oil filled transformers standard testing procedure

Site Test Plan For Oil Filled Transformer STP-04-OFT

1. PURPOSE: The purpose of this procedure is to verify functions of transformer.

2. APPLICABILITY: This procedure applies to all types of power transformers.

3. DEFINITIONS: Non

4. FORM: Site Test Report For Oil Filled Transformer STR-04-OFT.

5. REFERENCES: All inspections and tests shall utilize the following references;A. Project design drawings and specificationsB. Manufacturer’s instruction manuals applicable to each

particular apparatus.

6. STANDARDS:

The following codes and standards apply,

A. National Electrical Testing Association: NETA B. Institute of Electrical and Electronic Engineers: IEEE.C. SEC Construction Standard TCS-P-105

7. EQUIPMENTS REQUIRED: 1) Megger.2) Transformer Turn Ratio (TTR) test set.3) 3 ph., 380 V AC power supply.4) OMICRON CPC-1005) Current Secondary Injection Unit.6) Digital multimeter, Clamp on Ammeter.

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8. PROCEDURE:

SAFETY PRECAUTIONS:

Always refer to instruction manuals of equipment under test and test equipment used for detailed safety instructions and precautions.

MECHANICAL CHECK AND VISUAL INSPECTION:

1. Check impact recorder records for any abnormal impacts during transit.

2. Check that the as-received transformer tank pressure is positive.

3. Inspect for physical damage/defects and oil leaks.

4. Check nameplate information for correction.

5. Check quality of paintwork, condition of lifting lugs, quality of weld areas and rust spots.

6. Check tightness of all bolted connections (torque wrench method).

7. Check that all grounding is securely connected (including star neutral points).

8. Check that piping to Buchholz relay has proper slope.

9. Check integrity of diaphragm/air bag in the conservator.

10. Check proper operation of all auxiliary devices:

a) Cooling fans/pumpsb) Tap Changerc) Oil level gaugesd) Winding temperature gaugese) Top oil temperature gaugesf) Buchholz relayg) OLTC oil/Gas surge (Pressure) Relayh) Pressure relief devicesi) Push buttons and indicatorsj) Oil sampling port (main tank and OLTC)k) Upper and lower main tank valves

11. Check vertical/horizontal clearances of live parts to adjacent grounded parts to conform to the Standard.



12. Check liquid in the tank, conservator and bushing for proper level.

13. Bleed trapped air in the bushing turrets and tank top.

14. Check that the valves between the tank and the radiators are open.

15. Performs all of the manufacturer’s specific checks.

16. Check HV, LV and TV (if applicable) bushings for damages and completeness of accessories.

17. Check condition (color and quantity) of Silica gel in breathers and oil in bath level.

ELECTRICAL TESTS

1. Core insulation resistance:

2. Winding insulation resistance and polarization index at 5 KV dc: Connect the test circuit as per FIGURE – 1-a or 1-b as applicable. Measure insulation resistance between each winding and ground and between the

windings. Take readings at 30 seconds , 1,5 and 10 minutes then calculate the Polarization Index

as per the following formula :

3. Turns ratio (all taps) : Connect the test circuit as per FIGURE – 2. Measure turns ratio at all taps. Compare the measured ratio with calculated ratio and check the tolerance.

4. Polarity and vector relationship test: Connect the test circuit as per FIGURE – 3. Apply 3 ph., 380 V AC and take the required measurements shown in the test report. Check the voltage relations required for correct polarity as shown in the test report.

5. Winding resistance measurement (at max., min. And nominal tap): Connect the test circuit as per FIGURE – 4-a or 4-b as applicable. Measure the winding resistance for both HV and LV windings at Maximum, Nominal and

Minimum taps as applicable.

6. Insulation power factor and bushing tests:


PI = R 10 min / R 1 min

Site Test Plan For Oil Filled Transformer STP-04-OFT Connect the test circuit as per FIGURE –5-a, 5-b as applicable. Refer to CPC-100 test set instruction manuals for detailed procedure for both windings

and bushings.

7. Winding excitation current test. Connect the test circuit as per FIGURE –6-a, 6-b as applicable if you are using three

wattmeter method , other wise refer to CPC-100 test set instruction manuals for detailed procedure.

8. Calibrate all temperature gauges (OR confirm calibration certificates). Connect the test circuit as per FIGURE –7. Calibrate Oil and Winding temperature gauges and check contact operation and

function.

9. Perform adjustments and tests on the OLTC according to the manufacturer’s instructions.

10. Functional check : Perform function check of the following:

a) Liquid level alarm (OR confirm via FAT record)b) Top oil temperature device: fans (pumps) stop, start, alarm, and tripc) Winding temperature device: fans (pumps) stop, start, alarm, tripd) Buchholz relay: alarm, tripe) Oil/gas surge (pressure) relay: alarm, tripf) Pressure relief device: alarm trip

g) Measure fans/pumps motor currents.

11. Measure fans/pumps motor current.

12. On load tap changer operation checks:Perform adjustments and test on the OLTC according to the manufacturer’s instructions.

a) Raise/lower control (local, remote) and indicationsb) End of tap travel controlc) End of winding travel control (both ends)d) : setting of bandwidth, midpoint, time delay, etc.e) Master/slave – check either transformer as masterf) Master/slave – check out of step blocking alarmg) Parallel operation disturbed – check alarmh) Check that the windings are not open circuited during tap changing



14. Insulating oil tests:

a) Dielectric strength:I) sat d 877 (with 2.5 mm gap) for unprocessed oil & for oil in OLTC.Ii) sat d 1816 (with 1.0 mm gap) for oil in transformer main tank.

b) Neutralization number (sat d 974)c) Interfacial tension (sat d 971)d) Color (sat d 1500)e) Moisture content (sat d 1533a)f) Power factor test (sat d 924)g) Dissolved gas in oil analysis (sat d 3612)

15. Bushing current transformer tests:

A) Polaritya) Insulation resistanceb) Secondary winding resistance (all winding and taps)c) Current ratio (by current injection)d) Magnetization characteristics (minimum of 5 points below and 2 points above the knee points of the magnetization curve)e) Verify secondary circuits, terminal to terminalf) Burden testg) Demagnetize ct cores after all testsh) Ensure that there are no open circuited secondaries

16. Check all external wiring for correctness and tightness.

17. Check each transformer trip device has an individual trip cutout located at the transformer protection panel via ft switches.

18. Check ct terminal block for shorting facilities.

19. Check ct wiring for correctness, tightness and for ring type terminal lugs. (no spade lugs permitted).

20. Adjust AVR to final operational setting according to ESPD'S recommendations.

21. A main tank insulating oil sample for dissolved gas analysis shall be taken immediately prior to first energizing a power transformer and another sample three days after continuous Energization.


Site Test Plan For Oil Filled Transformer STP-04-OFT9. ACCEPTANCE CRITERION :

Check the Test results against applicable standards and/or manufacturer’s instructions.


oil filled transformers standard testing procedure

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