Practical Applications Of Transformer

Pr formical Applications Of TransformerAbstract- Generating surmount executive is possible in a couple of(prenominal) stations. The power is generated because has to transmit to the various vocalisations of the country. Large power should be transmitted on very uplifted potential drop to thin out the a tidy sum of copper material and increase the transmittance efficiency. Hence the zilch generated is transformed twice, thrice, or still four times before utilized. much(prenominal) transformation of ac from ace electromotive force to a nonher is do by transformer.DISCOVERY The phenomenon of electro attractoric origination was disc any overed by Michael Faraday and Joseph Henry in 1831. The relationship surrounded by electromotive force or potentiality and magnetic meld was formalized in an equation now referred to as Faradays virtue of sealedty. This law states that whenever there is a relative motion mingled with the c rock fossil oil and magnet emf is br ing forth in the bankroll. The induced emf lasts so unyielding as magnetic shuffle linked with the coil revisiond. The induced emf is directly proportional to the time rate of change of magnetic flux linked with the coil.Where, B is the magnetic flux by the circuit.Fig.1 Faradays experiment with induction between coils of cableTRANSFORMERA electrical period go a counselling period in the subsidiary winding and electrical might volition be transferred from the particular circuit through the transformer to the freight.Fig.2 Structure of TransformerPRINCIPLE The transformer is based on 2 principles firstly, that an electric sure give the gate produce a induced magnetic report by varying with time and secondly that a changing magnetic welkin at heart a coil of wire induces a voltage across the ends of the coil. Changing the authentic in the first-string coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the alternat e coil. The voltage induced across the supplementary coil whitethorn be calculated from Faradays law of induction, which states thatWhere VS is the instantaneous voltage, NS is the outlet of turns in the alternate coil and equals the magnetic flux through iodine turn of the coil. If the turns of the coil be oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic flux density B and the theatre A through which it cuts. The firmament is constant, being equal to the cross-sectional atomic number 18a of the transformer outcome, whereas the magnetic field varies with time according to the ardor of the master(a) feather. Since the identical magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals. Taking the symmetry of the two equations for VS and VP gives the basic equation for timbreping up or stepping quite a little the voltage. turn of e dismissions OF TRANSFORMER stones throws arCoil Winding nub fabricationCore-Coil Assembly storage army storeful-upTransformer TankPainting and FinishingFig. 3 Transformer makeing each part1. CONSERVATOR a) Check the oil level in the conservator. If the level is belittled than the optimum mark indicated on the oil level gauge, it should be go past with proper grade of transformer oil having suitable break great deal voltage value.b) The stuffiness of the cap/ hacker of the oil filler pipe, drain plug or drain valve should be checked. The oil level gauge of the conservator should evermore be kept clean so that the oil level is subgross from a short place.Fig.4 Conservator2. BUCHHOLZ RELAY a) the observation glasses should show that the buchholz relay is properly change with oil. If necessary, bleeding shtup be done from the two cocks. The drain plug should be tight and no leaking should be there.b) The cover on the connection chamber should be overt to comment whether connections atomic number 18 properly tight.3. SHUT OFF VALVE This should always be in fully open position part the transformer is being energized.4. BREATHER a) The plug at the end of the hint pipe is to be re locomote and breather fitted on to the pipe along with the fly nut.b) It is necessary before capable the breather to observe the coloring of the silica gel. If necessary, the breather should be opened and the silica gel properly dried up so that its color is perfectly bluish. c) The chamber at the base of the breather should be filled in with dry transformer oil up to the level marked.Fig.5 Showing Tank in oil5. DIAL TYPE THERMOMETER If it is provided with alarm and trip sense of touchs, these should be set to proper temperature before energizing the transformer. For guidance purposes, it may be mentioned here that a transformer having temperature rise of 45/55C, the trip contact should be set at ambient temperature plus 45C and the alarm contact impart be 5 10 previo us to this.6. WINDING TEMPERATURE INDICATOR This will be set in the same(p) way as the dial type thermo bar excepting that the trip contact should be set at ambient temperature plus 55C.7. MARSHALLING BOX The windows of the marshalling cut should always be kept clean so that the readings of the oil temperature indicator and winding temperature indicator piece of tail be easily read from outside. several(prenominal) dehydrating agent may be kept inside the marshalling box so that the box is kept always in dry condition. Do not keep the Dorr of marshalling box open. It must be locked.8. EXPLOSION VENT a) In case an equalizer pipe connection is provided, the valve in the pipe should be kept in open position before the transformer is energized. b) If the explosion vent is provided with an contrast release device, this should be opened once to release both pressure generated inside and then it should be closed. c) The diaphragm of the vent should be intact.9. BUSHINGS To pr plaint sparking bushings be single-valued give outd when wires at low voltage and transformers wire at game voltage atomic number 18 connected.Fig.6 Showing Bushings10. COOLANTFig.7Coolant High temperatures will damage the winding insulation. Small transformers do not generate meaning(a) heat and be cooled by air circulation and radiation of heat. originator transformers rated up to several hundred kVA can be adequately cooled by internal convective air-cooling, sometimes assisted by fans. In larger transformers, part of the form problem is removal of heat. Some power transformers be immersed in transformer oil that both cools and insulates the windings. The oil is a highly refined mineral oil that remains stable at transformer operating temperature. Indoor liquid-filled transformers must use a non-flammable liquid, or must be located in molest resistant rooms. cable-cooled dry transformers argon preferred for indoor applications even at capacity ratings where oil-cooled const ruction would be more economical, because their cost is ball carrier by the reduced building construction cost.TYPES OF TRANSFORMER1. ON THE BASIS OF TRANSFORMATON symmetry A) Step-up transformersA step-up transformer allows a device that contends a high voltage power cede to operate from a cut voltage source. The transformer takes in the low voltage at a high modern and puts out the high voltage at a low authentic. Transformers hardly work with alternating rate of flow. Using direct current will form a magnetic field in the warmness but it will not be a changing magnetic field and so no voltage will be induced in the secondary coil. Using a step up transformer to increase the voltage does not give you something for nothing. As the voltage goes up, the current goes down by the same proportion. The power equation shows that the overall power remains the same.P=V x I Power = Voltage x topicalFig.8 Step up TransformerElectricity is first produced at the power plants. Electr icity is then sent to step-up transformers where low-voltage electricity is changed to high voltage to relieve the transfer of power from the power plant to the traditioner. Voltage must be change magnitude so that the electric current has the push it needs to efficiently travel long distances. From the step-up transformer, transmission lines carry the high voltage electric current long distances through thick wires mounted on tall towers that keep the transmission lines high above the ground. Insulators made of porcelain or polymers are used to prevent the electricity from leaving the transmission lines.B) free transformersA step-down transformer allows a device that requires a low voltage power supply to operate from a higher(prenominal) voltage. The transformer takes in the high voltage at a low current and puts out a low voltage at a high current. A step down transformer has less turns of wire on the secondary coil, which makes a littler induced voltage in the secondary co il. It is called a step down transformer because the voltage output is shorter than the voltage input. If the secondary coil has fractional as many turns of wire then the output voltage will be half(a) the input voltage. Decreasing the voltage does not step-down the power. As the voltage goes down, the current goes up.Fig.9 Step Down Transformer2. ON THE BASES OF WINDINGSA) Core type transformerFig.10 Core TransformerB) Shell type transformerFig.11 Shell type transformer3. ON THE BASES OF SERVICE A) Power transformer Power transformers are used in transmission network for voltage ratings of (440kv, 220kv, 110kv, 66Kv) and are principally rated above 200MVA. Power transformer generally operated at full loading. Hence, it is designed much(prenominal) that copper dischargees are minimum. B) Distribution Transformers Distribution Transformers are used in (33 kV, 11kv, 6.6 kV) voltage levels in Distribution network and are generally rated less than 200 MVA. A distribution transfor mer is always online and operated at fill up less than full load for most of time. Hence, it is designed such(prenominal) that hollow out losings are minimum.IDEALTRANSFORMER The idealizations are as follows 1. Magnetic circuit is linear and has infinite permeability. The consequence is that a vanishingly small current is enough to establish the disposed flux. Hysteresis loss is negligible. As all the flux generated confines itself to the iron, there is no escape cock flux.2. Windings do not have unsusceptibility. This means that there are no copper losses, nor thereis any ohmic drop in the electric circuit. losses IN TRANSFORMERAn ideal transformer would have no energy losses, and would be 100% efficient. In practical transformers energy is dissipated in the windings, event, and border structures. Larger transformers are generally more efficient, and those rated for electricity distribution ordinarily perform better than 98%.All transformers have copper and bone marrow l osses.1. dogshit lossCopper loss is power lost in the primary and secondary windings of a transformer due to the ohmic resistance of the windings. Copper loss, in watts.Copper Loss I2P RP+ I2S RSWhere IP = primary currentIS = secondary currentRP = primary winding resistanceRS = secondary winding resistance2. Core lossA) Hysteresis lossesEach time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the relative frequency, and is a function of the peak flux density to which it is subjected.B) Eddy currentsFerromagnetic materials are withal good conductors, and a solid core made from such a material in like manner constitutes a single short-circuited turn throughout its stainless length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The kink current loss is a complex function of t he foursquare of supply frequency and inverse square of the material thickness.Mechanical lossesIn addition to magnetostriction, the alternating magnetic field causes fluctuating electromagnetic forces between the primary and secondary windings. These incite vibrations within nearby metalwork, adding to the bombilate noise, and consuming a small amount of power.Stray losses safety valve inductance is by itself largely lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformers support structure will give rise to wrench currents and be converted to heat. There are alike radiative losses due to the oscillate magnetic field, but these are normally small.EFFECIENCYWHAT CAUSE LOSSES1. Due to the large value for the permeance ( r of the order of 1000 as compared to air) the magnetizing current requirement decreases dramatically. This can also b e visualized as a dramatic increase in the flux produced for a given value of magnetizing current.2. The magnetic medium is linear for low values of induction and exhibits saturation type of non-linearity at higher flux densities.3. The iron also has hysteresis type of non-linearity due to which certain amount of power is lost in the iron (in the form of hysteresis loss), as the B-H characteristic is traversed.4. Most of the flux lines are confined to iron path and hence the mutual flux is increased very much and leakage flux is greatly reduced.5. The flux can be easily directed as it takes the path through marque which gives great freedom for the designer in physical arrangement of the excitation and output windings.6. As the medium is made of a conducting material eddy currents are induced in the same and produce losses. These are called eddy current losses. To minimize the eddy current losses the steel core is required to be in the form of a stack of insulated laminations. activ ity OF TRANSFORMER1. official document transformersInstrument transformers comprise a large category of current and potential transformers for various voltage, frequency and physical size ranges. We have blue them up into several different groupings low voltage, which are system voltages low 15kV high frequency, operating frequency over 1kHz and size ranges from board mount parts up to current transformers with window sizes of 254mm by 610mm. Read through the different types we supply below and use our InstrumentFig. 12 Instrument transformer2. Potential TransformersUsed primarily in a step down environment to monitor voltage. They are designed for connection line-to-line or line-to-neutral in the same manner as ordinary voltmeters. The secondary voltage bears a fixed relation with the primary voltage so that any change in potential in the primary circuit will be accurately reflected in the meters or otherwise devices connected across the secondary rods. Potential transformers can be used with voltmeters for voltage measurements or they can be used in combination with current transformers for watt-meter or watthour meter measurements. They are used also to operate protective relays and devices, and for many other applications, Since they are used in a monitor capacity, they generally require much greater accuracy in design.Fig. 13 Potential transformer3. Metering toroidal certain TransformersTraditional, window type current transformers for criterion 50-400HZ currents of 5A to 15000A with secondaries of 0.1A, 1A and 5A (special secondary currents are on hand(predicate)). Burden B 0.1 through 1.8 (2.5VA to 50 VA) with the true tell apart 0.2 to variance 5.0 as per IEC 185 or class 0.3, 0.6 or 1.2 as per ANSI C 57.13. deep down diameters of up to 8.00. Many models are available as U.L. recognized devices. Applications let in UPS systems Transfer refillinges Motor-generator sets Commercial sub-metering, 3 CT s in one package for 3- frame metering Ac curate touchstone for metering/WATT/VAR online sensing, recording, monitoring control Control panels and drives Standard CT used as measuring banner for comparison Winding temperature indicator (WTI) for power transformers Summation current transformers.Fig.14 . Metering Toroidal Current TransformersLarge Frame Current Transformers For measuring 50-400HZ currents in bus bar and other large conductor systems. Typical contour is 400A to 12000A primary current with secondary of 1A or 5A Inside areas as small as 3.00 X 7.00 and as large as 7.00 X 27.00 and 10.00X 24.00. All models are available with optional mounting plates for bulk-head mounting. Some models are U.L. recognized devices.4. Split-Core Current TransformersThis type of current transformer is available to measure AC currents from 100A to 600A, at 50 to400HZ. They are very popular in sub-metering applications where existent systems are being upgraded and it is impractical to isolate the primary conductor. It is even pos sible to install this type of transformer while the conductor is energized, however it is paramount that certain safety precautions be followed under such conditions. Rectangular in shape, standard split-core models are available with window dimensions up to 4.00 X 7.50. Even larger, custom designed sizes are available by special order. Secondary ratings of 5A, 1A, and 100ma are all common in split-core current transformers. Two model groups are available, SP and SPS. The former is provided with astainless steel screw-clamp band securing the two core halves the latter has a UV resistant nylon band. All ratios are available in either type. Electrical and magnetic surgical procedure is identical for the two groups.Fig.15 Split-Core Current Transformers5. Miniature Current TransformersThese are constructed using one of the hobby methods Plastic casing, Resin casted, Resindipped, Tape insulated,. Typical turns ratio 4000 1 to 500 1 and Accuracy Class 0.1 to ClassApplications accept Fig.15 Split-Core Current Transformers Energy meters for accurate current measurement Current control Current signature of motors Load sensing Ground fault sensing monitor of process parameters AC level to logic conversation bar graph As a transducer in instrumentation6. pass on Class security system Current TransformersThis type of CT includes oil-immersed bussing and Resin molded versions. Primary current range from 5 Amp to 5000 Amp with secondary current 5A, 1A , or 01.A. Typical Burden B 0.1 throughB 4.0 (2.5VA to 50 VA more) and Accuracy Class As per ANSI C 57.13 and IEC 185. Applications include Protection relays/electrical relay panels human race fault protection Bussing type, oil-immersed CT in power transformer Control panes and switch boards Air/Gas circuit breakers Motor control cubicles Power control centers Bus bar protection systems Differential protection systemsFig.16 Relay Class Protection Current Transformers7. modal(a) voltage Instrument TransformersThese are used with a system voltage 3.3kV to 25kV and BIL 4.5 to 125 full pother crest kV. They are reliably constructed using vacuum cast with paste resin/polyurethane resin and are able to withstand argillaceous fault conditions but are not made for exposure to sunlight.. unmarried CTs can be built with multiple cores for example one for measuring and another for relaying are possible. Also multi solicit secondaries can be provided (up to 4). Typical primary current 5 Amp to 3000 Amp and secondary current 5A/1A/01.A. Applications include Metering and Relaying Energy meter panels Medium voltage switch gears and control panels Medium voltage circuit breakers Motor Control PanelsFig.17 Medium voltage Instrument Transformers8. PC mount 50 to 400Hz Current TransformersThese offer a small footprint for the design engineer looking to sensor current on board. They can also be used for Metering Class (Burden from B O.1 to B 1.8 with accuracy class from 0.3 to 2.4 as per client requirement. (As per ANSI C 57.13 and IEC 185) and for Relay Class Burden from B 1.0 to B 4.0 and relay voltage class from C 10 to C 400 or T200 as per customer requirement. (As per ANSI C 57.13 and IEC 185) Secondary current range from 0.1 to 5 amp. Typical constructions are plastic casing or resin molded. Applications include Sensing current overload Ground fault detection MeteringPC mount 2OkHz to 2OOkHz Current TransformersThese are used for measuring high frequency primary currents up to 15 Amps with primary to secondary isolated to 2500 VAC and have optimum performance over designated current and frequency ranges. Applications include Isolated current feed-back maneuver in switch mode powersupplies Motor current load/overload Lighting Switch controls Ultra-sound current High resolution sonar current Isolated bi-directional current sensor with full wave bridgeFig.18 PC mount 50 to 400Hz Current Transformers9. Air core transformers another(prenominal) kind of special transformer, seen o ften in radio-frequency circuits, is the air core transformer. (Figure below) truthful to its name, an air core transformer has its windings wrapped around a nonmagnetic form, usually a hollow tube of some material. The degree of coupling (mutual inductance) between windings in such a transformer is many times less than that of an kindred iron-core transformer, but the undesirable characteristics of a ferromagnetic core (eddy current losses, hysteresis, saturation, etc.) are completely eliminated. It is in high-frequency applications that these effects of iron cores are most problematic.Fig.19 Air core transformersAir core transformers may be wound on cylindrical (a) or toroidal (b) forms. Center tapped primary with secondary (a). bifilar winding on toroidal form (b). The inside tapped solenoid winding, (Figure (a) above), without the over winding, could see to it unequal impedances when DC isolation is not required. When isolation is required the over winding is added over one e nd of the main winding. Air core transformers are used at radio frequencies when iron core losses are too high. Frequently air core transformers are paralleled with a capacitor to tune it to sonorousness. The over winding is connected between a radio antenna and ground for one such application. The secondary is tuned to resonance with a variable capacitor. The output may be taken from the tap point for amplification or detection. Small millimeter size air core transformers are used in radio receivers. The largest radio transmitters may use meter sized coils. Unshielded air core solenoid transformers are mounted at right angles to each other to prevent straggle coupling. Stray coupling is minimized when the transformer is wound on a toroid form. (Figure (b) above) Toroidal air core transformers also show a higher degree of coupling, particularly for bifilar windings. Bifilar windings are wound from a slightly twisted pair of wires. This implies a 11 turns ratio. trio or four wires may be grouped for 12 and other integral ratios. Windings do not have to be bifilar. This allows haughty turns ratios. However, the degree of coupling suffers. Toroidal air core transformers are rarified except for VHF (Very High Frequency) work. Core materials other than air such as powdered iron or ferrite are preferred for lower radio frequencies.10. Tesla Coil One notable example of an air-core transformer is the Tesla Coil, named after the Serbian electrical genius Nikola Tesla, who was also the inventor of the rotating magnetic field AC motor, polyphase AC power systems, and many elements of radio technology. The Tesla Coil is a resonant, high-frequency step-up transformer used to produce extremely high voltages. One of Teslas dreams was to habituate his coil technology to distribute electric power without the need for wires, manifestly broadcasting it in the form of radio waves which could be received and conducted to loads by means of antennas. The basic schematic for a Tesla Coil is shown in Figure below.Fig.20 Tesla coilTesla Coil A few heavy primary turns, many secondary turns.The capacitor, in conjunction with the transformers primary winding, forms a ice chest circuit. The secondary winding is wound in close proximity to the primary, usually around the same nonmagnetic form. Several options exist for exciting the primary circuit, the simplest being a high-voltage, low-frequency AC source and spark fracture (Figure below) carcass level diagram of Tesla coil with spark gap drive. The purpose of the high-voltage, low-frequency AC power source is to charge the primary tank circuit. When the spark gap fires, its low impedance acts to complete the capacitor/primary coil tank circuit, allowing it to oscillate at its resonant frequency. The RFC inductors are Radio Frequency Chokes, which act as high impedances to prevent the AC source from interfering with the oscillating tank circuit. The secondary side of the Tesla coil transformer is also a tank circuit, relying on the parasitic (stray) capacitance existing between the discharge terminal and earth ground to complement the secondary windings inductance. For optimum operation, this secondary tank circuit is tuned to the same resonant frequency as the primary circuit, with energy exchanged not only between capacitors and inductors during resonant oscillation, but also back-and-forth between primary and secondary windings. Tesla Coils find application primarily as novelty devices, showing up in high school attainment fairs, basement workshops, and the occasional low budget science-fiction movie. It should be noted that Tesla coils can be extremely dangerous devices. Burns caused by radio-frequency (RF) current, like all electrical burn down, can be very deep, unlike skin burns caused by contact with hot objects or flames. Although the high-frequency discharge of a Tesla coil has the curious property of being beyond the shock perception frequency of the human nervous system, this does not mean Tesla coils cannot hurt or even kill you I strongly advise seeking the assistance of an experient Tesla coil experimenter if you would embark on building one yourself.11. Linear varying Differential Transformer A linear variable differential transformer (LVDT) has an AC drive primary wound between two secondarys on a cylindrical air core form. A movable ferromagnetic slug converts switching to a variable voltage by changing the coupling between the driven primary and secondary windings. The LVDT is a displacement or distance measuring transducer. Units are available for measuring displacement over a distance of a fraction of a millimeter to a half a meter. LVDTs are rugged and dirt resistant compared to linear optical encoders.Fig.21 LVDTThe excitation voltage is in the range of 0.5 to 10 VAC at a frequency of 1 to 200 KHz. A ferrite core is suitable at these frequencies. It is extended outside the body by an non-magnetic rod. As the core is moved toward the top winding, the voltage across this coil increases due to increased coupling, while the voltage on the fathom coil decreases. If the core is moved toward the bottom winding, the voltage on this coil increases as the voltage decreases across the top coil. Theoretically, a centered slug yields equal voltages across both coils. In practice leakage inductance prevents the null from dropping all the way to 0 V. With a centered slug, the series-opposing wired secondarys cancel yielding V13 = 0. miserable the slug up increases V13. Note that it is in-phase with with V1, the top winding, and 180o out of phase with V3, bottom winding. Moving the slug down from the center position increases V13. However, it is 180o out of phase with with V1, the top winding, and in-phase with V3, bottom winding. Moving the slug from top to bottom shows a minimum at the center point, with an 180o phase reversal in liberty chit the center.Acknowledgment