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    High Voltage Distribution System-A Lasting Solution For The ILLs of

    the Last Mile of the Power Chain

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    High Voltage Distribution System

    Distribution is called the last mile in the power supply chainbeing closest to the consumer.

    Its quality controls / governs the consumer satisfaction

    However it is the most neglected segment of the power sector formany years due to paucity of funds

    Major challenge of reforms process is the up gradation ofDistribution system

    -To maintain the Standards of performance fixed by the

    Regulator.

    --To achieve the targets set Under National Electricity policy.

    -- To meet the stipulations of various codes like Supply Codes,Grid code etc., in all its functioning

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    High Voltage Distribution System

    National Electricity Policy stipulates achieving thefollowing targets, among others, by 2012

    - Extension Power supply of quality , continuity and reliability

    to all areas including rural areas as per the standards fixed

    by the respective Commission, meeting the demand in full,all at affordable price.

    - Bringing down AT&C losses to 15.5%

    Both the targets are of a very tall order, requiring adoptingof every conceivable method of system improvement.

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    High Voltage Distribution System

    Parameters for assessing supply quality Voltage Frequency, Harmonics

    Parameters for assessing Reliability Power CutsNo Supply Periods Interruptions - Frequency & Duration

    ---Measured variables

    Number of interruptionsDuration of interruptions

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    MAX. TOLERABLE TARGET LEVEL

    TRANSMISSION 4 4.00 2.00

    SUB TRANSMISSION 4 4.50 2.25HIGH VOLTAGE DISTRIBUTION 6 5.00 3.00

    LOW VOLTAGE DISTRIBITION 8 2.00 1.00

    TOTAL 22 15.50 8.25

    SYSTEM COMPONENTSEXISTING

    LEVELS

    INTERNATIONAL NORMS

    NORMS FOR TECHNICAL LOSSES

    REVIEW OF SYSTEM LOSSES

    Source:World Bank Energy Department Paper No 6-July 1982 on

    "Energy Efficiency:Optimization of Electrical Power Distribution System losses"

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    Objectives of a power utility

    Supplying of Power of quality, continuity andReliability

    Extending supply network to all parts in the area

    under its jurisdiction

    Meeting the demand in full

    Operating plants and network at Optimum

    efficiency

    Keeping the losses at bare minimumProviding effective consumer services

    Supplying power at affordable price

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    PRESENT STATUS OF DISTRIBUTION SYSTEM

    Power supply for few hours on any day. Number of interruptions even during the hours of supply due to

    the bad condition of net work.

    Poor quality of power supply with low voltages

    Growing consumer dissatisfaction. Poor revenue realization

    Comparatively higher losses.

    Financial status which permits only little investment in the systemimprovement.

    Achieving targets set in NEP by 2012, against the above back

    ground, calls for drastic changes in the set up.

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    Low Voltage Distribution System

    The two widely prevalent distribution practices invogue across the world are:

    Low Voltage Distribution System (LVDS):

    It is based on European practice. A Three phase transformer of considerable capacity,

    say 63kVA and above, is installed and a large group

    of loads are fed through longer LV lines .

    This system is best suited to meet the concentratedloads of high load density.

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    Low Voltage Distribution System

    This system is widely adopted in our power sector despitethe contrasting status, particularly in rural areas, of

    scattered loads with low load density.

    This has resulted in system losses well beyond the tolerablelimits, poor Voltage profile and host of other ills, many a

    times compounding in nature

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    Problems of Existing Distribution

    As Power is drawn through longer L.T. lines with higher current,

    there is increased power and energy losses

    Higher voltage drop in lengthy LT lines resulting in Low Voltages atconsumer end.

    Frequent motor burning outs due to low voltage at consumer end andconsequent expenditure on repairsHigher rate of transformer failures due to commonly ocuring defectsin L.T. network and over loading increased expenditure on repairs-increased interruptions to the consumer.

    For any transformer failure large number of consumers gettingaffected.

    For any delays in replacing failed transformers , damages to standingcrops

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    Problems of Existing Distribution

    As more number of consumers are connected under eachtransformer , more fluctuations.

    Higher possibilities for theft of energy by direct hooking to thebare L.T. lines, running in remote areas

    More number of interruptions due to the defects in the lengthyL.T net work. lesser reliability

    As bare L.T network has only fuse protection ,without anybreaker, Chances for accidents are more by coming in to contact

    with snapped bare wires.

    Poor quality of supply resulting in lesser end use efficiencyThe above drawbacks are automatically call for adopting a

    different distribution system devoid of these defects

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    High Voltage Distribution System (HVDS):

    It is the best remedy for all the prevailing ills in the existing LowVoltage Distribution System (LVDS)

    It is based on North American practice.

    A Three phase or single phase HV line is taken as near to a smallgroup of loads as possible, and a distribution transformers of smaller

    capacities , single phase or three phase transformer as the case may

    be , are installed to feed a small group of loads through AB cables

    and service wire , such that the length of the LV lines is minimum or

    is eliminated altogether.

    To the extent LV lines are permitted, they are with insulated ABcables only

    This system is best suited to meet the scattered loads of low loaddensity.

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    Different Types of High Voltage

    Distribution System

    There are three types of High Voltage distribution system in vogue:

    Phase Neutral HVDS (PN-HVDS)

    Phase Phase HVDS (PP-HVDS)

    Phase-Ground HVDS (PG HVDS)

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    Phase-Neutral HVDS

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    Phase-Neutral HVDS

    It is widely adopted in North America. Under this system:

    - the main line from substation is three-phase 4 wire (3 phases +

    Neutral)

    -- laterals are single-phase 2 wire line or two-phase 3-wire line orthree-phase 4-wire line depending upon the loads and feeding

    arrangement.

    Unique feature of the system lies in providing the neutral rightthrough the system, viz from substation to all nodes on the network.

    Single-phase Loads:11 KV single phase line (phase neutral) branch isextended from main line and 1 No. 6350/230-0-230 V distribution

    transformer is erected to feed single phase loads as shown in Part (A)

    of Fig.

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    Phase-Neutral HVDS

    Three-phase loads: Three alternative arrangements for feeding threephase loads are described.

    11 KV two-phase 3-wire branches are extended from the main lineand 2 Nos. of single-phase 6350/230-0-230 V distribution transformer

    is connected, star on HV side and open delta on LV side to feed three-

    phase loads, as shown in part (B) of Fig. Effective capacity of thetransformer bank is 86.6% of the total capacity of 2 transformers. Ie.

    . if 2 No.s 10 kVA, transformers are used ,maximum 3 ph. load that

    Can be fed is 17.32 kVA

    11 KV three-phase, 4-wire line is extended and 3 Nos. 6350/230-0-230 V single phase transformers are connected, star- delta to feedthree-phase loads as shown in Part (C)of Fig.

    Existing 11 KV three-phase 4-wire line is extended and three-phaseDelta/Star distribution transformer is used as shown in art D of Fi .

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    Phase - Phase HVDS

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    Phase - Phase HVDS

    Three-Phase loads: Three alternate arrangements for feeding three-phase loads are described.

    11 KV three-phase 3-wire branches are extended from main line and 2Nos. of single phase 11000/230-0-230 V distribution transformer is

    connected HV side/ LV side V-V (Open delta ) to feed three phase

    loads as shown in Part (F) of Fig. Effective capacity -86.6%

    11 KV three-phase 3-wire line is extended and 3 Nos. 11000/230-0-230 V single phase distribution transformer are connected delta on

    HV side and delta on LV side, as shown in Part (G) of Fig.

    11 KV three-phase, 3-wire line is extended and existing three-phase11000/415V delta / star distribution transformer is used as shown inPart (H) of Fig.

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    Phase - Ground HVDS

    It is similar to Phase- Neutral HVDS in all respects exceptthat ground is used as return path and neutral wire is notprovided all along the system.

    The transformer HV neutral or star point on HV side (when

    more than one transformer is used) is earthed solidly atevery location, and thereby ground is used as return path.

    This system is used in certain parts of North America andAustralia.

    Since ground forms return path, soil resistivity plays a keyrole.

    Good quality of earthing is required for the safety of

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    Phase - Ground HVDS

    It is unsuitable to Indian conditions due to technical and practical reasonslike :

    Since ground is used for return path of the current, the soil resistivityof the area plays a vital role. The system may be hazardous in areas

    where soil resistivity is high.

    Good quality Earthing is required for the safety of personnel andanimals. The code of practice stipulates that the voltage rise ie., Load

    current x and resistance of HV earthing system, at the point of

    Earthing shall not exceed 20 V.

    Providing effective Earthing and ensuring its maintenance throughoutthe period at a number of locations in rural areas is beset with severalpractical problems.

    Interference with telecommunication lines.

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    Advantages under HVDS

    All the ills of LVDS get eliminated under HVDS

    a)Drastic Reduction in system losses, both Power and energy losses

    (In S.ph.HVDS energy losses are 13% of that in LVDS)

    b) Improvement in system voltage profile (In S.ph.HVDS vol.drop is

    10% of that in LVDS)

    c)Reduction in possibilities for theft of energy by direct hooking from

    LT linesas the LV lines are virtually eliminated and even the short LV

    lines required are of AB cable..

    d) Reduction in transformer failures as there will be no over loading andminimum or no LT line defects.

    . Lesser interruptions, lesser delays in replacement of failed transformers

    and lesser damage to standing crops .Better consumer satisfaction

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    Advantages under HVDS

    e)Increase in end use efficiency causing better delivery of water,drawing lesser current.

    g)Sense of ownership of the transformer develops among theconsumers as the transformer caters to only two to three consumers)

    Possibilities for fluctuations get reduced due to fewer consumers.

    i) 11KV lines are controlled by breakers and LT lines are of ABcables. Chances for accidents due to snapping of conductors get

    reduced.

    J) With increase in the reliability of supply and better end use

    efficiency resulting in higher delivery of water, 2 crops are beingraised increasing productivity.

    k) Improvement in voltage profile, brings down cases of consumersmotor burning out drastically.

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    Advantages under HVDS

    l) Better socio economic development in rural areas. m) In case of any failure of a transformer only 2to3 consumers

    will be affected.

    n) In view of reduction in losses, additional loads can be fed

    with the same generation , without adding any new capacity. o) schemes covering conversion of LVDS to HVDS are eligible forSale carbon emission reductions (CMRs) under Clean Development

    Mechanism (CDM) . This additional benefit to the utilities will bring

    down the Pay back period to a considerably lesser time frame

    p) LT line maintenance is almost absent No tree cutting is requiredfor LT lines

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    Advantages of HVDS compared to LVDS

    System is more reliable because:

    The LV lines are short and insulated, avoiding all LV faults. The faults on HT line comes to the notice of the operator immediately

    due to the tripping of substation breaker.

    The failure of transformer affects only a very small number of

    consumers served by it. Voltage fluctuations: The voltage drop on the LV line is negligible.

    The additional drop due to extension of HV line up to consumer

    premises is also negligible. Thus the voltage profile is very stable and

    there is no need to use voltage stabilizer.

    With least or No possibilities for theft of energy , load management iscomparatively easier

    Ad t f S h HVDS d

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    Advantages of S ph. HVDS compared

    to LVDS

    The important drawbacks of LVDS and the way in which these areautomatically solved by adopting popular PhaseNeutral HVDS are:

    Line Losses:The loss in Sph.HVD system for the distribution of the

    same amount of power is less than 1% as compared to that of LV line.

    In fact it is lesser than the losses under 3 ph. HVD system

    Voltage Drop: The voltage drop for distribution of same quantum of

    power is less than 1% as against that in LVDS and this ensures proper

    voltage profile at all customer points.

    System Power Factor : The single phase motors can be used for all

    Agricultural services. The single phase motors have built in capacitorsessentially required for starting the motors.

    Thus system power factor is always maintained high with good

    capacitive compensation at theload end

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    Advantages of S ph.HVDS Capital cost is less as Transformer, surge arrestor requiring 1 No.

    Instead of 3, protection system cost less in sph.HVDS

    compared to 3 ph. system

    Protection requirements are simpler

    For cost effectiveness new villages with lesser load demand can beelectrified through S ph. HVDS, which can be converted in to 3

    ph. HVDS once the load picks up

    Thus if Existing LVD systems are converted in to HVD systemstaking due care of the System improvement aspects in respect of

    33 and 11kV Systems, HVDS will prove to be a boon forotherwise tottering Distribution networks.

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    CAPITAL COST

    HIGHER INVESTMENT ON TRANSFORMATION EQUIPMENT

    LARGER CAPACITY DUE TO LOW DICERSITY

    HIGH COST/KVA DUE TO SMALL CAPACITY OF TR

    LOWER INVESTMENT ON LINES

    SMALL SIZE CONDUCTORS ARE ADEQUATE DUE TO

    LOW CURRENTS

    LESS NUMBER OF CONDUCTORS

    OPERATING COST.

    HIGHER TRANSFORMATION LOSSES DUE TO HIGHER NO.OF. DTrs

    NO LOAD LOSSES PER KVA CAPACITY

    LOWER LINE LOSSES DUE TO LOW CURRENTS HANDLED

    QUALITY OF SUPPLY

    BETTER VOLTAGE PROFILE

    LOWER SYSTEM LOSSES

    BETTER RELIABILITYPREVENTS DIRECT TAPPING OF LINES

    LOAD MANAGEMENT IS EASIER

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    PROBLEMS AND SOLUTIONS fOR

    PROBLEM SOLUTION1 Voltage bandwidth limited

    to 10 %

    Bandwidth can be

    extended up to 20%

    with a AVB online

    2 Maintenance of large

    number of Transformers .

    ADOPT cast resin dry

    technology for maintenancefree operation and reliability

    These units are 25% costlier

    than oil filled units.

    3 Reconfiguration of

    network

    HVDS requires running of

    continuous neutral wire from

    substation.Line strengthened with

    intermediate supports and stays

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    . Capacitive compensation Provide online switchedcapacitor banks with automatic

    SF6/VACCUM switches for

    maintenance free operation and

    switching on and off capacitorwith load.

    Sectionalisation of primary

    distribution feeder .

    Provide automatic

    VACCUM/SF6 line

    sectionalisation on the SPUR

    lines which sense the voltage on

    and off sequence generated bycircuit breaker at the substation

    and isolate the faulty section

    automatically.

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    Sphase motors Indigenous manufacturing

    capacity for high efficiency

    and high power factor motors

    developed.

    High transformation losses No load losses constitute50% of total system losses

    Use of metal AMORPHOUS

    ALLOYS for TR core which

    reduces losses by 80% is very

    attractive in the long run as

    cost of AMORPHOUS metalis expected to come down

    with increased production

    immediately load

    management of pump sets

    can be adopted by

    S f i l i

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    Strategy for implementation

    The strategy for implementation of high voltage distribution system can

    be broadly divided into two parts.First part relates to extension of HVDS to meet new loads. This

    ensures that the new distribution system built is energy efficient.

    Second part relates to conversion of existing LV distribution system

    to HVDS.

    The two parts are inter dependent and can be executed simultaneously.

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    Part-I of Strategy

    The important problems likely to be encountered under this part are

    investigated and appropriate solutions are presented.

    Manufacture of small capacity single phase transformers which arerobust and fail proof.

    Integration of new HVDS with existing LVDS.

    Running of continuous neutral wire.

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    Part -II of Strategy

    Part II relates to making the existing distribution system energy efficient

    by conversion to HVDS.

    The work involved in this phase is :

    Conversion of existing low voltage lines to single-phase 2-wire HVline.

    Replacement of existing three-phase distribution transformers ofconsiderable capacity with small capacity single-phase transformers

    Replacing all LT Guy insulators of Stay sets by HT Guy insulators

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    Discussion

    HVDS is technically superior and provides ready solution to theproblems of distribution system.

    Capital investment required for building new HVDS is 16.5% lowerthan that of LVDS. The Peak Power loss and energy losses of HVDSare 33% and 18% lower than that of LVDS respectively.

    Capital investment required to restructure the existing network asHVDS is marginally cheaper than restructuring the network as LVDS. The peak power loss and energy losses of restructuring HVDS are

    lower by 25% and 27% respectively compared to that of LVDS.

    The peak power losses and energy losses reduction by restructuring as

    HVDS are 80% and 66 % respectively. Restructuring of existing distribution network as HVDS is highly

    viable as the pay back period is about 18 months.

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    Conclusions

    Phase neutral HVDS is identified as the best system among thedifferent HVDS schemes.

    HVDS effectively tackles the problems faced by the utilities in theexisting LVDS.

    The strategy proposed for implementation of HVDS and itsintegration with the existing network is found to be technicallyfeasible and financially viable.

    The cluster based algorithm proposed for restructuring the existingLVDS as HVDS is an effective tool for large scale restructuring of the

    existing network. The restructuring of existing LVDS as HVDS is practically feasible

    and financially viable.

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    Summing up, the recommendation is that the utilities should adopt

    HVDS in place of the prevailing LVDS; extend it to all newextensions; also restructure the existing network as HVDS

    simultaneously. This is the only technically feasible and least cost

    solution approach for reduction of losses in Low Voltage network.

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    CASE STUDY

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    Case Study 1-HVDS 1 Ph

    In order to propogate the concept and as a technology demonstration the

    following Two schemes are formulated.

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    g

    H V D S SCHEMES

    WARANGAL NALAGONDA

    1.Noofpumpsets 7000 3200

    2. Year of sanction 1993-94 1997-98

    3. Cost of the projects Rs 8.0 cr Rs 8.4 cr

    4. Pay back period 3 years 3 years

    5. Achivements 2500 nos 1100 nos

    6. Financed by OECF(Japan) DFID( U K )

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    REASONS FOR POOR PROGRESS

    1. Conversion of 3 ph motors to 1 ph motors.

    2. Unauthorized pump sets

    3. Higher H P

    4. Industrial services above 10 HP

    5. Local mechanics

    EVALUATION REPORT

    M/S EEEC BANGLORE

    OBSERVATION AND FINDING

    1. Over all losses reduced from 20% to 4%.

    2. Voltage level has improved substantially

    3. P.F increased to 0.91 from 0.7

    4. No of pump sets increased to 36% from 25%5. Possibility of theft of energy reduced

    6. Pay back periods are in line with anticipated results.

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    SUGGESTIONS

    To go for 3 HVDS by providing small capacity DTR ie 10 / 15 / 16 KVA

    ADVANTAGE1.Loss reduction is same in both cases

    2.Pay back period is faster

    3.Consumer involve is avoided

    4.All benefits relating to s HVDS conversion ie

    Better VoltageReduction in interruptions and Break do wnsTheft of energy controlledReduction in DTR failuresLoss reduction etc

    SI No. Item LVDS HVDS

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    1. Distribution Transformer 1. No 100 KVA11kv/415V

    11 NOS 15 kVA

    11kV/415 V

    distribution Trs

    2. Line LT 3 phase 4 wire line(3phase one 1 neutral)

    11KV line (3wires)LT

    line with AB cable

    having 4 core cable

    3. Length of the line LT-3.6mm HT(11kv)-2.6km & LTAB cable-1km

    ( both are cases of

    conversion from LTLine)

    4. NO. of agriculture loads

    (Pumpsets)

    39Nos. 39Nos.

    5. Connected Load 179.5 HP 179.5 HP

    6. Crop pattern Rice and Sugarcane Rice and Sugarcane but

    2 crops

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    (a) No. of days of study 13 days 15 days

    (b) Input 4290 Units 5310 Units

    (c) Output 3490.4 Units 5019.8 Units

    (d) Loss of units 799.06 Units 290.8 Units

    (e) %Line losses 18.63% 5.47%

    (f) Voltage at tail end 350V 420V

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    Table C: Cost benefit Analysis

    Line losses before conversion :18.63%Line losses before conversion :5.47%

    Connected load :179.5HPNo. of units fed into LT network per annum

    (approximately 900 units/H.P) :161550

    5) (a) Line losses under LVD System (units) :30097

    ( b)Line losses HVD System (units) :8837

    6) a) Savings in losses (units) by conversion to

    HVDS (units) 21260

    b) Hence with the same input energy, additional units

    available for sale after meeting the load demand

    of 179.5HPagl.loads :21260

    HVDS t ti P ti

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    HVDS construction Practices

    HVDS conversion can be in two ways

    A)Erecting a new HVDS network altogether, transferring theloads to the new system and dismantling the old system, as is

    being adopted in Rajasthan where a large portion of LVDS is

    already converted in to HVDS .

    Push-fit covers for meters and armoured cabels for service wiresare used to curb thefts.

    Where only 1 or 2 services are to be fed, Meters and capacitorsare located in a separate compartment on the backside of the

    transformer.

    This method permits free flow of work and reduces interruptionsto the consumer during conversion.

    But it is costly and suffers from right of way problems.

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    B) By converting LT 3ph. 4wire into 11kV line to the extentrequired.

    No new lines are needed to be laid to execute this new concept.

    Re- configuration and modification of the existing lines is done,using the materials that are already in use except for a few items.

    ie converting existing LT lines in to 11kV (HT) lines by replacingonly insulators, suspension and tension hardware and x arms,

    introducing new stay sets where required etc.

    Existing poles are continued except for introducing 9.01 mt polesin the new transformer locations, for obtaining standard

    clearances.

    If the existing conductors are of adequate size, 3 out of 4 areused dismantling the fourth n is carriedout during the hours when

    there is no su l in a ricultural feeders. .

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    Using polymer insulators for 11kV line extension, for easyinstallation and puncture proof life

    This method is less costlier and involves no right of wayproblems. As adopted in APSPDCL, Constructio

    Specific steps needed to derive benefits in full

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    Specific steps needed to derive benefits in full

    The new system also requires certain steps to be taken to make itwork successfully.

    With increased transformers their maintenance requiresadditional attention, particularly in remote areas. Better to use

    Fail proof / Cast Resin transformers.

    Perfect Earthing of transformers is essential to lessentransformer failures and accidents, as these locations cannot be

    revisited frequently.

    HT line shall be maintained systematically, particularly in case oftree trimming, as even a momentary fault will trip the feeder.

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    Each transformer shall be provided with drop out switches tolocalize the unavoidable interruption.

    Measures to prevent theft of oil or winding from transformers ortransformer itself, shall be adopted.

    It is equally important to upgrade and strengthen the up stream

    systems ie., 11kV and 33 kV systems adequately, to reap thebenefits of change in full.

    In either case, survey of existing 3 phase or single phase motorloads has to be carried out ( using tongtester and measuring load

    current of each motor

    This is required to ensure that small capacity transformers beinginstalled under HVDS do not get over loaded and fail

    Erecting New Line

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    Erecting New Line

    Route survey to be conducted ( Preliminary walk over fallowed bydetailed survey)Route shall be as close to the loads it has to feed as

    Possible, as short as possible ,avoiding difficult country side,naturalhazards, higher transportation costs etc

    Transportation of RCC/PCCpoles:

    a) Generally heavier and stronger on the longer axis than shorter axis.This shall be considered

    b)Un loading from trucks and trailers shall be by using suitable skid

    boards(Not to be dropped).Preferable to use chain pulley block and a

    beam arrangement.c) Shall not be dragged on rough surfaces.Use Small carts

    Pole locations

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    Pole locations

    A) spans shall be limited by the tensile strength of the conductor,wind pressure .

    In a given length span shall be uniform with horizontal grade to theextent possible

    Not to be located along the edges or cuts

    Cut points for a section, geneally not longer than 1,6 km (10 poles/km for HT and 15 poles/ km for LT)

    Right of way shall be identified and tree and vegetation clearanceshall be carried out

    HTLine Erection

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    HTLine Erection

    Pit marking and digging

    Erection of poles and concreating

    Providing of Stays with guy insulators

    Mounting x arms, insulators

    Paying out and Stringing the conductor

    Sagging and tensioning the conductor

    Providing earthing and gaurdings

    Testing and commissioning

    Pit- 1.2mtx o.6mt

    poles to be erected with its longer axis in the direction of the line.

    Planting depth for pole 1/6 th of the pole length

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    Each pole shall be raised on a base plate or RCC padding for betterload distribution on the ground below

    For smooth sliding an inclined trench of a length of 15.2cmWx10.2cm L is made adjacent to the pit and a piece of MS channel

    is placed on the other side in an inclined position so that pole can

    smoothly slipped in to the pit Using a Bipod and 3 ropes pole is erected and kept in vertical position

    using manila ropes. Verticality checked with spirit level, earth filling

    in the balance pit and ramming is done. In Swamp locations poles are

    concreted up to pit level

    Stay sets with 7/3.15 mm stay wire and turn buckle rod of 16mm diaae erected to prevent tilting of poles. Most commonly used is anchor

    guy

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    .

    Guy is used at angle locations, Dead ends, Tee offs, steep geadientsand where wind pressure is more than 50 kg/Sq.m Guy insulator kept

    at a level of 3.5mts .Stay rod shall project 2mts. above ground level

    (A type for LT line and C type for 11kV line)

    At 35 to 40 inclined. After concreting and backfilling the balance 7

    days are allowed for settling X-arms and insulators are fixed

    Conductor drum or conductor shall not get damaged while transport,paying out.

    Conductor is passed through Wooden or Aluminium rollers or snatchblock

    Mid point joint through compression crimping o if helical fittings areused manually

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    Conductor is pulled using come along clamp, tensioned and passed onto the insulator after Sag tensioning as per the Chart

    Sag d= WI/2T

    I= half the Span, T= tension in the conductor

    W= w+ww., w= wt. of the unit length of conductor acting

    vertically

    Ww= Wind pressure on the conductor

    Up to 33kV sag is checked by sighting

    Pin binding with tie wire

    Soft annealed Aluminium wire so that may not be brittle and injurethe conductor

    Length of wire 1mt to 3 mt(33kV) required for a complete

    Constuction Practices

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    Constuction Practices

    Metal supports Facto

    Lattice type& compound type- not less than 1.5

    Mechanically processed concrete pole- 2.0

    Hand moulded concrete pole --------------- 2.5

    Lattice & compound type -- not less than 1.5( under broken wire condition)

    Minimum factor of safety for Guard wire,

    stay wireand bearer shall not be less than 2.5, based on

    Ultimate strength of the wire

    Minimum FS for a conductor shall be 2 based on its Ultimate

    strength

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    For calculating F.S.:

    Max. wind pressure as specified by the State govt.

    For cylindrical bodies, the effective area shall be taken as 2/3 of theprojected area exposed to wind pressure

    For lattice or compound structures the wind pr. On the lee side shall

    be taken as one half of the wind pressure on the windward side

    Factor safety shall be calculated on the the crippling loads for thesupports used as struts and up on the Elastic limit of the tension

    members

    Max. and Minimum temperatures as specified by the State govt. Not withstanding any thing stated above, in locations susceptible forice accumulation loadings to be stated by govt.

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    Conductor tension at 32degC without external load shall not exceedthe following % of the ultimate tensile strength of the conductor

    Initial unloaded tension- 35%

    Final unloaded condition 25%

    Conductors having a cross section of a triangular shape like

    conductors composed of 3 wires, final unloaded tension at 32C shallnot exceed 30% of the ultimate tensile strength of the conductor

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    Rule 82: When conductors forming part of circuits of differentvoltages are to be erected on the same support, proper clearance

    between circiuits of different voltages shall be ensured.

    Once a line is commissioned , if any building / structure is to beerected/ extended fouling the clearances, corrective action shall be at

    the cost of building / structure owner. Cost shall include a) cost of the material giving credit for depreciated

    cost b) cost of retrieved material giving credit C) Cost of labour d)

    supervision charges@ 15% of wages and e) any other charges

    involved

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    TYPE Voltage level Ground clearance in mts

    Across the street Low and medium voltage lines 5.8

    High voltage lines 6.1 mts

    Along the street Low and medium voltage lines 5.5

    High voltage lines 5.8.mts

    Else WhereLow and medium voltage and highvoltage lines up to 11kV bare 4.6

    Low and medium voltage and high

    voltage lines up to 11kV(Insulated) 4.0

    High voltage lines above 11kV 5.2

    Extra high voltage linesProvided minimum clearance across or

    along

    5.2 + 0.3 mt for every 33 kV6.1

    Min. CLEARANCES in mts AT LINE

    CROSSINGS

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    CROSSINGS

    Line

    volt.

    22kV 33kV 66kV 110kV 132kV 220kV

    250V 2.44 2.44 2.44 2.75 3.05 4.58

    11kV 2.44 2.44 2.44 2.75 3.05 4.58

    22kV 2.44 2.44 2.44 2.75 3.05 4.58

    33kV 2.44 2.44 2.44 2.75 3.05 4.58

    66kV 2.44 2.44 2.44 2.75 3.05 4.58

    110kV 2.75 2.75 2.75 2.75 3.05 4.58

    132kV 3.05 3.05 3.05 3.05 3.05 4.58

    220kV 4.58 4.58 4.58 4.58 4.58 4.58

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    Rule 87: When two lines cross

    It shall be as nearly at right angle as possible

    As near to the support as possible

    Support in the lower line shall not be erected below the upper line

    Rule 88:Guarding at crossings :

    Every guard wire is to be connected with earth at each point at whichits electrical continuity is broken.

    Every guard wire shall have an actual breaking strength of not lessthan 635.02 kgs and if made of Iron or steel it shall be galvanized

    Every guard wire or cross connected system of guard wire shall haveenough current carrying capacity so that they shall not melt or fuse

    before the live line wire is rendered dead or removed

    CLEARANCES of OH LINE &

    S i Wi AS PER RULE 77

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    Service Wire AS PER RULE 77 Rule 89:No service line or tapping shall be taken of from any over

    headline except from the point of support

    Rule 90: Earthing

    All metal supports and metallic fittings attached there to shall bepermanently & efficiently earthed.

    A continuous earth wire shall be secured fastened to each pole andconnected to the earth at 4 points per every 1.609 km

    Each stay wire shall be earthed efficiently or a guy insulator shall beprovided in it at a height not less than 3 mts from the ground

    Spacing between the 4 points shall be equal to the extent possible Alternatively each pole and metallic fittings attached there to shall beefficiently earthed.

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    Metallic bearer wires supporting insulated low/ medium voltageservice lines shall be efficiently earthed/ insulated

    Each stay wire shall be earthed unless guy insulator is placed at aheight not less than 10 from the ground

    Rule 91 Safety devices

    Every over head line laid along/ across the street shall have aprotective device to render it harmless when it brakes,

    Every over head line Shall be fitted with an anti- climbing device toprevent unauthorized persons climbing the poles/towers

    Rule92: Every over head line Shall be fitted with a device toprotect the line from lightning by diverting the surge to the earth

    connected to earth mat

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    The earthing lead from a LA shall not pass through any metallic pipebut taken directly to an earth electrode in a separate earth pit

    Guard wire shall be earthed at each point where its electricalcontinuity is broken

    Guard wire minimum breaking strength-635 kgs

    To be galvanized if made of iron or steel Guard shall have sufficient capacity not to melt or fuse till the live

    wire in contact is removed

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    1/6th of the pole height be buried in the pit.

    Base plate shall be provided underneath the pole for uniformdistribution of load on a larger area.

    Pole shall be earthed through earths and combined earth resistanceshall not be more than 5 ohms

    Danger boards to be fixed at a conspicuous position as per IS 2551 onevery motor, generator, transformer, Electrical equipment, pole

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    THANK YOU