parts of transformer

8/18/2019 Parts of Transformer

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PARTS OF TRANSFORMER

Double-foat Buchholz relay

For sudden pressure rise and gas detection in oil-immersed transformer tanks

with conserator! "nstalled in the connecting pipe #etween tank and conserator

and responding to internal arcing faults and slow decomposition of insulating

materials! Additionall$% #ackup function of oil alarm! The rela$ is actuated either

#$ pressure waes or gas accumulation% or #$ loss of oil #elow the rela$ leel!

Separate contacts are installed for alarm and tripping! "n case of a gas

accumulation alarm% gas samples can #e drawn directl$ at the rela$ with a small

chemical testing kit! &iscolouring of two li'uids indicates either arcing #$

products or insulation decomposition products in the oil! No change in colour

indicates an air #u##le!

VECTOR GROUP

2.1 Y-, D-, and Z-connected windingsThere are two principal three-phase connections of transformer windings: star (Y-connection)

and delta (D-connection). For special prposes, particlarl! in small power transformers,another connection named "ig"ag or Z is also sed. #istoricall!, se$eral other schemes ha$e%een in se (sch as &trncated delta&, &e'tended delta&, &T-connection&, &-connection&, etc.).hile sch connections are sed in transformers for special applications, the! no longer appear in common power transmission s!stems.

2.1.1 *d$antages of a Y-connected windingThis t!pe of winding: + is more economical for a high-$oltage winding + has a netral point a$aila%le + permits direct earthing or earthing throgh an impedance + permits redced inslation le$el of the netral (graded inslation) + permits the winding taps and tapchanger to %e located at the netral end of each phase

+ permits single-phase loading with netral crrent (see 2.2 and .).

2.1.2 *d$antages of a D-connected winding


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This t!pe of winding: + is more economical for a high-crrent, low-$oltage winding + in com%ination with a star-connected winding, redces the "ero-se/ence impedance inthat winding.

2.1.0 *d$antages of a Z-connected winding

This t!pe of winding: + permits netral crrent loading with inherentl! low "ero-se/ence impedance. (t is sedfor earthing transformers to create an artificial netral terminal of a s!stem) + redces $oltage n%alance in s!stems where the load is not e/all! distri%ted %etweenthe phases.

(onnection and phase displacement s$m#ols for three-phase transformers

The star% delta% or )ig)ag connection of a set of phase windings of a three-phase

transformer

or of windings of the same oltage of single-phase transformers associated in a

three-phase

#ank shall #e indicated #$ the capital letters *% & or + for the high-oltage ,./

winding and

small letters $% d or ) for the intermediate and low-oltage ,0./ windings! "f theneutral point of

a star-connected or )ig)ag-connected winding is #rought out% the indication

shall #e *N ,$n/

or +N ,)n/ respectiel$!

Open windings in a three-phase transformer ,that are not connected

together in the

transformer #ut hae #oth ends of each phase winding #rought out to terminals/are indicated

as """ ,./% or iii ,intermediate or low-oltage windings/!

For an auto-connected pair of windings% the s$m#ol of the lower oltage

winding is replaced

#$ 1auto1% or 1a1% for e2ample% 1*Nauto1 or 1*Na1 or 1*Na31% 1+Na441!


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E2ample 4

A distri#ution transformer with high-oltage winding for 53 k.% delta-connected! The low-

oltage winding is 633 . star-connected with neutral #rought out! The 0. winding

lags the .

#$ 7738!

S$m#ol9 &$n44

E2ample 5

A three-winding transformer9 457 k. star with neutral #rought out! 7: k.

star with neutral

#rought out% in phase with the . winding #ut not auto-connected! ;%5 k.

delta% lagging

#$ 4


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parts of transformer

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