Engineering Delivery of 161kV Overhead Transmission Line: Chirano–Wassa Project, Ghana

Project Overview

The Chirano–Wassa 161kV Overhead Transmission Line Project in Ghana represents a complete engineering delivery covering design, manufacturing, installation, and commissioning of high-voltage transmission infrastructure. Executed by ZHM Metal Engineering Co., Ltd., the project connects key power nodes between Chirano and Wassa, supporting grid stability and regional power distribution.

The scope includes lattice steel towers, phase conductors, overhead ground wire (OHGW/OPGW), earthing system, and line hardware fittings, all delivered in compliance with applicable international standards and adapted to local environmental conditions in West Africa.

Engineering Scope and Technical Features

1. Transmission Line Design

The line is designed as a 161kV double-circuit overhead transmission line, optimized for:

▶Electrical performance: adequate insulation coordination, corona control, and power transfer capacity
▶Mechanical reliability: wind load resistance (≈25 m/s), terrain adaptability, and long-span stability
▶Environmental conditions: tropical climate, corrosion exposure, and lightning density

Design references include IEC standards and aligned methodologies comparable to GB, ASTM, and BS specifications.

Key design elements:

▶Typical span: ~300–400 m
▶Conductor configuration: twin bundled conductor system
▶Ground wire: combined GJ steel wire and OPGW (optical fiber composite ground wire)

▶Tower types: suspension tower, tension tower, terminal tower

2. Steel Tower System

All towers are fabricated as galvanized lattice steel structures, designed for durability and ease of installation.

Technical highlights:

▶Steel grade: Q355 / equivalent ASTM A572 Grade 50
▶Surface treatment: hot-dip galvanization (HDG) in accordance with ISO 1461
▶Structural configuration: angle steel bolted connections
▶Load cases: normal operation, broken conductor, wind load, installation condition

Advantages:

▶Modular fabrication for efficient transport
▶High corrosion resistance in humid tropical environments

▶Optimized weight-to-strength ratio

3. Conductors and Ground Wire

The project adopts high-performance aluminum-based conductors:

▶Phase conductor: ACSR (Aluminum Conductor Steel Reinforced) or equivalent (e.g., LGJ series)
▶Configuration: twin bundled conductors to reduce corona loss and radio interference
▶Ground wire:
▶▶GJ galvanized steel wire for shielding
▶▶OPGW integrating fiber optic communication and lightning protection

Technical considerations:

▶Sag and tension calculation (stringing chart optimization)
▶Thermal rating and ampacity

▶Vibration control using dampers

4. Insulation and Line Hardware

The insulation system utilizes high-strength disc insulators (glass or composite polymer) suitable for 161kV operation.

Key components:

▶Suspension insulator strings
▶Strain insulator assemblies
▶Hardware fittings: clamps, yoke plates, shackles, spacers, vibration dampers

Standards:

▶IEC 60383 / IEC 61109
▶Mechanical load rating up to 100kN class

Features:

▶High pollution performance
▶UV and aging resistance

▶Reliable mechanical strength under dynamic loads

5. Earthing and Lightning Protection System

A robust earthing system is implemented to ensure safety and lightning protection:

▶Tower footing resistance control (<10 ohms typical target)
▶Grounding electrodes: copper-clad steel rods or galvanized steel
▶Counterpoise wire where required
▶Integration with overhead ground wire system

The design enhances:

▶Lightning current dissipation
▶System protection against overvoltage

▶Personnel safety

6. Installation and Stringing Works

Installation works include:

▶Foundation construction (reinforced concrete pad & chimney type)
▶Tower erection using derrick or crane methods
▶Conductor stringing via tension stringing method
▶OPGW installation with fiber optic continuity testing

Quality control measures:

▶Bolt torque inspection
▶Sag-tension verification
▶Alignment and clearance checks

7. Testing and Commissioning

The project has been fully tested and commissioned, including:

▶Electrical continuity and grounding resistance tests
▶Optical fiber testing (OTDR for OPGW)
▶Line energization and trial operation

All systems have been verified to meet operational and safety requirements.

Project Value

This project demonstrates a full-scope EPC capability in high-voltage transmission line engineering, with emphasis on:

▶Integrated design-to-delivery workflow
▶Adaptation to African grid and environmental conditions
▶Compliance with international engineering standards
▶Reliable long-term operation performance

ZHM Metal Engineering Co., Ltd. continues to focus on practical engineering solutions and technical optimization in global transmission infrastructure projects.

1 Ghana 161kV OHTL Construction Method Statement

1A Angle strain Straight Alignment Tower Family Selection

2 Chirano Wassa Power Transmission Line Gold Mines

3 Scalfold Section Cross Over Existing 11kV ECG Tower Pylons

4 Scalffold Netting Over 11kV Crossing 35KV Catenary Wires

5 Lattice Angle Tower Concrete Rebar Schedule Foundation

6 Tower Foundation Excavation Pedestal Blinder reinforcement

7 Anchor Bolts Formworks Template Plate Rebars Pedestal RC Pouring

8 Foundation Formworks Disassembly Backfilling Plinth width Eccentricity Measurement

9 RC composition Ratio Gravel Mixing Testing Bock Vibration Plinth

10 Copper Bonded Steel Rod Earthing Trench Tower Foots

11 Wiring Rod Grounding Earthing Rod

12 Trench Depth Earthing Wire Rod Weld CADweld

13 Earthing Grounding Inpsection Testing

14 Latticed Angle Tower Products Packing Marking

15 Latticed Angle Tower Crossarms Products Packing Marking

16 Chirano OHTL 2D1 SJ1 21M Straight Alignment Towers

16 Conduct Cable Coil Shipment

17 Wassa OHTL Tower Container Loading Shipment

18 Lattice Tower Steel Structure Erection Drawing

20 Bottom Column Footing Brackets Mounting Anchor Bolts

21 Twin Bundle Conduct ACSR JL G3A 300 LGJ

21-Twin-Bundle-Conduct-ACSR-JL-G3A-300-LGJ

22 Crossarm Tip Conduct Insulator Hanging Plate

23 Tension strain String Twin Bundle Conduct Disc Suspension Insulator

24 Substation Gantry Structure String Tension Suspension T Connector

25 Angle Strain Jumping Conduct treatment

26 Straight alignment Latticed Self standing towers

27 Earthing Wire String Details Angle Strain Tower Gantry Earthing Wire

28 Tower Break In Tie In Solution T Connection Pai Existing Tower Terminal

29 Antivibration Damper Installation FD 4D 30 OPGW Earthing Wire

Why ZHM Huawu Metal 161kV OHTL Transmission Line Solutions?

Reliable and Customized Designs	Cutting Edge Designing Process	Free Online Price System	Easy Bolt-by-number Assembly
Over Two Decades of Experience	Value For Money	Unmatched in Quality and Craftmanship	Excellent Customer Service

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HOW CAN WE HELP YOU?

ZHM’s world-class team — together with our raw material suppliers and subcontractors — works to solve your most challenging design, engineering, farbrication or construction issues.

Contact ZHM by telephone at +86 135-8815-1981 (wechat and whatsapp) or send us your questions via email to info@zhmsteelworks.com