r

Oy Chief Eng, nC't."r .sr \1 JO:lmodar YlIllt'Y Cnrp"rl1tHln

Dye Tow~rs. C"kuulI-54

GOVERNMENT OF INDIAMINISTRY OF POWER

CENTRAL ELECTRICITY AUTHORITY

MA VALON

TRANSMISSION PLANNINGCRITERIA

NEW DELHI

JUNE 1994

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D y Chief Enginc"r ISPMJDamod:lr Valley Corp 'fJltinn

1)VC Tuwers, CllkUtla•.S4

GOVERNMENT OF INDIAMINISTRY OF POWER

CENTRAL ELECTRICITY AUTHORITY•

MANUALON

TRANSMISSIO PLAN INGCRITERIA

NEW DELHI

JUNE 1994

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t.p.7":l'

fi~ l ~ JffufT'Rf nf;:r'.'l '1·HPI' '[rq:;rr

~~ 'l1f..J·<nJi11

MEMBER& EX OFFICIO ADOL SECRETARY TO GOVER NMENT Of INDIA

CENTRAL ELECTRICI TY AUTHORITYSEWA BHAWAN n. K PURM!

:rt TRH 10066

New Delhlll~

22nd June 1994

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The power transmissio n network of the co untry owned by the State Electricity Boards andCentral Sector Organisations fully integrated with each other presently stands unique in termsof its vastness. We have today over 29,000 ckt kms of EH V lines at 400 kV and above including1634 ckl kms of HVDC besides 1,90,000 ckl kms 01 lines at 220 kV and below. The grid system israpidly expanding and transmission lines in the 800 kV class are in the process of beingintroduced. A centrally own ed and operated National Power Grid is also getting establi shed.The need for defining Transmission System Planning Criteria keeping in view the specific needsof the country and the international developments in this field has assumed added significancein th is contex t.

A mod est effort was made by CEA in 1985, when a ' Manual on Transmission PlanningCriteria' was brought out incorporating the views and suggestions received from the differentPower Utilities in the country . It was also envisaged then that in course of time this manualshould be reviewed and revised , if necessary, on the basis of experience and advancements inthe transmission technology. Accord ingly a co mmittee was consti tuted in June 1992 under th echairmanship of Member (Power System), CEA to review the exis ting manual and bring out anew document incorporating the feed back and experience gained on EHV transmission systemtill date. The present document is the result of efforts put in by this committee . CEA have alsohad the benefit of consultations with1 Sh. Mata Prasad , Advisor NTPC , Dr. M. Ramamurthy,Director General CPRI, Dr K. Parthasarathy, Professo r Electrical Engineering, Indian In.stMuteof Science and Mr Giancarlo Manzoni, Chairman SC37 CIGRE.

The cri teria and guidelines described in the document are to be used in the planning anddesign of interconnected power system in such a way that the objectives of efficienttransmission system are achieved to provide a good service whi le operating the power systemin an integrated mode . It wi ll be the responsibility of individual beneficiaries, utili ties in the stateand central sector to ensure that it is planning and designing the system conform ing to thesecriteria. Any deviation will have to be formally documented and its ramification adequatelyhighlighted ..

It is hoped that the power utilities in the country will find th is manual useful in developing astrong and reliable power transmission network for thp country.

(:He.MI'lYlL)

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CO NTENTS

PREAMBLE

I. SCOPE

2. PLANNING PH ILOSOPHY & GENERAL,.GUIDELINES

3. LOAD-GENERATION SCENARIOS

3.1 General

3.2 Load Demands

3.3 Generation Despatches

4 , PERM ISSIBLE LINE LOADING LIMITS

5. STEADY STATE VOLTAGE LIMITS

6. SECURITY STA DARDS

6. 1 Genera l

6.2 Steady State Operations

6.3 Stability Cons iderat ions

A. Trans ient Stability

B. Voltage Stability

C. Steady State Oscillatory Sr.ability

7. REACTIVE POWER COMPENSATION

7.1 ShullI Capacitors

7.2 Shunt Reactors

7.3 Static VAR Compenstors

g. SUB STATION PLAN i ' G CRITERIA 14

DEFIN ITIONS 17

ANNEX- I PEAK ING CA PABILITY OF GENERATING STATIONS. 21

ANNEX-II LINE LOADING AS FUNCTIO OF LENGTH 23

ANNEX-III THERMAL LINE LOADI G LIM IT 25

ANNEX- IV OPERATIONAL STANDARDS 27

ANNEX-V DATA PR EPA RAT ION FOR TRANSM ISSI ON 29

PLANNING STUD IES

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PREAMBLE

The objective of system planning is to evolve a power system with a level of~

pelformance characterised by an acceptable degreepf adequacy and security based on

a trade-off between costs and risks involved. lnsofaras power transmission systems are

concemed, there are no widely adopted uniform guidelines which determine the criteria

for transmi ssion planning vis-a-vis acceptable degree of adequacy and security. The

criteria generally depends on the factors such as availabi lity of generation vis-a-vis

demand, voltage levels, size and configuration ofthe system,control and communication

faci lities, and resource constmints. Practices in this regard vary from country to country.

The common theme in the various approaches is the" acceptable system performance".

Even though the factors affecting system perfomlance are probabilistic in nature,- deterministic approach has been used most commonly, being rather easy to apply. For- adopting probabitistic approach, long operating experience and availability of reliable

Slatisticaldata regarding perfOimance of system components, namely equipment failure

rate, outage duration ,etc. are essential. Such data are presently being compiled by a few~

_ utilities: but these are still inadequate to go in for a totally probabilistic approach. Hence

_ it is considered prudent to adopt a deterministic approach for the present with a

_ committed thrust towards progressive adoption of probabilistic approach (An Action

_ Plan for adoption of probabilistic approach has been initiated). Keeping in line with the

_ above broad approach, this manual covers the planning criteria proposed to be used in

evolving powertransmission system on regional basis (EHY AC - 132 kY & above and

_ HYDe). ultimately leading to an All India Power Grid.

A brief write-up on Operational Standards and Data preparation for transmission

planning studies is also annexed to the manual.

..1

-1. SCOPE

The Planning Criteria detai led herein are primarily meanl for Long Tenn

Pe rspective ( 10 years and above) and Medium Telm (5- 10 years)

Transmission Planning Studies of large inter-connected power sys tems.

1.2 The manual covers in detail the planning philosophy. load demands and

generati on despatches to be considered and security standards. It also

indicates tlle broad scope ofsystem studies and gives guide-l ines fo r provision

of reac tive compensa tion and for plann ing of substa tions as are relevant to

pe rspective tnmsmiss ion syslem planning, A list of defin it ions of tellllS us.ed. 'in the manual is also appended.

2. PLANNING PHILOSOPHY & GENERAL GUIDELINES

2. 1 The transmission system shall be planned on the basis of reg ional self­

sufficiency with an ultimate objective of evolving a Nationa l Power Grid.

The regional self-sufficiency criteria based on load generation balance may

still dictate to have inter-regional exchanges with adequate inter-connection

capacity at appropr iate po ints taking into account the topo logy of the two

networks, the plant mix consideration, generation sllOrtages due to forced

oUlages, diversity in weather pauem and load forecasting errors in ei ther

regions. Such inter-reg ional power exchanges shall also be considered in

these studies.

2. 2 Thesyste m sha ll be evolved based on detailed power system stud ies which '

shall incl ude

i) Power Flow Studies

ii) Short Circuit Studies

ii·i) Stab ilit y Stud ies (including transient stability, voltage stability and

steady state oscillatory stability studies)

iv) EMTP Studies to detcnninc swi tching / temporary overvo ltages

Note: Voltage stability, oscil/atOlY stability and EMTP stlidies may not

farm part of perspective planning stlidies. These are however

reqnired to be done before any scheme report is finalised.

2 .3 The adequacy of the transmi ssion system shou ld be tested for different

feasible load generat ion scenarios as detailed in para 3.

2.4 The fo llowing options may be conside red for stengthening of the

transmission ne twork.

Addition of new Transmission lines to avoid overloading of ex istin g

system. ( Whenever three or more ci rcuits of the same voltage c lass

arc envisaged be tween two sub stations, the next transmiss ion voltage

should also be considered. )

App lication of Series Capacitors in ex ist ing transm ission line to

increa se power transfer capab ili ty.

Upgradation or the existing AC transmiss ion lines

Reconcluctoring of the ex isting AC lransmiss ion line wi lh higher size

conductors or with AAAC.

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Adoption of multi -vo ltage level and multi-circuit tr:lnsmiss ion lines.

The choice shall be based on cost. reliability. right-or-way requirements.

energy losses.down time (in caseof upgradation and reconductoring options)

etc. The adoption of existing or emerging semi conductor based lechnology

(e.g. FACTS) in transmiss ion upgradation may al so be kept in view.

in case of generating station close to a major load centre, sensitivity of it s

complete closure with loads to be met (to the ex tenl possible) from other

generating stations (refer para 3.3.3) shall also be studied.

2.6 In case of transmi ssion system associated with Nuclear Power Stations

there shall be two independent sources of power supply for the purposeof

providing start-up power facilities. FUl1her the angle between stal1-up

power source and the NPP switchyard should be, as far as possible,

maintained within 10 degrees.~

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The evacuation system for sensitive power stalions V IZ. . Nuclear Power

Stations, shall generally be planned so as to te rminate it aflarge load centres

10 facilitate islanding of the power station in case of contingency.

Where on ly two circuits are planned for evacuation of power from a

generating station , these should be ( as far as poss ible) two single circuit

lines instead of a double circuit line.

2.9 Reactive power flow through ICTs shall be minimal. omlally it shall nOI

exceed 10% of the rating of the ICTs. Wherever voltage on HV side of le T

is less than 0.975 pu no reactive power shall flow through ICT.

2. 10 Thet111al/N uciear Generating units shall normally not run at leading power

factor. However. forthe purpose of charging generating unit may be allowed

3

to operate at leading power factor as per tile respective capabilit y curve.

2.11 Intcr-regional links shall, in the present context, be planned as asynchronous

ties unless otherwise pennillcd from operatio nal consideration.

3. LOAD-GENERATION SCENARIOS

3. 1 The load-generation scenarios shall be worked out so as to reflect III a

pragmatic man ner the daily and seasonal variations in load demand and

gene ra tion availab ility.

3.2 LOAD DEMANDS

3.2. 1 The profile of annua l and daily demands will be determined from past data.

These daia will usually give the demand at grid supply points and for the

whole system identifying the annual and daily peak demand .

3.2.2 Active Power (MW)

The system peak demands shall be based on the latest reports of Electric

Power Su rvey (E PS) Comm iltce . In case these peak load figures arc

morc than the peaking availabilit y. the loads w ill be suitabl y adju sted

substation-wise to match with the availabi lity. The load demands at other

periods (seasonal va rimions and minimum loads) shall be derived based on

the annual peak demand and past pauel1l of load variations.

From practical considerations the load variation:-; over the year shall be

considered as under:

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Annual Peak Load

Seasonal variation in Peak loads (corresponding ro high themlal and

high hydro generation)

Minimum load.

Off -Peak Load relevant where Pumped Storage Plants are invo lved

or inrer-regional exchanges are envisaged.

Reactive power (MVAR)•

Reactive power plays an impo l1ant role in EHV tranSl11lSSIOI1 system

planning and hence forecast of reactive power demand on an area-wise or

substation-wise basis is as important as active power forecas!. This forecast

would obviously require adequate data on the reactive power demands at

the different substations as well as the projected plans for reactive power

compensat ion.

For developing an optimal power system. the utilities Illu st clearly spell OLit

the substation-wise maximum and minimum demand in MWs and MVARs on

seasonal basis. This will require compilat ion of past data in order to arrive at

reasonably accumte load forecast. Recognising the fact that this data is

presently nO! available it is suggested that pending availability of such data,

the load power facror at 220/132KV vo ltage levels shall be Iaken as

0.85 lag during peak load condition and 0.9 lag during light load cond ition

excepting areas feeding predominantly agriculruralloads where powerfacror

can be taken as 0.75 and 0.85 for peak load and light load conditions

respectively.. In areas where power factor is less than the limit specified

above, it shall be the responsibility of the respective utility to bring

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3.3. 1

33 .2

the load power factor to these limits by providing shum ca~acitors

at appropriate p laces in the system.

GENERATION DESPATC HES

Generation despatch of Hydro an(j-;l T hermal/Nuclea r un its wou ld be

dClcIl11ined judiciously on the basis of hydro logy as well as scheduled

maintenance program of the Generating Stations. The norms for working

QuI Ihe peaking availabili ty of different types of generating units is given

at Annex l.ln c,\se o f nuclear units the minimulll level ofo utput shall be take n

as not less than 70% of the rated capacity.

Generation despatches corresponding to the following operating cond itions

shall be considered depending on the nature and characteri stics of t-he

system

Annual Peak Load

•

Maximum thennal generation

Maximum hydro genera tion

Annual Minimum Load

Special area despatches

Special despatches corresponding to high agricultural load w ith I~w

power faclor. wherever applicab le

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4.

4.1

Off peak condit ions with max imum pumping load where Pumped

Storage stations exi st and also w ith the in ter- reg ional exchanges.

if envisaged

Comp lete closure ofa generating station close to a major load centre.

The generation despatch for purpose of carry ing out sensitiv ity studies

co rresponding to com plete c losure or a generating slat ion close [ 0 a major

load centre shall be worked out by increasing generation at other stations to

the extent possible keeping in v iew the maximum likely avai lability a l these

s tations. ownership pauen!. shares, e lC.• •

PERMISSIBLE LINE LOADING LIMITS

Pe lln issible line loading limit depend on many fac tors such as vo ll3ge

regulation, stability and current carrying capacity (thermal capac ity) etc.

While Surge Impedance Loading (SI L) gives a general idea of the loading

capability of the line. it is lIsual lO load the shol1lines above SfL (,Iud long lines

lower th~n S IL (because of the stabi lity limil3tions). S IL at di fferent vol tage

leve ls is g iven at Annex -II . Annex-II also shows Iine load ing (in tellllSof surge

impedance loading of uncompensated line )as a function o f line length

assuming a voltage regulation of 5% and phase angular difference of 30°

between the two ends of the line. In case of shunt compensated lines. the S IL

wi ll get reduced by a fa cto r k, where

k = ! ( I-degree of compensation)

For lines whose penn issible line load ing as dete lll1ined from the curve is

'higher than the thermal loading limit , permissible load ing limit shall be

. restricted to thennal loading limil.

7Dy Chief Engineer (SP M)

Dam 'd3.r V .11. Y CNporationD \'C T " W"; . lio. (.:.lkUll lt-54

4.2 Thermal loading limits are generally decided by design practice on the basis

of ambient temperature, maximulll pennissible conductor temperature, wind

velocity, eiC. In India, the ambient temperatures obt£lin ing in the variouspa'I1s

of the; country are different and vary considenlbly durilJg the variousseasons

of the year. Designs of transmission line with ACSR conductors in EHV

systems w ill normally be based on a conductor temperature limit of75 ('l c.However, for some of the existing lines wh ich have been designed for a

conductortempCrature of65 · C the loading slu" I be correspondingly reduced.

In thecase of AAAC conductors, maximum conductor temperature limit w il l

be taken as 85 • C. The maximum permissible line loadings in respect of

standard sizes of ACSR and AAAC conductors employed in EHV

transmission lines fordifferent ambiel1l temperatures and different maximum

conductor temperatures are given in Annex-Ill and the same can be followed

if permitted by stability and voltage regu lation consideration.

S. STEADY STATE VOLTAGE LIMITS

T he steady state voltage shall be m aintained wi thin the limit s given below

VOLTAGE (kV nn,)

Nominal Maximum Minimum

765 800 728

400 420 380

220 245 198

132 145 122

Note: The step change in vo ltage may exceed the above limits where

simultaneous double circuit outages of 400 kY lines are considered.

In such cases it Illay be . necessary to supplement dynamic YAR

resources at sensiti ve nodes.

8

TEM PO RARY OVERVOLTAGES due to sudde n load rejection.

420 kY system 1.5 p.u. peak phase to ne utral ( 343 kY = I p.u. )

800 kY system 1.4 p.u. peak phase to ne utral ( 653 kY = I p.u. )

SW ITCHI NG OVERVOLTAGES

420 kY system 2.5 p.u. peak phase 10 neutra l ( 3-13 kV = I p.u.)

800 kY system 1.9 p.u. peak phase to neutral ( 653 kY = I p.u.)

6. SECU RITY STANDARD S:

6.1 The securi ty §tandards are dictaled by the operationa l rcquiremcnts.

A brief wri le-up on rhe same is given at A nnex - IV.

For (he pllrpl )~ \'" of transmiss ion planning rhe following securi ly standards

shall be foll owed:

6.2 STEADY STATE OPERATI ON

i) As a general rule. the EHY grid system sha ll be capable of

. w ithstanding wi thout necess itating load shedding or rescheduling.of

generation. the follmO!ing contingencies:

Outage of a 132 kY DIC line or.

Ou tage of a 220 kV DIC line or,

O utage of 400 kV single circuit line or.

Outage of 765 kY single circuit line or

Outage of one pole of HVDe Bipolar linc or

Outage of an Inrerconnectin!! TransfonllCr- -

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6.3

The above contingencies shall be considered assumll1g a pre­

contingency system depletion (planned outage) of another 220

kY double circuit l ine or 400 kY single circuit line in another

corridor and not emanating from the same substation. All the

generating plants shall operate within their reactive capability curves

and thenetwork voltage profi le shall also be maintained w ithin voltage

limits specified in para 5.

ii) The power evacuation system from major generating station!

complex shall be adequate to withstand outage of a 400 k Y Double

Circuit line if the terrain indicates such a possibility.

iii) III case of large load complexes wi th demands exceeding 1000 MW the

need for load shedding in theevenl of outage of a400 kY Doublecircuit

I ineshall beassessed and kept minimum.System strengthening required,

ifany. on account Of lh is shall be planned on an individual case-la-case

basis.

iv) The maximum angular separation between any lwo adjacent buses

shall not nonnally exceed 30 degrees.

STABILITY CONSIDERATIONS

A . Transient Stability

i) T he system shall remain slab le under the contingency of outage

of single largest unit.

ii ) The syslem shall remain stable under the contingency of a

tempora rx single-phase-to-ground fault on a 765 sIc kY line

close 10 Ihe bus assuming si l ' ~ pole opening of Ihe fault,ed

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iii)

iv)

phase from both ends sl in 100 Illsec (5 cycles) and successful

reclosure (dead time I sec).

The system shall be able to sUIvivea single phase-to-ground fau It

on a 400 kY line close to Ihe bu s as per follow ing cri teria :

A. 400 kY SIC line: System shall be capab le of withstanding a

pemlanem fault . Accordingly. single po le opening (100 Illsec) of

the fau lled phase and unsuccessful reclosure (dead time I sec.)

followed by 3-pole opening (100 Illsec) of the faulled line shall

be considered.•

B. 400 kY DIC line: System shall be capab le of wi thstand ing

a pemlanent fault on one ortlle circuitswilen both ci rcuitsare in

service and a lransient faull when the system isalready depleted

with one circu it under maintenance/oulage. Accordingly, 3 pole

opening ( 100 msec) of the faulted circuit shall be considered

when both circuits are assu med in operation ( single pole

opening and unsuccessfu l auro-reclosure is not considered

generally in long 400 kY ole lines since the reclosure facility is

bypassed when both circuits are in operalion. due to difficullies

in sizing of neutral grounding reaclors) and single pole opening

(1 00 msec ) of the faulted phase w ith successfu l reclosure (dead

time I sec) when only one circuit is in serv ice.

In case of 220/ 132 kY networks, Ihe system shall be ab le to

survive a Ihree-phase fault wi th a faull clearing lime of 160 msec

(8 cycles) assuming 3-pole opening.

I I

v) TIle system shall be able to survive a faul t in ,HYDe converter

sta tion resulting in pernianent outage of one of the poles of

HVDe Bipoles

Besides rheahove the systemmoyalso he sJ(/~jected to rare cOfuingencies

like outage of HIIDC hipole . (ielayed faul l cleamuce due to stuck

/Jreaker cOllditions elc. The impact of these 011 system stahility l1iay

also he studied ~I'hile ~\'o,.killg out the defence mechonisms required in

system operation such as load sheddillg, gelleratim/ rescheduling.

islanding , etc.

B. Vo lt age slabi lit y

Each bus shall operate above knee point of Q-V curve under normal

as well as the contingency condit ions as discussed above in para 6.2.

C. Stead y Stat e Osci ll atory Stabilit y

The steady stateosci!Iatary stabi lity may be evaluated through Eigen­

value analysis. In case all the real pans of Eigen-va lues of linearized

system matri x arc negative. the system may be considered to have

steady stale oscillatory stability.

7. R EACTIVE POWER COM PE NSAT ION

7.1 Shunt Ca pacitors

Reactive Compensation should be provided as far as possible in the low

vo ltage systems with a view to meeting the reacti ve power requirements

of load close 10 tile load poin ts thereby avo iding Ih~ need for VA R transfer

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from hiQh voJraQe s\srem !O [h~ low \'olra!!e s\ stem. In rhe cases where~ .... . ~ .

nel\l,.'ork be low 132/220 k V Vo/[age level is nor represenred in [he system

planning stud ies, the shunt capacitors required for meeting the reactive

power requirements of loads sha ll be provided at the 132/220 kV buses .

Shunt Reactors

7.2. \ Switchable reactors shall be provided at EHV substations for controlling

voltages w.ithin Ihe limi ls defined in the Para 5 wi thout res0l1ing to

swirching-offoflines. The size ofreac!Ors should be such that under steady

state condition, sw itching on and off of the reactors shall not cause-a vol tage c1mngc exceeding 5%. The standard sizes (MVAR) of rcaciors are

400 kV (3-ph unit s)

765 kV ( I-ph units)

50, 63 & 80 at 420 kV

50, 63 & \ 10 at 800 kV

7.2.2 Fixed line reactors may be prov ided to cont ro l Temporary Power

Frequency overvo ltage [afterall voltage regulation action has taken placel

within the limits as defined in para 5 under all probable operating conditions.

7.2.3 Line reactors (sw itchable/controlled /fixed) may be provided if it is ·not

possib le to charge EHV line wi thout exceeding the voltage limits defined

in para 5. The possibility of reducing pre-charging voltage of the charging

end shall also be considered in the context of establislling the need for

reaClOrs.

7.3 Static VAR Compensation (S VC)

7.3'.1 Static Var Compensation shall be prov ided where found necessary to damp

the power swings and provide the system stability under conditions defined

13

111 Ihe para 6 on "Security Sianclards ". The c1ynami'c range of stalic

compensatorsslmll not be utilized under steady state operating condition as

far as possible.

8. SUB -STATIO PLA NING CRITERIA,

8. 1 The requirements in respect ofEHV sub-stations in a system such as the IOtal

load to be catered by the sub-station of a particular vo ltage leve l, its

MVA ca pacily, number of feeders pellnissible etc. are imponant 10 Ihe

planners so as to provide an idea to them about the time for go ing in for

the adopt ion of nexi higher voltage level sub-station and a lso the number of

substations required for meeling a panicular quantum of load. Keeping these

in view the following criteria have been laid clown for planning an EHV

substation:

8.2 The maximum fault level on any new substation bus should 110t exceed

80 % of the rated rupturing capacily of the ci rcuit breaker. The 20% margin

is intended 10 take care of the increase in short-ci rcu it levels as the system

grows. The rated breaking current capabi lity ofswitchgear at different voltage

levels may be laken as -

132 kV

220 kV

400 kV

765 kV

25/3 1kA

3 1.5/40 kA

40kA

40kA

8.3 Higher breaking current capability would require major design change in

the tenninal equipment and shall be avoided as far as possible.

14

Dy Chief Engineer (SP~

Damn.br Vllll ey Corpor:ltio tl .DVC Tuw.:rs. C'alcuna·S4

8.4 The capacity of any single sub-station at different voltage levels shall not

normally excced :

765 kY

400 kY

220 kY

132 kY

2500 MYA

1000 MYA

"320 MYA

150 MYA

8.5 Size and number of interconnecting transfonners (leTs) shall be planned in

such a way that the outage ofany single unit would not over load the remaining

JCf(s) or the underlying system.

8.6 A stuck breaker condition shall not cause disruption ofmore than four feeders

for 220 kY system and two feeders for 400 kY system and one feeder for

765 kY system.

15

l.

2.

DEFINITIONS

System Elements : All switchable components of a transmISSion system

such as Tidnsmission lines, transfonners, reactors etc.

Contingency : Temporary removal of one or more system e lements from

service. The cause or reason for such removal may be a fault , planned

I

maintenance/repair etc. ,

i) Single Contingency: The cOl1lingency arising out of remova l of onesystem element from service .

ii) Double Contingency : The contingency arising out of removal of two

system elementsfrom selvice. It inc ludes a Ole line, two SIC lines in

same corridor or different corridors, a SIC line and a transformer etc.

iii) Rare contingency: Temporary removal of complete generating

station or complete sub-station (including all the incoming &

outgoing feeders and transfomle rs) from service, HYDC bipole a"nd

stuck breaker condition.

3. Annual Peak Load: It is the s imultaneous maximum demand of the system

being stud ied. It is based on latest Electric Power Survey (EPS) or lotal

peaking power avai lab ility. whichever is less .

4. Minimum Load: It is the expected min imum system demand and is

detemlined from average ratio of annual peak load and minimum lo"ad

observed in the system forrhe la ' t 5 years.

17

5. Maximum Hydro Generation: It is the condition when hydro power

availability is maximum during the year. It is also known as High Hydro

condilion.

6. Maximum Thermal Generation: It is the condition when hydro

generation is low (not necessari ly mi9jmum) and thelmal generation is kepI

maximum to meet seasonal peak loads (not necessarily annual peak load). In

other words it is the condition when the gap between monthly peak demand

and hydro power availability is maximum.

7. Special Area Despatch : It is the condition when power output fonTI all the

gencrdling stations located in a area ( in close proximity) is kept at the

maximum feasible level.

M aximum Feasible Level of a generating station is the maximum power

output when all the un it s in a power station are in service assuming 110

planned or forced outages. However. in case of power station/complex

where six or more unitsex ist, for every six unitsone unit - secorid largest

- is assumed to be under annual planned maintenance.

1llllstratioll: While preparillg special area despatch for Villdhyac!wl

(6X210 MW + 2X500 MW) & Korba (3X200 MW + 2X500 MW) cOlI/plex.

Due ul1it of 2 /0 MW is assumed as under mailllel1011ce at \Iilldhyaclwl and

aile ullit of200 MW at Korba.

8. System Stabilit )' : A stable power system is one in which synchronous

machines. when IJel1urbed, will either rerum to their ori ginal stale if there is

no change in exchange of power or wi ll acquire new state asymptotically

without los ing synchronism. Usually the perturbation causes a tmnsient

that isosc illatory in nature, but if the system is stable the osc illations will be

damped.

18

•

9. Damping: A syslem is sa id to be adequately damped when halving lime of

the least damped electro-mechanical mode of oscillation is not morc than

5 seconds.

10. Oscillatory Stability: When vo ltage or rolor angle osci llat ions are

positively damped following a grid disturb:ance, the system is said to have

oscillatOly stability.

II. Voltage Stability: It is the abili ly ofa system to maintain voltage so Ihat when

load admittance is increased, load power will also increase so that both power

and voltage are controllable.

12. Transient Stability : This refers to the stability following a major

distu rbance (faults, opening of a major line, tripping of a generator) and

re lates to the firsl few swings following disturbancc.

~ 3. Temporary overvoltages :Theseare powerfrequency ovelVoltages produced

in a power system due to sudden load reject ion, single-phase-to -grou"nd

fau lt s, elc.

4. Switching ovcrvoltages : These ovclvollages generated during sw it ching of

lines. transfonners and reactors etc. having wave fronts 250/2500

micro sec.

.5. Surge Impedance Loading : It is the unit power factor load overa resistance

line such that series reac tive loss (PX) along the line is equal to shunt

capacitive gain (y2y ). Under these cond itions the sending end and receiving

end voltages and current are equal in magnitude bu tdifferent in phase position.

6. Thermal capacity of line: It is the amount of cu rrent that can be carried by

a Ii n~ onductor without exceed ing its design operating temperature.

t9

•

ANNEX·}.(refer para 3.3. / )

PEAKING CAPABILITY OF GENERATING STATIONS.

The peaking availabi lity of generating units wou ld be taken on the basis ofthe latest

nomlS laid down by CEA. The spinning reserve of 5% for TheffilaJ, Nuclear, Hydro

generation and Backing down allowance of 5% for Gas based generation as laid in

the present nOffilS of Generation Planning Criteria of CEA may not be taken

into consideration for Transmission Planning due to continuing peaking shortage of

power in a ll the regions during eighth plan period and beyond.-NOllllS for peaking Capability of Thellnal Stations:

The peaking capability of generating units would be computed as given below.

Outage rales Aux. Capaci ty PeakingUnit Planned Forced Panial consu- avai labilil capabi li

Capacity mplion factor factor(MW) (PMR) (FOR) (PaR) (AC) (CAF) (PCF)

% % % % % %

200MW 10.0 14.0 9.0 10.0 670 60.3& AboveBelow 10.0 16.0 14.0 10.5 60.0 53.7200MW

.ote: i)

i i)

CAF=IOO-(PMR+FOR+POR)

PCF=CAF-CAF x AC

In case of Eastern and Nonh-Eastem Regions forced outage rate

will be increased by 5%.

21

-

Norms for peaking eapabili t)' of Hydro stations

.Capital Maintenance (C M) =

Forced·Outage rate (FOR) =

Aux iliary Consumption (AC) =

Capacity availability facLor (CAF) =

Peaking CapabiliLy Factor (PCF) =

3 %

4.5 %

1.0 %,100 - ( CM + FOR ) = 92.5 %

CAF - CAF x AC = 9 1.5 %

•

Norms for peaking Capability of Gas based Stations:

The gas based power stat ionsare grouped into two categories mllllely base load. .stations and peak load sLat ions. The base loadstaLi ons are nOllnally Combined cycle

power plant which have Gas Turbine units and Steam Turbine uniLs. The peak load

stations arc open cyc le Gas Turbines which are generally used for meeti ng peak load

forabouL 8 Hours in a day at 80 % of ,heir raLed capaciLY. For combined cycle gas based

power station, the peaking capabili ty would be as given below:

Outage rales Aux. Capac ity PeakingUnit Planned Forced Partial conslI- availabilty capabilityCapacity mplioll faclor factor(MW) (PMR) (FOR) (PaR) (AC) (CAF) (PCF)

% % % % % %

Gas turbine units 15.0 10.0 10.0 1.0 65.0 64.4Steam Turbine 15.0 10.0 10.0 4.0 65.0 62.4units

Note: CAF= IOO-(PMR+FOR+POR)

PCF=CAF-CAF x AC

22

r

.,

- ANNEX-U(refer para 4:I )

LINE LOADING AS FUNCTION OF LENGTH

-SIL for different voltage levels and

conductor conti urationsVOLTAGE Number S. I. L.

(kV) & size of (MW )conductor

765 4 x 686 2250

765 4 x 686 6 14

Op at 400

400 2 x 520 515

400 4 x 420 614

400 3 x ~2() 560400 2 x 520 155

Op at 220

220 42() 13~

132

23

•. ,

#. . .

ANNEX-III(refer !'ara 4.2)

THERMAL LOADING LIMITS

Ambient A~1PACITY FORConclllclOr M aximulll Conductor Temperatu re (Oe )type and temperature

dimension ("C) 65 75 85

ACSR PANTHER 40 312 413210 sqmm 45 244 366

48 199 33450 311

ACSR ZEBR A 40 454 622420 Sq. mOl 45 339 546

48 240 49350 454

ACSR MOOSE 40 487 684 -520 Sq mill ~5 345 I 595

48 214 53250 487

ACS R BERSIMIS 40 565 804680 Sq. mOl 45 388

I697

48 220 62 1, 50 565I

AIIAC I 40 762420 Sq 111111 -15 I 70 1

48 1 66 150 632

AAAC 40 843.520 Sq. llllll 45 773

48 72650 694

AAAC 40 882560 sq mill 45 808

~8 7'\950 725

Ass umptions: so lar r(lcl iatiolls = 1045 \\//sq. 1111.. \Vind ve locit y =2k fvl/hour

Absorption coefr. =0.8. Emiss ivity coeff =0.45 Age > 1 year

_ !&- "t'2...","~ ~

--"l.,~. )II; l...

r",~

- .

ANNEX·IV

OPERATIONAL STANDARDS

The operational standards nonllally define the expected level of power systemperfoffi1ance under different conditionsof syslFm operationsand thus provide theguiding objectives for the planning and design of transmission systems. ill theabsence of any detailed document on operational standards, the followingobjectives are considered in the context of fannulating the manual:

I . The system parameters (voltage and frequency) shall be as close to the nominalvalues as possible and there shall be no overloading of any system element under

110l1nal conditions and different feasible load-generation conditions.

2. The system parameters and loading of system elements shall remain withinprescri bed limits and not necess itate load shedding or generation re-schedulingin the event of olltage of any single system element over and above a prc­contingency system depletion of another elemenl in another conidar. In the case01220 k V and 132 kV systems th is shall hold good for outage of Double Circuitlines.. In case ofpower evacuatioll frommajor generatingstation/complex (whenthe terrain indicates poss ibil ities of tower failure) the system shall withstand theoutage of two 400 kY circuits if these are on the same tower. Also in the case oflarge load complexes with demands exceeding 1000 MW the irnpact of outageof two incoming 400 kV circuits (if these are on the same towers) shall bemmUlllllTI.

3. The system shall remain in synchronism without necessitating load shedding orislanding in the event of Singlc-phase-lo-ground fault (three- phase fault in thecase of 220 kV llil d 132 kV systems) assuming successful clearing of fault by

iso lating/opening of the faulted system element .

4. The system shall have adequate margins in tenns of voltage and steady stateoscillatol)' stabilit y.

5. No more than fOlll-220 kV feeders/ two 400 kV feeders/ one 765 kV feeder shallbe disrupted in the event of a stuck breaker situation.

27

ANNEX-VDATA PREPARATION FOR

TRANSMISSION PLAN ING STUDIES

Actual syslem dala wherever available should be used. In cases where data is not

axailable standard data given below can be assumed.

Load fl ow & Short circuit studies

i) Load power factor shall be laken as per pam 3.2.3 of Ihe manual

ii) Reaclive power limits for genemlOr buses can be taken as

Qmax = Fifty percent of active generdlion

Qmin = (-) Fifty percent of Qmax

iii) Desired voltage of generalOr (PV) buses may be taken between 1.03 and 1.05

for peak load conditions and belween 0.98 10 1.0 for light load conditions.

iv) Line pammeters (p.u. / km / ckl at 100 MVA base)

Line vollage conductor Posilive Zero(kV) configuration Sequence Sequence

R X B R X B

765 Quad Bersim is 1.9513E-6 4.475E-5 2.4E-2 4.5E-5 1.8E-4 1.406E-2-

400 Twin Moose 1.862E'5 2.0751i·4 j.55E-J 1.012E-4 7.75E-4 J.584E-J

400 TwinAAAC 1.934E-5 2.065E-4 5.67E-3 1.05[E-4 7.73E-4 3.66E·3

400 Quad Zebra 1.05E-5 1.59E-4 6.65E-J 5.708E-3 5.94E-4 4.294E-:I

400 Quad AAAC 0.979E-5 1.676E-4 6.99E-J 5.32E-J 6.26E-4 4.5IE-3

400 Triple Zebra. 1.40IE-5 [ .87E-4 5.86E-3 7.616E-J 6.949E-4 3.783E-3

220 Zebra 1.547E-4 8.249E-4 1.42£-3 ·U45E-4 2.767E-3 8.906E-4

132 Panther 9.3 [E-4 2.216E-3 5.1£-4 2.328E-3 9.JIE-J

v) Tmnsformer reactance Generating Unit Inter-connecting

(AI·ils own base MVA) 14-15 %' < i2.5 %

lIfpla,ming studies alllhe tmnsformers should be kepI al nominal lapS and On Load Tap

Changer (OLTC) should not be considered. The effecI of Ihe laps should be kept as

operalional margin.29

" J •

-

For Shon circuit studies transient reactance (X'd) of the synchronous machines shallbe used. [Although sub-transient reactance (X"d) is generally lower than transientreactance and therefore shOlt circuit levels computed using X"d shall be higher thanthose computed using X'd, but since circuit breaker would operate only after 100 msecfrom fault initiation, the effect of sub-transient reactance would not be present. ·1 .

'"For shott ci rcuit studies fo r asymmetrical faul ts vector group of transformers shall beconsidered. Inte r-winding reactances in case of three winding transformers shall alsobe considered.

Forevaluating shon circuit levels at generating bus ( II kV, 13.8 kV etc.) that unit alongwith its unit tranSf0l111er shall be represented separately .

.Transient Stability Studies

Transient stability studies shall be carried out on regional basis. Expon/lmpon to/fromneighbouring region sha ll be represented as passive loads .

Voltage Dependency of the system loads

Act ive loads (P) shall be taken as P; Po(VlVo) _.Reactive loads (Q) shall be taken as Q ; Qo( VIVo) ,

Frequency Dependency of the system loads

Active loads (P) shall be taken as p; Po(f/fo)Reactive loads (Q) shall be taken as independent of frequency.

.where Po' Q0 ' V 0 and f 0 are values at the initial system operating conditions.

Synchronous machines may be represented as given below(for all regions except Nonh-eastem region)

Machine Size.less than 30 MW30 to 100 MW100tol90MW

200 and above

To be represented asmay be represented as passive loads.C lassical model ( IEEE type 1)Trans ient model .( IEEE type 2 for Hydro)

( IEEE type 3 for Thermal)Sub-lrdnsie,nt model (IEEE type 4 k . Iydro)

(IEEE type 5 for Thermal)

30

TYPICAL PARAMETERS FOR THERMAL & HYDRO MACHINES

MACHINE DATA- THERMAL/ HYDRO

MACHINE RATING (MW)MACHINEPARAMETERS

.

THERMAL500 210

HYDRO200

Rated Voltage (kV) 21.00 15.75 13.80RatedMVA 588.00 247.00 225.00

Inertia Constant (H) 3.07 2.73 3.5.ReactanceLeackage (XI) 0.1 4 0.18 0. 16

Directaxis (Xd) 2.31 2.23 0.96

Quadrature ax is (Xq) 2.19 2. 11 0.65

Transient reactanceDirectaxis (X'd) 0.27 0.27 0.27

Quadrature axis (X'q) 0.70 "0.53 0.65,

Sub-transientreactanceDirectaxis (X" d) 0.2 12 0.214 0.18

Quadrature axis (X"q) 0,233 0.245 0.23

OpenCircuitTimeContTransientDirectaxis (Tdo) 9.0 7.0 9.7

Quadrature axis (T'qo) 2.5 2.5 0.5

Sub-transientDirect axis (T 'do) 0.04 0.04 0.05

Quadrature axis (T"qo) 0,2 0.2 0.10

Soura : MIS Shara' Heal')' Electricols Ltd.

31

TYPICAL PARAMETERSFOR EXCITERS

Hydro ThermalTypical para meters

<2 1OMW >21OMW..Transdu. TimeCons.(TR) 0.040 0.040 0.QI5

Amplifiergain (KA) 25-50 25 , 50 50-200

Amplif. TimeCons.(TA) .04-.05 .04-.05 .03-.05

Regulator limiting voltageMaximum (VRmax) 4.0 6.0 5.0

Minimum (VRmin) -4.0 -5.0 -5.0

Feed backsignalGain (KF) 0.01 0.01 .0 1

Time Constant (TF) 1.00 1.00 1.00

ExciterGain (KE) 1.0 1.00 1.00

TimeConstant(TE) 0.7 0.3 0 .00 1

1

" .VRmax

/KA KE UF

1+sTA l+sTE

VRmin /

I sKFl+sTF .

vs

32

I), ,'"fl'Il"lh' :-)1' \.-'1

D.l1n, -d.lf V.lll. y C r .ra t ion

Dve Tuw<:rs. c"lcu([Ii-54

H. V.D.C. data : No standardised DC control model has been developed so far as

this model is usually built 10 the load requirements of the DC tenninal s. Based on

the pastexperience in carrying out stability studies, the foll owing models have been

suggested forrectifierand invertor!erminals.

DC CONTROL MODEL FOR RECTIFIER (POWER CONTRO L)

CURRENT ORDER REGULATOR CURRENT REGULATOR

1 AU'/\~- --~

l+sTr

AL RX_. _ - -------------_._._._ - - - _._- - --

Id

~J . lOR0-' MtNVdi I I

VALUES5

900_002

200020. 100.850.30

TYPICALALA NALRXTRKTIIMNn tAXV i\I IN

VDCOLI

IMN

_ . _ • -' _ _ . _ ALJL" . ALJL'i . _

----- ~ ·--- -- I

I Va I IMAX

MIN I~v~w.. VMA.:

L . _ . _ALFO ALFO

f---+iIIHj L_F.~,\ LRX

ld

CURRENT REG ULATORr'::T::-y=P"'JC"'AC':L-'VC:-A::-L"'UC:-E=.S:::-l

CU RRENT ORDER REGULATOR tM ARALON

0.1092

ALFO l:'il VAL

D C CONTROL MODEL FOR INVERTOR

33

E .M .'1'. P. Stu dies : SySieln shall be, to the ex tcnt possible, represented in detail. Pa ralle l

circuits/ altemate paths shall a lso be considered. At least one source sha II be represented

as type 59 (detail representation). Saturation chardcteristics of lmllsfomlcrs and

reactors shall a lso be conside red.

Voltage Stability Studies :T hese studies are carried out uSlllg load now analysis

program bycrealing a fi ctiloUSsynchronousconden scr at most vo ltage sensitive bus i.e.

bus isCOllvcI1ed into PV bus. By reduc ing des i red voltage of thi sbus M VAR generation/

absorp ti on is monitored. When voltage is reduced to some leve l it may be observed that

MVAR absorp tion does not increase by reducing vo ltage fUliller instead it also gelS

reduced. The voltage where MVAR absorption does not increase any further is know"n

as Knee Point ofQ -V curve. T he knee point ofQ-V curve represe nts the point ofvoltagc

instability. The horizontal 'distance ' of the knee point to the zero-MVAR vet1ica l axis

measured in M VARs . is therefore an indicator o f the proximity to the voltage col lapse.

0 :-, Ch,c! I'n:"'l~"~ ~i''\q

Dam' \.Ir '" ,., p'r.llmnDve T"w..:)~, L.a, ••!l.I<\-5 ;l

NOTES:-

35

,

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