1

WELCOMES ALL OF YOU

2

Bus Switching Scheme& Substation Layout

K K Sarkar (E_mail:kksarkar95@gmail.com)

Chief Design Engineer (Engg-s/s)

Power Grid Corporation of India

3

Important considerations in layout..

Reliability and Security

- Selection of Bus Scheme

- Ease of Maintenance

- Operational Flexibility

Short Circuit Level

Shape of the land

Altitude of the land above mean sea level

Feeder orientation

Safety of Equipment and personnel

Possibility of future expansion

Cost

4

Bus Switching Schemes…

Single Main Scheme

Double Main Scheme

Single Main & Transfer Scheme

Double Main with by-pass isolator scheme

Double Main & Transfer Scheme

One & Half Breaker Scheme

Double breaker Scheme

Ring Bus Scheme

5

Simplest and cheapest bus bar scheme

Maintenance and extensions of busbars are not possible without shutdown of the substation.

Operation & maintenance of bus bar is easy.

SINGLE BUS SCHEME

6

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

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

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

SINGLE MAIN AND TRANSFER SCHEME

7

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

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

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

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

DOUBLE BUS SCHEME

8

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

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

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

DOUBLE BUS WITH BY-PASS SCHEME

9

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

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

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

DOUBLE MAIN AND TRANSFER SCHEME

10

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

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

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

ONE AND HALF BREAKER SCHEME

11

Each feeder is controlled by two breakers.

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

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

DOUBLE BUS TWO BREAKER SCHEME

12

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

Extension of ring scheme is difficult.

No bus bar protection required.

RING BUS SCHEME

13

Selection 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

14

Important considerations in layout..

Reliability and Security

- Selection of Bus Scheme

- Ease of Maintenance

- Operational Flexibility

Short Circuit Level

Shape of the land

Altitude of the land above mean sea level

Feeder orientation

Safety of Equipment and personnel

Possibility of future expansion

Cost

15

Bus Bar Design, Selection of conductor 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 circuit

Stresses in tubular bus

Cantilever Strength of post insulator

Deflection of the tube

Natural frequency of tubular bus bar

Aeolian Vibration

16

Bus Bar Design & Selection of conductor levels..

Electrical Clearances (IEC-60071)

Corona

Electric Field (10kV/m)& Magnetic Field (500μT)

Short Circuit Forces (IEC-60865)

Sag-Tension Calculation

Normal Tension (Factor of safety 2.0) and Short Circuit Tension (Factor of Safety 1.5)

Height of conductor levels

Bay width & Phase to Phase spacing

17

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

Voltage Level

(Rated)

Ph-Ph

(m)

Ph-E

(m)

Sectional

Clearance

(m)

BIL

(kVp)

SIL

(kVp)

765 kV 7.6

(cond-cond)

9.4

(rod-str)

4.9

(cond-str)

6.4

(rod-str)

10.3 2100 1550

400 kV 4 3.5 6.5 1550 1050

220 kV 2.1 2.1 5 1050 650

18

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

Voltage Level (Rated)

Ph-Ph

(mm)

Ph-E

(mm)

Sectional

Clearance

(mm)

132 kV 1300 1300 4000

110 kV 1100 1100 3800

66 kV 630 630 3500

33 kV 320 320 2800

Altitude corrections w.r.t clearances, insulation levels, creepage and oil

temperature rise of the equipment shall be considered for altitudes more

than 1000 m above mean sea level.

19

Bay widths & levels…

Voltage Level

Bay width

First Level

Second Level

Third level

BIL SIL

400 kV 24m 8m 15m 22m 1550 1050

220 kV 16m 5.9m 11.7m 16.2m 1050 650

132 kV 12m 4.6m 8m 12m 650 NA

66 kV 7.6m 4m 6m 9.5m 325 NA

20

Type of Isolator & Structure in Layout

Type of Isolator Horizontal Centre Break Isolator (HCB)

Horizontal Double Break Isolator (HDB)

Pantograph Isolator (Panto)

Vertical Break Isolator (VB)

Staggered

Type of Structure Pie (╥) structure

Enclosed (Π) structure

21

Height of shield wire, Height & Location of 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 Potential

Step Potential

Grid Resistance

Earth Potential Rise (EPR)

22

Location of other buildings, auxiliaries..

Control Room

Fire fighting pump house (FFPH)

DG set

LT station placement

Roads & rail tracks

Switchyard Panel Room

Open Store

Colony and other infrastructures

23

SLD & LAYOUT (PLAN) -400kV D type layout

24

LAYOUT (SECTIONS) -400kV D type layout

25

SINGLE LINE DIAGRAM -220kV DMT layout

26

LAYOUT (PLAN) - 220kV DMT layout

27

LAYOUT (SECTIONS) - 220kV DMT layoutTransformer Bay

28

LAYOUT (SECTIONS) - 220kV DMT layout220kV Line Bay

29

LAYOUT (SECTIONS) - 220kV DMT layout220kV TBC Bay

30

LAYOUT (SECTIONS) - 220kV DMT layout220kV Bus Coupler Bay

31

LAYOUT (PLAN) -400kV I-type layout

32

LAYOUT (SECTIONS) - 400kV I-type layout

33

N 4

775.

0

N 4

800.

0

N 4

825.

0

N 4

850.

0

N 4

875.

0

N 4

900.

0

N 4

925.

0

N 4

950.

0

N 4

975.

0

N 5

000.

0

N 5

025.

0

N 5

050.

0

N 5

075.

0

N 5

100.

0

N 5

125.

0

N 5

150.

0

N 5

175.

0

N 5

200.

0

N 5

225.

0

N 5

250.

0

N 5

275.

0

N 5

300.

0

N 5

325.

0

N 5

350.

0

N 5

375.

0

5000.0 E

5025.0 E

5050.0 E

5075.0 E

5100.0 E

5125.0 E

5150.0 E

5175.0 E

5200.0 E

5225.0 E

5250.0 E

5275.0 E

5300.0 E

5325.0 E

5350.0 E

5375.0 E

5400.0 E

N 4

750.

0

4975.0 E

30

1. ALL DIMENSIONS ARE IN METRE UNLESS SPECIFIED.

2. LOCATION OF ALL BUILDINGS ARE INDICATIVE.

3. ROUTE OF APPROACH ROAD IS INDICATIVE ONLY. THE SAME SHALL BE DECIDED BY SITE.

400 kV M

AIN

BU

S - II

PRESENT SCOPE

FUTURE

FOR TENDER PURPOSE ONLY

400 kV M

AIN

BU

S - I

GA Drawing of 400/132kV Substation

34

A. DSLP by Lightning Mast

0.2h

h

2h/3

hx rx

0.75h 0.75h

1.5h 1.5h

rx

Fig. 2 (a) : Zone of Protection for single lightning mast

35

Zone protected by two lightning mast around themselves

R

a c

b 0.2h

h

hox rx

hx

a 0.75h

1.5h

rx

Box

rx

Fig. 2.(b): Zone of protection for two lightning masts

Where R is the circumradius of the triangle formed by a, b & c.

36

Calculation of overlappings (Bx) :

Bx=1.5.hox.px( 1-(hx/0.8hox)) if hx<2/3rd of hox

Bx=0.75.hox.px.( 1-(hx/hox)) if hx>2/3rd of hox

where,

h is the height of the lightning mast/tower including peak

hox is the maximum hight protected is given by, hox=h-(a/7p)

a is the distance Lightning Masts / Tower Peaks

hx is the maximum height of the objects to be protected from side strokes

px= 5.5/sqrt(hox) if hox>30.0 m

px= 1.0 if hox<30.0 m

DSLP Calculation

37

PROTECTION ZONE OF THREE LIGHTNING MAST

LM1

Bx

a1

D

a3

LM2 LM3

a2 rx

38

Zone protected by three(3) lightning masts :

The condition that the area among the three (3) lightning masts

at a level 'hx' will be protected is given as :

D <= 8(h-hx)p

where,

D is the circumdiameter of the triangle formed

by the three lightning masts.

D=a1 /sin{arccos((a22+a3

2-a1

2)/2a2a3)}

DSLP Calculation

39

LIGHTNING PROTECTION BY OVERHEAD SHIELD WIRES:

0.2h

h

2h/3

hx bx

0.6h 0.6h

1.2h 1.2h

2bx

Fig : Protective Zone of a ground/ shield wire

40

The breadth of the protective zone offered by a single shield

wire on the ground level in a plane perpendicular to the shield

of wire is equal to 1.2 h , where h is the height suspension

of the shield wire.

Half the breadth of the protective zone "bx" at level hx is given by:

bx=1.2 h ( 1-(hx/0.8h)) if hx<2/3rd of h

bx=0.6 h ( 1-(hx/h)) if hx>2/3rd of h

where,

h is the height of the tower including peak

hx is the height of the objects to be protected

from side strokes

DSLP Calculation

41

The radius of protective zone offered by a lightning mast at height "hx"

from ground level is given by:

rx=1.5hp( 1-(hx/0.8h)) if hx<2/3rd of h

rx=0.75hp( 1-(hx/h)) if hx>2/3rd of h

where,

h is the height of the lightning mast/tower including peak

hx is the height of the objects to be protected from side strokes

p= 5.5/sqrt(h) if h>30.0 m

p= 1.0 if h<30.0 m

DSLP Calculation

42

POWERGRID 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

43

POWERGRID 220 kV STANDARD LAYOUT

Bus Scheme adopted : Double Main & Transfer Scheme Scheme

First (Equipment Level)- 5.9m

Second Level (Main Bus) – 11.7m

Third Level (Jack Bus) – 17.2m

Bay Width – 16m

Main Bus : Quad ACSR Moose

Main Bus Span: 48m

Equipment Interconnection: 4” IPS Al tube

Normal Tension for gantry Structure: 4T/phase or 2T/Phase

Normal 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

44

THANKS FOR

LISTENING