CEP: Professional Certificate in Essential Practices for Electrical Assessment

Assignment Overview

How is this course assessed?

After completion of this assessment, you will receive a result of ‘Satisfactory’ or ‘Not Satisfactory’.
Your assessor will provide feedback via Moodle, and if you receive a ‘Not Satisfactory’ outcome, you will have the opportunity to submit additional evidence.

You are allowed one (1) opportunity to re-submit the same assessment task if required.

To achieve a ‘Satisfactory’ result:

• All questions must be answered to a satisfactory standard.

• You must achieve an overall mark of 60% or above.

Once all assessment tasks have been completed, you will receive a final course result of:

• Competent, or

• Not Yet Competent

If you are deemed ‘Not Yet Competent’ after all attempts, you will be required to re-sit the course.

How is this assessment task assessed?

To achieve a satisfactory result in this assessment:

• All assessment criteria must be completed to a satisfactory standard.

• Critical questions require a result of 100?fore a satisfactory outcome can be awarded.

Assessors also consider:

• All parts of the assessment meet requirements set out in the course outline.

• All work submitted is the student’s own work, with appropriate referencing.

• Evidence is recent and reflects up-to-date knowledge.

Introduction

This assessment focuses on developing practical engineering skills by integrating theoretical principles of earthing grid design with hands-on simulation and validation using ETAP software. Students will apply the IEEE 80 standard to design a safe and effective earthing system for electrical substations, with emphasis on managing hazards associated with touch and step voltages.

The project encourages critical thinking, problem solving, and the application of international standards to real-world electrical engineering scenarios. By completing this assessment, students will demonstrate their ability to design, simulate, and validate an earthing grid that complies with safety standards while improving their understanding of power system protection.

Q1: Report

Write a report on the earthing design of the system shown in Figure 1. The report must include:

• Single-phase-to-ground current calculation (Figure 1)

• Earth grid design for the entire substation (Figure 2)

• Touch and step potential calculations

• Bonding details for all steel structures in the area

The report should be 800–1200 words (excluding references) and must answer the questions listed in Points 1–6 below.

Figure 1. Substation Single Line Diagram

Transformer: 1500 kVA ONAN
HV/LV = 22 / 0.433 kV
Primary Tap: -2.50%
Impedance Voltage: 6.25% on 1500 kVA

Motor (Connected to 415 V MCC @ 415 V Bus):

• Motor ID: MTR_G6903

• Rated Power: 220 kW

• Full Load Current: 361 A

• Load Factor: 1.00

Cable Information:

• Cable #1: 460 m, 3C, 35 mm⊃2;, Cu XLPE/PVC

• Cable #2: 48 m, 4 × 1C, 500 mm⊃2;, Cu PVC/PVC

1. Calculating Single Phase to Ground Fault at 22 kV and 433 V

A system study must be conducted to determine the single-phase-to-ground fault level at the 22 kV side of the 22/0.433 kV transformer (T1).

The following must be calculated and tabulated:

• Single-phase-to-ground fault current at 22 kV

• Single-phase-to-ground fault current at 433 V

• Fault current for a 1-second clearance time

2. Two-Layer Soil Model Calculation

Finite Element Analysis (FEM) must be used to determine ground resistance of the earth grid.
FEM allows modelling of:

• Single rods or multi-rod systems

• Uniform or non-uniform soil resistivity

A two-layer soil model shall be used (refer to Figure 3):

• Upper layer with finite depth h and resistivity ρ₁

• Lower layer with infinite depth and resistivity ρ₂

Use IEEE 80 – Sunde’s graph (Figure 4) when performing calculations.

3. Earth Conductor

Determine the earth conductor size required for bonding all steel structures throughout the facility, in accordance with IEEE Std 80.

4. Simulation for Earth Grid

Using ETAP, simulate the earth grid layout and dimensions as shown in Figure 2.
The simulation must include:

• Number of rods

• Spacing between rods

• Length of each rod

All results must be presented in tabulated format.

5. Achieving Safe Voltages

Calculate the following:

• Touch voltage

• Step voltage

• Tolerable voltage

Note:
A concrete layer with an effective depth of 0.1 m must be included as a surface protective layer to achieve safe touch and step potentials.

6. Bonding Protection

Describe the requirements to ensure that:

• All steel structures are properly bonded to earth

• Bonding continuity is maintained throughout the system

• Bonding meets safety and performance requirements

Summary of Assessment Requirements

The assessment requires students to demonstrate their competence in designing, simulating, and validating an electrical substation earthing grid in accordance with IEEE 80 standards. The task involves applying theoretical knowledge and practical engineering tools specifically ETAP software to ensure safety against touch and step voltages. To achieve a satisfactory result, all criteria must be completed to the required standard, and critical questions must be answered with full accuracy.

The key components of the assessment include:

Key Pointers to Be Covered

1. Single-phase-to-ground fault current calculations

   • Determine fault levels at both 22 kV and 433 V transformer sides.

   • Calculate 1-second fault current values.

2. Two-layer soil model analysis

   • Use Finite Element Analysis (FEM) to evaluate soil resistivity and earth grid resistance.

   • Apply IEEE 80 Sunde’s graph for layered soil modelling.

3. Earthing conductor selection

   • Determine conductor size based on prospective fault levels and IEEE 80 requirements.

4. Earth grid simulation using ETAP

   • Model grid geometry including rods, spacing, conductor layout, and system dimensions.

   • Tabulate simulation results.

5. Touch, step, and tolerable voltage calculation

   • Include the effect of a 0.1 m concrete surface layer for safety improvement.

6. Bonding and continuity requirements

   • Explain how all steel structures will be bonded to the earthing system.

   • Ensure system-wide bonding integrity and compliance with safety standards.

How the Academic Mentor Guided the Student Through the Assessment

The academic mentor supported the student with a structured, step-by-step approach to help them understand the technical requirements, apply standards accurately, and use ETAP effectively. Below is a summary of how each section was approached and explained during mentoring.

1. Understanding the Assessment Context and Objectives

The mentor first clarified the purpose of the assessment designing a safe and compliant earthing system using engineering standards and simulation tools. The student was guided to understand:

• why earthing is critical for personnel and equipment safety

• how IEEE 80 defines the acceptable limits for electrical hazards

• how to interpret ETAP outputs for validating safety compliance

This foundational understanding helped the student connect theory with practical engineering tasks.

2. Fault Current Calculations

Mentor’s Guidance:

• The mentor explained the importance of fault current values in determining conductor sizing and grid design.

• The student was shown how to extract transformer impedance values, apply base calculations, and compute single-phase-to-ground faults at both voltage levels.

• Step-by-step formulas and sample calculations were demonstrated before the student attempted their own analysis.

Outcome:

The student produced accurate tables showing the 22 kV and 433 V fault currents and calculated the 1-second fault rating required for later steps.

3. Two-Layer Soil Modelling Using FEM

Mentor’s Guidance:

• The mentor explained soil resistivity concepts and how varying soil layers affect earth grid performance.

• FEM was introduced as the preferred method for complex soil profiles.

• The student was guided on how to reference IEEE 80 Sunde’s curves for two-layer soil adjustments and how to interpret FEM software outputs.

Outcome:

The student successfully modelled the upper and lower soil layers and derived the equivalent soil resistivity values required for grid simulation.

4. Selecting the Correct Earthing Conductor

Mentor’s Guidance:

• The mentor explained how conductor sizing depends on thermal capacity, fault duration, and material properties.

• The IEEE 80 formula for conductor sizing was broken down into simpler terms.

• The student was shown how the previously calculated fault current feeds into this step.

Outcome:

A compliant conductor size was selected, ensuring the earthing system could withstand the thermal effects of fault currents.

5. ETAP Simulation for Earth Grid Layout

Mentor’s Guidance:

• The mentor walked the student through importing grid dimensions and defining conductor mesh patterns.

• They reviewed how to input rod spacing, depth, quantity, and conductor interconnections into ETAP.

• The student was taught how to generate and interpret ETAP tables, including grid resistance, mesh voltage, and surface potentials.

Outcome:

A full ETAP simulation was completed, including tabulated results showing rod count, grid resistance, mesh and step voltages, and layout dimensions.

6. Touch and Step Voltage Compliance

Mentor’s Guidance:

• The mentor explained the IEEE 80 criteria for safe touch and step voltages.

• They demonstrated how to calculate tolerable voltage based on worker body resistance and surface material.

• The importance of the 0.1 m concrete layer was clarified, including its role in reducing surface potentials.

Outcome:

The student accurately calculated touch, step, and tolerable voltages and demonstrated that the grid design met safety requirements.

7. Bonding Protection and Continuity

Mentor’s Guidance:

• The mentor explained that bonding ensures equal potential across metallic structures to prevent hazardous voltages.

• The student learned how to document bonding requirements for steel structures, transformer frames, panel enclosures, and cable trays.

• Continuity testing and compliance documentation were also reviewed.

Outcome:

The student provided a comprehensive bonding strategy demonstrating that all steel structures and equipment were safely connected to the grid.

Final Outcome and Learning Achievements

By following the structured guidance, the student successfully completed all parts of the assessment and met each requirement to a satisfactory standard. The final submission demonstrated:

What Was Achieved

• A complete earthing grid design aligned with IEEE 80.

• Accurate fault current calculations and soil modelling.

• Selection of compliant earthing conductors.

• ETAP simulation with correct interpretation of results.

• Validated touch and step voltage compliance.

• Thorough bonding and continuity documentation.

Learning Objectives Covered

• Application of international engineering standards (IEEE 80).

• Understanding of electrical safety principles related to earthing.

• Use of ETAP for engineering simulations and verification.

• Integration of theoretical and practical engineering skills.

• Problem-solving using real-world electrical design constraints.

• Technical report writing and documentation.

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