transformer general data

8/3/2019 Transformer General Data

http://slidepdf.com/reader/full/transformer-general-data 1/4

TRANSFORMER GENERAL DATA

• This format contained the general data of the Transformer.• The data shall be filled in the formatReference: a) Nameplateb) Factory acceptance test reportc) Approved drawingsd) Standards

For example: HV Voltage------------- 132 kVLV Voltage ------------- 12 kVVector ------------------ YNd1Capacity----------------- 50000 KVA

Type of tap changer--- On Load Tap Changer

02 FINAL CHEKS

• This ********s contained the items to be checked before energisation of the Transformer.• We have to verify each and every item specified in this format prior to energisation and after completion of all test and checks.• Comments shall be reported and recorded• Reference: a) Name plateb) Valve schedule platec) Factory acceptance test reportd) Approved drawingse) Standards

03 INITIAL CHECK

This ********s contained following check items. (To be carried out prior to any test)Initial check

All items specified under this heading are to be verified and recorded. These areessential to verify whether the transformer is fit for starting any test.

• To ensure whether the Transformer received at site was safely.(based on safe receipt report and shock recorder data)• To ensure the site processing (Erection, assembling, oil processing and etc.)• To ensure the record keeping.(Specification, drawing, instruction manual, factory test report, s ite note etc.)

Reference: a) Nameplateb) Valve schedule platec) Factory acceptance test reportd) Approved drawingse) Standards

04 SITE PROCESSING DETAILS

All points mentioned under this heading are to verified and recorded.

• To ensure the oil processing were completed as per the procedure given bymanufacturer or based on any relevant ********s/ standards.• To ensure the condition of purifier, vacuum pump, gauge etc.during oil processing.• To ensure the degree of vacuum maintained during processing.• To ensure the condition of hot oil cir culation.

05 MEASUREMENT OF INSULATION RESISTANCE

Standards: IEC 60076-2000(part 1) General, clause 10.1.3)

a. Winding

Aim

• To determine the insulation resistance from individual winding to Earthand between individual windings.• To evaluating the condition of the Transformer insulation

General

• Insulation Resistance is commonly measured in Meg. Ohm.• Insulation Resistance shall be depending up on the design, temperature,dryness, cleanliness of parts, especially bushing porcelain, condition of oiland atmospheric condition etc.• Insulation Resistance falls below the specified value it can be increased upto some certain level by cleaning and drying of Bushing porcelain and repeatoil processing.• Insulation Resistance varies with applied voltage during measurement.So any comparison required should always be carried out at same voltage• .Insulation resistance is inversely proportional to the temperature.• Applied voltage during measurement is DC• The temperature of the Transformer under test must be noted and shall be near to the reference ambient temperature.• Measurement shall be made at 15th, 60th and 600th seconds.• In any case the measured value at 60th seconds should not be less than 2000Meg. Ohm.• Polarization Index (PI) can be determined and PI is the ratio between 600th and 60th seconds• The value of the PI gives a rough guide to the condition of the Transformer.• PI value shall be ≥ 1 .3 (satisfactory)≥ 1.5 (good)≥ 2.0 (very good)≤1.0 (bad –unsatisfactory condition)

Test preparation / procedure.

Test preparation

• Insulation Tester (Megger) – 500V with valid calibration sticker and certificate.• Check Earthing of the main body / tank, core /clamp etc.• Check the temperature of Transformer oil.• Check the cleanliness and dryness of the Bushing porcelain• Check the leveling of the Megger and access of the supply in put.• Check the tightness of the connection• The test leads shall not be allowed to touch with Transformer bodyand leads between each other.• Make / sl.no. and calibration details of the instruments are note down and recorded.

Test procedure

• The test shall be conducted at 500V• All terminals of each winding shorted together.



• Reading shall be checked at 15th, 60th and 600th seconds.• Verify the measured insulation resistance values and PI values.• Test results shall be recorded.

HV-LV & Earth HV-LV LV-HV& Earth

5.2 Core and clamp

Aim

• To determined the core insulation, clamp insulation and between core and clamp insulation.• To ensure the power frequency voltage withstand (2kVrms).

Test preparation / procedure

Test preparation

• Insulation Tester (Megger) - 500 V with valid calibration sticker and certificate.• Check Earthing of the main body• Remove the Earthing from core and clamp.• Check the temperature of the Transformer oil.• Check the cleanliness and dryness of the Bushing porcelain of core and clamp.• Check the leveling of the Megger and access of the supply in put.• Check the tightness of the connection• The test leads shall not be allowed to touch with Transformer bodyand leads between each other.Make, sl.no. and calibration details are note down and recorded

Test procedure

• The test shall be conducted at 500 V at 60th seconds for the followingcondition and recorded.Core to EarthClamp to EarthCore to clamp• Verify the test results

• Test results shall be reported and recorded.

06 2 kV TEST ON CORE AND CLAMPING STRUCTURE

Standards: IEC 60076-2000, clause-11

Aim

• To ensure the insulation is capable to withstand the specified test voltage.


Preparation

• Source Transformer – sufficient capacity.• Test voltage – 2kV rms.• Voltage Transformer• Slide arc – sufficient capacity• Stop watch – calibrated one• Volt meter and Ammeter• Ensure the input supply, connecting leads, tightness of the connection etc• Test duration – 60 seconds.

Procedure

• The voltage is varying from minimum to the specified test voltage of 2 kV rms and kept for 60 seconds. During this keeping time there should not be any collapse involtage orsudden increase in leakage current.o Note down the charging current.o Test result shall be reported and recorded

Test condition

• Core to Tank (Clamp connected to Tank Earth)• Clamp to Tank (Core connected to Tank Earth)

07 RATIO AND VECTOR GROUP OR PHASE DISPLACEMENT CHECK

Standards: IEC 60076-2000, Part 1 Clause 6, and 10.3

Aim

• Measuring the voltage ratio and phase displacement are essential because of their bearingon the parallel operation of the transformer• Parallel operation of the transformer is requires that the no load ratio and the vector group issame to avoid circulating current• To ensure the voltage ratio of the Transformer is designed / manufactured as per theSpecification/ requirements.• To ensure the phase displacement or vector group of the Transformeris design/ manufactured as per the specification.

General

• The individual winding of poly phase Transformer can be connected in star, delta orzig zag depending up on the application• The phase displacement of the winding between 0-3600 according to the connectionmethod• The vector diagram of the high voltage winding is actually placed on a clock faceso that the tip of vector 1U i s at 12 0' clock and vector diagram of the low voltage windingis placed on top with the same phase orientation, then the direction of vector 2U identifiesthe clock number of the vector group.• For the three phase Transformer the phase angle of the intermediate and low v oltagewinding is referred to the high voltage winding for the vector group.• For zigzag connection the winding half closet to the terminals determine the terminals



is on limb V, the terminal is also called 2V.• The allowable maximum ratio error or percentage deviation of the actual to the declaredratio is ± 0.5%.


Preparation• Ensure the availability of 3 phase or 1 phase slide arc.• Ensure the Earthing main tank, core and clamp etc.• Ensure the availability of 3 phase and 1 phase supply in put.• Voltmeters, sufficient numbers with proper calibration status.• Ratio Bridge meter (3 phase or 1 phase with code) and proper calibration status.

• Ensure the neutral is not connected to Earth.• Ensure the connection and tightness• Ensure the sufficient length and size of connecting leads.• Measuring voltage: Low voltage (3 phase, 50Hz or 1 phase, 50 Hz supply)• Note down the make, sl.no. and calibration status of the equipments used for themeasurement.

Procedure for voltage ratio measurement

• The voltage ratio can be determined by using either of two methods.1. Direct measuring the voltage with voltmeter2. Using Ratio Bridge.

1 Direct measuring the voltage with voltmeter

• The result is determined from the measured two voltmeter readings.• The voltage shall be applied to the high voltage side and induced voltage acrossthe low voltage side measured.• If a star windings Transformer the applied and measured voltage shall be checkedbetween line and neutral.Two winding Transformer with HV as star winding and LV as delta is shown for measurement.• Test shall be made for all taps position

Voltage shall be applied on high voltage side between lines / l ine and neutral. The inducedvoltage on other winding measured between l ines/ line and neutral.

• Suppose the HV and LV voltage is = 132 kV and 12 kV(star/ delta)• So the declared HV/LV ratio is 132 /√3/12 = 6.351• The HV applied voltage between line and neutral = 231.8 V• Corresponding voltage measured on LV = 36.37V• So the measured ratio = 231.8 / 36.37= 6.373• There for the measured percentage deviation: ﴾ measured ratio- declared ratio﴿ X100 = (6.373 – 6.351) X 100

Declared ratio 6.351= 0.364• Test shall be done at all taps.• Test result shall be checked and recorded

2 Ratio measurement with Ratio Bridge.

• The applied and measured voltage is compared in a bridge by the null indication.method.• This is the direct measurement for the ratio error and need not required anycalculation.• This can be done either with 3 phase or 1 Phase Bridge.• Test shall be done at all taps.• Supply shall be switched off before tap changing• Test results shall be checked and recorded.

Procedure for polarity / Vector group checking

Single phase Transformer

• For single phase Transformer, the polarity shall be either additive or subtractive.• Polarity shall be checked by using voltmeters or by DC kick method.

1 Voltmeter method

a) Subtractive polarity

• Short HV 1.1 and LV 2.1 terminals together.• Assume HV /LV ratio is 10• Applied voltage across the HV is 100V• Then the induced voltage on LV (V3) is applied voltage/ HV LV ratio =100/ 10 =10V(in opposite direction)• There for the voltage between HV 1.2 and LV 2.2 terminals V2 is V1-V3 =100-10 = 90VThat is♣ V2 is less than V1, hence polarity is subtractive

b) Additive polarity

Short HV 1.1 and LV 2.2 terminals together and 1.2 and 2.1♣ terminals together(HV and LV are connected in series)Assume HV / LV♣ ratio is 10.Applied voltage V1 across the HV winding is 100V♣Then the♣ induced voltage on LV (V3) is applied voltage / HV LV ratio, =100 / 10= 10V

(in opposite direction)There fore the voltage between HV 1.2 and LV♣ 2.1 terminals V2 is V1+V3=

100+10 = 110VThat is V2 is greater than V1,♣ hence polarity is additive.

2 DC Kick method

The DC♣ positive is connected the HV 1.1 terminal through a switch K and negative connected to 1.2 terminal.The LV 2.1 terminal is connected to +ve and 2.2♣ terminal is connected to –ve of a center zero galvanometer



As per the above♣ circuit, while closing the switch K, the galvanometer got clock wise kick(+ve) and anti clock wise kick (-ve) when the switch is opening, the polarity is subtractive.The additive polarity will be reverse kick as the♣ same condition above.

Three phase Transformer

For three♣ phase Transformer the polarity / phase displacement shall be verified by checking vector groupFor example a three phase, two winding Transformer♣ ’ clock direction in LV with star connection (YN) and delta 1.0 (d1)

Short HV 1U and LV 2U terminals together to bring into in♣ phase of HV U phase and LV U phase.

After that the above vector shall be redrawn as given below.

A balanced three phase 400Volt shall be♣ applied across the HV winding and inducedvoltage across the following combination shall be measured.Voltage across

1V - 2V = a1V - 2W = b1W -2W = c1W- 2V = d1U/2U - 1N = eIf a = b = d, b is > a, b, d and e = Applied voltage / √3, then the vector will be Ynd1, ok..

OLTC Continuity

Aim

• To ensure that the Transformer winding s are not open circuited during OLTC operation

General

• The OLTC normally connected at the neutral end of the winding.• For large capacity Power Transformer, three separate OLTC may be provided each of the phase according to the design.


Preparation• Analog type volt meter minimum 3 nos• Three phase or single phase supply in put• Dimmer stat three phase or single phase according to above• If single phase supply, phase one by one can be checked• Ensure the connection and tightness

Procedure

• Preferebouly 3 phase voltage shall be applied across the low voltage winding of the Transformer• The applied voltage shall be slowly raised to get a readable value in the voltmeters put across the line and neutral of the HV winding.• The OLTC shall be operated for one complete cycle (minimum tap-maximum-minimum tap)• There should not be any zero indication in the voltmeters during the OLTC operation.• If any winding break through the OLTC, the respective voltmeter will indicate zero reading during the OLTC operation at that particular tap.• The test results shall be verified and recorded.

transformer general data

Documents