Calculate Size of Motor-Pump


1

Calculate Motor-Pump size:

  • Calculate Pump Hydraulic Power
  • Calculate Motor-Pump Shaft Power
  • Calculate Pump Size.
  • Calculate Motor Size.

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Calculate Numbers of Plate/Pipe/Strip Earthings (Part-3)


Calculate Min. Cross Section area of Earthing Conductor:

  • Cross Section Area of Earthing Conductor As per IS 3043
  • Cross Section Area of Earthing Conductor (A) =(If x√t) / K

  • Where t= Fault current Time (Second).
  • K= Material Constant.
  • Example:
  • Calculate Cross Section Area of GI Earthing Conductor for System has 50KA Fault Current for 1 second. Corrosion will be 1.0 % Per Year and No of Year for Replacement is 20 Years.
  • Cross Section Area of Earthing Conductor (A) =(If x√t) / K
  • Here If=50000 Amp
  • T= 1Second
  • K=80 (Material Constant, For GI=80, copper K=205, Aluminium K=126).
  • Cross Section Area of Earthing Conductor (A) =(50000×1)/80
  • Cross Section Area of GI Earthing Conductor (A)=625 Sq.mm
  • Allowance for Corrosion = 1.0 % Per Year & Number of Year before replacement say = 20 Years
  • Total allowance = 20 x 1.0% = 20%
  • Safety factor = 1.5
  • Required Earthing Conductor size = Cross sectional area x Total allowance x Safety factor
  • Required Earthing Conductor size = 1125 Sq.mm say 1200 Sq.mm
  • Hence, Considered 1Nox12x100 mm GI Strip or 2Nox6 x 100 mm GI Strips

 Thumb Rule for Calculate Number of Earthing Rod:

  • The approximate earth resistance of the Rod/Pipe electrodes can be calculated by
  • Earth Resistance of the Rod/Pipe electrodes R= K x ρ/L

  • Where ρ = Resistivity of earth in Ohm-Meter
  • L= Length of the electrode in Meter.
  • d= Diameter of the electrode in Meter.
  • K=0.75 if 25< L/d < 100.
  • K=1 if 100 < L/d < 600
  • K=1.2 o/L if 600 < L/d < 300
  • Number of Electrode if find out by Equation of R(d) =(1.5/N) x R

  • Where R(d) = Desired earth resistance
  • R= Resistance of single electrode
  • N= No. of electrodes installed in parallel at a distance of 3 to 4 Meter interval.
  • Example:
  • Calculate Earthing Pipe Resistance and Number of Electrode for  getting Earthing Resistance of 1 Ω ,Soil Resistivity of ρ=40, Length=2.5 Meter, Diameter of Pipe= 38 mm.
  • Here L/d = 2.5/0.038=65.78 so K=0.75
  • The Earth Resistance of the Pipe electrodes R= K x ρ/L =0.75×65.78=12 Ω
  • One electrode the earth resistance is 12 Ω.
  • To get Earth resistance of 1 Ω  the total Number of electrodes required =(1.5×12)/1 =18 No

 Calculating Resistance & Number of Earthing Rod:

  • Reference: As per EHV Transmission Line Reference Book page: 290 and Electrical Transmission & Distribution Reference Book Westinghouse Electric Corporation, Section-I Page: 570-590.
  • Earthing Resistance of Single Rods: R = ρx[ln (2L/a)-1]/(2×3.14xL)

  • Earthing Resistance of Parallel Rods: R = ρx[ln (2L/A]/ (2×3.14xL)

  • Where L= length of rod in ground Meter,
  • a= radius of rod Meter
  • ρ = ground resistivity, ohm- Meter
  • A= √(axS)
  • S= Rod separation Meter

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 Factor affects on Ground resistance:

  •  The NEC code requires a minimum ground electrode length of 2.5 meters (8.0 feet) to be in contact with the soil.  But, there are some factor that affect the ground resistance of a ground system:
  • Length / Depth of the ground electrode: double the length, reduce ground resistance by up to 40%.
  • Diameter of the ground electrode: double the diameter, lower ground resistance by only 10%.
  • Number of ground electrodes: for increased effectiveness, space additional electrodes at least equal to the depth of the ground electrodes.
  • Ground system design: single ground rod to ground plate.

 The GI Earthing Conductor sizes for various Equipments:      

No Equipments Earth Strip Size

1

HT switchgear, structures, cable trays & fence, rails, gate and steel column

55 X 6 mm (GI)

2

Lighting Arrestor

25 X 3 mm (Copper)

3

PLC Panel

25 X 3 mm (Copper)

4

DG & Transformer Neutral

50X6 mm (Copper)

5

Transformer Body

50X6 mm (GI)

6

Control & Relay Panel

25 X 6 mm (GI)

7

Lighting Panel & Local Panel

25 X 6 mm (GI)

8

Distribution Board

25 X 6 mm (GI)

9

Motor up to 5.5 kw

4 mm2 (GI)

10

Motor 5.5 kw to 55 kw

25 X 6 mm (GI)

11

Motor 22 kw to 55 kw

40 X 6 mm (GI)

12

Motor Above 55 kw

55 X 6 mm (GI)

 Selection of Earthing System:

Installations/       Isc Capacity

IR Value Required

Soil Type/ Resistivity

Earth System

House hold earthing/3kA 8 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Single Electrode
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
Commercial premises,Office / 5kA 2 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
Transformers, substationearthing, LT line equipment/ 15kA less than 1 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
LA, High current Equipment./ 50kA less than 1 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes
PRS, UTS, RTUs, Data processing centre etc./5KA less than 0.5 ohm Normal Soil/ up to 50 ohm-meter Single Electrode
Sandy Soil/ between 50 to 2000 ohm- meter Multiple Electrodes
Rocky Soil/ More than 2000 ohm- meter Multiple Electrodes

 Size of Earthing Conductor:

  • Ref IS 3043 &Handbook on BS 7671: The Lee Wiring Regulations by Trevor E. Marks.

Size of Earthing Conductor

Area of Phase Conductor S (mm2) Area of Earthing conductor (mm2) When It is Same Material as Phase Conductor Area of Earthing conductor (mm2) When It is Not Same Material as Phase Conductor
S < 16 mm2 S SX(k1/k2)
16 mm2<S< 35 mm2 16 mm2 16X(k1/k2)
S > 35 mm2 S/2 SX(k1/2k2)
K1 is value of Phase conductor,k2 is value of earthing conductor
Value of K for GI=80, Alu=126,Cu=205 for 1 Sec

 Standard Earthing Strip/Plate/Pipe/wire Weight:

GI Earthing Strip:

Size (mm2) Weight
20 x 3 500 gm Per meter
25 x 3 600 gm Per meter
25 x 6 1/200 Kg Per meter
32 x 6 1/600 Kg Per meter
40 x 6 2 Kg Per meter
50 x 6 2/400 Kg Per meter
65 x 10 5/200 Kg Per meter
75 x 12 7/200 Kg Per meter

 GI Earthing Plate:

Plate Weight
600 x 600 x 3 mm 10 Kg App.
600 x 600 x 4 mm 12 Kg App.
600 x 600 x 5 mm 15 Kg App.
600 x 600 x 6 mm 18 Kg App.
600 x 600 x 12 mm 36 Kg App.
1200 x 1200 x 6 mm 70 Kg App.
1200 x 1200 x 12 mm 140 Kg App.

 GI Earthing Pipe:

Pipe Weight
3 meter Long BISE 5 Kg App.
3 meter r Long BISE 9 Kg App.
4.5 meter (15′ Long BISE) 5 Kg App.
4.5 meter (15′ Long BISE) 9 Kg App.
4.5 meter (15′ Long BISE) 14 Kg App

 GI Earthing Wire:

Plate Weight
6 Swg 5 meter in 1 Kg
8 Swg 9 meter in 1 Kg
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