AREVA PPT

Power Transformer Design Aspect

Didik Susilo Widianto Technical Director

PT UNINDO – AREVA

Contents

1.

Introduction

2. Transformer core 3.

Inrush Current

4. Transformer Winding 5.

Insulation and Cooling Medium

6.

Transformer Losses

7.

Insulation Structure & Dielectric Withstand

8.

Transformer Thermal Aspect

9.

Short Circuit Analysis

10. Engineering 11. Manufacturing Process 12. Accessories, Protection & control 13. Final Acceptance Test 14. Technology Application 3

> Title Title of presen presentat tation ion - Date Date - Refere Reference nces s

3

1. Introduction

4

> Title of presentation - Date - References

4

Basic Theory Faraday ’ ’s law The electromotive force ( e.m.f ) is proportional to e.m.f the rate of linked flux changes

E = - N x dΦ/dt  E = Electro motive force  N = Number of turn  dΦ/dt = Change the flux against time

Lenz ’ ’s law The e.m.f is such any current produced acts to opposite the linked flux. Current Flux Current Counter Flux

5


5

NO LOAD Condition

E = - N dΦ/dt = - N d(Φm Sin(ωt))/ dt = - Nω. ΦmSin(ωt – π/2) At f = 50 Hz, Φ = Β.Α  E = 222.14 . Ν.Β.Α At f = 60 Hz, E = 222.14 .N.B.A.(f/50)

E1

 E = e.m.f (electromotive force) in Volt  Φ = Flux in Weber  B = Peak Induction in Tesla  A = Core cross section in

I0

Ip

Φ

m2

 I0 = No load current in Amp.

Im

I0

 Im = Magnetizing current in Amp.  Ip = Losses current in Amp.

E2

E1

E2 N1 6


N2 6

ON LOAD Condition

V1 I2

I0 + I1

R2

I 1.X 1

X2

I 1.R 1

X1

R1

V1

E1 E2

E1 N1

V2

I1 Ip

N2

E 1 : N 1 = E 2 : N 2 I 1 x N 1 = I 2 x N 2

I1 + I0 I0

I2

Im

Φ

Θ Θ

V2 I 2 R 2

Θ 7

= the load power factor


I 2 .X 2

E2 7

Power Transformer Main Parts Oil Preservation

Bushing Core Transformer Tank Winding Control Cubicle

Cooler 8


Transformer Liquid 8

Transformer Power Rating  Transformer power rating is expressed by MVA as a product of

rating voltage and rating current.  The power rating [S] is a product of reactive power [Q] and

active power [P];

S [MVA] = S(Q2 [MVAR] + P2 [MW] )  Referring to IEC 60076 – 1;

S [MVA] = S S3 x E2[kV] x I2[Amp] 10-3  Referring to ANSI/IEEE C57.12.00;

S [MVA] = S S3 x V2[kV] x I2[Amp] 10-3 = S S3 x (E2 + ∆V)[kV] x I2[Amp] 10-3 Hence, in ANSI/IEEE standard the power rating has considered voltage drop at stated power factor

9


9

Voltage Drop/Rise

∆V = V 2 – V 1 R2

I2

I1

X2

X1

R1

V1

E2

E1 N1

V2

N2

∆V = K (VR.CosΘ + VX.SinΘ) + K2/200 x (VR.Sin Θ – VX.CosΘ)

V Z

V X

Θ Θ

∆V K V R V X V Z Θ Θ

= Voltage drop/rise [%] = Loading factor = Transformer resistance [%] = Transformer reactance [%] = Transformer impedance [%] = Load power factor

V R 10


10

Tap Regulation  Tap Regulation ; the required voltage ratio to control the

fluctuated voltage of network to deliver the expected constant voltage.  Two type of tap regulator = Tap Changer ;

1.OLTC (On Load Tap Changer) = Tap regulation when the transformer energized/under loading. 2.OCTC (Off Circuit Tap Changer) = Tap regulation when the transformer de-energized (no transformer terminal is connected to any network/generator)  Tap regulation is expressed by the number of step & the

percentage of nominal voltage for each step regulation.  Example = 150 kV + 7 x 1.5% / -10 x 1.5%

11


11

Flux Behavior Due To Tap Regulation  Two type of tap regulation ;  CFVV = Constant Flux Variable Voltage 



The transformer volt/turn as well as the core flux will constant along the tap regulated positions. This is the most common tap regulation system.

 VFVV = Variable Flux Variable Voltage 



12

The transformer volt/turn as well as the core flux will vary referring to the tap regulated positions. This is used due to high current tap regulation at furnace application or booster type regulation.


12

Position Of Tap Changer

 Normally, the most optimum solution for tap changer

location is the neutral end of winding for STAR connected winding.  For DELTA connected winding with insulation class of

72.5 kV and lower, the line end location of tap changer is normally the most optimum solution.  For DELTA connected winding with insulation class

higher than 72.5 kV class, the middle electrical location of tap changer will be the optimum.  The electrically as well as geometrically location of tap

changer will also determine the impedance & losses behavior.

13


13

Tap Regulation vs Power Rating  There are two kinds of power rating;  CONSTANT Power Rating;

The power is constant for all tap regulation position.  REDUCED Power Rating;

The power is reduced with constant current rating from a certain tap regulation position.

Constant Power S V

Tap 1

14

Reduced Power from tap n V

I

n


p

Tap 1

S I

n

p

14

Autotransformer Concept Seri Winding

I2 = Is

Ns = N2 – N1

Tap Changer I1 V2 V1

I1, I2

N1 = Nc

Ic = I1 – I2

Common Winding

= Current primary (1) & secondary (2)

V1, V2 = Voltage primary (1) & secondary (2) Common Winding = N1 x (I1 – I2) Seri Winding = (N2 – N1) x I2 15


15

On Load Tap Changer

ON TANK OLTC

16


IN TANK OLTC

16

ACTIVE PART - Areva definitions Upper Yoke

Frame Insulation

Top Frame

Tank Location Cup

Coil Clamping Block Cross Brace Top Platform

Tie Rod

Bottom Platform

Flux Packet Coil Support Blocks Oil Diaphragm Tank Base 17


17

2. Transformer Core

18


18

CORE  Purpose :

the path for the flux lines with low magnetic reluctance

Core material in power transformer ;  Cold Rolled Grain Oriented Silicon Steel.  Available thickness = 0.23 mm, 0.27 mm, 0.30 mm  Lamination insulation = CARLITE 0.012 mm  Grade ;  Conventional Grain Oriented = High losses.  Hi-B Grain Oriented

= Medium losses.

 Laser/plasma refinement GO = Low losses.

19


19

Induction vs Core Loss

20


20

Core Stacking - Mitred Joints

But Lap Joint

Step Lap Joint

21


21

Core Cutting

Three Legs Core

½ W

W

Five Legs Core (3 wounds + 2 return) 22


22

Bandaged Core

23


23

Core Determination Factors  No Load Loss (and No Load Current) ;

 No load loss is independent with the loading of the transformer, but it is

dependent with the applied voltage per turn of the winding.  It has more significant economical component cost in capitalization than other

losses due to it’s appearance independency with the cyclic loading.  IEC standard tolerance for no load loss = +15%, no load current = +30%.  Over excitation capability ;

 For generator application, the transformer shall be designed for over excitation

up to 140% in 5 second during load rejection.  For distribution application (and general purpose), the transformer has to be

designed by considering 

Over voltage up to 110% continuous at no load condition.



Over voltage up to 105% continuous at full load condition.



Core temperature limit at required maximum ambient temperature (Design limit < 140oC at center, < 105oC at surface to avoid gassing).

 Sound power / sound pressure level.

 The local regulation for sound pressure/sound power limit.  Installation location ; populated area, remote area. 24


24

Core Saturation Capability For Load Rejection

145 140 n135 o i t a130 t i c x 125 E t n e120 c r e P 115

110 105 0.1

25


1

Time - Minutes

10

100

25

3. Inrush Current

26


26

Definition Inrush Current is the excitation current that will occur due to the existence of magnetic flux remnant when the transformer is first switched into the service.

The inrush current can have the peak value up to 5 times the nominal current. The most unfavorable inrush current arises when switching in take place at a zero voltage transition.

Due to the magnitude of the inrush current, the over current relay may interpret this current as the failure current to open the circuit breaker on the system.

27


27

Inrush Current Calculation  Maximum Inrush Current can be estimated with the some

empirical factors referring to the core stacking method, gap between core and the first excited winding, primary winding connection, network & transformer impedance and transformer core behavior. This is an important information to determine the over current and differential relays setting point.  The actual inrush current is difficult to be estimated as this will

be dependent to the existence of remanence flux due to previous system cut out at certain voltage angle.  Maximum inrush current estimation method;

 Empirical formula.  Electromagnetic transient computer software;

28



EMTP (Electro Magnetic Transient Program), CANADA.



SLIM – electromagnetic function, AREVA


28

Estimating Inrush Current Empirical formula to calculate the peak of inrush current is as followings; S2.U

I peak = Z . Sin(ωt – y) – e-(t-t0)/τ.SinQ). K t Where;

29

K

= Constanta value referring to the transformer connection (Grounded STAR, DELTA) and other circumstantial.

U

= Applied voltage (rms)

Zt

= Transformer + network impedance.

y

= Energization angle.

τ

= Transformer time constant.

t

= Core saturation time referring to maximum, remnant & saturation induction behaviour.

Q

= Angle function of core induction.


29

Some Aspect Effecting Inrush Current  Transformer number of phases and primary winding

connections;  Single phase transformer and/or shell type has higher inrush current than three phase transformer and/or core type.  DELTA connection of primary winding three phase transformer has lower inrush current than grounded STAR.  Transformer capacity;  Higher transformer MVA rating has lower ratio between inrush current and primary nominal current, but longer decay time.  Transformer core steel, core design and nominal induction;  HiB core steel has lower inrush current than CRGO material.  But lap joint has lower inrush current than Step lap joint.  Lower impedance transformer normally has lower air core reactance and then higher inrush current.

30


30

B

Flux nominal + remnant

Φrem

H

time Flux nominal nomina l

Inrush current Excitation current

31


e m i t

31

4. Transformer Windings

32


32

Winding

Type of winding; Layer winding; 

Single layer.



Multilayer.

Helical winding. Disc winding. 

Plain/continuous disc



Intershielded disc.



Interleaved disc.

Multistart winding. 33


33

Winding Conductor Type of material conductor; Electrolytic copper. Aluminum.

Form of conductor; Round wire.( for small distribution transformer) Rectangular wire. Twin/Tripple/Quadrople conductor. CTC (Continuous Transposed Cable). Netting-CTC/Paper less CTC 34


34

Winding – Areva terminology Axial/Radial Packing for transposition

Directed Oil Flow washers External DOF washer Internal DOF washer Transposition set Segment Spacer

35


35

Disc Winding

PROTECTION FOR SCISSOR EFFECT

Extra paper = 2 layers overlapped of Clupack

36


36

CTCs winding

Epoxy bonded

Try to use CTC with max. 55 strands per cable. Epoxy bonded in low chip type is recommended for force capability. Strand thickness 1.2 mm to 2.6 mm. Strand width 5.0 mm to 12.5 mm. Insulation increase of each strand = 0.10 PVA + 0.05 low chip epoxy. Insulation increase of bundle, minimum 0.50 mm. Minimum key spacer thickness for ZIG-ZAG cooling = 4.0 mm.

37


37

Soft Cross Over for CTC – DISC winding Missing turn block = 1 cable thick

Inside cross over protection

Cross over block = thick pressboard

38


38

Heavy current helical winding

39


39

Intershielded Disc Winding

Provide the best controllable high frequency dielectric voltage distribution 40


40

Intershield Disc Winding Technology Research

 In 2007 : To Tests Models ISDW With Few Turns/Disc With Results To Be

Used As Input For The Design Of A Full Size 800 kV UHVDC ISDW Prototype

 To Design With EDT&PD Team; To Build And To Test A Full Size 800 kV

UHVDC ISDW Prototype

41


41

Intershielded Disc Winding

42


42

5. Insulation and Cooling Medium

43


43

Cooling Medium

INTERNAL COOLING MEDIUM

Besides the thermal absorption, the internal cooling medium also functions as the insulation medium. 

Class A; 



44

Mineral oil (Inhibited or Un -inhibited oil).

Class K; 

Silicon oil



Synthetic ester



Hi-Temp natural liquid (seeds).


44

Oil Molecules

45


45

Oil Specification

46


46

Oil Finger Print

47


47

Oil ’ ’s Aromatic Check (Sulphur Content and other)

48


48

Future – Environmental Friendly Liquid  Environmental liquid

= Enviro-Temp FR3 by COOPER

 Inhibited oil

= Nitro 10XT by NYNAS

Property – typical values

Inhibited oil

FR3

0.08% per Wt

n.a.

500 hours

continuous

25%

100%

80 ppm

1200 ppm

60/65/78 K

80/110/130 K

Flash point

145oC

330oC

Pour point

-57oC

-18oC

Antioxidant, phenols Oxidation stability by 120oC Biodegradable in 21 days Saturated moisture at 25oC Temp. rise for unity life time *)

49


49

Natural ester dielectric behavior Dielectric Strength versus Water Content 80

) V k ( n w o d k a e r B c i r t c e l e i D 6 1 8 1 D

70 60 50 40 30 Envirotemp FR3 fluid conventional transformer oil

20 10 0 0

100

200

300

400

500

600

Water Content (ppm)

50


50

Eco - -Design/vegetable D esign/vegetable oil transformer History ; ; 

2005: order for joint development with customers of vegetable oil transformers 2006: oil characteristics review and prototype transformers design, manufacture and test  2007 Q1: commissioning and monitoring of 90MVA 132kV transformer in UK  2007 : devel of PTR design rules book, oil specification , manufacturing and filling process , maintenance rules and nominal parameters  2007 : commercial agreement with oil supplier Cooper for local vegetable oil distribution. 

Achievement  Environmentally friendly transformers and reactors

filled with vegetable oil

 Vegetable oil totally biodegradable , with higher fire point

than mineral oil (envirotempFR3 oil from COOPER)  transformers and reactors up to 245kV, and rated power up to 100 MVA (existing new references)  Application for Higher ratings to be evaluated if potential for joint development with customers

51


51

6. Transformer Losses

52


52

Power Transformer Losses Losses is the active energy component

to be absorbed by the transformer and associated component such as fan, pump, control circuit. Mainly this losses will become the heat energy. Losses contain; Core loss = No load loss. Load loss Auxiliary loss

53


53

Core Loss  Core Loss = No Load Loss ; is the loss of the

energy when the transformer under no load condition (the primary terminal is connected to the power source, the secondary/tertiary etc are open). This loss is expressed by Watt or kWatt.  Core loss contains;  Hysteresis loss; The magnetic power that inherently

absorbed due to the magnetic behavior of the transformer core material. This energy is required to realign the magnetic domain for the flux at certain time.

 Eddy-current loss; The loss of active power caused by

the circulating current as the result from the perpendicular flux into the core plate with it’s resistive component characteristic. Thinner plate will give lower eddy-current loss of core material.

54


54

Hysteresis Core Loss

B max [T] P h = k h .f.B max n k h = Hysteresis constant depend on the 3 to 20x10 - 3 3 ) core material (3x10 - 3

n = Exponent varies from 0.5 to 2.3 dependent on the core material

δ δB B

H peak [A/m]

55


55

Eddy - -Current C urrent core loss

P e = k e .f 2 .t 2 .B max 2 k e = Constant depends on the core grade, typical values = 200 to 1000 t = core plate thickness [m]

B

t

56


56

Load Loss The current flowing through the windings

of a loaded transformer will create loss energy in the form of heat. The load loss is normally expressed at

75oC or 85oC. 85oC shall use thermally upgraded paper

This load loss is containing  DC losses = the dominant component loss is caused by

the product of current to the DC resistance of winding conductor

 Stray losses = the loss is caused by the leakage

magnetic impinging on the winding conductor and other internal conductive material inside the transformer.

57


57

DC loss

1

2

3

DC losses = I 12 R dc1 + I 2 2 (R dc2 + R dc3 ) R dc = ρ . L/A  I1, I2 = current flowing in winding 1,2,3 [A]  Rdc = DC resistance of each winding. [Ω]  ρ = winding conductor resistivity. [Ωm]  L = Length of winding conductor. [m]  A = Winding conductor cross section. [m 2] 58


58

Winding Conductor Property

Propeties

Unit

Copper

Aluminum

Conductivity

% IACS

100

60.97

Resistivity@20oC

ρ (Ω.m)

1.7241 x 10-8

2.8280 x 10-8

K

235

225

Kg/m3

8890

2703

Temperature reference

Specific mass

59


59

Conductivity vs temperature  For Copper at temperature T1 and T2

ρ2 = ρ1 x (235 + T2) / (235 + T1) Resistivity at 75oC = 2.1 x 10-8 Ωm. DC loss at 75oC in Watt = 2.36 x 10-12.τ2.M  

τ = curr current ent den density sity [A/m2]

M = conductor mass [kg]

 For Aluminum at temperature T1 and T2

ρ2 = ρ1 x (225 + T2) / (225 + T1) Resistivity at 75oC = 3.46 x 10-8 Ωm. DC loss at 75oC in Watt = 12.8 x 10-12.τ2.M  

60

current ent den density sity [A/m2] τ = curr M = conductor mass [kg]


60

Eddy Current Loss in AC system  When the winding is AC (Alternating Current) loaded, the

leakage flux impinges on the winding conductors and as a consequence eddy currents are generated in these conductors. This eddy current will push the distributed current on the skin area of conductor. This phenomena is known as SKIN EFFECT.

Conductor

Flux line

AC current line 61


61

Eddy loss distribution

The eddy loss distribution is not uniform along the winding. Normally the eddy losses at winding end is higher than at winding middle. It is important to control the eddy loss at top end winding to avoid very high hot spot gradient temperature. Brad B rad

Brad

1

2

1 62


2 62

Stray losses of inside metallic parts & tank  Inside tank of a power transformer is containing a lot

number of leakage flux.  The higher transformer impedance will result the bigger

number of leakage flux.  Leakage flux impinging onto metallic structural parts and

tank wall + cover will contribute the additional load loss. This loss is normally controlled between 5% to 15% of the total load losses.  This additional loss due to leakage flux is controlled by

the following methods;  Magnetic shunt panel to collect the leakage flux.  Copper or aluminum flux rejecter.  A-magnetic metallic part.  Splitting the wide plate width.

63


63

Infra Red Thermal Investigation

Infra Red Thermal Check To avoid local hot spot > 125oC

64


64

7. Insulation Structure & Dielectric Withstand

65


65

Dielectric Voltage Withstand Test  International standard reference;  SPLN  IEC 60076 part 3.  ANSI/IEEE C57.12.00 & C57.12.10

 Continuous over voltage up to 110% no load, 105% full load

condition.  Applied voltage withstand = the over voltage withstand between

each winding to other part in the transformer for one minute.  Induced voltage withstand = the over voltage withstand between

each turn and/or disc of each winding and the winding to earth for few seconds dependent on the testing frequency 120 x fnetwork /ftesting [seconds]. This over voltage may have magnitude up to twice of nominal voltage.  Transient over voltage withstand = the over voltage withstand due

to switching and /or lightning. The wave shape has duration up to few microseconds with it’s instantaneous peak over voltage withstand may have magnitude up to 3.5 times the nominal peak voltage for

66


66

IEC Standard Insulation Level

67

Highest voltage

Power frequency

(kV r.m.s)

(kV r.m.s)

7.2

Full wave impulse (kV peak)

Minimum air clearance (mm)

20

60

90

12

28

75

110

17.5

38

95

170

24

50

125

210

36

70

170

280

72.5

140

325

630

115

185

450

830

123

230

550

900

170

275

650

1250

325

750

1450

245

395

950

1900

2250

300

460

1050

2300

2650

362

510

1175

2700

3100


67

Voltage Withstand Criterium No Flash over (puncture and creepage) Partial Discharge under requirements; Less than 100 pC at 110% voltage. Less than 300 pC at 130% voltage. Less than 500 pC at 150% voltage.

FREE PARTIAL DISCHARGE ; 

68

Less than 50 pC at 150% voltage.


68

INSULATION Coordination

»The

Radial and Axial stresses between windings and to Earth have to be managed by an insulation structure which considers the combined individual stresses.

»This

structure has to consider both electrical requirements and thermal requirements for oil flow

»It

has to consider the effects of voltage transients and the problems of manufacture and processing

»It

has to be economic using minimum clearances and minimum of expensive components.

69


69

Oil Strength Behavior

70


70

Water Content in Paper

»0.5% dryness   PD PD inception voltage is 83% induced voltage. »1.0% dryness   PD PD inception voltage is 41% induced volatge .

71


71

Water Content Equilibrium

72


72

Dryness of insulation vs voltage withstand Water Content in paper shall be less than 0.5% (from 17% originally). Oil breakdown shall be greater than 60 kVrms/2.5 mm (IEC) from 30 kV/2.5 mm.

73


73

Transformer Active Part Insulation: a. MINOR INSULATION : Insulation between individual sections and pairs of discs in a winding or inter turn of layer winding. b. MAJOR INSULATION : Insulation between windings c. END INSULATION : Insulation between windings and the core. d. LEAD INSULATION : Insulation on exit leads. e. CLEAT BAR : Insulation on interconnecting leads 74


74

Top End Insulation

Optimised number of angle rings Stress Ring Profile

Standard Block thickness

Standard Oil Ducts

75


75

Cleat bar clearances

A = Cylinder to Plane OR treat as Tie Rod profile for analysis. B = Cylinder to Plane. C = Cylinder to plane. D & E will affect calculation limits. F = Point to Plane ?

76


76

FEM Models

High Voltage Stress Detection 77


77

Insulation Structures Validation Criteria

 Peak Stress in paper coverings  Peak Stress in Oil adjacent to covered electrodes  Peak and Average Stress in Oil ducts  Cumulative Stress in Oil  Bulk Oil Volume Stresses  Peak and Cumulative Creep Stress  Failure Probability of small oil volumes at peak

stress

78


78

608 series (4% grading): Bulk oil stress critical path from HV winding to LV winding 100

] m m / V 10 k [ | E |

²

stress (absolute value) cumulative stress Strength gas saturated oil Strength degassed oil 1 0

5

10

15

20

25

30

35

40

45

50

path [mm]

Stress in duct next to HV Stress Ring 79


79

ACTIVE PART - clearances Creep is an electrical failure using a solid object as a path Electrical Creep = Y

Y

80


80

ACTIVE PART (coil erection cleat bar) Tap changer (or Tap switch)

HV Line Lead T&D

Tap lead connections

Tap lead connections 81 PTR Quality


Cable Run/Channel 81

Bus Bar Connection For High Current Lead Exit 82


82

Tap Changer Connection 83


83

Inside CT Connection Lead Exit = Ground Level

84


84

Flash Over To Sharp Edge Of Metal Steel Flash is the distance between two objects, using Oil or Gas as a path (sharp edges, corners e.t.c. are high risk) Consider the closest point is not always the RISK! Electrical Clearance checks

- FLASH

X x = FLASH DISTANCE 85


85

PARTIAL DISCHARGES > 1000 nano Coulomb A track path can display a “tree” shaped pattern

86


86

CREEPAGE - FAILURES Creep from HV to tank wall along the support board

87


Creep from HV wdg to LV leads during Impulse tests

87

FLASH OVER / BREAKDOWN - FAILURE

88


88

8. Transformer Thermal Aspect

89


89

Thermal Aspect To Control Ageing & Lifetime

90


90

Transformer Life Time Transformer life time is mostly determined by the life time of winding conductor insulation paper.

Cellulose insulation paper is built of several chain of glucose molecules. The number of glucose molecule in the cellulose paper is known as DEGREE POLIMERIZATION.  New insulation paper  Degree polymerization > 850.  End life of insulation paper  Degree polymerization < 200.  At DP < 200  paper will be brittle as it has the tensile strength of HALF of new paper tensile strength.

THERMAL ASPECT has significantly contributed in the reducing of glucose chains on paper.

91


91

Glucose Molecule Of Cellulose Insulation

92


92

HEAT Source

Total Active Losses in kiloWATT

»(A) »(B) »(C) »(D)

I2R + Eddy losses (Max Loss > Minimum Tap) Stray Losses (Steel Structure + Tank) Core Losses Sun Radiation

TOTAL Losses to be evacuated = A + B + C + D

93


93

COOLING MEDIUM

 INTERNAL COOLING MEDIUM

The internal cooling medium has function also as internal insulation medium. 

Mineral oil (Inhibited or Un-inhibited oil)



Silicon oil



Synthetic ester



Hi-Temp natural liquid (seeds).

 EXTERNAL COOLING MEDIUM

94



Air



Water


94

Directed Cooling

»Convection

»Conduction

»Fan

95


95

Temperature Identification 1.3 x gradient

core

cooler

gradient

winding

l i o m o t t o B

96


l i o n a e M

l i o p o T

g n i d n i w e g a r e v A

t o p s t o H

96

Temperature Rise and Driven Factors  Temperature Rise for Class A (IEC / ANSI C57);  Top oil rise ; = 60K / 55 K or 65 K.  Average oil rise ; = 65 K / 55 K or 65 K (By resistance method)  Hot spot rise ; = 78 K / 65K or 80K.  Site elevation height;  The standard elevation height is 1000 m above sea level.  Climatic temperature behaviors;  Yearly average ambient temperature (IEC std = 20oC)  transformer life time.  Hot monthly average ambient temperature (IEC std = 30 oC)  Maximum ambient temperature (IEC std = 40 oC)  transformer loading capability Insulation class Operating temperature 97


A

E

B

F

H

105oC

120oC

125oC

145oC

220oC 97

Class A Temperature Design Limits

*) suitable for thermally up graded paper insulation

Oil

Winding

Metal part

Consequences

Annual average

80

98 / 110 *

110

Life time

Cyclic load

105

120 / 130 *

130

Gas generation

Emergency

115

140

140

Gas generation

Short emergency

115

160

160

Gas generation

1.Copper

115

250

160

Conductor softening

2.Aluminum

115

200

160

Maximum temperature design limit [oC]

Thermal short circuit

98


98

Cooling Method – Oil Immersed

Oil circulation

External cooling

IEC 60076

ANSI C57

BS 171

Natural flow

Air Natural flow

ONAN

OA

ON

Natural flow

Air Forced flow

ONAF

FA

OB

Forced/Blasted

Air Natural flow

OFAN

*)

*)

Forced/Blasted

Air Forced flow

OFAF

FOA

OFB

Forced & Directed

Air Forced flow

ODAF

FOA

OFB

Forced & Directed

Water Forced flow

OF(D)WF

FOW

OFW

*) not specifically indicated

99


99

Rules Reference List Material Properties Material Paper Pressboard Nomex PVA Enamel

Thermal Conductivities of Solid Dielectric Materials Thermal Conductivity (W/ m/ K) 0.17 0.21 0.125 0.16

Thermal Conductivities of the Core Direction Thermal Conductivity (W/ m/ K) In the plane of the laminations 21 Perpendicular to the plane of the laminations 3.3

Thermodynamic Properties of Cooling Liquids Property (units) Oil Ester Synthetic Oil Cubic Expansivity (/ K) 0.000795 0.000750 0.000700 Density (kg/ m3) 849 931 810 Dynamic Viscosity (kg/ m/ s) 0.00399 0.009589 0.01500 Specific Heat Capacity (J/ kg/ K) 2080 2216 2400 Thermal Conductivity (W/ m/ K) 0.1272 0.1535 0.1000

100


Silicone 0.001040 912 0.02052 1525 0.1500

100

Directed Oil Flow  Examples of washer applications (External) :

Duct maintained with sticks

Duct maintained with segments

101


101

dire rect cted ed oi oill flo flow w PRE-ASSEMBLY - di Directed Oil Flow arrangements arrangements may may not be present in TX designs, designs, dependa dependant nt upon local Design influences

Bottom Oil Annulus (Ring) Directed Oil Flow entry point

Check that the Oil path is clear & free from leaks

102


102

Future Material Insulation

103


103

Alternative Insulation - Hybrid Design

CALENDERED KRAFT BOARD CALENDERED KRAFT BOARD NOMEX® NOME X® T-9 T-993 93 Creped NOMEX® CALENDERED KRAFT BOARD

Support Washers Static Rings Cylinders

NOME NO MEX® X® T-4 T-410 10

Conductor Insulation

NOME NO MEX® X® T-9 T-994 94

Axial & Radial Spacers

PRECOMPRESSED KRAFT BOARD

104

Angle Rings and Caps

Clamping Rings, Blocks


104

Transformer life Time

105


105

106


106

107


107

108


108

9. Short Circuit Analysis

109


109

Definition Short circuit current is the current flowing thru the transformer part at the condition that the secondary side of power flowing from primary to secondary has been short circuited. Since the power transformer is the reactive apparatus, the short circuit current will be limited by this transformer impedance inherently. There are two kind of short circuit analysis; Symmetrical short circuit analysis such as three phases short circuit. Asymmetrical short circuit such as single phase to ground or two phases short circuit and/or to ground. Symmetrical short circuit current will be the biggest short circuit current for all loaded winding with all the winding terminals are brought out. For unloaded winding such as stabilizing winding, the single phase short circuit as well as the two phases short circuit shall be analyzed. 110


110

Short Circuit Withstand A). Thermal capability. The transformer conductor shall be designed to limit the produced heat due to short circuit below the temperature where the conductor material will start to loose it’s designed tensile strength for certain period of time. This clearance time will be used as the protection coordination reference. 1. Thermal limit for Copper conductor

  250 o C .

2. Thermal limit for Aluminum conductor

  200 o C .

B). Dynamic capability. Each part inside the power transformer has to be supported and clamped sufficiently to anticipate the forces happen due to the result of the peak of short circuit current and the leakage induction. 111


111

IEC 60076 – 5 ; Minimum Short Circuit Impedances Impedances

112


112

Oscillogram Showing The SC Current and Forces

113


113

Short Circuit Current

Ipeak = S 2 x Iccrms 

DC Offset K = 1 + e

 x  Π  r +   r  2  x

−  arctan 



× sin arctan x

U

x r

r

Icc

Clearance time = 3 seconds 114


114

Short Circuit - Thermal Thermal Withstand For Copper Conductor, Θ1 shall be less than 250oC Θ1 = Θ0 +

2 x ( Θ0 + 235) 106000 J2

xt

-1

For Aluminum Conductor, Θ1 shall be less than 200oC Θ1 = Θ0 +

2 x ( Θ0 + 225) 45700 J2

-1

xt

Θo = Initial temperature in oC Θ1 = Average winding temperature at certain time in oC

J = RMS short circuit current density in A/m2 t = Clearance time in second, max. 10 seconds 115


115

Short Circuit - Dynamic Withstand

A moving charge q, at the speed V, in a magnetic field B, is subject to a force F according to LAPLACE' s law

V q r

r

r

F = qV ∧ B

B F

116


116

Axial & Radial Stresses  Axial Stresses come from radial component of the

leakage field. This axial stresses can be minimized by an adequate balancing of the magneto motive forces on the whole height of the winding.  The clamping device through flitch plate, tie rod,

clamping beam are pre-loaded with the bigger force than axial short circuit force to anticipate any movement and deformation due dynamic short circuit force.  Radial Stresses come from axial component of the

leakage field. This type of force can not be minimized as this is directly dependent on the magneto motive force of inner and outer side windings.  The concentrically winding shape is the best geometry

to resist the radial stresses.  The inherently conductor tensile/compressive strength

shall be higher than the available short circuit forces. Sometime the reinforced material (e.g. CPR) is required. 117


117

B RADIAL FORCES Frad

mmf

I

I

Frad

F = I dl x B core

AXIAL FORCES

I Fax

118


I Fax

118

Mean Hoop Stress dl

α

p Leakage/flux

σS Rav

e

I

2B

α

e

F

B Rav

119

σS


Y

119

Hoop Stresses Of Multilayers  leakage field in the middle of the layer

 J −1 ni I i 12 n J I J   B = µ 0 µ r  ∑ + H J   i H i 

Hi = electrical height of the layer

W1

B k

W2 F

Wn

F

F F

H

F

 Electromagnetic pressure

F

R1

R2

B2

r r

r

p = I ∧ B

120


R2

120

Self Supporting / Counter Pressure

 Layer type winding: self supporting reaction equivalent

counterpressure with the thin cylinder hypothesis (R J>>eJ)

σ =

P J . R J e J

Hooke’s law ⇒ σ = E.I = E.

PJ

pJ

E= Young modulus of material

as

i=

∆(2.Π. R J ) 2.Π. R J

=

∆ R J R J

Internal counterpressure

P J = e J . E .

RJ ∆RJ 121


∆ R J 2

R J

121

Bending Stress Between Supports

 Layer type winding : Bending stress ; reaction of support

F tJ = ( p J R J − F nJ )

Ft

d bs RJ

+ 0

-

d bs

2 R J

or

x

F tJ = −

dMf dx

-Ft and Hook law : EIy’’=-Mf

122


E

: Young modulus

I

: inertia

Mf

: bending torque

122

Buckling Stress

123


123

Axial Forces

124


124

Tilting Stress

125


125

Compressive Stress On Radial Spacer

e

e1

e2

en

Swidth 126


126

Shearing Stress on CTC

Epoxy cab cable le : shea shearin ring g stres stress s on ep epoxy oxy  Epoxy

F τ

with epoxy without epoxy Epoxy avoid any relative movement from one strand to another

127


127

Clamping Forces

 Clamping forces : reduction of number of elements

F4,0

F3,1= F4,0

F3,0

F2,1= F3,0

F2,n = F2,n-1 + F3,n-1

F2,0 F1,1= F1,0 + F2,0

F1,0 initial nb of elements : 4

128

step 1 nb of elements : 3


F1,n = F1,n-1

step n nb of elements : 2

128

Clamping Structure

 Clamping structure reactions Rt= -F2,n

Rt= 0

if F2,n > F1,n Rt= 0

if F1,n > F2,n Rt= - (F1,n -F2,n )

F2,n

F2,n

F1,n

F1,n

F1,n

Rb= 0

Rb= - (F2,n -F1,n )

Rb= 0

Rt= - (F1,n + F2,n )

F2,n F2,n

F1,n

F2,n

F1,n

Rb= -F1,n Rb = - (F1,n + F2,n )

Clamping forces ≥ Σ of reactions on each layer

129


129

Axial Clamping System Clamping the winding assembly with pre -compressed load >

the axial force per phase & active part weight/3

130


130

Maximum Allowed Forces And Stresses

131


131

10. Engineering

132


132

Mechanical Design

kV 1200

H-Range 220

N-Range 110

E-Range 25

75

2500

MVA

Mechanical Design   standardize the best practice 133


133

Transformer Tank TOP BEAM TOP END WEDGE

TIE-ROD CRADLE

 E RANGE  Maximum Voltage ≤ 170 kV  Weight of core steel sheet, max 20 Ton  Center-center distance max 1350 mm

UPPER CLAMPRINGS

LOWER CLAMPRINGS

134


134

Transformer Tank TOP BEAM

 N RANGE  Maximum Voltage ≤ 275

FLITCH PLATE

kV

UPPER CLAMPRINGS

 Weight of core steel

sheet, max 40 Ton

LOWER CLAMPRINGS

 Weight of Part active max

80 Ton

 Center-center distance

max 1600 mm

YOKE SUPPORT

135


135

Engineering Tools  Full integrated engineering program :  TARGET (Transformer Architecture Generating Tools) 



136

As Main Program to design main variable of transformer part active, optimation tools for choosing design vs Price level Link (export/import) to verification tools


136

Vérification Tools  Verification tools :  Overload  capability of overloaded  Invodat  capacitance network and voltage distribution  Corecalc  Core losses and temp  Annuli  Force oil entry evaluation  ASC  Detailed core Design Program  Choc  Transient impulse voltage Analysis  Clearstress  Voltage Stress Evaluation  DOF  Direct Oil Flow Evaluation  Fluxshunt  Dimensional analysis for flux within tank shunt  Gradcalc  Winding Gradient Evaluation  Radinsulation  Lead clearances, thermal performances  RothFEM  Forces, stresses, impedances and flux ploting

137


137

Vérification Analyses

TRANSFORMERLEAKAGE FLUX (GRID-FLUX LINES)

U

Example of impulse wave 1.2µs / 50µs 50 µs Breaking time

100%

Full wave

50%

Wave chopped on the tail 0% 1.2 µs

Falling time

times in µs Undershoot Voltage

30%

138


138

11. Manufacturing Process

139


139

Manufacturing Process

Core cutting

Winding

Core stacking

Insulation

Active part assembly

Drying Repack

Assembly Testing 140


140

Core Stacking

141


141

Winding Manufacturing

142


142

Check Cross Over Of Winding

143


143

Connection & Insulation

144


144

Active Part Tanking After Repack

145


145

146


146

Single Phase Reactor: New Design

147


147

Single Phase Autotransformer 240 / 3 MVA 250 / 150 kV 148


148

Yoke Shield for reactor

149


149

12. Accessories, Protection & Control

150


150

Protection and Additional Accessories A. PROTECTION DEVICE - Protective Relay (Bucholz) Function : to trip out the trafo if there is a release of gas arising from the decomposition of the solid and liquid insulating material due to the action of heat or electric arcing.

Principal Of Operation - During normal operation, the relay is completely filled with oil. - When gas forms inside the transformer, it tends to flow towards the conservator - it accumulated progressively inside the relay there by LOWERING the oil level. - If gas continues to form, the oil level will affect the lower float B and relative switch which is connected to the circuit and causes disconnection of the transformer power supply.

151


A. Upper Float B. Lower Flat

151

Protection and Additional Accessories

- Protective Relay (Bucholz)

152


152


- RS 2001 relay for OLTC Function : to protect tap changer and transformer from any damage if a defect arises in the tap changer . This relay operates to put the trafo off circuit Principal Operation: It responds only if oil flows occur from tap changer head to the oil conservator

153


1. Flap Valve 2. Permanent Magnet 3. Reed Switch

153

Protection and Additional Accessories - Winding

Temperature Indicator

Function : to measure temperature

the

winding

Principal Of Operation: measure the winding temperature by means of a special bulb surrounded by heating resistance through which passes a current proportional to the current passing through the transformer winding subject to a given load and immersed in insulating oil at temperature

1. Case

9. Microsw. Setting Pointer

2. Locking Glass Ring

10. Junction Box

3. Fixing Rear Flange 4. Air Hole 5. Capillary Output 6. Dial

11.Glass or polycarbo-nate window 12. Potentiometer for heating resistance adjustment

7.Microsw. Setting Dial 8. Max. indicating pointer

154


154

Protection and Additional Accessories - Oil Temperature Indicator

Function : to measure the oil temperature inside power transformer tank

1. Case

8. Max. indicating pointer

2. Locking Glass Ring

9. Microsw. Setting Pointer

3. Fixing Rear Flange 4. Air Hole 5. Capillary Output

10. Junction Box 11.Glass or polycarbonate window

6. Dial 7.Microsw. Setting Dial

155


155

Protection and Additional Accessories - Oil Level Indicator Function : to measure the level reached by the oil in a transformer conservator Principal Of Operation - The changing oil level in the conservator is detected by a float attached to a suitably – long rod which is connected to the magnetic transmission axle - A permanent magnet, whose flux passes through attachment flange 2.0, is coupled to the pin turned by the float-carrying arm. The aforementioned parts fitted to flange 2.0 are placed inside the conservator through a hole made in a suitable position which is perfectly sealed by the flange it self. - A second permanent magnet inside instrument gauge 1.0, dragged round by the first magnet, moves a second shaft on which the optical level- indicator pointer and a cam are fitted. The cam trips the microswitch (Es) which electrically indicate that the oil has reached a certain level.

156


156

Protection and Additional Accessories - Pressure Relief Device

Function : an equipment to relieve large volumes of gas or insulating fluid rapidly when the pressure inside a transformer reaches a pre-determined limit.

157


157

Protection and Additional Accessories B. ACCESSORIES - Oil Sampling Valve

- Butterfly Valve

F=close position O=open position

158


158

Automatic Voltage Regulator - KVGC

159


159

Fibre Optic Temperature monitor  1 - 8 Channels  Cooling/Alarms/Protection  -30°C to +200°C  Programmable relays  Analog output 

0–1ma or 4–20ma

 Ring Lug Terminals  Memory Retention 

90 days at 1/minute – factory set

 Power Input 

Universal AC/DC

 Self Diagnostics  Applications 

Small to Large Power Transformers

 RS 232 Port  Options for RS 485 and Protocol Converter 160


160


- Screw and Globe Type Valve

161


161

13. Final Acceptance Test

162


162

Definition  Final Acceptance Test is the crucial moment for a

transformer , verifying the manufactured transformer has met the guaranteed performances and is ready to function under specified circumstance.  Purpose of testing is to ensure that the transformer has

fulfilled the quality performance and to validate the specific contractual requirements.  Validate the design  Validate the manufacturing process.  Compare the measurements with the technical data specification.  Establish a finger print of the transformer, useful for comparison with the future/on site measurement such as SFRA, capacitance, insulation resistance etc.

163


163

Testing Procedures The testing procedures are divided in three parts as followings; 1. Routine Tests; These tests are subjected to be performed on each individual transformer prior to delivery. 2. Type Tests (IEC) / Design Tests (ANSI/IEEE); These kind of tests are performed on one transformer representing the other transformers with the similar design. 3. Special Tests (IEC) / Other Tests (ANSI/IEEE); These tests are non-mandatory tests and have to be agreed between the manufacturer and the purchaser. 164


164

Routine Tests Routine Test is containing the following tests; 1. Insulation resistance measurement. 2. The electric strength of the transformer liquid. 3. Winding resistance measurement. 4. Voltage ratio & polarity/vector group checks. 5. Load loss & impedance measurement. 6. No load loss & no load current measurement. 7. Dielectric – routine tests (induced & applied tests) 8. Tap changer test (OLTC and/or DETC). 9. Functional tests on control devices, CT ratio checks.

165


165

Type/Design & Special/Other Tests Type tests (IEC) /Design tests (ANSI/IEEE); 1. Temperature rise test. 2. Dielectric – type test (lightning impulse test) Special tests (IEC) /Other tests (ANSI/IEEE); 1. Dielectric – special test (PD measurement) 2. Zero sequence impedance measurement. 3. Sound level measurement. 4. Capacitance and power factor. 5. Harmonic measurement of no load condition. 6. Fans and/or oil pump power consumption measurement. 7. SFRA (Swept Frequency Response Analysis). 8. DGA (Dissolved Gas Analysis) measurement. 9. Tank destructive test. 10. Transformer short circuit.

166


166

Insulation Resistance Measurement  This insulation is normally known as MEGGER insulation

test. This measures the DC insulation value containing the oil or other transformer liquid, cellulose pressboard, insulation paper and other insulation material between windings and winding to core.  The power supply is DC voltage source 1000 VDC up to

5000 VDC. Due to capacitance of different insulation medium, the insulation value of combined materials will take some times prior to get the stabilized result.  The acceptance criterium ;  Interwinding insulation = minimum 500 Ohm.  Winding to core = minimum 200 Ohm.  The wet insulation material may result very low insulation

resistance.

167


167

Winding DC Resistance Measurement  Winding DC resistance is measured thru two bushings for

each winding. The measurement is performed with bridge connection of VOLT – Ampere meters or high accuracy digital multimeter.  Care shall be taken for the effect of self-inductance. Hence

the oil temperature shall be recorded.  Anomalous result can detect bad connection joint within

the winding, inter winding or winding to bottom terminal of bushing. R std

V 2 DC power supply

x

R 1 V

R x = R std x V 1 /V 2 168


168

Load loss & impedance measurement This test will measure the load loss and impedance referring to the rated current at some of tap changer positions. The AC 3 phases supply is normally injected on the HV side of the transformer. The power supply voltage is increased until the nominal current is reached. The voltage giving the rated current is the impedance voltage. This is normally expressed as percentage of the rated voltage at particular tap changer position. If the rated current can not be reached due to testing limitation or other reasons, the following correction factor will be used. The minimum test current is 50% rated current Pextrapolation = Ptest x (Irated : Itest)2 During test, the transformer oil has to measured to correct the copper temperature as ambient temperature reference. The measured resistance has to be extrapolated to 75 oC (85oC for ANSI/IEEE with 65oC rise). 169


169

Correction factor for load loss due to temperature The load loss [Pcu/Pal] is containing I2Rdc + stray loss and guaranteed at 75 oC for IEC standard transformer and ANSI/IEEE standard transformer with 55 oC temperature rise. For ANSI/IEEE standard transformer with 65 oC temperature rise, the temperature reference for load loss is 85 oC. The DC resistance & load loss are measured at testing laboratory ambient temperature ( Θambient). For in case the oil temperature during load loss measurement has exceeded 3oC different with the actual ambient temperature, this oil temperature shall be used for measurement ambient temperature.

K CU =

[235 + 75 (or 85)] [235 + Θ ] Θambient

K AL =

[225 + 75 (or 85)] [225 + Θ ] Θambient

P cu(al) 75 o C (or 85 o C) = I 2 R dc x K + Stray loss / K 170


170

No Load loss and Current  The 3 phase, AC, power supply at 90%, 100%, 110% of

rated voltage is connected to the LV winding to induced the nominal voltage on HV as well as the other winding. The total (3 phases) losses & injected current to reach the rated voltage are known as no load loss, no loda current respectively.  Correction factor for no load losses;

P0 = Pm x ( 1 +

171

U’-U ) U’

P0

= Corrected no load loss

Pm

= Measured no load loss

U’

= Mean Voltage

U

= RMS voltage


171

Applied Over Voltage Test Purpose ; to check the voltage withstand between the tested winding to other separated windings (not in series/parallel connection), core, steel structure and tank. The test is made of single phase AC voltage at rated frequency for 60 seconds duration applied to one winding while other windings & core are grounded. The test is successful if no collapse of the test voltage occurs.

V HVN

172


172

Induced Over Voltage Withstand Test  Purpose; To ensure that the insulation between turns, between

discs, inter windings, winding to core/steel structure, cleat bars withstand the over voltage switching referring to guaranteed power frequency insulation class.  Two type of induced test;  Short duration Over Voltage Test (ACSD); 



AC single phases power supply for STAR connection non-uniform insulation. For ANSI/IEEE standard and some customer requirements are requiring the three phases power supply for STAR connection non-uniform insulation. AC three phase power supply for WYE or DELTA connection of uniform insulation.

rated frequency Time (seconds) =

test frequency

x 120 , but no less than 15 seconds

 Long duration Over Voltage Test (ACLD); Over voltage up to 130% or 150% Um for 30 minutes with partial discharge measurement. 173


173

Time Duration For ACSD & ACLD Induced Test U1 tinduced

U2 1.1Um

5 min

5 min

5 min

5 min

ACSD

U1 = induced voltage U2 = 1.3 Um for < 300 pC = 1.5 Um for < 500 pC 1.1Um < 100 pC For phase to earth Um : S 3

U1 tinduced

U2 1.1Um

5 min 5 min

30 min 5 min

ACLD 174


174

Partial Discharge Measurement Partial Discharge Measurement is measuring the small discharge activity inside as well as outside around the transformer prior to flash over occurrence. This measurement is a good tool to ensure the transformer quality. •

Corona discharges occurs due to the sharp edge electrode.

•

Surface discharges (creepage) occurs due to overstress component parallel to the dielectric medium surface.

•

Internal discharges occurs due to the non-homogenous dielectric medium.

•

Electric trees due to the particle or cavity in the solid insulation.

•

Floating discharging occurs due to badly grounded component.

•

Contact noise occur in case bad contact terminal.

175


175

Single Phase Induced Voltage Vectorial HV = WYE non - -uniform uniform U 1

2/3 U Induced LV = DELTA

U Induced

v 2 = 1/2u 2 U supply

N

u 2

1 phase

w 2 = 1/2u 2

1/3 U Induced

V 1 & W 1

176


176

Three Phases Induced Voltage Vectorial HV = WYE uniform U 1 LV = DELTA u 2 UInduced :S S3

v 2

w 2

e d c d u n I U

N

U supply 3 phase

W 1 177


V 1 177

Temperature Rise Test  Purpose : to check the temperature rises (top oil, average

winding & hot spot) do not exceed the guaranteed temperature rises.  The test can be performed by BACK TO BACK test or SHORT

CIRCUIT methods. The short circuit method is mostly used for this temperature rise test.  In the short circuit method, all three phases low voltage

windings are short circuited to generated the total losses as well as the current, Principally the test is performed by supplying the current to provide the total losses (no load + load losses) for oil temperature check and then to provide the rated current for winding temperature check.  Since the oil time constant is very long (it can take several

hours) while the conductor time constant is practically only few minutes, the injected current for total losses is performed first to get stabilized oil temperature then followed by reduced current to rated current to get winding temperature at rated capacity one hour prior to shut down. 178


178

DC Resistance For Temperature Analysis  Oil temperature can be detected by direct measurement

referring to oil temperature indicator.  Winding temperature at rated capacity is calculated by

comparing the DC resistance value at cold condition with known ambient temperature and the DC resistance value at rated current just prior to shut down.  The transformer has to be cleared for any capacitive

charge before taking the hot DC resistance measurement by using charging stick. The charging time has to be kept as short as possible to keep measurement accuracy, but this period may need several minutes.  The hot DC resistance is extrapolated from several

measured DC resistance values after shut down and cleared charging.  If there is tap changer with several tap positions, the tap

position with highest load loss is taken as reference for temperature analysis. 179


179

Some Of Equations For Temperature Rise Analysis 1. Power Supply is provided on HV tap pos. with highest load los s. I injected = I rated x

(P load loss + P no load ) P load loss

V injected = V rated x Z(%) x

I injected I rated

2. Top Oil Rise and Average Oil Rise at Rated Capacity DToil = (max. {T cover , ,T top rad ’ } – T amb ) x

DAOT = ½ x (T top rad + T bot rad ) – T amb ) x

180


(P load loss + P no load )

x

P load loss (P load loss + P no load )

x

P load loss 180

Some Of Equations For Temperature Rise Analysis 3. Winding Temperature Gradient at Rated Current.

GR CU =

GR AL =

R 2 R 1 R 2 R 1

x (234.5 + T 1 ) – (234.5 + T 2 ) – DAOT x

x (228.1 + T 1 ) – (228.1 + T 2 ) – DAOT x

I rated

y

I inject I rated

y

I inject

4. Average Winding Temperature Rise and Hot Spot Rise.

181

DT CU = DAOT + GR CU

DT AL = DAOT+ GR AL

HS CU = DT oil + HSF x GR CU

HS AL = DT oil + HSF x GR AL


181

Some Of Equations For Temperature Rise Analysis Definitions; 1. Iinjected 2. Irated 3. Vinjected 4. Pload loss 5. Pno load loss 6. T1, T2 7. Tcover 8. Ttop rad 9. Tbot rad 10. DToil 11. DAOT 12. DT 13. GR 14. x

= Injected current [A] = Rated current at stated tap [A] = Testing Voltage [kV] = Maximum load loss [kW] =Measured no load loss [kW] = Ambient temperature at condition 1,2 respect.[oC] = Oil temperature on top cover [oC] = Oil temperature on top radiator [oC] = Oil temperature on bottom radiator [ oC] = Top oil temperature rise [K] = Mean oil temperature rise [K] = Average winding temperature rise [K] = Winding gradient temperature [K] = Exponent for oil temperature due to losses. 

0.8 for ON cooling of < 2500 kVA.  0.9 for ON cooling  1.0 for OF or OD cooling

15. Y

= Exponent for winding gradient due to current. 

1.6 for ON or OF cooling  2.0 for OD cooling

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Lightning Impulse Tests  Purpose ; To check the transformer capability against

the fronted over voltage caused by atmospheric discharge with time peak between 0.1 ms to 20 ms and tail duration of less than 300 ms.  Considering the transformer as a complex network of

RLC component, the distribution of such very high frequency over voltage such as lightning impulse will be highly influenced by the capacitive component of transformer.  The lightning impulse test is performed by comparing

the result of 100% impulse test against the 50% and/or 75% impulse test result. If there is failure, the voltage wave form as well as the current wave form will have different shape as the wave of reduced level.

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Full Wave Impulse 100%

50%

front time

tail time

Front time = 1.2 ms + 30% Tail time = 20 ms + 20% Peak value + 3% 184


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Voltage Wave

Current Wave

50% impulse

100% impulse

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14. Technology Application

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Single Phase Solution

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Single Phase Reactor: Original Design

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Less Maintenance

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ATT expérience in Industrial Transformers  Electrolysis Industry

=> Rectifier Transformers

(Aluminium, Zinc, Copper, Chlorine)

 Chemical, Oil&Gas Industry => Converter Transformers

 Steel Industry

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=> Electrical Arc Furnace (EAF)Transformers

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Furnace transformer on UTR SLN LE-NICKEL 3 x 1 PHASE 33.3 MVA 50 Hz, 63 Kv / 300 ~ 1800 Volt OLTC ± 16 x 750 Volt ODWF

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AREVA PPT

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