Test Methods

Končar PowerTransformers Ltd.

TEST METHODS FOR POWER TRANSFORMERS

QT No: xx-yy Page : 1 / 2

TEST METHODS FOR POWER TRANSFORMERS Contract number: XXXXXXX

Transformer type: 0 XXX 000 000 – 000

TESTING POWER TRANSFORMERS Test procedures and equipment used for the testing of large power transformers at Končar Power transformers are dealt with in the following Sections. The electrical characteristics and dielectric strength of the transformer are checked by means of measurements and tests defined by standards. The tests are carried out in accordance with IEC Standard 60076, Power transformers, unless otherwise specified in the contract documents. CONTENTS

Item 1.

Title Summary of dielectric tests

ID KPT-QTPT 001E

issue 08.2003.

KPT-QTPT 002E

issue 08.2003.

3.

Measurement of voltage ratio and check of connection symbol Measurement of winding resistance

KPT-QTPT 003E

issue 08.2003.

4.

Impedance and load loss measurement

KPT-QTPT 004E

issue 08.2003.

5.

Measurement of no-load loss and current

KPT-QTPT 005E

issue 08.2003.

6.

Induced overvoltage withstand test

KPT-QTPT 006E

issue 08.2003.

7.

Partial discharge measurement

KPT-QTPT 007E

issue 08.2003.

8.

Separate-source voltage test

KPT-QTPT 008E

issue 08.2003.

9.

Operation tests on on-load tap-changer

KPT-QTPT 009E

issue 08.2003.

10.

Measurement of the zero-sequence impedance

KPT-QTPT 010E

issue 09.2003.

11.

Capacitance and the insulation power factor measurement Insulation resistance measurement

KPT-QTPT 011E

issue 11.2004.

KPT-QTPT 012E

issue 09.2003.

KPT-QTPT 013E

issue 08.2003.

14.

Measurement of the electric strength of the insulating oil Temperature rise test

KPT-QTPT 014E

issue 11.2004.

15.

Lightning impulse test

KPT-QTPT 015E

issue 08.2003.

16.

KPT-QTPT 016E

issue 09.2003.

17.

Test with the lightning impulse chopped on the tail Switching impulse test

KPT-QTPT 017E

issue 09.2003.

18.

Measurement of acoustic sound level

KPT-QTPT 018E

issue 09.2003.

19.

Measurement of higher harmonics in magnetizing current Tightness (leakage) test

KPT-QTPT 019E

issue 08.2003.

KPT-QTPT 020E

issue 09.2003.

2.

12. 13.

20.

Prepared by:

Approved by:

F. Juraković Issue:

08.2003.

KPT-QT.001E, izdanje 08.2003.

I. Šulc 09.2003.

06.2004.

11.2004.

03.2006.

07.2006.

Končar PowerTransformers Ltd.

TEST METHODS FOR POWER TRANSFORMERS

QT No: xx-yy Page : 2 / 2

Item 21.

Title FRA measurement

ID KPT-QTPT 021E

issue 06.2004.

22.

Core insulation measurement

KPT-QTPT 022E

issue 03.2006.

23.

Power consumption of cooling system

KPT-QTPT 023E

issue 03.2006.

24.

Measurement of transferred surges

KPT-QTPT 024E

issue 07.2006.

Issue :

08.2003.

KPT-QT.001E, izdanje 08.2003.

09.2003.

06.2004.

11.2004.

03.2006.

07.2006.

Končar PowerTransformers Ltd.

1.

KPT-QTPT 001E Page: 1 / 4

SUMMARY OF DIELECTRIC TESTS

SUMMARY OF DIELECTRIC TESTS

The Basic rules for insulation requirements and dielectric tests are summarized in table 1 (IEC 60076-3). Levels of standard withstand voltages, identified by highest voltage for equipment Um of winding are given in tables 2, 3 and 4. The choice between the different levels of standard withstand voltage in these tables depends on the severity of over voltage conditions to be expected in the system and on the importance of the particular installation.

Tests Category of winding

Highest voltage for equipment Um

Lightning impulse (LI)

Switching impulse (SI)

Long duration AC (ACLD)

Short duration AC (ACSD)

Separate source AC

Not applicable

Not applicable (note 1) Special

Routine

Routine

72,5170 kV) a long duration induced voltage test including observation of partial discharges, should be specified as a routine test (see table 1 in KPT-QTPT 001E). A three-phase transformer shall be tested preferably in a symmetrical three-phase connection (see Fig. 6-2a) or in some cases in a single-phase connection that gives voltages in the line terminals according to Fig.6-2b (successively applied to all three phases).

U U

U

U

-0,5U -0,5U

G G a)

b)

Fig. 6-2

A three-phase transformer supplied from the low-voltage winding side with a delta-connected high-voltage windings can receive the proper test voltages only in a three phase test with a floating high-voltage winding. The neutral terminal, if present, of the winding under test and/or other separate windings shall be earthed. Tapped windings shall be connected to the principal tapping, unless otherwise agreed. The test time and the time sequence for the application of test voltage shall be as shown on Fig. 6-3. The voltage to earth shall be: U1=1,7Um/√3 U2=1,5 Um/√3

Issue : KPT-QA.029E.

08.2003. 2/2 izdanje 03.2002.

Končar PowerTransformers Ltd.

INDUCED OVERVOLTAGE WITHSTAND TEST

KPT-QTPT 006E 4 / 4

Page :

C

B

D E

A

U1 = 1,7 ⋅ Um / 3 1,1⋅Um / 3

U2 =1,5⋅Um / 3

U2 =1,5⋅Um / 3

U start

1,1⋅Um / 3 < Ustart

Fig. 6-3 Time sequence for the application of test voltage for induced AC long-duration tests (ACLD) A= 5 min; B= 5 min; E= 5 min;

C= test time (30 or 36 s) D= 60 min for Um≥300 kV or 30 min for Um> R2 and Cg >> C

(15.1)

T1 = 3 ⋅ R2 ⋅ C t

and the half time to half value from the equation

T2 ≈ 0,7 ⋅ R1 ⋅ C1 In practice the testing circuit is dimensioned according to experience. Issue : KPT-QA.029E.

08.2003. 2/2 izdanje 03.2002.

(15.2)

Končar PowerTransformers Ltd.

KPT-QTPT 015E

LIGHTNING IMPULSE TEST

3 / 5

Page :

15.3 CONNECTION OF THE TEST OBJECT The testing impulse test is normally applied to all windings. The impulse test-sequence is applied successively to each of the line terminals of the tested winding. The other line terminals and the neutral terminal are earthed (single-terminal test, Fig. 15-4a and b). When testing low voltage windings of high power, the time to half-value obtained is often too short ( Fig. 15-5). However, the time to half value can be increased by connecting suitable resistors ( Ra in Fig. 15-4b) between the adjacent terminals and earth. According to the IEC 60076-3 standard the resistances of the resistors must be selected so that the voltages at the adjacent terminals do not exceed 75% of the test voltage and the resistance does not exceed 500Ω. RECORDER RECORDER

S1

S1

RECORDER

Ra

a

S1

c

Ra

b RECORDER

Ra

S1

RECORDER

S1

RECORDER

RECORDER

Ru

d Fig. 15-4

Ra

S1

Rb

e

Transformer impulse and fault detection connections. a and b l-terminal testing c and d neutral terminal testing

When the low voltage winding in service cannot be subjected to lightning overvoltages from the low voltage system (e.g. step-up transformers, tertiary windings) the low voltage winding may be impulse tested simultaneously with the impulse tests on the high voltage winding with surges transferred from the high voltage winding to the low voltage winding (Fig. 15-4e, test with transferred voltages). According to the standard IEC 60076-3 the line terminals of the low voltage winding are connected to earth through resistances of such value (resistances Ra in Fig. 15-4e) that the amplitude of transferred impulse voltage between line terminal and earth or between different line terminals or across a phase winding will be as high as possible but not exceeding the rated impulse withstand voltage. The resistance shall not exceed 5000 Ω.

Issue : KPT-QA.029E.

08.2003. 2/2 izdanje 03.2002.

Končar PowerTransformers Ltd.

LIGHTNING IMPULSE TEST

KPT-QTPT 015E 4 / 5

Page :

The neutral terminal is normally tested directly or indirectly by connecting a high-ohmic resistor between the neutral and earth (voltage divider Ra, Ru) and by applying the impulse (Fig. 15-4c and d) to the line terminals connected together. The impulse test of a neutral terminal is performed only if requested by a customer. The front time is allowed to be up to 13 µsec. The failure detection is normally accompolished by exmination of the oscillograms of the applied test voltage, the neutral current and / or the capacitively transferred current.

15.4 PERFORMANCE OF THE IMPULSE TEST The test is performed with standard lightning impulses of negative polarity. The front time (T1) and the time to half-value (T2) are defined in accordance with the standard.

U 1,0 0,9

0,5

0,3

0

T

t

T1 =1,67 T T2

Fig. 15-5

Standard lightning impulse Front time T1 = 1,2µs ± 30% Time to half-value T2 = 50 µs ± 20%

In practice the impulse shape may deviate from the standard impulse when testing low-voltage windings of high rated power and windings of high input capacitance. The impulse test is performed with negative polarity voltages to avoid erratic flashovers in the external insulation and test circuit. Waveform adjustments are necessary for most test objects. Experience gained from results of tests on similar units or eventual precalculation can give guidance for selecting components for the wave shaping circuit. The test sequence consists of one reference impulse (RW) at 75% of full amplitude followed by the specified number of voltage applications at full amplitude (FW) (according to IEC 60076-3 three full impulses). The equipment for voltage and current signal recording consists of digital transient recorder, monitor, computer, plotter and printer. The recordings at the two levels can be compared directly for failure indication. For regulating transformers one phase is tested with the on-load tap changer set for the rated voltage and the two other phases are tested in each of the extreme positions. Issue : KPT-QA.029E.

08.2003. 2/2 izdanje 03.2002.

Končar PowerTransformers Ltd.

LIGHTNING IMPULSE TEST

KPT-QTPT 015E Page :

5 / 5

Detection of correctness at impulse testing is based on comparison of voltage and current records obtained at reduced and full amplitudes. The two traces should have a perfect match to constitute evidence that the insulation has passed the test.

15.5 TEST REPORT The detailed test record cover setting of impulse generator, values for all components in the impulse shaping and measuring circuits, connection of the test object, parameters for the wave-shape and oscillogram records for each voltage application.

Issue : KPT-QA.029E.

08.2003. 2/2 izdanje 03.2002.

Končar PowerTransformers Ltd.

TEST WITH THE LIGHTNING IMPULSE CHOPPED ON THE TAIL

16.

TEST WITH THE LIGHTNING IMPULSE CHOPPED ON THE TAIL

16.1

PURPOSE OF THE TEST

KPT-QTPT 016E Page :

1 / 2

The purpose of the chopped lightning test is to secure that the transformer insulation withstand the voltage stresses caused by chopped lightning impulses, which may occur in service. 16.2

TEST EQUIPMENT

For the chopped lightning impulse test the same testing and measuring equipment and the same testing and fault detection connections are used as for the standard lightning impulse test. The impulse is chopped by means of triggered-type chopping gap connected to the terminal to which the impulse is applied. The delay of the chopping–gap ignition impulse in relation to the impulse generation is adjustable, thus the time Tc from the start of the impulse to the chopping can be adjusted (Fig. 16-1). 16.2

PERFORMANCE OF THE TEST

The test is performed with impulses of negative polarity. The duration Tc from the beginning of the impulse to the chopping can vary within the range of 2...6µs (Fig. 16-1) According to the standard IEC 60076-3 the amount of overswing to opposite polarity shall be limited to not more than 30% of the amplitude of the chopped impulse (Fig. 16-1). If necessary the overswing amplitude will be limited to the value mentioned by means of damping resistor inserted in the chopping circuit.

α

1,0 0,9

0,3

β

T1 Tc

Fig 16-1

Chopped lightning impulse Front time Time to chopping

Yc =

β 100% < 30% α

Prepared by:

Controlled by:

J. Bujanović Issue: KPT-QA.029E

T1 = 1,2 µs ± 30% Tc = 2....6 µs

08.2003.

Approved by:

I. Šulc 09.2003.

1/2 izdanje 03.2002.

I. Šulc

Končar PowerTransformers Ltd.

TEST WITH THE LIGHTNING IMPULSE CHOPPED ON THE TAIL

KPT-QTPT 016E Page :

2 / 2

The voltage measurement is based on the peak voltmeter indication. The test with chopped lightning impulse is combined with the test carried out with standard impulse. The following order of pulse application is recommended by the standard IEC 60076-3 - one 75% full impulse - one 100% full impulse - one or more 75% chopped impulses - two 100% chopped impulses - two 100% full impulses 16.4

THE FAILURE INDICATION

The fault detection is also for chopped impulses primarily based on the comparison of voltages and winding currents obtained at 75% and 100% test voltages. At high test voltages there is a small delay in the ignitions of the chopping-gap, which causes differences in the fault detection of voltages and winding currents. Furthermore differences in the instant of firing of the stages in the impulse generator may give rise to initial high-frequency oscillations in the first part of the voltage front. In this case the fault detection must be based primarily on the recordings obtained at the application of full impulses. When carrying out the chopped-impulse test, unless otherwise agreed, different tappings are selected for the tests on the three phases of a three-phase transformer, usually the two extreme tappings and principal tapping. 16.5

TEST REPORT

The test voltage values, impulse shapes, tappings and the number of impulses at different voltage levels are stated in the report. The oscillographic records and measurement records are stored in the archives, where they are available when required.

Issue : KPT-QA.029E.

08.2003.

09.2003.

2/2 izdanje 03.2002.

Končar PowerTransformers Ltd.

KPT-QTPT 017E

SWITCHING IMPULSE TEST

Page :

1 / 2

17. SWITCHING IMPULSE TEST 17.1 PURPOSE OF THE TEST The purpose of the switching impulse test is to secure that insulation between windings, between windings and earth, between line terminals and earth and between different terminals withstand the switching overvoltages, which may occur in service.

17.2 PERFORMANCE OF THE TEST The same testing and measuring equipment as for the lightning impulse test are used here. According to the IEC 60076-3 the switching impulse test is carried out on each high voltage line terminal of a three-phase winding in sequence. A single-phase no-load test connection is used in accordance with Fig. 171. The voltage developed between line terminals during the test is approximately 1,5 times the test voltage between line and neutral terminals. The flux density in the magnetic circuit increases considerably during the test. When the core reaches saturation the winding impedance is drastically reduced and a chopping of the applied voltage takes place (Fig. 17-2). The time to saturation determines the duration of the switching impulse. Because the remanent flux can amount to even 70 to 80 % of the saturation flux, the initial remanence of the core has a great influence on the voltage duration. By introducing remanent flux of opposite polarity in relation to the flux caused by the switching impulse, the maximum possible switching impulse duration can be increased. The remanence of opposite polarity is introduced in the core by applying low voltage current impulses to LV winding of opposite polarity to the transformer before each full voltage test impulse.

U

-0,5U - 0,5 U

current recorder

Loading resistor

C1 S1 C2

voltage recorder

Fig. 17-1

Transformer switching impulse testing and fault detection connections

The test is performed with impulses of negative polarity. The requirements on the switching impulse shape given in the standard IEC 60076-3 are summarized in Fig. 17-2.

Prepared by:

Controlled by:

J. Bujanović Issue: KPT-QA.029E

08.2003.

Approved by:

I. Šulc 09.2003.

1/2 izdanje 03.2002.

I. Šulc

Končar PowerTransformers Ltd.

SWITCHING IMPULSE TEST

KPT-QTPT 017E Page :

2 / 2

The voltage measurement is based on the peak voltmeter indication.

1.0 0.9

Tp = 1,67 T

0,3 T

Td T0

Fig. 17-2

Switching impulse

Front time Time above 90% Time to the first zero passage

Tp> 100µs Td> 200µs T0> 500µs ( preferably 1000 µs )

At full test voltage each phase will be tested with the number of impulses required by the relevant standard. When comparing the wave shape it is to be noticed that the magnetic saturation causes drastic reduction of voltage and increase in winding current and the time to saturation is dependent on the amplitude of the applied voltage. Thus voltage and current oscillograms obtained at full test voltage and at 75% voltage level will deviate from each other in this respect. The fault detection is mainly based on the voltage oscillograms. The test is successful if no sudden collapse of voltage caused by flashover or breakdown is indicated on the voltage oscillograms and no abnormal sound effects are observed. When the core reaches saturation a slight noise caused by magnetosriction can be heard from the transformer. Test report The test voltage values, impulse shapes, and number of impulses at different voltage levels are stated in the report. The oscillographic records are stored in the archives, where they are available when required.

Issue : KPT-QA.029E.

08.2003.

09.2003.

2/2 izdanje 03.2002.

Končar PowerTransformers Ltd.

18.

MEASUREMENT OF ACOUSTIC SOUND LEVEL

KPT-QTPT 018E Page :

1 / 2

MEASUREMENT OF ACOUSTIC SOUND LEVEL

18.1 PURPOSE OF THE MEASUREMENT The purpose of the sound level measurement is to check that the sound level of the transformer meets the specification requirements given in relevant standards e.g. IEC 60076-10 or guarantee values given by the transformers manufacturer. A sound spectrum analyses are carried out for the transformer at the customer's request. The sound spectrum indicates the magnitude of sound components as a function of frequency.

18.2 MEASURING EQUIPMENT A precision sound pressure level meter type 1 complying with IEC 60651 is used in the sound level measurements. The measurements are performed using the weighing curve A. The sound spectrum analysis of the transformer is carried out by recording the sound band levels as a function of frequency. This is done with sound level meter Brűel & Kjaer type 2236 and calibrator type 4231.

18.3 PERFORMANCE OF THE MEASUREMENT The A-weighted sound pressure level of the Background noise shall be measured at points on the prescribed counter immediately before and after the measurements on the transformer. Power is supplied to the transformer under no load condition at the rated voltage and the frequency with the tapping selector on the principal tapping. The sound pressure level is the measured at various points around the transformer as detailed in the standards: at a distance (D) of 30 cm for ONAN or 2 m for ONAF cooling system spaced at an interval (X) of 1 meter; as it is shown on Fig. 18-1. The microphone position in the vertical direction shall be on horizontal planes at one third and two thirds of one transformer tank height when the height of the tank is equal to or greater than 2,5 m. When the tank height is less than 2,5m, the measurement plane is located at half the tank height. Preferably the background sound level should be at least 9 dB(A) below the measured combined sound level. If the difference is less than 9 dB(A) bat not less than 3 dB(A) a correction for background level will be applied according to standards.

9 15

19

1

STV

HV 40 LV

38 22

30 D=2m; x=1m

D

31

36

x

Fig. 18-1 Basic layout of measuring points

Prepared by:

Controlled by:

J. Bujanović Issue: KPT-QA.029E

08.2003.

Approved by:

I. Šulc 09.2003.

1/2 izdanje 03.2002.

I. Šulc

Končar PowerTransformers Ltd.

MEASUREMENT OF ACOUSTIC SOUND LEVEL

KPT-QTPT 018E Page :

2 / 2

18.4 CALCULATION OF AVERAGE SOUND PRESSURE LEVEL The uncorrected average A-weighted sound pressure level shall be calculated from sound pressure levels, LpAi, measured with the test object energized by using equation: −

L

pA

 1 N = 10 lg  Σ 10  N i =1

0 , 1 LpAi

 

or when the range of values of LpAi does not exceed 5dB, a simple arithmical average will be used. Corrections for background level and environmental correction, in case of need or as circumstances require, should be done in accordance with relevant standard.

18.5 CALCULATION OF SOUND POWER LEVEL The A-weight sound power level of the transformer LwA shall be calculated from average A-weight sound pressure level LpA according to equation: −

L WA

or

= L

pA

+ 10 lg S

[dB ]

S = the equivalent surface area in m2, defined by equation : a) for ONAN system S = 1,25 h ⋅ lm b) for ONAF system S = (h+2) ⋅ lm

where: h= height in meters of transformer tank lm = the length in meters of the prescribed counter More details can be found in relevant standard.

Issue : KPT-QA.029E.

08.2003.

09.2003.

2/2 izdanje 03.2002.

Končar PowerTransformers Ltd.

19.

MEASUREMENT OF HIGHER HARMONICS IN MAGNETISING CURRENT

KPT-QTPT 019E Page :

1 / 1

MEASUREMENT OF HIGHER HARMONICS IN MAGNETIZING CURRENT

19. 1 GENERAL At imposed sinus voltage on a transformer, because of non-linear magnetic curve of the core, magnetizing current at no-load contains besides basic harmonics also higher harmonics. Higher harmonics in the current can cause in electric grid voltage distortion, that is, they can cause even higher harmonics. Such current and voltage harmonics can cause disturbances in electric grid or in connected appliances. However, since the portion of higher harmonics in relation to transformer rated current is smaller than 1%, they are insignificant for a user. 19.2

MEASURING EQUIPMENT

In the Test Station, the measurement of higher harmonic contents, as a rule, is carried out during the measurement of no-load losses and in the same connection (see in KPT-QTPT 005E Fig 5-1). The test generator and intermediate transformer are used, as a rule, only in the linear range of their characteristics. The test circle is carried out without a feedback line so that the third degree harmonics cannot flow. The transmitting ratio of voltage transformers as well as the load of current transformers are selected in such a way that their working points lie in the linear range of the magnetizing characteristics. The measurement of higher harmonics in magnetizing currents is carried out with a Wide Band Power Analyser, producer NORMA, type D 6000. 19.3

PERFORMANCE OF THE MEASUREMENT

For the measurement, first, a required voltage is adjusted, usually 100% of rated voltage, gradually increasing the value from zero to higher values. The measurement of voltage is carried out with a meanvalue voltmeter. During the measurement of higher harmonics the power voltage should be maintained so that it has a constant value. Therefore, in the Test Station, during this period, the above mentioned fast-registering analyser with the memory in real-time procedure is used. 19.4

PROCESSING OF THE MEASUREMENT RESULTS

By using this registering analyser, the final measured values of higher harmonics are immediately obtained for the test protocol. Higher harmonics are expressed in percentage of the fundamental one.

Prepared by:

Controlled by:

J. Bujanović Issue: KPT-QA.029E

08.2003. 1/2 izdanje 03.2002.

Approved by:

I. Šulc

I. Šulc

Končar PowerTransformers Ltd.

20. 20.1

KPT-QTPT 020E

TIGHTNESS (LEAKAGE) TEST

Page :

1 / 1

TIGHTNESS (LEAKAGE) TEST PURPOSE

The purpose of the test is to prove tightness of transformer tank and accessories assembled on the transformer.

20.2

PERFORMANCE OF THE TEST

Transformer is assembled and filled with oil. Overpressure of 35 kPa is applied on the tank cover and kept for 12 hours. Welds and joints on the tank are checked on leak. If requirements in the contract differ from those stated procedure and values as per contract should apply.

20.3.

TEST REPORT

Value of overpressure and elapsed time are recorded with confirmation of tightness.

Prepared by:

Controlled by:

J. Bujanović Issue: KPT-QA.029E

09.2003. 1/2 izdanje 03.2002.

Approved by:

I. Šulc

I. Šulc

Končar PowerTransformers Ltd.

21. 21.1

KPT-QTPT 021E

FRA MEASUREMENT

Page :

1 / 2

FRA MEASUREMENT PURPOSE

The purpose of the FRA (Frequency Response Analysis) measurement is to detect displacement (or movement) of windings in the transformer. Usually the first measurement in the factory is used as a fingerprint. Results of later measurements are compared with the first one in the factory.

21.2

MEASURING EQUIPMENT TrafTek – B&C Diagnostics, Budapest, Hungary Test connection - 20 m long measuring cable (triple coax cable)

The TRAFTEK equipment is designed for scanning the geometrical and mechanical movements and distortions of transformer windings using the swept frequency measuring methods. It is known that a transformer winding with its stray capacitances and inductances form a complicated RLC network. If we apply small AC voltage (about 4Vrms) with frequency range of 50 Hz to 1 MHz we shall get a typical voltage attenuation or winding impedance curve as a function of frequency.

21.3

PERFORMANCE OF THE MEASUREMENT

The transformer under the test and measuring equipment are connected acc. to the Fig. 21-1.

Transform er

N

a

A

b

B

c

C

T rafT ek 75 Ω

SW G , 50Hz-1MHz

≈

486 DX 100 CPU

75 Ω 75 Ω

AD Conversion

Display

Fig. 21-1 Connection of the transformer and measuring equipment The software controlled sine wave generator produces output voltage of max. 4 Vrms with frequency range of 50 Hz to 1 MHz. It has 75 Ω output impedance. Input impedance is 75 Ω. Voltage from the generator is applied to the one transformer terminal (one winding end) and response voltage is measured on another terminal (the other winding end). Prepared by:

Controlled by:

R. Gardijan Issue: KPT-QA.029E

06.2004. 1/2 izdanje 03.2002.

Approved by:

I. Šulc

I. Šulc

Končar PowerTransformers Ltd.

21.4

FRA MEASUREMENT

KPT-QTPT 021E Page :

2 / 2

TEST REPORT

Impedance value Z in kΩ versus frequency or attenuation A (or damping) in dB (20 log (Uoutput / Uinput ) versus frequency can be plotted on the diagram with indication of terminals with applied and response voltage. Examples are given below.

Z (kΩ)

10,00

1,00

0,10 1000

10000

100000

1000000

frequency (Hz)

A (dB)

0,00

-10,00

-20,00

-30,00

-40,00

-50,00 1000

10000

100000 frequency (Hz)

Issue : KPT-QA.029E.

06.2004. 2/2 izdanje 03.2002.

1000000

Končar PowerTransformers Ltd.

22. 22.1

CORE INSULATION MEASUREMENT

KPT-QTPT 022E Page :

1 / 1

CORE INSULATION MEASUREMENT PURPOSE

The purpose of the measurement is to check and prove that the transformer core is insulated from the tank and core frame.

22.2

PERFORMANCE OF THE MEASUREMENT

Earthing links from core to earth and from core frame to earth (if the latter one exists) are removed (disconnected) in earthing connection box (terminal box). Several combinations of measurement of insulation resistance are possible depending upon the performance of core and frame earthing : core to frame; core to tank; core frame to tank; core to (tank + core frame); (core + core frame) to tank. At least combination core to (tank + core frame) or core to tank is to be measured. In all measurements tank is assumed as earth potential. The measurement is performed by by means of an insulation resistance meter (“Megger”). For each measurement a DC voltage of at least 500 V (but not greater than 2500 V) is applied between pair of terminal bushings in earthing terminal box for a measuring period ≥ 1 min. or until the measuring insulation resistance become stable. Measured values for each combination shall be above 50 MΩ.

22.3

TEST REPORT

Measured values with indication of measured combination are documented in transformer routine test report.

Prepared by:

Controlled by:

S. Maroš Issue: KPT-QA.029E

03.2006. 1/2 izdanje 03.2002.

Approved by:

F. Juraković

I. Šulc

Končar PowerTransformers Ltd.

23. 23.1

POWER CONSUMPTION OF COOLING SYSTEM

KPT-QTPT 023E Page :

1 / 1

POWER CONSUMPTION OF COOLING SYSTEM PURPOSE

The purpose of the test is to measure power consumption of transformer cooling plant or saying by another words to measure losses consumed by transformer cooling system. Depending upon the transformer cooling system this power can be consumed by fans and oil pumps. This measurement is performed only if required by the contract or transformer specification.

23.2

PERFORMANCE OF THE TEST

The measuring circuit and used equipment is in principle the same as for load and/or no-load measurement (described in KPT-QTPT 04E and KPT-QTPT 05E). The transformer cooling system is supplied from voltage adjustable power source. The voltage is adjusted to rated value for motors or acc. to specified value in transformer specification. Values of current, voltage and loss are measured and recorded. Power consumption for each cooling group is measured if the transformer cooling system is divided into several groups.

23.3

TEST REPORT

Measured values of current, voltage and loss at specified frequency are recorded in transformer test report.

Prepared by:

Controlled by:

S. Maroš Issue: KPT-QA.029E

03.2006. 1/2 izdanje 03.2002.

Approved by:

F. Juraković

I. Šulc

Končar PowerTransformers Ltd.

MEASUREMENT OF TRANSFERRED SURGES

KPT-QTPT 024E Page :

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24. MEASUREMENT OF TRANSFERRED SURGES – determination of transient voltage transfer characteristics 24.1

PURPOSE

Measurements of lightning or switching surges transferred from the HV winding to the LV winding on power transformer – determination of transient voltage transfer characteristics

24.2

MEASURING EQUIPMENT Recurrent surge generator, Haefelly, type 481, 400 Vpp Digital oscilloscope, Tektronix, Type: TDS 544A, 1Gs/sec.

The reccurrent surge generator is the low voltage equipment and equivalent of a high voltage impulse generator. Its wide range of applications includes the testing of models, the study of voltage distribution on high voltage windings during the impulse voltage stresses and the predetermination of the circuit parameters of impulse test plants. The components in the impulse circuit (impulse and load capacitances, front and tail resistors as well as inductances) are adjustable in steps. The wave form can thus be adjusted over a wide range with a high degree of precision.

24.3

PERFORMANCE OF THE MEASUREMENT

The transformer under the test and measuring equipment are connected acc. to the Fig. 24-1.

N A

a2

B

b2

C

c2

RSG a1

c1 b1

TDS Fig. 24-1 Connection of the transformer and measuring equipment

The manual adjustable impulse wave (lightning, chopped and switching) up to 400 Vpp, shape T1 = 0,06µs up to 500µs and T2 = 2µs up to 5000µs. Voltage from the generator is applied to the one transformer terminal (one winding end) and response (or distribution) voltage is measured on another terminal (the other winding end). Prepared by:

Controlled by:

R. Gardijan Issue: KPT-QA.029E

07.2006 1/2 izdanje 03.2002.

Approved by:

I. Šulc

I. Šulc

Končar PowerTransformers Ltd.

24.4

MEASUREMENT OF TRANSFERRED SURGES

KPT-QTPT 024E Page :

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TEST REPORT

a) Example of test report for lightning impulse for the transformer 48,4 MVA, 237 / 3,6 / 3,6 kV :

N

C…….………………..….− applied voltage A,B…………………..….. − earthed through 450 Ω

450Ω A

a2

450Ω

B

b2

C

c2

N.…………………………− isolated a1,b1,c1,a2,b2,c2.…….. − isolated

c1

Voltage % +100

Transferred voltage on the terminal

b1

a1

C−⊥

Oscillogram No 01

front wave

+100

C−⊥

02

tail wave

-5,35

a1 − ⊥

03

-5,80

b1 − ⊥

04

120 % 100

120 % 100

80

80

60

60

40

40

20

20

0

0

-20

Remark

-20

0

1

2

3

4

µs

5

0

20

01 – Front of wave

40

60

80

µ s 100

40

µs

02 – tail of wave

6

6 %

%

4

4

2

2

0

0

-2

-2

-4

-4

-6

-6

-8

-8 0

10

20

30

40

µs

03 – transferred voltage on terminal a1

Issue : KPT-QA.029E.

07.2006 2/2 izdanje 03.2002.

50

0

10

20

30

04- transferred voltage on the terminal b1

50