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    Fault Level Calculation (Base MVA Methode) : Data

    Uploaded by

    Treesa Archnana
    This document provides details on calculating fault levels at different points in an electrical system. It includes: 1. Data on the supply voltage, substation fault level, feeder length, conductor size, spacing, and resistance. 2. Calculations to determine source impedance, line impedance, and fault levels at the 11kV and 433V sides for different transformer sizes of 160kVA, 400kVA, and 750kVA. 3. Recommendations for earthing conductor sizes at the 11kV and 433V sides and number of earth pits required based on the calculated fault currents.

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    Fault Level Calculation (Base MVA Methode) : Data

    Uploaded by

    Treesa Archnana
    1K views2 pages
    This document provides details on calculating fault levels at different points in an electrical system. It includes: 1. Data on the supply voltage, substation fault level, feeder length, conductor size, spacing, and resistance. 2. Calculations to determine source impedance, line impedance, and fault levels at the 11kV and 433V sides for different transformer sizes of 160kVA, 400kVA, and 750kVA. 3. Recommendations for earthing conductor sizes at the 11kV and 433V sides and number of earth pits required based on the calculated fault currents.

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    faul level

    Original Title

    FaultLevel Calculation

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    This document provides details on calculating fault levels at different points in an electrical system. It includes: 1. Data on the supply voltage, substation fault level, feeder length, conductor size, spacing, and resistance. 2. Calculations to determine source impedance, line impedance, and fault levels at the 11kV and 433V sides for different transformer sizes of 160kVA, 400kVA, and 750kVA. 3. Recommendations for earthing conductor sizes at the 11kV and 433V sides and number of earth pits required based on the calculated fault currents.

    Copyright:

    © All Rights Reserved
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
    1K views2 pages

    Fault Level Calculation (Base MVA Methode) : Data

    Uploaded by

    Treesa Archnana
    This document provides details on calculating fault levels at different points in an electrical system. It includes: 1. Data on the supply voltage, substation fault level, feeder length, conductor size, spacing, and resistance. 2. Calculations to determine source impedance, line impedance, and fault levels at the 11kV and 433V sides for different transformer sizes of 160kVA, 400kVA, and 750kVA. 3. Recommendations for earthing conductor sizes at the 11kV and 433V sides and number of earth pits required based on the calculated fault currents.

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    © All Rights Reserved
    Download as DOC, PDF, TXT or read online from Scribd
    Download as doc, pdf, or txt
    of 2

    Fault level calculation (Base MVA Methode)

    Data:
    1. Supply Voltage = 11 KV
    2. Fault level at 11KV side at Sub-station (Thrissur) = 218 MVA
    3. Length of 11KV feeder from sub-station to = 1000 M.
    premises (Lf)
    4. 11KV conductor size (Racoon) = 12.27mm
    6. Spacing of conductors (d) = 1000 mm.
    7. Resistance of line = 0.377728 Ohms/ Km.
    8. Rating of transformer (1 No.) = 1. 160 KVA - 1No, 11KV/433V, % Z=4%
    2. 400 KVA - 1No, 11KV/433V, % Z=4%
    3. 750 KVA - 1No, 11KV/433V, % Z=5%
    9. Soil resistivity (ℓ) = 75 Ohms-Mtrs.

    Fault level calculation:


    Assume base MVA as 100
    Source impedance at base MVA = (100 x 100) / 218 = 45.87%
    Radius of 11KV conductor (r) = 12.27/2 = 6.135mm
    Inductance of line (L) = [2 x loge (d/r) + 0.5] x 10-7 x Lf
    = [2 x log e (1000/6.135) + 0.5] x 10-7 x 1000 = 0.001Hentrys

    Inductive reactance (XL) = 2ΠfL


    = 2 x 3.14 x 50 x 0.001 = 0.314 Ohms
    Resistance of 1 Km line (R) = 0.377728 x 1 = 0.38 Ohms
    Impedance of line (Z) = √ (XL2 + R2)
    = √ (0.314) 2 + (0.38) 2 = 0.49 Ohms
    % line impedance at base MVA = (0.49 x 100 x 100) / 112 = 40.5%
    Total % impedance up to premises = 45.87 + 40.5 = 86.37%
    S/C MVA at 11KV side at premises = (100 x 100) / 86.37 = 115.78MVA
    Considering future increase, 150MVA shall be taken as fault level at 11KV side.
    Fault current at 150MVA level at 11KV side = 150 x 103 / √3 x 11 = 7.873 kA
    % Impedance corresponding to 150MVA fault level = (100 x 100) / 150 = 66.67%
    Transformer-1 :-
    % Impedance of transformer 1 at base MVA = (4 x 100) / 0.16 = 2500%
    Total % impedance up to 433V bus = 66.67 + 2500 = 2566.67 %
    S/C MVA at 433V bus (100 x 100) /
    = 2566.67 = 3.89 MVA
    Corresponding fault level

    (3.89 x 1000) / √3 x
    = 433 = 5.19- KA

    Earthing design:
    Size of conductor for earthing 11KV side
    (copper) = 7873 / 118 = 66.7 Sq.mm.
    Nearest standard size (HT) 25 x 3 mm Cu
    = Strips
    Size of conductor for earthing MV side 43.98
    (copper) = 5190 / 118 = Sq.mm.
    Nearest standard size (LT) 25 x 3 mm Cu
    = Strips
    Transformer-2 :-
    % Impedance of transformer 2 at base MVA = (4 x 100) / 0.4 = 1000%
    Total % impedance up to 433V bus = 66.67 + 1000 = 1066.67 %
    S/C MVA at 433V bus (100 x 100) /
    = 1066.67 = 9.37 MVA
    Corresponding fault level (9.37 x 1000) / √3 x
    = 433 = 12.5 kA

    Earthing design:
    Size of conductor for earthing 11KV side
    (copper) = 7873 / 118 = 66.7 Sq.mm.
    Nearest standard size (HT) 25 x 3 mm Cu
    = Strips
    Size of conductor for earthing MV side 105.93
    (copper) = 12500 / 118 = Sq.mm.
    Nearest standard size (LT) 38 x 3 mm Cu
    = Strips

    Transformer-3 :-
    % Impedance of transformer 3 at base MVA = (5 x 100) / 0.75 = 666.66%
    Total % impedance up to 433V bus = 66.67 + 666.66 = 733.33 %
    S/C MVA at 433V bus = (100 x 100) /733.33 = 13.63 MVA
    Corresponding fault level (13.63 x 1000) / √3
    = x 433 = 18.19 kA

    Earthing design:
    Size of conductor for earthing 11KV side
    (copper) = 7873 / 118 = 66.7 Sq.mm.
    Nearest standard size (HT) 25 x 3 mm Cu
    = Strips
    Size of conductor for earthing MV side 154.15
    (copper) = 18190 / 118 = Sq.mm.
    Nearest standard size (LT) 32 x 6 mm Cu
    = Strips

    Permissible current density at an electrode = [(7.57 x 103) / √ (ℓ x t)]


    = [(7.57 x 103) / √ (75 x 3)] = 504.66 A/m2
    Plate electrodes of size 1200x1200x12.3mm Cast Iron plate is using
    Then total area of both sides of one plate electrode = 1.2 x 1.2 x 2 = 2.88 m2
    Area required for dissipating fault current at 11KV side = 7873 / 504.66 = 15.6 m2
    Number of plate electrodes required = 15.6/ 2.88 = 5.4 ~ 6Nos.
    As installation includes 3 Nos. transformer and 2 Nos. generator, hence number of earth pits provided is
    6 Nos., hence adequate.
    Earth pits shall be interlinked with 32x6 mm Cu Strips.

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