Wire library files (.ohlw)#

A wire library describes conductors, shield wires and other cables. Each file can hold any number of cables. OpenOHL loads every *.ohlw file of a library directory (default libraries/cables/), or a single file given in a job.

• Fill-in template: libraries/cables/TEMPLATE.ohlw.example — every field, commented.
• Machine-readable schema: docs/schema/ohl-wire-1.schema.json (JSON Schema 2020-12) — for tools that create or check files.
• Working example: libraries/cables/acsr-examples.ohlw.

File format at a glance#

A .ohlw file is plain TOML text (any text editor works; editors highlight it if you associate .ohlw with TOML). Rules:

1. One [[cable]] block per cable; sub-tables [cable.outer], [cable.core] and their stress_strain follow it.
2. Quantities are text with a unit: "28.14 mm", "1.094 lbm/ft", "31200 lbf". The space is optional ("28.14mm"). A bare number means SI (m, m², N, kg/m, Pa, K) — convenient for tools, risky by hand.
3. A bare number is never guessed: "12.5" (text without unit) is an error.
4. Unknown field names are errors (typos are caught, not ignored).
5. # starts a comment.

Header (optional)#

[[cable]]#

Cable models#

The three models of line design programs, used for the conditions after creep and after load (a section's calculation, line file; the weather cases from Criteria › Creep-Stretch):

Bimetallic cables (aluminium on steel…): give the outer layers and the core each their own stress_strain (initial and creep polynomials, final modulus, thermal expansion), on the total area (basis = "total": the actual material values × component area / total area, as tables give them).

The outer strands expand more with temperature than the core. Above a transition temperature they are no longer in tension. What they do then is a property of the conductor, bimetallic_behavior. A cable that does not give it (as older cable files) follows the line's bimetallic conductor model (Criteria › Bimetallic conductor model…, kept with the line's settings: one undoable edit, every section solved again); a cable that gives it keeps its own:

Virtual stress = actual stress × Ao / At (Ao the outer strands' area, At the total area). Past the limit the core alone carries the tension, so a hot cable expands as the core does. Both methods use this: the ruling span through the cable's stress-strain model; the finite elements through the same curves when the cable has them (each span's length follows the curves, see Finite-element wire systems), otherwise with one branch per section (the core alone when, at the section's mean tension, the outer strands are past their limit). A curve's own max_compression (below) still applies, whichever is smaller.

Components: [cable.outer], [cable.core]#

The cable's composite stiffness and expansion are computed from the components (\( EA = \sum E_k A_k \), \( \alpha = \sum E_k A_k \alpha_k / EA \)); do not enter composite values.

Non-linear curves: [cable.outer.stress_strain], [cable.core.stress_strain]#

The curves follow the published polynomial method:

\[ \sigma(\varepsilon) = a_0 + a_1\varepsilon + a_2\varepsilon^2 + a_3\varepsilon^3 + a_4\varepsilon^4 + \dots \]

Any number of coefficients (at least two) is accepted; published curves are usually degree 4.

How the curves are used#

• Both components stretch by the same amount; each one's thermal strain \( \alpha_k (t - t_0) \) is removed before its curve is applied; the cable tension is the sum of the component loads.
• Initial state: loading along initial. After creep: from creep. Final: elastic along final_modulus from the permanent set left by creep or by the heaviest load, whichever is larger — see the sag-tension theory.

Converting a data sheet#

Validation when loading#

OpenOHL refuses a library with any of these problems, naming the cable and the field:

• unknown fields, missing required fields, unknown units, duplicate ids, id with characters other than letters, digits, -, _;
• non-positive diameter, mass_per_length, rated_tensile_strength, area;
• modulus outside 1–500 GPa or thermal_expansion outside 0–50×10⁻⁶ /K (catches mm² vs m², MPa vs GPa, a missing e-6);
• total area larger than the area of a circle of the given diameter;
• a curve that stops rising before max_strain; a non-positive final_modulus; components with different reference_temperatures;
• a format other than "ohl-wire", or a version newer than supported.

Minimal example (homogeneous, linear)#

format = "ohl-wire"
version = 1

[[cable]]
id = "aaac-example"
name = "Example AAAC"
kind = "aaac"
source = "Data sheet …"
diameter = "21.0 mm"
mass_per_length = "0.75 kg/m"
rated_tensile_strength = "75 kN"
outer = { area = "270 mm²", modulus = "60 GPa", thermal_expansion = 23.0e-6 }

For tool developers#

1. Parse with any TOML 1.0 library; validate the parsed object against docs/schema/ohl-wire-1.schema.json.
2. Write quantities as "<number> <unit>" with the units listed above, or as SI numbers.
3. Run the semantic checks listed above, or let OpenOHL do it: ohl sagtension and the library loader report the first problem with its file, cable id and field.
4. Keep comments and field order stable when rewriting files, so manual edits survive (TOML libraries that preserve formatting, such as toml_edit in Rust or tomlkit in Python, help).

Electrical data: [cable.electrical]#

Optional electrical and thermal data of the cable, for losses, impedances and thermal rating. The voltage and the phases are not cable data: they belong to the line's electrical systems, and sections link the two through their cable.

[cable.electrical]
ac_resistance = [
    { temperature = "20 °C", resistance = "0.0618 Ω/km" },
    { temperature = "40 °C", resistance = "0.0661 Ω/km" },
]
dc_resistance = { temperature = "20 °C", resistance = "0.0605 Ω/km" }
geometric_mean_radius = "11.779 mm"
emissivity = 0.6
solar_absorptivity = 0.5

Cable files of other line design programs often hold the same data (AC resistances at two temperatures, DC resistance, geometric mean radius, emissivity); no importer for them is built.