PLS-CADD Complete Professional Guide: Transmission Line Design, Spotting, Sag-Tension, Structures, and Engineering Workflow
This guide covers the FULL engineering workflow using PLS-CADD, from survey import to final plan & profile sheets, sag-tension charts, structure loading trees, and construction deliverables.
Table of Contents
- 1. What is PLS-CADD?
- 2. Importing Survey Data
- 3. Creating the Terrain Model (DTM)
- 4. Defining Alignment, Stations, and Centerline
- 5. Design Criteria Setup
- 6. Conductor and OPGW Modeling
- 7. Tower Spotting (Automatic & Manual)
- 8. Sag-Tension Calculations
- 9. Structure Loads & Load Trees
- 10. Plan and Profile Sheets
- 11. Foundation Outline
- 12. Bill of Materials (BOM)
- 13. Clearance Checks
- 14. Exporting Reports
1. What is PLS-CADD?
PLS-CADD (Power Line Systems – Computer Aided Design and Drafting) is the industry-standard tool for designing overhead transmission lines. Utilities such as NGCP, National Grid UK, AEMO, FERC-regulated operators, Eskom, and RE/utility EPC contractors use it for:
- 3D survey terrain modeling
- Tower spotting
- Sag & tension computation
- Electrical/mechanical clearance checks
- Structure loading and strength checks
- Plan & profile sheet generation
- Material take-off (MTO/BOM)
ASCII Diagram: Basic PLS-CADD View
+---------------------------------------------------------+ | PLS-CADD 3D View | | | | Tower A Tower B Tower C | /\ /\ /\ | / \ / \ / \ |------/----\-----------------/----\------------------/----\------- | Conductor Sag Curve (per temperature & load case) +---------------------------------------------------------+
2. Importing Survey Data
PLS-CADD supports multiple survey formats:
- LiDAR point clouds
- Drone photogrammetry
- Total station or RTK CSV files
- DEM/contour files
Steps:
- File → Import → Survey Data
- Select format (XYZ, LAS, DEM, TXT, CSV)
- Assign point types: ground, road, vegetation, structures
- Generate the terrain surface
ASCII Terrain Model Diagram
Elevation Profile ^ | /\ /\ /\ x (Tower Location) | / \ / \ / \ |______/____\________/____\_____/____\__________________→ distance
3. Creating the Terrain Model (DTM)
A DTM (Digital Terrain Model) is essential for:
- Clearance checks
- Tower heights
- Spotting optimization
- Sag behavior above ground
Procedure:
- Survey → New Surface From Points
- Set TIN (triangulated irregular network)
- Filter vegetation using classification tools
4. Defining Alignment and Centerline
The centerline is the exact path of the transmission line.
Steps:
- Import KML/shape alignment
- Assign stationing (0+000 etc.)
- Define PIs (Points of Intersection)
ASCII Alignment Path
(PI1)-----\____(PI2)______/(PI3)---------Straight Line---------
5. Design Criteria Setup
This determines sag behavior, structure loads, and safety clearances.
Key Input Required:
- Conductor type (ACSR, ACCC, AAAC)
- Temperature cases (min, max, everyday)
- Wind and ice loading (ASCE 74 / IEC 60826)
- Safety clearances:
- Ground clearance
- Road/river crossing
- Building clearances
- Electrical constraints (SIL, blowout)
6. Conductor and OPGW Modeling
Important Properties to Enter:
- Diameter
- Weight
- Modulus of Elasticity
- Thermal expansion coefficient
- Creep characteristics
ASCII Conductor Model
Conductor ------------------ OPGW ------------------ Conductor
PLS-CADD uses these inputs to calculate the correct sag for each temperature & load case.
7. Tower Spotting (Automatic & Manual)
PLS-CADD can automatically optimize tower locations using:
- Minimum/maximum span limits
- Slope limitations
- Clearance constraints
- Tower families and height options
Automatic Spotting Procedure
- Line → Spot Structures → Automatic
- Select tower family
- Set span limits (e.g., 200 m – 400 m)
- Run optimizer
ASCII Tower Spotting Diagram
T1 T2 T3 T4
/\ /\ /\ /\
-----/--\------/--\-------/--\-------------/--\---------
210m 260m 235m 290m
8. Sag-Tension Calculations
Sag-tension is performed for:
- Initial (post-stringing)
- Final (after creep)
- Maximum temperature
- Minimum temperature
- Wind/ice loading
Ruling Span Formula Used by PLS-CADD
LR = Σ(L³) / Σ(L²)
Sag Curve ASCII Illustration
Tower A Tower B /\ /\ / \_________________________________/ \
9. Structure Loads & Load Trees
PLS-CADD generates loading trees for:
- Transverse loads
- Vertical loads
- Longitudinal loads
- Wind-on-conductor
- Wind-on-structure
ASCII Load Tree
(Top)
↓ Wind
+----------+
| Tower |
+----------+
↑ ↑ ↑
Vert Long Trans
10. Plan & Profile Sheets
Plan & Profile sheets are required for construction and regulatory compliance.
Generating PNP Sheets
- Reports → Plan & Profile
- Select template (NGCP, IEC, utility standard)
- Include:
- Tower positions
- Span lengths
- Sag profiles
- Ground clearance
- Crossings (roads, rivers)
ASCII PNP Snapshot
| Station | Elev | Tower | Sag | Clearance | | 0+000 | 56 | T1 | 14m | OK | | 0+240 | 61 | T2 | 12m | OK |
11. Foundation Outline
PLS-CADD can generate foundation reactions (DXF compatible) for:
- Pier footings
- Pad foundations
- Pile foundations
12. Bill of Materials (BOM)
Automatically compute:
- Conductor length
- Insulator sets
- Tower heights
- Hardware fittings
- Foundations volume
13. Clearance Checks
Clearance checks include:
- Ground clearance
- Vegetation
- Road/river crossings
- Building proximity
- Substation entry
14. Engineering Reports
PLS-CADD can export:
- Sag-Tension Reports
- Loading Trees
- Tower Spotting Report
- Plan & Profile PDFs
- KMZ/KML files for Google Earth
- DXF files for CAD drafting
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