Sag And Tension Overhead Conductors On Ohte Under Isolated And Earthed Conditions Training

Objectives:
• Understand the basic principles of overhead transmission and distribution lines.
• Identify safety protocols for working on or near overhead lines under isolated and earthed conditions.
• Explain the importance of sag and tension in conductor performance.
• Describe the components of overhead line hardware and their functions.

Topics:
• Overview of overhead power lines (OHTE) and their role in the grid.
• Safety regulations: OHS Act, SANS 10219, and relevant standards.
• Introduction to conductor materials (ACSR, AAC, AAAC).
• Basic mechanical properties: tensile strength, elasticity, and thermal expansion.
• Key terms: sag, tension, span, ruling span, and clearance.
• Personal protective equipment (PPE) and safe work procedures.
• Risk assessment and method statements for line work.

Objectives:
• Derive the catenary equation for a suspended conductor.
• Apply the parabolic approximation for level spans.
• Calculate sag and tension under uniform loading conditions.
• Interpret sag-tension charts and tables.

Topics:
• Conductor as a flexible cable: catenary vs. parabola.
• Derivation of the catenary equation (y = c cosh(x/c)).
• Parabolic approximation for small sag-to-span ratios.
• Effect of conductor weight and span length on sag.
• Sag-tension relationships: tension as a function of sag.
• Use of sag templates and sag-tension nomographs.
• Practical exercise: manual sag calculation for a level span.

Objectives:
• Evaluate the impact of temperature on sag and tension.
• Incorporate wind and ice loading into calculations.
• Apply loading zones as per SANS 10219.
• Understand the concept of everyday stress and maximum design stress.

Topics:
• Thermal effects: expansion coefficient, stringing temperature, and operating temperature.
• Wind loading: pressure coefficients and projected area.
• Ice loading: radial ice thickness and density.
• Combined loading: wind-on-ice and wind-on-conductor.
• Loading districts in South Africa: light, medium, heavy.
• Safety factors and maximum allowable tension.
• Example: recalculating sag for extreme weather.

Objectives:
• Distinguish between isolated (dead) and earthed (grounded) conductor states.
• Calculate sag and tension for conductors under isolated conditions (no current).
• Calculate sag and tension for conductors under earthed conditions (short-circuit).
• Apply appropriate correction factors for each condition.

Topics:
• Definitions: isolated (de-energised, no fault current) vs earthed (grounded for maintenance or fault).
• Thermal behaviour under no-load (isolated) vs short-circuit (earthed) currents.
• Sag increase due to heating from fault current.
• Calculation methods for transient thermal effects.
• Clearance requirements for earthed conductors during faults.
• Practical differences: stringing sag vs operating sag.
• Case studies: typical scenarios for isolated and earthed conditions.

Objectives:
• Plan and execute conductor stringing procedures.
• Determine initial sag values for stringing.
• Use sagging methods: dynamometer, transit, and sag boards.
• Adjust for creep and initial stretch.

Topics:
• Stringing plan: pulling tension, reel placement, and snatch blocks.
• Sagging methods: visual (transit), tension-based (dynamometer), and sag-tension charts.
• Initial sag tables: temperature correction and creep allowance.
• Conducting a sagging operation: step-by-step.
• Measuring and recording sag after stringing.
• Common errors and troubleshooting.
• Safety during stringing: guarding and earth bonding.

Objectives:
• Apply the ruling span concept for multi-span lines.
• Create and use sag templates for line design.
• Analyze sag and tension for unequal spans.
• Understand the effect of dead-ends and angle structures.

Topics:
• Ruling span definition and calculation.
• Equivalent span method for irregular terrain.
• Sag template construction: plotting conductor curve on profile.
• Using sag templates for structure spotting and clearance checks.
• Tension distribution in multi-span sections.
• Effect of insulator strings and hardware weight.
• Software tools for sag-tension analysis (overview).

Objectives:
• Conduct field measurements of sag, tension, and temperature.
• Use instruments: transit, GPS, infrared thermometer, and tension meter.
• Record data accurately for compliance and reporting.
• Verify clearances against statutory requirements.

Topics:
• Field equipment: theodolite, total station, clinometer, and tension dynamometer.
• Measuring sag: methods and accuracy.
• Measuring conductor temperature: contact vs non-contact.
• Recording weather conditions: ambient temperature, wind speed.
• Data logging and documentation.
• Comparison of measured vs calculated values.
• Practical exercise: field measurement at a training line.

Objectives:
• Apply SANS 10219 and NRS 034 requirements for sag and tension.
• Prepare technical reports for sag and tension assessments.
• Interpret clearance violations and recommend corrective actions.
• Understand the role of the Saqa unit standard 119890 in competence assessment.

Topics:
• SANS 10219: overhead line design and construction.
• NRS 034: distribution systems.
• Clearance requirements: ground, vegetation, buildings, and crossings.
• Reporting format: scope, methodology, results, and conclusions.
• Case study: clearance violation analysis.
• Corrective actions: re-tensioning, raising structures, or reconductoring.
• Assessment criteria for unit standard 119890.

Objectives:
• Synthesise all knowledge in a comprehensive sag and tension project.
• Demonstrate competence in calculations, field measurements, and reporting.
• Complete the practical assessment for unit standard 119890.
• Receive feedback and certification.

Topics:
• Integrated project: design a sag and tension plan for a sample line.
• Practical assessment: stringing sag calculation, field measurement, and report writing.
• Oral questioning and portfolio evidence review.
• Feedback session and areas for improvement.
• Issuance of certificate of competence.
• Course evaluation and closing.