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7. Calculate Earthing Strip Size for Electrical Equipment’s in Power Distribution Network

CALCULATE EARTHING STRIP SIZE FOR ELECTRICAL EQUIPMENT’S IN POWER DISTRIBUTION NETWORK

EXAMPLE:

Calculate Earthing Strip / Cable Size for Electrical Equipment’s / Panels in Power Distribution Networks.

  • At RMU * At Transformer * At D.G Set * At Main Distribution Panel * At Sub Panel-1 * At Sub Panel-2

1

CALCULATION:

(1) EARTHING STRIP SIZE AT RMU:

  • Shot circuit capacity at RMU is 18.37 KA for 1 Second. * Corrosion in Strip is 1% per year * Earthing Strip shall be replaced after 25 Years. * Safety Factor for Strip is 1.5 * Earthing Strip Material is GI

Calculation

  • As per IS: 3043, clause 17.2.2.1: * Cross section area of Earthing Strip (A) =(Isc x√t)/k * Where Isc= Shot circuit current capacity in Ampere. * t= Time for Shot circuit current in Second. * K= Material Constant

Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material TABLE 11A (IS:3043) Material K value (1 second) K value (2 second) Steel 80 46 Aluminum 126 73 Copper 205 118

  • Cross section area of Earthing Strip (A) = (Isc x√t)/k * Cross section area of Earthing Strip (A) = (18.37×1000 x√1)/80 * Cross section area of Earthing Strip (A) = 229.69 Sq.mm * Allowable corrosion =1% per Year * No of Year for replacement = 25 Year * Allowable corrosion in 25 Years = 229.69x1x25% =57.40 Sq.mm * Allowable Safety Factor = 229.69×1.5%=3.44 Sq.mm * Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor * Required Earthing Strip size=229.69+57.40+3.44 Sq.mm * Required Earthing Strip size=290.47 Sq.mm * Proposed GI Earthing Strip shall be 50×6 mm = 300 Sq.mm. * Here Proposed Earthing Strip Size > Required Earthing Strip Size * Proposed Earthing Strip is OK

(2) EARTHING STRIP SIZE AT TRANSFORMER:

  • Shot circuit capacity at Transformer is 25.32 KA for 1 Second. * Corrosion in Strip is 1% per year * Earthing Strip shall be replaced after 25 Years. * Safety Factor for Strip is 1.5 * Earthing Strip Material for Transformer Neutral is Copper * Earthing Strip Material for Transformer Body is GI

Calculation

  • For Neutral * As per IS: 3043, clause 17.2.2.1: * Cross section area of Earthing Strip (A) =(Isc x√t)/k * Where Isc= Shot circuit current capacity in Ampere. * t= Time for Shot circuit current in Second. * K= Material Constant

Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material TABLE 11A (IS:3043) Material K value (1 second) K value (2 second) Steel 80 46 Aluminum 126 73 Copper 205 118

  • Cross section area of Earthing Strip (A) = (Isc x√t)/k * Cross section area of Earthing Strip (A) = (25.32×1000 x√1)/205 * Cross section area of Earthing Strip (A) = 125.51 Sq.mm * Allowable corrosion =1% per Year * No of Year for replacement = 25 Year * Allowable corrosion in 25 Years = 125.51 x1x25% =30.87 Sq.mm * Allowable Safety Factor = 125.51 x1.5%=1.85 Sq.mm * Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor * Required Earthing Strip size=125.51+30.87+1.85 Sq.mm * Required Earthing Strip size=156.24 Sq.mm * Proposed Cu Earthing Strip shall be 32×6 mm = 192 Sq.mm. * Here Proposed Earthing Strip Size > Required Earthing Strip Size * Proposed Earthing Strip is OK * For Body * As per IS: 3043, clause 17.2.2.1: * Cross section area of Earthing Strip (A) =(Isc x√t)/k * Where Isc= Shot circuit current capacity in Ampere. * t= Time for Shot circuit current in Second. * K= Material Constant

Bare Conductor Material with No Risk of Fire or Danger to any Other Touching or Surrounding Material TABLE 11A (IS:3043) Material K value (1 second) K value (2 second) Steel 80 46 Aluminum 126 73 Copper 205 118

  • Cross section area of Earthing Strip (A) = (Isc x√t)/k * Cross section area of Earthing Strip (A) = (25.32 x1000 x√1)/80 * Cross section area of Earthing Strip (A) = 316.5 Sq.mm * Allowable corrosion =1% per Year * No of Year for replacement = 25 Year * Allowable corrosion in 25 Years = 316.5 x1x25% =79.12 Sq.mm * Allowable Safety Factor = 316.5 x1.5%=4.74 Sq.mm * Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor * Required Earthing Strip size=316.5+79.12+4.74 Sq.mm * Required Earthing Strip size=400.37 Sq.mm * Proposed GI Earthing Strip shall be 75×6 mm = 450 Sq.mm. * Here Proposed Earthing Strip Size > Required Earthing Strip Size * Proposed Earthing Strip is OK

(3) EARTHING CABLE SIZE AT D.G SET:

  • Shot circuit capacity at D.G Set is 10KA for 1 Second. * Corrosion in Strip is 1% per year * Earthing Strip shall be replaced after 25 Years. * Safety Factor for Strip is 1.5 * Earthing Wire Material is Copper, XLPE Insulated

Calculation

  • As per IS: 3043, clause 17.2.2.1: * Cross section area of Earthing Strip (A) =(Isc x√t)/k * Where Isc= Shot circuit current capacity in Ampere. * t= Time for Shot circuit current in Second. * K=…