Test Procedure

THAI TRAFO MANUFACTURING CO.,LTD. OFFICE: 115 Preedaview Building, Soi Chokechai Chongjumroen, Rachadapisek Rd,(Rama 3), Yannava, Bangkok 10120 THAILAND. Tel.(66)022952121-32, Fax: (66) 02295-2132

TEST ITEMS

ROUTINE TEST

• Measurement of Winding Resistance • Measurement of Voltage Ratio and Checked of Phase Displacement • Measurement of Insulation Resistance • Oil-Dielectric Strength Test • Separate-Source Voltage Withstand Test • Induce Over voltage Withstand Test • Measurement of Short-Circuit Impedance and Load Loss • Measurement of No-Load Loss and Exciting Current • Transformer oil leakage test

TYPE TEST

• Lightning Impulse Withstand Test (BIL) • Temperature Rise Test


MEASUREMENT OF WINDING RESISTANCE

Reference Standard

1. IEC Publication 60076-1: Power transformer Part1: Sub-Clause 10.2 2. ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed Distribution,

Power, and Regulating Transformers: Sub-Clause 5 Purpose and Method of Measurement The resistance of transformer winding is routinely measured to verify its continuity and connection. The resistance between all pairs of phase terminal of each transformer winding is measured using direct current. The measurement is performed for each connection of connectable winding and for each tapping connection. Furthermore the corresponding winding temperature is measured. In the report the terminals, between which the resistance are measured, the connection, the tapping position and the temperature of the winding during the measurement are state Circuit and Apparatus

RD1

RESISTOMAT

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C

Ba

b

c

n


List of Equipment and Instrument

1. RD1, Resistomat, Type 2304, Accuracy ±0.068% 2. Digital Thermometer, Fluke 52, Accuracy ±1°C 3. Digital thermometer, PD-2 mc ,RKC , accuracy ±1°C

Acceptance Criterion The measured resistance should be similar to designed value at reference temperature and reasonable with the connection diagram.


MEASURMENT OF VOLTAGE RATIO AND CHECK OF PHASE DISPLACEMENT

Reference Standard

1. IEC Publication 60076-1: Power transformer Part 1 2. ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed Distribution,

Power, and Regulating Transformers: Sub-Clause 6 Purpose and Method of Measurement

The purpose of measurement is to check that the deviation of the voltage ratio from the specific value does not exceed the limit given in the relevant standard (generally +/-0.5%). The phase displacement of the transformer is checked in the same time. Test Circuit and Apparatus

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HX Multi-amp Ratio Meter


List of equipment and instrument

Ratio Meter Multi-Amp, TR800, Accuracy ±0.2% Acceptance Criterion

The percentage deviation of voltage ratio shall be ±0.5% of declared ratio. The polarity of single-phase transformer and the connection symbol of three-phase transformer shall be right.


MEASUREMENT OF INSULATION RESISTANCE Reference Standard

1. IEC Publication 60076-3 : Power transformers Part 3 : Insulation levels and dielectric tests

2. ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed Distribution, Power, and Regulating Transformers: Sub-Clause 10.11

Purpose and method of measurement

The purpose of the measurement is to determine the leakage current resistance of the insulation. This is a function of moisture and impurity contents of the insulation and of its temperature. Measurement of insulation resistance shall be measured from winding to earth and between winding by mega-ohm meter and the temperature of the winding shall be records. Measurement of the insulation resistance shall be record. Measurement of insulation resistance shall be measured as following:

• Between HV and ground (2500 V) • Between LV and ground (2500 V) • Between HV and LV (2500 V)

Test Circuit and apparatus

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+ -

Megger BM11D

Digital insulation tester HV to LV under tested


List of Instrument and Equipment

1. Digital insulation tester, BM11D, AVO, Accuracy ± 5% 2. Digital Thermometer, Fluke 52, Accuracy ±1°C

Acceptance Criterion Permissible insulation resistance of the transformer shall be more than 2000 Mohm


OIL DIELECTRIC STRENGTH TEST

Reference Standard

1. IEC publication 60156: Insulating liquids-Determination of the breakdown voltage at power frequency test method

Purpose and method of measurement The test method is performed in accordance with IEC publication 60156. Sampling the transformer oil to the container with 2.5 mm gap setting. The voltage 50Hz shall be applied between the electrode and rising up the voltage until breakdown occurs. The maximum voltage shall be recorded in kV. Test circuit and Apparatus

V Test Vessel

Test Transformer

AC Voltage 61.8 Hz

Electrodes Sample oil


List of Equipment and Instrument Automatic dielectric strength test set “AVO”, OTS80 AF/2, Accuracy ±5% Acceptance Criterion

Transformer oil dielectric strength shall not be less than 50 kV.


SEPARATE-SOURCE VOLTAGE WITHSTAND TEST

Reference Standard

1. IEC publication 60076-3: Power transformer Part 3: Insulation levels and dielectric tests


Purpose and Test Method Dielectric tests with separate source voltage are performed to prove the strength of the main insulation between the test winding and the insulation between winding and earth parts, withstand the temporary over voltage and switching over voltages which may occur in service. The separate-source voltage test shall be made with single-phase approximately sinusoidal at rated frequency (not less than 80% of rated). The voltage shall be applied for 60 s between the winding under test and the other part of transformer connected to earth as following

• Between HV and LV + ground • Between LV and HV + ground

Test Circuit and Apparatus

DMI 551

AC B

abc n

Transformer 20KVA220V-80KV



1. AC. Voltage Measuring System, Accuracy ±3%

• Digital measuring instrument, DMI 551 • Capacitor voltage divider 100pF, 100kV

2. Test transformer, single phase transformer 10 KVA 100kV/220V

Acceptance Criteria There is no collapse of the test voltage occurs.


INDUCE OVER VOLTAGE WITHSTAND TEST

Reference Standard

1. IEC publication 60076-3: Power transformer Part 3 : Insulation levels and dielectric tests


Purpose and Test Method Dielectric tests with induce voltage are performed mainly to proved the strength of the insulation between turn and winding for double power frequency stresses. The test will also demonstrate the strength of insulation from winding to earth and between phase of multi-phase unit. The induce over voltage test shall be made with approximately sinusoidal. The twice voltage shall be applied on one of the windings. The remaining winding shall be left open-circuited, the duration of the test shall be 120 x (rated frequency/test frequency) but not less than 15 second (according to IEC Standard) or applied for 7200 cycles (according to ANSI Standard) Test Circuit and Apparatus

CT PT

A1

A2

A3

V

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Generator 160KVA 400Hz

Test Object


List of Equipment and Instrument

1. Test set generator 400 Hz 2. Current transformer 50/5 A, Accuracy 1% 3. Ammeter “Norma”,1.2..6 A 4. Potential Transformer 1000/100 V, Accuracy 1% 5. Voltmeter “Norma” model 500029

Acceptance Criteria There is no collapse of the test voltage occurs.


MEASUREMENT OF SHORT-CIRCUIT IMPEDANCE AND LOAD LOSS

Reference Standard

1. IEC publication 60076-1 : Power transformer Part 1 : General 2. ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed

Distribution, Power, and Regulating Transformers: Sub-Clause 9

Purpose and Test method The short-circuit impedance and load loss of winding shall be measured at rated frequency and relevant rated current (tapping current) not less than 50% with approximately sinusoidal voltage applied to one winding. The temperature of the winding shall be record to rated current and reference temperature of 75 °C or 85 °C Test Circuit and Apparatus

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C

B

a

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A V ±±

DIGITAL POWER METER

SET UP TRANSFORMERitem2.1

VARIABLE VOLTAGETRANSFORMER item 2.2

CT PT

TEST OBJECT



1. Current transformer “YOKOGAWA”, Accuracy 1% 2. Potential transformer “YOKOGAWA”, Accuracy 1% 3. Power meter “YOKOGAWA”, 2533, Accuracy 0.5%

Acceptance criteria The acceptance of transformer load loss shall be lower than the guarantee values or within tolerance of +15% of guarantee values and voltage impedance shall be ±10% of guarantee values


MEASURMENT OF NO-LOAD LOSS AND CURRENT Reference standard

1. IEC publication 60076-1 : Power transformer Part 1 : General 2. ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed


Purpose and test method The no-load loss and current shall be measure on one of the winding at rated frequency and voltage on principle tapping. The remaing winding shall be left open-circuited. Test circuit and Apparatus

A V ±±

DIGITAL POWER METER

CT PT

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C

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nTEST OBJECT



1. Current transformer “YOKOGAWA”, Accuracy 1% 2. Potential transformer “YOKOGAWA”, Accuracy 1% 3. Power meter “YOKOGAWA”, 2533, Accuracy 0.5%

Acceptance Criterion

The acceptance of transformer no-load loss and current shall be lower than guarantee values or within tolerance of +15% of no-load loss guarantee values and +30% of no-load current guarantee values.


LIGHTNING IMPULSE WITHSTAND TEST

Reference standard

1. IEC publication 60076-3 : Power transformer 2. IEC publication 600722 : Guide to lightning impulse and switching

impulse testing of power transformer and reactor. 3. ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed

Distribution, Power, and Regulating Transformers: Sub-Clause 10.3

Purpose and Test method

The test method was performed in accordance with ANSI C57.12.00 The test impulse is a full standard lightning impulse 1.2 ± 30% / 50 ± 20% μS, negative polarity. The time to chopping (TC) is 1-3 μS. The test voltage was applied to the power transformer winding under tested with the connection circuit as shown in figure below. The test was carried out on each phase and the test sequence per line terminal are one reduced full impulse at a voltage between 50% - 75% of the full voltage followed by two 115% chopped impulse ,one 100% full impulse.

Test Circuit and apparatus

Rsi

Cs

Rp

Rse

ToVoltage

Recorder

SphereGap A CB

a b c n

ToCurrent

Recorder

3 φ Transformer

ImpulseGenerator



1. Impulse voltage test system 400 kV “HAEFELY” type SGS400

Acceptance Criterion

The absence of significant difference between voltage & current record at reduced impulse and those full impulse evidence that the insulation has withstand the test.


TEMPERATURE-RISE TEST

Reference standard

1. IEC publication 60076-1 : Power transformer General 2. IEC publication 60076-2 : Power transformer Temperature-Rise 3. ANSI C57.12.90-1999: Standard Test Code for Liquid-Immersed


Purpose and Test method The transformer is subjected to a test voltage equal to the total losses of the transformer. The test is continued until a steady-state oil temperature rise is established or oil temperature rise has fallen below 1 °K per hour and has remained there for a period of 3 hours. The test current is reduced immediately to rated current and maintained for 1 hour, then disconnected the test power supply. The resistance of HV and LV winding are measured for a sufficient time. Test circuit and apparatus

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A V ±±

DIGITAL POWER METER

CT PT

Top oilupper

lower

Amb. 1

Amb. 2

Amb. 3

Temperature Recorder



1. Current transformer “YOKOGAWA”, Accuracy 1% 2. Potential transformer “YOKOGAWA”, Accuracy 1% 3. Power meter “YOKOGAWA”, 2533, Accuracy 0.5% 4. Resistomat, Type 2304, Accuracy ±0.068% 5. Digital Thermometer, Fluke 52, Accuracy ±1°C

Acceptance criterion The limits temperature rise for top oil and average winding temperature rise are not exceed than guarantee values.

Documents

Test Procedure