Three phase shifter appliance

Anil Maurya
Electrical & Electronics Engineer 1
A
REPORT
ON
THREE PHASE
SHIFTER
APPLIANCE
BY
ANIL MAURYA
ELECTRICAL & ELECTRONICS ENGINEER

Anil Maurya
CHAPTER 1
INTRODUCTION
Power instability in developing countries creates a need for automation of
electrical power generation or alternative sources of power to back up the utility
supply. This automation is required as the rate of power outage becomes
predominantly high. Most industrial and commercial processes are dependent on
power supply and if the processes of change-over are manual, serious time is not only
wasted but also creates device or machine damage from human error during the
change-over connections, which could bring massive losses.
The starting of the generator is done by a relay which switches the battery
voltage to ignition coil of the generator while the main power relay switches the load
to either public supply or generator. Fig 1 shows the general-ized block diagram of
the system. The approach used in this work is the modular approach where the overall
design was first broken into functional block diagrams, where each block in the
diagram represents a section of the circuit that carries out a specific function. The
functional block diagram of Fig. 1 also shows the interconnection between these
blocks. Each section of the block is analyzed below.
A manual change-over switch consists of a manual change-over switch box,
switch gear box and cut-out fuse or the connector fuse as described by Rocks and
Mazur (1993). This change-over switch box separate the source between the generator
and public supply, when there is power supply outage from public supply, someone
has to go and change the line to generator. Thus when power supply is restored,
someone has to put OFF the generator and then change the source line from generator
to public supply.
In view of the above manual change- over switch system that involves
manpower by using ones energy in starting the generator and switching over from
public supply to generator and vice-versa when the supply is restored. The
importance attached to cases of operation in hospitals and air ports in order to save

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life from generator as fast as possible makes it important for the design and
construction of an automatic change-over switch which would solve the problem of
manpower and the danger likely to be encountered changeover. The electronic
control monitors the incoming public supply voltage and detects when the voltage
drops below a level that electrical or electronic gadgets can function depending on
the utility.

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CHAPTER 2
COMPONENT LIST
Component name Quantity
Step down transformer(220V-12V 300 mA) 3
Fuse(F1-F3=5A) 3
IC(IC1-IC3=741) 3
Transistor(T1,T2,T3=BC557) 3
Relay(RL1-RL3=12V,1C/O RELAY) 3
Zener diode(ZDI-ZD3=5.1V) 3
Variable resistance(VR1-VR3=10K) 3
Resistance(R1,R2,R4,R5,R7,R8=3.3K,R3,R6,R9=10K) 9
Diode 9
Capacitor(C1-C4=1000Uf 25v,C5- C7=470Uf 35v) 7
Wires Acc. To requirement

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CHAPTER 3
BLOCK DIAGRAM
Fig.3 Block diagram of automatic change over switch.

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CHAPTER 4
CIRCUIT DIAGRAM
Fig.4 Systematice Diagram of Phase Changer.

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CHAPTER 5
COMPONENT DESCRIPTION
5.1 COMPARATOR
The IC 741 i.e. the operational amplifier is used as a comparator in
the circuit given above. As shown in the figure the IC 741 is a 8 pin IC in
which the pin no. 2 is known as the inverting terminal of the IC 741
because it is connected to the negative potential.
The pin no. 3 is known as the non inverting terminal of the IC 741. The pin
no. 2 is connected to the reference voltage. The reference voltage is the voltage
which we set as a standard voltage in the circuit. The pin no. 2 is connected to the
input voltage. Now if we applied the input voltage to the IC
741 then it will compare the input voltage to the reference voltage and if the input
voltage goes low then the output of the comparator is goes low. And if the input
voltage is equal to the reference voltage then the output of the comparator is high.
5.2 ZENER DIODE
A Zener diode is a type of diode that permits current not only in the forward
direction like a normal diode, but also in the reverse direction if the voltage is larger
than the breakdown voltage Breakdown voltage.

Anil Maurya
Electrical & Electronics Engineer
The breakdown voltage of an Insulator is the minimum voltage that causes a
portion of an insulator to become electrically conductive. The breakdown voltage of a
diode is the minimum reverse voltage to make the diode conduct in reverse direction.
known as "Zener knee
Clarence Zener
CLEARANCE ZENER
Clarence Melvin Zener was the American physicist who first described the
electrical property exploited by the Zener diode, which Bell Labs then named after
him..., who discovered this electrical property.
A conventional solid
electronic component that conducts electric current in only one direction. The term
usually refers to a semiconductor diode, the most common ty
crystalline block of semiconductor material connected to two electrical
terminals...will not allow significant current if it is reverse
breakdown voltage. When the reverse bias breakdown voltage is exceeded, a
conventional diode is subject to high current due to avalanche breakdown. Unless this
current is limited by circuitry, the diode will be permanently damaged. In case of
large forward bias (current in the direction of the arrow), the diode exhibits a voltage
drop due to its junction built
& Electronics Engineer
n voltage of an Insulator is the minimum voltage that causes a
known as "Zener knee voltage" or "Zener voltage". The device was named after
CLEARANCE ZENER
discovered this electrical property.
A conventional solid-state diode. In electronics, a diode is a two
usually refers to a semiconductor diode, the most common type today. This is a
terminals...will not allow significant current if it is reverse-biased below its reverse
onventional diode is subject to high current due to avalanche breakdown. Unless this
drop due to its junction built-in voltage and internal resistance. The amount of the
8
n voltage of an Insulator is the minimum voltage that causes a
voltage" or "Zener voltage". The device was named after
diode. In electronics, a diode is a two-terminal
pe today. This is a
biased below its reverse
onventional diode is subject to high current due to avalanche breakdown. Unless this
in voltage and internal resistance. The amount of the

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voltage drop depends on the semiconductor material and the doping concentrations.
A Zener diode exhibits almost the same properties, except the device is
specially designed so as to have a greatly reduced breakdown voltage, the so-called
Zener voltage. By contrast with the conventional device, a reverse-biased Zener diode
will exhibit a controlled breakdown and allow the current to keep the voltage across
the Zener diode at the Zener voltage. For example, a diode with a Zener breakdown
voltage of 3.2 V will exhibit a voltage drop of 3.2 V if reverse bias voltage applied
across it is more than its Zener voltage. The Zener diode is therefore ideal for
applications such as the generation of a reference voltage (e.g. for an amplifier
Amplifier
Generally, an amplifier or simply amp, is any device that changes, usually
increases, the amplitude of a signal. The relationship of the input to the output of an
amplifier—usually expressed as a function of the input frequency—is called the
transfer function of the amplifier, and the magnitude of... stage, or as a voltage
stabilizer for low-current applications.
The Zener diode's operation depends on the heavy doping.
Doping (semiconductor)
In semiconductor production, doping is the process of intentionally
introducing impurities into an extremely pure semiconductor to change its
electrical properties. The impurities are dependent upon the type of semiconductor.
Lightly and moderately doped semiconductors are referred to as extrinsic...of its p-
n junction
P-n junction
A p–n junction is formed by joining p-type and n-type semiconductors
together in very close contact. The term junction refers to the boundary
interface where the two regions of the semiconductor meet...allowing electron

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Electron
The electron is a subatomic particle carrying a negative electric charge. It has
no known components or substructure, and therefore is believed to be an elementary
particle. An electron has a mass that is approximately 1/1836 that of the proton. The
intrinsic angular momentum of the electron is as to tunnel from the valence band of
the p-type material to the conduction band of the n-type material. In the atomic scale,
this tunneling corresponds to the transport of valence band electrons into the empty
conduction band states; as a result of the reduced barrier between these bands and
high electric fields that are induced due to the relatively high levels of dopings on
both sides. The breakdown voltage can be controlled quite accurately in the doping
process. While tolerances within 0.05% are available, the most widely used
tolerances are 5% and 10%. Breakdown voltage for commonly available zener diodes
can vary widely from 1.2 volts to 200 volts.
Another mechanism that produces a similar effect is the avalanche effect as
in the avalanche diode
Avalanche diode
An avalanche diode is a diode that is designed to go through avalanche
breakdown at a specified reverse bias voltage and conduct as a type of voltage
reference..... The two types of diode are in fact constructed the same way and both
effects are present in diodes of this type. In silicon diodes up to about 5.6 volts, the
Zener effect is the predominant effect and shows a marked negative temperature
coefficient. Above 5.6 volts, the avalanche effect
Avalanche breakdown
Avalanche breakdown - is a phenomenon that can occur in both insulating
and semiconducting materials. It is a form of electric current multiplication that can
allow very large currents to flow within materials which are otherwise good
insulators. It is a type of electron avalanche.- Explanation... becomes predominant

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and exhibits a positive temperature coefficient. In a 5.6 V diode, the two effects
occur together and their te
the 5.6 V diode is the component of choice in temperature
Modern manufacturing techniques have produced devices with voltages lower than
5.6 V with negligible temperature coef
encountered, the temperature coefficient rises dramatically. A 75 V diode has 10
times the coefficient of a 12 V diode.
All such diodes, regardless of breakdown voltage, are usually marketed
under the umbrella term of "Zener diode".
occur together and their temperature coefficients neatly cancel each other out, thus
the 5.6 V diode is the component of choice in temperature-critical applications.
5.6 V with negligible temperature coefficients, but as higher voltage devices are
times the coefficient of a 12 V diode.
rm of "Zener diode".
Fig. Characterstics of Zener Diode
11
mperature coefficients neatly cancel each other out, thus
critical applications.
ficients, but as higher voltage devices are

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5.3 DIODE
Symbol
Diode Function
Diodes allow electricity to flow in only one direction. The arrow of the circuit
symbol shows the direction in which the current can flow. Diodes are the electrical
version of a valve and early diodes were actually called valves.
Forward Voltage Drop
Electricity uses up a little energy pushing its way through the diode, rather like
a person pushing through a door with a spring. This means that there is a small
voltage across a conducting diode, it is called the forward voltage drop and is about
0.7V for all normal diodes which are made from silicon. The forward voltage drop of
a diode is almost constant whatever the current passing through the diode so they have
a very steep characteristic (current-voltage graph).
Reverse Voltage
When a reverse voltage is applied a perfect diode does not conduct, but all real
diodes leak a very tiny current of a few µA or less. This can be ignored in most
circuits because it will be very much smaller than the current flowing in the forward
direction. However, all diodes have a maximum reverse voltage (usually 50V or
more) and if this is exceeded the diode will fail and pass a large current in the reverse
direction, this is called breakdown.

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Diode Construction
The physical construction of a diode with a diffusion junction is shown in the
figure below. When a diode is reverse biased ie. a positive voltage is
cathode with respect to the anode, an electric field is formed between the cathode and
anode specifically across the depletion region. The diode is 'reverse biased' and cannot
conduct except for small leakage currents. However, if the electr
strong 'avalanche breakdown' occurs and the diode will become a short circuit and
often be damaged. To counteract this the physical distance between the anode and
cathode is increased by increasing the size of the bulk region and chang
atom doping levels.
Fig. V-I Characterstics of Diode
Diode Construction
figure below. When a diode is reverse biased ie. a positive voltage is
conduct except for small leakage currents. However, if the electric field becomes too
cathode is increased by increasing the size of the bulk region and chang
13
figure below. When a diode is reverse biased ie. a positive voltage is applied to the
ic field becomes too
cathode is increased by increasing the size of the bulk region and changing impurity

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In the construction process, N type silicon substrate heated to ~1000oC in
presence of vapour containing positive charged impurity atoms. P region diffused into
N region. The resultant effect is to cause more charge carriers to be present within the
diode when it is conducting. For the diode to switch OFF, the charge carriers must
either recombine (minority) or be removed, the latter mechanism appearing as a
reverse current (reverse recovery) flowing in the diode as it turns OFF. Put simply,
diodes with higher voltage ratings have larger bulk regions, require more time to
remove internal charges at turn OFF and are thus slower switching.
Standard Rectifiers
Rectifiers are electronic high voltage diodes, which allow current to flow in
only one direction. Essentially, they act as one-way valves, and are used to convert
AC current to DC current. The performance of high voltage diodes is determined by
a number of voltage, current and time coefficients:
VRRM: Maximum Reverse Voltage, which is the maximum reverse voltage of
the diode.
VF: Forward Voltage, which is the voltage across the diode terminals
resulting from the flow of current in the forward direction.
IR: Reverse Current flows when reverse bias is applied to a semiconductor
junction.

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trr: Reverse Recovery Time is the time required for the current to reach a
specified reverse current (IR) after instantaneous switching from a specified forward
condition (IF).
IF: Forward Current is the current flowing through the diode in the direction
of lower resistance.
Tj: Junction Operating Temperature is the range of temperatures in which the
high voltage diodes are designed to operate.
Fast Rectifiers
Figure 3a and b show typical styles of reverse recovery. The area within the
negative portion of each curve, , is the total reverse recovery charge Qrr and
represents the charge removal from the junction and the bulk regions of the diode and
is effectively independent of the forward current in the diode. The recovery time t2 -
t1 is dependant on the size of the bulk region thus high di/dt currents can be obtained
when using fast diodes. If the di/dt of the snap recovery is too high and stray
inductance exists in the circuit then extremely high and possibly damaging voltage
spikes can be induced.
(Note: ). Qrr can be found from manufacturers specifications thus the
maximum reverse recovery current Irr is given by:
If ta is very small compared to ta then ta trr and knowing the rate of decrease of
current di/dt = Irr/ta Irr/trr leads to:
Figure 3:
(a) Reverse recovery of a general purpose diode, (b) fast diode. Reverse recovery
time trr = t2 - t0.

Anil Maurya
Electrical & Electronics Engineer& Electronics Engineer 16

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The effect of reverse recovery on the output voltage of a rectifier feeding a resistive
load is shown in figure 4.
Figure 4: Bridge rectifier output voltage showing diode reverse recovery effects.
Ultra Fast Rectifiers
ABSTRACT: International Rectifier's new series of Ultra-fast recovery diodes
are aimed specifically at the 12/24/48V SMPS output stage, and extend the company's
current product range of Ultra-fast recovery diodes with industry standard part
number products. The new product series has been developed to meet today's
requirement of high frequency operation and power ratings, using a technology
platform flexible enough to match the performance improvement curve of the market
requirements in the years to come. The new IR Ultra-fast recovery diode series (200-
400V) adopts platinum diffusion in order to overcome the limitation of gold diffusion
and the electron irradiation technology. With this approach, the best trade off for
leakage current, forward voltage drop and reverse recovery, has been achieved with a
maximum operating junction temperature of 175 degrees Celsius and a reverse
recovery time as low as 15-20ns. With this type of performance, the maximum
allowable switching frequency for this Ultra-fast diode family would be up to 500-
750kHz. This assumption is verified.
by the diode loss calculation used for the IR MUR1620 operating in a typical
output rectification in a forward converter..

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5.4 RELAY
OPERATING PRINCIPLES
There are really only two fundamentally different operating principles: (1)
electromagnetic attraction, and (2) electromagnetic induction. Electromagnetic
attraction relays operate by virtue of a plunger being drawn into a solenoid, or an
armature being attracted to the poles of an electromagnet. Such relays may be
actuated by d-c or by a-c quantities.
Electromagnetic-induction relays use the principle of the induction motor
whereby torque is developed by induction in a rotor; this operating principle applies
only to relays actuated by alternating current, and in dealing with those relays we
shall call them simply "induction-type" relays.
DEFINITIONS OF OPERATION
Mechanical movement of the operating mechanism is imparted to a contact
structure to close or to open contacts. When we say that a relay "operates," we mean
that it either closes or opens its contacts-whichever is the required action under the
circumstances. Most relays have a "control spring," or are restrained by gravity, so
that they assume a given position when completely de-energized; a contact that is
closed under this condition is called a "closed" contact, and one that is open is called
and "open" contact. This is standardized nomenclature, but it can be quite confusing
and awkward to use. A much better nomenclature in rather extensive use is the
designation ÒaÓ for an "open" contact, and ÒbÓ for a "closed" contact. This
nomenclature will be used in this book.
The present standard method for showing "a" and ÒbÓ contacts on connection
diagrams is illustrated in Fig. 1. Even though an ÒaÓ contact may be closed under
normal operating conditions, it should be shown open as in Fig. 1; and similarly, even
though a ÒbÓ contact may normally be open, it should be shown closed.
When a relay operates to open a ÒbÓ contact or to close an ÒaÓ contact, we
say that it "picks up," and the smallest value of the actuating quantity that will cause
such operation, as the quantity is slowly increased from zero, is called the "pickup"

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value. When a relay operates to close a ÒbÓ contact, or to move to a stop in place of a
ÒbÓ contact, we say that it "resets"; and the largest value of the actuating quantity at
which this occurs, as the quantity is slowly decreased from above the pickup value, is
called the "reset" value. When a relay operates to open its ÒaÓ contact, but does not
reset, we say that it "drops out," and the largest value of the actuating quantity at
which this occurs is called the "drop-out" value.

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TRANSFORMER
A transformer consists of two coils (often called 'windings') linked by an iron
core, as shown in figure 1. There is no electrical connection between the coils, instead
they are linked by a magnetic field created in the core.
Transformers are used to convert electricity from one voltage to another with
minimal loss of power. They only work with AC (alternating current) because they
require a changing magnetic field to be created in their core.
Transformers can increase voltage (step-up) as well as reduce voltage (step-down).
Alternating current flowing in the primary (input) coil creates a continually
changing magnetic field in the iron core. This field also passes through the
secondary (output) coil and the changing strength of the magnetic field induces an
alternating voltage in the secondary coil. If the secondary coil is connected to a load
the induced voltage will make an induced current flow. The correct term for the
induced voltage is 'induced electromotive force' which is usually abbreviated to
induced e.m.f.
The iron core is laminated to prevent 'eddy currents' flowing in the core.
These are currents produced by the alternating magnetic field inducing a small
voltage in the core, just like that induced in the secondary coil. Eddy currents waste

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power by needlessly heating up the core but they are reduced to a negligible amount
by laminating the iron because this increases the electrical resistance of the core
without affecting its magnetic properties.
Transformers have two great advantages over other methods of changing voltage:
1. They provide total electrical isolation between the input and output, so they
can be safely used to reduce the high voltage of the mains supply.
2. Almost no power is wasted in a transformer. They have a high efficiency
(power out / power in) of 95% or more.
Mains transformers are the most common type. They are designed to reduce
the AC mains supply voltage (230-240V in the UK or 115-120V in some countries)
to a safer low voltage. The standard mains supply voltages are officially 115V and
230V, but 120V and 240V are the values usually quoted and the difference is of no
significance in most cases.
To allow for the two supply voltages mains transformers usually have two
separate primary coils (windings) labeled 0-120V and 0-120V. The two coils are
connected in series for 240V (figure 2a) and in parallel for 120V (figure 2b). They
must be wired the correct way round as shown in the diagrams because the coils must
be connected in the correct sense (direction):

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Most mains transformers have two separate secondary coils (e.g. labeled 0-
9V, 0-9V) which may be used separately to give two independent supplies, or
connected in series to create a centre-tapped coil (see below) or one coil with double
the voltage.
Some mains transformers have a centre-tap halfway through the secondary
coil and they are labeled 9- 0-9V for example. They can be used to produce full-wave
rectified DC with just two diodes, unlike a standard secondary coil which requires
four diodes to produce full-wave rectified DC.
A mains transformer is specified by:
1. Its secondary (output) voltages Vs.
2. Its maximum power, Pmax, which the transformer can pass, quoted in VA
(volt-amp). This determines the maximum output (secondary) current, Imax...
...where Vs is the secondary voltage. If there are two secondary coils the
maximum power should be halved to give the maximum for each coil.
3. Its construction - it may be PCB-mounting, chassis mounting (with solder

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tag connections) or toroidal (a high quality design).
STEP DOWN TRANSFORMER
If the first coil has more turns that the second coil, the secondary voltage is
smaller than the primary voltage:
This is called a step-down transformer. If the second coil has half as many
turns as the first coil, the secondary voltage will be half the size of the primary
voltage; if the second coil has one tenth as many turns, it has one tenth the voltage.
In general:
Secondary voltage ÷ Primary voltage = Number of turns in secondary ÷
Number of turns in primary
The current is transformed the opposite way—increased in size—in a step-
down transformer:
Secondary current ÷ Primary current = Number of turns in primary ÷ Number
of turns in secondary
So a step-down transformer with 100 coils in the primary and 10 coils in the
secondary will reduce the voltage by a factor of 10 but multiply the current by a factor
of 10 at the same time. The power in an electric current is equal to the current times
the voltage (watts = volts x amps is one way to remember this), so you can see the
power in the secondary coil is theoretically the same as the power in the primary coil.
(In reality, there is some loss of power between the primary and the secondary

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because some of the "magnetic flux" leaks out of the core, some energy is lost
because the core heats up, and so on.

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5.6 FUSE
An electrical fuse is a current interrupting device which protects an electrical
circuit in which it is installed by creating an open circuit condition in response to
excessive current. The current is interrupted when the element or elements which
carry the current are melted by heat generated by the current. Fuse terminals typically
form an electrical connection between an electrical power source and an electrical
component or a combination of components arranged in an electrical circuit. A fusible
link is connected between the fuse terminals, so that when electrical current flowing
through the fuse exceeds a predetermined limit, the fusible link melts and opens the
circuit through the fuse to prevent electrical component damage.
A standard fuse is a one time use device that must be replaced after an
overload condition has been cleared because the thin strip or ribbon of metal
cannot be rejoined after it has melted through. Over-current protection may be
provided by fuses as well as by circuit breakers, switches, relays and other devices.
Each type of equipment has variations in ratings, service requirements and costs.
Fuses generally present the most cost-effective means for providing automatic high-
voltage current protection against a single over-current failure. Most types of fuses are
designed to minimize damage to conductors and insulation from excessive current.
Fuses are employed in many electrical systems that are used by people on an everyday
basis. For example, fuses are part of electrical systems found in automobiles, boats,
motorcycles and other vehicles. These fuses function to stop electricity from flowing
to a particular component of the system by creating an open circuit as a result of an
unsafe electrical condition.
Fuses are typically employed in the electrical utility industry to protect
distribution transformers, cables, capacitor banks and other equipment from damaging
overcurrents. The fuses are arranged to disconnect the faulted equipment or circuit
promptly from its source of supply before damage can occur. Fuses are used
extensively in high voltage electrical networks in order to protect the electrical
equipment in the network from damage caused by surges through the system,

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generally occasioned by short-circuits or overloads. Fuses are used as necessary to
protect semiconductors. Safety fuses that basically can be electrically connected in
series with the semiconductor power elements require special installation space and
the construction expense that goes along with it. They add electrical series resistance,
which results in current-dependent heat loss.
Fuses are very important in protecting circuitry from overload conditions.
Fuses are devices which, by melting of one or more of their parts intended and
designed for this purpose, open the circuit by interrupting the current if the current
exceeds a predetermined value for a sufficiently long period of time. They are
designed to blow open at predetermined current levels and are selected based upon
safety specifications designated for a particular circuit.
The fusible element or fuse link is intended to melt away under the influence
of a current which exceeds a particular value for a particular length of time.
There are thermal fuses, mechanical fuses, spark gap surge arrestors, varistors,
and other similar devices, each designed specifically as a solution to one or more
extreme electrical events. Each device provides benefit in particular situations that
may be greater than other types of devices. In general, an electrical fuse combines
both a sensing and interrupting element in one self-contained device and is direct
acting in that it responds only to a combination of magnitude and duration of current
flowing through it. The fuse normally does not include any provision for making or
breaking the connection to an energized circuit but requires separate devices to
perform this function.
A fuse is a single-phase device, such that only the fuse in the phase or phases
subjected to overcurrent will respond to de-energize the affected phase or phases of
the circuit that is faulty. After having interrupted an overcurrent, it is replaced to
restore service. Currently, two basic types of fuses are employed, the expulsion fuse
and the current limiting fuse. Each type employs a fusible element designed to melt
when a current of a predetermined magnitude and duration passes through the
element. The expulsion type fuse interrupts overcurrents through the deionizing action

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of gases that are liberated when the fusible element melts. An expulsion fuse typically
employs a relatively short length of a fusible element contained within a tubular
enclosure that is part of a larger assembly known as a fuseholder. The enclosure used
in the expulsion type fuse is lined with an organic material. Interruption of an
overcurrent takes place within the fuse by the deionizing and explosive action of the
gases which are liberated when the liner is exposed to the heat of the arc that is
created when the fusible element melts in response to the overcurrent. The operation
of the expulsion-type fuse is characterized by loud noise and violent emission of
gases, flame and burning debris, all of which pose a danger to personnel who may be
in close proximity to the fuse when it operates. Because of its violent mode of
operation, this type of fuse has generally been restricted to outdoor usage only. The
current-limiting type interrupts overcurrents when the arc that is established by the
melting of the fusible element is subjected to the mechanical restriction and cooling
action of a sand filler that surrounds the fusible element.
A current-limiting fuse typically consists of one or more silver wire or ribbon
elements of a required length which are electrically connected at their ends to a pair of
electrical terminations. The assembly is placed in a tubular housing that is made of a
highly temperature-resistant material, and the housing is then typically filled with
high-purity silica sand and sealed.
Electrical fuses have taken many forms and generally comprise fuses having a
fusible link extending between a pair of terminal portions.
The fusible link may be provided either with notches cut in one or more sides
of the fusible portion or with holes formed therethrough to create narrower and
therefore weaker portions within the fusible portion. One of the more common types
of fuses is the thermal fuse (electrothermal fuse). In the thermal fuse, electrical
current flowing through the fuse causes the fuse to heat. The current path within a
typical fuse is through the end caps or ferrules to a metallic fusible element. The
resistance of the fusible element develops heat that causes a portion of the metal to
melt or disintegrate upon reaching the melting temperature of the metal. This property
is exploited to achieve accurate thermal activation of a fuse in response to a particular

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level of overload current. In normal operation, the temperature of the device remains
relatively low and the resistance of the device also remains low.
When an overload current flows through the device, the internal temperature
of the fuse rises sufficiently to cause the fuse to electrically open. An alloy type
thermal fuse is widely used as a thermo-protector for an electrical appliance or a
circuit element, for example, a semiconductor device, a capacitor, or a resistor. Such
an alloy type thermal fuse has a configuration in which an alloy of a predetermined
melting point is used as a fuse element, the fuse element is bonded between a pair of
lead conductors, a flux is applied to the fuse element, and the flux-applied fuse
element is sealed by an insulator.
A time delay fuse is a type of fuse that is designed to allow temporary and
harmless currents to pass there through without triggering the fuse.
Time delay fuses are used in connection with equipment having temporary
current surges, such as motors and transformers. Time delay fuses often employ a
fusible element and a spring-loaded heat mass. A deposit of solder retains the heat
mass from movement by the spring. The dimensions of the fusible element are
selected such that it melts quickly under short-circuit conditions. Time delay fuses are
typically used in circuits subject to temporary transients such as motor starting
currents. A typical high-voltage, current-limiting fuse comprises a tubular insulating
housing, an elongated core within the housing, and one of more fusible elements
wound about the core and connected between terminals at opposite ends of the
housing. A core is needed in fuses of this type rated at 5 KV and above in order to
enable the fuse to accommodate the required length of fusible element within a
housing of practical length. The fuse housing materials may consist of glass, ceramic,
porcelain, and glass-filament-wound epoxy tubing. Copper ferrules or sand cast caps
are typically glued to the ends of the fuse body with an epoxy or pressed onto the fuse
housing with an interference fit to form end enclosures. A card type fuse is suitable
for use in various devices having a low electrical power of less than 1A. For example,
such a fuse is suitable for fuse-matching in a wire harness composed of wires having a

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small diameter, and which connects a series of electronic elements in a car. In such
fields, utilization of card type fuses has been increasing.
Solid state fuses are also known in which transistors and thyristors are placed in series
with the load and turn off in response to a load fault condition. Fuses are commonly
used in automotive electrical systems to protect circuits against damage caused by
overload conditions. Fuses for various circuits are often grouped together at clustered
locations where circuit junctions exist in a fuse box, power distribution block, or
junction block. Many automotive vehicles are equipped with a fuse junction box
which serves to hold a plurality of fuses associated with the various electrically
powered devices of the vehicle. A typical automotive fuse has a generally rectangular
plastic body with a pair of parallel, blade-like fuse terminals extending therefrom.
The outer surface of the fuse box is provided with fuse sockets to allow the
fuse terminals to be inserted into electrical engagement with the circuit terminals,
thereby completing and fuse-protecting the associated circuits. Typical fuse boxes are
connected to the positive pole of the motor vehicle battery via one or more cables
leading to the fuse box whereat power is supplied to a plurality of fuses contained
within the box. The ends of the fuses opposite the end connected to the positive
terminal of the battery generally are connected to outgoing cables or cable strands to
supply power to electrical consumers such as, for example, motor vehicle lighting
systems, sensors and switches, and power accessories. Generally, the type of fusion of
fuses used for protecting an electric circuit in an automobile or the like is classified
into the fusion in a high current region and the fusion in a low current region.

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CHAPTER 6
WORKING
In three-phase applications, if low voltage is available in any one or two
phases, and you want your equipment to work on normal voltage, this circuit will
solve your problem. However, a proper-rating fuse needs to be used in the input lines
(R, Y and B) of each phase. The circuit provides correct voltage in the same power
supply lines through relays from the other phase where correct voltage is available.
Using it you can operate all your equipment even when correct voltage is available on
a single phase in the building.
The circuit is built around a transformer, comparator, transistor and relay.
Three identical sets of this circuit, one each for three phases, are used. Let us now
consider the working of the circuit connecting red cable (call it ‘R’ phase).
The mains power supply phase R is stepped down by transformer X1 to
deliver 12V, 300 mA, which is rectified by diode D1 and filtered by capacitor C1 to
produce the operating voltage for the operational amplifier(IC1). The voltage at
inverting pin 2 of operational amplifier IC1 is taken from the voltage divider circuit of
resistor R1 and preset resistor VR1. VR1 is used to set the reference voltage
according to the requirement. The reference voltage at non-inverting pin 3 is fixed to
5.1V through zener diode ZD1. Till the supply voltage available in phase R is in the
range of 200V -230V, the voltage at inverting pin 2 of IC1 remains high, i.e., more
than reference voltage of 5.1V, and its output pin 6 also remains high. As a result,
transistor T1 does not conduct, relay RL1 remains de-energized and phase ‘R’
supplies power to load L1 via normally closed (N/C) contact of relay RL1.
As soon as phase-R voltage goes below 200V, the voltage at inverting pin 2

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of IC1 goes below reference voltage of 5.1V, and its output goes low. As a result,
transistor T1 conducts and relay RL1 energizes and load L1 is disconnected from
phase ‘R’ and connected to phase ‘Y’ through relay RL2.
Similarly, the auto phase-change of the remaining two phases, viz, phase ‘Y’ and
phase ‘B,’ can be explained. Switch S1 is mains power ‘on’/’off’ switch.
Use relay contacts of proper rating and fuses should be able to take-on the
load when transferred from other phases.
While wiring, assembly and installation of the circuit, make sure that you:
1. Use good -quality, multi-strand insulated copper wire suitable for your
current requirement.
2. Use good -quality relays with proper contact and current rating.
3. Mount the transformer(s) and relays on a suitable cabinet. Use a Tag
Block (TB) for incoming/outgoing connections from mains

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CHAPTER 7
APPLICATION
1.Residential.
2.Commercial offices.
3.Factories operating with 1 phase machineries.
4.Hospitals/Banks.
5.Institutions.
It automatically supplies voltage in case of power failure or low voltage in up
to 2 of the 3 incoming phases. Automatic Phase Changer automatically cuts supply
during low voltage thus, protects equipment from the harmful effects of unhealthily
low voltage.

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REFERENCES
1. “TRANSFORMER BASED DC MOTOR SPEED CONTROL”
http://www.electronicsmaker.com/em/admin/pdf/free/transformer.pdf
2. Relay Information and datasheet.
http://www.atmel.com/images/relay_l_datasheet.pdf
3. Information and Data Sheet PT7C5027 series Crystal Oscillator
http://www.pti-ic.com/new/manage/doc_datasheet/PT0276%20PT7C5027-5.pdf
4. Information and data sheet of NPN Transistor 2N2222 Discrete Semiconductors
http://www.csus.edu/indiv/t/tatror/projects/met%20highway%20safety%20project%2
02010/npn%20transistor.pdf
5. Sourceforge.net, “WINAVR”.
http://winavr.sourceforge.net/
6. Introduction to Pulse Width Modulation (PWM) by Michael Barr, author of
Programming Embedded Systems in C and C++ ‘07/02/2003’
http://www.oreillynet.com/pub/a/network/synd/2003/07/02/pwm.html?page=last&x-
maxdepth=0
7. Joerg Wunsch, “AVRDUDE”
http://www.nongnu.org/avrdude/user-manual/avrdude.html
8. .http://en.wikipedia.org/wiki/
9. www.google.com/images

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