Sag-Tension Analysis Example

This example shows a complete sag-tension calculation workflow using Ohmly: from loading a conductor to evaluating multiple mechanical hypotheses.

1. Load a conductor

from ohmly import ConductorRepository

repo = ConductorRepository()
conductor = repo.get(legacy_code="LA 280 HAWK")

print(conductor)

If you print the conductor, you should see the following output in your terminal

  Attribute              Unit             Value  
 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 
  designation               -   242-AL1/39-ST1A  
  legacy_code               -       LA 280 HAWK  
  al_area                 mm²             241.6  
  steel_area              mm²              39.5  
  total_area              mm²             281.1  
  al_strands                -                26  
  steel_strands             -                 7  
  core_diameter            mm              8.04  
  overall_diameter         mm              21.8  
  mass                  kg/km             976.2  
  rated_strength          daN            8489.0  
  resistance_dc          Ω/km            0.1195  
  elastic_modulus      kN/mm²            7300.0  
  thermal_exp_factor     1/°C          1.89e-05  
  unit_weight           daN/m            0.9573

2. Create a mechanical analysis context

The mechanical analysis context binds:

• the conductor, and
• the environmental zone (ITC-LAT 07)

from ohmly import MechAnalysis, MechAnalysisZone

mech = mechanalysis(
    conductor=conductor,
    zone=mechanalysiszone.b,  # 500–1000 m, ice considered
)

3. Define mechanical hypotheses

Each hypothesis represents a load scenario defined by:

• temperature,
• fraction of rated tensile strength (RTS),
• wind speed, and
• ice presence.

from ohmly import MechAnalysisHypothesis

eds = MechAnalysisHypothesis(
    name="EDS",
    temp=15,
    rts_factor=0.15,
)

chs = MechAnalysisHypothesis(
    name="CHS",
    temp=-10,
    rts_factor=0.20,
)

wind = MechAnalysisHypothesis(
    name="Wind",
    temp=-10,
    rts_factor=0.40,
    wind_speed=120,
)

ice = MechAnalysisHypothesis(
    name="Ice",
    temp=-15,
    rts_factor=0.40,
    with_ice=True,
)

hypotheses = [eds, chs, wind, ice]

4. Define spans and compute sag-tension

spans = [200, 300, 400]  # meters

table = mech.stt(hypotheses, spans)
print(table)

You should see the following sag-tension table in your terminal.

               EDS               CHS              Wind               Ice        
          T (daN), RTS      T (daN), RTS      T (daN), RTS      T (daN), RTS    
  Span         (%)               (%)               (%)               (%)        
 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 
   200     1273.3500,        1574.4966,        2039.8037,        2408.7764,     
             15.0000           18.5475           24.0288           28.3753      
   300     1273.3500,        1415.2515,        1988.6685,        2401.1087,     
             15.0000           16.6716           23.4264           28.2849      
   400     1273.3500,        1353.7002,        1965.2758,        2397.3542,     
             15.0000           15.9465           23.1509           28.2407      

Complete example

from ohmly import ConductorRepository, MechAnalysis, MechAnalysisHypothesis, MechAnalysisZone

repo = ConductorRepository()
conductor = repo.get(legacy_code="LA 280 HAWK")

# Optionally, you can print the conductor's information.
# print(conductor)

mech = mechanalysis(
    conductor=conductor,
    zone=mechanalysiszone.b,  # 500–1000 m, ice considered
)

eds = MechAnalysisHypothesis(
    name="EDS",
    temp=15,
    rts_factor=0.15,
)

chs = MechAnalysisHypothesis(
    name="CHS",
    temp=-10,
    rts_factor=0.20,
)

wind = MechAnalysisHypothesis(
    name="Wind",
    temp=-10,
    rts_factor=0.40,
    wind_speed=120,
)

ice = MechAnalysisHypothesis(
    name="Ice",
    temp=-15,
    rts_factor=0.40,
    with_ice=True,
)

hypotheses = [eds, chs, wind, ice]
spans = [200, 300, 400]  # meters

table = mech.stt(hypotheses, spans)

print(table)