THREE PHASE FAULT ANALYSIS WITH AUTO RESET
ABSTRACT:
This paper to develop an automatic tripping mechanism for the three phase
supply system. The project output resets automatically after a brief interruption in the
event temporary fault while it remains in tripped condition in case of permanent fault.
The electrical substation which supply the power to the consumers, have failures due to
some faults which can be temporary or permanent. These faults lead to substantial
damage to the power system equipment. In India it is common, The faults might be LG
(Line to Ground), LL (Line to Line), 3L (Three lines) in the supply systems and these
faults in three phase supply system can affect the power system. To overcome this
problem a system is built, which can sense these faults and automatically disconnects the
supply to avoid large scale damage to the control gears in the grid sub-stations.
This system is built using three single phase transformers which are wired in star
input and star output, and 3 transformers are connected in delta connections, having input
220 volt and output at 12 volt. This concept low voltage testing of fault conditions is
followed as it is not advisable to create on mains line. 555 timers are used for handling
short duration and long duration fault conditions. A set of switches are used to create the
LL, LG and 3L fault in low voltage side, for activating the tripping mechanism. Short
duration fault returns the supply to the load immediately called as temporary trip while
long duration shall result in permanent trip.
CHAPTER I
INTRODUCTION
1.1 1.1 Background
In this chapter, it explains briefly on the background and system overview of
this project. Also in this chapter it explains the objectives of the project, the scope of
study and the thesis outline.
1.2 System Overview
An electromagnetic or induction instrument used to indicate the phase sequence in threephase electric circuits. The phase sequence determines the direction of rotation of threephase electric motors; the correct operation of some measuring instruments and automatic
control devices also depends on the phase sequence. Phase-sequence indicators are
usually constructed as miniature asynchronous electric motors in which an aluminum
disk serves as the rotor. The disk rotates when acted upon by a magnetic field excited by
currents in three windings when the windings are connected to the conductors of the
circuit being tested. A certain order of phase sequence is marked on the terminals of the
phase-sequence indicator. If the disk rotates in the direction of an arrow marked on the
disk, the phase sequence corresponds to the marks on the terminals of the instrument.
General-purpose phase-sequence indicators can be used to determine the power factor
and the phase shift between voltage and current.
In indicator there is a led light source. It gives us the presence of the current
source by indicate its light. If the phase of the indicator is not equal to the supply voltage
then it can not give us the presence of current source by its led light off. If the phase of
indicator is equal with the mane supply phase then its remaining bright and continuous
gives us the indication of current source.
Phase sequence' is the order, or sequence, in which each of the line voltages of a
three-phase system reach their peak values. If 'normal' phase sequence is considered to be AB-C
(or
R-S-T,
etc.),
then
'reverse
phase
sequence'
would
be
A-C-B.
Phase sequence detection and controlled power supply system provide mainly used to detect
the phase sequence of any machine or any other electrical equipment which works on three
phase supply.
In this system the extra feature we introduced is controlling of supply voltage. We can also
say that the over voltage and under voltage protection is also introduced in this system.
As we know that in three phase supply there is three phase r y b. It is mandatory that
these three phase are in correct order, because if it is not in correct manner than there is
damage in windings of machines.
Machine whose phase sequence is to be detect is connected to the input of our system, now if
the phase sequence is correct the array of green led’s ring are glowing in clock wise
direction. When the sequence is wrong than the array of red led’s ring is glowing in anti
clock wise direction.
If the voltage of input is less than the required one, means that when under voltage condition
comes on that time the system is amplify the input voltage and comes it to the normal voltage
range. Than the phase sequence detection is starts.
If the input voltage is much over than the required range, means that when over voltage
condition come on that time system trip the ckt. Means that cut out the supply by the use of
relay, and we protect our equipments. So our main aim is to provide a simpler and efficient
system which gives a better phase sequence detection, in comparison of conventional lamp
method and synchronoscope method.The best use of this system in sub-station, where after
maintenance of m/c it is very difficult to connect the right phase r y b. So at that place we
easily used this system.
Phase sequence is very important if, for example, you want to ensure that your
three-phase motors rotate in the correct direction. So, after disconnecting them for
maintenance, you can confirm the phase sequence of your incoming conductors by using
a phase-sequence meter, before you reconnect that motor.
In a three-phase ac system, a power source with three wires delivers ac potentials of equal
frequency and amplitudes with respect to a zero-potential wire, each shifted in phase by
120° from one wire to the next. Two possibilities exist for establishing a phase sequence.
In the first, voltage on the second wire shifts by 120° relative to the first, and, in the
second, a –120° shift occurs with respect to the first wire. Phase order determines the
direction of rotation of three-phase ac motors and affects other equipment that requires
the correct phase sequence: a positive 120° shift. You can use a few low-cost passive
components to build a phase-sequence indicator.
1.3 Objectives
The objective of this project is to indicate the order of succession in time off the different
voltage peaks of a multiphase supply. In addition the knopp sequence indicaor enables
one to make continuity tests. It is valuable instrument in diverse fields involving
polyphase power apparatus, being employed by line and installations crews for public
utility systems and industrial plant electrical departments. It is, furthermore, helpful in the
testing department of public utility systems for laboratory and field testing.
Various studies have shown that anywhere from 70%, to as high as 90%, of faults
on most overhead lines are transient. A transient fault, such as an insulator flashover, is a
fault which is cleared by the immediate tripping of one or more circuit breakers to isolate
the fault, and which does not recur when the line is re-energized. Faults tend to be less
transient (near the 80% range) at lower, distribution voltages and more transient (near
the90% range) at higher, sub transmission and transmission voltages. Lightning is the
most common cause of transient faults, partially resulting from insulator flashover from
the high transient voltages induced by the lightning.
Other possible causes are swinging wires and temporary contact with foreign objects.
Thus, transient faults can be cleared by momentarily de-energizing the line, in order to
allow the fault to clear.Autoreclosing can then restore service to the line.
The remaining 10 - 30% of faults are semi-permanent or permanent in nature. A
small branch falling onto the line can cause a semi-permanent fault. In this case,
however, an immediate de-energizing of the line and subsequent auto reclosing does not
clear the fault. Instead, a coordinated time-delayed trip would allow the branch to be
burned away without damage to the system. Semi-permanent faults of this type are likely
to be most prevalent in highly wooded areas and can be substantially controlled by
aggressive line clearance programs. Permanent faults are those that will not clear upon
tripping and reclosing.
An example of a permanent fault on an overhead line is a broken wire causing a
phase to open, or a broken pole causing the phases to short together. Faults on
underground cables should be considered permanent. Cable faults should be cleared
without auto reclosing and the damaged cable repaired before service is restored. There
may be exceptions to this, as in the case of circuits composed of both underground cables
and overhead lines.
Although auto reclosing success rates vary from one company to another, it is
clear that the majority of faults can be successfully cleared by the proper use of tripping
and auto reclosing. This de-energizes the line long enough for the fault source to pass and
the fault arc to de-energize, then automatically recloses the line to restore service. Thus,
autoreclosing can significantly reduce the outage time due to faults and provide a higher
level of service continuity to the customer. Furthermore, successful high-speed reclosing
auto reclosing. on transmission circuits can be a major factor when attempting to
maintain system stability. For those faults that are permanent, auto reclosing will reclose
the circuit into a fault that has not been cleared, which may have adverse affects on
system stability (particularly at transmission levels).
VOLTAGE REGULATOR
The LM78XX/LM78XXA series of three-terminal positive regulators are
available in the TO-220/D-PAK package and with several fixed output voltages, making
them useful in a Wide range of applications. Each type employs internal current limiting,
thermal shutdown and safe operating area protection, making it essentially indestructible.
If adequate heat sinking is provided, they can deliver over 1A output Current. Although
designed primarily as fixed voltage regulators, these devices can be used with external
components to obtain adjustable voltages and currents.
Fig1 (a) Block diagram of voltage regulator
It has some features:
• Output Current up to 1A.
• Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V.
• Thermal Overload Protection.
• Short Circuit Protection.
• Output Transistor Safe Operating Area Protection
CHAPTER II
BLOCK DIAGRAM
FIG 1. BLOCK DIAGRAM OF 3 PHASE FAULT DECTECTION
The project is designed to check the sequence of the 3 phase supply. It is very
important to know the phase sequence particularly for 3 phase motors. For example, if
the 3 phase motor is used for pumping action, any phase reversal accidentally resulting
in wrong sequence could force the motor run in the wrong direction. This could result
in dry run of the motor to develop permanent fault.
In this project direct 3-phase AC supply 50Hz is fed through voltage drop
arrangement duly stabilized by zener diodes to a logic circuit comprising of NAND
gates and OR gates to detect the proper sequence of RYB by series of pulses of fixed
duration.
In the event of changing the sequence from RYB to say YBR, the combination of
NAND and OR gates develops an output with a missing pulse during the fixed time
duration. This pulse is used in triggering a monostable 555 timer. Thus, while the
sequence is not there the triggering to the timer is missed which is indicated by an
LED driven from the output of the 555 timer. DC requirement of the circuit is powered
from a step down transformer along with a bridge rectifier and filter capacitor.
Further this project can be enhanced by providing an inbuilt digital sequence checker
comprising of LEDs in a circle to indicate wrong sequence by glowing of LEDs in anticlockwise direction. The LEDs can be driven from a programmable microcontroller
WORKING PRINCIPLE:
The project uses 6numbers step-down transformers for handling the entire circuit under
low voltage conditions of 12v only to test the 3 phase fault analysis. The primaries of 3
transformers are connected to a 3 phase supply in star configuration, while the secondary
of the same is also connected in star configuration. The other set of 3 transformers with
its primary connected in star to 3 phase have their secondary’s connected in delta
configuration.
The outputs of all the 6 transformers are rectified and filtered individually and are
given to 6 relay coils. 6 push buttons, one each connected across the relay coil is meant to
create a fault condition either at star i.e. LL Fault or 3L Fault. The NC contacts of all the
relays are made parallel while all the common points are grounded. The parallel
connected point of NC are given to pin2 through a resistor R5 to a 555 timer i.e. wired in
monostable mode. The output of the same timer is connected to the reset pin 4 of another
555 timer wired in astable mode. LED’S are connected at their output to indicate their
status.
The output of the U3 555 timer from pin3 is given to an Op-amp LM358 through
wire 11 and d12 to the non inverting input pin3, while the inverting input is kept at a
fixed voltage by a potential divider RV2. The voltage at pin2 coming from the potential
divider is so held that it is higher than the pin3 of the Op-amp used as a comparator so
that pin1 develops zero logic that fails to operate the relay through the driver transistor
Q1.
This relay Q1 is ‘3CO’ relay i.e. is meant for disconnecting the load to indicate fault
conditions.
Operating procedure:
While the board is powered from a 3phase supply all the 6 relay coils get DC voltage and
their common point disconnects from the NC and moves on to the NO points there by
providing logic high at pin2 of 555 timer U1 i.e. that is kept on monostable mode.
While any push button across the relay is pressed it disconnects that relay and in
the process in common contacts moves to the NC position to provide a logic low at
trigger pin of 555 timer to develop an output that brings the U3 555 timer which is used
in astable mode for its reset pin to high such that the astable operation takes place at its
output which is also indicated by flashing D11 LED.
If the fault is off temporary in nature i.e. if the push button pressed is released
immediately the U1 monostable disables U3 the output of which goes to zero in the event
of any push button kept pressed for a longer duration the monostable output provides a
longer duration active situation for U3 the astable timer the output of which charges
capacitor C13 through R11 such that the output of the comparator goes high that drives
the relay to switch off three phase load.
The output of Op-amp remains high indefinitely through a positive feedback
provided for its pin1 to pin3 through a forward biased diode and a resistor in series. This
results in the relay permanently switched on to disconnect the load connected at its NC
contacts permanently off. In order to maintain the flow of DC supply the star connected
secondary set DC’S are paralleled through D8, D9 & D10 for uninterrupted supply to the
circuit voltage of 12v DC and 5v DC derived out of voltage regulator IC 7805.
HARDWARE TESTING
1. Conductivity Test:
In electronics, a continuity test is the checking of an electric circuit to see if
current flows (that it is in fact a complete circuit). A continuity test is performed by
placing a small voltage (wired in series with an LED or noise-producing component such
as a piezoelectric speaker) across the chosen path. If electron flow is inhibited by broken
conductors, damaged components, or excessive resistance, the circuit is "open".
Devices that can be used to perform continuity tests include multi meters which
measure current and specialized continuity testers which are cheaper, more basic devices,
generally with a simple light bulb that lights up when current flows.
An important application is the continuity test of a bundle of wires so as to find the two
ends belonging to a particular one of these wires; there will be a negligible resistance
between the "right" ends, and only between the "right" ends.
This test is the performed just after the hardware soldering and configuration has
been completed. This test aims at finding any electrical open paths in the circuit after the
soldering. Many a times, the electrical continuity in the circuit is lost due to improper
soldering, wrong and rough handling of the PCB, improper usage of the soldering iron,
component failures and presence of bugs in the circuit diagram. We use a multi meter to
perform this test. We keep the multi meter in buzzer mode and connect the ground
terminal of the multi meter to the ground. We connect both the terminals across the path
that needs to be checked. If there is continuation then you will hear the beep sound.
Power ON Test:
This test is performed to check whether the voltage at different terminals is
according to the requirement or not. We take a multi meter and put it in voltage mode.
Remember that this test is performed without ICs. Firstly, if we are using a transformer
we check the output of the transformer; whether we get the required 12V AC voltage
(depends on the transformer used in for the circuit). If we use a battery then we check if
the battery is fully charged or not according to the specified voltage of the battery by
using multimeter.
Then we apply this voltage to the power supply circuit. Note that we do this test
without ICs because if there is any excessive voltage, this may lead to damaging the ICs.
If a circuit consists of voltage regulator then we check for the input to the voltage
regulator (like 7805, 7809, 7815, 7915 etc) i.e., are we getting an input of 12V and a
required output depending on the regulator used in the circuit.
EX: if we are using 7805 we get output of 5V and if using 7809 we get 9V at output pin
and so on. This output from the voltage regulator is given to the power supply pin of
specific ICs. Hence we check for the voltage level at those pins whether we are getting
required voltage. Similarly, we check for the other terminals for the required voltage. In
this way we can assure that the voltage at all the terminals is as per the requirement.
TRIPPINNG CIRCUIT BLOCK DIAGRAM
The project is designed to check the sequence of the 3 phase supply. It is very important
to know the phase sequence particularly for 3 phase motors. For example, if the 3 phase
motor is used for pumping action, any phase reversal accidentally resulting in wrong
sequence could force the motor run in the wrong direction. This could result in dry run of
the motor to develop permanent fault.
In this project direct 3-phase AC supply 50Hz is fed through voltage drop
arrangement duly stabilized by zener diodes to a logic circuit comprising of NAND gates
and OR gates to detect the proper sequence of RYB by series of pulses of fixed duration.
In the event of changing the sequence from RYB to say YBR, the combination of NAND
and OR gates develops an output with a missing pulse during the fixed time duration.
This pulse is used in triggering a monostable 555 timer. Thus, while the sequence is not
there the triggering to the timer is missed which is indicated by an LED driven from the
output of the 555 timer. DC requirement of the circuit is powered from a step down
transformer along with a bridge rectifier and filter capacitor.
Further this project can be enhanced by providing an inbuilt digital sequence checker
comprising of LEDs in a circle to indicate wrong sequence by glowing of LEDs in anticlockwise direction. The LEDs can be driven from a programmable microcontroller.
CHAPTER III
HARDWARE DESCRIPTION
POWER SUPPLY SECTION:
STEP DOWN
TRANSFORMER
BRIDGE
RECTIFIER
FILTER
CIRCUIT
REGULATOR
SECTION
The variable dc power supply and the main working principle of this
project is full wave rectification which is done by bridge configuration in which we are
using 4 diodes which rectifies the output of the step -down transformer which
step-down the 220 AC v to 9 AC volts .here we are usi ng a voltage regulator
which give constant voltage, here we are using 7805 which give 5 volts . Now the main
task is to get variable output for this we use the pair of voltage divider resistors to
increase the output of the regulator and in which of resistance is variable so when we
increase or d e cr e as e t he v al u e of t h a t r e si st or t h e out put vo l t a g e o f t he
r e gu l a t o r wi l l a l s o change and we get a range of 5 to 12 v , here we can’t get less
than 5 volts because of this is the output of the regulator In this circuit we use three
capacitor , c1 and c2are use to get constant input to the regulator moreover it also
help to reduce the sharp peaks in the output . connect the 0.27uF capacitor to
close to the input of the regulator and the 10uf capacitor to the output because
these capacitor reduce the noise and also help to reduce the ripples produce by the
regulator so that regulated output has less ripples.
3.1 CIRCUIT DIAGRAM
3.1.1 POWER SUPPLY CIRCUIT
CIRCUIT DIAGRAM:
CHAPTER – 3
LM78L05:
The LM78LXX series of three terminal positive regulators is available
with several fixed output voltages making them useful in a wide range of
applications.When used as a zener diode/resistor combination replacement,
the LM78LXX usually results in an effective output impedance
improvement of two orders of magnitude, and lower quiescent current.
These regulators can provide local on card regulation, eliminating the
distribution problems associated with single point regulation.The voltages
available allow the LM78LXX to be used in logic systems, instrumentation,
HiFi, and other solid state electronic equipment. The LM78LXX is available
in the plastic TO-92 (Z) package, the plastic SO-8 (M) package and a chip
sized package (8-Bump micro SMD) using National’s micro SMD package
technology.With adequate heat sinking the regulator can deliver 100 Ma
output current. Current limiting is included to limit the peak output current
to a safe value. Safe area protection for the output transistors is provided to
limit internal power dissipation. If internal power dissipation becomes too
high for the heat sinking provided, the thermal shutdown circuit takes over
preventing the IC from overheating.
Circuit Diagram:
LM78L05 Electrical Characteristics
Limits in standard typeface are for TJ = 25°C, Bold typeface applies
over 0°C to 125°C for SO-8 package and −40°C to 85°C for micro SMD
package. Limits are guaranteed by production testing or correlation
techniques using standard Statistical Quality Control (SQC) methods.Unless
otherwise specified: IO= 40 mA, CI = 0.33 μF, CO = 0.1 μF.
Air Conditioner Wiring The figure 3.7.1 show how the connection of
the air conditioner is done.Firstly, this is how and where the wiring of the air
conditioner is done. It should be tested using the multi meter. The purpose of
testing with the multi meter is to identify which wires need to be bypassed at
the switch.There are two main devices that will be turned on during the
switch-on air conditioner operation. So the wiring needs to be connected in
pairs to two single relays in the RCCS. It needs two different relays because
it will turn on two different devices which the pair of wiring should not be
connected together. The two devices are the air conditioner fan and the
compressor of the air conditioner. Both relays will energize during the
operation of turning on the air conditioner. At the same time it will turn on
the air conditioner. It will allow current to flow through and the air
conditioner will be turned on. Figure 7.3.1 shows how the complete
connection of the air conditioner. With this connection one channel is
complete and ready to operate.
Features of LM78L05:
i. LM78L05 in micro SMD package Output voltage tolerances of ±5% over
the temperature range
ii. Output current of 100 Ma
iii. Internal thermal overload protection
iv. Output transistor safe area protection
v. Internal short circuit current limit
vi. Available in plastic TO-92 and plastic SO-8 low profile packages
vii. No external components
viii. Output voltages of 5.0V, 6.2V, 8.2V, 9.0V, 12V, 15V
3.2 TRANSFORMERS:
A transformer is a static electrical device that transfers energy by inductive coupling
between its winding circuits. A varying current in the primary winding creates a varying
magnetic flux in the transformer's core and thus a varying magnetic flux through the
secondary winding. This varying magnetic flux induces a varying electromotive force
(emf) or voltage in the secondary winding.
Transformers range in size from thumbnail-sized units hidden inside microphones to
units weighing hundreds of tons interconnecting the power grid. A wide range of
transformer designs are used in electronic and electric power applications. Transformers
are essential for the transmission, distribution, and utilization of electrical energy.
As it is recommended start working by identifying the components and separating
them in groups. Place first of all the sockets for the ICs and the pins for the external
connections and solder them in their places. Continue with the resistors. Remember to
mound R7 at a certain distance from the printed circuit board as it tends to become quite
hot, especially when the circuit is supplying heavy currents, and this could possibly
damage the board. It is also advisable to mount R1 at a certain distance from the surface
of the PCB as well. Continue with the capacitors observing the polarity of the electrolytic
and finally solder in place the diodes and the transistors taking care not to overheat them
and being at the same time very careful to align them correctly.
Mount the power transistor on the heatsink. To do this follow the diagram and
remember to use the mica insulator between the transistor body and the heatsink and the
special fibber washers to insulate the screws from the heatsink. Remember to place the
soldering tag on one of the screws from the side of the transistor body, this is going to be
used as the collector lead of the transistor. Use a little amount of Heat Transfer
Compound between the transistor and the heatsink to ensure the maximum transfer of
heat between them, and tighten the screws as far as they will go.
Attach a piece of insulated wire to each lead taking care to make very good joints as
the current that flows in this part of the circuit is quite heavy, especially between the
emitter
and
the
collector
of
the
transistor.
It is convenient to know where you are going to place every thing inside the case that is
going to accommodate your power supply, in order to calculate the length of the wires to
use between the PCB and the potentiometers, the power transistor and for the input and
output connections to the circuit. (It does not really matter if the wires are longer but it
makes a much neater project if the wires are trimmed at exactly the length necessary).
Connect the potentiometers, the LED and the power transistor and attach two pairs of
leads for the input and output connections. Make sure that you follow the circuit diagram
very care fully for these connections as there are 15 external connections to the circuit in
total and if you make a mistake it may be very difficult to find it afterwards. It is a good
idea to use cables of different colours in order to make trouble shooting easier.
The external connections are:
- AC input, the secondary of the transformer.
- DC output.
- power transistor Q4.
- The LED should also be placed on the front panel of the case where it is always visible
but the pins where it is connected at are not numbered.
When all the external connections have been finished make a very careful inspection
of the board and clean it to remove soldering flux residues. Make sure that there are no
bridges that may short circuit adjacent tracks and if everything seems to be all right
connect the input of the circuit with the secondary of a suitable mains transformer.
Connect a voltmeter across the output of the circuit and the primary of the transformer to
mains.
DO NOT TOUCH ANY PART OF THE CIRCUIT WHILE IT IS UNDER POWER.
The voltmeter should measure a voltage between 0 and 30 VDC depending on the
setting of P1, and should follow any changes of this setting to indicate that the variable
voltage control is working properly. Turning P2 counter-clockwise should turn the LED
on, indicating that the current limiter is in operation.
Power supplies
Power supplies for electronic devices can be broadly divided into line-frequency
(or "conventional") and switching power supplies. The line-frequency supply is usually a
relatively simple design, but it becomes increasingly bulky and heavy for high-current
equipment due to the need for large mains-frequency transformers and heat-sinked
electronic regulation circuitry. Conventional line-frequency power supplies are
sometimes called "linear," but that is a misnomer because the conversion from AC
voltage to DC is inherently non-linear when the rectifiers feed into capacitive reservoirs.
Linear voltage regulators produce regulated output voltage by means of an active voltage
divider that consumes energy, thus making efficiency low. A switched-mode supply of
the same rating as a line-frequency supply will be smaller, is usually more efficient, but
would be more complex.
AC power supply
An AC power supply typically takes the voltage from a wall outlet (mains supply)
and lowers it to the desired voltage. Some filtering may take place as well. Here 230V
AC is given to transformer.
TRANSFORMER
A transformer is a static electrical device that transfers energy by inductive
coupling between its winding circuits. A varying current in the primary winding creates a
varying magnetic flux in the transformer's core and thus a varying magnetic flux through
the secondary winding. This varying magnetic flux induces a varying electromotive force
(emf) or voltage in the secondary winding.
Transformers range in size from thumbnail-sized units hidden inside microphones
to units weighing hundreds of tons interconnecting the power grid. A wide range of
transformer designs are used in electronic and electric power applications. Transformers
are essential for the transmission, distribution, and utilization of electrical energy.
The transformer is based on two principles: first, that an electric current can
produce a magnetic field and second that a changing magnetic field within a coil of wire
induces a voltage across the ends of the coil (electromagnetic induction). Changing the
current in the primary coil changes the magnetic flux that is developed. The changing
magnetic flux induces a voltage in the secondary coil.current passing through the primary
coil creates a magnetic field.
The primary and secondary coils are wrapped around a core of very high
magnetic permeability, such as iron, so that most of the magnetic flux passes through
both the primary and secondary coils. If a load is connected to the secondary winding, the
load current and voltage will be in the directions indicated, given the primary current and
voltage in the directions indicated (each will be AC in practice).
The ideal transformer model assumes that all flux generated by the primary
winding links all the turns of every winding, including itself. In practice, some flux
traverses paths that take it outside the windings.[46] Such flux is termed leakage flux, and
results in leakage inductance in series with the mutually coupled transformer windings.[42]
Leakage flux results in energy being alternately stored in and discharged from the
magnetic fields with each cycle of the power supply.
It is not directly a power loss (see Stray losses below), but results in inferior
voltage regulation, causing the secondary voltage to not be directly proportional to the
primary voltage, particularly under heavy load.[46] Transformers are therefore normally
designed to have very low leakage inductance. Nevertheless, it is impossible to eliminate
all leakage flux because it plays an essential part in the operation of the transformer. The
combined effect of the leakage flux and the electric field around the windings is what
transfers energy from the primary to the secondary.[47]
In some applications increased leakage is desired, and long magnetic paths, air gaps, or
magnetic bypass shunts may deliberately be introduced in a transformer design to limit
the short-circuit current it will supply.[42] Leaky transformers may be used to supply loads
that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon
signs or for safely handling loads that become periodically short-circuited such as electric
arc welders.[48]
Air gaps are also used to keep a transformer from saturating, especially audio-frequency
transformers in circuits that have a DC component flowing through the windings.[49]
Knowledge of leakage inductance is for example useful when transformers are operated
in parallel. It can be shown that if the percent impedance (Z) and associated winding
leakage reactance-to-resistance (X/R) ratio of two transformers were hypothetically
exactly the same, the transformers would share power in proportion to their respective
volt-ampere ratings (e.g. 500 kVA unit in parallel with 1,000 kVA unit, the larger unit
would carry twice the current). However, the impedance tolerances of commercial
transformers are significant.
FUSE:
In electronics and electrical engineering, a fuse (from the French fuser, Italian
fuso, "spindle"[1]) is a type of low resistance resistor that acts as a sacrificial device to
provide overcurrent protection, of either the load or source circuit. Its essential
component is a metal wire or strip that melts when too much current flows, which
interrupts the circuit in which it is connected. Short circuit, overloading, mismatched
loads or device failure are the prime reasons for excessive current.
A fuse interrupts excessive current (blows) so that further damage by overheating
or fire is prevented. Wiring regulations often define a maximum fuse current rating for
particular circuits. Overcurrent protection devices are essential in electrical systems to
limit threats to human life and property damage. Fuses are selected to allow passage of
normal current plus a marginal percentage and to allow excessive current only for short
periods. Slow blow fuses are designed to allow harmless short term higher currents but
still clear on a sustained overload. Fuses are manufactured in a wide range of current and
voltage ratings and are widely used to protect wiring systems and electrical equipment.
Self-resetting fuses automatically restore the circuit after the overload has cleared; these
are useful, for example, in aerospace or nuclear applications where fuse replacement is
impossible. This ouput is given to regulator IC’s;
Light-Emitting Diode (LED):
A light-emitting diode (LED) is a semiconductor device that emits visible light
when an electric current passes through it. The light is not particularly bright, but in most
LEDs it is monochromatic, occurring at a single wavelength. The output from an LED
can range from red (at a wavelength of approximately 700 nanometers) to blue-violet
(about 400 nanometers). Some LEDs emit infrared (IR) energy (830 nanometers or
longer); such a device is known as an infrared-emitting diode (IRED).
Diagram:
LED Discription:
An LED or IRED consists of two elements of processed material called P-type
semiconductors and N-type semiconductors. These two elements are placed in direct
contact, forming a region called the P-N junction. In this respect, the LED or IRED
resembles most other diode types, but there are important differences. The LED or IRED
has a transparent package, allowing visible or IR energy to pass through. Also, the LED
or IRED has a large PN-junction area whose shape is tailored to the application.
Benefits of LEDs and IREDs, compared with incandescent and fluorescent illuminating
devices, include:

Low power requirement: Most types can be operated with battery power
supplies.

High efficiency: Most of the power supplied to an LED or IRED is converted into
radiation in the desired form, with minimal heat production.

Long life: When properly installed, an LED or IRED can function for decades.
Typical applications include:

Indicator lights: These can be two-state (i.e., on/off), bar-graph, or alphabeticnumeric readouts.

LCD panel backlighting: Specialized white LEDs are used in flat-panel
computer displays.

Fiber optic data transmission: Ease of modulation allows wide communications
bandwidth with minimal noise, resulting in high speed and accuracy.

Remote control: Most home-entertainment "remotes" use IREDs to transmit data
to the main unit.

Optoisolator: Stages in an electronic system can be connected together without
unwanted interaction.
CHAPTER IV
LOGIC CIRCUIT
OR GATE:
The OR gate is a digital logic gate that implements logical disjunction - it behaves according to
the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are HIGH
(1). If neither input is HIGH, a LOW output (0) results. In another sense, the function of OR
effectively finds the maximum between two binary digits, just as the complementary AND function
finds the minimum
Symbols:
There are two symbols for OR gates: the German (GNSI or 'military') symbol and the
IEC ('European' or 'rectangular') symbol, as well as the deprecated DIN symbol.[2][3] For
more information see Logic Gate Symbols.
MIL/ANSI Symbol
IEC Symbol
DIN Symbol
This schematic diagram shows the arrangement of OR gates within a standard 4071 CMOS integrated circuit.
Hardware description and pinout
OR Gates are basic logic gates, and as such they are available in TTL and CMOS ICslogic
families. The standard 4000 series CMOS IC is the 4071, which includes four independent twoinput OR gates. The traditional TTL version is the 7432. There are many offshoots of the original
7432 OR gate. All have the same pinout but different internal architecture, allowing them to
operate in different voltage ranges and/or at higher speeds. In addition to the standard 2-Input
OR Gate, 3- and 4-Input OR Gates are also available. In the CMOS series, these are:

4075: Triple 3-Input OR Gate

4072: Dual 4-Input OR Gate
TTL variations include:

74LS32: Quad 2-input OR gate (Low power Schottky version)

74HC32: Quad 2-input OR gate (High Speed CMOS version) - has lower current
consumption/wider Voltage range

74LVC32: Low voltage CMOS version of the same.
Hardware description language[edit]
module(a,b,c); input a,b; output c; or (c,a,b); end ;
Implementations[edit]
CMOS OR Gate
OR gate using diodes
Alternatives[edit]
If no specific OR gates are available, one can be made from NAND or NOR gates in the
configuration shown in the image to the right of this text. Any logic gate can be made from a
combination of NAND or NOR gates.
NAND GATE:
In digital electronics, a NAND gate (Negated AND or NOT AND) is a logic gate which
produces an output that is false only if all its inputs are true. A LOW (0) output results
only if both the inputs to the gate are HIGH (1); if one or both inputs are LOW (0), a
HIGH (1) output results. It is made using transistors.
The NAND gate is significant because any boolean function can be implemented by
using a combination of NAND gates. This property is called functional completeness.
Digital systems employing certain logic circuits take advantage of NAND's functional
completeness.
The function NAND(a1, a2, ..., an) is logically equivalent to NOT(a1 AND a2 AND ...
AND an).
TIMER 555:
The 555 Integrated Circuit (IC) is an easy to use timer that has many
applications. It is widely used in electronic circuits and this popularity
means it is also very cheap to purchase, typically costing around 30p. A
'dual' version called the 556 is also available which includes two
independent
555
ICs
in
one
package.
The following illustration shows both the 555 (8-pin) and the 556 (14-pin).
In a circuit diagram the 555 timer chip is often drawn like the illustration
below. Notice how the pins are not in the same order as the actual chip, this
is because it is much easier to recognize the function of each pin, and makes
drawing
circuit
diagrams
much
easier.
For the 555 to function it relies on both analogue and digital electronic
techniques, but if we consider its output only, it can be thought of as a digital
device. The output can be in one of two states at any time, the first state is
the 'low' state, which is 0v. The second state is the 'high' state, which is the
voltage Vs (The voltage of your power supply which can be anything from
4.5 to 15v. 18v absolute maximum).
The most common types of outputs can be categorized by the following
(their names give you a clue as to their functions):

Monostable mode: in this mode, the 555 functions as a "one-shot".
Applications include timers, missing pulse detection, bouncefree
switches,
touch
switches,
frequency
divider,
capacitance
measurement, pulse-width modulation (PWM) etc

Astable - free running mode: the 555 can operate as an oscillator.
Uses include LED and lamp flashers, pulse generation, logic clocks,
tone generation, security alarms, pulse position modulation, etc.

Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if
the DIS pin is not connected and no capacitor is used. Uses include
bouncefree latched switches, etc.
Pin Description:
Pin
Function
Name
1
Ground (0V)
Ground
2
Voltage below 1/3 Vcc to trigger the pulse
Trigger
3
Pulsating output
Output
4
Active low; interrupts the timing interval at Output
Reset
5
Provides access to the internal voltage divider; default Control Voltage
No
2/3 Vcc
6
The pulse ends when the voltage is greater than Control
Threshold
7
Open collector output; to discharge the capacitor
Discharge
8
Supply voltage; 5V (4.5V - 16 V)
Vcc
Pin Configuration of the 555 Timer
When drawing a circuit diagram, always draw the 555 as a building block, as
shown below with the pins in the following locations. This will help you
instantly recognise the function of each pin:
Using the Output of a 555 Timer:
The output (Pin 3) of the 555 can be in one of two states at any time, which
means it is a digital output. It can be connected directly to the inputs of other
digital ICs, or it can control other devices with the help of a few extra
components. The first state is the 'low' state, which is the voltage 0V at the
power supply. The second state is the 'high' state, which is the voltage Vcc at
the power supply.
Sinking and Sourcing:
When the Output goes low, current will flow through the device and switch
it on. This is called 'sinking' current because the current is sourced from Vs
and flows through the device and the 555 to 0V.
When the Output goes high, current will flow through the device and switch
it on. This is called 'sourcing' current because the current is sourced from the
555 and flows through the device to 0V.
Sinking and sourcing can also be used together so that two devices can be
alternately switched on and off.
The device(s) could be anything that can be switched on and off, such as
LEDs, lamps, relays, motors or electromagnets. Unfortunately, these devices
have to be connected to the Output in different ways because the Output of
the 555 can only source or sink a current of up to 200mA. Make sure your
power supply can provide enough current for both the device and the 555,
otherwise the timing of the 555 will be affected.
The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse
generation, and oscillator applications. The 555 can be used to provide time delays, as an
oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in one
package.
PIN OUT DIAGRAM:
The connection of the pins for a DIP package is as follows:
Pin Name Purpose
1
GND
Ground reference voltage, low level (0 V)
The OUT pin goes high and a timing interval starts when this input falls
2
TRIG below 1/2 of CTRL voltage (which is typically 1/3 of VCC, when CTRL is
open).
3
OUT
This output is driven to approximately 1.7V below +VCC or GND.
A timing interval may be reset by driving this input to GND, but the timing
4
RESET does not begin again until RESET rises above approximately 0.7 volts.
Overrides TRIG which overrides THR.
5
CTRL
6
THR
7
DIS
8
VCC
Provides "control" access to the internal voltage divider (by default, 2/3
VCC).
The timing (OUT high) interval ends when the voltage at THR is greater
than that at CTRL.
Open collector output which may discharge a capacitor between intervals. In
phase with output.
Positive supply voltage, which is usually between 3 and 15 V depending on
the variation.
CONTACTOR
In semiconductor testing, contactor can also refer to the specialised socket that
connects the device under test.In process industries a contactor is a vessel where
two streams interact, for example, air and liquid.
A contactor is an electrically controlled switch used for switching a
power circuit, similar to arelay except with higher current ratings.[1] A contactor
is controlled by a circuit which has a much lower power level than the switched
circuit.Contactors come in many forms with varying capacities and features.
Unlike a circuit breaker, a contactor is not intended to interrupt a short
circuit current. Contactors range from those having a breaking current of several
amperes to thousands of amperes and 24 V DC to many kilovolts. The physical
size of contactors ranges from a device small enough to pick up with one hand, to
large devices approximately a meter (yard) on a side.
Contactors are used to control electric motors, lighting, heating, capacitor banks,
thermal evaporators, and other electrical loads.
A contactor has three components. The contacts are the current carrying part of
the contactor. This includes power contacts, auxiliary contacts, and contact springs.
Theelectromagnet (or "coil") provides the driving force to close the contacts.
The enclosure is a frame housing the contact and the electromagnet. Enclosures are made
of insulating materials like Bakelite, Nylon 6, and thermosetting plastics to protect and
insulate the contacts and to provide some measure of protection against personnel
touching the contacts. Open-frame contactors may have a further enclosure to protect
against dust, oil, explosion hazards and weather.
Magnetic blowouts use blowout coils to lengthen and move the electric arc. These are
especially useful in DC power circuits. AC arcs have periods of low current, during
which the arc can be extinguished with relative ease, but DC arcs have continuous high
current, so blowing them out requires the arc to be stretched further than an AC arc of the
same current. The magnetic blowouts in the pictured Albright contactor (which is
designed for DC currents) more than double the current it can break, increasing it from
600 A to 1,500 A.
Sometimes an economizer circuit is also installed to reduce the power required to keep a
contactor closed; an auxiliary contact reduces coil current after the contactor closes. A
somewhat greater amount of power is required to initially close a contactor than is
required to keep it closed. Such a circuit can save a substantial amount of power and
allow the energized coil to stay cooler. Economizer circuits are nearly always applied on
direct-current contactor coils and on large alternating current contactor coils.
A basic contactor will have a coil input (which may be driven by either an AC or DC
supply depending on the contactor design). The coil may be energized at the same
voltage as a motor the contactor is controlling, or may be separately controlled with a
lower coil voltage better suited to control by programmable controllers and lower-voltage
pilot devices. Certain contactors have series coils connected in the motor circuit; these are
used, for example, for automatic acceleration control, where the next stage of resistance
is not cut out until the motor current has dropped.
Operating principle
Unlike general-purpose relays, contactors are designed to be directly connected to
high-current load devices. Relays tend to be of lower capacity and are usually designed
for both normally closed and normally open applications. Devices switching more than
15 amperes or in circuits rated more than a few kilowatts are usually called contactors.
Apart from optional auxiliary low current contacts, contactors are almost exclusively
fitted with normally open ("form A") contacts. Unlike relays, contactors are designed
with features to control and suppress the arc produced when interrupting heavy motor
currents.
When current passes through the electromagnet, a magnetic field is produced,
which attracts the moving core of the contactor. The electromagnet coil draws more
current initially, until its inductance increases when the metal core enters the coil. The
moving contact is propelled by the moving core; the force developed by the
electromagnet holds the moving and fixed contacts together. When the contactor coil is
de-energized, gravity or a spring returns the electromagnet core to its initial position and
opens the contacts.
For contactors energized with alternating current, a small part of the core is
surrounded with a shading coil, which slightly delays the magnetic flux in the core. The
effect is to average out the alternating pull of the magnetic field and so prevent the core
from buzzing at twice line frequency.
Because arcing and consequent damage occurs just as the contacts are opening or
closing, contactors are designed to open and close very rapidly; there is often an
internal tipping point mechanism to ensure rapid action.
Rapid closing can, however, lead to increase contact bounce which causes
additional unwanted open-close cycles. One solution is to have bifurcated contacts to
minimize contact bounce; two contacts designed to close simultaneously, but bounce at
different times so the circuit will not be briefly disconnected and cause an arc.
A slight variant has multiple contacts designed to engage in rapid succession. The
first to make contact and last to break will experience the greatest contact wear and will
form a high-resistance connection that would cause excessive heating inside the
contactor. However, in doing so, it will protect the primary contact from arcing, so a low
contact resistance will be established a millisecond later.
Another technique for improving the life of contactors is contact wipe; the
contacts move past each other after initial contact on order to wipe off any contamination.
APPLICATION:

D.C. variable bench supply (a bench power supply usually refers to a power
supply capable of supplying a variety of output voltages useful for bench testing
electronic circuits, possibly with continuous variation of the output voltage, or
just some preset voltages; a laboratory (lab) power supply normally implies an
accurate bench power supply, while a balanced or tracking power supply refers to
twin supplies for use when a circuit requires both positive and negative supply
rails).

Mobile Phone power adaptors

Regulated power supplies in appliances
CHAPTER – 5
CONCLUSION
This project is designed in the form of Hardware for three single phase
transformers 230v to 12V of output for to develop an automatic tripping mechanism for
the three phase supply system while temporary fault and permanent fault occurs. Here we
used 555 timer with relay for the fault is temporary or permanent.
Short duration fault returns the supply to the load immediately called as
temporary trip while long duration shall result in permanent trip. The concept in the
future can be extended to developing a mechanism to send message to the authorities via
SMS by interfacing a GSM modem.
The phases sequence indicators that constitutes the current technical stage are
made after the principle: induction motor principle; direct and inverse filter sequence
principle; the stroboscopic effect principle.In all those cases the common deficiency
approached after a long period of analyze consists in reduced sensibility. The mentioned
indicators can be used only when the three-phases controlled source have circuit voltage
of volt decimal order. In indicator case made on induction motor principle intervene
another disadvantage connection with vulnerability at mechanically impulse and
vibration.
The authors contribution have like object the indicators sensibility increase so to
can be use forthree-phases controlled source with voltage of volt order. One of the
contributions is made on induction motor principle and on adhesion and cohesive force
manifested on liquid-solid interface. At this indicators the motive crew deceleration was
possible in a voltage three-phase system of 3×9 V; 50 Hz.
The second contribution has like object the realization of a indicator on direct and
inverse filter sequence principle. The determined sequence depends of electric signal
polarity delivered on the outlet, and the indicator sensibility depends of polarity indicator
sensibility. The galvanometer, with sensibility 1×10-6 A/div indicator needle,
appropriation make the premise of three-phases
source with circuit voltage of volt fraction order.