum voltage source. A fuse rated at 32 volts would not reliably interrupt current from a voltage source of 120 volts. If it is used, an arc is formed and plasma inside the glasstube(if it is glass tube fuse) may continue to conduct current.
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Fuse Part 3

#channel2

[ to read previous parts
Click part 1 & part 2]

#Desirable_Character_of_fuse_element.
   • low melting point
             - because you would like a wire that responds to current flow without heating up too much thus avoiding a fire hazard.
  •   High Conductivity.
  •   Free from deterioration due to oxidation.
  •   Low cost.
Low melting point material comes with high specific resistance and with higher mass.
High melting point material comes with low specific resistance and with low mass.
Oxidation of fuse element(e.g. copper and iron) tends to generate an outer layer which may be strong enough to support the metalic core of fuse element when it is in molten state.
Part1 Part2  Part3 Part4  Part5
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Fuse Part 2

#channel2

[to read previous part. Click on part1]

#Fuse_element
A fuse consisting of a fuse element mounted between a pair of electrical terminals and usually enclosed by a non-combustible housing. It is the part of the fuse which melts when excessive current flows through it. At normal current, the fuse element can dissipate heat easily. But at higher current,it will melt due to excessive heat produced in it.
The fuse element must not be damaged by minor harmless surges of current and must not oxidize or change its behaviour after possibly years of service.

Large fuse has more than one metal strips.
A dual element of fuse has two strips, one is for short circuit and another for overload value.
The most commonly used fuse elements are lead,tin,copper,zinc,silver.
Upto 15A alloy of lead(37%) and tin(63%) is used as fuse element. For larger currents tinned copper or silver is used.
Most Low Voltage fuse elements are made of copper.
Fuse elements of fast acting fuses and high voltage fuses are primarily made of silver. Silver plated copper is also commonly used.
As a rule, fuse elements of time delay fuses contain low melting point materials e.g. tin, zinc and alloys there of. Formerly used alloys containing ead and Cadmium have widely been eliminated.
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Fuse (Part-1)

#channel2

#What_is_fuse?
Fuse is a sacrificial device used in a circuit(connected in series) for protecting electrical equipments from short circuits,overloading,mismatched loads or device failure.

#Type - Passive

#WorkingPrinciple - Melting of internal conductor due to heat generated by excessive current flow.

#ADS - Automatic Disconnection of supply (sometimes it is called by --)

#Inventor - A fuse was patented by Thomas Edison in 1890 as part of his electric distribution system.

#External Body - may be made of ceramic, glass, plastic, fiberglass, molded mica laminates or molded compressed fibre depending on application and voltage.
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What is dangerous Voltage or Current?

⚡Have You Ever notice a signboard with 

       ⚠
high Voltage !!
warning!!
danger!!
Ofcourse you have.

Old saying says,
Volt_Jolts_Amp_kills

lets Start. You know Van de Graaff generator . It is able to produce very high voltages, for example, upto 50,000 volts. When someone touches the dome of the generator, it will cause just hair to stand.
Touching the generator is not so dangerous because current is low here. Current is what provides energy to the load. As you pointed out before, ohm's law ties current and voltage together. But a person is not a linear resistor. There are some factor like- frequency, points of current entry and exit etc. So in simple, If there is no charge moving through your body, then you are not going to suffer any harm, absolutely safe. On the other side of coin, a transformer with 220 volt secondary can kill you easily if you touch it because it will force a high current into your body. Low voltage and high current sources can also be dangerous in a different way. A car battery, with just 12-13 volts, is delivering 50-100 amp current. This is more than enough to start a fire. So here we comes to conclusion, high voltage can kill you obviously when it will able to produce a high current through your body and same for the low voltage. Like a 6 V battery can produce just a little current, so you can not get a high shock from it. So power is working behind single 'voltage' word or single 'current' word.
Anyway,
Be Careful While Working On Electrical Appliances…

•Body Resistance :
  ¡) 500 ohm for wet skin
     ¡¡) 100 kOhm if skin is dry.

• Permissible Current For human body
     ¡) 6 mA for 3 sec (for female )
        ¡¡) 9 mA for 3 sec (for  male)
• 10 mA A.C. can Cause muscle contraction.
• More Than 30 mA will cause cardiac arrest.
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