# Grounding Design Calculations – Part Seventeen

In Article Grounding Design Calculations – Part One ", I indicated the following:

 Grounding System Design Calculations according to type of the building The procedures for performing the Grounding System Design Calculations can differ slightly according to the type of the building as follows: Domestic, commercial and industrial premises, High and medium voltage electricity substations.

 First: Domestic, commercial and industrial premises We mean by domestic, commercial and industrial premises, all installations up to 1,000 V ac and 1,500 V dc - between phases, with some minor exceptions.

And I explained Methods of Grounding Design Calculations of Domestic, commercial and industrial premises in the following Articles:

 Second: High And Medium Voltage Electricity AC Substations

I began explaining Grounding Design Calculations for second type of buildings: AC Substations in Article
Grounding Design Calculations – Part Ten "  where I explained the following:

• Design Procedures for grounding system design as per IEEE 80: Guide for safety in AC substation grounding,
• Step#1: Field Data Collection,
• Step#2: Earthing Grid Conductor Sizing.

Grounding Design Calculations – Part Eleven : Step#3: Calculation Of Tolerable Touch And Step Voltages.

Grounding Design Calculations – Part Twelve: Step#4: Preliminary Design of Grounding System for AC Substations.

Grounding Design Calculations – Part Thirteen: Step#5: Calculation of the Preliminary Grid Resistance, Rg, Of the Grounding System in Uniform Soil.

Grounding Design Calculations – Part Fourteen: Step#6: Determination of Maximum Grid Current, IG.

Grounding Design Calculations – Part Fifteen, I explained the following steps:
• Step#7: Calculation of Maximum Grid Potential Rise and Comparing With the Tolerable Touch Voltage from Step#3
• Step#8: Calculation of Mesh and Step Voltages

Grounding Design Calculations – Part Sixteen, I explained the following steps:

• Step#9: Comparing The Computed Mesh Voltage From Step#8 With The Tolerable Touch Voltage From Step#3
• Step#10: Comparing The Computed Step Voltage From Step#8 With The Tolerable Step Voltage From Step#3
• Step#11: Preliminary Design Modification
• Step#12: Detailed Final Design

 Excel Spreadsheets for Grounding System Design Calculations of AC Substation

Today, I will introduce to you, the most powerful excel spreadsheet for Grounding System Design Calculations of AC Substation.

 Important Use this excel spreadsheet for AC Substation only, and don’t use it for Domestic, commercial and industrial premises. (Please review the above definition for domestic, commercial and industrial premises). Another excel spread sheet was provided for Grounding System Design Calculations for Domestic, commercial and industrial premises. Just follow the Link.

 Benefits For Using This Excel Spreadsheet List all data that must be known in the starting of Grounding System Design Calculations for AC Substation , Facilitate the design process by using the auto excel mathematical functions in performing the calculations, Provide a professional design concept for any Grounding System of AC Substation as per Standard IEEE 80-2000, Provide and make reference for all used equations from IEEE 80-2000 Standard, Provide a printable Results Summary Report.

This excels spreadsheet includes (5) nos. worksheets and (9) nos. pages (see below image) as follows:

 S/N Worksheet Name No. of Pages 1 Table Of Contents 1 2 Design Procedure Block Diagram 1 3 Grounding System Calculations 5 4 Results Summary Report 1 5 Used Tables 1 Total 9

 Excel Spreadsheets for Grounding System Design Calculations of AC Substation

This worksheet lists the other worksheets in an index as shown in below figure, you can go to a specific worksheet by just clicking on its name.

You can send email to me directly by clicking on the phrase “Designed by: Ali Hassan” for any inquiries or notes.

Second: Design Procedure Block Diagram Worksheet

 Design Procedure Block Diagram Worksheet

This worksheet includes the block diagram which illustrates the sequences of steps to design the ground grid of AC Substations and it is divided to (2) types of shapes as follows:
• Rectangular shapes: for data entering and data calculation,

• Diamond shape: for logical comparison between different values.

 Note: The diamond shapes based on their logical answer “yes or no” will change the calculations sequence i.e. you may continue to next step or you may move forward or backward to other steps.

Third: Grounding System Calculations Worksheet

 Grounding System Calculations Worksheet

This worksheet includes general data that must be known in the starting of Grounding System Design Calculations of AC Substations, which are included in step#1 as follows:

• Soil Resistivity, ρ
• Gravel Resistivity, ρs
• Symmetrical Short Circuit Current, Ig
• Duration of Earth Fault Current, ts
• Maximum Allowable Conductor Temperature
• Design Ambient Temperature
• Thickness of Crushed Gravel, hs
• Depth of Earth Grid, h
• Reference depth of the Grid, ho

 STEP#1: GENERAL DESIGN DATA

 Important: The data input cells are the yellow color ones

 Important The blue areas include the used rules in calculations referred to Standard IEEE 80-2000, The gray areas list the design parameters description included in each Rule. The light green areas include the intermediate data results that will be used in getting the required data results in pink areas.

Also, this worksheet helps you to calculate the following:

• Step#2: The size of the grid conductor in Kcmil, mm2 and its diameter

• Step#3: Tolerable touch voltage and step voltages (Etouch and Estep)
• Step#5: Grid resistance calculation, Rg
• Step#6: Maximum Grid Current calculation, IG
• Step#7: Ground Potential Rise GPR
• Step#8: Calculation for Actual Derived Step & Mesh Voltage (Es and Em)

For step#2

You need to select the grid conductor material type from the drop-down menu existing in this step, the choices are:

1. Copper, annealed soft-drawn
2. Copper, commercial hard-drawn
7. Aluminum, 5005 alloy
8. Aluminum, 6201 alloy
10. Steel, 1020
12. Zinc-coated steel rod
13. Stainless steel, 304

 STEP#2: SIZE OF EARTHING CONDUCTOR

Based on your selection, the Material Constants will change according to Table-1 Material Constants included in Used Tables Worksheet and extracted from standard IEEE 80-2000, page 42.

Note: The default of this excel sheet for Tolerable touch voltage and step voltages in Step#3 was made for 70 Kg persons, if there is a need to calculate for 50 Kg persons, just send email to me as a modification request.

 Step#3: Tolerable touch voltage and step voltages

 Important: The data Results cells are the Pink color ones

For Step#4: Initial Design Assumptions

This step depends on the experience of the designer to provide good initial design parameters that suit the case under design, for more information about this step and how to assume its data, please review our Article " Grounding Design Calculations – Part Twelve ".

 Step#4: Initial Design Assumptions

 Step#5: Grid resistance calculation

 Step#6: Maximum Grid Current calculation

In addition to the above, this worksheet helps you to logically compare between the different designs parameters as follows:

• In Step#7: comparing the computed GPR with the Tolerable Touch Voltage from Step#3,
• In Step#9: Comparing the Computed Mesh Voltage from Step#8 with the Tolerable Touch Voltage from Step#3,
• In Step#10: Comparing the Computed Step Voltage from Step#8 with the Tolerable Step Voltage from Step#3.

Important: The results of the logical comparison for the above (3) steps are included in the yellow cells between brackets.

 Step#7: Ground Potential Rise

 Step#9: Comparing the Computed Mesh Voltage from Step#8 with the Tolerable Touch Voltage from Step#3

 Step#10: Comparing the Computed Step Voltage from Step#8 with the Tolerable Step Voltage from Step#3

 Step#8: Calculation for Actual Derived Step and Mesh Voltage

Fourth: Results Summary Report Worksheet

 Results Summary Report Worksheet

This worksheet gives results summary under three sections as follows:

Section#1: Earth Grid Conductor, it gives:

• Type of Conductor,
• Size of Conductor,
• Length of Conductor,
• Depth of Conductor.

Section#2: Ground Rods, it gives:

• Total Length of Ground Rods,
• Length of Individual Ground Rods,
• No. of Ground Rods.

Section#3: Human Safety, it gives:

• The permissible (Tolerable) values of the touch and step voltages,
• The designed value of the touch and step voltages,
• The result of logical comparison between the Computed Mesh Voltage from Step#8 with the Tolerable Touch Voltage from Step#3,
• The result of logical comparison between the Computed Step Voltage from Step#8 with the Tolerable Step Voltage from Step#3.

Fifth: Used Tables Worksheet

 Used Tables Worksheet

This worksheet includes the used table in calculations which is Table-1 for grid conductor Material Constants. This table is extracted from standard IEEE 80-2000, page 42.

The Material Constants provided by Table-1 are as follows:

• Material conductivity (%)
• αr factor at 20 °C (1/°C)
• Ko at 0 °C (0 °C)
• Fusing temperature Tm (°C)
• ρr 20 °C (μΩ·cm)
• TCAP thermal capacity [J/(cm3·°C)]

And the grid conductor materials will be as indicated in above Grounding System Calculations worksheet.

In the next Article, I will explain Lightning Design Calculations. Please, keep following.

#### 1 comment:

1. Ali
The building grounding spreadsheet looks great. However you have used various formulas and there is no reference to any of the formulas. Would you be able to explain where the formulas were taken so that we understand it better.
Regards
SK