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TRANSFORMER POST FOUNDATION GROUNDING CALCULATIONS

1-GENERAL DESIGN DATA

 

Soil Resistivity, ρ             ohm.m
Gravel Resistivity, ρs        ohm.m

Thickness of Crushed Gravel, hs

   cm
Symmetrical Short Circuit Current, Iefs   A
Duration of Earth Fault Curren, ts   sn
Maximum Allowable Conductor Tem. Temp   0C
Design Ambient Temperature, Ta   0C
Depth of Earth Grid, h   m
Reference depth of the Grid, h0   m

2-SELECTION OF THE CONDUCTOR TO BE USED IN THE MESH GROUNDING

Select Material for Earthing:  
Resistivity of Conductor Material   (Ohm.m) αr  
Thermal co-efficient of resistivity at  °C(μΩ.cm) ρr  
Max. allowable temperature in  0C Tm  
1/α0 or 1/αr - 0C in Tr   K0  
Thermal capacity per unit volume from [J/(cm³.°C] TCAP  

Conductor cross section A mm2

  57,67
Cable Diameter mm  18

3-TOUCH VOLTAGE - STEP VOLTAGE

for 50 kg body weight person step voltage  Estep50  1911,17  V
for 70 kg body weight person step voltage  Estep70  2586,67  V
for 50 kg body weight person touch voltage Etouch50  600,83  V 
for 70 kg body weight person touch voltage Etouch70  813,19  V

4-INITIAL DESIGN ASSUMPTIONS

Preliminary Layout of Grid Length/Wide   / 
Conductor Spacing  
No. of Ground Rods Number / Length   /
Grid Resistance:  0,67

 

Maximum Grid Current IG  7.700,00 A
Ground Potantial Rise GPR  5.159,00 V
Spacing factor for Mesh Voltage : Km  0,78
E mesh(Design) Voltage :Em  773,72 V
E step(Disign) Voltage: Eadım  592,11 V

 

for 70 kg body weight person Result:
Step Voltage Calculated in Design :(Estep < Estep70) =592,11 < 2586,67  since Tasarım Uygundur.
Mesh Voltage Calculated in Design :(Em < Etouch70) =773,72 < 813,19  since Tasarım Uygundur.

 

50 kg body weight person Result:
Step Voltage Calculated in Design :(Estep < Estep50) =592,11 < 1911,17  since Tasarım Uygundur.
Mesh Voltage Calculated in Design :(Em > Etouch50) =773,72 > 600,83  since Tasarım Uygun Değildir.