KT Ntpc Power Transformers

7/28/2019 KT Ntpc Power Transformers

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WELCOMETRANSFORMERS AND

ACCESSORIES

KARAN TRIPATHI


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CONTENTS Principles of Transformers

Materials used in transformers

Magnetic circuit

Winding and insulation

Tap Changers Accessories

Drying and Impregnation

Structural Design. DGA

Transformer Testing

Loading and life of Transformer.


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Principles of Transformers

A transformer is a static piece of apparatus usedfor the transferring power from one circuit to the

other without change in frequency. It can raise or

lower the voltage with a corresponding decreaseor increase in current.

Primary winding

Secondary winding

Linkage of the two by Mutual Inductance


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Voltage transformation ratio

E1 = 4.44* f *N1* m

E2= 4.44* f *N2* m

E2 / E 1 = N1/N2


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LOW VOLTAGE WINDING DESIGN

Since voltage is less ,hence turns will also be less.

Phase Current = MVA/(3*line voltage in kV) if winding

is star connected.Phase Current = MVA/(3*line voltage in kV) if winding is

Delta connected.

This indicates current in Low voltage winding shall be high.


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7/63Directed Oil Flow Arrangement

k l


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8

Leakage Flux

Flux entering the tank


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9Flux enters the Shunt

LV Wi di


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To carry high current thearea of cross section of

the conductors should be

high. This is

accomplished by

adopting more no. of

conductors per turn.

Helical winding which isspring like, suits most forthe LV windings.

LV Windings

HELICAL WINDING


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HIGH VOLTAGE WINDING

Large no. of turns

Less current.

Disc coils are the best choice for the HVwindings where a single disc can have turns ashigh as 25 nos.


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l d f


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Materials used in transformers1. CONDUCTORS:

P.I.C.C.

C.T.C.

Bunched P.I.C.C.

Glued C.T.C.

l d f


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Materials used in transformers1. Insulators:

1. Paper Insulation2. Perma-wood

3. Transformer oil.

4. Solid Polymer Insulation.

M i l d i f


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Materials used in transformers1. Core:

o The material used for core making is lowreluctance magnetic steel containing

silicon.This is called CRGO i.e cold rolled

grain oriented steel.

o The grain orientation is technology which

ensures that the flux flow through the

laminations with minimumresistance,resulting in low core loss.


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M i l d i f


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Materials used in transformers1. Core:

YOKE BOLT:BOLTS USED IN YOKES TO CLAMPTHE LAMINATIONS TOGETHER.

TOP YOKE LEVEL(TYL)/BOTTOM YOKE

LEVEL(BYL): EDGE OF THE TOP OR BOTTOMYOKE IN THE WINDOW.

PIN PAD ASSEMBLY: THE ARRGMT. TO TOJOIN CLAMP PLATE WITH END FRAME ISCALLED PIN PAD ASSY.


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Ch


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Tap Changers

1. On Load Type (OLTC)

2. Off Load Type (OFTC)

Used for variation in terminal voltage inHV side.

Voltage in the system can be varied bychanging turns ratio of the transformer.

Tap changer can be used for adding orcutting out turns of primary or secondarywinding of transformer.

Provision for manual and DM movement.

TAP SELECTION SWITCHDIVERTER SWITCH


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SWITCHING CYCLE OF DIVERTER & SELECTOR SWITCH


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Accessories

BUSHINGS

PRESSURE RELIEF VALVE (PRV) SUDDEN PRESSURE RELAY (SPR) COOLING BANK RTD BUCCHOLZ RELAY BREATHER MAGNETIC OIL GAUGE (MOG) AIRCELL OIL / WINDING TEMP INDICATORS (OTI) / (WTI)

AIR CELL LEAKAGE DETECTORS (ACLD) OIL PUMPS OIL FLOW INDICATORS (OFI) OIL SURGE RELAY (OSR)

Bushings (HV)


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Bushings (HV)


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POLLUTION LEVELS CREEPAGE DISTANCE

I. Light ( areas without industries,agricultural or mountain areas ) 16mm/kV

II. Medium ( areas with industriesnot producing pollution smoke,

Low density of house areas not exposed

to the coast)

20 mm/kV

III. Heavy (Areas with high density ofindustries, high density of

Heating plants producing pollution,

areas close to the sea.)

25mm/kV

IV. Very Heavy(Areas close to

the coast and exposed to sea spray,

desert areas, areas exposed to strong

winds carrying salt and sand etc )

31mm/kV

Example: for 145 kV Bushing with heavy pollution level minimum creepagedistance works to be.

145 kVX 25mm/kV = 3625mm


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Major Partsof

Condenser Bushing

Top Cap

1. Condenser Core

2. Porcelain.3. Oil level Gauge

4. Top cap.

5. Test Tap.

6. Mounting Flange.

7. Oil side Stress Shield.


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d l


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Tan delta test cap


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Bushings (LV)


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Bushings (LV)

LOW CURRENT HIGH CURRENT

Pressure Relief Valve


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Pressure Relief Valve

Sudden Pressure Relay (SPR)


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Protection and detection of Devices calibrated to quickly alarmor trip during dangerous sudden pressure changes rapidpressure rise changes (see response curves below) Actuation only occurs based on rate of pressure rise and will

not occur under normal pressure variations caused bytemperature change and vibration Can be subjected to full vacuum or 20 PSI positive pressurewithout damage Standard operation from -40 to 180F ( -40 to 82C) Special units available for operation at -67F (-55C)

Sudden Pressure Relay (SPR)

D i d I i


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Drying and Impregnation

St t l D i


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Structural Design

TRANSFORMER TANK IS AN ENCLOSURE WHICH

CONTAINS INSIDE IT THE LIVE PARTS SUCH AS COREAND WINDING ASSEMBLY, ELECTRICALCONNECTIONS AND INSULATING OIL.

CONVENTIONAL TYPE TANK BELL TYPE TANK.

Bell type tank design

OIL TESTS


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OIL TESTS

Moisture Content

Break down value (BDV)

Dissolved gas analysis (DGA)

Inter facial tension (IFT) Acidity/Neut. Number.

Visual Inspection.

Tan delta and resistivity.


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DUVAL TRIANGLE


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DUVAL TRIANGLE


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Loading and Life of Transformer


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Loading and Life of Transformer


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31.3C

45.9C

35

40

45

NORMAL THERMAL IMAGE OF A TRANSFORMER

ABNORMAL THERMAL IMAGE OF A TRANSFORMER


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SP01: 46.8C

SP02: 48.2C

SP03: 47.7C

ABNORMAL THERMAL IMAGE OF A TRANSFORMER

Bl k d di


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Blocked radiator

LINE-01: 22.4C

LINE-02: 34.3C

I fl f P i h i f h


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Influence of Paper moisture content on the ageing rate of thePaper (Fabre, CIGRE 1960)

100

30

10

10.1 0.3 1 3 10

AgeingRate

Moisture content in weight %

At 4.5 % papermoisture and 90C top oil temp.,

flash over will

occur.


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THANK YOU

HV Winding terminal


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HV Winding terminal

5 Limb core


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5 Limb core

Windings and OLTC


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Windings and OLTC

Directed oil flow in windings


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Directed oil flow in windings


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KT Ntpc Power Transformers

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