Zig Zag Transf_1

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    Anal

    ysiso f t

    he Probl

    em

    3.1 G

    eneral actio

    n ofZig-Zag

    eart

    h in g)

    Transforme

    r

    Earthing

    tr ansformer i

    s oil-immers

    ed type suita

    ble for outdo

    or installatio

    n. t has an

    interco

    nnected star

    w inding whi

    ch is directly

    connected t

    o the low vo

    ltage termina

    ls

    of

    th e

    associated s

    ystem transfo

    rm er. Earthi

    ngtransform

    er is also prov

    id ed with a s

    ta r

    con

    nected auxil

    ia ry winding

    arranged to

    give a 400

    /230V, three

    phase, four

    wire

    s

    upply.

    Specif

    ic ations

    of

    th

    e transforme

    r are as follow

    s.

    33 /0.400kV,

    200kVA

    ONAN

    No-load

    voltage ratio

    Rat ing

    of

    nterconnected star winding

    n

    30Sec

    E

    arth fault cur

    rent duty lO

    Sec)

    Continuous

    rated current

    in neutral

    Vector G

    roup

    Extern

    alSecondary

    lo ad

    Ze

    ro sequence

    im pedance

    4

    4/0.4kV

    800A

    750A

    50 A

    Zynll

    200kVA

    80

    hms per phase

    A zigz

    ag wound tra

    nsformer is u

    sed as the g

    rounding tra

    nsformer to m

    ake a neutra

    l

    poin

    t in the delta

    sid e

    of

    he p

    ower transfo

    rm er in GSSs

    .

    Aground fa

    ult condition

    on wye zigz

    agtransform

    er is shown

    in Fig. 3.1. In

    order for

    in-phas

    e ground cu

    rre nt to flow

    , the current

    ineach zig

    zag circuit m

    ust be equal

    .

    N

    ote that the

    zero sequen

    ce current, Io

    , in the two

    windings

    of thesame cor

    e is in

    opposite di

    rections. Th

    e flux cause

    d b

    y

    the gr

    ound curren

    t in the

    windings

    cancels a

    nd there is n

    o flux linkag

    e to the wye

    winding. Th

    erefore, its cu

    rrent

    is

    zero

    i.e. th

    e line curren

    t ofwye conn

    ected auxilia

    ry winding is

    zero. This c

    ould be used

    as

    a z

    ig zag earthin

    g transforme

    r as shown in

    Fig 3.2.

    2

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    v

    j

    V

    all

    ~

    (a)-

    Winding Co

    nnection for

    a W ye-Zigz

    ag Transform

    er

    \ b t

    az

    t

    I e 1

    t

    v.

    (b

    ) Prima

    ry

    P

    hases

    (c)

    Sp

    li t Secondar

    y Phases

    d) Seconda

    ry Phases Re

    connected

    F i g . ~ ye-Z

    igzagTransf

    orm er Wind

    ing Connecti

    ons and Vec

    tor Diagram

    I c

    7

    __

    l

    ~ J b l

    Fig3

    4

    G

    rounding

    Zigz

    ag T r 2nsforme

    r Sho,,ing

    G r

    ou

    ndC

    urrent Fl ws

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    )-

    or

    0

    Primaryto Seco

    ndary

    Phase Shifl

    -*

    3rf

    Cf

    -*

    00

    Posi t iv

    e N egat ive S

    equence

    D

    iagrams

    \

    or

    or

    I

    Prim

    ary toSeconda

    ry

    Pha

    se Shifl

    Cf

    ~

    Cf

    Zero Se

    quence Diagr

    am s

    Positiv

    e N egative andZero

    e

    quenceDiag

    ram s for Delta-Zigzag

    and

    W ye-ZigzagTransformers

    ___

    Posi t ive

    N egative andZero

    Se

    quence Diag

    ram s for Zigz

    ag Groundin

    g T ransform

    ers

    Fig 8Se

    q uence Diag

    ram s ofZigz

    ag Transform

    ers

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    Genera

    lly zigzag

    earthing tr

    ansformers

    are used wh

    ere high g

    round curre

    nts are

    desi red

    on solidly gr

    ounded syst

    ems. On 13

    .8 kV and l

    owervoltag

    e systems w

    here

    th e

    g round cu

    rrent is limi

    ted by a gr

    ounding resi

    stor

    or

    reac

    tor the delt

    a-grounded

    w ye

    transforme

    r is normall

    y used. Del

    ta-wye trans

    formers at t

    he lower vo

    ltages are

    high volu

    m e items an

    d m ore com

    petitively pr

    iced.W i th e

    ssentially o n

    ly one wind

    ing

    the

    z igzag co

    nnection sh

    ould cost

    less than a

    delta-wye

    transformer

    used for

    groundi

    ng. Howev

    er because

    zigzag is le

    ss commo n

    and the int

    ernal connec

    tions

    s ligh tly m or

    e com plex

    the cost diffe

    rential m ay

    not be much

    .

    The

    seq

    uence diagr

    ams for a tra

    nsformer w

    ith a zigzag

    winding are

    shown in Fig

    . 3.3.

    /

    n

    constructio

    n the trans

    form er is ge

    nerally the

    sam e as an

    ordinary th

    ree-phase

    core-ty

    pe po

    wer

    tr

    ansformer b

    ut h aving a

    single wind

    ing o

    n

    each

    limb which

    is split

    up into t

    w o parts th

    e halves

    of

    t

    he windings

    on th e three

    limbs being

    interconnec

    ted

    as sh o wn i

    n Fig. 3.2.

    The

    neutr

    al point o

    f the earthing

    transforme

    r is connect

    ed to earth

    either direct

    or

    through a

    current-lim

    iting imped

    ance while

    the termin

    als

    of

    the

    apparatus a

    re

    ..

    conn

    ected

    to the th ree-pha

    se lines. T

    he rating

    of the earthin

    g transform

    er is

    of

    course

    different fr

    om that of

    a

    pow er trans

    former as th

    e latter is d

    esigned to ca

    rry its

    total load co

    ntinuously

    w hile the f

    ormer has o

    nly to

    be

    su

    pplied with

    the iron los

    s

    w h ilst the copper loss due to the passage

    of

    the short-circuit fault current occurs only;

    fo r a frac

    tionof a m

    inute.

    N

    eutral earth

    ing transfo

    rmers are n

    ormally des

    igned to ca

    rry the max

    im um fault

    cur

    rent for up

    to thirty se

    conds or a

    lternatively

    a time dep

    ending upon

    ear thing

    transfor

    mer . t is

    more usual

    to sp ecify th

    e sin gle-ph

    ase earth fau

    lt current th

    at the

    earthing tr ansformer m ust carry rather than the equivalent

    r e q u i r e m e n t s ~ f

    3

    is the

    total

    e

    arth

    fault curren

    t and the

    line voltage

    the earthin

    g transform

    er sh ort tim

    e

    rating is e

    qualto ./ 3

    VI

    t som

    etim es happ

    ens that an

    LV supply i

    s required a

    t an

    V

    su b

    station. A 4

    15/240

    V sup

    ply could b

    e obtained by

    installing a

    conventiona

    l step-down

    transformer

    butif

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    '\-

    I

    l

    ~

    ~ ~

    "

    L,

    \

    I

    '

    i

    z:..c...J w 4

    1 2.

    LV w c

    .\

    .

    .

    3.4(o .)

    Side

    View

    o

    Ground

    ing Tr

    o.nsforMe

    r

    -

    Zig

    Zo.g W in

    ding 1

    .

    ~

    --HI f--1-I--

    ZigZo.g

    \J

    inding 2

    /

    ..

    .

    -

    , \ . .

    .

    , .

    ..

    '

    O

    J

    I I II ; I

    L

    v

    \J

    inding

    '

    W/_y

    t

    _

    ;

    .

    ~

    H r

    tt

    L 1 . .

    . ~

    n

    ; .p sions

    in

    3.4(b) Sec

    tion o G

    rounding

    Tro.n

    sforMer

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    it

    is

    in te

    nde

    d to

    e

    mp

    lo y

    a

    n ea

    rth

    in g

    tra

    nsf

    orm

    er

    it i

    s p

    oss

    ib le

    to

    in

    co rp

    ora

    te

    a s

    tar

    c

    onn

    ect

    ed

    aux

    il ia

    ry

    win

    din

    g o

    f,

    sa y

    , 1

    00 to

    200

    kV

    A

    rat

    ing,

    a n

    d h

    enc

    e a

    su

    pp

    ly i

    s

    a

    vai

    la b

    le f

    or t

    he

    loca

    lL

    V

    l

    oad

    .

    n

    op

    era

    tion

    th

    e

    in te

    rco

    nn

    ect

    ed

    sta

    r e

    arth

    ing

    tr

    ans

    for

    me

    r is

    re

    all

    y t

    he

    acm

    e

    of

    sim

    pl

    ic it

    y.

    Th

    e t

    ota

    l fa

    ult

    c u

    rre

    nt to

    e

    art

    h d

    ivid

    es

    up

    w h

    en

    r ea

    ch

    ing

    the

    ea

    rth

    ing

    tr

    ans

    fo r

    mer

    ne

    utr

    al p

    oin

    t i

    nto

    a p

    pro

    xim

    ate

    ly

    equ

    al

    par

    ts

    in e

    ach

    p

    has

    e, s

    o t

    hat

    th e

    c

    urr

    ent

    in

    th e

    w in

    din

    gs

    w i

    th a

    si

    ngl

    e li

    ne e

    art

    hfa

    ult

    i s

    ap p

    rox

    im a

    tel

    y o

    ne-

    thir

    d of

    th

    e

    to ta l fa

    ult

    c u

    rren

    t

    t

    o

    ea

    rth

    . T

    he

    cu

    rren

    td

    istr

    ibu

    tion

    un

    de

    r fa

    ult

    con

    dit

    ion

    s, a

    ssu

    min

    g

    equ

    al

    cur

    ren

    ts i

    n al

    l w

    in d

    in g

    s, i

    s sh

    ow

    ni

    n F

    ig. 3

    1

    and

    it

    wil

    l be

    se

    en t

    hat

    the

    cu

    rre

    nts

    i

    n the

    h a

    lve

    s o

    f h

    e w

    in d

    in g

    s

    onth

    e s

    am

    e li

    mb

    f lo

    wi

    n o

    ppo

    site

    d i

    nt

    ion

    s so

    th

    att

    hey

    i

    ntr

    odu

    ce

    no

    cho

    kin

    g e

    ff e

    ct,

    th u

    s p

    erm

    itt i

    ng

    a f

    ree

    flo

    w o

    fc

    urr

    ent

    fro

    m t

    he

    ear

    th in

    g

    t

    ran

    sfo

    rm

    er

    neu

    tra

    l to

    eac

    h

    line

    w

    ire

    .

    T

    his,

    o

    f c

    our

    se,

    is

    th

    e

    rea

    son

    fo

    r

    in

    te rc

    onn

    ec

    ting

    the

    w

    ind

    ing

    s, a

    s a

    sta

    r co

    nn

    ecti

    on

    wo

    uld

    pro

    duc

    ea

    na

    ddi

    tion

    al s

    ing

    le

    ph

    ase

    m

    agn

    etic

    f lu

    xi

    n ea

    ch

    lim

    b .

    3.

    2

    C

    ore

    - fl

    ux

    und

    er

    ear

    th

    fau

    lt

    con

    dit

    ion

    s

    Acc

    ord

    in

    g to

    Am

    pe

    re s

    la

    w , i

    tc

    an

    be

    e

    xp

    lain

    ed

    tha

    t ev

    en

    the

    tw

    o w

    ind

    ing

    s ar

    ef

    edb

    y

    eq

    ual

    and

    op

    po

    site

    cu

    rren

    t; s

    till

    t he

    re

    can

    be

    a r

    esu

    ltan

    tfl

    ux

    in t

    he

    co r

    e be

    cau

    se o

    f

    he

    t

    w o

    dif

    fe re

    nt

    rad

    ii of

    th

    e w

    in d

    in g

    s.

    .

    Th

    ea

    ver

    age

    fie

    ld

    in te

    ns

    ity

    in

    th e

    co

    re d

    ue

    to

    the

    o u

    te r

    win

    din

    g i

    s s

    mal

    ler

    tha

    n t

    hat

    du

    et

    o th

    ei

    nne

    rw

    ind

    ing

    f o

    r th

    e s

    om

    e cu

    rre

    nt.

    Th

    is

    phe

    nom

    en

    on

    can

    b e

    e x

    pla

    ined

    as

    f

    ollo

    ws

    .

    ..

    .

    26

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    Fig 3 .6

    Say

    n u m b er of

    urns in the

    winding

    n and

    Current thr

    ough the zigz

    ag winding i

    s

    I

    i l

    d strengthin

    duced in the

    position P b

    ecause of th e

    current I flo

    wn through t

    he

    co

    nductor posit

    ioned at

    r

    di

    stance fromt

    he centre wi

    th n No. ofu

    rns is given

    by

    dH

    := 4.n x

    2

    2rXCosa

    I r

    de

    Sina

    2 7

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    I

    I

    ~ X

    l

    l

    2

    XrCose)

    - x

    Sin 9o-

    e)

    =

    I

    I

    2

    ;ose

    X

    r -

    2

    XrCose = I -

    ::imCl

    r

    XCose)

    1

    Sina := ~ r = = = = = =

    = = = = = = = = = =

    ~

    0 +

    l

    2XrCo

    se

    B:=

    d

    [ l rde. r- XCoseTI

    ;

    1

    l l i : =

    ~ = = = =

    = = = = = 7

    ~ ~

    ~

    T I ~ X l r

    2

    -

    2 X r

    e { ~

    2XrC

    ose

    dH := J.t{r

    - XCo

    se).de)

    I

    3

    4n {Xl

    l

    2X.rCose

    2

    2n

    r- x.

    eose)

    ~ = =

    de

    [{ +

    2

    -2

    X

    o ~ H

    0

    X:=

    0 O.oi 0.02

    0.03 0.04 0

    .05 0.06 0.0

    7 0.08 0.09

    n

    -

    2

    2

    7

    say r =

    0.090

    n

    2

    r - Xc

    os o))

    de

    [

    0 ? 2

    x,.,..e));l

    ~ X ) : =

    0

    ~ 0 ) =

    194.004

    ~ 0 . 0

    =2

    23.37

    ~ 0 . 0 =

    257.402

    0 . 0 3 ) =

    298.181

    ~ 0 . 0 4 =

    349

    .822

    . 0 5 ) =

    420.823

    ~ 0 . 0 6 )

    =530.9

    95

    ~ 0 . 0 7

    =738

    .936

    ~ 0 . 0

    =

    1.332 X

    10

    3

    0 . 0 9 ) =

    1.139X

    10

    3

    _

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    r:= f.lo l r

    l.. :.fr ~ X ) d X

    2 0

    J

    .08

    :=

    2r (3000

    0 X

    4

    88 00 :>2

    3 ~

    194.004X)d

    X

    = 0.22

    4 f.lo l r

    -

    1

    for

    a Unit C

    urrent

    X:= (0 0

    .02 0 .04 0.06

    0.08 0.10

    0 .12 0. 14 0.

    16 0.18)

    0

    := 22

    7

    say r :=

    0.

    135

    ~ X )

    : =

    n

    2

    r-

    Xcos e

    )) de

    [{x>

    2Xr :=

    1-lof.lrl..

    :.fr

    4 X

    d

    2 0

    1

    =2{(

    370o-x

    4

    3700-x 100

    0-X' 86.224X}d

    X] _

    I> =

    0.

    131

    1-lo J.lr

    - - - - -

    - - - - - - -

    2

    for a U

    nit Current

    29

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    X:=

    0 0.02 0.0

    4 0.06 0.08

    0.10 0.12 0.

    14 0.16 0.18)

    n

    := 22

    7

    say r:=

    0.180

    n

    ~

    ~ X ) . = \

    (r

    - xcoJ.

    ..e ))

    ~

    l{x 2 x,,

    { e ~

    0

    ~ 0 )

    =

    48.501

    =

    105.206

    . 0 2 ) =

    55.842

    0 . 1 2 ) =

    132 749

    =

    64.351

    ~ 0 . 1 4 )

    =

    18

    4.734

    0 . 0 6 )

    =

    74.54

    5

    ~ 0 . 1 6

    = 3

    33.072

    0 . 0 8 )

    =

    87.45

    5

    =

    284.729

    r

    :=

    J o J l r . Z . . ~

    f r 4X.f3(X

    ) dX

    2 0

    [

    08

    ]

    '

    z.. J

    {

    400x

    4

    1400 3

    00 :0 48.50

    x)

    dX

    I

    =0.0

    8 Jo

    J r---

    3

    for

    a Unit Curren

    t

    X:= 0 0.0

    3 0.06 0.09

    0.12 0.15 0

    .18 0.21 0 .2 4

    0.27)

    ==

    22

    7

    ~

    X ) : =

    rr

    2

    0

    say r

    :=

    0.225

    (r-

    x

    cos{a

    de

    [ :0

    ,

    2

    -

    2 x , , . . e )

    ) ~ ]

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    ~ 0 )

    = 31.041

    . 0 3 ) =

    36.761

    ~ 0 . 0 6 ) =

    43.638

    ~ 0 . 0 9 ) =

    52.394

    13(0.12

    ) =

    64.703

    0 . 1 5 =

    84.959

    ~ 0 . 1 =

    129.027

    0 . 2 1 )

    = 336.22

    3

    r

    :=

    ~ r J : J

    X ~ X ) dX

    2

    0

    [

    .08

    1

    ' '

    h o

    (uoo.x

    4

    soo.x so

    .x 31.041 X

    )dXJ

    =

    0.059 ~ o f l

    --4>4

    for a Unit Cu

    rrent

    X:

    = 0

    O

    .o3

    0.06 0.09

    0.12 0.15 0.1

    8

    0.21

    0.24

    0.27

    n

    -

    2

    2

    7

    say r

    := 0.270

    .

    ..

    n

    ~ X ) : =

    2

    r- Xcos(e))

    de

    [(x /

    -2 x ,, .

    .{ i ]

    0

    =2

    1.556

    =

    46.758

    0 3 ) =

    24.819

    ~ 0 . 1 8 )

    = 58.99

    9

    ~ 0 . 0 6 )

    = 28.6

    ~ 0 . 2 1 )

    = 82.10

    4

    ~ 0 . 0

    =

    33.131

    2 4 ) =148.0

    32

    . 1 2 ) =

    38.869

    13(0.27) = 129 1

    8

    r :=

    J.loJ.lrI.:..J r

    4Xl3 X) dX

    2 0

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    ' ,. 2

    08

    (,s5-

    X

    4

    + 5oo-x

    +

    110-x

    +

    21

    .556-xd>:J

    0.05 ll o

    llr

    - < >5

    for a U nit C

    urrent

    X:

    =

    0

    0.03

    0 .

    06

    0 09 0 12

    0.15 0 18 0.21

    24 0

    .2 7

    n -

    22

    .- -

    7

    say

    r := 0 .

    315

    ~ X ) : =

    n

    2

    r

    -

    Xcos

    (a))

    de

    [(x'

    + ,

    2

    - 2-x

    '.{e)

    )+]

    0

    =

    15

    .

    837

    =

    30 006

    0 . 0 3 )

    = 17 .

    8

    71

    0 . 1 8 )

    35 .383

    0 6 ) =2017

    2 2 1 )

    = 43 346

    ..

    0 . 0 9 ) =

    22 .831

    0 2 4 ) 56.9

    88

    -

    26 .

    011

    0 2 7 )

    87.481

    r := ll

    O Ilr.J .-:..Jr

    4 - X . ~ X dX

    2

    0

    ' ,. 2{(

    8

    {185-x

    4

    9o-x + 68-x

    15.837

    -x) dX]

    =

    0.04

    llO Ilr

    -

    6 for c?onitCurrent

    Variati

    on

    of

    Flux, a

    gainst distan

    ce

    to

    the core

    isplotted in G

    ra ph A 1

    3

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    The

    results can b

    e presented

    graphically a

    s in Fig 3.5,

    variation

    of flux in the c

    ore

    w i

    th the dista

    nce of the

    winding from

    the core.

    Therefore e

    ven when th

    e tw

    o

    win dings

    of hezigzag c

    onnection in

    oneleg are fe

    d with equal

    andopposite

    currents,

    there i

    s a resultant

    flux.

    3.3

    Sim ulated

    flux phase vo

    ltages unde

    r fa ult

    o

    ndi

    tio n

    o

    model th

    e substation

    setup, MatLa

    b version 6.0

    was used in

    theprelimin

    ary stages

    of

    the project. No in -b uild models are available for zigzag transformer. A zigzag

    transf

    ormer mode

    l was tried

    to build b

    y combining

    windi lgs

    of single-pha

    se

    tran

    sformers. T

    his model w

    as simulated

    when there

    is a singfe-p

    hase earth fa

    ult is

    pre sent. Unf

    ortunately th

    e desired res

    ultscould no

    t obtain as t

    he simulator

    assumes

    that all th

    e equipment

    b ehave in id

    le manner. M

    odeling

    of

    th

    e earthing a

    nd auxiliary

    transfo

    rm er with zig

    zagwinding

    arrangemen

    t made the sim

    ula tion mor

    e complex.

    S i

    ncethe mod

    eling

    of

    the G

    SSusing M

    atlab failed

    in the prelim

    inary stages,

    it was

    decided to w

    ound a prot

    oty pe

    of

    a gr

    ounding tran

    sformer and

    simulate an e

    arthfault

    in the la

    boratory. Th

    e earthing tra

    nsformer wit

    h the auxiliar

    y winding us

    e inGSSs ha

    s

    th e

    fo llowing s

    pec ifications

    .

    Prim

    ary

    w

    inding:

    33 kV zigza

    g connected

    Aux

    iliary windin

    g: 415 V s

    tar connected

    Impedan

    ce :

    70 -80 Ohm

    s

    The

    transformer

    has a voltage

    ratio of 156

    :156:10 amon

    g the section

    s of the zigz

    ag

    wi

    ndings and

    auxiliary w

    inding. Th

    e prototype

    transformer

    w

    ~ woun

    d by

    maintaining

    the above

    ra tio amon

    g the windin

    gs. But the

    re were diff

    iculties to

    maintain

    im pedance

    of 70-80 O

    hms in the p

    rototype tra

    nsformer. Th

    e small size

    tr a

    nsformer ma

    nufacturers

    do not hav

    e the contro

    l over the

    im pedance

    of the

    tr

    ansformer. T

    heyjus t use

    the insulating

    materials av

    ailable with

    themwithout

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    F

    g

    3

    5

    V

    a

    o

    o

    F

    u

    n

    t

    h

    c

    o

    e

    w

    i

    t

    h

    t

    h

    D

    i

    s

    a

    n

    o

    t

    h

    w

    i

    n

    n

    0

    2

    .

    '

    C

    '

    .

    s

    1 :

    C

    c

    1

    Q

    .

    -

    =

    -

    \

    '

    '

    0

    2

    \

    .

    \

    I

    0

    1

    I

    H

    Q

    ~

    . .

    : 1

    ~

    c

    : .

    .

    E

    -:

    J

    0

    :

    J

    >

    0

    5

    1o

    I

    15

    15

    10

    5

    >

    5

    10

    15

    R Phase

    Time

    I

    y phas

    e

    T im

    e

    BPhase

    Time

    Fig:3.1 0 Observa

    tionsof

    Exp

    eriment 03

    4

  • 8/11/2019 Zig Zag Transf_1

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    3.4.3

    Experiment

    setup 3 resu

    lts

    T

    he o

    served

    waveforms a

    re indicated

    in

    fi

    g 10

    3.5 An

    alysis ofExp

    erim ent Re

    sults

    o

    observ

    e the effect of

    fault curr

    ent o

    n

    the a

    uxiliary w in

    ding

    at

    an e rth

    fault, a

    prototy

    pe

    o

    f a groun

    ding transfo

    rmer with tw

    o auxil iary w

    indings with

    same num b

    er

    o

    f turns)

    was used.

    h

    e in

    duced voltag

    es in the aux

    iliary w indin

    g 1 and 2 we

    re measured

    in experimen

    tal

    se

    tup 1 and e

    xperimental

    setup 2 . he

    results are

    tabulated i

    n table 1

    The

    s uperim pose

    d results are

    tabulated in t

    able 3.2 .

    F i

    g. 3 .11 show

    s the variat

    ion

    o

    f induc

    ed voltages i

    n two auxili

    ary windings

    , when

    different v

    oltagesare a

    pplied to the

    pr imary zig

    zag) winding

    . Curves 1 a

    nd 2 in Fig .

    3.1 1

    are almost

    identical. Th

    is implies th

    at the voltag

    e induced in

    the two auxi

    liary

    windings in experimental setup-1 are equal. C urves 3 and 4 show some deviation

    between

    them with t

    he increase of

    supplyvolta

    ge. This imp

    lies that som

    e additional

    vol

    tage is induc

    ed in auxiliar

    y windings in

    exper imenta

    l setup 2

    F ig 3.

    12 shows the

    induced vol

    tage revel in

    two auxiliar

    y windings a

    s a percentag

    e

    of nd

    uced voltage

    s

    at

    th erespe

    ctive auxilia

    ry windings i

    n experiment

    setup 1.

    .

    43

  • 8/11/2019 Zig Zag Transf_1

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    0.700

    0

    .600 - 1 - - -

    r - -

    ~ 0 .500

    do

    ~ ~ ~ . ~

    -

    '

    0.400

    -

    1:

    i

    ~ ~ ~ ~

    ~

    i

    ~ ~ ~ ~ ~ ~

    2

    ,

    0 0 I

    ::

    .

    0000

    1

    1 I

    I

    I I

    I

    I

    I

    I-

    RYB1

    -

    RYB2

    RYB3

    R Y B 4

    F ig 3.11

    Graph

    : V

    oltage induc

    ed inAux.

    Wind ing ag

    ainstthe in

    jectedcurrent

    to

    theneutral

    25.00

    2000

    .

    15 00

    .

    s 1 00

    . _

    5 00

    .

    -

    - - - - - - - - - - -

    - - . - - - - - - - . -

    - - - - - - - - - -

    - - - - r - - - - -

    - - ~ - - - - - -

    - - - - - - - - - - -

    -

    1A

    6 2V

    Curr t

    iVoltall

    R Y B 1 1 R Y B 2

    RYB2JRYB4

    a .g1

    ayg

    2

    J

    F ig 3.1

    2 Grap

    h

    :

    Voltage in

    creased in A

    ux. W indin

    g dueto the

    injected

    current

    tothe neutr

    al

    44

  • 8/11/2019 Zig Zag Transf_1

    24/24

    Theore

    tically two

    conditions n

    eed to

    e

    sa t

    isfied to ope

    rate the grou

    nding trans

    former

    at an earth

    fault

    1

    The zero sequence current flow through ea ch winding should

    e

    equal

    in

    each phase

    2 T he

    net

    flux ind

    uced

    in

    th e

    limb

    y

    th e

    zero sequen

    ce compone

    nt

    of

    the cur

    rent

    flownt h

    rough the w

    indings sho

    uld

    e

    zero

    Base

    on

    the experim ent results

    on

    the prototy pe transform er there are two

    conclusi

    ons

    1 There

    is

    a resultan

    t voltage in d

    uced in aux

    iliary w indi

    ngs wound

    on

    each limb

    To induce

    a voltage the

    re should

    e

    a net flux

    in

    the limb

    Therefore th

    e flow

    of

    curr

    ent through

    t

    he

    pr imary

    windings

    n opposite dir

    ection

    is

    sti l

    l creating a f

    lux

    in the limb

    2 T h ei

    nduced volt

    age

    in

    the

    auxiliary w i

    nding is dif f

    erent for tw

    o locations

    i e

    fo rlo

    cation

    o

    f

    au

    xiliary wind

    ing 1 and lo

    cation

    o

    f

    aux

    iliary windin

    g 2