AUTO SELECTION OF ANY AVAILABLE PHASE, IN 3 PHASE SUPPLY SYSTEM ABSTRACT: The project is designed to provide uninterrupted AC mains supply i.e., 230 volt to a single phase load. This is achieved by automatic changeover of the load from the missing phase to the next available phase in a 3 phase system. It is often noticed that power interruption in distribution system is about 70% for single phase faults while other two phases are in normal condition. Thus, in any commercial or domestic power supply system where 3 phase is available, it is advisable to have an automatic changeover system for uninterrupted power to critical loads in the event of missing phase. In this system auto selection is achieved by using a set of relays interconnected in such a way that if one of the relay feeding to the load remains energized always. Under the phase failure condition the corresponding step down transformer secondary delivers zero voltage which is duly rectified to DC and then fed to the logic gates comprising of AND & OR to switch on the next relay that delivers the power to the load. It also has a provision of connecting to an inverter source which delivers uninterrupted power to the load incase all the 3 phases go missing. The project is supplied with three transformers connected to the 3 phases supply. Further the project can be enhanced by incorporating power semiconductor devices such as thyristors /IGBTs for instantaneous changeover to the next available phase. This overcomes the drawback of the changeover time generally witnessed by relay switching operations. Also, microcontroller can be used to monitor the any fault phase it automatically trip the load..
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
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.
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 using 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 ec r e as e t he va l ue o f t ha t r es is to r t he o ut pu t v ol t ag e o f t he r eg ul a to r w il l a ls 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 regu lator 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 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 heat sink. To do this follow the diagram and remember to use the mica insulator between the transistor body and the heat sink and the special fibber washers to insulate the screws from the heat sink. 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 heat sink 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 audiofrequency 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
This schematic diagram shows the arrangement of OR gates within a standard 4071 CMOS integrated circuit.
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
No 1
Ground (0V)
Ground
2 3 4 5
Voltage below 1/3 Vcc to trigger the pulse Trigger Pulsating output Output Active low; interrupts the timing interval at Output Reset Provides access to the internal voltage divider; default 2/3Control Voltage
6 7 8
Vcc The pulse ends when the voltage is greater than Control Open collector output; to discharge the capacitor Supply voltage; 5V (4.5V - 16 V)
Threshold Discharge 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.
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. 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
3
OUT
4
RESET does not begin again until RESET rises above approximately 0.7 volts.
5 6 7 8
open). 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
Overrides TRIG which overrides THR. CTRL 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 THR that at CTRL. Open collector output which may discharge a capacitor between intervals. In DIS phase with output. VCC 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.
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.
