jurnal 2

Developmefor Power

J. Haema Department of Electrical Engineering T

College of Industrial TechnologKing Mongkut’s University of Technology N

Bangkok, THAILAND [email protected]

Abstract—The development of condition evatransformer maintenance are presented intechniques consist of three types: electrical testand visual inspection, which is considered byDissolved Gas Analysis, Load History, PoweScan, Oil Quality, Furan, General ConditioArrester, Conservator Tank, Main Tank, HRadiator and Cooling System, TransformerNeutral Ground Reactor (NGR), ProteRegulating PT, OLTC Compartment, OLTCDGA of OLTC, and OLTC Oil Quality. The cofor transformer is performed by the analysiindicated by scoring and weighting factor omethod with further development could be plan the maintenance of power transformer.

Keywords-power transformer condition, heatransformer, power transformer maintenance.

I. INTRODUCTION Nowadays, Power transformer an expe

important equipment in power system, playsin the transmission and distribution networkto transfer an electrical power, step up and levels to an appropriate use with connected side. In the CIGRE survey about failures of p[1], it shows that 40% of failures happen Then 35% of failures occur with internawinding and magnetic core, whereas other fon bushing, tank, and accessories as shown in

Figure 1. Percentage of failures in power t

ent of Condition Evalur Transformer Maintena

Technology gy North Bangkok

R. PhaDepartment of Electroni

College of InduKing Mongkut’s University

Bangkok, rpt.kmutnb

aluation for power n this paper. The t, insulating oil test y 21 test methods: er Factor, Thermo

on, Bushing, Surge ot Line Oil Filter,

r Control Cabinet, ction Equipment,

C Control Cabinet, ondition assessment is of each method, of each tests. This used to effectively

alth index of power

ensive and one of s a significant role k. Its functions are step down voltage equipment in each power transformer with tap changer.

al components as failures take place n Fig. 1.

transformer

Therefore, this paper propotechniques to development of transformer maintenance [2]-[three types of test to determine which are electrical test, ininspection as well as display in

Figure 2. Percentage of fa

II. METHODS TO CONDITTRANSFORMER

In this section, this purpooverall condition of transformconsidered: Dissolved Gas AFactor, Thermo Scan, Oil QuaBushing, Surge Arrester, ConsLine Oil Filter, Radiator and Control Cabinet, Neutral GrouEquipment, Regulating PT, Control Cabinet, DGA of OLTseparated into three types of tepower transformer as follows:

Ele

Ins

Visu

POWER

TRANS FORMER

MA I NTENANCE

uation ance

adungthin ics Engineering Technology ustrial Technology of Technology North Bangkok THAILAND

[email protected]

oses the appropriate diagnostic condition evaluation for power 3]. The work is separated into the health of power transformer, nsulating oil test and visual

n Fig. 2.

ailures in power transformer

TION EVAUATION FOR POWER R MAINTENANCE se of this paper is to estimate

mer. Testing of 21 methods are Analysis, Load History, Power ality, Furan, General Condition, servator Tank, Main Tank, Hot

Cooling System, Transformer und Reactor (NGR), Protection

OLTC Compartment, OLTC TC, and OLTC Oil Quality. It is esting to determine the health of

ectrical Test Power factor test

ulating Oil Test Dissolved Gas Analysis (DGA) Furfural Oil Quality

ual Inspection Load History Thermo Scan General Condition Bushing Surge Arrester Conservator Tank Main Tank Hot Line Oil Filter Radiator and Cooling System Transformer Control Cabinet Neutral Ground Reactor Protection Equipment

978-1-4673-6392-1/13/$31.00 ©2013 IEEE620

4th International Conference on Power Engineering, Energy and Electrical Drives Istanbul, Turkey, 13-17 May 2013

POWERENG 2013

A. Electrical test Electrical test is used to inspect the condition of winding,

which is insulation power factor test. This method detects the insulation integrity of winding and determines a power factor of overall insulation including winding and bushing. Then, it is a measure of the ratio of the power (I2R) losses to the volt-amperes applied during the test [4].

The power factor is from the measured values of watts lost in the total transformer insulation system including the bushings. The power factor should not exceed 0.5% at 20 C. The equation to find the percentage of power factor is expressed in Eq. (1).

The limit of such a power factor should not exceed 0.5 at 20 C, the limits of power factor are displays in Table I.

TABLE I. LIMIT OF POWER FACTOR

Condition Limit of power factor, %PF at 20 C Good %PF < 0.5

Acceptable 0.5 %PF < 0.6 Need Caution 0.6 %PF < 0.8

Poor 0.8 %PF < 0.9 Very Poor %PF 1

B. Insulating Oil test Insulating oil test is performed to inspect the condition of

insulating oil [4]. The evaluation of oil integrity consists of three:

1) Dissolved Gas Analysis (DGA): DGA test has been used as a tool in determining the condition of a transformer. It indicates several problems and can identify the deterioration of insulating oil. This analysis is separated into two kinds as:

a) DGA of oil in main tank Table II presents the limit value of scoring and weighting

factor for DGA of oil in main tank. The score is classified into six levels: one means good condition and six means poor. The lower number of weighting factor implies less important than upper number. The scoring and weighting factor are calculated to get percent DGA factor (%DGAF) as written in Eq. (2).

The health index factor (HIF) of DGA can be achieved subsequently for each %factor (%DGAF) as displayed in Table III. The HIF has ranking codes as 0, 1, 2, 3 and 4. Code ‘0’ means very poor condition as shown with red color while ‘4’ represents good condition with green color. The %factor is first set up as a model, and then be rearranged to match the suitable condition. In addition, the setting concerns safety margin in

order to do maintenance before critical problems occur. The HIF result of DGA can be then used for calculating overall condition.

TABLE II. SCORING AND WEIGHTING FACTOR FOR DGA MAIN TANK [5]

Gas Score (Si)

Wi (1-5)

1 Good 2 3 4 5 6

PoorH2 100 101-200 201-300 301-500 501-700 >700 2

CH4 75 76-125 126-200 201-400 401-600 >600 3

C2H6 65 66-80 81-100 101-120 121-150 > 150 1

C2H4 50 51-80 81-100 101-150 151-200 >200 3

C2H2 3 4-7 8-35 36-50 51-80 > 80 5

CO 350 351-700 701-900 901-1100 1100-1400 > 1400 1

CO2 2500 3000 4000 5000 6000 > 7000 1

TABLE III. HIF COMPARISON WITH % DGAF

HI Factor Condition Description Color Band 4 Good DGAF 20% Green 3 Acceptable 21% DGAF 30% Blue

2 Need Caution 31% DGAF 40% Yellow 1 Poor 41% DGAF 50% Orange 0 Very Poor DGAF 51% Red

b) DGA of oil in OLTC component

Table IV presents the limit value of scoring and weighting factor for DGA of oil in OLTC [6]. The score is classified into six levels. The scoring and weighting factor are calculated to get percent DGA factor (%DGATF) as Eq. (3). The HIF of %DGATF shows in Table V.

(3)

TABLE IV. SCORING AND WEIGHTING FACTOR FOR DGA OLTC

Gas Score (Si)

Wi (1-5)

1 Good 2 3 4 5 6

PoorRatio1:

(CH4+C2H6+C2H4)/ (H2+CH4+C2H2+C2H6)

< 0.5 N/A N/A N/A N/A 0.5 4

Ratio2: (CH4+C2H6+C2H4)/(C2H2)

<2.0 N/A N/A N/A N/A 2.0 4

Ratio3: (C2H4/C2H2)

<1.0 N/A N/A N/A N/A 1.0 4

TABLE V. HIF COMPARISON WITH % DGATF

HI Factor Condition Description Color Band

4 Good DGATF 25% Green

3 Acceptable 26% DGATF 40% Blue 2 Need Caution 41% DGATF 60% Yellow 1 Poor 61% DGATF 80% Orange

0 Very Poor DGATF 81% Red

(2)

(1) 100% xVIPPF =

100)(

)((%)

2

2

2

2

max

xxWS

xWSDGAF COi

Hiii

COi

Hiii

=

=

=

==

100)(

)(

(%)

1max

1 xxWS

xWS

DGATF ni

iii

ni

iii

=

=

=

==

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POWERENG 2013

2) Furfural: The analysis of furan is especially the decaying of paper insulation in transformer oil. This test is additionally performed, which the transformer has a high level of carbon monoxide and carbon dioxide, which cause overheat problem.

Furan is a method to determine the condition of paper insulation inside transformer. Measuring the furfural content of the oil pays attention to 2-furaldehyde (2-FAL), presented limit are indicated in Table VI.

TABLE VI. HIF COMPARISON WITH TO 2-FURALDEHYDE (2-FAL)

HI Factor Condition Description Color Band 4 Good 2-FAL < 0.5 Green 3 Acceptable 0.5 2-FAL 1 Blue 2 Need Caution 1.1 2-FAL 1.5 Yellow 1 Poor 1.6 2-FAL 2 Orange 0 Very Poor 2-FAL 2.1 Red

3) Oil Quality: Oil quality testing is performed to check the general condition of insulating oil. The analysis is divided into two ways as below:

a) Quality of oil in main tank Oil quality testing is performed to check the general

condition of insulating oil. The evaluation of oil quality is performed by considering five testing: Dielectric Strength, Interfacial Tension (IFT), Neutralization Number (NN) or Acidity, Water Content and Color. Show in Table VII. The scoring and weighting factor are calculated to get percent oil quality factor (%OQF) from Eq. (4), shown limit are indicated in Table VII.

TABLE VII. SCORING AND WEIGHTING FACTOR FOR OIL QUALITY [7]

Testing Oil Quality

U 69kV 69kV < U <230kV

U 230kV Score Wi

Dielectric Strength ASTM

D1816 Gap 1mm

> 46 > 53 > 56 1=Good

3 44-46 51-53 54-56 242-44 49-51 52-54 3< 42 < 49 < 52 4= Poor

IFT 32 > 40 > 40 1=Good

2 27-32 32-40 32-40 222-27 25-32 25-32 3

22 25 25 4= Poor

NN (Acidity)

0.05 0.04 0.03 1=Good

1 0.05-0.1 0.04-0.1 0.03-0.07 2 0.1-0.2 0.1-0.15 0.07-0.1 3

0.2 0.15 0.1 4= Poor

Water Content (ppm)

25 15 10 1=Good

4 25-30 15-20 10-15 2 30-35 20-25 15-20 3 > 35 > 25 > 20 4= Poor

Color 1.5 1=Good

2 1.5-2.0 2 2.0-2.5 3

2.5 4=Poor

b) Quality of oil in OLTC compartment Oil quality testing is performed to check the general

condition of insulating oil by considering three testing: dielectric strength, water content and color. Show in Table VII. The scoring and weighting factor are calculated to get percent oil quality factor (%TOQF) from Eq. (5), presented limit are indicated in Table VIII.

TABLE VIII. SCORING AND WEIGHTING FACTOR FOR OIL QUALITY

HI Factor Condition Description Color Band

4 Good OQF/TOQF 25% Green 3 Acceptable 26% OQF/TOQF 40% Blue 2 Need Caution 41% OQF/TOQF 60% Yellow 1 Poor 61% OQF/TOQF 80% Orange 0 Very Poor OQF/TOQF 81% Red

C. Visual Inspection Visual Inspection provides mostly an external inspection on

a weekly or monthly basis. It checks Load History, Thermo Scan, General Condition, Bushing, Surge Arrester, Conservator Tank, Main Tank, Hot Line Oil Filter, Radiator and Cooling System, Transformer Control Cabinet, Neutral Ground Reactor (NGR), Protection Equipment and Regulating PT [8].

Hence, Visual inspection of the transformer exterior reveals important condition information. The method requires knowledge and experience of operation personnel.

III. ANALYSIS AND TEST RESULT The condition assessment for transformer is performed by

analyzing each condition of such 21 testing, as shown in Table IX. First of all, scoring and weighting factor are summarized to get the %factor of each method. The HIF can be obtained subsequently by comparing with %factor. Next, the transformer health, denoted as %Health Index (%HI), is computed. The overall condition of the transformer is determined from the known %HI, as shown in Table X. The HI value is grouped from “very good” to “very poor”. By this means, the %HI result of overall condition is used to identify the actual condition transformer.

Overall condition of the transformer known as health index in percentage (%HI) is calculated by substituting several parameters as shown in Eq. (6).

100)4(

)(4.0

)(

)(6.0(%) 21

18

21

1817

1max

17

1 xxK

xHIFK

xKHIF

xHIFKHI j

jj

j

jjj

j

jj

j

jjj

+= =

=

=

==

=

=

=

100)(

)(

(%)

max

xxWS

xWS

OQF Colori

BDiii

Colori

BDiii

=

=

=

==

(6)

(5) 100)(

)((%)

max

xxWS

xWSTOQF Colori

BDiii

Colori

BDiii

=

=

=

==

(4)

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POWERENG 2013

TABLE IX. TEST METHODS AND FACTOR FOR OVERALL TRANSFORMER CONDITIO

No Transformer condition Criteria K HIF (

1 Dissolved Gas Analysis (DGA) 10 2 Load History 10 3 Power Factor 10 4 Thermo Scan 10 5 Oil Quality 8 6 Furan 6 7 General Condition 1 8 Bushing 5 9 Surge Arrester 3

10 Conservator Tank 1 11 Main Tank 1 12 Hot Line Oil Filter 1 13 Radiator and Cooling System 1 14 Transformer Control Cabinet 1 15 Neutral Ground Reactor (NGR) 1 16 Protection Equipment 1 17 Regulating PT 1 18 OLTC Compartment 1 19 OLTC Control Cabinet 1 20 DGA of OLTC 6 21 OLTC Oil Quality 3

TABLE X. HEALTH INDEX FOR OVERALL CONDIT

%HI Condition Requirement

86-100 Very Good Normal Maintenanc71-85 Good Normal Maintenanc51-70 Fair Increase Diagnostic Te

31-50 Poor Start Planning Process to or Rebuild Considering

0-30 Very Poor Immediately Assess R

In this case, overall conditions of nine trvery good condition, while three units are iThe rests are in fair and very poor conditionone unit, respectively. Furthermore, the decrewith respect to the age of transformers wmanufacturers is shown in Fig. 3. Moreoverrelationship of overall condition and number

Figure 3. Overall condition of 115/22 kV

=%HI

=%HI

EVALUATING THE ON

(4=Good,…0=Poor)

TION OF TRANSFORMER

Color Band

ce Green ce Blue esting Yellow Replace

g Risk Orange

Risk Red

ransformers are in in good condition. ns with seven and easing health index ith eight different

r, the Fig. 4 shows in service.

V 50MVA

Figure 4. Relationship of Overal

CONCL

In this paper, the results sho115/22kV, 50 MVA several transformer by means of this anfor the appropriate mainmaintenance before severe damtest results will be studied adeterioration trend of poSubsequently, weighting and scassigned in order to use inevaluation. This analysis and abe subsequently implemented to

Furthermore, the methodoloto apply to other equipments efficiency and reliability of elec

ACKNOWL

Special thank to Prof. Dr.helping and valuable suggesgratefully acknowledge KinTechnology North Bangkok Generating Authority of Thaildata and support for this work.

REFER

[1] CIGRE Working Group 12.05, large power transformer in servic

[2] T.suwanasri, J. Haema, R. PhaTechniques to Evaluate InternECIT-CON 2009, Pattaya, Thaila

[3] Brian Sparling, SMIEEE, JacqueAging Transformer in View of 2010, Tokyo, Japan, Sep 6-11, 20

[4] FIST Volume 3-30, Transformer [5] FIST Volume 3-31, Transformer [6] J. Haema, R. Phadungthin, “Cond

Load Tap Changer via Web ApThailand, March 6-8, 2012.

[7] J. Haema, R. Phadungthin, “Powby the Analysis of DGA methoMarch 26-28, 2012.

[8] J. Haema, R. Phadungthin, “Confor Power Transformer”, PEAM

= =

=

=

=17

1max

17

1

)(

)(6.0 j

jj

j

jjj

xKHIF

xHIFK

= =

=

=

=21

18

21

18

)4(

)(4.0 j

jj

j

jjj

xK

xHIFK

ll Condition and Number in Service

LUSION ow that the overall conditions of transformers. The deteriorated

nalysis can be, carefully focused ntenance as condition-based mage occurs. Then, the historical and analyzed to determine the ower transformer condition. coring of each diagnostic test are n power transformer condition assessment are reliable and can o the real work.

ogy in this work can be applied in the power system for better

ctrical power system.

LEDGMENT .-ing Thanapong Suwanasri for tion. In addition, the authors

ng Mongkut’s University of (KMUTNB) and Electricity

land (EGAT) for providing the

RENCES “An international survey on failure in

ce”, Electra, no.88, May 1983. adungthin, C. Suwanasri, “Diagnostic al Condition of Power transformer”, and, 6-9 May, 2009. es, “Determination of Health Index for Substation Asset Optimization”, CMD

010. Maintenance, October 2000. Diagnostics, June 2003. dition Evaluation of Power Transformer pplication”, MDEATED 2012, Pattaya,

wer Transformer Condition Evaluation ods”, APPEEC 2012, Shanghai, China,

ndition Assessment of the Health Index 2012, Wuhan, China, Sep 14-16, 2012

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jurnal 2

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