Commissioning Of Transformers And Reactors -arun.pptx
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A.K Goel, Chief Manager(HRD) [email protected] Ph-9599192366
8/22/2018
1
8/22/2018
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Pre-commissioning checks/ tests are the activities carried out to ascertain the correctness, completeness of installation and healthiness of the equipment before its charging. Commissioning TeamResponsibilities of Commissioning team: The responsibilities of the commissioning team are to go through statutory clearances and standing instructions before initial charging of new equipment,. 8/22/2018
3
Witness Pre-Commissioning tests after erection of individual equipment as per requirement of guidelines issued by Corporate Asset Management or in line with manufacturer's recommendation and test charging. Investigate failure of equipment during test charging, declare commencement of trial operation and evaluate guaranteed test results and recommend acceptance as may be provided in the contract. List out deviations/ exception/ incomplete work, for acceptance/ rejection. Proper documentation also to be ensured by the Commissioning team based upon the observations for the above for future reference
8/22/2018
4
Checks after the receipt of transformer/reactor at site Insulating oil Internal inspection Tightness test with vacuum Oil filling and circulation Testing Preliminary checks before charging Checks of auxiliaries and protection
Charging
Post commissioning checks
8/22/2018
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All personals should be apprised of safety procedures Personnel protective equipment Warning signs Safety barriers Fully equipped and functional fire fighting system
8/22/2018
6
Nitrogen pressure or dry air pressure of the main tank Dew point of the nitrogen or dry air inside tank Core insulation test Impact recorder ( to be sent to manufacturer or if software available can be analysed at site) NOTE:- THE ABOVE MENTIONED CHECKS ARE TO BE CARRIED OUT ON THE TRAILER ITSELF BEFORE UNLOADING OF MAIN TANK
8/22/2018
7
Unpacking without damaging Any damaged or missing component to be intimated to the manufacturer Materials repacked and stored if commissioning not immediate Fragile instruments indoor storage eg:- oil level gauge, temperature indicators etc. Packing cases to be placed on suitable supports to allow free flow of air no water logging, easy for inspection and handling/transportation, Proper drainage, no component gets submerged
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Main tank filled with nitrogen or dry air Daily check of pressure If drop in pressure found, dew point to be taken If drop in dew point, fresh nitrogen or dry air has to be filled Leak has to be detected and tightened
8/22/2018
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Filled with processed oil ( BDV > 70KV, moisture content < 5ppm) BDV AND water CONTENT TESTED EVERY THREE MONTHS If value beyond limits, oil filtration done
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Oil in 209L drums or oil tanks Proper record of drums to be maintained To be checked for free moisture and appearance Oil sample to be sent to nearest lab for testing BDV > 50kv, moisture content < 40ppm, resistivity > 150x1012 ohm-cm, tan delta < 0.01 @90 0c Oil tanker- 02 samples 209L oil drums- given table
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Oil drums vertical with lid upwards for 24 hours Clean the area around lid Use glass or brass tube to sample the oil Discard first two samples Suitable receptacle preferably glass bottles cleaned with same oil then final sample taken
8/22/2018
13
PRECAUTIONS WHAT
IS TO BE
DONE
8/22/2018
14
Along with manufacturer’s representative Dry and sunny weather Dry air should be used if main tank filled with nitrogen Avoid any foreign materials Loose materials should be removed from pockets Protective clothing and shoes Tools securely fastened An inventory of all materials taken inside tank to be maintained and checked before closing of inspection cover
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Removal of any shipping blocking or temporary support. Examination for indication of core shifting. Tests for unintentional core or core clamp grounds. Visual inspection of windings, leads, and connections including clamping, bracing, Blocking, spacer alignment, phase barriers, oil boxes, and coil wraps. Checks for dirt, metal particles, moisture, or other foreign material. 8/22/2018
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Minimize exposure of active parts (core+coil) Presence of dry air ( dry air generators or dry air cylinders ) Transformer sealed off after working hours If tank has nitrogen then first vacuum then dry air pushing. For safe breathing. A slight overpressure at night to check any leakage (<30 mbar)
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Check leakage if any leak detecting instruments or soap solution or plastic bags tied around valves Get transformer under oil as soon as possible All fittings and auxiliaries with oil sealing to the tank should be fitted first. Oil filling becomes easy.
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Oil is drained out below the inspection covers Other exposure activities are as below: 1) bushing erections 2) jumper connections of bushings 3) fixing bushing turrets 4) core insulation checking (in case the checking point not accessible outside) 5) buchholz relay pipe work fixing on cover 6) gas release pipes/equalizer pipe fixing 7) entering inside the tank for connections/inspection etc
DEPENDING UPON THE DURATION OF EXPOSURE OIL PROCESSING (DRYING) AND OIL FILLING IS DONE
8/22/2018
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Before oil filling, leakage test is a must. Evacuate transformer from top of tank till pressure < 50mbar. Vacuum stopped. After 1 hour take pressure reading p1 After 30 minutes reading p2 (P2 – P1) x V < 3.6 ; V= VOLUME OF TANK (see rating plate) Take 2 to 3 readings, if ok , then leak test successful, and further vacuum till 1torr done and maintained as per given table. If not , then leak attended OLTC chamber to be vacuumed simultaneously and vacuum released simultaneously 8/22/2018
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After passing leakage test, vacuum maintained in tank for the duration as mentioned below
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Transfer oil from drums to tanks for filtration Filtration done Oil parameter testing :
1. Break down voltage (bdv) : 70kv (min.) 2. Moisture content : 5 ppm (max.) 3. Tan-delta at 90 °c : less than 0.01 4. Interfacial tension : more than 0.035 n/m
Nitrogen filled transformer to be oil filled under vacuum
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Oil filled from bottom valve Oil fill speed in main tank < 5klph Continue oil filling until the level reaches approximately 200 mm above the ambient oil level indicated on the magnetic oil level gauge in the expansion vessel. Then, release the vacuum with dry air of dew point -40 0c or better. Oil filled in OLTC at atmospheric pressure Oil filled in cooler banks without vacuum at atmospheric pressure Care must be taken not to pressurise the cooler bank
8/22/2018
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Upon completion, open the top cooler isolating valve in order to equalize the pressure in the cooler with the transformer tank Before filling oil into the conservator, the air cell/ bellow to be inflated to 0.5 psig i.E.0.035kg/cm2 max. By applying pressure (N2/compressed dry air) so that it can take Breather pipe attachment Filling rate maximum 2klph Oil filled from main tank 8/22/2018
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Oil extracted from bottom valve in main tank and poured in from top valve Oil heated in filter machine till 60 0c. Above 70 0c oil oxidises Circulation done for at least 2 times of tank volume. (At freezing ambient temperature the circulation time is increased, circulate 3 times the volume at temperature down to minus 20 ° c, increase to 4 times below that temperature)
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Break down voltage (BDV) : 70 KV (min.) Moisture content : 5 ppm (max.) Tan-delta at 90 °c : 0.01 (max.) Total gas content : < 1% Resistivity at 90 °c : 6 x 10 ohm-cm (min.) Interfacial tension : 0.035 n/m (min.) *Oxidation stability (test method as per iec 61125 ,method c, test duration: 500 hour for inhibited oil) A) acidity : 0.3 (mg koh /g) (max.) B) sludge : 0.05 % (max.) C) tan delta at 90 °c : 0.05 (max.) * Separate oil sample shall be taken and test results shall be submitted within 45 days after commissioning for approval of POWERGRID.
8/22/2018
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WET TRANSFORMER/REACTOR MEANS THE SOLID INSULATION HAS ABSORBED MOISTURE
If transformer/reactor received without positive pressure If dry air not used during erection activities Overexposure of active part of transformer/ reactor during erection (overexposure when exposure > 12 hrs) 8/22/2018
31
Carefully watched and recorded Fire fighting ready as we deal with heat and inflammable oil All openings of main tank for conservator, cooler banks, OLTC etc shall be isolated and blanked Fill tank with N2 till positive pressure of 0.15 kg/cm2 Keep for 24 hours During this nitrogen circulation, heaters installed around tank till 70-80 0c achieved by the core & winding indicated in OTI. Check dew point.
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If dew point ok then oil filling done else Vacuum done till pressure of 1-5 tor for 48 hrs with less than 40ml/hour condensate If more than 40 ml/hour comes then up to 96 hours After this again nitrogen circulation for 24 hours with heating done, then dew point checked If achieved then ok, IF NOT THEN NITROGEN CYCLE WITH HEATING INCREASED FOR 48 HOURS
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Core insulation test Earth pit resistance measurement Insulation resistance (IR) measurement Capacitance and tan delta measurement of bushings Capacitance and tan delta measurement of windings Turns ratio (voltage ratio)measurement Vector group and polarity Magnetic balance test Floating neutral point measurement
8/22/2018
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Measurement of short circuit impedance Exciting/magnetising current measurement Operational checks on OLTC Tests/check on bushing current transformers (BCTs) Operational check on protection system Stability of differential, REF of transformer/reactor Frequency response analysis measurement (FRA) Winding resistance measurement Dissolved gas analysis (DGA)
8/22/2018
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Done when the transformer/reactor is still on trailer, also done when integrity of core insulation is affected, in charged transformers when DGA indicates ethane, ethylene and methane Disconnect the three terminals from each other ( core clamp, core lamination and ground) Test the insulation between core clamp to ground and core lamination to ground at 1kv ( should be > 10Mohm at 60 seconds ) Connect the three terminals once again (normal condition) 8/22/2018
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An earth tester kit is used Pit earthing connection removed from main grid Measurement by three point method Working of earth tester…… Two spikes at a distance of 25m and 50m are placed in one line There is a dc generator Dc current converted to ac current using rectifier and fed to spike to prevent electrolytic effect due to dc current Earth resistance is displayed which should be less than 1ohm, if not the treatment with salt and charcoal is to be done
8/22/2018
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Tests insulation between winding and tank and between windings (rest of the windings being earthed) Neutral should be disconnected from earth A 5KV Insulation Tester is used
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Two measuring factors, dielectric absorption coefficient or index (DAI) & polarization index (PI) DAI=RATIO OF IR at 60 secs to IR at 15 secs, it should be > 1.3 at 30 0C PI= RATIO OF IR at 600s to IR at 60s, it should be as follows:-
8/22/2018
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Measurement of loss in insulation of bushings Dissipation factor or loss factor (tan delta)= ratio of resistive current to capacitive current Kit used= 10KV or 12 KV fully automated capacitance and tan delta measurement kit C1 measurement in UST mode at 2KV and 10 KV (UST= ungrounded sampling test mode) C2 in GSTg at 1KV (grounded sampling test with guard mode ) Limit is 0.5%
WHAT IS C1 & C2 ?.....
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The combination for C & tan ä measurement of winding is same as that of measurement of IR value.
8/22/2018
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Winding combination for auto transformer.
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Kit used= Automatic Transformer Turns Ratio Meter
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Purpose:- Paralleling of transformers
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Purpose:- Paralleling of transformers
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Purpose:- Detect damage to winding during transportation
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Purpose:- Detect fault in winding
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Purpose:- detect winding movement that usually occurs due to heavy fault current or mechanical damage during transportation or installation since dispatch from the factory.
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Purpose:- It is performed to locate defects in the magnetic core structure, shifting of windings, failure in turn to turn insulation or problem in tap changers Change in reluctance of magnetic circuit thus affecting the current required to establish flux in the core. Done before all DC tests ( DC may cause saturation of winding) Single phase voltage upto 10KV applied on one winding while the rest of the winding are open
8/22/2018
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Purpose:- To assess the mechanical integrity of the transformer which may get disturbed due to transportation shocks. Done after erection and oil filling. Results compared with factory value The FRA signatures should be analyzed in conjunction with Impact Recorder readings
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Purpose:- It is carried out to calculate the I2R losses and to calculate winding temperature at the end of a temperature rise test. It is also done at site to ensure healthiness of a transformer that is to check loose connections, broken strands of conductor, high contact resistance in tap changers, high voltage leads and bushings etc. The winding resistance shall be preferably done when the difference in the top and bottom temperature of the winding (temperature of oil in steadystate condition) is equal to or less than 5 °C.
The winding resistance should preferably be carried out last after completion of all other LV tests, as after this test core gets saturated and tests like magnetizing current, magnetic balance etc. carried out after winding test may be affected and indicate a misleading results, if the core is not de-magnetized before carrying out these tests.
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Measurement done using Automatic Kit
At all taps in forward and reverse direction, resistance measured between HV to IV winding At normal tap between IV-N winding In LV winding between phases All the readings taken converted to reading at 75 0C with formula
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Purpose:- Tap changer functioning properly Manual operation of drive. Tap position in drive and TC should be same. Motor drive push button test. Should get switched off automatically after one switching operation Changeover from 9b to 10 and vice versa requires high torque. Tap changer end position to be checked to see there is no slipping over causing failure Continuity of winding at all taps to be checked. At no point should the voltage should indicate zero With the transformer energised at rated voltage and frequency but on no load, one complete cycle of operation to be taken
8/22/2018
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Continuity of all cores using multi meter Polarity using a 9V battery . Secondary winding resistance tests of individual cores of Bushing CTs using a multi-meter Insulation Resistance Measurement of winding to earth and between winding to winding for all HV, IV and LV turrets Current Ratio test:- Apply 20%, 40% and 80% of rated current on the primary and measure the secondary current. (Permissible limit: Protection core-±3% and Metering core- ±0.5%) 8/22/2018
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Magnetising Curve Performance:- (Not done for metering core) Purpose:- To check that the current transformer is working in the linear region of its magnetising curve. Various values of Knee point voltage (0.25, 0.5,0.75, 1, 1.10) applied to primary and then secondary current measured to see the linear relationship of Voltage and current. It should not saturate even at 1.1 Knee Point voltage
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Breather silica gel is blue in Main Tank, OLTC MOG level ok Marshalling Box and other kiosks OK Valves OK Checks on Cooling System such as (1) Checks on cooling fans-rotation, speed & Control (Manual /temp /load) setting checks (2) Checks on Cooling pumps- rotation, vibration/noise, oil flow direction OTI&WTI check, calibration, cooler control, alarm, trip settings Check on gas actuated relays such as PRD, Buchholz relay, Oil Surge Relay Contact Resistance Measurement of Terminal connectors Checks on Transformer/ Reactor protection (differential, REF, Over-current & stability tests etc.)
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Purpose:- To detect faults within the Transformer/Reactor
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Two ways to conduct: (1) through Primary test Tap (M point) if available (2) using actual earthing if M point not available Through Primary Test Tap Measure the spill current in REF relay which should be nearly zero. Switch off Current Injection. Reverse the polarity of R phase Bushing CT and again start Current Injection. Appreciable spill current will appear in REF relay. Repeat the same procedure for Y and B phases and note down the results. This test has to be performed from both HV side & LV side w.r.t. Neutral. Testing of Reactor will be done similarly 8/22/2018
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Primary test tap not available Apply 440V three phase voltage at three phase bushing of H.V. side with the help of three phase variac. Earth the R phase of the LV side (through isolator earth switch or discharge rod). Measure the spill voltage (in mV)/ spill current (in mA) at REF relay which should be nearly zero. Reverse the polarity of R phase Bushing CT and again switch on 440V supply. Appreciable spill voltage/ current will appear in REF relay. Repeat the same procedure for Y and B phases and note down the results in formats.
. Testing of Reactor will be done similarly 8/22/2018
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Release air at the high points, like oil communicating bushings, buchholz petcock, tank cover and the cooling devices including headers, radiators, pumps, expansion joints etc. of the transformer. Air release should be resorted from low points to high points. Check tightness Check that the valves are in the correct position Silica gel in breather is blue and oil cup is fill with oil CC, CL properly grounded Check oil level in main tank and OLTC conservators, bushings Connection of terminal connectors Bushing CT terminal properly shorted and earthed Neutral bushing earthed Tan delta test taps earthed 8/22/2018
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Tap position should be same at control cubicle and the tap head Step by step operation- local and remote electrical operation as well as manual operation and parallel operation, if any Electric and mechanical limit switches and protective relays Oil parameter results should conform to the limits mentioned Check OTI and WTI settings Ensure oil in thermometer pockets as well as OTI and WTI pockets Installation of buchholz relay, Oil surge relay, PRD Check Insulation resistance of auxiliary circuit at 2KV Check the earthing of main tank and cooler banks at two different places Measure the supply of the auxiliary circuits Check the direction of installation of oil pumps Check the direction of rotation of the pumps and fans Check the working of the oil flow indicators Check the setting of the thermal overload relays, heating and lighting of cubicles Check the protection of the Transformer/reactor
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Thermo-vision Scanning:- To be done after 24 hours of charging to detect any hot spots and then after a week. Oil sample to be sent after 24 hours of charging for DGA testing Online Moisture measurement Vibration measurement of reactors :-Movement of the core-coil assembly and shielding structure caused by the time –varying magnetic forces results in vibration of the tank and ancillary equipment. These vibrations have detrimental effects such as excessive stress on the corecoil assembly
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Just before charging, an oil sample has to be taken for DGA, BDV, and moisture measurement The equipment charged from incoming side whether 400 or 220 KV on no load Initial Magnetising current is very high depending upon the moment of cycle Transformer should be kept on no load for 12 hours During this time, vibrations, abnormal cracking noise, etc. are to be observed After that it may be checked for gas collection. After successful charging, performance of transformer / rector should be checked under loading; OTI/WTI readings should be monitored for 24 hours and ensured that they are as per loading. DGA samples may be sent as per Standard practice (after 24 hrs of energizing, one week, 15 days, one month and three months after charging, thereafter as per normal frequency of 6 months ). 8/22/2018
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Pre-commissioning checks/ tests are the activities carried out to ascertain the correctness, completeness of installation and healthiness of the equipment before its charging. Commissioning TeamResponsibilities of Commissioning team: The responsibilities of the commissioning team are to go through statutory clearances and standing instructions before initial charging of new equipment,. 8/22/2018
3
Witness Pre-Commissioning tests after erection of individual equipment as per requirement of guidelines issued by Corporate Asset Management or in line with manufacturer's recommendation and test charging. Investigate failure of equipment during test charging, declare commencement of trial operation and evaluate guaranteed test results and recommend acceptance as may be provided in the contract. List out deviations/ exception/ incomplete work, for acceptance/ rejection. Proper documentation also to be ensured by the Commissioning team based upon the observations for the above for future reference
8/22/2018
4
Checks after the receipt of transformer/reactor at site Insulating oil Internal inspection Tightness test with vacuum Oil filling and circulation Testing Preliminary checks before charging Checks of auxiliaries and protection
Charging
Post commissioning checks
8/22/2018
5
All personals should be apprised of safety procedures Personnel protective equipment Warning signs Safety barriers Fully equipped and functional fire fighting system
8/22/2018
6
Nitrogen pressure or dry air pressure of the main tank Dew point of the nitrogen or dry air inside tank Core insulation test Impact recorder ( to be sent to manufacturer or if software available can be analysed at site) NOTE:- THE ABOVE MENTIONED CHECKS ARE TO BE CARRIED OUT ON THE TRAILER ITSELF BEFORE UNLOADING OF MAIN TANK
8/22/2018
7
Unpacking without damaging Any damaged or missing component to be intimated to the manufacturer Materials repacked and stored if commissioning not immediate Fragile instruments indoor storage eg:- oil level gauge, temperature indicators etc. Packing cases to be placed on suitable supports to allow free flow of air no water logging, easy for inspection and handling/transportation, Proper drainage, no component gets submerged
8/22/2018
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Main tank filled with nitrogen or dry air Daily check of pressure If drop in pressure found, dew point to be taken If drop in dew point, fresh nitrogen or dry air has to be filled Leak has to be detected and tightened
8/22/2018
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Filled with processed oil ( BDV > 70KV, moisture content < 5ppm) BDV AND water CONTENT TESTED EVERY THREE MONTHS If value beyond limits, oil filtration done
8/22/2018
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Oil in 209L drums or oil tanks Proper record of drums to be maintained To be checked for free moisture and appearance Oil sample to be sent to nearest lab for testing BDV > 50kv, moisture content < 40ppm, resistivity > 150x1012 ohm-cm, tan delta < 0.01 @90 0c Oil tanker- 02 samples 209L oil drums- given table
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Oil drums vertical with lid upwards for 24 hours Clean the area around lid Use glass or brass tube to sample the oil Discard first two samples Suitable receptacle preferably glass bottles cleaned with same oil then final sample taken
8/22/2018
13
PRECAUTIONS WHAT
IS TO BE
DONE
8/22/2018
14
Along with manufacturer’s representative Dry and sunny weather Dry air should be used if main tank filled with nitrogen Avoid any foreign materials Loose materials should be removed from pockets Protective clothing and shoes Tools securely fastened An inventory of all materials taken inside tank to be maintained and checked before closing of inspection cover
8/22/2018
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Removal of any shipping blocking or temporary support. Examination for indication of core shifting. Tests for unintentional core or core clamp grounds. Visual inspection of windings, leads, and connections including clamping, bracing, Blocking, spacer alignment, phase barriers, oil boxes, and coil wraps. Checks for dirt, metal particles, moisture, or other foreign material. 8/22/2018
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Minimize exposure of active parts (core+coil) Presence of dry air ( dry air generators or dry air cylinders ) Transformer sealed off after working hours If tank has nitrogen then first vacuum then dry air pushing. For safe breathing. A slight overpressure at night to check any leakage (<30 mbar)
8/22/2018
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Check leakage if any leak detecting instruments or soap solution or plastic bags tied around valves Get transformer under oil as soon as possible All fittings and auxiliaries with oil sealing to the tank should be fitted first. Oil filling becomes easy.
8/22/2018
22
Oil is drained out below the inspection covers Other exposure activities are as below: 1) bushing erections 2) jumper connections of bushings 3) fixing bushing turrets 4) core insulation checking (in case the checking point not accessible outside) 5) buchholz relay pipe work fixing on cover 6) gas release pipes/equalizer pipe fixing 7) entering inside the tank for connections/inspection etc
DEPENDING UPON THE DURATION OF EXPOSURE OIL PROCESSING (DRYING) AND OIL FILLING IS DONE
8/22/2018
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Before oil filling, leakage test is a must. Evacuate transformer from top of tank till pressure < 50mbar. Vacuum stopped. After 1 hour take pressure reading p1 After 30 minutes reading p2 (P2 – P1) x V < 3.6 ; V= VOLUME OF TANK (see rating plate) Take 2 to 3 readings, if ok , then leak test successful, and further vacuum till 1torr done and maintained as per given table. If not , then leak attended OLTC chamber to be vacuumed simultaneously and vacuum released simultaneously 8/22/2018
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After passing leakage test, vacuum maintained in tank for the duration as mentioned below
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Transfer oil from drums to tanks for filtration Filtration done Oil parameter testing :
1. Break down voltage (bdv) : 70kv (min.) 2. Moisture content : 5 ppm (max.) 3. Tan-delta at 90 °c : less than 0.01 4. Interfacial tension : more than 0.035 n/m
Nitrogen filled transformer to be oil filled under vacuum
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Oil filled from bottom valve Oil fill speed in main tank < 5klph Continue oil filling until the level reaches approximately 200 mm above the ambient oil level indicated on the magnetic oil level gauge in the expansion vessel. Then, release the vacuum with dry air of dew point -40 0c or better. Oil filled in OLTC at atmospheric pressure Oil filled in cooler banks without vacuum at atmospheric pressure Care must be taken not to pressurise the cooler bank
8/22/2018
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Upon completion, open the top cooler isolating valve in order to equalize the pressure in the cooler with the transformer tank Before filling oil into the conservator, the air cell/ bellow to be inflated to 0.5 psig i.E.0.035kg/cm2 max. By applying pressure (N2/compressed dry air) so that it can take Breather pipe attachment Filling rate maximum 2klph Oil filled from main tank 8/22/2018
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Oil extracted from bottom valve in main tank and poured in from top valve Oil heated in filter machine till 60 0c. Above 70 0c oil oxidises Circulation done for at least 2 times of tank volume. (At freezing ambient temperature the circulation time is increased, circulate 3 times the volume at temperature down to minus 20 ° c, increase to 4 times below that temperature)
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Break down voltage (BDV) : 70 KV (min.) Moisture content : 5 ppm (max.) Tan-delta at 90 °c : 0.01 (max.) Total gas content : < 1% Resistivity at 90 °c : 6 x 10 ohm-cm (min.) Interfacial tension : 0.035 n/m (min.) *Oxidation stability (test method as per iec 61125 ,method c, test duration: 500 hour for inhibited oil) A) acidity : 0.3 (mg koh /g) (max.) B) sludge : 0.05 % (max.) C) tan delta at 90 °c : 0.05 (max.) * Separate oil sample shall be taken and test results shall be submitted within 45 days after commissioning for approval of POWERGRID.
8/22/2018
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WET TRANSFORMER/REACTOR MEANS THE SOLID INSULATION HAS ABSORBED MOISTURE
If transformer/reactor received without positive pressure If dry air not used during erection activities Overexposure of active part of transformer/ reactor during erection (overexposure when exposure > 12 hrs) 8/22/2018
31
Carefully watched and recorded Fire fighting ready as we deal with heat and inflammable oil All openings of main tank for conservator, cooler banks, OLTC etc shall be isolated and blanked Fill tank with N2 till positive pressure of 0.15 kg/cm2 Keep for 24 hours During this nitrogen circulation, heaters installed around tank till 70-80 0c achieved by the core & winding indicated in OTI. Check dew point.
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If dew point ok then oil filling done else Vacuum done till pressure of 1-5 tor for 48 hrs with less than 40ml/hour condensate If more than 40 ml/hour comes then up to 96 hours After this again nitrogen circulation for 24 hours with heating done, then dew point checked If achieved then ok, IF NOT THEN NITROGEN CYCLE WITH HEATING INCREASED FOR 48 HOURS
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Core insulation test Earth pit resistance measurement Insulation resistance (IR) measurement Capacitance and tan delta measurement of bushings Capacitance and tan delta measurement of windings Turns ratio (voltage ratio)measurement Vector group and polarity Magnetic balance test Floating neutral point measurement
8/22/2018
35
Measurement of short circuit impedance Exciting/magnetising current measurement Operational checks on OLTC Tests/check on bushing current transformers (BCTs) Operational check on protection system Stability of differential, REF of transformer/reactor Frequency response analysis measurement (FRA) Winding resistance measurement Dissolved gas analysis (DGA)
8/22/2018
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Done when the transformer/reactor is still on trailer, also done when integrity of core insulation is affected, in charged transformers when DGA indicates ethane, ethylene and methane Disconnect the three terminals from each other ( core clamp, core lamination and ground) Test the insulation between core clamp to ground and core lamination to ground at 1kv ( should be > 10Mohm at 60 seconds ) Connect the three terminals once again (normal condition) 8/22/2018
37
An earth tester kit is used Pit earthing connection removed from main grid Measurement by three point method Working of earth tester…… Two spikes at a distance of 25m and 50m are placed in one line There is a dc generator Dc current converted to ac current using rectifier and fed to spike to prevent electrolytic effect due to dc current Earth resistance is displayed which should be less than 1ohm, if not the treatment with salt and charcoal is to be done
8/22/2018
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Tests insulation between winding and tank and between windings (rest of the windings being earthed) Neutral should be disconnected from earth A 5KV Insulation Tester is used
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Two measuring factors, dielectric absorption coefficient or index (DAI) & polarization index (PI) DAI=RATIO OF IR at 60 secs to IR at 15 secs, it should be > 1.3 at 30 0C PI= RATIO OF IR at 600s to IR at 60s, it should be as follows:-
8/22/2018
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Measurement of loss in insulation of bushings Dissipation factor or loss factor (tan delta)= ratio of resistive current to capacitive current Kit used= 10KV or 12 KV fully automated capacitance and tan delta measurement kit C1 measurement in UST mode at 2KV and 10 KV (UST= ungrounded sampling test mode) C2 in GSTg at 1KV (grounded sampling test with guard mode ) Limit is 0.5%
WHAT IS C1 & C2 ?.....
8/22/2018
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The combination for C & tan ä measurement of winding is same as that of measurement of IR value.
8/22/2018
43
Winding combination for auto transformer.
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Kit used= Automatic Transformer Turns Ratio Meter
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Purpose:- Paralleling of transformers
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Purpose:- Paralleling of transformers
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Purpose:- Detect damage to winding during transportation
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Purpose:- Detect fault in winding
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Purpose:- detect winding movement that usually occurs due to heavy fault current or mechanical damage during transportation or installation since dispatch from the factory.
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Purpose:- It is performed to locate defects in the magnetic core structure, shifting of windings, failure in turn to turn insulation or problem in tap changers Change in reluctance of magnetic circuit thus affecting the current required to establish flux in the core. Done before all DC tests ( DC may cause saturation of winding) Single phase voltage upto 10KV applied on one winding while the rest of the winding are open
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Purpose:- To assess the mechanical integrity of the transformer which may get disturbed due to transportation shocks. Done after erection and oil filling. Results compared with factory value The FRA signatures should be analyzed in conjunction with Impact Recorder readings
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Purpose:- It is carried out to calculate the I2R losses and to calculate winding temperature at the end of a temperature rise test. It is also done at site to ensure healthiness of a transformer that is to check loose connections, broken strands of conductor, high contact resistance in tap changers, high voltage leads and bushings etc. The winding resistance shall be preferably done when the difference in the top and bottom temperature of the winding (temperature of oil in steadystate condition) is equal to or less than 5 °C.
The winding resistance should preferably be carried out last after completion of all other LV tests, as after this test core gets saturated and tests like magnetizing current, magnetic balance etc. carried out after winding test may be affected and indicate a misleading results, if the core is not de-magnetized before carrying out these tests.
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Measurement done using Automatic Kit
At all taps in forward and reverse direction, resistance measured between HV to IV winding At normal tap between IV-N winding In LV winding between phases All the readings taken converted to reading at 75 0C with formula
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Purpose:- Tap changer functioning properly Manual operation of drive. Tap position in drive and TC should be same. Motor drive push button test. Should get switched off automatically after one switching operation Changeover from 9b to 10 and vice versa requires high torque. Tap changer end position to be checked to see there is no slipping over causing failure Continuity of winding at all taps to be checked. At no point should the voltage should indicate zero With the transformer energised at rated voltage and frequency but on no load, one complete cycle of operation to be taken
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Continuity of all cores using multi meter Polarity using a 9V battery . Secondary winding resistance tests of individual cores of Bushing CTs using a multi-meter Insulation Resistance Measurement of winding to earth and between winding to winding for all HV, IV and LV turrets Current Ratio test:- Apply 20%, 40% and 80% of rated current on the primary and measure the secondary current. (Permissible limit: Protection core-±3% and Metering core- ±0.5%) 8/22/2018
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Magnetising Curve Performance:- (Not done for metering core) Purpose:- To check that the current transformer is working in the linear region of its magnetising curve. Various values of Knee point voltage (0.25, 0.5,0.75, 1, 1.10) applied to primary and then secondary current measured to see the linear relationship of Voltage and current. It should not saturate even at 1.1 Knee Point voltage
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Breather silica gel is blue in Main Tank, OLTC MOG level ok Marshalling Box and other kiosks OK Valves OK Checks on Cooling System such as (1) Checks on cooling fans-rotation, speed & Control (Manual /temp /load) setting checks (2) Checks on Cooling pumps- rotation, vibration/noise, oil flow direction OTI&WTI check, calibration, cooler control, alarm, trip settings Check on gas actuated relays such as PRD, Buchholz relay, Oil Surge Relay Contact Resistance Measurement of Terminal connectors Checks on Transformer/ Reactor protection (differential, REF, Over-current & stability tests etc.)
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Purpose:- To detect faults within the Transformer/Reactor
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Two ways to conduct: (1) through Primary test Tap (M point) if available (2) using actual earthing if M point not available Through Primary Test Tap Measure the spill current in REF relay which should be nearly zero. Switch off Current Injection. Reverse the polarity of R phase Bushing CT and again start Current Injection. Appreciable spill current will appear in REF relay. Repeat the same procedure for Y and B phases and note down the results. This test has to be performed from both HV side & LV side w.r.t. Neutral. Testing of Reactor will be done similarly 8/22/2018
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Primary test tap not available Apply 440V three phase voltage at three phase bushing of H.V. side with the help of three phase variac. Earth the R phase of the LV side (through isolator earth switch or discharge rod). Measure the spill voltage (in mV)/ spill current (in mA) at REF relay which should be nearly zero. Reverse the polarity of R phase Bushing CT and again switch on 440V supply. Appreciable spill voltage/ current will appear in REF relay. Repeat the same procedure for Y and B phases and note down the results in formats.
. Testing of Reactor will be done similarly 8/22/2018
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Release air at the high points, like oil communicating bushings, buchholz petcock, tank cover and the cooling devices including headers, radiators, pumps, expansion joints etc. of the transformer. Air release should be resorted from low points to high points. Check tightness Check that the valves are in the correct position Silica gel in breather is blue and oil cup is fill with oil CC, CL properly grounded Check oil level in main tank and OLTC conservators, bushings Connection of terminal connectors Bushing CT terminal properly shorted and earthed Neutral bushing earthed Tan delta test taps earthed 8/22/2018
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Tap position should be same at control cubicle and the tap head Step by step operation- local and remote electrical operation as well as manual operation and parallel operation, if any Electric and mechanical limit switches and protective relays Oil parameter results should conform to the limits mentioned Check OTI and WTI settings Ensure oil in thermometer pockets as well as OTI and WTI pockets Installation of buchholz relay, Oil surge relay, PRD Check Insulation resistance of auxiliary circuit at 2KV Check the earthing of main tank and cooler banks at two different places Measure the supply of the auxiliary circuits Check the direction of installation of oil pumps Check the direction of rotation of the pumps and fans Check the working of the oil flow indicators Check the setting of the thermal overload relays, heating and lighting of cubicles Check the protection of the Transformer/reactor
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Thermo-vision Scanning:- To be done after 24 hours of charging to detect any hot spots and then after a week. Oil sample to be sent after 24 hours of charging for DGA testing Online Moisture measurement Vibration measurement of reactors :-Movement of the core-coil assembly and shielding structure caused by the time –varying magnetic forces results in vibration of the tank and ancillary equipment. These vibrations have detrimental effects such as excessive stress on the corecoil assembly
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Just before charging, an oil sample has to be taken for DGA, BDV, and moisture measurement The equipment charged from incoming side whether 400 or 220 KV on no load Initial Magnetising current is very high depending upon the moment of cycle Transformer should be kept on no load for 12 hours During this time, vibrations, abnormal cracking noise, etc. are to be observed After that it may be checked for gas collection. After successful charging, performance of transformer / rector should be checked under loading; OTI/WTI readings should be monitored for 24 hours and ensured that they are as per loading. DGA samples may be sent as per Standard practice (after 24 hrs of energizing, one week, 15 days, one month and three months after charging, thereafter as per normal frequency of 6 months ). 8/22/2018
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