”INSTRUMENT TRANSFORMER”

Presented by :*Nishant kumar

Reg. No. 0701209350Electrical & Electronics Engineering

Silicon institute of technology , Bhubaneswar

[ Contents ]▪ Instrument transformer Introduction Classification

▪Current transformerPrinciple of OperationConstruction & Classification Application & Specification

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▪ Potential Transformer Principle of operationConstruction ,Classification & Application▪Electromotive voltage

transformerIntroduction Construction & Application▪ Capacitive voltage transformer IntroductionConstruction & Application 3

[ Introduction of instrument transformer ]A electrical device which help in measurement

of high voltage or current.It provide low range current and voltage to the

protection system.By using low range ammeter can measure

high current.By using low range voltmeter can measure

high voltage.

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[ Types of instrument transformer ]

Instrument transformer has two type1) Current transformer 2)Potential transformer

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[ current transformer ] It is normally known as CT.This is a type of step up transformer.This is step up transformer because when

we step up, the voltage increases and current decrease.

The current is step down in a known ratio called current ratio.

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[Construction of current transformer]

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The current transformer has primary coil of one or less no. of turns of thick wire which is connected in series with the transmission line.

It’s core is made of by rolled steel.The secondary consist of large number of

turns of fine wire.The secondary and primary winding are

insulated to each other and oil immersed.

Current transformer

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CURRENT TRANSFORMER

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[classification of current transformer] On the basis of primary winding1) Wound type2) Bar type

On the basis of secondary winding1) Ring type2) Stadium type3) Rectangular type

On the basis of working1) Summation CT.2) Core balance CT.3) Interposing CT. 10

[ Standards ]The Indian and international standard for CTo Standard Standard no. Year⁞ ⁞-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

British BS 3938 1973⁞ ⁞ American ANSI C.57.13 1978⁞ ⁞ Australian AS 1675 1986⁞ ⁞ India IS 2705 1992⁞ ⁞ IEC IEC 60044-1 1996 ⁞ ⁞(International electro technical commission)----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Manufacturing company BHEL,CGL,ABB,Joti,Siemens… Etc.

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[ Testing of current transformer ]

Different type of test : Accuracy test Dielectric insulation test Temperature rise test Verification of polarity test

Different method of testing Mutual induction method Silsbee’s method 12

[ Specification ] For a 11 kv CT. --------------------------------------------------------------------------------------------

System voltage : 11 kv Insulation level voltage : 12/28/75 kv Ratio : 200/1-1-0.577 A Core 1 : 1 A metering Core 2 : 1 A protection Core 3 : 0.577 A, Class power supply Short time rating 20 kA for 1 sec Insulation security factor : ISF<10 13

[ POTENTIAL TRANSFORMER ]Potential transformer normally known as

PT.That is a type of step down transformer.Step down transformer ,step down the

voltage and rise the current.The voltage is step down in the known

ratio called voltage ratio.

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[ principle of operation ]It is always connected in parallel to the

transmission line.It’s secondary winding is very low with

respect to the primary.The secondary winding is designed so

that a voltage of 100 to 150 v is delivered to the instrument load.

Line voltage =voltmeter reading/Ratio Ratio=no. of turn in secondary/no.of turn in primary

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POTENTIAL TRANSFORMER

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POTENTIAL TRANSFORMER

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[ construction of potential transformer ]Core size is large and made of by steel.Primary side large no. of turn.Secondary side only few no. of turn.Secondary and primary winding are

insulated to each other and oil immersed.

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[ classification of potential transformer ]Types of potential transformer1) Shell type2) Dry type

3) Oil type -----------------------------------------------------------------------------------------------------------------------------------------

Rating Type ------------------------------------------------------------------------------------------------------------------------------------------

Below 5000 v Shell type 5000 – 138000 v Dry or oil type Above 138000 v Only Oil type --------------------------------------------------------------------------------------------------------------------------------------------

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[ Standards ]The Indian and international standard for PTo Standard Standard no. Year⁞ ⁞ ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

British BS 3841 1973⁞ ⁞ American ANSI C.57.13 1978⁞ ⁞ Australian AS 1243 1982⁞ ⁞ India IS 3156 1992⁞ ⁞ IEC IEC 186 1987 ⁞ ⁞ (International electro technical commission) -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Manufacturing company BHEL,CGL,ABB,Joti,Siemens… Etc. 20

[ Testing of Potential transformer ]Different type of test : Accuracy test Dielectric insulation test Temperature rise test Verification of polarity test

Different method of testing Absolute null method Employing capacitance divider method

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[ specification ]

For a 11 kv VT :System voltage : 11kvInsulation level voltage : 12/28/75 kvNumber of phase : ThreeVector Group : star/starRatio : 11 kv/ 110 kvBurden : 100 VA

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[ Electro motive voltage transformer ]o Why not conventional type potential

transformer.Above 100 kv , size are very large.Insulation problemHigh heating effectCostly to build

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[ designs ]1. Insulated casing Use high voltage insulated oil2. Moulded rubber potential transformer Replace oil and porcelain bushing to

the synthetic rubber.3. Cascaded transformer For voltage divider cascaded n no. of

transformer.24

[ capacitive voltage transformer ]

A less expensive alternative of electro magnetic voltage transformer.

Use no. of capacitor as a voltage divider.

Less insulation problem.Very cheaper.Simple circuit.

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CAPACITIVE VOLTAGE TRANSFORMER

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[ Design ] Use capacitor band.Use an Auxiliary transformer.Secondary have very low voltage.Any bus bar protection system or any

measuring device connect to the secondary of the auxiliary transformer.

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CAPACITIVE VOLTAGE TRANSFORMER

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Application of instrument transformer

* It help in measurement of high voltage or current.* It provide low voltage and current to the electrical device.* It’s measure application is in the protection system where relay is work on low amount of voltage and current

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REFERENCES :

• Introduction to the electrical machines. Macmillan.

• Hand book of transformer design and applications. McGraw-Hill.

• IEEE Transactions on power Apparatus And System.

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ANY Query ???

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Thank You !