MINOR PROJECT REPORT ON “AUTOMATIC PHASE CHANGER” Submitted in the partial fulfillment of the requirement For the award of the degree ofBachelor of Technology In Electronics & Communication Engineering From KURUKSHETRA UNIVERSITY, KURUKSHETRA Guided By: Miss. Priyanka Garg (Lecturer,ECE) Submitted To: Submitted By: Mr. Jagtar Singh Krishan Malik(1507245) Ms. Rajni Meelu Sumit Kumar(1507246) Anil Kumar (1508823) Department of Electronics & Communi cation Enginee ring. N. C. College of Engineering Israna (Panipat) (July-Dec. 2010)
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We are very happy on the completion of the Minor Project “AUTOMATIC PHASE
CHANGER ”. For this we would like to thank our Project guide “Ms. Priyanka Garg”
under whose visionary enlightenment we were able to complete this project.We would also like to acknowledge the help and support by Ms. Priyanka Garg who
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 sameway 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 breakdownAvalanche 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 and exhibits a positive temperature coefficient. In a
5.6 V diode, the two effects 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. Modern manufacturing techniques have
produced devices with voltages lower than 5.6 V with negligible temperature
coefficients, but as higher voltage devices are 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 marketedunder the umbrella term of "Zener diode".
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 RectifiersABSTRACT: International Rectifier's new series of Ultra-fast recoverydiodes 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
There are really only two fundamentally different operatingprinciples: (1) electromagnetic attraction, and (2)electromagnetic induction. Electromagnetic attraction relaysoperate by virtue of a plunger being drawn into a solenoid,or an armature being attracted to the poles of anelectromagnet. Such relays may be actuated by d-c or by a-c
quantities.Electromagnetic-induction relays use the principle of theinduction motor whereby torqueis developed by induction in a rotor; this operating principleapplies only to relays actuated by alternating current, and indealing with those relays we shall call them simply"induction-type" relays.
DEFINITIONS OF OPERATION
Mechanical movement of the operating mechanism isimparted to a contact structure toclose or to open contacts. When we say that a relay"operates," we mean that it either closes or opens itscontacts-whichever is the required action under thecircumstances. Most relays have a "control spring," or arerestrained by gravity, so that they assume a given position
when completely de-energized; a contact that is closedunder this condition is called a "closed" contact, and onethat is open is called and "open" contact. This isstandardized nomenclature, but it can be quite confusingand awkward to use. A much better nomenclature in ratherextensive 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 illustratedin Fig. 1. Even though an ÒaÓ contact may be closed undernormal operating conditions, it should be shown open as in
Fig. 1; and similarly,even though a ÒbÓ contact may normally be open, it shouldbe shown closed.When a relay operates to open a ÒbÓ contact or to close anÒaÓ contact, we say that it "picks up," and the smallestvalue of the actuating quantity that will cause suchoperation, as the quantity is slowly increased from zero, iscalled the "pickup" value. When a relay operates to close aÒbÓ 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, butdoes not reset, we say that it "drops out," and the largestvalue of the actuating quantity at which this occurs is calledthe "drop-out" value.
To allow for the two supply voltages mains transformers usually have two
separate primary coils (windings) labelled 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):
Most mains transformers have two separate secondary coils (e.g. labelled 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 labelled 9-0-9V for example. They can be used to producefull-wave rectified DC with just two diodes, unlike a standard secondary coil
which requires four diodes to produce full-wave rectified DC.
The only trick involved in using this equation is to keep the units consistent.
Capacitance is in farads, the area “A” is in square meters and the distance
between electrodes “D” is in meters. “K” is a ratio and a pure number
without dimensions.
Sometimes different constants are used in the equation. This comes about
when units other than farads and meters are used. Microfarads and inches
might be used, for example.
To get an idea of what a farad is, calculate the area which would be
necessary in a capacitor built to have one farad, to operate in a vacuum, and
to have a spacing between electrodes of one millimeter. First, turn the
equation around to solve for the area and then plug in the values known.
This calculates to 113 million square meters, which would be a field about
6.5 miles on a side. It’s not hard to see why one farad capacitors aren’t made
very often and when they are, they are never made with a vacuum dielectricand a one millimeter spacing. Vacuum capacitors are made, but the market is
pretty well limited to laboratory standards.
All commercial capacitors use some different dielectric
material with a higher value of K.
Materials
C = (8.85 X 10 -12) K ADor A =(8.85 X 10 -12) KCDGiven: K = 1C = 1 faradD = 1 millimeter (or 0.001 meters)A = 1 x 0.001 = 113,000,000 sq. meters(8.85 X 10 -12) x 1
An electrical fuse is a current interrupting device which protects an electrical
circuit in which it is installed by creating an open circuit condition inresponse 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 metalcannot 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 inautomobiles, 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
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 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.
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 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. Fuses of the relatively flat, plug in type which have a
fuse link encapsulated in a plastic fuse body with a pair of terminal legs
extending from the body have become very popular, especially in
automotive applications. One commonly used type of automotive fuse takes
the form of a pair of parallel blade type contacts with the fusable portionconstituting a bridge between the two blades. Blade type fuses are
increasingly used in automobile equipment, for the purposes of space
requirements, protective qualities and ease of plugging in. Blade type fuses
generally comprise an insulating case or body in which is partially mounted
a conductive unit constituted by two connection terminal blades joined
together by a fuse link element or gauging part. The fusable link is encased
The pnp transistor works essentially the same as the npn transistor.
However, since the emitter, base, and collector in the pnp transistor are made
of materials that are different from those used in the npn transistor, differentcurrent carriers flow in the pnp unit. The majority current carriers in the
pnp transistor are holes. This is in contrast to the npn transistor where the
majority current carriers are electrons. To support this different type of
current (hole flow), the bias batteries are reversed for the pnp transistor. A
typical bias setup for the pnp transistor is shown in figure 1.
Notice that the procedure used earlier to properly bias the npn transistor also
applies here to the pnp transistor. The first letter ( p) in the pnp sequence
indicates the polarity of the voltage required for the emitter (positive), and
the second letter (n) indicates the polarity of the base voltage (negative).
Since the base-collector junction is always reverse biased, then the opposite
polarity voltage (negative) must be used for the collector. Thus, the base of
the pnp transistor must be negative with respect to the emitter, and the
collector must be more negative than the base. Remember, just as in the case
of the npn transistor, this difference in supply voltage is necessary to have
current flow (hole flow in the case of the pnp transistor) from the emitter to
the collector. Although hole flow is the predominant type of current flow in
the pnp transistor, hole flow only takes place within the transistor itself,
while electrons flow in the external circuit. However, it is the internal holeflow that leads to electron flow in the external wires connected to the
Figure 2: The forward-biased junction in a pnp transistor .
pnp Forward-Biased Junction
Now let us consider what happens when the emitter-base junction is forward
biased. With the bias setup shown, the positive terminal of the battery repels
the emitter holes toward the base, while the negative terminal drives the base
electrons toward the emitter. When an emitter hole and a base electron meet,they combine. For each electron that combines with a hole, another electron
leaves the negative terminal of the battery, and enters the base. At the same
time, an electron leaves the emitter, creating a new hole, and enters the
positive terminal of the battery. This movement of electrons into the base
and out of the emitter constitutes base current flow (IB), and the path these
electrons take is referred to as the emitter-base circuit.
pnp Reverse-Biased Junction
In the reverse-biased junction (figure 3), the negative voltage on the
collector and the positive voltage on the base block the majority current
carriers from crossing the junction.
However, this same negative collector voltage acts as forward bias for the
minority current holes in the base, which cross the junction and enter the
The interaction between the forward- and reverse-biased junctions in a
pnp transistor is very similar to that in an npn transistor, except that in the pnp transistor, the majority current carriers are holes. In the pnp transistor
shown in figure 4, the positive voltage on the emitter repels the holes toward
the base. Once in the base, the holes combine with base electrons. But again,
remember that the base region is made very thin to prevent the
recombination of holes with electrons. Therefore, well over 90 percent of the
holes that enter the base become attracted to the large negative collector
voltage and pass right through the base. However, for each electron and hole
that combine in the base region, another electron leaves the negative
terminal of the base battery (V BB) and enters the base as base current (IB). At
the same time an electron leaves the negative terminal of the battery, another electron leaves the emitter as IE (creating a new hole) and enters the positive
terminal of VBB. Meanwhile, in the collector circuit, electrons from the
collector battery (VCC) enter the collector as Ic and combine with the excess
holes from the base. For each hole that is neutralized in the collector by an
electron, another electron leaves the emitter and starts its way back to the
In three-phase applications, if lowvoltage 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
yourequipment even when correct voltage is available on a single phase inthe building.
The circuit is built around a transformer, comparator,transistor and relay. Three identical sets of this circuit, oneeach for three phases, are used. Let us now consider theworking of the circuit connecting red cable (call it ‘R’ phase).
The mains power supply phase R is stepped down bytransformer X1 to deliver 12V, 300 mA, which is rectified by
diode D1 and filtered by capacitor C1 to produce theoperating voltage for the operational amplifier(IC1). Thevoltage at inverting pin 2 of oprational amplifier IC1 is takenfrom the voltage divider circuit of resistor R1 and presetresistor VR1. VR1 is used to set the reference voltageaccording to the requirement. The reference voltage at non-inverting pin 3 is fixed to 5.1V through zener diode ZD1. Tillthe 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 itsoutput pin 6 also remains high. As a result, transistor T1does not conduct, relay RL1 remains de-energised and phase‘R’ supplies power to load L1 via normallyclosed (N/C)contact of relay RL1.
As soon as phase-R voltage goes below 200V, the voltage atinverting pin 2 of IC1 goes below reference voltage of 5.1V,and its output goes low. As a result, transistor T1 conductsand relay RL1 energises and load L1 is disconnected from
phase ‘R’ and connected to phase ‘Y’ through relay RL2.Similarly, the auto phase-change of the remaining twophases, 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 ableto 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 wiresuitable for your current requirement.2. Use good-quality relays with proper contact and currentrating.3. Mount the transformer(s) and relays on a suitable cabinet.Use a TagBlock (TB) for incoming/outgoing connections from mains.