SUBSTATION OVERVIEW

-B. PrasadChartered Engineeramieclub@gmail.com

TYPE OF SUBSTATION

Classification based on voltage levels, e.g. : A.C. Substation : EHV, HV, MV, LV; HVDC Substation.Classification based on Outdoor or Indoor : Outdoor substation is under open sky. Indoor substation is inside a building.Classification based on configuration, e.g. : Conventional air insulated outdoor substation orSF6 Gas Insulated Substation (GIS)Composite substations having combination of the above two

Classification based on application

Step Up Substation : Associated with generating station as the generating voltage is low.Primary Grid Substation : Created at suitable load centre along Primary transmission lines.Secondary Substation : Along Secondary Transmission Line.Distribution Substation : Created where the transmission line voltage is Step Down to supply voltage.Bulk supply and industrial substation : Similar to distribution sub-station but created separately for each consumer.Mining Substation precaution for safety needed in the operation of electric supply.Mobile Substation: Temporary requirement

PROMARY/SECONDARY/DISTRIBUTION SUBSTATIONPrimary Substations receive power from EHV lines at 400KV, 220KV, 132KV and transform the voltage to 66KV, 33KV or 22KV (22KV is uncommon) to suit the local requirements in respect of both load and distance of ultimate consumers. These are also referred to EHV Substations.Secondary Substations receive power at 66/33KV which is stepped down usually to 11KV.Distribution Substations receive power at 11KV, 6.6 KV and step down to a volt suitable for LV distribution purposes, normally at 415 volts

SUBSTATION PARTS AND EQUIPMENTS

Outdoor Switchyard Incoming LinesOutgoing LinesBus barTransformersBus post insulator & string insulatorsSubstation Equipment such as Circuit-beakers, Isolators, Earthing Switches, Surge Arresters, CTs, VTs, Neutral Grounding equipment.

SUBSTATION PARTS .CONTDStation Earthing system comprising ground mat, risers, auxiliary mat, earthing strips, earthing spikes & earth electrodes.Overhead earth wire shielding against lightening strokes.Galvanised steel structures for towers, gantries, equipment supports.PLCC equipment including line trap, tuning unit, coupling capacitor, etc.Power cablesControl cables for protection and controlRoads, Railway track, cable trenchesStation illumination system

SINGLE LINE DIAGRAM

Transformer part

Batteries for industrial or substation applications Vented / Flooded Lead Acid batteriesSealed maintenance free batteries/Valve Regulated Lead AcidNickel Cadmium (Ni-cd) batteries

Battery AHLOAD CURRENT 10A for 3 hrs.Cell voltage =12V DCCALCULATION , AH=10X3CAPACITY =30/(0.75X0.8)=50AHDischarge factor=0.7Ageing factor =0.8Drain capacity =C10

CHARGER Type of charger Input voltageoutput voltage Application Protection Metering Indication Alarms Auto operation

Clearance around an Indoor electrical panel (NES 110.26)

Description of ClearanceDistance(min)Left to Right the minimum clearance0.9 Meter (3 Ft)Distance between Panel and wall1.0 MeterDistance between Panel and Ceiling0.9 MeterClear Height in front of Panel >480V2.0 MeterClear Height in front of Panel

Clearance between Bare Metal Busbar in Panel (NES 408.5)

VoltageOpposite Polarity Mounted on Same SurfaceOpposite Polarity Where Held Free in AirLive Parts to GroundUp to 125 V19.1 mm12.7 mm12.7 mm125 V to 250 V31.8 mm19.1 mm12.7 mm250 V to 600 V50.8 mm25.4 mm25.4 mm

Clearance of Outdoor electrical panel to Fence/Wall (NES 110.31)

VoltageDistance(min)600 V to 13.8 KV3.05 Meter13.8 KV to 230 KV4.57 MeterAbove 230 KV5.49 Meter

GROUND CLEARANCE

VOLTAGE LEVELMINIMUM GROUND CLEARANCEless than 66kV6.1m66kV - 110kV6.4m110kV - 165kV6.7mgreater than 165kV7.0m

Earth resistance value

Major power station= 0.5 Ohm.Major Sub-stations= 1.0 OhmMinor Sub-station = 2 OhmNeutral Bushing. =2 OhmService connection = 4 OhmMedium Voltage Network =2 OhmL.T.Lightening Arrestor= 4 OhmL.T.Pole= 5 OhmH.T.Pole =10 OhmTower =20-30 Ohm

Measurement of Earth Resistance (Three point method)

Size of earth wire for motor

Sr.Capacity Size of earth wire Size Of Earth Electrode Cu GICu GI101- 10 HP8 SWG8 SWG60cmX60cmX3.18mm60cmX60cmX6.35mm210 15 HP8 SWG6 SWG60cmX60cmX3.18mm60cmX60cmX6.35mm315 30 HP6 SWG4SWG60cmX60cmX3.18mm90cmX90cmX6.35mm430 50 HP4SWG25mmX3 mm90cmX90cmX6.35mm90cmX90cmX6.35mm

IR Value of Submersible Motor

IR Value of Submersible MotorMotor Out off Well (Without Cable)IR ValueNew Motor20 MA used motor which can be reinstalled10 MMotor Installed in Well (With Cable)New Motor2 MA used motor which can be reinstalled0.5 M

IR Value of Transformers:

VoltageTest Voltage (DC) LV side Test Voltage (DC) HV sideMin IR Value415V500V2.5KV100MUp to 6.6KV500V2.5KV200M6.6KV to 11KV500V2.5KV400M11KV to 33KV1000V5KV500M33KV to 66KV1000V5KV600M66KV to 132KV1000V5KV600M132KV to 220KV1000V5KV650M

Standard voltage

Type Voltage EXTRA LOW VOLTAGE Up to 50V AC/DCLOW VOLTAGE 50-1000V AC/DCMEDIUM VOLTAGE ABOVE 1000V AC/DC UPTO 6.6KV ACHIGH VOLTAGE ABOVE 6.6KV AC TO 33 KV ACEXTRA HIGH VOLTAGE ABOVE 33KV AC TO 400 KV ACULTRA HIGH VOLTAGEABOVE 400 KV AC TO 765 KV AC

Cable end termination

Breaker ACB/VCB/SF6/OCB

EARTHING The following steps, when put into practice, will ensure a reliable, safe and trouble-freesubstation grounding system:Size conductors for anticipated faultsUse the right connectionsGround rod selectionSoil preparationGrounding using building foundations Grounding the substation fenceSpecial attention to operating pointsSurge arrestors must be grounded properlyGrounding of cable traysTemporary grounding of normally energized parts

Earthing .....contd

Cabling Depth of the trench 750 mm for cables up to 1.1KV Depth of the trench 1200 mm for cables up to 1.1KVSand - covered with 150 mmWidth of the trench - 350 mm minimumLoop approximate -3 meter each side

Cable laying Laying direct in ground In pipes, Closed or Open ducts, Cable trays and On surface of wall

BUILDING Administrative buildingConference room etc.Battery Room Operator room Check and change room Adjacent maintenance roomECC room

Switchgear and Control Panel Building

Low voltage AC. SwitchgearHigh voltage AC. SwitchgearControl Panels, Protection PanelsCapacitor panel room

Mechanical, Electrical and Other Auxiliaries

Fire fighting systemD.G. SetOil purification system

ACT FAST AND INITIATE FIRST

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