Calculate Size of Motor-Pump

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

 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