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

December 30, 2024 5 Comments


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= Material Constant
Insulated Protective Conductors Not Incorporated in Cables or Bare Conductors Touching Other Insulated Cables
TABLE 11B (IS:3043)
Material K value (1 second) K value (3 second)
Copper , PVC Insulated 136 79
Copper, Rubber Insulated 150 92
Copper, XLPE Insulated 170 98
Aluminum, PVC Insulated 90 52
Aluminum, Rubber Insulated 106 61
Aluminum, XLPE Insulated 112 65
Steel, PVC Insulated 49 28
Steel, Rubber Insulated 58 33
Steel, XLPE Insulated 62 36
  • Cross section area of Earthing Strip (A) = (Isc x√t)/k
  • Cross section area of Earthing Strip (A) = (10×1000 x√1)/170
  • Cross section area of Earthing Strip (A) = 58.82 Sq.mm
  • Allowable corrosion =1% per Year
  • No of Year for replacement = 25 Year
  • Allowable corrosion in 25 Years = 58.82x1x25% =14.70 Sq.mm
  • Allowable Safety Factor = 58.82 x1.5%=0.88 Sq.mm
  • Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
  • Required Earthing Strip size=58.82+14.7+0.88 Sq.mm
  • Required Earthing Strip size=74.41 Sq.mm
  • Proposed Earthing Single Core Copper, XLPE Cable=95 Sq.mm
  • Here Proposed Earthing Cable Size > Required Earthing Cable Size
  • Proposed Earthing Cable is OK

(4) Earthing Strip Size at Main Panel :

  • Shot circuit capacity at Main Panel is 21 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) = (21 x1000 x√1)/80
  • Cross section area of Earthing Strip (A) = 262.5 Sq.mm
  • Allowable corrosion =1% per Year
  • No of Year for replacement = 25 Year
  • Allowable corrosion in 25 Years = 262.5 x1x25% =65.62 Sq.mm
  • Allowable Safety Factor = 262.5 x1.5%=3.93 Sq.mm
  • Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
  • Required Earthing Strip size=262.5+65.62+3.93 Sq.mm
  • Required Earthing Strip size=332.06 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

(5) Earthing Strip Size at Sub Panel-1 :

  • Shot circuit capacity at Sub Panel-1 is 11 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) = (11 x1000 x√1)/80
  • Cross section area of Earthing Strip (A) = 137.5 Sq.mm
  • Allowable corrosion =1% per Year
  • No of Year for replacement = 25 Year
  • Allowable corrosion in 25 Years = 137.5 x1x25% =34.37 Sq.mm
  • Allowable Safety Factor = 137.5 x1.5%=2.06 Sq.mm
  • Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
  • Required Earthing Strip size=137.5+34.37+2.06 Sq.mm
  • Required Earthing Strip size=173.93 Sq.mm
  • Proposed GI Earthing Strip shall be 32×6 mm = 192 Sq.mm.
  • Here Proposed Earthing Strip Size > Required Earthing Strip Size
  • Proposed Earthing Strip is OK

(5) Earthing Strip Size at Sub Panel-2 :

  • Shot circuit capacity at Sub Panel-2 is 6 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) = (6 x1000 x√1)/80
  • Cross section area of Earthing Strip (A) = 75.0 Sq.mm
  • Allowable corrosion =1% per Year
  • No of Year for replacement = 25 Year
  • Allowable corrosion in 25 Years = 75 x1x25% =18.75 Sq.mm
  • Allowable Safety Factor = 75 x1.5%=1.12 Sq.mm
  • Required Earthing Strip size = Cross sectional area + Total Corrosion allowance + Safety factor
  • Required Earthing Strip size=75+18.75+1.12 Sq.mm
  • Required Earthing Strip size=94.87 Sq.mm
  • Proposed GI Earthing Strip shall be 25×6 mm = 150 Sq.mm.
  • Here Proposed Earthing Strip Size > Required Earthing Strip Size
  • Proposed Earthing Strip is OK

CONCLUSION:

  • At RMU=GI Earthing Strip: 50x6MM
  • At Transformer Neutral=CU Earthing Strip: 32x6MM
  • At Transformer Body=GI Earthing Strip: 75x6MM
  • At D.G Set=CU, XLPE Earthing Cable: 1Cx95 SQ.MM
  • At Main Distribution Panel=GI Earthing Strip: 75x6MM
  • At Sub Panel=1=GI Earthing Strip: 32x6MM
  • At Sub Panel-2=GI Earthing Strip: 25x6MM.

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Calculate Size of Diesel Generator for various types of Load

June 21, 2024 Leave a comment


Calculate Size of Diesel Generator set for following types of various equipment’s

D.G Set Detail:

  • G Set Phase-Phase Voltage=415V, Phase-Neutral Voltage=230V, Future Load expansion=10%, D.G overload capacity =130%.

Connected Load:

  1. Fire Fighting Pump: 1No,3 Phase, 90KW, starting P.F is 0.7 & running P.F is 0.8, Soft Starter, Continuous use.
  2. HVAC Load: 1No, 3 Phase, 20KW, starting P.F is 0.7 & running P.F is 0.8, Intermediate use.
  3. UPS Load: 1No, 3 Phase, 7KW, starting P.F is 0.7 & running P.F is 0.8, Continuous use.
  4. Lighting Load: 10No, 1Phase ,400Watt, starting P.F is 0.7 & running P.F is 0.8, Continuous use.
  • Linear Load =General Electrical equipment, Heater
  • Non-Linear Load = UPS, Inverter, Ballast, Drives

CALCULATION:

LOAD NO:1 (MOTOR LOAD)

  • Total Load (KW)= No of Equipment X Size of Equipment
  • Total Load (KW)=01×90 =90KW
  • Diversify Load (KW)= Total Load X Duty factor (0=Stand by Load,1=continuous Load, 0 to 1 =Intermediate Load)
  • Diversify Load (KW) = 90×1= 90KW————————————–(1)
  • Running KVA = Diversify Load (KW) / Running P.F
  • Running KVA = 90 x 0.8
  • Running KVA =113 KVA————————————–(2)
  • Running Amp (Amp) = Diversify Load (KW) / 1.732 x Volt x Running P.F
  • Running Amp (Amp) =90×1000 / 1.732 x 415 x 0.8
  • Running Amp (Amp) =156.7 Amp
  • Starting Amp = Running Amp X Multiplying Factor of Starter
  • Multiplying Factor of Starter is as under.
Starter Starting current
Method Starting current
Direct-on-Line (DOL) 5 to 10 times the full load current
Star-Delta Starter 3 to 4 times the full load current
Auto-transformer 2 to 3 times the full load current
Soft starter 1.1 to 2 times full load current
Variable Speed drive 1.1 to 1.5 times full load current
  • Considering Multiplying Factor for Soft Starter is 2
  • Starting Amp = 156.7 X 2
  • Starting Amp =313Amp
  • Starting KVA = (Diversify Load (KW) / Starting P.F) X Multiplying Factor of Starter
  • Starting KVA = (90/0.7) X 2
  • Starting KVA = 257 KVA——————————————–(3)

LOAD NO:2 (HVAC LOAD)

  • Total Load (KW)= No of Equipment X Size of Equipment
  • Total Load (KW)=01×20 =20KW
  • Diversify Load (KW)= Total Load X Duty factor (0=Stand by Load,1=continuous Load, 0 to 1 =Intermediate Load)
  • Diversify Load (KW) = 20×0.8= 16KW————————————–(4)
  • Running KVA = Diversify Load (KW) / Running P.F
  • Running KVA = 16 x 0.8
  • Running KVA =20 KVA————————————–(5)
  • Running Amp (Amp) = Diversify Load (KW) / 1.732 x Volt x Running P.F
  • Running Amp (Amp) =16×1000 / 1.732 x 415 x 0.8
  • Running Amp (Amp) =28 Amp
  • Starting Amp = Running Amp X Multiplying Factor of HVAC
  • Multiplying Factor of Starting Current for various type of Load is as under.

Starting current
Type of Load Starting current for Load
Linear 1 time the full load current
Non-Linear 1.2 to 1.6 times the full load current
HVAC 1.2 to 1.5 times the full load current
  • Considering Multiplying Factor of HVAC is 1.3
  • Starting Amp = 28X 1.3
  • Starting Amp =36Amp
  • Starting KVA = (Diversify Load (KW) / Starting P.F) X Multiplying Factor of HVAC
  • Starting KVA = (16/0.7) X1.3
  • Starting KVA = 30 KVA——————————————–(6)

LOAD NO:3 (NON-LINEAR LOAD)

  • Total Load (KW)= No of Equipment X Size of Equipment
  • Total Load (KW)=01×7 =7KW
  • Diversify Load (KW)= Total Load X Duty factor (0=Stand by Load,1=continuous Load, 0 to 1 =Intermediate Load)
  • Diversify Load (KW) = 7×1= 7KW————————————–(7)
  • Running KVA = Diversify Load (KW) / Running P.F
  • Running KVA = 7 x 0.8
  • Running KVA =9 KVA————————————–(8)
  • Running Amp (Amp) = Diversify Load (KW) / 1.732 x Volt x Running P.F
  • Running Amp (Amp) =7×1000 / 1.732 x 415 x 0.8
  • Running Amp (Amp) =12 Amp
  • Starting Amp = Running Amp X Multiplying Factor of Non-Linear Load
  • Multiplying Factor of Starting Current for various type of Load is as under.

Starting current
Type of Load Starting current for Load
Linear 1 time the full load current
Non-Linear 1.2 to 1.6 times the full load current
HVAC 1.2 to 1.5 times the full load current
  • Considering Multiplying Factor of Non-Linear Load (UPS) is 1.6
  • Starting Amp = 12X 1.6
  • Starting Amp =19Amp
  • Starting KVA = (Diversify Load (KW) / Starting P.F) X Multiplying Factor of HVAC
  • Starting KVA = (7/0.7) X1.6
  • Starting KVA = 16 KVA——————————————–(9)

LOAD NO:4 (LINEAR LOAD)

  • Total Load (KW)= No of Equipment X Size of Equipment
  • Total Load (KW)=10×0.4 =4KW
  • Diversify Load (KW)= Total Load X Duty factor (0=Stand by Load,1=continuous Load, 0 to 1 =Intermediate Load)
  • Diversify Load (KW) = 4×1= 4KW————————————–(10)
  • Running KVA = Diversify Load (KW) / Running P.F
  • Running KVA = 4 x 0.8
  • Running KVA =5 KVA————————————–(11)
  • Running Amp (Amp) = Diversify Load (KW) / 1.732 x Volt x Running P.F
  • Running Amp (Amp) =4×1000 / 230 x 0.8
  • Running Amp (Amp) =22 Amp
  • Starting Amp = Running Amp X Multiplying Factor of Linear Load
  • Multiplying Factor of Starting Current for various type of Load is as under.

Starting current
Type of Load Starting current for Load
Linear 1 time the full load current
Non-Linear 1.6 times the full load current
HVAC 1.2 to 1.5 times the full load current
  • Considering Multiplying Factor of Linear Load is 1
  • Starting Amp =22×1
  • Starting Amp =22Amp
  • Starting KVA = (Diversify Load (KW) / Starting P.F)
  • Starting KVA = (4/0.7)
  • Starting KVA = 6 KVA——————————————–(12)

TOTAL LOAD CALCULATION:

  • Total Starting KVA= Starting KVA of (Load 1+ Load 2+ Load 3 +Load 4)
  • Total Starting KVA= 257+30+16+6
  • Total Starting KVA= 309 KVA————————————(A)
  • Total Running KVA =Running KVA of (Load 1+ Load 2+ Load 3 +Load 4)
  • Total Running KVA =113+20+9+5
  • Total Running KVA = 146 KVA—————————–(B)
  • D.G set Size (KVA) = Total Starting KVA x Future Load Expansion.
  • D.G set Size (KVA) = 309×1.1 (10% Future expansion)
  • D.G set Size (KVA) = 339 KVA—————————————-(C)

CONDITION FOR SELECTING D.G SET:

  • CONDITION-1:
  • Total Non-Linear Load < 30% of D.G Size
  • Here Value no (9) < Value no (C)
  • 16 KVA < 102 KVA
  • Condition-1 is full fill
  • CONDITION-2:
  • Overloads withstand Capacity of D.G > Total Required starting KVA
  • Overload withstand capacity of D. G= D.G size X D.G over Load Capacity
  • Overload withstand capacity of D. G= 339 x 130%
  • Overload withstand capacity of D. G= 401 KVA——————–(D)
  • Total Required starting KVA = Total Load (KVA) -Largest Motor rating (KVA)+ Largest Motor starting (KVA)
  • Total Required starting KVA =146 -113+257
  • Total Required starting KVA =291 KVA ————————(E)
  • Here Value no (D) > Value no (E)
  • 401 KVA > 291 KVA
  • Condition-2 is full fill

 CONCLUSION:

  • Here Condition-1 & Condition-2 is full fill hence selected D.G Size is OK.
  • Hence D.G size is 339 KVA or near its 380 KVA

 

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