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					                                   SCIENTIFIC AND ENGINEERING CENTER
                                               ZTZ-Service Co.

                                  11, Dnepropetrovskoye sh., Zaporozhye, 69069, Ukraine
                                       tel.: (380 612) 595-821, fax: (380 612) 526-498
                          E-mail: root@ztz-service.com.ua
  SEC «ZTZ-SERVICE Co.»                       http://www.ztz-service.com.ua




                                          Report
On preliminarily assessment the condition of generator transformers
at the Dhekelias Power Station of the Electricity Authority of Cyprus
                on the basis on oil testing by portable
                     Kelman device Transport X


                                 1.NIC.D10. 1043.00




                                                     Technical director

                                                     _________________ V.V. Sokolov
                                                     «_____»__________ 2005


                                                     Chief of the material laboratory
                                                     ________________ V.N. Berezhnoy
                                                     «______»________ 2005




                                  Zaporozhye, Ukraine
                                        April, 2005
                                        SEC «ZTZ-Service Co.»


Introduction

On the 5nd April 2005 it was carried out assessment of the condition of generator transformers at
the Dhekelias Power Station using portative gas-in oil analyzer Transport-X Kelman Co.
This report presents the results of assessment and relevant proposals on improvement
transformers reliability.


Subjects of assessment

Six generator transformers rated 73 MVA, 11/142± 6x2.5 % kV, OFWF cooling system. See
water is used for cooling.
There are three groups of the transformers:

   KTAT 145X73 manufactured by Strömberg (Finland) 1n 1881, which installed at the units
   No 1 and 2.
   Transformers was specified for insulation level 550 kV BIL and 230 kV 1 min power
   frequency test. No-load losses are 40-41 kW




   KTAT 145X73. manufactured by Stroemberg (Finland) 1n 1888-89, which installed at the
   units No 3 and 4.
   Transformers was specified for insulation level 650 kV BIL and 275 kV 1 min power
   frequency test. No-load losses are 29 kW




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   Transformers manufactured by EFACEC (Portugal) 1n 1992, level of no-load loss 32 kW




Methods of assessment

Rough identification of transformers design.
Analysis of oil samples taken from the bottom part of tank for measurement of concentration of
dissolved water, H2, CH4, C2H6, C2H4, C2H2, CO, CO2 by portative device Transport –X
Kelman Co. and assessment of oil color.

Comparative tests

One of the sample taken from transformer Unit #3 (S/N 5800516) was tested later in the ZTZ-
Service material Lab (table 1) .The results are quite consistent.

                                   Table 1
                              Comparative tests
  Type      Lab.           Manufacturer, Year             Concentration of gases and H2O, ppm
                           S/N
                                                  H2    H2O    CO2   CO    C2H4 C2H6 CH4         C2H2
             Transport X
  KTAT                     Stroemberg              8     14    7731 313      32    5      8       Abs.
  145x73                   5800516        1988
  Unit #3    ZTZ-Service                           11    13    8680 346      32    3      6       Abs.


                                        History

During the total period of operation the only one failure occurred associated with overheating
LV leads connections and LV bushing on the transformer No 5800517. The problem was fixed
On-site




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Maintenance program include periodical change of oil in the diverter switch and cleaning the
coolers.
Oil tests include acidity and water by Karl Fisher titration.
The test results presented by the Power Station have shown elevated oxidation of oil and
elevated moisture content in the transformers of the units No 5 and 6.

                         Table 2
        Oil test results performed by Dhekelias Power Station

    No unit, SN       Date        T°C         Acidity             Water
                                              mgKOH/g
    549952 T/X1       15/3/2005   55          0.05                9.2
    549951 T/X2       15/3/2005   55          0.04                10
    5800516 T/X3      15/3/2005   54          0.05                11
    5800517 T/X4      15/3/2005   55          0.05                6
    C-12390 T/X5      11/3/2005   65          0.082               19
    C-12388 T/X6      11/3/2005   55          0.076               22

Methods of assessment on the 5th April performed by ZTZ-Service-Entegro

Roughly identification of transformers design
Analysis of oil samples taken from the bottom part of tank for
Concentration of dissolved water, H2,CH4, C2H6, C2H4, C2H2, CO,CO2
Assessment of oil color.

Table 3
Formal criterion usin approach of various standards and servising firms are following.
Boundary value of gas concentrations point out the defects in transformer.
Standards, firms            Boundary value of gas concentrations, ppm
                             H2     CO2     CO C2H4 C2H6 CH4 C2H2 TCG* CxHy** CO2+
                                                                               CO
IEC 60599                  60-      5100- 540- 60-  50-90 40- 3-50
                           150      13000 900 280         110
Electric           Warning <400        -  <300 <10  <150 <100 <0.5 <500
technology         Level 1
Research           Warning                       >10                    >0.5   >500
Association in     Level 2                                              <5     <700
Japan

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                  Trouble                          >100                  >5     >700
                  Level
Guidelines of SIGRE Task >100                                            >20           >500   >10000
Force 15.01
IEEE Std.C57.    Lvel 1  100  2500          350    50     65       120   35
104-1991 (USA)
                  Lvel 2    101-    2500-   351-   34-    65-      121- 36-50
                            700     4000    570    100    100      400
                  Lvel 3    701-    4001-   571-   101-   101-     401- 51-80
                            1800    10000   1400   200    150      1000
                  Lvel 4    >1800   >       >      >200   >150     >    >80
                                    10000   1400                   1000

* - The total combustible gas (TCG) means a total sum of H2, CH4, C2H6, C2H4, C2H2 and
CO.
** - CxHy total sum of CH4, C2H6, C2H4 and C2H2


Tests results and discussion

Tests results of DGA and water content are summarized in the table 4.

Unit #1
Manufacturer: Strömberg
Year of production: 1981
Serial number: 549952
Color of oil (by ASTM 1500 Scale) : 5


Unit #2
Manufacturer: Strömberg
Year of production: 1981
Serial number: 549981
Color of oil (by ASTM 1500 Scale) : 5


Unit #3
Manufacturer: Strömberg
Year of production: 1988
Serial number: 5800516
Color of oil (by ASTM 1500 Scale) : 1,5


Unit #4
Manufacturer: Strömberg
Year of production: 1989
Serial number: 5800517
Color of oil (by ASTM 1500 Scale) : 5




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Unit #5
Manufacturer: Efacec
Year of production: 1992
Serial number: C-12390
Color of oil (by ASTM 1500 Scale) : 2,5




Unit #6
Manufacturer: Efacec
Year of production: 1992
Serial number: C-12388
Color of oil (by ASTM 1500 Scale) : 3




1) The problems, which may affect on short-term reliability, were found in the transformer of the
units #6.
 1,0



                                        Estimated temperature in localized zone is 600 – 700°C
 0,5




 0,0
       Н2     СН4    С2Н6 С2Н4 С2Н2




2) Some elevated gas concentration was found also in the unit No4 that exhibited earlier failure
of LV connection
   1,0




   0,5




   0,0
         Н2    СН4    С2Н6 С2Н4 С2Н2

Estimated temperature in a localized zone is nearly 600°C.
This phenomenon can be to come out from residual faulty gases and gases from new defect.
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However considering the fact that unit No 3 exhibits also symptoms of overheating.
The condition of both transformers requires further investigations.

3) A number of transformers, particularly at the units 1, 4, 5 and 6 exhibit a high level of oil
oxidation (color and CO, CO2).
The following questions should be answered in association with this phenomenon:
What is level of oil aging in terms of sludge formation, residual life of the oil, possibility for
regeneration.
Determination of aggressive by-products, which can affect condition of windings paper.
Verification of whether significant cellulose deterioration involved.
Assessment of the condition and effectiveness of cooling system including check of factual
cooling capacity.

4) Transformers that manufactured by EFACEC require a special attention.
Inspection of cooling system shown poor cooling effectiveness – the drop of the oil temperature
in the cooler was only 1.5 - 3°C.

5) To evaluate possible state of insulation sample of oil was taken from transformers of the unit
No 4 and tested in the ZTZ-Service Lab for furans identification.
It was found that in the unit No concentration of 2FAL = 400 ppb showing symptom of
insulation deterioration. It means that the state of other transformers for the degree of aging and
oxidation, especially of units 5 and 6 require special attention.

6) Unfortunately during oil sampling it was not possibility to take samples from OLTC,
especially from diverter switch compartment due to poor arrangement of sampling point.
It would be important to arrange the relevant sampling point and to perform the tests.

7) Condition of the 145 kV bushings should be a subject of special consideration because during
the service time bushings were never tested.

8) The scope of tests performed could not cover assessment of dielectric state of equipment with
the exception of evaluation of water content, which shown symptom of moisture contamination
in the units 5 and 6. We believe that the next step should include performance of the Water Heat
Run Test, determination of bound water and particles identification. Assessment of possible sign
of see water in the cooler should be a subject of special attention.

Conclusion and proposals
Results of works have shown that it would be possible to assess the condition of transformer
population for rather a short period using portative test device.

Assessment of the condition of the generator transformers revealed some serious abnormalities,
which motivate necessity of more detailed assessment transformer population for verifying the
assumed problems and determination of further maintenance program.

A program should include also auxiliary transformer population

Such work could be performed for 8-10 days and would allow to develop adequate measures to
improve transformer condition, recommendation of minimum scope of maintenance tests and
relevant limited data and interpretation, and also advise an effective on-line monitoring system


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Table 4

Type      Manufact.       Year    Unit H2 H2O CO2              CO    C2H4 C2H6       CH4      C2H2
          S/N                     No



KTAT*     Stroemberg      1981    1     5    11      3599      228   7     3         2        abc.
145x73    549952
KTAT*     Stroemberg      1981    2     6    12      4121      253   7     <1        4        abc.
145x73    549951
KTAT** Stroemberg         1988    3     8    14      7731      313   32    5         8        abc.
145x73 5800516

KTAT** Stroemberg         1989    4     11   14      6937      654   66    38        48       abc.
145x73 5800517
          EFACEC***       1992    5     14   13      8765      335   13    8         7        abc.
          C-12390
          EFACEC          1992    6     23   28      6692      273   117   30        54       abc.
          C-12388
    Insulation level: 550/230; Impedance: 1-16.9; 7-15.7;13-15.2; 20 to of oil;Pxx=41.5
   ** Insulation level: 650/275; Impedance: 1-17,1;.7-15.9;13-15.4; 20.8 to of oil;Pxx=28.9
   *** 32.250l=26000kG of oil




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                     SCIENTIFIC AND ENGINEERING COMPANY ZTZ-Service Co.
                                    Materials Test Laboratory



                           REPORT № 10/8 – 5668 c              Date 13.04.2005
                                                                  Sample Identification: 0504039
Site of Installation: Dhekelias PS, Cyprus                        Customer: Sokolov V.V.
Transf. Type: KTAT 145x73                                         Date of Test: 11.04.2005
MVA: 73.0                             kV: 150                     Sampled: 05.04.2005
Serial № 5800516                      Station № 3                 Sampling Place: Tank
MFR: Stromberg
Oil Protection Type: Free breathing             Oil: -             Oil Temp.: 54 °C
Reason of Sampling: Examination
Notes:

         CHARACTERISTICS                          UNIT           RESULT               METHOD
Hydrogen H2                                        ppm              11.0
Methane CH4                                        ppm               6.0                 IEC 60567
Acetylene C2H2                                     ppm              n/d
Ethylene C2H4                                      ppm              32.0
Ethane C2H6                                        ppm               3.0
Carbon Monoxide CO                                 ppm             376.0
Carbon Dioxide CO2                                 ppm            8680.0
Propane + propylene  C3                           ppm               4.0
Buten 1-C4H8                                       ppm            1159.0
Air gas
            - Oxygen O2                           % vol.            3.40
            - Nitrogen N2                         % vol.            6.20
Total Gas Content                                 % vol.           10.63
Water Content                                     ppm               13.0                 IEC 60814
Furan Content
 2 FAL                                             ppb             400                  IEC 61198




   Tested:                                                     Stecenko O.G.
                                                               Povstyanaya Y.V.




    Checked:                                                   Berezhnoy V.N.




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