Maintenance Procedure for Switchyard Equipment Volume-II (EH

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GENERAL INSTRUCTIONS FOR MAINTENANCE OF SWITCHYARDEQUIPMENTS

1.0 PurposeThe equipments shall be inspected at regular intervals in line with general guidelinesalready circulated vide document no: D-4-02-XX-01-04, Rev. 04 or manufacturersrecommendations for such equipments for which guidelines have not been circulatedby CC/OS so far.

2.0 General checks/maintenance instructionsi) External cleaning

The insulators of the Breaker / CT / CVT / Isolator shall be cleaned from salt and dirt/dust deposition together with the cleaning of the other insulators in the substation. Thetime interval for this cleaning shall be based on the polluting atmosphere or the periodicitymentioned in document No. D-4-02 XX-01-04 (whichever is earlier).

ii) Rust ProtectionSome parts of the mechanism in the operating mechanism are made of steel and aresurface treated against rust. In spite of the good rust protection, minor corrosion willoccur after some years, especially when the breaker / isolator is standing in strongcorrosive surroundings. The rust stains shall be sand papered away and new rustprotection shall be painted or sprayed on. As rust protection, grease G or Tectyl 506is recommended.

iii) Tightness checkThe breakers are provided with density monitor switches (temperature compensatedpressure gauges). Every density monitor switch, is provided with an alarm contact whichgives an electrical signal if abnormal leakage takes place. All the bolted joints on thebreaker and operating mechanism shall be tightened up. All the wiring joints in theterminal blocks of the operating mechanism shall be re-tightened at regular interval asper doc.no. D-4-02-XX-01-04. SF6 gas leakage is to be detected using suitable gasleak detector as shown in the figure given below:

SF6 gas leak detector

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iv) LubricationFor lubrication, the lubricants recommended as given below shall primarily be used.The bearings of the breaker and operating mechanism of isolator and breaker are to belubricated with grease G

v) Treatment of gaskets and sealing surfacesWhenever any gasketted part is opened, all the gaskets shall always be replaced bynew ones.

General Sealing surfaces and O-rings shall be sparsely greased to accomplish a better

sealing against this surface and at the same time protecting it against corrosion. Material for de-greasing and cleaning : Tricloroethane. Material for greasing of O-ring : Grease - G Material for greasing of O-ring and : Grease - G

nitrate rubber in moving sealings Material for removal of contact glue : Acetone Material for rust protection of : valvoline Tectyl 506

untreated or phosphatised steelvi) Treatment of contact surfaces

The contacts of breaker / isolator / ground switch shall be treated according tothe following directions.Silvered contact surfaces : Silvered contact surfaces shall be cleaned, if necessary,with a soft cloth and solvent (trichloroethane). Steel brushing or grinding is not allowed.Copper surfaces : Copper surfaces shall be clean and oxide free. If necessary, theyshall be cleaned with cloth and solvent (Trichloro - ethane) or steel brushing - After steelbrushing, the surface shall always be cleaned from loose particles and dust.Aluminium surfaces : Aluminium contact surfaces shall be cleaned with steel brush oremery cloth. Directly afterwards the surface is thoroughly cleaned from particles anddust with a dry cloth. After this, a thin layer of Vaseline is applied. This shall be donewithin 5 min. after the cleaning. The joint shall be assembled within 15 minutes.Moving contact surfacesSilvered : Cleaned if necessary, with soft cloth and solvent (tri-chloro ethane). No steelbrushing.Lubrication : Lubricant - Grease K is applied in a very thin layer on the surfaces of themale contact and the puffer cylinder. The superfluous grease is carefully removed.

vii) Emptying and re-filling of gasThe breaker is evacuated by means of the gas treatment equipment that purifies andcompresses the gas, so that it can be re-used. For economic and ecological reasons,

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SF6 contained in electrical equipments, should not be vented into atmosphere. Prior tothe gas removal, the quality of the SF6 gas should be verified. The gas from theEquipments is temporarily stored in a suitable vessel having following features: Material of vessel/container should be such that it resists the potentially corrosive

effects of SF6 decomposition products. Oil free Gas storage in liquid or gaseous phase Removal of gas from CB upto 50 mbar Transportable and easy to handleOperational contamination should be absorbed with suitable filter unit provided in thegas handling plant. Such filters/sieves should already be installed into the SF6 gasmaintenance/handling unit. Filters must meet the following requirements: Transportable and easy to handle Dust particles must safely be filtered Molecular filters remove humidity and SF6 decomposition products Desiccative in easily exchangeable cartridges for safe and trouble free disposal Inputs and outputs should be equipped with self-closing couplings in order to avoid

a saturation of the desiccative by ambient air.

Block diagram of SF6 gas handling plant

When SF6 is suctioned from a gas compartment, the gas is passed automatically throughfilters which dry and purify the gas.Filling of re-generated SF6 gas in the equipmentService devices have to be used to enable the maintenance personnel to fill regeneratedSF6 from the storage tanks in SF6-switchgears. The following criterions, should begranted by such a device: Gas tightness Oil free

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Filling pressure which can be pre- set by pressure reducer Easy handling and mobilityEvacuation of SF6 gas Circuit BreakersAfter maintenance/overhaul of the Circuit Breaker, it should be evacuated by vacuumpump before filling in the SF6 gas so that SF6 gas does not mix with ambient air andalso humidity and dust particles are removed from the Breaker. With vacuum pump, afinal vacuum must be reached less than 5 mbar.

3.0 Tools for General Maintenance:The tools required for general maintenance as well as overhauling of breaker / isolator /ground switch etc. as follows :

I. Tools: A normal tool kit with torque wrenches (10-300 Nm). Lifting equipment and slings. Special tools as prescribed in the overhaul instructions of the breaker.

II. Gas treatment equipment for evacuating, cleaning, compression and storage of usedSF6 gas together with instruments for pressure and vacuum monitoing. TAN & ANDCAPACITANCE MEASUREMENT

Gas Handling Plant

4.0 Safety Reference

Refer the POWERGRID Safety Instruction 02 (PSI-02) DEMARCATION OF WORKAND TESTING AREAS IN SUBSTATION.Testing shall be carried out during Shut down period and all testing which requireremoval of earth switch, shall be done under SFT (Sanction for Test).

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1. TEST NAMECapacitance and Tan delta measurement for: Current Transformers (CTs) CB Voltage Grading Capacitors Capacitive Voltage Transformers (CVTs)

2. PURPOSETo measure dissipation factor/loss factor (Tan delta) and Capacitance measurement ofEHV class CTs, CVTs and Voltage Grading Capacitors by applying test voltages upto10kV. The purpose of the dissipation factor measurement of high voltage insulation is todetect incipient weaknesses in HV insulation.The most important benefit to be gained from this measurement is to obtain a bench-mark reference reading on costly and high voltage equipment when the equipment isnew and insulation is clean, dry and free from impurities. Later readings taken duringservice can be compared with the benchmark reference.

3. DEFINITIONDissipation FactorDissipation factor/loss factor (Tan delta)is defined as the ratio of resistive component(Ir)of current to that of capacitive current (Ic) flowing in an insulating material.Power FactorPower factor is the ratio of resistive current to that of totalcurrent. For very low value of resistive currents, values ofdissipation factor and power factor are same (upto 2%).Tan delta = Ir / IcCapacitance C = A/ d, where = permittivity, A = Areaand d = distance between Capacitance electrode/terminalsHigh Voltage TerminalThe terminal to be connected to the power line.USTTest set connected for Ungrounded Specimen Test mode. This is used when specimenis isolated from earth e.g. Transformer bushing, CTs with test tap, CVTs and CB voltagegrading capacitors. The test mode is often used to reduce the effect of stray capacitancelosses to ground, and to reduce the effect of interference pickup from energizedapparatus.

TAN DELTA CAPACITANCE MEASUREMENT

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GSTTest set connected for grounded specimen test mode. This is used when specimen donot have two specific points (isolated from ground) for Tan delta measurement e.g. Trans-former/Reactor winding, CTs without test tap etc.GSTgThis test is used to separate the total values of a GST test into separate parts for betteranalysis. Often this test is used with GST test to confirm the test readings made usingthe UST mode.

4. ABBREVIATIONSSFT : SANCTION FOR TESTPTW : PERMIT TO WORKEHV : EXTRA HIGH VOLTAGEHF TERMINAL : HIGH FREQUENCY TERMINALAC : ALTERNATING CURRENTUST : UNGROUNDED SPECIMEN TEST MODEGST : GROUNDED SPECIMEN TEST MODEPSI : POWERGRID SAFETY INSTRUCTION

5. TESTING SCHEDULE AND FREQUENCYAs per Maintenance Schedule Doc. No: D-4-02-XX-01-04.

6. TEST EQUIPMENT10 kV Capacitance and Tan Delta test set having normal and reverse mode of operationas well as Interference Suppression Units.

7. ISOLATION REQUIREDCTsa) Open jumper from HV terminal of CT (not provided with test tap) and line CTs.b) Test tap of CT should be disconnected from ground.Circuit Breakersc) CB should be in open condition with isolators on both the sides should also be inopen condition.CVTsd) Open jumper from HV terminal of line/bus CVTs.e) Remove earth connection/earth from neutral point/bushing of EMU tank.

8. SAFETY INSTRUCTIONSAs per PSI No.03 of Safety Rule Hand Book of POWERGRID.

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9. PRECAUTIONSa) Ensure that SFT/PTW is taken as per norms.b) There should be no joints in testing cables.c) HV lead should be double shielded / screened. Both the shields should not get

shorted otherwise tests in GST/GSTg modes, shall not be possible. Check thesame by Insulation Tester(100V)

d) Test leads should not touch any live part.e) Never connect the test set to energised equipmentf) The ground cable must be connected first and removed at lastg) High voltage plugs should be free from moisture during installation and operation.h) It should be ensured that whole testing equipment alongwith Operation Manual of the

kit testing procedures are available at testing site. Testing must be carried out inpresence of testing personnel only.

i) After testing with high voltage (10 kV), test terminals must be grounded before beingtouched by any personnel.

Note:Before carrying out the measurement, the insulator petticoats of CTs/CVTs/GradingCapacitor should be cleaned from moisture, sand, dust particles or salt deposition etc.otherwise measured values shall not be accurate.Test tap of CTs/ Earth connection of CVTs should be re-connected to ground after thetest.

10. MAINTENANCE/TESTING PROCEDURE:Typical arrangement for Tan delta measurement is given below:

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A) CURRENT TRANSFORMERSa) CTs with test taps:1. Tan delta tap should be disconnected from ground.2. High voltage lead from tan delta kit should be connected to primary(HV) Terminal and

LV lead should be connected to the Tan delta test tap.3. Before applying HV, interference is to be nullified using Interference suppression unit

(ISU).4. Measurements have to be taken in UST Mode.5. Standard procedure(as specified by kit supplier) for measuring Capacitance and Tan

delta in charged switchyard/induced voltage conditions should be followed for measure-ment of Capacitance and Tan delta values.

6. Measurement to be carried out at 2kV and then at 10kV.7. Carry out the measurements in main and reverse mode/polarity and then compute the

average value.b) CTs without test tap:1. Jumpers are to be opened before carrying out measurements.2. High voltage lead from tan delta kit should be connected to primary (HV) Terminal and

LV lead should be connected to the CT tank/ground/earth.3. Before applying HV, interferrence is to be nullified using Interferrence suppression

unit(ISU).4. Measurements have to be taken in GST Mode.5. Standard procedure (as specified by kit supplier) for measuring capacitance and tan

delta in charged switchyard/ induced voltage conditions should be followed.6. Measurement to be carried out at 2kV and then at 10kV.7. Carry out the measurements in main and reverse mode/polarity and then compute the

average value.B) CB VOLTAGE GRADING CAPACITOR1. Connect LV cable to the middle of the double interrupter.2. Connect HV cable to the other end of the Grading capacitor to be tested.3. The opposite end of the grading capacitor has to be grounded using earth switch.4. Before applying HV, interference is to be nullified using Interference suppression unit

(ISU).5. Measurements have to be taken in UST Mode only6. Disconnect the HV cable and connect the same to the other grading capacitor and ground

the previous grading capacitor. Now the second grading capacitor is ready for testing.7. Standard procedure (as specified by kit supplier) for measuring capacitance and tan

delta in charged switchyard/induced voltage conditions should be followed.8. Measurements are to be carried out at 10 kV.

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9. Carry out the measurements in main and reverse mode/polarity and then compute theaverage value.

C) CAPACITOR VOLTAGE TRANSFORMES1. Testing Procedure for Top and Middle Stacks:

(a) Apply 10 kV between flanges of Top/Middle stacks (whichever is being tested).(b) Carry out measurements in UST mode at 10,0 kV.

2. Testing Procedure for Bottom Stack connected to EMU PT.(a) Connect HV of the test kit at the top flange of bottom stack and LV of the test kit to

the EMU Tank/Ground. HF point to be grounded. Earth connection of neutral of thePT to be opened/isolated from ground.

(b) Top of CVT to be guarded.(c) Carry out measurements in GSTg mode at 10.0 kV.(d) Repeat the Test with neutral of PT connected to ground.(e) In case Tan delta value is negative or irratic, only capacitance values are to be

monitored.3. Standard procedure (as specified by kit supplier) for measuring capacitance and tan

delta in charged switchyard/ induced voltage conditions should be followed.4. Carry out the measurements in main and reverse mode/polarity and then compute the

average value.11. EVALUATION OF TEST RESULTS(A) Factors affecting the Measurement

Significance of TemperatureInsulation measurements have to be interpreted based on the temperature of thespecimen. The dielectric losses of most insulation increases with temperature. A rise intemperature causes a rise in dielectric loss which in turn causes a further rise intemperature etc.The change in Tan delta value w.r.t. temperature depends on moisture content in paperinsulation. The moisture content in insulation depends on moisture entry and also ageingpattern of the Equipment. Hence, rate of change of Tan delta w.r.t. temperature even fora particular make / type shall be different. Hence, no standardized temperature correctionfactors can be used for practical purpose.Significance of HumidityThe exposed surface of the CT/CVT Insulators bushings may under adverse humidityconditions, acquire a deposit of surface moisture which can have a significant effect onsurface losses and consequently on the results. Dielectric strength of insulation decreaseswith increase in moisture content. Surface leakage errors can be minimized if dissipa-

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tion factor measurements are made under conditions where the weather is clear andsunny and where the relative humidity does not exceed 80%.Surface LeakageAny leakage over the insulation surfaces of the specimen will be added to the losses inthe insulation and may give false impression of the condition of the test specimen. Sur-faces of insulators should be clean and dry when making a measurement. CTs providedwith power factor test tap, the effect of leakage current over the surface of porcelainbushings may be eliminated by measuring in UST mode.Electrostatic InterferenceWhen tests are conducted in energised Substations, the readings may be influenced byelectrostatic interference currents resulting from the capacitive coupling betweenenergised lines and the specimen. Jumpers connected need to be opened while carry-ing out the measurement in GST and GSTg modes to avoid effect of high interference. InEHV Substation, the effect of electrostatic interference currents can also be cancelledby using the interference suppression circuit. Measurements are to be taken in Normaland Reverse polarity to cancel any residual interference currents.Negative Tan deltaIn isolated case, negative tan delta are recorded in measurement of dielectric specimenof low capacitance. This condition most likely arises when making UST and GSTg mea-surements on specimen which have capacitance of a few hundred Pico-farads such asbushings, Circuit breaker grading capacitors. Sometimes Tan delta of CVTs may givenegative values. This may be due to the tan delta value of the EMU transformer windingbeing higher.

(B) Interpretation of test resultsMain reason for increase of tan delta value is because of presence of inherent air voidswhich are created during manufacturing process. In course of application of high volt-age, these voids are ionized which result in deterioration of insulating properties of theinsulation. Increase in the value of tan delta will indicate the following conditions:a) Chemical deterioration due to age and temperature, including certain cases of acute

deterioration caused by localized overheating.b) Contamination by water, carbon deposits, bad oil, dirt and other chemicals.c) Severe leakage through cracks and surfaces.d) Ionization.Adverse effect of moisture in Paper insulationDielectric strength of insulation decreases with increase in moisture content. And also,moisture in cellulosic insulation can lead to bubble formation under high load conditions.Moisture accelerates the ageing of paper insulation. If moisture content in paper insula-tion increases from 1% to about 2%, it will lead to increase in ageing of the insulation byalmost two times.

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At high temperature, moisture is pushed out of the paper insulation into the oil. Asinsulation cools down, water begins to migrate slowly from the oil into the paper. Thetime for the temperature drop in the oil may be much quicker than the water can return tothe cellulosic insulation. Hence depending upon these conditions, dissipation factor alsochanges.Monitoring of dissipation factor/capacitance valueA large number of equipment insulation failures can be anticipated in advance by carryingout testing of Tan delta/dissipation factor and capacitance measurement. Changes inthe value of capacitance, indicate abnormal conditions such as presence of moisture,layer short circuits or open circuits in the capacitor elements of CVT stacks.An increase in only tan delta value (not appreciable change in capacitance value)indicates deterioration of cellulosic insulation whereas increase in both tan delta andcapacitance values indicates entry of moisture in the insulation.Effect of ambient temperatureIf tan delta measurement is carried out at Ambient other than 20C, then there is likelyhood that the values may vary since tan delta values are temperature sensitive. In absenceof temperature correction factors, effort should be made to carry out this measurementat 20 to 40 C. Correction factors circulated vide document no D-5-02-XX-01-00 maynot be applicable for all make/types of equipments and hence may not be applied.However, it is must to record the ambient temperature while carrying out the measurementfor future references.Effect of system frequencyTan delta values are also affected by system frequency since capacitive current is directlyproportional to system frequency. If tan delta kit is not provided with device which producesoutput voltage of constant frequency, then it is essential to record the system frequencyat the time of carrying out these tests.

12. MANPOWER REQUIREDEXECUTIVES - 1SUPERVISOR - 1TECHNICIAN - 1

13. Duration of Testing :Two hrs. per Equipment (Average)

14. FORMATSAs per DOC. NO : D-3-02-XX-01-03

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INSULATION RESISTANCE MEASUREMENT FOR EHV CLASSCURRENT TRANSFORMERS

1. EQUIPMENT AND TEST NAMEInsulation Resistance measurement for EHV class Current Transformers.

2. PURPOSEIR measurement of 400 & 220 kV Current Transformer between HV (Primary) Windingand Test tap (for CTs having test taps) and between HV and Earth (for CTs not havingtest taps).

3. DEFINITIONInsulation Resistance: is defined as ratio of applied voltage (DC) to total leakagecurrent (capacitive, absorption and conduction currents).

4. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONSFT : SANCTION FOR TESTPTW : PERMIT TO WORKEHV : EXTRA HIGH VOLTAGEHF TERMINAL : HIGH FREQUENCY TERMINALAC : ALTERNATING CURRENT

5. TESTING SCHEDULE AND FREQUENCYAs per Maintenance Schedule Doc. No: D-4-02-XX-01-04

6. TEST EQUIPMENT5 kV Motorized Megger and associated accessories like test leads etc.

7. ISOLATION REQUIREDa) CB should be in open position.b) Isolators from both sides of CT should be in open position.c) Earth switch should be open at the time of IR measurement.

8. SAFETY REFERENCEAs per PSI No.03 of Safety Rule Hand Book of POWERGRID.

9. PRECAUTIONSa) Ensure that SFT/PTW is taken as per norms.b) There should be no joints in testing cables.c) Test leads should not touch any live part.d) Megger body should be earthed (if separate terminal is provided).e) Surface/terminals should be cleaned.f) IR measurement should be carried out preferably in dry and sunny weather.

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g) Never connect the test set to energised equipment.h) The ground terminal must be connected first and removed at last.i) High voltage plugs should be free from moisture during installation and operation.j) If oil traces are found on the surface of CT, the same should be cleaned by Methyl

Alcohol only. Petrol or diesel should never be used.k) It should be ensured that whole testing equipment alongwith testing procedures are

available at testing site. Testing must be carried out in presence of testing engi-neer only.

l) After testing with high voltage, test terminals must be grounded before beingtouched by any personnel.

m) Test leads should be properly screened/ shielded.10. MAINTENANCE/TESTING PROCEDURE

Connect the Megger as per figure given below. Connect the HV terminal to the Primaryterminal of CT by using crocodile clip for firm grip.

Carry out the measurement as per standard procedure given by the kit supplier. Notedown the values as per format in Doc. No: D-3-02-XX-01-03A test voltage as specified is applied as per the above connections and successivereadings are taken. Values of IR should be recorded after 15 seconds, 60 seconds and600 seconds. Ambient temperature and weather conditions are to be recorded.

11. EVALUATION OF TEST RESULTSChanges in the normal IR value of CT indicate abnormal conditions such as presence ofmoisture, dirt, dust, crack in insulator of CT and degradation of insulation. Changes in IRvalue of CT are also based on the weather conditions. It is advised to carry out IR mea-surement during sunny & dry weather preferably. Insulation Resistance changes withdeterioration in insulating properties. Absolute value of IR is important to monitor but therate of change is equally important.

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Analysis of IR valuesIf readings of IR increase with time, the insulation is good. However, if readings remainsame over the time span, insulation is contaminated. This is due to the fact that chargingcurrent and absorption currents subside with time and only conduction current remains.This indicates that total current taken by insulation changes with time. However, if there isno appreciable change in the total current drawn by the insulation, it is an indication ofdomination of conduction current over charging and absorption currents. The differentcurrents involved in IR measurement are given below:a) Charging CurrentDue to the application of Voltage to a Capacitance, it gets charged to the applied volt-age. The length of time it would take to charge the capacitance would vary according tothe magnitude of the capacitance and the resistance of the voltage source.b) Dielectric Absorption CurrentWhen capacitor is insulated with material other than vacuum or air, the current that flowswhen a direct voltage is applied is no longer the charging current alone. The additionalcurrent is known as dielectric absorption current. This current is due to the presence ofpolar molecules in the insulation system.c) Conduction currentWhen a direct voltage is applied to a capacitor, the steady state value of the current isknown as the conduction current. This is if one waits until the dielectric absorption cur-rent has decayed to zero, the remaining current is the conduction current. Conductioncurrent is directly affected by temperature, humidity, contaminants and voltage stress. Insolid insulating materials which have absorbed moisture, there will be a non-linear largeincrease of the conduction current for increase in the voltage stress. This is known asthe EVERSHED affect.

IR value after 60 seconds1. Dielectric absorption ratio =

IR value after 15 seconds

IR value after 600 seconds2. Polarisation Index =

IR value after 60 seconds

If Dielectric Absorption Ratio is above 1.5 then insulation quality is assumed to be good.If Polarisation Index is more than 1.3 then also insulation quality is assumed to be good.

12. MANPOWER REQUIREDEXECUTIVES - 1TECHNICIAN/OPERATOR - 1

13. DURATION OF TESTINGTWO HOURS FOR A SET OF CT (AVERAGE)

14. FORMATSAs per DOC. NO : D-3-02-XX-01-03

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DEW POINT MEASUREMENT OF SF6 GAS/ OPERATING AIRFOR CIRCUIT BREAKERS

1. EQUIPMENT AND TEST NAMEDew Point measurements of SF6 gas/operating Air for CBs.

2. PURPOSETo measure Dew point of SF6 gas & Air for 400/220/132 kV CBs.

3. DEFINITIONDew Point:Dew Point is the temperature at which moisture content in SF6 gas/air starts condensing.Dew Point at rated pressure of CB:Dew Point when measured keeping regulating valve in service at the outlet of dew pointkit to allow required flow rate of gas/air, is called at rated pressure of CB.Dew Point at atmospheric pressure :Dew Point when measured by regulating the gas flow at the inlet of dew point kit andkeeping outlet regulating valve ( if provided) in fully open condition so that flow rate ofgas/air is maintained as required, is called at atmospheric pressure.

4. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONPTW : PERMIT TO WORKAC : ALTERNATING CURRENT


6. TEST EQUIPMENTDew Point kit and associated accessories.

7. ISOLATION REQUIRED CB should be in open condition.8. SAFETY REFERENCE

As per PSI No.03 of Safety Rule Hand Book of POWERGRID.9. PRECAUTIONS

a) Ensure that PTW is taken as per norms.b) Pipe should be of PTFE (Teflon) or having stainless steel tubing (as per IEC 61634 /

60480)c) All the joints/connectors should be dust and moisture free. If required, same should

be cleaned by clean cloth. Dry the joints and pipe by dry air.10. MAINTENANCE/TESTING PROCEDURE

a) Make the connections to the kit from CB pole ensuring that regulating valve is fullyclosed at the time of connections of the Dew Point kit.

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b) By regulating the flow rate of SF6 gas (0.2 liter/min to 0.5 liter/min - ref. IEC 60480),the value of dew point is observed till it becomes stable.

c) If the regulating valve is provided at outlet of the dew point kit then values as given inDoc. no. for rated pressures are to be monitored.

SF6 gas Relation between dew pointand moisture content

Typical Arrangement for Dew Point Measurement

11. EVALUATION OF TEST RESULTSDew point Measurement of SF6 Gas in CBs:Measurement of Dew Point of SF6 gas is an adequate parameter for condition monitoringSF6 gas in a CB. Dew Point measurement of SF6 gas in a CB indicates the change inthe value of dielectric properties of SF6 gas. The dielectric properties of SF6 gas doget changed with time due to mixing of impurities like moisture, decomposition productsof SF6 gas i.e. Hydro Fluorides, lower valence Sulfur Fluorides, etc.a) Exudation of moisture contained during manufacturing from insulation

materials used in Circuit Breakers.

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b) Permeation of moisture through sealed sections i.e. gaskets, O-Rings etc.During Arc interruption in CBs, decomposition of SF6 gas takes place which in presenceof moisture, may result in deterioration of Organic Insulating materials inside interruptingchamber and also corrosion of metals due to formation of hydro fluorides. Therefore, inorder to avoid dielectric failure of CBs, monitoring of moisture content in SF6 gas is veryimportant. Chemical reactions under moisture conditions are given below:When moisture density is lowSF4 + H2O SOF2 + 2HFSOF2 + H2O SO2 + 2HFWhen moisture density is highSF4 + 3H2O H2SO3 + 4HF2SF2 + 3H2O H2SO3 + 4HFSulfur Oxyfluorides, Hydrogen fluoride and H2SO3 formed in these reactions vigorouslyattack all materials containing Silicon di-oxide. Primary and secondary decompositionproducts in presence of moisture forms corrosive electrolytes which may cause damageand operational failures.Powder DepositsThe solid deposit is composed of CuF2 produced from metal and metal scrap. The SulfurFluorides are electrical insulation material, featuring sublimation hydration and hydrolysisreaction. Powder deposits are observed after the discharging process, however, iftemperature is raised to the sublimation temperature of CuF2, then powder deposits areformed directly in the form of solid body from gas.CuF2 (Milky white) + 2H2O CuF2.2H2O (Blue)Frequency of Dew point measurementMoisture from the organic Insulating material is discharged at faster rate initially and therate of release is almost negligible after 4-5 years of commissioning and moisture entryis only through permeation. In the first year, about 50% of moisture is released and inanother 4 years, 90% moisture is released. The frequency of dew point measurement isas given below: First at the time of commissioning After six months After one year Once every two yearsMonitoring of Dew point valuesDew Point of SF6 gas varies with pressure at which measurement is being carried out.This is due to the fact that Saturation Vapour Pressure decreases with increase inPressure of the SF6 gas. Hence, dew point of SF6 gas at higher pressure is lower thandew point at atmospheric pressure. Therefore, it is to be ensured that if measurementhas been done at a pressure other than the atmospheric pressure, same is to be convertedto the atmospheric pressure as given in the table below for various CB manufacturers:Method for converting dew point at different gas pressures, is given/described inIEC-60480.

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Sl. No. Make Dew point at Dew point at RemarksPressureof CB rated pressure Atmospheric

pressure (limits)1. BHEL - 15 C - 36 C At the time of commissioning

- 7 C - 29 C During O&M- 5 C - 27 C Critical

2. M & G - 39 C At the time of commissioning- - 32 C During O&M

3. CGL - 15 C - 35 C At the time of commissioning- 10 C - 31 C During O&M

4. ABB - 15 C - 35 C At the time of commissioning- 5 C - 26 C During O&M

5. NGEF - 15 C - 36 C At the time of commissioning- 7 C - 29 C During O&M- 5 C - 27 C Critical

6. For all make - 15C () 35C To be followed for wagoora s/s orof CBs substations having ambient

temperature less than zero degreecentigrade

Dew point Measurement of Air in ABCBsMeasurement of Dew Point of air in ABCBs indicates the moisture content in the airbeing used as insulating and arc quenching medium in these breakers. The arc quenching/dielectric properties of dry air do get changed with aging of CB and quality of airdeteriorates as moist air travels to the interrupting of circuit breaker. This will result indeterioration of internal insulation which could possibly lead to unsuccessful arc quenchingdue to poor dielectric strength of interrupting medium. It is , therefore, necessary to carryout measurement of Dew Point of air in ABCBs.The permissible limits of dew point of air in ABCBs are given in DOC. NO. D-5-02-XX-01-02.

12. MANPOWER REQUIREDEXECUTIVES - 1TECHNICIAN/OPERATOR - 1

13 DURATION OF TESTINGTWO HOURS PER CB (AVERAGE)

14. FORMATSAs per DOC. NO: D-3-02-XX-01-03

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MEASUREMENT OF CIRCUIT BREAKER OPERATING TIMINGSINCLUDING PRE INSERTION TIMINGS

1. EQUIPMENT AND TEST NAMEMeasurement of Circuit Breaker operating Timings including Pre Insertion Timings.

2. PURPOSETo measure Operating timings of Circuit Breakers.

3. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONSFT : SANCTION FOR TESTPTW : PERMIT TO WORKEHV : EXTRA HIGH VOLTAGEC : CLOSING OF CIRCUIT BREAKERC-O : CLOSE - OPEN OPERATION OF CIRCUIT BREAKERO-C-O : OPEN - CLOSE OPEN - OPERATION OF CIRCUIT BREAKER


5. TEST EQUIPMENTCircuit Breaker Operational Analyser and associated accessories.

6. ISOLATION REQUIREDa) Isolators on both sides of CB should be in open position.b) Earth switch should be in closed position.


8. PRECUATIONa) Ensure that SFT/PTW is taken as per norms.b) There should not be any joints in testing cables.c) Test leads should not touch any live part.d) Never connect the test set to energised equipment.

Doc No. D-2-03-XX-02-01 20

e) The ground cable must be connected first and removed at last.f) High voltage plugs should be free from moisture during installation and

operation.g) Circuit Breaker Analyser body should be earthed ( if separate earth is provided).h) It should be ensured that whole testing equipment alongwith testing procedures are

available at testing site. Testing must be carried out in presence of testing personnelonly.

i) Surface/terminals should be cleaned where the connections for testing are to bemade.

j) Clean earth point with sand paper/wire brush where earth terminal is to beprovided.

k) Ensure that all the poles trip simultaneously through single close/trip command.9. MAINTENANCE/TESTING PROCEDURE

a) Make connections as shown in the figure. It is to be ensured that R, Y, B phasemarking cables are connected with the proper place in the CB analyser and colourcodes are to be maintained for all the three poles of CB.

b) Make connections for recording operating timings of Auxiliary contacts.c) Extend power supply to Circuit Breaker Analyzer.d) Give closing command to closing coil of CB and note down the PIR and main contact

closing time. Take the print out from the analyser.e) Give tripping command to trip coil-I of CB and note down the main contact tripping

time.

Main Contact

PIR

Green

Black

CBAnalyser

Red

Typical Arrangement for Operating Timings Measurement of CB

Doc No. D-2-03-XX-02-01 21

f) Give tripping command to trip coil-II of CB and note down the main contact closingtime.

g) Note down the timings for CO, and OCO by giving respective commands. COcommand to be given without time delay but 300ms time delay to be given betweenO and CO operation in testing for OCO.

h) To find out opening time of PIR contacts, PIR assembly has to be electrically isolatedfrom Main contacts and then PIR contacts are to be connected to separate digitalchannels of the Analyzer.

10 EVALUATION OF TEST RESULTSA) CLOSING TIMINGSClosing timings and Discrepancy in operating times of PIR and main contacts shouldnot exceed the permissible limits as specified in the DOC NO: D-5-02-XX-01-01. In anycase, main contacts should not close prior to closing of PIR contacts and PIR contactsshould not open prior to closing of main contacts.In case, contact bouncing is observed in operating timings for PIR and main contacts,same should be rectified by tightening the cable connections.B) TRIPPING TIMINGSTrip time and pole discrepancy in operating timings should not exceed beyond permissiblevalue given in Doc. No. D-5-02-XX-01-02. In case of ABB, NGEF and CGL make CBs,while tripping, PIR contacts should not open after opening of main contacts.C) CO TIMINGSCO timings should be within permissible limits as specified by different manufacturers.If operating timings of CB poles are not within limits, same may be corrected by:a) Equalizing the SF6 gas pressure in all the polesb) Adjusting plunger movement of trip/ close coilsc) Adjustment in operating mechanismd) Changing of trip/ close coils (if required)It is also important to measure timings of auxiliary contacts from the point of view ofvariations w.r.t. the main contacts.

11. MANPOWER REQUIREDExecutives - 1Technician/lineman - 1

12. DURATION OF TESTINGTwo Hours Per CB (Average)

13. FORMATSAs per DOC. NO: D-3-02-XX-01-03

Doc No. D-2-03-XX-02-01 22

MEASUREMENT OF SECONDARY WINDING RESISTANCEFOR CURRENT TRANSFORMERS

1. EQUIPMENT AND TEST NAMEMeasurement of Secondary Winding Resistance for EHV Current Transformers.

2. PURPOSETo measure secondary winding resistance for 400/220 kV Current Transformers.

3. DEFINITIONSecondary DC winding resistance of CT.

4. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONSFT : SANCTION FOR TESTPTW : PERMIT TO WORKEHV : EXTRA HIGH VOLTAGEAC : ALTERNATING CURRENT


6 TEST EQUIPMENTCurrent source and volt meter or winding resistance meter with appropriate leads.

7 REQUIRED.ISOLATION CB should be in open position. Isolators from both sides of CT should be in open position.


9. PRECAUTIONSa) Ensure that SFT/PTW is taken as per norms.b) There should be no joints in testing leads/cables.c) It should be ensured that whole testing equipment along with testing procedures are


d) Test links should be opened in the CT MB prior to measurement of secondaryresistance.

e) It should be ensured that associated CTs are not in charged condition. For example,Main and Tie CTs for differential relays should not be in charged condition.

f) If any earth is provided in the secondary circuit of CT, same is to be removed prior tomeasurement.

Doc No. D-2-03-XX-02-01 23

10. MAINTENANCE/TESTING PROCEDUREConnect leads of OHM meter between different terminals of CT secondary cores. Selectthe range of OHM meter as per pre-commissioning/factory test results. Record thewinding resistance values in the format as per DOC. NO: D-3-02-XX-01-03.

11. EVALUATION OF TEST RESULTSValue of secondary winding resistance should be within acceptable limits. Extreme lowvalue of resistance indicates turn to turn shorting whereas if the value of is high, it indicatessome loose connection which is to be identified and tightened before repeating themeasurement.

12. MANPOWER REQUIREDExecutives - 1Technician/operator - 1

13. DURATION OF TESTINGOne Hour Per CT (Average)

14. FORMATSAs per DOC. NO: D-3-02-XX-01-03.

Doc No. D-2-03-XX-02-01 24

MAGNETIZATION CHARACTERISTICS OF CURRENT TRANSFORMERS

1. EQUIPMENT AND TEST NAMETo carry out Magnetization Characteristics of CT cores for EHV class CurrentTransformers.

2. PURPOSETo carry out Magnetization Characteristics of CT cores for 400/220 kV CurrentTransformers.

3. DEFINITIONKNEE POINT VOLTAGEKnee Point Voltage is defined as the voltage at which a 10 % increase in flux densitywould cause 50% increase in exciting ampere-turns.

4. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONSFT : SANCTION FOR TESTPTW : PERMIT TO WORKEHV : EXTRA HIGH VOLTAGEAC : ALTERNATING VOLTAGE


6. TEST EQUIPMENTVoltage source of 5 kV, Voltmeter of range 0 to 5 kV, Ammeter, of range 0 to 100 Amps,testing leads/cables etc.

7. ISOLATION REQUIRED CB should be in open position. Isolators from both sides of CT should be in open position.


9. PRECAUTIONSa) Ensure that SFT/PTW is taken as per norms.b) There should be no joints in testing leads/cables.c) It should be ensured that whole testing equipment along with testing procedures are


Doc No. D-2-03-XX-02-01 25

d) Test links should be opened in the CT MB prior to measurement.e) It should be ensured that associated CTs are not in charged condition. For example,

Main and Tie CTs for differential relays should not be in charged condition.f) If any earth is provided in the secondary circuit of CT, same is to be removed prior to

measurement.

g) Applied voltage to the CT core should not exceed the rated Knee Point Voltage of theCT.

10. MAINTENANCE/TESTING PROCEDUREAfter making proper connections, applied voltage is increased from zero to rated KneePoint Voltage in steps of 25%, 50%, 75% and 100%. Measure the current drawn by theCT secondary core at respective applied voltages and record the test results as performats given in DOC NO: D-3-02-XX-01-03.

11. EVALUATION OF TEST RESULTSThe magnetization test is conducted in order to see the condition of turns of CT secondary.This test shall give indications regarding shorting of turns of CT secondary winding.Magnetization characteristics also indicate the suitability of CT for keeping it in serviceor not.

Knee Point Voltage is normally defined as the voltage at which 10% increase in theapplied voltage causes 30 to 50% increase in secondary current. The magnetizationcurrent at rated Knee Point Voltage should not be more than the specified/designedvalue.A curve can be drawn between applied voltage and magnetizing current. From themagnetisation curve, it can be implied that up to rated KPV (Knee Point Voltage), the VIcurve should be almost a straight line. However, if this line is not linear, this indicates thatthe magnetizing characteristics are not desirable. If the slop of the curve starts increasing,it indicates that magnetizing induction becomes low and total primary current is utilizedin exciting the core alone. Consequently, out put of CT secondary disappears.

12. MANPOWER REQUIREDExecutives - 1Technician/operator - 2

13. DURATION OF TESTINGTwo Hours

14. FORMATSAs per DOC. NO: D-3-02-XX-03

Doc No. D-2-03-XX-02-01 26

MEASUREMENT OF STATIC CONTACT RESISTANCE OF EHVCIRCUIT BREAKERS

1. EQUIPMENT AND TEST NAMEMeasurement of Static Contact Resistance of EHV CB Main Contacts and Isolator MainContacts.

2. PURPOSETo Measure Contact Resistance of 400 & 220 kV Circuit Breaker and Isolator MainContacts.



5. TEST EQUIPMENTContact resistance kit (100A DC minimum)

6. ISOLATION REQUIRED CB should be in open position. Isolator on either side of CB should be in open position. Earth switch of both side of the CB should be in closed position.


8. PRECAUTIONSa) Ensure that proper SFT/PTW is taken as per norms.b) There should be no joints in testing leads/cables.c) It should be ensured that whole testing equipment along with testing procedures are


At the time of connections, both sides of isolator should be earthed by closing earthswitches or by temporary earths. After the connections, earthings should be removed.

Doc No. D-2-03-XX-02-01 27

9. MAINTENANCE/TESTING PROCEDUREThe measurement is taken at CB in closed position. The Ohm Meter operates on thefour wire measurement principle. To measure the contact resistance connect therespective leads and adjust the veri A.C. so that app. 100 amps current flow through thecontacts. Value of contact resistance is directly displayed on the digital LED displayscreen.

By using four terminal method, we can nullify the resistance of test leads if input impedance

of measuring device (IC) is very high.10. EVALUATION OF TEST RESULTS

Contact resistance of the main contacts indicates wear out and misalignment of themain contacts. If the value of contact resistance exceeds the permissible limit i.e. 150micro ohms for CBs and 300 micro ohm for Isolators ( Ref. DOC. NO: D-5-02-XX-01-02), this could result in overheating of the contacts. Therefore, the problem of high contactresistance should be attended immediately by making proper alignment of contacts orby replacing finger contacts.

11 MANPOWER REQUIREDExecutives - 1Technician/operator - 1

12. DURATION OF TESTINGOne Hour


I

C1 V1 V2 C2

Four Terminal method of Contact Resistance Measurement

Doc No. D-2-03-XX-02-01 28

DYNAMIC CONTACT RESISTANCE MEASUREMENT (DCRM)AND CONTACT TRAVEL MEASUREMENT OF EHV

CIRCUIT BREAKERS

1. EQUIPMENT AND TEST NAMEMeasurement of Dynamic Contact Resistance (DCRM) and Contact Travel of EHV CBs.

2. PURPOSETo monitor condition of CB main and arcing contacts without opening the interrupterhence decision regarding major/final overhauling/inspection of main/arcing contacts maybe taken.



5. TEST EQUIPMENT100 Amp. DCRM kit with CB operational analyzer with 10k Hz sampling frequency.

6. ISOLATION REQUIREDa) CB should be in open position.b) Isolator of both sides of CB should be in open position.c) Earth switch of one side of CB should be in open position.


8. PRECAUTIONSa) Ensure that proper SFT/PTW is taken as per norms.b) There should be no joints in testing leads/cables.c) It should be ensured that whole testing equipment along with testing procedures are


d) Current leads should be connected such that voltage leads are not outside area ofcurrent flow.

9. MAINTENANCE/TESTING PROCEDUREa) Follow the standard procedure as given in instruction manual of DCRM kit.b) The tightness of connections at CB flanges is most important to ensure error free

measurement. CB during CO operation generates lot of vibrations and failure ofconnections during this period can dramatically change the dynamic signature of CBresistance.

Doc No. D-2-03-XX-02-01 29

c. DCRM signatures should be recorded for CO operation. Open command should beextended after 300 ms from the close command.

d. Clean portions of incoming and outgoing flanges of CB with polish paper to removepaint, oxidation etc, at points where Current clamps are mounted.

e. Select this point of connection, as close as possible to the end of porcelain insulatorto ensure that minimum resistance is offered by flanges, bolts, terminal connectorsetc.

f. It should be ensured that Travel Transducers are properly fitted.g. Sampling frequency during measurement should be 10 KHz.

10. EVALUATION OF TEST RESULTSDynamic Contact Resistance Measurement (DCRM) is the technique for measuringContact Resistance during operation (Close/ Trip) of a Circuit Breaker. A DC current isinjected through the circuit breaker. The current and voltage drop are measured andresistance is calculated. The resistance versus time data provides useful information onthe condition of the circuit breaker contacts as is used as a diagnostic tool.The variations in the measured resistance versus time will be seen as a finger print forthe breaker contacts and can be used as a bench mark for comparing with futuremeasurements on the same breaker. This provides information on the condition of thebreaker contacts.Dynamic Contact Resistance Measurement for Arcing Contact conditionsBy application of Dynamic Contact Resistance Measurement, condition of arcingcontact can be predicted. If DCRM signature shows vide variations and also there ischange in arcing contact insertion time, it indicates erosion of the arcing contacts andmain contacts and subsequent failure.

Basic Connection for DCRM Testing

Doc No. D-2-03-XX-02-01 30

Contact Travel MeasurementTransducers are attached to the operating rod or interrupting chamber in order to recordthe contact travel. When CB closes, contact travel is recorded. Contact bounces or anyother abnormality is also clearly indicated by the Contact Travel Measurement.If contact travel, contact speed and contact acceleration signature are compared withthe original signatures, then it may indicate problems related with the operatingmechanism, operating levers, main/ arcing contacts, alignments etc.DCRM alongwith Contact Travel measurement is useful in monitoring length of Arcingcontacts. Erosion of Arcing contacts may lead to commutation failures and current mayget transferred to Main contacts. Due to heat of arc, main contacts may get damaged.

11 MANPOWER REQUIREDExecutives - 1 Supervisor - 1Technician/operator - 1

12. DURATION OF TESTING - Four Hours per CB13. FORMATS

As per DOC. NO: D-3-02-XX-01-03.

Typical DCRM Signature

Doc No. D-2-03-XX-02-01 31

CHECKING OF POLE DISCREPANCY RELAY FORCIRCUIT BREAKERS

1. EQUIPMENT AND TEST NAMEChecking of Pole Discrepancy relay and timer for EHV Circuit Breakers.

2. PURPOSEPole Discrepancy and timer checking for 400 & 220 kV CBs.

3 DEFINITIONPole Discrepancy is defined as the difference in closing & opening timings of differentpoles of CB.

4. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONSFT : SANCTION FOR TESTPTW : PERMIT TO WORKEHV : EXTRA HIGH VOLTAGEHF TERMINAL : HIGH FREQUENCY TERMINALAC : ALTERNATING CURRENT


6. TEST EQUIPMENTTesting Leads, Standard timer etc.

7. ISOLATION REQUIREDIsolators on both sides of CB should be in open position.Earth switch should be in closedposition.

8 SAFETY REFERENCEAs per PSI No.03 of Safety Rule Hand Book of POWERGRID.

9 PRECAUTIONSa) Ensure that SFT/PTW is taken as per norms.b) There should be no joints in testing cables.

10 MAINTENANCE/TESTING PROCEDUREWHEN CB IN OPEN POSITIONClosing Command is extended to close one pole, say R-Pole, of CB. After closingR-Pole of CB, this Pole should automatically open after 2.5 seconds (as per polediscrepancy timer settings). Repeat the test for remaining two poles of CB.

Doc No. D-2-03-XX-02-01 32

WHEN CB IN CLOSED POSITIONTripping Command is extended to trip one pole, say R-Pole, of CB. Remaining Y and B-Poles of CB should automatically open after 2.5 seconds. Repeat the same test forremaining two poles of CB.

11. EVALUATION OF TEST RESULTSPermissible value of pole discrepancy between two poles of CB is 3.33 msec.

12. MANPOWER REQUIREDExecutives - 1Supervisor - 1Technician/operator - 1

13. DURATION OF TESTINGOne Hour


Doc No. D-2-03-XX-02-01 33

OPERATIONAL LOCKOUT CHECKING FOR EHVCIRCUIT BREAKERS

1. EQUIPMENT AND TEST NAMEOperational Lockout checking for EHV Circuit Breakers.

2. PURPOSETo check operational lockouts for 400/220kV CBs.

3. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONSSFT : SANCTION FOR TESTPTW : PERMIT TO WORK

4. TESTING SCHEDULE AND FREQUENCYAs per maintenance schedule document No. D-4-02-XX-01-04.

5. TEST EQUIPMENTMultimeter, testing leads etc.

6. ISOLATION REQUIREDa) CB should not be in serviceb) Isolators on both sides of CB should be in open position.c) DC supply should be switched off as a precautionary measure.


8. PRECAUTIONS:Ensure that SFT/PTW is taken as per norms.

9. MAINTENANCE/TESTING PROCEDURE:A. SF6 GAS PRESSURE LOCKOUT

a) Low Pressure AlarmClose Isolation Valve between CB Pole(s) and density monitor. Start releasing SF6 gas fromdensity monitor till the low pressure gas alarm contacts are actuated which is detected byMultimeter. Note down the pressure and temperature at which the contacts get actuated.b) Operational LockoutContinue releasing SF6 gas from isolated zone till the operational lockout Alarm Contacts areactuated which are detected by Multimeter. Note down the pressure and temperature atwhich the contacts get actuated. This is called operational lockout pressure.

B. PNEUMATIC OPERATING SYSTEM LOCKOUTa) Compressor START/STOP SwitchClose the isolating valve of CB. Release air into atmosphere from the compressor. Notedown the value of pressure at which Compressor starts building up air pressure and pressureat which Compressor stops.b) CB AUTO RECLOSE LOCKOUTClose Isolation valve between pneumatic system and pressure switches. Release air fromthe isolated zone to atmosphere. Note down pressure at which A/R L/O contacts of pressureswitch get actuated which are detected by Multimeter. The leads of the Multimeter should beconnected to the contactor where the AR L/O of CB are made.

Doc No. D-2-03-XX-02-01 34

c) CB CLOSING LOCKOUTRelease air from the isolated zone to atmosphere. Note down pressure at which CB ClosingL/O contacts of pressure switch get actuated which are detected by Multimeter.d) CB OPERATIONAL LOCKOUTRelease air from the isolated zone to atmosphere. Note down pressure at which CBOperational L/O contacts of pressure switch get actuated which are detected by Multimeter.e) MECHANICAL CLOSING INTERLOCK(FOR ABB CBs ONLY)CB should be in closed position. Release air from pneumatic systemof CB to atmosphere and observe whether CB poles start opening, if so, note down the pressureat which tie rod starts coming down. In such case the closing interlock is to be opened forinspection and if required, replace the closing interlock.

C. HYDRAULIC OPERATING SYSTEM LOCKOUTa) Pump START/STOPBy opening pressure release valve, note down the pressure at which Pump starts building upoil pressure and pressure at which pump stops.b) CB AUTO RECLOSE LOCKOUTClose Isolation valve between hydraulic system and pressure switches. Release oil from theisolated zone to oil tank. Note down pressure at which A/R L/O contacts of pressure switchget actuated which are detected by Multimeter.c) CB CLOSING LOCKOUTRelease oil from the isolated zone to oil tank. Note down pressure at which CB Closing L/Ocontacts of pressure switch get actuated which are detected by Multimeter.d) CB OPERATIONAL LOCKOUTRelease oil from the isolated zone to container. Note down pressure at which CB OperationalL/O contacts of pressure switch get actuated which are detected by Multimeter.

10. EVALUATION OF TEST RESULTSA.SF6 GAS PRESSURE LOCKOUTAll the SF6 gas pressure switches settings should be checked and corrected with ambienttemperature. Settings of SF6 gas pressure switches should be within 0.1 bar/ Kg/cm2 ofthe set value ( after taking into account the temperature correction factor).B. AIR PRESSURE LOCKOUTAll the air pressure switches settings should be checked and corrected and should be within 0.3 bar/ Kg/cm2 of the set value.C. OIL PRESSURE LOCKOUTAll the oil pressure switches settings should be checked and corrected and should be within 0.3 bar/ Kg/cm2 of the set value.

11. MANPOWER REQUIREDEXECUTIVES - 1SUPERVISOR - 1TECHNICIAN/OPERATOR - 1

12. DURATION OF TESTINGONE HOUR

13. FORMATSAs per DOC. NO: . D-3-02-XX-01-03

Doc No. D-2-03-XX-02-01 35

MEASUREMENT OF THIRD HARMONIC RESISTIVE CURRENTFOR SURGE ARRESTERS

1. EQUIPMENT AND TEST NAMEMeasurement of Leakage Current (Third harmonic resistive current) for EHV SurgeArresters.

2. PURPOSETo monitor health of Surge Arresters by monitoring third harmonic resistive current fromthe leakage current.

3. ABBREVIATIONSPSI : POWERGRID SAFETY INSTRUCTIONSSFT: SANCTION FOR TEST

4. TESTING SCHEDULE AND FREQUENCYAs per maintenance schedule document No. D-4-02-XX-01-04.

5. TEST EQUIPMENTLeakage Current Monitor suitable to filter out third harmonic resistive current from totalleakage current.

6. ISOLATION REQUIREDNo isolation required since it is an On line measurement.

7. SAFETY REFERENCEAs per PSI No. 03 of Safety Rule Hand Book of POWERGRID.

8. PRECAUTIONS Ensure that SFT is taken as per norms. Test leads should be fully screened to nullify the effect of electromagnetic interference. Ensure that Arrester is mounted on isolated base.

9. MAINTENANCE / TESTING PROCEDUREa. Make the connections as per the diagram

given below (Fig.I)b. The kit should be properly earthed as per the

recommendations of the kit suppliers.c. Clamp On type CT should be placed above

the surge monitor to pick up the total leakagecurrent.

d. Carryout the measurements as per standardprocedure supplied by the test kitmanufacturer.

e. Note down the system voltage and ambienttemperature along with the test current value.

f. Avoid measurement during monsoon.

Doc No. D-2-03-XX-02-01 36

10. EVALUATION OF TEST RESULTSA. ZnO Surge Arrester continuously conducts a small leakage current (Fig.2). The

resistive component of this leakage current may increase with time due to dif ferentstresses causing ageing and finally cause arrester failure.

B. The limiting value of third harmonic resistive current is given in the technical circularno.23/ 2004 issued by CC/OS. Arresters are to be removed from service if norms areviolated.

C. While monitoring third harmonic resistive current, temperature and voltage correctionfactors are to be applied because leakage resistive current also depends on these factorsapart from ageing of the arrester discs. As Indian manufacturers are yet to develop thecorrection factors and still working on to it, it is advisable to carry out the measurementsat temperature from 20C to 30C.

D. If Harmonics are present in the system voltage, it shall effect the value of measured thirdharmonic current. Compensating device provided to be used to nullify the effect.

11. MANPOWER REQUIREDEXECUTIVE - 1TECHNICIAN/ OPERATOR - 1

12. DURATION OF TESTINGHalf an hour per Surge Arrester

13. FORMATSAs per DOC. NO:. D-3-02-XX-01-03

HVside

CapacitanceNon-linerResistor

MAINTENANCE PROCEDURESFOR

SWITCHYARD EQUIPMENTSVolume II

(EHV CBs, CTs etc.)

Corporate Operation ServicesPower Grid Corporation of India Ltd.

(A Government of India Enterprise)6th Floor, Saudamini, Plot No. 2

Sector 29, Gurgaon, Haryana-122 001

ikojfxzM

Doc D-2-03-XX-02-01

Power Grid Corporation of India Ltd.Corporate Operation Services

Maintenance Procedures for Switchyard EquipmentsVolume-II (EHV CBs, CTs etc.)

Sl. No. Chapter Page No. Action

01 All Chapters 1 to 36

Doc. No. D-2-03-XX-02-01Revision Department Date Signature Signature00 CC/OS 07.07.1999 Sd/- Sd/-01 CC/OS 28.07.2005

PROPOSED BY REVIEWED BY RECOMMENDED BY APPROVED BY

(S.K. JHA)Dy. Manager (OS)

(S. VICTOR)DGM (OS)

(N.S. SODHA)AGM (OS)

(UMESH CHANDRA)ED (OS)

(R.K. TYAGI)Ch. Manager (OS)

To be replaced

Doc D-2-03XX-02-01

Sl. No. Description Page

01. General instructions for maintenance of Switchyard Equipments 1

02. Tan delta and Capacitance Measurement 5

03. Insulation Resistance Measurement for Current Transformers 12

04. Dew Point Measurement of SF6 Gas/Operating Air for Circuit Breakers 15

05. Measurement of Circuit Breaker Operating Timings includingPre-Insertion Timings 19

06. Measurement of Secondary Winding Resistance forCurrent Transformers 22

07. Magnetization Characteristics of Current Transformers 24

08. Measurement of Static Contact Resistance of EHV Circuit Breakers 26

09. Dynamic Contact Resistance Measurement (DCRM) andContact Travel Measurement of EHV Circuit Breakers 28

10. Checking of Pole Discrepancy Relay for Circuit Breakers 31

11. Operational Lockout Checking for EHV Circuit Breakers 33

12. Measurement of Third Harmonic ResistiveCurrent for Surge Arresters 35

Documents

Maintenance Procedure for Switchyard Equipment Volume-II (EH