Transformer rating indicated in (kVA) inlight of the fact that copper loss of a transformer relies upon current andiron misfortune on voltage. Along these lines, add up to transformer reliesupon volt ampere (VA) and not on stage point amongst voltage and current. It isfree of load power factor. That is the reason rating of transformer in (kVA)and not in KW(kilowatt).                        5.

Why transformerrating specified in KVA?Thefour fundamental setups of a three-stage transformer, we can list thetransformers optional voltages and streams as for the essential line voltage,VL and its essential line current IL as appeared in the accompanying table.Where: n breaks even with the transformers “turns proportion” (T.R.)of the quantity of optional windings NS, partitioned by the quantity ofessential windings NP. (NS/NP) and VL is the line-to-fix voltage with VP beingthe stage to-unbiased voltage.   Three phase transformerline and voltage current. Where once more, VL is the line-to-linevoltage, and VP is the stage to-unbiased voltage on either the essential or theoptional side.

 Three phase voltage and current.  (vi)  Scottconnection-  Twotransformers are utilized as a part of this sort of association. One of thetransformers has focus taps on both essential and auxiliary windings.

Scott-association can likewise be utilized for three stage to two stage change.The association is made as appeared in the figure above.    (v)  Open delta connection- Opendelta association can be used when one of the transformers in delta-delta isincapacitated and the administration is to be continued until the point whenthe defective transformers is repaired or supplanted. It can in like manner beused for little three stage loads where establishment of full three transformerbank is un-fundamental. The aggregate load passing on limit of open deltaassociation is 57.

7% than that would be for delta-delta association.  Formulae showsdelta star turns ratio. (iv)                 Delta-star connection-The essential winding is related in delta and the optional winding isrelated in star with unbiased grounded. This sort of connection isfundamentally used in step up transformer toward the begin of transmissionline. The extent of auxiliary to essential line voltage is ?3 times the changeproportion. There is 30 degree move between the essential and optional linevoltages.  Formulae shows star-delta turns ratio.

  (iii) Star-delta connection-The essential winding is star-star associated with grounded impartial and thesecondary winding is delta associated. Step down transformer at the substationend of transmission line is mainly utilized for this connection. The proportionof secondary to primary line is 1/?3 times the transformation proportion. Theshift between the primary and secondary voltage line voltages is 30 degree. (ii) Delta-deltaconnection –Generally, large and low voltage transformer use this connection.

Number of required turns is decently greater than star-star association. Thetransformation proportion of the transformer is equivalent to the proportion ofline voltages on the primary and secondary side. This connection can be usednotwithstanding for unbalanced loading. Regardless of whether one transformeris not balanced, system can keep on operating in open delta association is oneof the benefit of the connection  (i)   Usually small, high voltage transformersuse Star-star connection.

In starconnection number of required turn is reduced. Thus, reduction of the amount ofinsulation also takes place. On the off chance that the associated load isbalanced, this association can be utilized.

                     VI.         Scottconnection                       V.         Opendelta and                     IV.

         Delta-star                     III.         Star-delta                       II.         Delta-delta                         I.         Star-starStaror delta can be connected in the winding of primary or secondary windings. Itwill provide a total of 4 possible connections for 3 phase transformer.Threephase transformer connection In a shell type three phasetransformer, three stages are more autonomous than they are in core type. Eachstage has its individual magnetic circuit.

The development of shell type threestage transformer is shown in the figure above. The development is like that ofthree single stage shell compose transformers kept on the highest point of eachother. The development of a core kind threestage transformer is as appeared in the figure. The core comprises of threelegs or limbs. Of course, the coreis comprised of thin overlaid sheets todecrease eddy current misfortunes. Every limb has essential and secondary windingsin cylindrical shape arranged concentrically. Three phase ac systempresent in almost all major generation and distribution systems in the world.

It constructed from 3 single phase transformers. A three-stage transformer isset up by three arrangements of essential and auxiliary windings, each setwound around one leg of an iron center get together. Fundamentally it wouldseem that three single-stage transformers sharing a joined center as in figure.Three phase transformer center contains three arrangements of windings. Thosearrangements of essential and optional windings will be associated in either ?or Y setups to shape a whole unit.3.

  Three phase transformer (operation andtypes)Presently we will examine the saving of copper in autotransformer contrasted with two windings electrical power transformer. Werealize that weight of copper of any winding relies on its length and cross -sectional zone. Again length of conductor in winding is corresponding to itsnumber of turns and cross – sectional area changes with evaluated current. Soweight of copper in winding is straightforwardly corresponding to result ofnumber of turns and evaluated current of the winding. 2.How copper is saving in autotransformer?3.    Absent of galvanic isolation.2.

     Used just in theconstrained places where a slight variation of the output voltage from inputvoltage is required. 1.    The auxiliary winding isn’t protected from theessential winding. On the off chance that an auto transformer is utilized tosupply low voltage from a high voltage and there is a break in the auxiliarywinding, the full essential voltage comes across the optional terminal which isrisky to the operator and equipment. Disadvantages of auto transformer. 3.

     higher efficiencythan two winding transformer. 2.     voltageregulation as voltage drop in resistance 1.    smaller in size and cheaper.Advantagesof auto transformerExampleof step down transformer.

The picture shows that number of primary higher thannumber of secondary coil.  B.   Step Down Transformer- Atransformer in which Np >Ns is called a step down transformer. A step downtransformer is a transformer which converts high alternating voltage to lowalternating voltage.Exampleof step up transformer.

The picture shows that Ns>Np. A.   Step Up Transformer –At the point whenthe number of secondary coil is higher than the primary coil, it will be calledas step up transformer. It converts low alternative voltage to high alternativevoltage.

Principleof working operation.Alongthese lines, the part of the windings passes on the contrast between the twocurrents cab be made from a smaller conductor size, since the currents are muchsmaller saving on the cost of an equivalent double wound transformer. An autotransformer is used principally for theadjustments of line voltages to either change its value or to keep itconsistent. If the voltage modification is by a small amount, either up ordown, at that point the transformer ratio is small as Vp and Vs are almostequal. Currents Ip and Is, are also nearly equivalent. Auto transformer terminalmarkings. The standard procedure for denoting an auto transformerwinding is to name it with capital letters.

Essentially the normal unbiasedassociation is set apart as N or (n). For the secondary tapping’s, suffixnumbers are utilized for all tapping points along the auto transformersecondary winding. These number generally begin at number1 and continue inascending order for all tapping points as shown.  Autotransformer with multiple tappingpointsThe autotransformer canalso be constructed with more than one single tapping point.

Auto-transformerscan be utilized to provide different voltage points along its winding orincrease its supply voltage concerning its supply voltage VP as shown.Atthe point when the essential current Ip, is moving through the single windingtoward the arrow as shown up, the secondary current, Is, streams in theopposite direction. Along these lines, in the part of the winding thatgenerates the secondary voltage, Vs the present streaming out of the winding isthe difference of Ip and Is.  The type with programmedvoltage alteration can be utilized as programmed voltage regulator, to keep upan steady voltage at the clients administration during a wide range of line andload conditions. Another application is a lighting dimmer that doesn’t createEMI typical of most thyristor dimmers.The yield voltage alteration canbe manual or automatic. The manual kind is relevant just for moderately lowvoltage and it known as variable AC transformer.

These are regularly utilizedas a part of repair look for testing gadgets under various voltages or toreproduce irregular line voltages. A constant variable turns ofratio can be observed by uncovering some part of the winding coils and makingthe secondary connection through a sliding brush. It is allowing for verysmooth control of output voltage. Discrete voltage represented by actual numberof turns does not effects the output voltage. The voltage can be smoothlyvaried between turns as the brush has a relatively high resistance (comparedwith a metal contact) and the actual output voltage is a function of therelative area of brush in contact with adjacent windings.

The relatively highresistance of the brush also prevents it from acting as a short circuited turnwhen it contacts two adjacent turns. Typically, the primary connection connectsto only a part of the winding allowing the output voltage to be varied smoothlyfrom zero to above the input voltage and thus allowing the device to be usedfor testing electrical equipment at the limits of its specified voltage range.  A variable autotransformer·       Construction: Auto transformer is a device that with only one winding wound on a laminatedcore. An auto transformer is similar to a two winding transformer but differ inthe way the primary and secondary winding are interrelated. Both primary sideand secondary side is common to a part of the winding. On load condition, apart of the load current is obtained directly from the supply and the remainingpart is obtained by transformer action. An Auto transformer works as a voltage regulator.·       Introduction:1)    utoTransformer