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-Asubstationis a vital part of an electricalgeneration, transmission anddistribution system. -Substations transformvoltagefrom high to low, or the reverse.-Substation is an interconnection between generating station and consumer through transmission network. -Electric power flows through several substations at different voltage levels to reach the actual consumer. -Switching is the major function which is needed to be performed satisfactorily using its components.SUBSTATIONCOMPONENTS OF A SUBSTATIONCIRCUIT BREAKERISOLATORCURRENT TRANFORMERPOTENTIAL TRANSFORMERBUS BAR/CONDUCTORSLIGHTENING ARRESTORSCONTROL CUBICLES/MARSHALLING BOX

Surge Monitor with CounterLightening ArrestorStack CStack BStack AInsulator BaseSupport StructureConnected to System EarthingLIGHTENING ARRESTORSRATING-198kV, 10kA, Metal Oxide Surge Arrestor.These lightening arrestors are gapless type.Consists of ZnO2 blocks arranged in series.Monitoring of leakage current is done online.The arresters leakage current, in particular, the third harmonic component of the resistive leakage current, is known to be directly related to the degree of degradation of the ZnO2 arrestor. Resistive component of leakage current and its trend is monitored (100micro amps).Insulation Resistance is measured in offline state.

Maintenance of Current TransformersTan Delta Testing Insulation ResistanceSecondary Resistance-to ensure tightness of connections.Oil LevelNitrogen PressureKnee Point ValuePolarity (For new installation)Ratio ErrorGeneral Cleanliness-removal of dust, dirt, oil seepage etc.Always have a look on de-link type terminals before primary circuit energisation

Maintenance of Potential TransformersInsulation ResistanceOil LevelNitrogen PressurePolarity (For new installation)Ratio ErrorGeneral Cleanliness-removal of dust, dirt, oil seepage etc.Check Fuses for tightness in the grip. Maintenance of Circuit BreakersGeneral Cleanliness-removal of dust, dirt etc.Insulation Resistance ValueBreaker Closing and Tripping TimingBreaker Contact ResistanceInterlocks checking-Low Gas Pressure Alarm/Lock out-Interlocks checking-Low Air Pressure Alarm/Lock out.

Condition Monitoring in a SubstationThermo vision scanning is done to locate the hot spots or any other loose connection. This is done using a Infrared Camera (FLIR, USA make).Scanning schedule is once in a month.This helps in detecting hot points at an early stage and thus gives us ample time to plan shutdown.

Condition Monitoring in a SubstationFor healthiness of Lightening Arrestors, 3rd Harmonic Leakage Current is measured in live condition.This is done using a special instrument-Transinor Make(Sweden).The resisitive component of the 3rd Harmonic leakage current is measured which indicates the watt loss in a lightening arrestor.Earthing in a substationThe purpose of substation grounding/ earthing is to protect the equipment from surges and lightning strikes. To protect the operating persons in the substation.The substation earthing system is necessary for connecting neutral points of transformers and generators to ground For connecting the non current carrying metal parts such as structures, overhead shielding wires, tanks, frames, etc to earth.Earthing in a substationStep Potential:Step potential is the potential difference between the feet of a person standing on the floor of thesubstation, with 0.5 m spacing between the feet (one step), through the flow of earth fault current through the grounding system.Touch Potential:Touch potential is a potential difference between the fingers of raised hand touching the faulted structure and the feet of the person standing on the substation floor. The person should not get a shock even if the grounded structure is carrying fault current, i.e, The Touch Potential should be very small.

Earthing in a substation

SAFETY CLEARANCES FOR WORKING ON EXTRA HIGH VOLTAGE (EHVPersons shall not be allowed any part of their body or objects to approach within the following Safety Clearances exposed EHV/HV conductors, which are Live. (Except during approved live line work). Rated Voltage (KV) Safety Clearance X (Meters) Up to 33 0.8 66 1.0 132 1.4 220 2.4 400 3.1

RATINGS OF EQUIPMENTS220kV AIR BLAST CIRCUIT BREAKER (ABCB)

Rated voltage 245kV rmsTypeOutdoor, ABCB, DLF-nC2No. of Poles3 poleFrequency 50 HzRated normal current2000 ARated short time withstand current 40 kARated peak withstand current100 kApRated duration of short circuit3 Sec.Operating mechanismPneumatic closing /tripping Auto-reclosing dutySingle phase & three phaseRated operating sequenceO-0.3sec-CO-3 min-CO First pole to clear factor1.31.2/50 micro sec impulse withstand voltage1050 kVp1minute dry & wet power frequency withstand voltage460 kV rmsRated short circuit breaking current 50 kANormal Air Pressure30kg/cm2RATINGS OF EQUIPMENTS220kV SF6 GAS CIRCUIT BREAKER

Rated voltage 245kV rmsTypeOutdoor, SF6, 200-SFM-40ANo. of Poles3 poleFrequency 50 HzRated normal current3150 ARated short time withstand current 40 kARated peak withstand current100 kApRated duration of short circuit3 Sec.Operating mechanismSpring closing & Pneumatic tripping Auto-reclosing dutySingle phase & three phaseRated operating sequenceO-0.3sec-CO-3 min-CO First pole to clear factor1.31.2/50 micro sec impulse withstand voltage1050 kVp1minute dry & wet power frequency withstand voltage460 kV rmsRated short circuit breaking current 40 kANormal Gas Pressure6kg/cm2Normal Air Pressure15kg/cm2220kV Current TransformerSr. No.DescriptionValue1.Highest System voltage 245kV rms2.Frequency 50 Hz3.TypeOil Filled (Hermetically Sealed)4.Insulation Level460 / 1050 kV Peak5.Short term current rating 40KA for 3 Sec.6.Rated continuous Thermal current1.2 times the rated primary current7.No. of Cores68.CT Ratio800-1200-1600/1A-1A-1A-1A-1A-1A9.10.Standard applicable : IS-2705 CoreRatioVAClass Accuracy limit factorKnee Point Voltage (KPV)ExcitingCurrent at KPVSecondaryResistance75C Max. (ohm)PurposeI800/11200/11600/1---PS -1200V1800V2400V25mA at 300V20mA at 450V15mAat 600V3.04.56.0O/A differentialII800/11200/11600/1255P 20--LBB, Back up O/CIII800/11200/1450.2 Isf < 5----For metering.IV800/11200/11600/1---PS -600V900V1200V30mA at 300V20mA at 450V15mA at 600V4.56.012.0Bus bar differential (Main.)V800/11200/11600/1---PS -600V900V1200V30mA at 300V20mA at 450V15mA at 600V4.56.012.0Bus bar differential (Check zone).VI800/11200/1450.2 Isf < 5-----For Check Metering.220kV Potential TransformerSr. No.DescriptionValue1Highest System voltage 245kV rms2Frequency 50 Hz3TypeOil Filled (Hermetically Sealed)4Insulation Level460 / 1050 kV PeakRated Voltage Factor1.2 Continuous and 1.5 for 30 SecStandard applicable : IS-3156 No. of Cores4Sr.No.CoreRatioVAAccuracy ClassPurpose1I (S1)220/ 3 KV / 110/ 3 V 110V1500.2Metering2II (S2)220/ 3 KV / 110/ 3 V 110V5000.2 / 3PMetering / Protection3III (S3)220/ 3 KV / 110/ 3 V 110V750.2 / 3PMetering / Protection4IV (S4)220/ 3 KV / 110/ 3 V 110V1500.2MeteringSr No.Conductor Dia (mm)Name Sr. No.Conductor Dia (mm)Name 110.05RABBIT2421.00PANTHER210.11RAVEN2521.78HAWK311.97BEAVER2622.26LION410.98MINK2723..45BEAR512.30RACCOON2825.15GROSBEAK612.66OTTER2925.97GOAT712.95SKUNK3026.73ANTELOPE813.50CAT3126.80KUNDAH913.95HORSE3227.00BISON1014.15DOG3327.00SHEEP1114.16HARE3428.13DRAKE1214.57HYENA3528.62ZEBRA1315.25COUGAR3628.95MALLARD1415.81LEOPARD3729.89DEER1515.89COYOTE3829.89SCORPION1616.52TIGER3930.15CAMEL1716.75DINGO4031.50ELK1817.36MERLIN4131.68CURLEW1918.05CARACAL4231.77MOOSE2018.13WOLF4333.12MORCULLA2118.28LINNET4435.81BERSIMIS2219.30JAGUAR4536.61TARANTULA2319.53LYNX4638.25BULL