Di Electrics

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ENGRAM Engineering Ltd.

description

JLHVDDSHLV

Transcript of Di Electrics

  • ENGRAM Engineering Ltd.

  • Insulation distances arround the active part in the tank

    End-Distances in the core window

    Main insulation distances between the windings

    Phase to phase distances in core window

    Spacer thicknesses in the winding

  • The insulation distances between the outer winding and the tank wall on the non regulated low voltage side

    Insulation level Minimum distance

    up to 12 kV 80 mm

    up to 24 kV 90 mm

    up to 36 kV 100 mm

    up to 45 kV 110 mm

    over 45 kV 120 mm

    The above distances are to be increased by 40 mm if the HV insulation level is over 120 kV

  • The insulation distances between the outer winding and the flux collector covered tank wall on the regulated high voltage side

    Insulation level Minimum distance

    up to 36 kV 120 mm

    up to 52 kV 160 mm

    up to 72.5 kV 180 mm

    up to 100 kV 200 mm

    up to 123 kV 220 mm

    up to 145 kV 240 mm

    up to 170 kV 270 mm

    up to 245 kV 300 mm

    up to 362 kV 320 mm

    up to 420 kV 340 mm

    up to 525 kV 390 mm

  • The HV side distances shall be used for distance between the tank wall and OLTC and for the OLTC and outer winding.

    The LV side distances shall be used for the distance between the outer winding and the short side of the tank.

    The given distances can be modified by the followings.

    the non usual arrangement of the leads

    LV side regulation

    high currents on LV side

    booster, auxiliary transformer or reactor inside the tank

    more tap changer in the tank

    etc

  • Under the core to the bottom of the tank:

    65 mm

    Above the core to the tank cover:

    80 100 mm

  • The given distances are with the consideration of 30 40 mm pressure ring

    In case of ODAF cooling the end distances are changed

  • LI AC UD + LD X Y

    325 140 200 60 90

    350 140 200 60 90

    380 152 210 65 95

    450 185 220 70 100

    550 230 240 75 105

    650 275 260 80 115

    750 325 280 115 150

    850 360 300 125 165

    900 395 320 140 175

    950 395 340 150 185

    1050 460 360 195 240

  • Radial clearances in the same phase

    Oil duct at the winding is 6 mm maximumEF EndFed, CF CenterFed, CR CourseRegulation, FR - FineRegulation

    BIL 75 95 125 170 250 325 380 450

    AC kV 30 38 50 70 100 140 152 185

    Main gapEF 16 16 16 16 17 24 25 32

    CF 16 16 16 16 17 22 24 29

    HV CR/FREF 16 16 16 16 17 25 27 32

    CF 16 16 16 16 17 22 24 29

    CR

    -FR

    no ZnO

    20% 16 16 16 16 16 16 16 20

    10% 16 16 16 16 16 16 16 16

    with ZnO

    20% 16 16 16 16 16 16 16 16

    10% 16 16 16 16 16 16 16 16

  • BIL 550 650 750 850 900 950 1050 1300 1425

    AC kV 230 275 325 360 395 395 460 570 630

    Main gapEF 38 46 54 60 66 66 76 96 106

    CF 36 44 50 56 62 62 72 90 100

    HV CR/FR

    EF 38 46 54 60 66 66 76 96 106

    CF 36 44 50 56 62 62 72 90 100

    CR

    -FR

    no ZnO

    20% 22 26 31 34 38 38 42 52 58

    10% 16 16 16 17 20 20 22 26 29

    with ZnO

    20% 16 17 20 24 25 25 29 36 38

    10% 16 16 16 16 16 16 16 17 20

  • No switching impulse test

    BIL 75 95 125 170 250 325 380 450

    AC kV 30 38 50 70 100 140 152 185

    FR

    -F

    R

    Y connected

    20% 20 20 20 20 20 20 20 20

    10% 20 20 20 20 20 20 20 20

    Delta connected

    20 20 20 20 20 26 28 33

    HV - HV 20 20 20 20 20 26 28 33

  • No switching impulse test

    BIL 550 650 750 850 900 950 1050 1300 1425

    AC kV 230 275 325 360 395 395 460 570 630

    FR

    -F

    R

    Y connect.

    20% 24 29 33 38 40 42 47 58 63

    10% 20 20 20 20 20 21 23 29 32

    Delta connected

    41 48 56 63 67 70 78 96 106

    HV - HV 41 48 56 63 67 70 78 96 106

  • The given minimum values are for the average spacer thickness in the winding.

    At internal directed oil flow the minimum spacer thickness is 3 mm.

    For position changing of parallel conductors the appropriate place should be ensured. This is the sum of conductor height and the spacer thickness.

    BIL of the winding end Minimum thickness of the spacers

    BIL 450 kV 3 mm

    450 kV < BIL 550 kV 4 mm

    550 kV < BIL 750 kV 4.5 mm

    750 kV < BIL 950 kV 5 mm

    950 kV < BIL 6 mm

  • DIL factors

    Weidmann curve safety margin

    T50

    Spacer thickness

    Combined stress

    Point stress

    Turn to turn

  • The reference voltage kVAC is calculated by dividing the actual occurring voltage by the corresponding DIL factor

    DIL factor

    BIL Chopped wave 2.75

    BIL full wave 1.2/50 s 2.50

    Switching impulse 1.90

    1 hour voltage 0.80

    AC test voltage 1.00

    Nominal voltage 0.59

  • Maximum allowed electrical stress in the oil ducts is given by the Weidmann curves (degassed oil):

    Adjacent to a winding:

    Between cylinders:

    Safety margin with respect to the curves of degassed oil: 10%

    Safety margin defined by

    Safety margin values (minimum):

    Regular transformer: 10 % (Limit = curve * 0.9)

    Large Power, Special, Critical, : 20 % (Limit = curve * 0.8)

    37.0

    max *5.17 dE

    37.0

    max *5.21 dE

    With d: width of the oil duct

    strength

    stressSF 1

  • Weidmann curves

    Bare electrodes + cooling ducts adjacent to windings

    1: degassed oil -> E = 17.539 * d-0.3581

    2: gas saturated oil -> E = 14.196 * d-0.3690

    Insulated electrodes

    1: degassed oil -> E = 21.407 * d-0.3684

    2: gas saturated oil -> E = 18.557 * d-0.3769

  • Use only T50 factor for situation between discs where:Safety margin is not metSafety margin can not easily be increased by standard measures.Well defined half-value time. Well defined peak.

    Increase withstand by multiplying with adequate factor in function of the half-value time.

  • T50 FACTOR

    Time, microsecondUnshrunk paper covering, mm

    0,65 0,75 0,80 0,85 1,00 1,15 1,25 1,50 2,00 2,50 3,00

    1 1,514 1,507 1,503 1,500 1,489 1,478 1,471 1,454 1,419 1,385 1,351

    2 1,343 1,341 1,340 1,340 1,332 1,323 1,319 1,309 1,289 1,269 1,249

    3 1,266 1,264 1,262 1,261 1,257 1,253 1,250 1,243 1,228 1,213 1,198

    4 1,220 1,218 1,217 1,216 1,213 1,210 1,208 1,202 1,191 1,180 1,167

    5 1,188 1,186 1,186 1,185 1,182 1,180 1,179 1,174 1,165 1,156 1,146

    7 1,146 1,145 1,145 1,144 1,142 1,141 1,140 1,137 1,130 1,123 1,116

    10 1,109 1,108 1,108 1,107 1,107 1,106 1,105 1,103 1,098 1,093 1,088

    15 1,073 1,073 1,072 1,072 1,072 1,071 1,070 1,069 1,067 1,064 1,061

    20 1,052 1,052 1,051 1,051 1,051 1,051 1,050 1,049 1,048 1,046 1,044

    25 1,037 1,037 1,037 1,037 1,037 1,036 1,036 1,035 1,034 1,033 1,032

    30 1,026 1,026 1,026 1,026 1,026 1,026 1,025 1,025 1,024 1,024 1,022

    35 1,017 1,017 1,017 1,017 1,017 1,014 1,006 1,000 1,017 1,016 1,016

    40 1,011 1,011 1,011 1,011 1,010 1,010 1,010 1,010 1,010 1,010 1,009

    45 1,005 1,005 1,005 1,005 1,005 1,005 1,005 1,005 1,005 1,005 1,004

    50 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000 1,000

    55 0,996 0,996 0,996 0,996 0,996 0,996 0,996 0,996 0,996 0,998 0,996

    60 0,992 0,992 0,992 0,992 0,992 0,992 0,992 0,992 0,992 0,993 0,993

    65 0,989 0,989 0,989 0,989 0,989 0,989 0,989 0,989 0,989 0,990 0,990

    70 0,986 0,986 0,986 0,986 0,986 0,986 0,986 0,986 0,986 0,987 0,987

    75 0,983 0,983 0,983 0,983 0,984 0,984 0,984 0,984 0,984 0,984 0,985

  • The target is the partial discharge free arrangement

    Partial discharge free curve as formula:

    Umax=(0.375*sp+15.75)*wire+9.5*sp+57

  • The minimum paper insulation on normal rectangular conductor is 0.45 mm.

    For Continously Transposed Cable this is 0.6 mm.

    The thickness of enamel on CTC individual strands depends on the CTC manufacturer. Typical value is arround 0.1 mm.

    In windings without key spacers the allowable maximum impulse voltage between wire:

    Umax=84.5* wire+10 [kV]

  • In case of a winding with internal directed oil flow the following minimum spacer thicknesses should be used.

    3 mm up to 60 mm winding radial dimension

    4 mm up to 100 mm winding radial dimension

    6 mm up to 140 mm winding radial dimension

    7.5 mm winding radial dimension over 140 mm

    4 mm is the minimum spacer thickness in case of CTC winding

    The above thicknesses must be increased for electrical reasons

  • AVERAGE COMBINED STRESS

    The equivalent radial gap clearence:

    t = oil clearance + pressboard clearance/2 + paper clearance/1.5 [mm]

    The equivalent axial gap clearance

    uncompressed thickness of key spacers + (thickness of paper insulation * (2.2/3.5)) [mm]

    Axial stress calculated maximum lghtning impulse voltage between discs

    Radial stress calculated maximum radial lightning impulse voltage to neighbouring winding

    Max. allowed value:

    BIL full wave: < 25 kV / mm

    BIL chopped wave: < 27.5 kV / mm

    22 ) . .

    ()

    . .

    (..

    gapaxeq

    stressax

    gapradeq

    stressradStressCombAv

  • POINT STRESS

    On critical points (if the average combined stress seems to be critical), electric field calculation should be made for checking the critical regions.

    The field calculation practical boundary conditions:Axi-symmetric

    Max voltage in time to be used, in axial and radial direction, independent from each other.

    Max radial voltage at same position of considered discs.

    Max allowed Point stress < 35 kV / mm (max. 6 mm duct at the winding)

  • TURN TO TURN IN DISC

    Strength is the 70% of the curve on page 303 (fig.5.79) from Large Power Transformers, Karsai-Kernyi-Kiss

    Continuous service

    Turn-to-turn voltage at nominal voltage < 2.5 kV / mm

  • Have a good job!