Transcript
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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_series8/11/2019 400kV Substation Design
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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:
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Detais a%!ut num%ers !* %a5s and num%ers !*
e+uipments re+uired:
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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>
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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.
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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
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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.
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AGTP T@AO?
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)(7 -+A $%% *+ autotransformer
The autotransformers are provided with a tertiary winding for a
few reasons. They are !
a.
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CUREN" "RANS#ORMER
This instrument transformer is connected to ac power circuit.
The secondary winding of the #Ts are fed to indicating,
metering instrument > and protective relays .#Ts are connected
to power circuit to watch over current ow > over power load.
In #T primary
inding is directly connected in series with the power circuit >
it is single turn. In the secondary winding number of turns ismore if the measuring current is more. The ratio of primary >
secondary current is known as #T transformation ratio.
The main purpose of use #Ts!
(. :ierential Krotection'. /us bar protection). /ackup protection for over current and earth fault$. -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.
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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
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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
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Krinciple of operation!
In the closed position of the breaker, the contacts remain
surrounded by ?
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-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!
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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
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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
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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.
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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.
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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.
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reduces with reduction in voltage. Induction disc type
construction is used for inverse undervoltage relay.
$. Directi!na p!)er rea5 ! this type of relay operates
when power in the circuit ows in a speci"c direction. A
directional power relay is so designed that it obtains its
operating torCue by the interaction of magnetic "elds
derived from both voltage and current source of the circuit
it protects.
In this type of relaysTorCue developed U +I cosV
U power in the
circuit.
hen the power in the circuit ows in the normal direction, the
driving torCue and the restraining torCue help each other to
turn away the moving contact from the "xed contacts.
#onseCuently, the relay remains inoperative. However reversal
of current in the circuit reverses the direction of driving torCueon the disc.
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NEGA"I&E SE$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
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W +ariants available with de"nite or inverse time delayed
output.
"rans*!rmer #aiures:/
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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!
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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.
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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
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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.
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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.
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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.
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/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
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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
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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.
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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.
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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
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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!
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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$7
%
CLASSI#ICA"ION O# EAR"2ING
Earthing can be classi"ed into the following categories based on the
purpose for which the part of the eCuipment connected to the general
mass of earth.
?S?TE- EA@THIOEQGIK-EOT EA@THIO
S(S"EM EAR"2ING
Earthing associated with current carrying parts of the eCuipment is
called ?ystem Earthing. The system security, reliability, performance,
voltage stabiliDation, all depends only on the ?ystem Earthing.
Eg. Earthing Oeutral of Transformer, ?urge arrester Earthing
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S(S"EM EAR"2ING ME"2ODS :
?olid Earthing The neutral is directly connected to ground without anyintentional impedance between neutral and ground.The coeNcient of earthing is less than 0%2 for suchsystems
@esistance Earthing @esistance is connected between neutral and ground
@eactance Earthing @eactance is connected between neutral and ground
@esonant earthing An ad=ustable reactor of correctly selected value tocompensate the capacitive earth current is connectedbetween neutral and earth. The coil is called Arcsuppression coil or earth fault neutraliDe.
E$UIPMEN" EAR"2ING
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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$UIPMEN" EAR"2ING:
ECuipment earthing ensures safety.The potential orearthed body does not rise to dangerously high valuesabove earth since it is connected to the ground.
Earth fault current ows through the earthing and mayrapidly cause operation of a fuse or an earth fault relay .
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CONNEC"ION O# ELEC"RICAL E$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
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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.
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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
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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 ''(
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?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!
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Famp 3wherenecessary4
#./. ]PO\indication
( Oo. @ed
1 #./. ]P
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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
$. Instruments shall be capable of indicating freely whenoperated continuous at any temperature from % to 7%
degree #.
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7. All circuits of instruments shall be capable of withstandingapplied load of '%2 greater than the rated capacity for aperiod of eight hours.
. The instruments shall be capable of withstanding the
eect of shock vibration and a dielectric test of '%%% +oltsr.m.s. to ground for one minute as per relevant I??.
The meters that are used are!
(. +oltmeter! A# voltmeter are generally moving coil type,
9mm [ 9mm siDe, '$%^scale, with range of %)%% *+3for
''% *+4 and %(7 *+3for ()'*+4
'. Ammeter! Ammeters are moving coil type, 9mm [ 9mm
siDe, '$%^scale and generally with dual scale.
).
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). *+A@H export$. 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
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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.
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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.
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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
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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.
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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: '%: )%:
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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
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#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.
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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
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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
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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.
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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
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(. 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.
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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
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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.
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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
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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
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/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
top related