EHV SWITCHYARDEQUIPMENTS, SWITCHING

SCHMES & LAYOUTS

Switchyard Type

Conventional Air Insulated Type. Gas Insulated type. Outdoor Gas Insulated type.

Selection of Bus Switching Scheme

PRE-REQUISITES

1)System security2)Operational flexibility3)Simplicity of protection arrangements4)Ability to limit short circuit levels (ease of

sectionalizing)5)Maintenance Its effect on system

security6)Ease of extension7)Total land area8)cost

DESIGN GUIDELINES CONTD

OPTIONS/ALTERNATIVES

1)Single sectionalised bus2)Main and transfer bus3)Sectionalised Main bus with transfer bus4)Sectionalised double main and transfer

bus5)Double Bus Scheme6)Ring bus7)One and a half breaker8)Double bus, double breaker

CONTD

DESIGN PRACTICES/PHYLOSOPHY

1) Consideration in Selection of BusSwitching Scheme

2) Comparison of Schemesa) Sectionalized main bus with transfer bus

(Scheme-I)

b) Sectionalized double main andtransfer bus (Scheme-II)

c) One and a half breaker (Scheme-III)

DISCUSSIONS OF SCHEMES

SCHEME 1

Main and Transfer Bus Scheme

SCHEMES CONTD

SCHEME 2

Sectionalised Double Main and Transfer Bus Scheme

SCHEMES CONTD

SCHEME 3

One and Half Breaker Bus Scheme

System Security(Reliability

i) feeder fault

ii) Bus fault

iii) Redundancy indesign

Main & Transfer

i) requireoperation ofone breakerii) supply wouldbe interrupteduntil all thefeeders aretransferred tothe healthy busiii) No alternatepath

(Offlineredundancyavailable)

Double Main &Transfer

i) requireoperation of

one breakerii) supply wouldbe interrupteduntil all thefeeders aretransferred tothe healthy busiii) No alternatepath

(Offlineredundancyavailable)

One & HalfBreaker

i)requireoperation oftwo breakersii) continuity ofsupply ismaintainedbecause eachcircuit gets fedthrough twopathsiii) Alternatepath isavailable(Onlineredundancyavailable)

OperationalFlexibility:

Simplicity ofProtectionArrangements

Ability to limitShort CircuitLevels (Ease ofSectionalizing)

Switching operationto take out thebreaker from the baymore extensive

Protectionarrangementinvolves AC & DCswitching .

Sectionalising ofbus bars orintroduction ofreactors in buseswith a view tolimit short circuitlevel is adoptable.

Switching operationto take out thebreaker from thebay more extensive

Protectionarrangementinvolves AC & DCswitching & busdifferentialprotection iscomplicated as itinvolves CTswitching.

Sectionalising ofbus bars orintroduction ofreactors in buseswith a view tolimit short circuitlevel is adoptable.

A breaker can betaken out of servicewithout the need foradditional switching

Protectionarrangement issimplified as noAC & DCswitching involveand Busdifferentialprotection issimple.

Sectionalising ofbus bars orintroduction ofreactors in buseswith a view tolimit short circuitlevel is adoptable.

Ease ofextension

Total land area

Cost

Switchyard shallbe suitable forfuture extensionwithout loss offeeders. Thisscheme isflexible for suchfuture additions

This schemeoccupy more orless the sameland area as ofthe other twoschemes.

one breaker perfeeder isrequired

Switchyard shallbe suitable forfuture extensionwithout loss offeeders. Thisscheme isflexible for suchfuture additions

This schemeoccupy more orless the sameland area as ofthe other twoschemes.

one breaker perfeeder isrequired

Switchyard shallbe suitable forfuture extensionwithout loss offeeders. Thisscheme isflexible for suchfuture additions

This schemeoccupy more orless the sameland area as ofthe other twoschemes.

Three breakerper 2 feeder isrequired

Switchyard layout

Objective:Substation layout consists essentially inarranging a number of switchgearcomponents in an orderly pattern governed bytheir function and rules of spatial separationas described in electrical single line diagram.

Pre-requisites:1) single line diagram2) general layout plan of power plant3) orientation of line evacuation4) control room building

LAYOUT CONTD

Options / AlternativesThe layout will vary for thefollowing:

1) Switching schemes2) Type of insulation - Air

Insulated/Gas Insulated.

LAYOUT CONTD

Design Philosophy / Practice

1) Space around the switchyard2) Switchyard location3) Switchyard fencing.

4) Clearance.i) phase to earth clearanceii) phase to phase clearanceiii) section clearanceiv) ground clearance

TABLE I: INSULATION LEVELS & CLEARANCEREQUIREMENTS AT DIFFERENT VOLTAGE LEVELS

NOMINALSYSTEMVOLTAGEKV

INSULATION LEVELS HIGHESTSYSTEMVOLTAGEKV

MINIMUM CLEARANCE GROUNDCLEARANCE(MM)

SECTIONALCLEARANCE(MM)

HEIGHTOFSUPPORTS (mm)LIGHTNING

IMPULSELEVEL(kVp)

SWITCHINGSURGELEVEL(kVp)

POWERFREQUENCYIMPULSELEVEL(kVrms)

BETWEENPHASEANDEARTH(MM)

BETWEENPHASES(MM)

3366132220400765

170325650

105014252100

-

-

-

-

10501550

70140275460630830

3672.5145245420800

3206301300210035006400

3206301300210040009400

37004000460055008000

--

2800300035004300650010300

250025002500250025002500

Clearance contd

5) Equipment spacinga) Ease of maintenance/removal of

equipment.b) Equipment foundation & their

cable trenches.c) Distance between LA and

equipment based on theprotection reach of LA.

d) The spacings are generally keptin order to achieve

various clearances specifiedat Table-I.

Clearance contd6) Bus bars:

The bus bars of 400 kV switchyard are generally made up 4 IPSaluminum tube or Quad Moose rated for 3000 A.The bus bars of 220/132kV switchyard are generally made up of 3 IPSaluminum tube or quad/ twin moose conductor. Bus bars are placed atright angles to the feeders for tapping the power.

7) Equipment Interconnection

8) Spacer spans and locations

9) Connection Level

10) Land & Road Layout

11) Sequence and mounting of line traps

Clearance contd.

12) Control Room Layout

13) Lighting System

14) Cabling Philosophy

15) Gravel Filling

16) Earthing System

17) Lightning Protection System

EVOLVING A SUBSTATIONLAYOUT

LAYING OUT A SUBSTATION INVOLVES STEP-BY-STEPPROCEDURE. MOST IMPORTANT POINTS TO BECONSIDERED ARE BRIEFLY DESCRIBED BELOW:

THE IMPORTANT ELECTRICAL PARAMETERS AREESTABLISHED BY THE SYSTEM DESIGN. THE MAINPARAMETERS ARE:

1) THE VOLTAGE AND BASIC INSULATION LEVEL ORSWITCHING SURGE LEVEL., THE SITE AND CLIMATICCONDITIONS, THE METHOD OF CIRCUIT CONNECTION,AND SWITCHING OVER-VOLTAGE CONDITIONS.

2) THE BUS BAR SYSTEM DIAGRAM, THE NUMBER OFCIRCUITS AND THEIR PURPOSE I.E. THE CONTROLOF GENERATORS, TRANSFORMERS, FEEDERS, ETC.

THE DIAGRAM SHOULD INCLUDE DETAILS OFEXTENSIONS AND FUTURE CONVERSION TO ADIFFERENT BUS BAR SYSTEM, IF INTENDED.

EVOLVING A SUBSTATIONLAYOUT

1) THE CONTINUOUS CURRENT RATING OF THE BUS BARSAND CIRCUITS.

2) THE SHORT CIRCUIT RATING OF BUS BARS ANDEQUIPMENTS.

3) PARTICULARS OF REACTORS, NEUTRAL EARTHINGEQUIPMENT AND REACTING, InterconnectingTransformers REQUIRED.

4) METHOD OF CONNECTION OF CIRCUITS, WHETHER BYOVERHEAD LINES OR BY CABLES.

5) DETAILS OF LIGHTNING PROTECTION EQUIPMENT.

6) DETAILS OF PROTECTIVE EQUIPMENT, DETERMININGTHE INSTRUMENT TRANSFORMERS REQUIREMENTS,CARRIER CURRENT EQUIPMENT ETC.

EVOLVING A SUBSTATIONLAYOUT

THE EXTENT TO WHICH CIRCUIT AND BUSBAR OUTAGES FORMAINTENANCE WILL BE POSSIBLE.

SOME PARAMETERS WHICH INFLUENCE THE FORM OF THELAYOUT ARE DETERMINED BY THE LOCAL CONDITIONS. THESEARE:

1) THE AVAILABLE LAND AREA, SITE AND CLIMATECONDITIONS, PLANNING AUTHORITY REQUIREMENTS ANDAESTHETIC CONSIDERATIONS DETERMINE THE TYPE OFSUBSTATION.

2) THE DIRECTION OF OVERHEAD LINE ENTIRES POSITIONAVAILABLE FOR TERMINAL TOWERS, LOCATION OFTRANSFORMERS AND REACTORS, ETC.

3) THE AVAILABILITY OF MATERIALS AND THE TRANSPORTAND ACCESS FACILITIES.

4) THE CAPABILITY AND SKILL OF THE MAINTENANCE STAFFDETERMINES THE IMPORTANCE OF CLARITY OF LAYOUTAND SIMPLICITY OF MAINTENANCE ZONING.

PREPARATION OF BASICLAYOUT

WHILE MEETING ALL THE NEEDS ESTABLISHED THEFOLLOWING IDEALS SHOULD BE AIMED AT IN MAKING THEBASIC CIRCUIT LAYOUT.

MINIMUM GROUND AREA

MINIMUM QUANTITIES OF CONDUCTOR, JOINTS ANDSTRUCTURE

MINIMUM NUMBER OF INDEPENDENT INSULATORS,ESPECIALLY IN THE BUS BAR ZONE.

AFTER HAVING DETERMINED THE ELECTRICAL CLEARANCE BEUSED A ROUGH CIRCUIT LAYOUT IS MADE. SEVERALPOSSIBLE ALTERNATIVES ARE PREPARED FROM WHICH THEMOST SUITABLE ONE WILL BE SELECTED. SOME VARIATIONIS NEEDED, TO MEET THE REQUIREMENTS OF DIFFERENTTYPES OF CIRCUIT.

IT IS ALSO NECESSARY TO CALCULATE SHORT CIRCUIT ANDATMOSPHERIC FORCES TO DETERMINE THE STRESSES INCONDUCTORS, INSULATORS AND STRUCTURES. THESE HELDIN DECIDING THE MOST OPTIMUM DIMENSIONS.

PURPOSE OF EARTHING

THE OBJECT OF EARTHING IS TO MAINTAIN ALOW POTENTIAL ON ANY OBJECT.

THE PURPOSE OF A EARTHING SYSTEM IN ASUBSTATION AREA IS TO LIMIT THE POTENTIALGRADIENT WITHIN AND IMMEDIATELY OUTSIDETHE AREA IS A VALUE, SAFE FOR THE WORKINGPERSONNEL. SAFETY IS TO BE ENSURED UNDERNORMAL AS WELL AS ABNORMAL OPERATINGCONDITION.

REQUIREMENTS OF A GOODEARTHING SYSTEM

FOLLOWING BASIC REQUIREMENTS ARE TO BE SATISFIED SO AS TOENSURE A PROPER AND SOUND EARTHING SYSTEM.

1) THE EARTH RESISTANCE FOR THE SWITCHYARD AREASHOULD BE LOWER THAN A CERTAIN LIMITING VALUERA IN ORDER TO ENSURE THAT A SAFE POTENTIALGRADIENT IS MAINTAINED IN THE SWITCHYARD AREAAND PROTECTIVE RELAY EQUIPMENT OPERATESATISFACTORILY. FOR MAJOR SWITCHYARDS ANDSUBSTATIONS IN INDIA, THIS LIMITING VALUE OF EARTHRESISTANCE (RA) IS TAKEN TO BE LESS THAN 0.5 OHM.

2) THE GROUNDING CONDUCTOR MATERIAL SHOULD BECAPABLE OF CARRYING THE MAXIMUM EARTH FAULTCURRENT WITHOUT-OVERHEATING AND MECHANICALDAMAGE. THE MAXIMUM FAULT LEVEL IN THE 400 KVSYSTEM HAS BEEN ESTIMATED TO BE 40 KA AND THISVALUE OF FAULT CURRENT TO USED IS THE DESIGN OFEARTH MAT FOR THE 400 KV SUBSTATION.

REQUIREMENTS OF A GOODEARTHING SYSTEM ALL METALLIC OBJECTS WHICH DO NOT CARRY

CURRENT AND INSTALLED THE SUBSTATION SUCHAS STRUCTURES, PARTS OF ELECTRICALEQUIPMENTS, FENCES, ARMOURING AND SHEATHSOF THE LOW VOLTAGE POWER AND CONTROLCABLES SHOULD BE CONNECTED TO THEEARTHING ELECTRODE SYSTEM.

. THE DESIGN OF THE GROUND CONDUCTOR

SHOULD TAKE CARE OF THE EFFECT OFCORROSION FOR THE TOTAL LIFE SPAN OF THEPLANT.

Switchyard Equipments.

Circuit Breaker. Disconnectors (Isolators) Current Transformers. Capacitor Voltage Transformers

(CVT). Lightning Arrestors. Post Insulators. Wave Traps

General Parameters

Dielectric Parameters .(IEC 694)- Power Frequency Voltage.- Lightning Impulse Voltage.- Switching Impulse Voltage.- Corona Extinction Voltage.- RIV Level.

General Parameters (Contd.)

Rated Current. Short Time Current. Creepage Distance.

400kV Equipmentsa. Rated voltage 420 kVb. Rated frequency 50 Hzc. Rated short time withstand

current capacity40 kA rms for one (1) second

d. Insulation levels for 420kV Circuitbreakers and DisconnectingSwitches

e. i) Rated one minute powerFrequency withstand voltage

a) 520 kV rms between liveterminals and earth.

b) 610 kV rms across isolatingdistance.

ii) Rated lightning impulsewithstand voltage

a) +/- 1425 kVp between live terminalsand earth.

b) +/- 1425 kVp impulse on oneterminal and 240 kVp powerfrequency of opposite polarity onother terminal (across isolatingdistance).

iii) Rated switching impulsewithstand voltage

a) +/- 1050 kVp between liveterminals and earth.

b) +/- 900 kVp impulse on oneterminal and 345 kVp powerfrequency of opposite polarity onother terminal (across isolatingdistance).

f. Max. Radio interference voltageat 266kVrms

1000 micro volts for frequencybetween 0.5 Mhz and 2.0 Mhz for allequipment. However, for insulatorstrings the measurement would beat 305 kV .

g. Corona extinction voltage Not less than 320 kV rms

Circuit Breakers Type (IEC: 62271-100)

MOCB. ABCB. SF6

Rated operating duty cycle- O-0.3 sec-CO-3 min.-CO

Operating mechanism Total Break Time Pre Insertion Resistor ( 300-450)

Disconnectors

HCB Type. Double Break Type. Pantograph type. Vertical Break type. Provision of Earth Switches. Motor / manual operated. Gang operated/Single pole type.

Current Transformer ( IEC 60044, IS2705)

Dead tank/Live tank type. Bar Primary type. Ring Type. No. of Cores. Ratio. Accuracy. rated primary current Rated burden for metering Knee Point voltage

Capacitor Voltage Transformer (IEC60044, IS 3156)

Capacitance. Voltage Ratio. No. Of Cores. Accuracy. Output Burden Rated Secondary Voltage

Lightning Arrestor ( IEC 60099)

Gap Type / Gapless Type. Voltage Rating. Energy Capability. Monitoring. Location. Nominal Discharge Current.

Post Insulators

Voltage Rating. Cantilever Strength. Fixing Details.

Wave Trap (IEC 60353)

Rated Inductance(0.5/1.0 mH). Rated current. Band Width. Coupling (Phase to Phase).

SWITCHYARD AUXILIARY SYSTEMS

CONTROL ROOM HVAC FOR CONTROL ROOM A RELIABLE 415V AC SUPPLY ( LT SWGR) 220 V & 48 V DC SUPPLY( BATTERY &

BATTERY CHARGER) POWER & CONTROL CABLE LIGHTING ( Yard lighting & indoor lighting of

control room) Other items-Clamps, connectors , Insulator strings ,

BMK etc.

192

69 ~10%400kV GIS

275kV GIS

Trfr 1 Trfr 2 Trfr 3 Trfr 4 SVC Trfrs

400kV AIS

275kV AIS

COMPARASON BETWEEN AIS AND GIS SUBSTATIONFOOTPRINT FOR HECTOR

INDOOR GIS

OUTDOOR GIS - SEISMIC AREAS

ConductorPhase Spacing

PHASE SPACING

OVERHEAD STRUNG BUSBARS

9,81.mi

fs

SAG DUE TO CONDUCTOR

fs = 9,81.mi.Lc28.T

fs = maximum conductor sag (m)

mi = mass of conductor (kg/m)

Lc = conductor span length (m)

T = tension per conductor (N)

T

Lc

LOW PROFILE SUPPORTED TUBULAR BUSBAR SUBSTATIONS

TUBE SAG EXCESSIVE INCORRECTLY SELECTED

TYPICAL TUBULAR BB BUS SECTION BAY

MMM

Attraction Repulsion

CANTILEVER FORCES DUE TO FAULT CURRENTCOMBINATION SUPPORT STRUCTURE FOR 3 PHASES

F S

TUBE

TUBULAR BUSBAR EXPANSION CLAMP

TRANSFORMER FIRE AT MINERVA

Upgradation of transmission voltagefrom 400kV AC to 765kV AC.

Presently the highest AC Transmission voltage is 400kV only.NTPC is fully geared up for implementing next AC voltage of765kV.

Advantages: Step up from generation voltage to 765kV. High Capacity Transmission to the order of 2500MW per line

with lower right of way requirement. 765kV Transmission system is techno economically better

option whenever power transmission system requires multipoint tapping at various location for catering the loadrequirement of high growth area.

765kV system offers low transmission losses, resulting inhigher utilisation of generating capacity and optimises theresource required for capacity addition.

765kV Major Parameters

Highest system voltage : 800 kV rms Lightning Impulse voltage : 2100 kVp Switching impulse voltage : 1550 kVp Power frequency withstand : 830kV(rms) for 1 min. (rms) : Max. fault level (1 sec.) : 40 kA Minimum creepage distance : 20000 mm Max. Radio Interference Voltage : 2500 micro volts. level at 508kV (rms). Corona extinction voltage : 508kV (rms minimum) Phase to earth clearance : 4900 mm Conductor to

Structure : 6400 mm Rod to

Structure Phase to phase clearance : 7600 mm Conductor to

Conductor : 9400 mm Rod to Conductor Section clearance : 10300 mm Average electric field at 1.8 m from ground 10kV/m Average magnetic field 500 micro tesla

((((

ADOPTION OF CONTROLLED SWITCHING OF TRANSFORMER ANDREACTORS.

Switching of transformer, shunt reactors, capacitors and uncharged overheadlines is normally a 'three-phase' process, where all three phases are switchedsimultaneously. The actual circuit closing or opening instant is left up tochance. This results in high inrush currents or switching surges causing unduerepercussions to switchgear equipment and networks system. For overcomingthis the switching in and out is done at desired point on wave so that theovervoltages are reduced.

765KV CIRCUIT BREAKER

765KV DISCONNECTOR WITH 1E/S

THANK YOU!