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POWERGRID Practices in EHV POWERGRID Practices in EHV Substation LayoutSubstation Layout

K K SarkarDy. Chief Design Engineer (Engg-s/s)Power Grid Corporation of India

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Important considerations in layout..Important considerations in layout..Reliability and Security- Selection of Bus Scheme- Ease of Maintenance- Operational FlexibilityShort Circuit LevelShape of the land Altitude of the land above mean sea level Feeder orientation Safety of Equipment and personnel Possibility of future expansionCost

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Bus Switching SchemesBus Switching Schemes……

Single Main SchemeDouble Main Scheme Single Main & Transfer SchemeDouble Main with by-pass isolator schemeDouble Main & Transfer SchemeOne & Half Breaker SchemeDouble breaker SchemeRing Bus Scheme

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Simplest and cheapest Simplest and cheapest bus bar schemebus bar schemeMaintenance and Maintenance and extensions of busbars are extensions of busbars are not possible without not possible without shutdown of the shutdown of the substation.substation.Operation & maintenance Operation & maintenance of bus bar is easyof bus bar is easy.

SINGLE BUS SCHEMESINGLE BUS SCHEME

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Individual CB can be taken out for Individual CB can be taken out for maintenance onmaintenance on--load at a time.load at a time.

The transfer bus coupler acts as the The transfer bus coupler acts as the breaker for the circuit under by breaker for the circuit under by pass.pass.

Individual circuits have a bypass Individual circuits have a bypass isolator to connect to the transfer isolator to connect to the transfer bus and this isolator will be closed bus and this isolator will be closed during bypass operation of that during bypass operation of that particular circuit.particular circuit.

SINGLE MAIN AND TRANSFER SCHEMESINGLE MAIN AND TRANSFER SCHEME

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Load will be distributed on both the buses Load will be distributed on both the buses and the bus coupler shall be normally and the bus coupler shall be normally closed.closed.

For maintenance & extension of any one of For maintenance & extension of any one of the buses the entire load will be transferred the buses the entire load will be transferred to the other bus.to the other bus.

On load transfer of a circuit from one bus to On load transfer of a circuit from one bus to the other bus is possible through bus the other bus is possible through bus isolators provided the bus coupler is closed isolators provided the bus coupler is closed and thereby two buses are at the same and thereby two buses are at the same potential.potential.

On load bypassing of any circuit for breaker On load bypassing of any circuit for breaker maintenance is not possiblemaintenance is not possible.

DOUBLE BUS SCHEMEDOUBLE BUS SCHEME

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This bus arrangement provides This bus arrangement provides the facilities of a double bus the facilities of a double bus arrangement & a main and arrangement & a main and transfer bus arrangement.transfer bus arrangement.

The bus to which the transfer The bus to which the transfer bus isolator is connected can be bus isolator is connected can be used as a transfer bus also.used as a transfer bus also.

During the time a circuit is During the time a circuit is under bypass, the bus coupler under bypass, the bus coupler will act as the breaker for the will act as the breaker for the bypassed circuit.bypassed circuit.

DOUBLE BUS WITH BYDOUBLE BUS WITH BY--PASS SCHEMEPASS SCHEME

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In this bus scheme, in addition to In this bus scheme, in addition to the two main buses there will be a the two main buses there will be a separate transfer bus also. separate transfer bus also.

Since separate transfer bus is Since separate transfer bus is available there will be no need of available there will be no need of transferring the load from one bus transferring the load from one bus to the other bus unlike in a double to the other bus unlike in a double main cum transfer bus main cum transfer bus arrangement.arrangement.

Other features are similar to the Other features are similar to the one described in double bus with one described in double bus with by pass arrangement.by pass arrangement.

DOUBLE MAIN AND TRANSFER SCHEMEDOUBLE MAIN AND TRANSFER SCHEME

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In this scheme, two circuit have three In this scheme, two circuit have three breakers, the middle breaker ties the breakers, the middle breaker ties the two circuits and hence is called the tie two circuits and hence is called the tie breaker. breaker.

Breaker or bus maintenance is Breaker or bus maintenance is possible without any shut down of the possible without any shut down of the feederfeeder

Even if both the buses are out of Even if both the buses are out of service, power can be transferred from service, power can be transferred from one feeder to another feeder through one feeder to another feeder through tie breakertie breaker

BREAKER AND HALF SCHEMEBREAKER AND HALF SCHEME

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Each feeder is controlled by two Each feeder is controlled by two breakers.breakers.

This arrangement is This arrangement is comparatively costlier than other comparatively costlier than other scheme and hence followed in scheme and hence followed in very important circuit only. very important circuit only.

In this arrangement breaker In this arrangement breaker maintenance for any feeder maintenance for any feeder circuit is easily possible without circuit is easily possible without any shutdownany shutdown..

DOUBLE BUS TWO BREAKER SCHEMEDOUBLE BUS TWO BREAKER SCHEME

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As long as the ring is closed load As long as the ring is closed load has two sources of supply and has two sources of supply and any circuit breaker can be taken any circuit breaker can be taken out of service without affecting out of service without affecting the supply.the supply.

Extension of ring scheme is Extension of ring scheme is difficult.difficult.

No bus bar protection requiredNo bus bar protection required..

RING BUS SCHEMERING BUS SCHEME

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Selection of Switching SchemesSelection of Switching Schemes……

No reliability in Single Main, Double Main, Single Main & Transfer Scheme w.r.t bus fault, feeder fault & breaker maintenance Double Main & Transfer Scheme, One & Half Breaker Scheme & Double breaker Scheme are characterized by reliable and interruption free supply.One & half breaker scheme can be selected for EHV substations due high reliability, operational flexibility, ease of maintenance, ease of expansion, due consideration of cost

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Bus Bar Design, Selection of conductor Bus Bar Design, Selection of conductor levels & Bay width calculation..levels & Bay width calculation..

Selection of conductor (AAC, ACSR, Tube)Current Carrying capacity with temperature rise of 35 deg.C over ambient of 50deg.C ambient (IEEE-738) Temperature Rise during short circuitStresses in tubular bus Cantilever Strength of post insulatorDeflection of the tubeNatural frequency of tubular bus barAeolian Vibration

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Bus Bar Design & Selection of conductor Bus Bar Design & Selection of conductor levels..levels..

Electrical Clearances (IEC-60071)Corona Electric Field (10kV/m)& Magnetic Field (500μT)Short Circuit Forces (IEC-60865) Sag-Tension CalculationNormal Tension (Factor of safety 2.0) and Short Circuit Tension (Factor of Safety 1.5)Height of conductor levelsBay width & Phase to Phase spacing

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Minimum Clearances for Layout (at altitude Minimum Clearances for Layout (at altitude <1000m above mean sea level)<1000m above mean sea level)……

6501050

1550

SIL(kVp)

10501550

2100

BIL(kVp)

566.5500

10.3

SectionalClearance

(m)4.9

(cond-str)6.4

(rod-str)

7.6 (cond-cond)

9.4 (rod-str)

765 kV

2.12.1220 kV3.54400 kV

Ph-E(m)

Ph-Ph(m)

Voltage Level

(Rated)

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Type of Isolator & Structure in LayoutType of Isolator & Structure in LayoutType of Isolator

Horizontal Centre Break Isolator (HCB) Horizontal Double Break Isolator (HDB) Pantograph Isolator (Panto) Vertical Break Isolator (VB)Staggered

Type of Structure Pie (╥) structureEnclosed (Π) structure

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Height of shield wire, Height & Location of Height of shield wire, Height & Location of LM & Location of Fence..LM & Location of Fence..

DSLP Calculation to decide the height of shield wire and/or Height & location of LM

Rolling Sphere Method (IEEE-998)Razevig Method

Earthmat Design (IEEE-80/CBI&P Report No. 302) – Location of switchyard fence

Touch PotentialStep PotentialGrid ResistanceEarth Potential Rise (EPR)

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Location of other buildings, auxiliaries..Location of other buildings, auxiliaries..

Control RoomFire fighting pump house (FFPH)DG set LT station placement Roads & rail tracks Switchyard Panel RoomOpen Store Colony and other infrastructures

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MethodologyMethodology –– SoilSoil EffectEffect

-QL

H

+QL

H

+VL

-VL

R

D

E

SOIL

∑=

⎟⎟

⎠

⎞

⎜⎜

⎝

⎛+εΠ

⋅−==

DDT

Y

R

220

L

2

DD

EE

a

DH2

H2QQFE

2

rr

r

43421

rr

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Electric Field CalculationElectric Field Calculation

R Q2

FR

QL

VL

SOURCE

QL = CHARGE PER UNIT LENGTH

+

( )

m/F10x85,8ttanconstypermittivi

aR2

QQFE

EFIELDELECTRIC

120

Ro

L

2

R

−==ε

εΠ==

rr

r

r

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[QL] = [C] [V]

QL = CHARGE / UNIT LENGTH

C = CAPACITANCE BETWEEN CONDUCTORS AND SOIL

= f (εo , H, d, D i j)

V = APPLIED VOLTAGE

MethodologyMethodology –– Charge Charge calculationcalculation

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MethodologyMethodology –– 3 phase 3 phase BusbarBusbar

CAPACITANCE CALCULATION

i' j' k'

i j k

[ ] [ ][ ][ ] [ ]

⎥⎥⎦

⎤

⎢⎢⎣

⎡

εΠ=Ρ

⋅=

⎥⎥⎦

⎤

⎢⎢⎣

⎡

εΠ=Ρ

⇒

=

′

−

jiDD

ln2

1

DdnDd

dH4ln

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PC

VCQ

ij

0ij

neqeq

x

0ii

1

∑=

=3

1iix EErr

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yl

dlr

dBxz

A wire with length (l) having a current I produces in the air a flux density dB and a magnetic field dH

µ0 = magnetic permeability of free space= 4 π ⋅ 10 -7 H/m

B = Magnetic flux density or magnetic induction= V ⋅ s/m2 or wb/m2 or tesla

H = Magnetic field strength= A/m

MethodologyMethodology –– MagneticMagnetic fieldfield calculationcalculation

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MethodologyMethodology –– MagneticMagnetic fieldfield attenuationattenuation

Single conductor with earth return magnetic field decreases as 1/rSystem of parallel conductors energized by a balanced current magnetic field decrease as 1/r2 (r » distance between conductors)Localized source (ex.: power transformer) magnetic field decrease as 1/r3 (r» transformer dimensions)H is a three-dimensional field in space. If source can be considered infinitely long the field component in the direction of the line is negligible

H(x, y)

y

I x

( )

( )

yi

3

1iy

xi

3

1 ix

22y

22x

HH

HH

yxx

2IH

yxy

2IH

=

=

+Π=

+Π−

=

∑

∑

=

=

r

r

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⎟⎟⎠

⎞⎜⎜⎝

⎛

⋅+⋅⋅⋅=

cc r

KEmEδ

δ 10

Corona Corona OnsetOnset gradientgradient

Where surface factor m is a constant

m = 1 Sleek and clean cylindrical conductor0.75 < m < 0.85 Stranded conductors

0.6 < m < 0.8 Presence of dust, irregularities0.3 < m < 0.6 Presence of moisture, snowflakes or heavy fog

m = 0.2 Presence of major pollution or accumulation of deposit

E0 and K are empirical constants depending on the nature of the applied voltage.

E0 = 29.8 kV peak / cm = 21.1 kV rms / cm for AC according to Peek [3]K = 0.301 For parallel conductorsK = 0.308 For concentric conductors

rc = Conductor radius in centimeter

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Corona Corona onsetonset gradient (gradient (ContCont’’dd))

The air pressure can be corrected as a function of the altitude

Where

A = Altitude in kmK = 10.7 (Linear approximation of published experimental data)

δ = 1.00 Temperature = 25 °C, Altitude = Sea levelδ = 0.94 Temperature = 25 °C, Altitude = 600 mδ = 0.87 Temperature = 50 °C, Altitude = 600 m

KA

pp

−= 10

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POWERGRID 400 kV STANDARD LAYOUTPOWERGRID 400 kV STANDARD LAYOUT

Bus Scheme adopted : One & Half Breaker SchemeLayout : I-TypeFirst (Equipment Level)- 8mSecond Level (Main Bus) - 15mThird Level (Jack Bus) – 22mBay Width – 24mMain Bus : Quad ACSR Bersimis/Quad AAC BULLMain Bus Span: 48mEquipment Interconnection: 4” or 4.5” IPS Al tubeNormal Tension for gantry Structure: 4T/phaseNormal Tension for O/H shield wire: 0.8T, 10.98mm dia GS

wire (7m peak)Fault Level: 40kA/50kA/63kA (1 sec)Cantilever Strength of Post Insulator : 800 kg

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POWERGRID 220 kV STANDARD LAYOUTPOWERGRID 220 kV STANDARD LAYOUT

Bus Scheme adopted : Double Main & Transfer Scheme SchemeFirst (Equipment Level)- 5.9mSecond Level (Main Bus) – 11.7mThird Level (Jack Bus) – 17.2mBay Width – 16mMain Bus : Quad ACSR MooseMain Bus Span: 48mEquipment Interconnection: 4” IPS Al tubeNormal Tension for gantry Structure: 4T/phase or 2T/PhaseNormal Tension for O/H shield wire: 0.8T, 10.98mm dia GS wire

(5m peak)Fault Level: 40kA/50kA (1 sec)Cantilever Strength of Post Insulator : 800 kg

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THANKS THANKS FORFOR

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