400kv substation design

8/11/2019 400kV Substation Design

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INTRODUCTION

An electrical substation is a part of an electricity generation,transmission and distribution system where voltage istransformed from high to low or in reverse using transformers.It also serves as a point of connection between various powersystem elements such as transmission lines, transformers,generators and loads. To allow for exibility in connecting theelements, circuit breakers are used as high power switches.Electric power may ow through several substations betweengenerating plant and consumer, and may be changed involtage in several steps. There are dierent kinds of substationsuch as Transmission substation, distribution substation,collector substation, switching substation and some other typesof substation. The general functions of a substation mayinclude!

voltage transformation connection point for transmission lines switchyard for network con"guration monitoring point for control center protection of power lines and apparatus #ommunication with other substations and regional control

center

The "rst step towards the design of a $%%&''%&()' *+

substation is to determine the load that the substation has to

cater and develop it accordingly. The substation is responsible

for catering bulk power to various load centres distributed all

around through ''% *+ and ()' *+ substations. The substation

is fed ()( - power from ) generating stations A,/,# through

$%% *+ single circuit lines working at around 012 loading. The

power is received on $%% *+ busbar 3double main and transferbus scheme4. ) - power is dispatched to a $%% *+

substation 5a6 catering an area having diversity factor (.(

through $%% *+ double circuit lines working at 1%2 loading.

The remaining 0% - is fed to three )(7 -+A 38) x

(%7 -+A units4 autotransformers working at an average 0%2

loading and %.9 power factor. The )(7 -+A transformers step

down the voltage from $%% *+ to ''% *+. 2 of the input power0% - i.e. around $% - power is lost in the transformers.


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The rest i.e.$% - is fed to the ''% *+ busbar 3double main

and transfer bus scheme4. To increase the reliability of the

system the ''% *+ busbar is also fed from ' other substations.

A single circuit line from station E working at 02 loading

supplies 07 - while a double circuit line from station :

working at 1%2 loading supplies (17 - power to the busbar.

This ensures continuity of supply to certain extent even when

an entire )(7 -+A transformer unit fails to operate. Thus total

incoming power on ''% *+ bus is 3$%;(17;07 849%% -.


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purposes within the substation to ensure its smooth

functioning.

To compensate for any reactive power de"cit or tobalance excess reactive power of lightly loaded lines ?tatic

+A@ #ompensators 3?+#s4 are used.

SURGE IMPEDENCE :

The characteristic impedanceor surge impedanceof a

uniform transmission line, usually written %, is the ratio of the

amplitudes of voltage and current of a single wave propagating

along the lineB that is, a wave travelling in one direction in the

absence of reectionsin the other direction. #haracteristic

impedance is determined by the geometry and materials of the

transmission line and, for a uniform line, is not dependent on its

length.

The general expression for the characteristic impedance of a

transmission line is!

where

is the resistanceper unit length, considering the twoconductors to be in series,
http://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Reflections_of_signals_on_conducting_lineshttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/In_serieshttp://en.wikipedia.org/wiki/Transmission_linehttp://en.wikipedia.org/wiki/Reflections_of_signals_on_conducting_lineshttp://en.wikipedia.org/wiki/Electrical_resistancehttp://en.wikipedia.org/wiki/In_series


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is the inductanceper unit length,

is the conductanceof the dielectric per unit length,

is the capacitanceper unit length,

is the imaginary unit, and

is the angular freCuency.


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SURVEY AREA

LOAD BALANCE SHEET


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Incoming power (MW O!"going power (MW

#rom $ gener%"ing &"%"ion&

A'B'C$)

To *++ ,V &!-&"%"ion ".ro!g.

*++ ,V /o!-0e c1" 0ine )$)

#rom &!-&"%"ion D ".ro!g. 22+,V /o!-0e c1" 0ine

34 To 22+ ,V %re% ".ro!g. 4 22+,V &!-&"%"ion&

)2

#rom &!-&"%"ion E ".ro!g. 22+

,V &ing0e c1" 0ine 54

To $2 ,V %re% ".ro!g. 4 $2

,V &!-&"%"ion& $+

#rom &!-&"%"ion # ".ro!g. $2

,V /o!-0e c1" 0ine 4* To In"ern%0 0o%/ing 4

A& 0o&& in $ $4 MVA

"r%n&6ormer&

*+

A& 0o&& in $ )+ MVA

"r%n&6ormer& 3

To"%0 )$+ To"%0 )$+

SELEC"ION O# SI"E:

?election of site for construction of a rid ?ub ?tation is the"rst and important activity. This needs meticulous planning,foresight, skillful observation and handling so that the selectedsite is technically, environmentally, economically and sociallyoptimal and is the best suited to the reCuirements.

The site should be!

3a4As near the load centre as possible.

3b4 As far as possible rectangular or sCuare in shape for ease ofproper orientation of busJ bars and feeders.


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3c4


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Hectare

CIVIL WOR,S #OR SUBSTATION

GENERAL7

All structures, buildings, foundations etc., layout & other details shall be designed and

developed keeping in view the functional requirement of the line and sub-station facilities to

meet the major technical parameters and project parameter.

LICENSED 8REMISES (SUBSTATIONS SITES7

9 Formation evels! Formation evel "F# of substations should be fi$ed minimum %

mm higher than the surroundings on the basis of the drainage conditions and the

'ighest Flood evel in the area.

29 (ite )reparation! *ecessary earth cutting+filling"spreading#,leveling, compaction and

dressing should be done. ackfilled earth should be free from harmful salts vi,

(ulphates,/hlorides and+or any 0rganic + 1norganic materials and compacted to

minimum 234 of the (tandard )roctor5s 6ensity "()6# at 0ptimum 7oisture /ontent

"07/#. 8he subgrade for the roads and embankment filling shall be compacted to

minimum 294 of the ()6 at 07/.

$9 (ite (urfacing in (witchyard Area! (ite surfacing should be carried out to provide

safe & haard free high earth resistivity working area "switchyard#

prevent growth of weeds & grass within the working area.


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8he site surfacing will be restricted up to :. m beyond the last structure +equipment

foundation.

A ; mm thick base layer of lean concrete of ;!

nominal sie shall be provided in the areas with covering with 7-: concrete layer

with minimum thickness of 3mm in the switchyard e$cluding roads, drains, cable

trenches etc.

>- mm deep toe wall :3 mm above top of gravel shall be provided.

All visible portions of toe-wall shall be plastered & cement painted.

*9 0utside (witchyard Area! Areas lying outside the switch yard should be landscaped,

developed and maintained in a clean and presentable fashion.

WATER SU88LY' SEWERAGE : DRAINAGE SYSTEM7

@ater (upply & (ewerage!@ater supply & sewerage system shall be designed to meet the

total water requirement of the substations, facilities and emergency reserve for complete

performance of the works. 8he design and construction of septic tanks and soak pits shall be

suitable for a minimum ; users with a minimum ; years span.

9 6esign of 6rainage! 8he concessionaire shall obtain rainfall data and design the storm

water drainage system including culverts, drains etc. to accommodate the most intense

rainfall "in one hour period on an average of once per ten years.#

29 (lope of 6rainage (ystem! 1nvert level of drainage system at outfall point shall be

decided in such a way that any water over flow from water harvesting recharge shafts

can easily be discharged outside the substation boundary wall. For easy drainage of

water !

7inimum slope of ;!; shall be provided from the ridge to the nearest drain.

7a$imum spacing between two drains shall be less than ; meter within the

switchyard


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(ide wall"s# of the drains shall be :3mm above the gravel level & covered with /1

grating

)ipe drains shall be connected through manholes within intervals of ma$imum >m

8wo portable pumps of adequate discharge capacity shall be provided for drainage ofwater

A sump pit of suitable capacity to hold water of at least 3 minutes discharge shall be

constructed at a suitable point.

RAINWATER HARVESTING7

Arrangements shall be made for rainwater harvesting in case the depth of water table is more

than =. m from finished ground level. ainwater harvesting shall be done by providing two

numbers recharge structures with bore wells suitably located within the sub-station with a

suitable arrangement to connect the overflow from these structures with sump-pit.

ROADS' CULVERTS : 8CC 8AVEMENT ; 8AR,ING7

All internal roads, culverts and )// pavements + parking within the sub-station area and

approach road from main )@6 road to the sub-station main entry gate"s# should be

constructed as per state )@6 specifications and as per layout in the )roject.

All e$ternal + internal substation roads should be constructed to permit transportation of

heaviest of the substation equipment that can ever roll over the concerned road.

8he main road leading to control room + switch yard + colony shall have a minimum % m

width with shoulder on either side.

9 (houlders, Footpaths, & (ide-walks! 8he shoulders + footpath + side-walk shall be

provided with /./. "7-;3# pre-cast kerbs on either side of the road. 8he top edge of

the kerbs shall be battered. 8he kerb stones with top : cm wide shall be laid with

their length running parallel to the road edge, true in line and gradient at a distance of

> cm from the road edge to allow for the drainage channel and shall project about

;:.3 cm above the latter as per )@6 specifications.


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29 oad 6rainage! Adequate provision shall be made for road drainage. 8he channel

stones with top > cm wide shall be laid in position in camber with finished road

surface and with sufficient slope towards the road gully chamber.

$9 ase (ub-?rade & (oling! (ub grade shall be compacted to achieve the density in

accordance with 1(! :9:.8he base course shall be e$tended on either side to at least

;3 cm "for switch yard roads# beyond the edge of the concrete pavement. 8he coarse

aggregate used shall be crushed or broken stone or any naturally occurring aggregates.

*9 (urfacing! 8he concrete to be placed shall conform to 7-: grade design mi$ using

approved materials & methods as per 1(! ;:%:. 8he concrete shall be distributed to

such depth that when consolidated and finished, the slab thickness obtained is as persite requirement but not less than 3 mm and equal at all points.

49 )aving+ )arking! /ement concrete paving + parking shall be provided as per layout.

TRANS#ORMER #OUNDATION7

9 ?eneral (cope!

// foundations & plinths shall be designed having minimum ?rade 7-: laid on base

concrete ";!

supporting the fire fighting system for placing >;3 7BA & ;% 7BA 8ransformers.

8he foundations of transformers and circuit breakers should be of block type.

(uitable arrangement for shifting the transformer from trailer like jacking etc. wherever

required should be made in plinth and in front of plinth on the road.

Adequate drainage outlets shall be provided and necessary slopes given to drain off rain

water+oil.

(uitable foundations shall be provided for all au$iliary equipment of the transformer

like radiators, fan supports etc. as required and the transformer plinth foundation shall

match the equipment drawings.


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1f trench + drain crossings are required then suitable ././. culverts shall be provided in

accordance with / standards + relevant 1(.

29 Cmergency 0il Cvacuation (ystem! 6esign & construction of Cmergency 0ilCvacuation (ystem should be suitable to the type of fire protection & emergency oil

drainage system.

#IRE 8ROTECTION WALLS7

Fire protection walls are designed in order to protect ;3 7BA single phase

8ransformers of the >;3 7BA unit against the effects of radiant heat and flying debris

from an adjacent fire in accordance with 8ariff Advisory /ommittee "8A/# stipulations.

8he partitions reduce the noise level of the transformers & should have adequate fire

resistance .

A minimum of :m clearance shall be provided between the equipments and fire walls.

8he building walls which act as fire walls shall e$tend at least ; m above the roof in

order to protect it.

CABLE : 8I8E TRENCHES7

9 ?eneral (cope!8he top of trenches should be kept at least :3 mm above the gravel

level so that rain water does not enter the trench. 8rench walls shall not foul with the

foundations and shall be designed for the following loads!

6ead load of ;33 kg+m length of cable support D93 kg on one tier at outer edgeof tier

Carth pressure D uniform surcharge pressure

8renches shall be constructed in // of 7-: grade. All metal parts inside the trench should

be connected to the earthing system.

29 0utdoor /able 8renches! // cable trenches shall be constructed in the switchyard

and fibre glass+pre-cast // removable covers with lifting arrangement, edge


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protected with suitable galvanied angle iron designed to withstand self weight of top

slab.

$9 1ndoor /able 8renches! // indoor cable trenches shall be provided with 3E3E%mm ?1 angles grouted on the top edge of the trench wall for holding minimum 9 mm

thick mild steel checkered plate covers "% mm in length e$cept at ends & bends#

with lifting arrangement. 1(7/ ?1 channels of 93$ m, suitable e$pansion joint

shall be provided at appropriate distances. 8he e$pansion joint shall run throughvertical wall and base of trench. All e$pansion joints shall be provided with approved

quality )B/ water stops of appro$. :>$3 mm sie. 7an holes shall be provided at

interval of not more than > meters. (umps, as necessary, shall be provided at suitable

places and at the dead end of all trenches. (umps shall be provided with drainage

pumps of adequate discharge capacity with all accessories for pumping out water

collected in the cable trenches. /able trenches shall not be used as storm water drains.

49 8rench - oad /rossings! (uitable bo$ culvert "(ingle span or multi spans# shall beprovided for any road crossing. 8he bo$ culvert shall e$tend ;.3 m on each side of

road and shall have :>-mm wide, 3 mm high brick parapet wall at ends.

#OUNDATIONS #OR CONSTRUCTION WOR,S7

9 ?eneral! All the foundations e$cept walls of switch house administrative and fire

handling building shall be of einforced /ement /oncrete.

29 6esign (tandards & )rocedure! 8he design and construction of foundations and other

// structures shall be carried out as per 1( specification.: layers of reinforcement

one each on inner and outer side of wall and slabs having thickness of ;3 mm and

above shall be provided. 8he tower and equipment foundations shall be checked for a

factor of safety for normal condition and ;.%3 for short circuit condition against

sliding, overturning and pullout.

$9 (liding & 0verturning (tability! All sub-structures shall be checked for sliding and

overturning stability both during construction and operating conditions for variouscombinations of loads.


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*9 6epth of Foundations!1n switchyard area, deeper foundation shall be constructed first.

For the foundations resting on filled up soil, earth filling is involved due to high

fi$ation of formation level. All foundations shall rest below virgin ground level and

minimum depth e$cluding lean concrete of all foundations GH3 mm.

49 'eight of Foundations! 8he (witch Iard foundations shall be at least ; mm above

the finished ground level or as per the manufacturersJ design. C$cavation shall e$tend

minimum ;3 mm around foundation "from // portion and not from lean concrete#.

1f the site is on a gradient + slope, the foundation height will be adjusted to maintain

the e$act level of the top of structures to compensate such slopes.

)9 )linth evels! 8he plinth level of the /ontrol oom-cum-Administrative building

should be minimum 3 mm above the finished ground level.

39 einforcement steel! einforcement steel "including 878 ars# of the designed grade

and manufactured by primary steel producers and conforming to 1(! ;9=% should only

be used.

59 Foundation olts! All the foundation bolts used for equipment foundations & for main

gantry tower foundations should be galvanied and embedded in concrete during

concreting .


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(uper-imposed loads in different areas shall include live loads, minor equipment loads,

cable trays, small pipe racks+hangers and erection, operation and maintenance loads.

Cquipment loads shall constitute, if applicable, all load of equipments to be supported

on the building 8A/ or other relevant code.

For crane loads an impact factor of >4 and lateral crane survey of ;4 of "lifted

weight D trolley weight#shall be considered in the analysis of frame according to

provisions of 1(! =93. 8he horiontal surge shall be 34 of the static wheel load.

8he wind loads and seismic forces shall be computed. esponse spectrum method shall

be used for the seismic analysis using at least first five modes of vibration. @ind and

(eismic force shall not be considered to act simultaneously.

For temperature loading, the total temperature variation shall be considered as :+> of the

average ma$imum annual variation in temperature. 8he average ma$imum annual

variation in temperature for the purpose shall be taken as the difference between the

mean of the daily minimum temperature during the coldest month of the year and mean

of daily ma$imum temperature during the hottest month of the year. 8he structure shall

be designed to withstand stresses due to 34 of the total temperature variation.

Floors + slabs shall be designed to carry loads imposed by equipment, cables, piping,

travel of maintenance trucks and equipment and other loads associated with the

building. 1n general, floors shall be designed for live loads as per relevant 1( and cable

and piping loads of no less than 3k* + sq. m. hanging from the underside. For

consideration of loads on structures, 1(! =93, K/ode of practice for structural safety of

buildingsL shall be followed. 8he following minimum superimposed live loads shall,

however, be considered for the design!

i oof ;3kg + m: for accessible roofs & 93kg + m: for non accessible roofs

ii // floors 3 kg +m:for non-accessible roofs. : for offices and minimum ;

kg+m:for equipment floors or actual, if higher than ; kg + m:

iii 8oilet ooms : kg + m:.

i= @alkways > kg + m:

$9 6? uilding /um Fire Fighting )ump 'ouse and // @ater (torage 8ank!

8he 6? and FF buildings designed to accommodate up to Mtwo ":#N 6? sets, motors

+pumps and a permanent crane, hoist and service trucks mounted on suitable steel

structure below the ceiling for servicing, lifting and maintenance of the heavy

equipment shall be constructed

Arrangement shall be made to drain the spill oil from oil diesel operated equipment

along the periphery for collection. )iping shall be provided for conveying oil from the

storage tank "common for all diesel + engines# to individual fuel tank of engine.


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*9 (torm @ater 6rainage for uildings! 8he building drains shall be provided for the

collection of storm water from the roofs in junction bo$es and these bo$es shall drain

to the main drainage system of the station. /ast iron + )B/ rain water down comers

"minimum ;mm diameter# with water tight joints shall be provided to drain off the

rain water from the roof. 8hese shall be suitably concealed with masonry work or

cement concrete or cladding materials. All drains inside the buildings shall have

minimum mm $:>mm thick 7-: //

plinth beams

39 )ainting and Finishing! All paints & allied materials shall be of superior quality,

conform to the relevant 1ndian (tandards and of approved brands and shades.

#LOORING7

8he flooring of /ontrol oom-cum-Administrative building e$cept conference room,

control room, reception hall & reception stairs shall be made of Oota stone.

)re-polished granite stone slabs, ;2 mm thick ">+ $ > $ 9.9 mm flooring in toilets and pantry.

Anti skid floor tiles of reputed makes having minimum > $ > mm nominal sie and

9.9 mm thick preferably in eige colour shall be provided in the toilets.

'eavy duty ironite concrete floor hardener shall be provided in 6? uilding cum Fire

Fighting )ump 'ouse.


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Cntire area around the /ontrol oom-/um-Administrative building, 6?- cum-fire

fighting building, (ecurity 'ut and the 6riverJs room shall be provided with )//

paving.

DOORS AND WINDOWS7

Aluminium frames + doors + windows + ventilators "single & double leaf# consisting frame

work including vertical styles, top rails, lock "middle# rails and bottom rails with metal

fastener & screws shall be fitted with nuts & bolts or using plastic plugs & screws. 8he

Aluminium doors & windows shall be fitted with minimum 3.3 mm thick glass of reputed

make with high-class rubber gaskets & beading complete so to make the glass airtight. 8he

toilet doors shall, however, be fitted with prelaminated board panels of appropriate sie withAluminium beading to make it airtight.

ROLLING SHUTTERS7

olling shutters with suitable operating arrangement according to sie & weight shall be

provided in buildings to facilitate handling and transportation of equipment.

TOILET : 8ANTRY SANITARY #ITTINGS7

All the water closets, wash basins, squatting pans etc. shall be of vitreous /hina clay in white

color, "first quality# as per 1(! :33%. 8he water closet in officerJs toilet shall be Curopean type

with single + double siphon and low-level cistern. 8he toilets & pantry shall be provided with

the best 1ndian make : mm diameter, % mm long towel rails and other normal fi$tures,

firmly fi$ed in position with plastic plugs and /) brass screws. All fi$tures + fittings shall be

chromium plated of good durable quality. 8he pantry shall be provided with reputed make

white vitreous chinaware sink of sie % $


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SWITCH > YARD #ENCING AND GATES7

Fencing & ?ates shall be provided for (witchyard area as per ?eneral Clectrical ayout )lan.

/hain link fence fabric shall have sie 93 mm coated wire shall be of >.;3 mm diameterhaving inc galvaniing after weaving. 8he barbed wire shall be of ;: (@? galvanied steel

with its weight ;33-;=% gm+m length of wire. 7a$imum distance between two barbs shall be

93mm. 8he barbs should carry four points and shall be formed by twisting two point wires,

each two turn tightly round one line wire making altogether < complete turns. 8he barbs shall

have a length of not less than ;> mm and not more than ;= mm. 8he points shall be sharp and

well pointed and single strand galvanied steel wire.

BOUNDARY AND RETAINING WALLS7

A oundary wall shall be constructed all around the entire substation land. 8he front wall

shall be ;.< m. high and in addition .% m galvanied iron grill & the boundary wall on the

other three sides shall be ;.= m with .% m P+/ barbed wire fencing over the wall.

SA#E"( CLEARANCES

L?afety orking #learanceM is the minimum clearance to bemaintained in air between the live part of the eCuipment onone hand and earth or another piece of eCuipment or conductor3on which it is necessary to carry out the work4 on the other.

The various eCuipments and associated & reCuired facilitieshave to be so arranged within the substation that speci"edminimum clearances are always available from the point of

view of the system reliability and safety of operating personnel.These include the minimum clearances from live parts to earth,between live parts of ad=acent phases and sectional clearancebetween live parts of ad=acent circuits & bays. It must beensured that suNcient clearance to ground is also availablewithin the ?ub ?tation so as to ensure safety of the personnelmoving about within the switchyard

"he "a%e %e!) gi'es the minimum 'aues !* cearances

re+uired *!r Su% Stati!ns upt! ,-- &:


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Oominalsystemvoltage

Highestsystemvoltage

Fighteningimpulselevel

?witchingimpulselevel

-inimumclearance 3mm4

?afetyclearance3mm4

roundclearance3mm4

/etweenphase

andearth

/etweenphases

(( (' 1% (10 ''9 '%% )1%%)) ) (1% )'% )'% '0%% )1%%()' ($7 77%

7% ((%%

()%%((%%()%%

)1%%)0%%

$%%$%%

''% '$7 97%(%7%

(9%%'(%%

(9%%'(%%

$)%%$%%

77%%77%%

$%% $'% ($'7 (%7%3Kh J E4

(7173Kh JKh4

)$%%

$'%%

$%% 0%%%

INSULA"ION CO/ORDINA"ION

Insulation coordination is the correlation of insulation of

electrical eCuipments and circuit with the characteristic of

protective devices such that the insulation is protected fromexcessive overvoltages.

The reCuirements need to be satis"ed!

3i4 a suitable basic insulation level3/IF4 is to be selected3ii4 it is to be ensured that the breakdown voltage of all

insulation in the station will exceed the /IF3iii4 choosing proper protective devices providing good

protection at a viable cost


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P( A (/'C7C(

There are several ways in which the switching eCuipments canbe connected in the electrical layout of substation. Theselection of the schemes is in general aected by followingaspects!

(. :egree of exibility of operations desired.'. Importance of load and local conditions.


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). :ouble bus bar.$. :ouble main and transfer bus bar.7. Pne and a half breaker scheme.

SINGLE 0US/0AR ARRANGEMEN":

This is the simplest switching scheme in which each circuit isprovided with one circuit breaker. This arrangement oers littlesecurity against bus bar faults and no switching exibilityresulting into Cuite extensive outages of bus bar and freCuentmaintenance of bus bar isolator3s4. The entire ?ub ?tation islost in case of a fault on the bus bar or on any bus bar isolatorand also in case of maintenance of the bus bar. Another

disadvantage of this switching scheme is that in case ofmaintenance of circuit breaker, the associated feeder has alsoto be shutdown.

MAIN AND AU1ILIAR( 0US ARRANGEMEN":

This is technically a single bus bar arrangement with an

additional bus bar called LAuxiliary busM energiDed from main


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bus bars through a bus coupler circuit, i.e., for 5n6 number ofcircuits, it employs 5n ; (6 circuit breakers. Each circuit isconnected to the main bus bar through a circuit breaker withisolators on both sides and can be connected to the auxiliary

bus bar through an isolator. The additional provision of buscoupler circuit 3Auxiliary bus4facilitates taking out one circuit breaker at a time for routineoverhaul and maintenance without de J energiDing the circuitcontrolled by that breaker as that circuit then gets energiDedthrough bus coupler breaker.As in the case of single bus arrangement, this scheme alsosuers from the disadvantages that in the event of a fault onthe main bus bar or the associated isolator, the entire

substation is lost. This bus arrangement has been extensivelyused in ()' k+ ?ub ?tations.


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DOU0LE 0US 0AR ARRANGEMEN":

In this scheme, a double bus bar arrangement is provided. Eachcircuit can be connected to either one of these bus bars

through respective bus bar isolator. /us coupler breaker is alsoprovided so that the circuits can be switched on from one busto the other on load. This scheme suers from thedisadvantage that when any circuit breaker is taken out formaintenance, the associated feeder has to be shutdown.

This /us bar arrangement was generally used in earlier ''% k+sub stations.


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DOU0LE MAIN AND AU1ILIAR( 0US 0AR ARRANGEMEN":

The limitation of double bus bar scheme can be overcome byusing additional Auxiliary bus, bus coupler breaker and

Auxiliary bus isolators. The feeder is transferred to the Auxiliarybus during maintenance of its controlling circuit breaker withoutaecting the other circuits.

This /us bar arrangement is generally used nowadays in ''%k+ sub stations.

ONE AND A 2AL# 0REA3ER ARRANGEMEN":


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In this scheme, three circuit breakers are used for controllingtwo circuits which are connected between two bus bars.Oormally, both the bus bars are in service. A fault on any one ofthe bus bars is cleared by opening of the associated circuit

breakers connected to the faulty bus bar without aectingcontinuity of supply. ?imilarly, any circuit breaker can be takenout for maintenance without causing interruption. Foad transferis achieved through the breakers and, therefore, the operationis simple. However, protectiverelaying is somewhat more involved as the central 3tie4 breakerhas to be responsive to troubles on either feeder in the correctseCuence. /esides, each element of the bay has to be rated forcarrying the currents of two feeders to meet the reCuirement of

various switching operations which increases the cost. Thebreaker and a half scheme is best for those substations whichhandle large Cuantities of power and where the orientation ofout going feeders is in opposite directions.This scheme has been used in the $%% k+ substations.


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/usbar -aterials

S n!. Descripti!n 0us 0ar and 4umper Materia


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( $%% k+ -ain /us (($.' mm dia. Aluminium pipe

' $%% k+

eCuipmentinterconnection

(($.' mm dia. Aluminium pipe

) $%% k+ overheadbus > droppersin allbays.

Twin A#?@ -oose

$ ''% k+ -ain /us Quadruple & Twin A#?@ ebra & TwinAA# Tarantulla

7 ''% k+ Auxiliary/us

A#?@ ebra

''% k+eCuipmentinterconnection

Twin A#?@ ebra & ?ingle A#?@ebra

1 ''% k+ overheadbus > droppersin allbays.

Twin A#?@ ebra & ?ingle A#?@ebra

0 ()' k+ -ain /us A#?@ ebra

9 ()' k+ Auxiliary/us A#?@ Kanther

(% ()' k+eCuipmentinterconnection

A#?@ ebra & A#?@ Kanther

0A( LA(OU" O# A ,,- & SU0S"A"ION:


29/117

Detais a%!ut num%ers !* %a5s and num%ers !*

e+uipments re+uired:


30/117

Oo. of bays $%% k+ ?I:E ''% *+ ?I:E ()' *+ ?I:E

Incoming ) 7

Putgoing 7 (( ((

/us coupler ( ( (

/us Tie ( (

Kowertransformer

Autotransfor

mer

) 3$%%&''%

*+4

) 3''%&()' *+4

Auxiliarytransformer

( 3()'*+&$(7+4

ave trap (' ))

#+T (' ))

#urrent

transformerKotentialtransformer#ircuit/reakers

)% 71 7(

Isolators )) (0 ()0

Earth switch

MAIN DATA O# A TY8ICAL *++;2$+ ,V OUTDOOR AC SUBSTATION7>


31/117

O8ERATING VOLTAGE *++ ,V 2$+ ,V

@ated current '%%%A '%%%A

-aximum short circuit current in

bus bar

$% *A $% *A

-inimum phase to phase clearance 7.17 m '.7 m

-inimum phase to earth clearance ).7 m '.% m

Oumber of horiDontal bus bar of "rst

level above ground

' '

Height of tubular bus bar of "rst

level above ground

1 m m

Height of tubular bus bar of second

level above ground

() m $ m

Tubular aluminum bus bar A( A?T-

/'$(

$MIK? $MIK?

S6I"C2(ARD:?witchyard may be de"ned as the combination of variousswitching, measuring and protecting devices, supported withstructures > hardwares that meant to establish the ow ofpower in an electrical network.

#UNC"IONS O# A S6I"C2(ARD:

(. Kroviding a link between enerating Klant and Transmission?ystem. '. ?tepping up or stepping down voltage as reCuired). #ontrolling reactive power which has eect on Cuality of

power. $. Krotection of substation and its components.


32/117

MAIN COMPONEN"S O# A S6I"C2(ARD:

Transformer.

#ircuit /reaker.

#urrent Transformer 3#T4. +oltage Transformer 3+T4.

#apacitor +oltage Transformer 3#+T4.

Isolators.

Earthing ?witch.

Fightning Arrester.

ave Trap.

/us /ar > #lamp


33/117

typically dierent voltage levels. Twowinding power

transformers with rating bigger than 7-+A are typically star

3wye4 connected or delta connected, and less freCuently, DigDag

connected. ?uch power transformers introduce a "xed phase

angle displacement 3i.e. phase angle shift4 R between the two

windings. The commonly used two winding connections are

shown below!

:d or :d% 3delta&delta4!This is an economical connection for

large low voltage transformers in which insulation problem is

not urgent as it increases the number of turns per phase and

reduces the necessary sectional area of conductors. /ut it can

meet large unbalanced load with ease as the third harmoniccurrents are damped out in closed mesh.

:y or Sd 3:elta&star or ?tar&delta4! It is the most common

connection for power supply transformers.It has the advantage

of star point for mixed loading and delta to carry the third

harmonic currents.

Sy 3star&star4! This is the most economical connection for small

high voltage transformers and as the number of turns perphase is minimum the amount of insulation is minimum./ut this

type of connection is favorable for shell type transformer and in

other cases presence of tertiary winding is essential for

stabiliDing the neutral.

SD or y 3star&DigDag or igDag&star4! This type of connection is

done where delta connection is mechanically weak on account

of large no. of turns for small copper cross sections.


34/117

AGTP T@AO?


35/117

)(7 -+A $%% *+ autotransformer

The autotransformers are provided with a tertiary winding for a

few reasons. They are !

a.


36/117

CUREN" "RANS#ORMER

This instrument transformer is connected to ac power circuit.

The secondary winding of the #Ts are fed to indicating,

metering instrument > and protective relays .#Ts are connected

to power circuit to watch over current ow > over power load.

In #T primary

inding is directly connected in series with the power circuit >

it is single turn. In the secondary winding number of turns ismore if the measuring current is more. The ratio of primary >

secondary current is known as #T transformation ratio.

The main purpose of use #Ts!

(. :ierential Krotection'. /us bar protection). /ackup protection for over current and earth fault$. -etering

&OL"AGE "RANS#ORMER

Kotential transformers serve a number of functions in a power

system. They are mainly used for stepping down of high

magnitude voltage to a safe value for incorporate measuring

and protection logics. They are used for metering and

instrumentation purposes in power system. These are also used

in relay protective system. In con=unction with current

transformers 3#Ts4 they can be used in measuring power.


37/117

CAPACI"I&E &OL"AGE "RANS#ORMER

The #+T is used for line voltage meter, synchroscope,

protective relays and tari meters. The performance of

#+T is inferior to electromagnetic voltage transformer.

Kerformance of #+T is greatly aected by variation of

freCuency.

CIRCUIT BREA,ERS

A circuit breaker is a mechanical device designed to close or

open contact members, thus, closing or opening an electrical

circuit breaker, under normal or abnormal conditions. It consist

of "xed > moving contacts which touch each other under

normal conditions i.e. when #/ is closed, considerable amount

of energy is stored in the spring contacts which are heldtogether by toggles. #/ is provided with trip coil connected to a


38/117

relay designed to open automatically under fault condition.

Pnly small pressure is reCuired to be applied on protective

relay. It trips > the potential energy of the springs is released >

contacts open in fraction of seconds.

+arious types of #./ are used !

7 .S#9 circuit %reaer

8. Oi circuit %reaer

. Air %ast circuit %reaer

,. &acuum circuit %reaer

MODES O# ARC E1"INC"ION

(4 2IG2 RESIS"ANCE IN"ERRUP"ION In this process the

arc is increased by lengthening and cooling to such an

extent that the system voltage is no longer able to maintain

the arc and the arc gets extinguished. This techniCue is

employed in air break circuit breakers and :.# circuit

breaker.'4 LO6 RESIS"ANCE OR ;ERO POIN" IN"ERRUP"ION Inthis process the arc gets extinguished at natural current Deroof the alternating current wave and is prevented fromrestriking again by rapid build up of dielectric strength ofthe contact space. This process is employed in almost all A.#circuit breakers

S#9 Circuit 0reaer


39/117

Krinciple of operation!

In the closed position of the breaker, the contacts remain

surrounded by ?


40/117

-ain disadvantage of the oil circuit breakers is the ammabilityof the oil, and the maintenance necessary to keep the oil ingood condition 3i.e. changing and purifying the oil4.

Two main types of oil circuit breakers are!


41/117

ISOLA"ORS

An isolator&disconnecting switch is used to open some given

parts of a power circuit after switching o the load by means of

a #/. This isolator serves only for preventing the voltage from

being applied to some given section of the bus bars in a

switchgear installation or to one or another piece of apparatusin the installation.

In some cases isolators are used as a circuit breaking device

but their purposes are strictly limited.

EAR"2ING S6I"C2

Earth switch discharges the capacitive voltage stored in line ongenerator side in the isolated system =ust after opening of #/ >isolator. hen earth switch is connected to the isolated butcharged system it discharges the stored energy to earth, sothat maintenance work can be carried out either in line ongenerator side. Earth switches should be operated only whenthe isolators are open.

All earth switches can be operated manually. ?emaphore

indicator can be seen for position feedback 3on&o4 inswitchyard control panel.

LIG2"NING ARRES"ER


42/117

Fighting arrestor is a device, which protects overhead lines andother electrical apparatus viD, transformer, and generator

against lightning. /asically it consists of an arc gap and a non

linear resistor. henever there is a lightning, the voltage strikes

the transmission line and the surge voltage begins to ow along

the line. Gnder this condition the value of nonlinear resistor

decreases to a low value thus providing a low resistance path

for the voltage wave. Thus the surge wave directly passes to

the earth without aecting any eCuipment in the line. It is alsoseen that if there is a positively charge cloud over a

transmission line, then it will produce a negative charge by

electrostatic induction. This negative charge will however

remain right under the cloud and portion of the line away from

that cloud will be positively charged. This positive charge will

ow gradually to earth slowly through insulator and metallic

parts. Thus the charge that remains is the negative charge. This

charge then ows along the transmission line as surge wave


43/117

and damages the eCuipment. Thus the lightning arrestor

provides protection against this wave.

6A&E "RAP

ave trap is used for protection of the transmission line and

communication between the ?ubstations!

+H< signal is transmitted from one end to another throughthe same power line.

?ends intertrip signal to the other end #/s so that faultcan be isolated at the earliest time.

Pr!tecti!n !* 0us%ars

/usbars in the substation form important link between the

incoming and outgoing circuits. If a fault occurs on a busbars,

considerable damage and disruption of supply will occur unless

some form of Cuickacting automatic protection is provided to

isolate the faulty busbar.

The busbar Done, for the purpose of protection, includes not

only the busbars themselves but also the isolating switches,

circuit breakers and the associated connections.


44/117

The two most commonly used schemes for busbar protection

are

(. :ierential protection

'. Gnder voltage protection.). Pver current protection with directional element.$. #ombined Earth fault and phase fault protection.7.


45/117

earth or leakage faults only. The overload relays have high

current setting and are arranged to operate against faults

between the phases. In the absence of earth fault the vector sum of three

line currents is Dero. Hence the vector sum of threesecondary currents is also Dero.Ias;Ibs;Ics8% so during normal condition no current ows

through earth fault relay and the relay will not operate.

However in the presence of earth fault the condition is

disturbed and Ias;Ibs;Ics% , so the current ows through

earth fault relay and if this current is above the pickup

value, relay operates.


46/117

reduces with reduction in voltage. Induction disc type

construction is used for inverse undervoltage relay.

$. Directi!na p!)er rea5 ! this type of relay operates

when power in the circuit ows in a speci"c direction. A

directional power relay is so designed that it obtains its

operating torCue by the interaction of magnetic "elds

derived from both voltage and current source of the circuit

it protects.

In this type of relaysTorCue developed U +I cosV

U power in the

circuit.

hen the power in the circuit ows in the normal direction, the

driving torCue and the restraining torCue help each other to

turn away the moving contact from the "xed contacts.

#onseCuently, the relay remains inoperative. However reversal

of current in the circuit reverses the direction of driving torCueon the disc.


47/117

NEGA"I&E SE$UENCE RELA(:

Oegative seCuence overcurrent relays are used to detect

unbalanced load on a generator which may cause excessive

rotor heating. The relay is also used to detect unbalanced loadcurrents in motor.

The advantage of the negative seCuence current over DeroseCuence currentis that mutually coupled parallel line currents are notinuencing the measurement and that only the three phasecurrents are used as inputs, i.e. the neutral current is notneeded

2ARMONIC RES"RAIN" RELA(!

(. The relay is used to delay earth fault protection in solidly

earth power system.

'. The most typical application is as a sensitive backup

protection in a transformer neutral or at a power line.

) . hen a transformer is switched in and energiDed,a highinrush currentusually appears. It can reach a peak value of several times thetransformer6s rated current, and it is gradually damped to anormal magnetiDing current of some percent of rated current.

$. The transformer inrush current is heavily distorted and has a

high percentage of second harmonic, which prevents relay

operation.

W @ated freCuency 7% or % HD

W Pperation blocked by 'nd harmonic component X'%2 of the

fundamental current

W Pperate time 7% 1% ms at ) x pickup

W @eset ratio X9%2


48/117

W +ariants available with de"nite or inverse time delayed

output.

"rans*!rmer #aiures:/


49/117

Krotection against Internal fault!

0uchh!@ rea5 < gas actuated rea5=:/

/uchholD relay is a gasactuated relay installed in oil

immersed transformers for protection against all kinds of

faults.Oamed after its inventor, /uchholD, it is used to give an alarmin

case of incipient 3i.e.slowdeveloping4 faults in the transformer and to

disconnect the transformer from the supply in the event of severe

internal faults. It is usually installed in the pipe connecting the

conservator to the main tank. It is a universal practice to use

/uchholD relays on all such oil immersed transformers having ratingsin excess of 17% k+

/G#HHPF J alarms for!


50/117

QFocal winding overheating alarm

QFocal core overheating 3short circuited laminations4

Q/ad contacts or =oints

QKartial discharge

Q/roken down core bolt insulation

Pperation. The operation of /uchholD relay is as follows !

3i4 In case of incipient faults within the transformer, the heat

due to fault causes the decomposition of some transformer oil

in the main tank. The products of decomposition contain morethan 1%2 of hydrogen gas. The hydrogen gas being light tries

to go into the conservator and in the process gets entrapped in

the upper part of relay chamber. hen a predetermined

amount of gas gets accumulated, it exerts suNcient pressure

on the oat to cause it to tilt and close the contacts of mercury

switch attached to it. This completes the alarm circuit to sound

an alarm.

3ii4 If a serious fault occurs in the transformer, an enormousamount of gas is generated in the main tank. The oil in the

main tank rushes towards the conservator via the /uchholD

relay and in doing so tilts the ap to close the contacts of

mercury switch. This completes the trip circuit to open the

circuit breaker controlling the transformer.

Advantages

3i4 It is the simplest form of transformer protection.

3ii4 It detects the incipient faults at a stage much earlier than is

possible with other forms of protection.

:isadvantages

3i4 It can only be used with oil immersed transformers eCuipped

with conservator tanks.


51/117

3ii4 The device can detect only faults below oil level in the

transformer. Therefore, separate protection is needed for

connecting cables.

EAR"2 #AUL" PRO"EC"ION:/

An earthfault usually involves a partial breakdown of winding

insulation to earth. The resulting leakage current is

considerably less than the shortcircuit current. The earthfault

may continue for a long time and cause considerable damage

before it ultimately develops into a shortcircuit and removed

from the system. Gnder these circumstances, it is pro"table toemploy earthfault relays in order to ensure the disconnection

of earthfault or leak in the early stage. An earthfault relay is

essentially an overcurrent relay of low setting and operates as

soon as an earthfault or leak develops. Pne method of

protection against earthfaults in a transformer is the core

balance leakage protection shown in "gure below!

The three leads of the primary winding of power trans former

are taken through the core of a current transformer which

carries a single secondary winding. The operating coil of a relay

is connected to this secondary. Gnder normal conditions 3i.e. no

fault to earth4, the vector sum of the three phase currents is

Dero and there is no resultant ux in the core of current

transformer no matter how much the load is out of balance.

#onseCuently, no current ows through the relay and it remains


52/117

inoperative. However, on the occurrence of an earthfault, the

vector sum of three phase currents is no longer Dero. The

resultant current sets up ux in the core of the #.T. which

induces e.m.f. in the secondary winding. This energises the

relay to trip the circuit breaker and disconnect the faulty

transformer from the system.

RES"RIC"ED EAR"2 #AUL" PRO"EC"ION

#onventional earth fault protection using overcurrent elements

fails to provide adeCuate protection for transformer windings.

This is particularly the case for a starconnected winding with

an impedanceearthed neutral. The degree of protection is very

much improved by the application of restricted earth fault

protection 3or @E< protection4. This is a unit protection scheme

for one winding of the transformer 3mainly for secondary

winding phase to earth fault4. It can be of the high impedance

type , or of the biased low impedance type.


53/117

other windings. /oth windings of a transformer can be

protected separately with restricted earth fault protection,

thereby providing highspeed protection against earth faults for

the whole transformer with relatively simple eCuipment. A high

impedance relay is used, giving fast operation and phase fault

stability.

C!m%ined Leaage and !'er!ad pr!tecti!n:/

The corebalance protection described above suers from

the drawback that it cannot provide protection against

overloads. If a fault or leakage occurs between phases, thecorebalance relay will not operate. It is a usual practice to

provide combined leakage and overload protection for

transformers. The earth relay has low current setting and

operates under earth or leakage faults only. The overload relays

have high current setting and are arranged to operate against

faults between the phases.


54/117

In this system of protection, two overload relays and one

leakage or earth relay are connected as shown. The two

overload relays are suNcient to protect against phasetophase

faults. The trip contacts of overload relays and earth fault relay

are connected in parallel. Therefore, with the energising of

either overload relay or earth relay, the circuit breaker will be

tripped.

/iased :ierential Krotection!

A simple rule of thumb is that the #T6s on any wye winding of a

power transformer should be connected in delta, and the #T6s

on any delta winding should be connected in wye. This rule

may be broken, but it rarely isB for the moment let us assume

that it is inviolate. Fater, we shall learn the basis for this rule.

The remaining problem is how to make the reCuiredinterconnection between the #T6s and the dierential relay.

Two basic reCuirements that the dierentialrelay connections

must satisfy are!

3(4 the dierential relay must not operate for load or external

faultsB and

3'4 the relay must operate for severe enough internal faults.


55/117

/iased dierential protection is used in case of low fault

settings and high operating speeds are to be obtained when the

following condition exist in a power transformer!

(. Pn Foad Tap #hanging.'. -agnetising Inrush #urrent). Gnmatched #Ts.

To take account of magnetiDing inrush current,a high speed

biased dierential relay incorporating harmonic restraint

feature is used.

Kercentage3/iased4 dierential protection scheme

O'ercurrent Pr!tecti!n:/

The over current protection is needed to protect the

transformer from sustained overloads and short circuits.

Induction type over current relays are used which in addition to

providing overload protection acts as back up relays for

protection of transformer winding fault. The arrangement is

such that the relay does not respond to any out of balance

/iased

windingPperati

ng coil


56/117

current between windings caused by tap changing

arrangement.

Auto transformer Krotection!

In this substation $%%&''%*+ and ''%&()'*+ transformers are

autotransformers.Their protection scheme is almost same with

that of a two winding Transformer.

O'eru> Pr!tecti!n:/

Pveruxing arises principally from the following system

conditions!

a. high system voltage

b. low system freCuency

c. geomagnetic disturbances

The latter results in low freCuency earth currents circulatingthrough a transmission system. ?ince momentary system

disturbances can cause transient overuxing that is not

dangerous, time delayed tripping is reCuired. The normal

protection is an I:-T or de"nite time characteristic, initiated if

a de"ned +&f threshold is exceeded. Pften separate alarm and

trip elements are provided.

SU0S"A"ION EAR"2ING S(S"EM


57/117

EAR"2ING : In power system grounding or earthing means

connecting frame of electrical eCuipment 3non current carrying

part4 or some electrical part of the system 3e.g. neutral point ina star connected system , one conductor of the secondary of a

transformer etc.4 to earth i.e.soil. this connection to earth may

be through a conductor or some other circuit element 3e.g.

through a resistor, circuit breaker etc4.

SU0S"A"ION EAR"2ING ! ?ubstation earthing is very

important for safety of personnel and needs careful attentionwhile designing , erection and routine maintainance. The

function of substation earthing is to provide a grounding mat

below ground surface in and around the substation which will

have uniformly Dero potential with respect to ground and lowest

earth resistance. The neutral points of all the transformers and

generators as well as the non current carrying metal parts

should be connected to this earth mat through risers.

O04EC"I&E O# SU0S"A"ION EAR"2ING

All the noncurrent carrying parts connected to theearthing system shall be uniformly at Dero potential withrespect to ground.

The oor on which the operation and maintainance stamoves shall be at ground potential 3safe step potential4.

:uring any earth fault in the substation, the potential ofstructures, tanks and other non current carrying partsdoes not rise to unsafe values. 3safe touch potential4.

RE$UIREMEN" O# GOOD EAR"2ING

ood earth should have low resistance

It should stabiliDe circuit potential with respect to groundand limit overall potential rise.


58/117

It should protect men , material from in=ury or damage dueto over voltage.

It should provide low impedance path to fault currentsto ensure prompt and consistent operation of protective

relays , circuit breakers etc. It should keep maximum potential gradient along the

surface of the substation within safe limits during groundfault.

#UNC"ION O# EAR"2ING IN A SU0S"A"ION

It shall be capable of passing maximum earth faultcurrent

The passage of fault current does not result in anythermal or mechanical damage to the insulation ofthe connected plant&eCuipment

Every exposed conductor part or extraneousconductive part may be connected to earth.

There is no danger to the personnel

Ensure eCuipotential bonding within the powersystem

Oo dangerous potential gradients 3step, touch ortransfer potential4 shall occur under normal orabnormal conditions.

To minimiDe interference between power >control&communication system.


59/117

DESCRI8TION O# AN EARTHING SYSTEM

7. EAR"2 ELEC"RODES :

Earth electrode is a metal plate or metal pipe or metal conductorsdriven vertically into earth at several locations. These electrodes are

connected to earth mat. Farge number of earth electrodes give lower

earth resistance. -aterials used as earthing electrode !

#opper Aluminium -ild steel alvaniDed iron

?iDe of earth electrodes !

Type of electrode -inimum diameterAluminium pipes ('.7 mmalvaniDed ironpipes

( mm

-ild steel rods $% mm dia 3used in India4


60/117

8. EAR"2ING RISERS:

Earthing risers are used for connection between the structures,

eCuipment bodies and the earthing mat. These are usually clamped

or welded or braDed.

. EAR"2ING CONDUC"ORS :

The earth mat is made from earthing conuctors. The design of the

cross section of earthing conductors depends on!


61/117

RE#ERENCE DA"A #OR "(PICAL EAR"2ING

S(S"EM

Earthing

electrodes '7 mm & $% mm dia steel bars

' to )m longEarthingmat

17Y(% mm' mild steel placed ) to $mapart in mesh form

:istance between parallel strips8 'm

:epth %.7m below surface

Zoints by electric arc welding welded=oints , covered by 'mm thick bitumen

paint@isers 17 Y (% mm' -? ats connected to

eCuipment structures and welded toearthmat.

Pverheadshieldingwire3earthed4

Fevel )%m above ground level , withadeCuate clearances.

1&9 ? steel wire.

?hielding angle8$7

%

CLASSI#ICA"ION O# EAR"2ING

Earthing can be classi"ed into the following categories based on the

purpose for which the part of the eCuipment connected to the general

mass of earth.

?S?TE- EA@THIOEQGIK-EOT EA@THIO

S(S"EM EAR"2ING

Earthing associated with current carrying parts of the eCuipment is

called ?ystem Earthing. The system security, reliability, performance,

voltage stabiliDation, all depends only on the ?ystem Earthing.

Eg. Earthing Oeutral of Transformer, ?urge arrester Earthing


62/117

S(S"EM EAR"2ING ME"2ODS :

?olid Earthing The neutral is directly connected to ground without anyintentional impedance between neutral and ground.The coeNcient of earthing is less than 0%2 for suchsystems

@esistance Earthing @esistance is connected between neutral and ground

@eactance Earthing @eactance is connected between neutral and ground

@esonant earthing An ad=ustable reactor of correctly selected value tocompensate the capacitive earth current is connectedbetween neutral and earth. The coil is called Arcsuppression coil or earth fault neutraliDe.

E$UIPMEN" EAR"2ING


63/117

ECuipment earthing 3also called safety earthing or body earthing4

relates to the manner in which the frames , enclosures , structures

and other noncurrent carrying exposed metallic parts in the

substation are interconnected and earthed.

Example! -otorbody, switchgear metal enclosure, transformer tanks ,

conduits of wiring , support structures , tower , poles, sheaths of

metals etc.

0ASIC O04EC"I&ES!

(4To ensure freedom from exposure to dangerous electrical shocksto persons working in the substation.

'4 To provide current carrying capability for ow of earth faultcurrent of speci"ed magnitude and duration, thus permittingovercurrent protection B without any "re, damage or explosivehaDards.

NECESSI"( O# E$UIPMEN" EAR"2ING:

ECuipment earthing ensures safety.The potential orearthed body does not rise to dangerously high valuesabove earth since it is connected to the ground.

Earth fault current ows through the earthing and mayrapidly cause operation of a fuse or an earth fault relay .


64/117

CONNEC"ION O# ELEC"RICAL E$UIPMEN"S "O S"A"ION

EAR"2ING S(S"EM

Apparatus Parts t! %eearthed

Meth!d !* c!nnecti!n

?upport of bushinginsulators,

lightningarrestor,

fuse

:evice angeor base plate

Each terminalof each pole of) phase surgearrestor

(. #onnect the earthing bolt ofthe device to station earthingsystem. In the absence ofearthing bolt or in case ofconnection to nonconducting

structures,connect devicefastening bolt to earth.

'. hen the device is mountedon a steel structure, weld thestructure, mounting the deviceangeB each supportingstructure of apparatus isconnected to earthing mesh via

separate conductor

#abinets ofcontrol >relay panel

cabintes

eld the framework of eachseparately mounted board andcabinet minimum at ' points tothe earth conductor of earthingsystem.

H+ circuit

breakers

Pperating

mechanism,frame

#onnect the earthing bolt on

the frame and to the operatingmechanism of #./. to theearthing system

Isolator Isolatorbase3frame4operatingmechanismbedplate

eld the isolator baseframe,connect it to the bolt onthe operating mechanism baseplate and station earth.

?urgearrestor

Fower earthpoint

To be directly connected toearth mat


65/117

Kotentialtransformer

Kotentialtransformertank, F+

neutral, F+winding phaselead

(. #onnect the transformerearthing bolt to earthingsystem

'. #onnect F+ neutral of phaselead to case with exiblecopper conductor

#urrenttransformer

?econdarywinding >metal case

#onnect secondary winding toearthing bolt on transformercase with exible copperconductor, the case beingearthed in the same way as

support insulators.

Kowertransformer

Transformertank

#onnect the earthing bolt onthe transformer tank to stationearth. #onnect the neutral toearthing system.

?teel doorsand wire

guards inchambers orcubicles

:oor or guardsteel mount

eld the mount of each doorand guard to earth system.


66/117

Indoor ECuipments

The indoor eCuipments inside a substation are of vitalimportance. These consist of communication systems, relays

and other protection schemes, backup power arrangement, :#

power supply eCuipments etc.

:E?IO P< #POT@PF AO: @EFAS KAOEF #P-KFETE ITH

K@PTE#TIPO


67/117

The standard siDe of individual panel is :epth J (90)mm,

width limited to (%%%mm, height J ')(' mm. the corridor is

1'mm wide and access doors on end panels are (9%%mm

high.

Kanels are dust, moisture and vermin proof. These are free

standing, oor mounting type but grounded with foundation

bolts.

#able entries to panel are from bottom. The bottom plates of

the panel are "tted with removable gland plates and "xed with

cable glands. The cable glands are screwed type made of brass

and suitable for K+# armoured cable.

The control switches for central breakers and isolators are

located on the mimic diagram corresponding to their exact

position of the control eCuipment in the single line drawing. The

locations of switches are within working height from the oor

level for easy and comfortable operation.

#olored mimic diagram and symbols showing exact

representation of the system are provided in the front panel.-imic diagram are made of anodiDed aluminum or plastic,

screwed to panel. The mimic buses are generally 'mm thickB

width of mimic bus is (%mm for bus bar and 1mm for other

connections. Indicating lamp, one for each phase for each bus

is provided on mimic of bus coupler panel to indicate bus

charged condition.

#olor scheme for mimic diagram

+PFTAE #FA?? #PFPG@ ?HA:E IO:E[ P< I?

''%*+ FIHT P@AOE 771

()'*+ ?IOAF @E: 7)1

*+ olden /rown $($

))*+ /rilliant reen ''(


68/117

?emaphore indicators for each earth switches, control switch

width on, o indicating lamps for isolators, and discrepancy

type control switch with builtin indicating lamp, ush type for

circuit breakers are mounted along mimic diagram at

appropriate location in panel.

#ontrol ?witches for #ircuit /reakers shall be of three positionspring return type with pistol grip handle and seCuence deviceto ensure that manual pumping of closing solenoid not possible.

The switches shall be robust construction and shall have foureective contact positions. LAt after #loseM\ position theswitches shall have a maintained contact for using with #ircuit/reaker AutoTrip Indication Famp #ircuit

F.E.:. Type Indicating Famps shall be provided on the #ontrolKanel to indicate the following!


69/117

Famp 3wherenecessary4

#./. ]PO\indication

( Oo. @ed

1 #./. ]P


70/117

alarm actuating device. Alarm ?cheme has facility for bell andis suitable for self reset as well as hand reset type initiatingcontact.

The control panels also consist of metering eCuipments. TheeCuipments have to ful"ll the following reCuirements!

(. ero ad=uster capable of being safely handled while theinstrument is in service. The ad=ustments above mark andbelow the Dero point shall not be less than )2 of the fullscale length and need not exceed 2. It shall havesuNcient friction to keep the ad=ustment in position.

'. The dials shall be made of such materials as to ensure

freedom from warping, fading, discoloring etc. during fulllife of instruments. -arking of ?cale shall be black onwhite background

). The limits of error shall be of class (.% type. Thecalibration of the instruments shall function satisfactorilywhen mounted on steel panels or alternativelymagnetically

$. Instruments shall be capable of indicating freely whenoperated continuous at any temperature from % to 7%

degree #.


71/117

7. All circuits of instruments shall be capable of withstandingapplied load of '%2 greater than the rated capacity for aperiod of eight hours.

. The instruments shall be capable of withstanding the

eect of shock vibration and a dielectric test of '%%% +oltsr.m.s. to ground for one minute as per relevant I??.

The meters that are used are!

(. +oltmeter! A# voltmeter are generally moving coil type,

9mm [ 9mm siDe, '$%^scale, with range of %)%% *+3for

''% *+4 and %(7 *+3for ()'*+4

'. Ammeter! Ammeters are moving coil type, 9mm [ 9mm

siDe, '$%^scale and generally with dual scale.

).


72/117

). *+A@H export$. Feading&lagging +A@

:isplay of reading shall be at regular interval of time and

also on demand.

#ontrol and @elay panels also have A# and :# circuits. They are

described as below!

DC CIRCUIT

There shall be only one :# incoming 3''%+4 for the #>@ board

through a )'Amp switchfuse unit. Pne H@# fuseunit both at

positive and negative side shall be provided for the :# incomer

at the bus coupler panel. The said :# incoming bus shall runcontinuously in the total #>@ board.

:# annunciation bus shall also be teed o from the incomer :#

bus through A H@# fuse at positive and a link in the negative

side with necessary :# supervision relay.

:# supply to each individual panel thus teed o and distributed

within the panel as below

(. #./. remote and local closing through H@# fuse and link.'. #./. remote and protection trip to trip coil ( with trip

circuit supervision relay through a separate H@# fuse and

link.). #./. remote and protection trip to trip coil ' with trip

circuit supervision relay through a separate H@# fuse and

link.$. Krotective relay and KT selection circuit with :#

supervision relay.7. Indication circuit through A H@# fuse and link.. Isolator control circuit through (%A H@# fuse and link.

/us bar protection and F// protection :# shall be teed o from

the ''%*+ #>@ board.

AC CIRCUIT


73/117

A ''%*+ single phase A# supply to the entire #>@ board will be

fed from A# distribution board through a )'A switchfuse unit.

The supply shall be provided in bus coupler& bus transfer panel.

A# circuit for incoming :# and annunciation :# fail alarmscheme is provided in bus coupler panel. The above bus is teed

o to each panel through separate switchfuse unit.

Pne supervision relay for incoming A# fail with test push button

and reverse ag indication shall be provided for monitoring of

A# supply healthiness through :# operated fascia annunciation

of bus coupler panel.

Kower and #ontrol #ables

CA0LE: An underground cable essentially consists of one or

more conductors covered with suitable insulation and

surrounded by a protecting cable. The auxiliary power for

substation is supplied through underground cables.


74/117

CONS"RUC"ION O# CA0LES :

C!mp!nent

s

Descripti!n

C!res !r

c!nduct!rs

A cable may have one or morecore3conductor4 depending on the service forwhich it is reCuired.

The conductors are tinned copper oraluminium

Gsually stranded in order to provide exibilityto the cable

Insuati!n Each conductor provided with suitable

thickness of insulation Thickness depends on the voltage to be

withstood Impregnated paper, varnished cambric or

rubber mineral compound.

Metaic

sheath

-ade of lead or aluminium

Krotects cable from moisture, gases, acids or

alkalis.


75/117

0edding Applied over metallic sheath

#onsists of "brous material like =ute or

Hessian tape Krotects metallic sheath against corrosion and

from mechanical in=ury due to armouring.

Arm!uring #onsists of one or two layers of galvaniDedsteel wire or tape

Applied over bedding

Krotects the cable from mechanical in=ury

while laying it and during course of handling

Ser'ing Fayer of "brous material like =ute providedover armouring

Krotects armouring from atmosphericconditions.

PO6ER CA0LES


76/117

The function of the power cables in the substation is to

transfer power from auxiliary transformer to various auxiliary

loads. The power cables are used for various voltages upto ((

*+. The power cables are laid on cable racks supported on

cable trenches. The underground distribution system in a

substation is generally at two or three ac voltages such as ((

*+, ).) *+, $(7 rms.


77/117

steel is provided over the sheath. To reduce electrostatic >

electromagnetic interference the power cables are shielded and

earthed. Thus a power cable is made up of the following basic

components !

3(4 conductor

3'4 core insulation

3)4 sheath

3$4 protective covering > armouring.

"(PES O# CON&EN"IONAL PO6ER CA0LES :

Kaper insulated cables. Klastic insulated cables3K+#4 Pil "lled cables as "lled cables

At present K+# insulated and K+# sheathed cables are

commonly manufactured for laying in the cable trenches

3undergound4 and in case the power cables are to be directly

laid in the aggressive ground, cables with metal sheath arenecessary. #ross linked poly ethelene 3[FKE4 cables developed

during (91%6s are being preferred for voltages upto '$7 *+.

LA(ING O# PO6ER CA0LES :

Kower cables should be laid preferably in separate trenches or

ducts. However, a well shielded power cable might be laid in

the ducts having measuring cables and control cables. A

minimum distance of %.)m 3(' inches4 should be keptbetween power > control cables. The power cable should be

supported on racks placed at an interval of %.0 to (.%m.

Heavy power cables should be supported on cable trays.

: 8 diameter of cable

@ating Gpto ((

*+

'' *+ )) *+, )

core

)) *+,

single core

-inimum (': (7: '%: )%:


78/117

bending

radius

ME"2ODS O# LA(ING CA0LES :

#ables supported on brackets above ground level #ables laid in trenches below ground level #ables laid in pipes. #ables laid in @## ducts > supported on galvaniDed slotted

steel fabricated trays.

PERMISSI0LE LOADING B "EMPERA"URE RISE O#CON"ROL CA0LES :

The maximum load on a power cable is determined for

maximum ambient temperature and permissible temperature

rise for the particular cable. The maximum load is determined

by conducting temperature rise test on a (%m long power

cable. hen the loads on a cable are less than the rated load,

the cables may be temporarily overloaded for a period

suggested by the manufacturer.

CON"ROL CA0LES


79/117

#ontrol cables are used in substations for connecting

control system, measurement, signaling devices protection >

communication circuits. They are generally at low voltage.3''%+ A#, ((%+ A#, $0+ A#, ((%+ :#, $0+ :# 4. They have

copper conductors. They may have another rubber or K+#

insulation. #ontrol cables have several cores, each having

independent insulations. The crosssectional area of control

cables is comparatively less. The colours of various core

insulations of cables are dierent.

#ontrol cables are wired between the control panels in the

control room, and the various eCuipments in the switchyard.

The various measurements, protection, control communication

functions are dependent on control cables. The control cables

are also laid on cable racks inside the cable trenches. The #T6s

are provided in the switchyard and control room building. To

avoid interference due to straymagnetic "elds, the control

cables should be properly laid and their sheeths should beproperly earthed so that protection and control functions are

performed without disturbance. #ontrol cables having several

cores are laid over large distances. To check the continuity of

cable a battery and telephone set is connected and installed at

both the ends. If the core is continous then the telephones at

both the ends will be in communication.


80/117

LA(ING O# CON"ROL CA0LES :

The main current current in these conductors being low,

these cables may be laid in a common duct, without separation.

However they should be separated from power conductors.

Highly sensitive measuring cables are sometimes laid inseparate steel pipes totally away from other cables.

SENSI"I&I"( O# &ARIOUS LOADS "O IN"ER#ERENCE

Application Type of cable ?ensitivity

of load

Kower cable -ulti core with one shield >protection conductor

Fow

#ontrol cable -ulti core with one shield ?ensitive

-easuring

cable

:ouble shielded multi

conductor

?ensitive

-easuring

cables

?hielded pairs common

external shielded

Highly

sensitive


81/117

Kower Fine #arrier #ommunication

KF##, P!)er Line Carrier C!mmunicati!n, is an approach to

utiliDe the existing power lines for the transmission of

information. In today6s world every house and building has

properly installed electricity lines. /y using the existing A#

power lines as a medium to transfer the information, it

becomes easy to connect the houses with a high speed network

access point without installing new wirings.

This technology has been in wide use since (97% and was

mainly used by the grid stations to transmit information at high

speed. Oow a days this technology is "nding wide use in


82/117

building&home automationas it avoids the need of extra wiring.

The data collected from dierent sensors is transmitted on

these power lines thereby also reducing the maintenance cost

of the additional wiring. In some countries this technology is

also used to provide Internet connection

Operating Principe

The communication device used for the communication over

the power lines is a -P:E-, commonly known as MODEM. It

works as both transmitter and receiver, i.e., it transmits and

receives data over the power lines. A power line modem not

only modulates the data to transmit it over the power lines and

but also demodulates the data it receives from the power lines.

/y using modulation techniCues, binary data stream is keyed

on to a carrier signal and then coupled on to the power lines by

-odem. At the receiver end another -odem detects the signal

and extracts the corresponding bit stream.
http://www.engineersgarage.com/articles/home-automationhttp://www.engineersgarage.com/articles/sensorshttp://www.engineersgarage.com/articles/home-automationhttp://www.engineersgarage.com/articles/sensors


83/117

The above image shows the working of a KF## system. :ata is

processed before transmission on power lines according to the

above "gure. "ltered and then by

using couplers, it is sent over the power lines.

Imp!rtant "echnica Parameters in PLC C!mmunicati!n

N!ise !n Residentia P!)er Circuit


84/117

(. Ooise synchronous to the power system freCuency 37%HD

or % HD4 J This type of noise is generated because of dierent

kind of switching devices.

'. Ooise with a smooth spectrum J The sources of such type

of noise are the appliances that are not operating

synchronously with the power line freCuency.


85/117

c. hile modulating the signal on to the power lines,

television line freCuencies should be avoided.

Signa t! N!ise Rati!:

?ignal to Ooise @atio 3?O@4 is a measurement of Cuality of the

signal. It indicates the amount of the noise in a signal. ?O@ can

be formulated in the following way!

SNR = Received Power / Noise Power

Increasing ?O@ means increasing the performance of the

communication system. /y applying noise "lters on household

appliances, the noise entering into the power system can be

reduced. However it will increase the cost of the appliances but

is a better solution to improve overall performance.

Signa Attenuati!n:

?ignal attenuation is basically the reduction in strength of the

signal. A signal attenuation of about (%%d/&*m occurs for low

voltage power lines and (%d/&km for high voltage lines. It

creates a need of continuous repeaters over a "xed distance. A


86/117

number of factors that are responsible for signal attenuation

include distance, time, freCuency of the signal, etc

PLCC S(S"EM: The freCuency range over which KF#freCuencies are transmitted is usually (7 *HD to 7%% *HD. Kower

line itself is the medium for transmission of carrier freCuencies

apart from transmission of those within the power freCuency

range. ?ince both the freCuencies are transmitted

simultaneously over the same power line, some essential

outdoor eCuipments are reCuired to discriminate the said two

freCuencies at the transmitting or receiving substation. These

are line traps and coupling capacitors. A line trap also called a5ave Trap6, oers high impedance to carrier freCuency 3(7 *HD

to 7%% *HD4 current and thus prevents it from entering into the

power eCuipments in the switch yard. The high inductance of

the line traps at high freCuency itself accounts for this property,

and hence, the line trap oers very low impedance to the

power freCuency current. Pn the other hand, a coupling

capacitor because of its high capacitive reactance oers high

impedance to power freCuency current and at the same timeoers low impedance to carrier freCuency current.

aX Channe Descripti!n ! A KF# channel connecting

two stations includes the following eCuipment at either

end.

iX Indoor #arrier Terminal 3#arrier ?et4

iiX ?ignal path including coaxial cableiiiX Putdoor coupling eCuipment and tuner 3line

matching eCuipment between transmission line and

the coaxial cable4.

The channels must be so planned that the signals are

con"ned to the desired path and unwanted signals are

excluded. As mentioned earlier these functions can be

achieved through the use of line traps and couplingcapacitors.


87/117

The arrangement of outdoor coupling eCuipment is shown

in the following "g.

bX Meth!ds !* C!uping! Gsually there are two types

of coupling

7 Phase t! Gr!und C!uping and

8 Phase t! Phase C!uping.

The arrangements are shown in the following "gure.

(. Phase t! Gr!und C!uping ! #oupling to the power line

is eected between the conductor of one phase of the

power line and the earth. Earth return path is employed


88/117

for the communication circuit for communication between

two stations.

'. Phase t! Phase C!uping!

#oupling to the power line is eected between the conductor

of one phase and the conductor of another phase of the

same power line. The two phases may belong to the same

circuit or to dierent circuits of the same power line 3Inter

#ircuit #oupling4.

Although for reasons of economy, phase to ground coupling is

employed between substation of less importance, phase to

phase coupling is essentially recommended for all practicalpurposes for all power lines of ()' k+, ''% *+ and $%% *+

system with the idea that in the case of a broken conductor or

snapping of conductor, communication can still be carried out

over the healthy phase conductor, though at a higher

attenuation. /esides phase to phase coyupling has also got the

advantage of lower signal attenuation over phase to ground

coupling under normal condition. Thus phase to phase coupling

is applicable not only for speech communication and expresschannels, but also for telemetering and teleprotection network,

where reliability of operation is an important factor.

cX Channe E+uipments!

iXLine "rap ! As discussed earlier, the function of a line trap

is to present a high

blocking impedance to the carrier freCuency currents, whileintroducing negligible impedance to the power freCuency

components. The carrier freCuency characteristics of the line

trap are determined by the inductance of the trap and the

impedance it oers to carrier freCuency components. Fine traps

generally fall into two categories. Pne is the resonant or tuned

trap and the second is the ide /and trap.

@esonant trap blocks only one or two components and have

very low inductance less than o.7mH 3generally %.' mH4. ide


89/117

/and trap blocks the available carrier freCuency range

completely or a larger portion thereof have typically inductance

up to 'mH 3generally ( mH4.

ave traps are generally rated for line operating current 3powerfreCuency4 with permissible overload capacity. ave traps are

generally inserted in series with the power lines. However the

IE# recommends a certain grading as to the rated currents and

associated short circuit resistance. Thus rated short duration

current related to the

line trap refers to the

maximum value of the

rms currents stated in*A, whose eect the

wave trap will withstand

for a period of ( second,

following a continuous

loading with r

400kv substation design

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