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    D. Babu(101798)

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    The first central electric station was

    installed by Edison in Newyork in1882 which is operated at 110v DC

    It is interesting to know as to why

    then AC almost replaced all DC lines

    and why DC is again being used forsome high voltage transmission lines

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    Reasons for power generated,

    transmitted, distributed andconsumed as alternating current

    Transformer

    Induction motors

    Commutators

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    Strong technical reasons for direct

    current transmission

    High charging currents in AC Asynchronous interconnection

    Economical after break even distance

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    Cost comparison of ac and dc

    transmission

    Cost of DC terminal

    Cost of AC terminal

    Cost

    Break even distance

    Distance in km

    Cost of AC Line

    Cost of DC Line

    500 700 km

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    Types of HVDC links

    Monopolar

    Bipolar

    Homopolar

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    Monopolar line

    Usually the line is operated with negative

    polarity as the corona loss and radio

    interferences are less

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    Modes of Operation

    DC OH Line

    Converter

    Transformer

    Thyristor

    Valves

    400 kVAC Bus

    AC Filters,

    Reactors

    Smoothing Reactor

    Converter

    Transformer

    Thyristor

    Valves

    400 kVAC Bus

    AC Filters

    Smoothing ReactorBipolar

    Current

    Current

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    Modes of Operation

    DC OH Line

    Converter

    Transformer

    Thyristor

    Valves

    400 kVAC Bus

    AC Filters,

    Reactors

    Smoothing Reactor

    Converter

    Transformer

    Thyristor

    Valves

    400 kVAC Bus

    AC Filters

    Smoothing ReactorMonopolar Metallic Return

    Current

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    Modes of Operation

    DC OH Line

    Converter

    Transformer

    Thyristor

    Valves

    400 kVAC Bus

    AC Filters,

    Reactors

    Smoothing Reactor

    Converter

    Transformer

    Thyristor

    Valves

    400 kVAC Bus

    AC Filters

    Smoothing ReactorMonopolar Ground Return

    Current

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    Homopolar link

    Two or more conductors with same polarity usually

    negative for the reason of corona and radio interference

    and always operate with ground as the return

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    Parallel and series connections ofthyristor

    o Parallel -Current rating will increase

    o Series voltage ratings will increase

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    Parallel operation of DC link with

    AC network

    Stability of AC network can be increased if it iskept in parallel with DC line

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    POWERGRID (Engg-HVDC)

    Single Line Diagram

    DC OH Line

    ConverterTransformer

    DC Filter:

    DT 12/24

    DT 12/36

    DC Filter:

    DT 12/24

    DT 12/36

    ThyristorValves

    400 kVAC Bus

    AC Filters,

    Reactors

    Talcher ConverterStation

    Smoothing Reactor

    ConverterTransformer

    DC Filter:

    DT 12/24

    DT 12/36

    DC Filter:

    DT 12/24

    DT 12/36

    ThyristorValves

    400 kVAC Bus

    AC Filters

    Kolar ConverterStation

    Smoothing Reactor

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    6-Pulse Convertor Bridge

    3

    6

    CiLs

    4

    E1 L

    s

    Ls

    Bi

    iA

    1

    2

    I

    V'd

    5

    Vd

    IddL

    d

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    12-Pulse Convertor Bridge

    Y

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    POWERGRID (Engg-HVDC)

    Salient Features

    Rectifier Talcher, Orissa

    Inverter Kolar, Karnataka

    Distance 1400 km

    Rated Power 2000 MW

    Operating Voltage 500 kV DC

    Reduced Voltage 400 kV DC

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    POWERGRID (Engg-HVDC)

    Simplified SLD at Talcher

    Y

    YACF3 ACF1

    Y

    Y ACF2

    Meramundali-I

    Meramundali-II Rengali-II

    Rengali-I

    Rourkela-II

    Rourkela-I

    ICT

    BS 1B

    BS 1A

    Gen 1Gen 2Gen 3Gen 4Gen 6

    BS 2B

    BS 2A

    BS 3A

    BS 3B

    Pole2 Pole1

    ICTGen 5

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    Bus # 3 Bus # 5

    Bus # 4 Bus # 6

    STAGE-II POWER FLOW SINGLE LINE DIAGRAM

    GENERATOR # 6GENERATOR # 5GENERATOR # 4

    ST # 2

    GENERATOR # 3

    ST # 3

    HVDC # 1 HVDC # 2

    GT # 5

    HVDC # 3 HVDC # 4

    HVDC POLE-2HVDC POLE-1

    400 KV BUS-1

    400 KV BUS-2

    TO FILTER-2

    MWT-6MWT-5MWT-4MWT-3

    GT # 3 GT # 4

    TO FILTER-1

    GT # 6

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    POWERGRID (Engg-HVDC)

    Simplified SLD at Kolar

    Y

    YACF2ACF1

    Y

    Y ACF3

    Future

    ICT

    BS 1A

    BS 1B

    ICT

    Pole1 Pole2

    Chennai Hosur

    I

    Hosur

    I

    Hosur

    II

    Hoody

    I

    Hoody

    II Bangalore

    Cuddapah Future

    Line

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    Logic for unit tripping during HVDC single

    pole outage

    block

    blockdeblock

    deblock

    Pole 1 Pole 2

    S

    Power

    >

    1750

    Trip

    Identified

    Unit

    TSTPP Stg II all four Units running with full capacity

    Ex-bus Generation shall be around 1850 MW or less.

    While all four Units running, if one HVDC pole isblocked & NTPC Ex-bus Generation is more than 1750

    MW, one identified unit shall trip instantaneously.

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    Logic for unit tripping during HVDC

    Both pole outage

    block block

    Pole 1 Pole 2

    S Power> 550

    S Power> 1100

    Trip Unit # 5

    Trip Unit # 4

    250 ms

    500 ms

    Trip

    Unit # 6

    T1

    T2

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    Logic for unit tripping during HVDC Both pole

    outage

    Both HVDC poles blocked & TSTPP Stg II Ex-bus generation is morethan 550 MW & less than 1100MW.

    Unit # 5 shall trip instantaneously.

    Unit # 4 shall trip after time delay of 250 m sec.

    Unit # 6 shall trip after time delay of 500 m sec.

    Both HVDC poles blocked & TSTPP Stg II Ex-bus generation is more than 1100

    MW.

    Unit # 5 & 6 shall trip instantaneously.

    Unit # 4 shall trip after time delay of 250 m sec.

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    Existing HVDC in INDIA

    1 Rihand-Dadri (1500MW)

    2 - Vindyachal (500MW)

    3 - Chandrapur-Padghe (1500MW)

    4 - Chandrapur-Ramagundam(1000MW)

    5 Barsoor-Lower Sileru(100MW)

    6 Gajuwaka (500MW)

    7 - Sasaram (500MW)

    8 - Talcher-Kolar (2000MW)

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    HVDC Bipolar LineChandrapur-PadgheRihand-Dadri

    Talcher-KolarBalia-BhiwadiBiswanath-Agra

    HVDC Back-to-backVindhachalChandrapurGazuwakaSasaram

    HVDC Monopole LineBarsur-Lower Sileru

    Existing HVDC projects in INDIA

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    Advantages

    Power per conductor

    Power per circuit

    No charging current

    No skin effect

    Less corona loss and radio interference

    No stability problem

    Less short circuit currents

    No compensation

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    Disadvantages

    Expensive converters and transmission lines

    Voltage transformations

    DC circuit breaking is difficult

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