TREX - Transmission Rating Explorer

System Configuration

Set static conductor properties and reference voltage levels.

Select Conductor Type (ASCR)

Base kV Rating

Max Cond Temp (°C)

Emissivity

Solar Absorptivity

Grid Location

Select line geographic coordinates or standard US city location.

Select US City

Latitude

Longitude

Elevation (m)

Atmosphere Condition

Weather Controls & Solar Irradiance Engine

Adjust dynamic environmental parameters or calculate astronomical solar heat flux via IEEE 738.

Ambient Temp 25 °C

Wind Speed 0.61 m/s

Wind Angle 90°

Solar Irradiance 1000 W/m²

Solar Irradiance Mode

Date

Time of Day (Local to Selected Location) 12:00

Today's Diurnal Solar Irradiance Curve (24h Q_se) -- W/m²

Calculated Ratings & Specs

Steady-state capacity calculated dynamically via IEEE 738 core equations.

Diameter: --

Heat Cap: --

R @ 20°C: --

R @ 75°C: --

Calculated Ampacity (Amps)

-- A

Calculated Capacity (MVA)

-- MVA

Temperature vs. Capacity Curve

Daytime vs. Nighttime Dynamic Line Rating (MVA) across ambient temperatures calculated dynamically via IEEE 738 (Nighttime has Q=0 solar heat gain).

Ambient Temperature Sensitivity

Capacity rating change (%) vs Ambient Temperature relative to current base rating.

Wind Speed Sensitivity

Capacity rating change (%) vs Wind Speed relative to current base rating.

Wind Angle Sensitivity

Capacity rating change (%) vs Wind Angle relative to current base rating.

Solar Radiation Sensitivity

Capacity rating change (%) vs Solar Radiation relative to current base rating.

Transient Temperature & Conductor Sag Simulation

Simulate conductor thermal step-response and calculate dynamic mechanical catenary sag, operating tension, and ground clearance over time.

Load Step Current Controls

Initial Current (Amps)

Stepped Current (Amps)

Load Step Time (mins)

Simulation Duration (mins)

Mechanical Sag & Tension Controls

Span Length (m) 250 m

Stringing Tension (% RTS) 20 %

Structure Height (m)

Stringing Temp (°C)

Profile Temp @ Time 30 mins

Temp @ 30 mins --

Calculated Sag --

Ground Clearance --

Operating Tension --

Temperature & Sag vs. Time

Catenary Conductor Profile vs. Ground T_cond = -- °C

Grid Settings & Forecast Controls

Set conductor orientation and select forecast variables for weather integration.

Conductor Orientation (Azimuth)

Use Forecast Data For:

Wind Speed Wind Direction Solar Irradiance Day/Night

Dynamic Rating Summary

Calculated statistics over the 8-day weather window (24h past + 7d forecast).

Minimum Expected Capacity

-- MVA

Maximum Expected Capacity

-- MVA

Average Expected Capacity

-- MVA

8-Day Dynamic Line Rating Profile

Hourly MVA capacity limits for the selected line based on historical and forecasted weather patterns.

About TREX (Transmission Rating Explorer)

Exploring Dynamic Line Ratings (DLR), Ambient-Adjusted Ratings (AAR), and FERC Order 881 compliance.

Purpose

TREX is an interactive tool designed to model and explore the thermal capacity of a simplified overhead power line. By integrating live meteorological data, physical conductor properties, and dynamic environmental inputs, TREX allows grid operators and engineers to intuitively understand the transition from static, conservative line ratings to dynamic, weather-informed ratings. This capability is central to maximizing the utilization of existing transmission infrastructure without compromising safety or reliability.

AARs, DLRs, & FERC Order 881

In the United States, the Federal Energy Regulatory Commission (FERC) issued Order 881, mandating that transmission providers implement Ambient-Adjusted Ratings (AARs) to reflect near-term forecasted temperatures rather than relying on worst-case seasonal assumptions. AARs significantly unlock hidden grid capacity. TREX takes this a step further by allowing interaction with all of the IEEE 738 variables. It supports Dynamic Line Ratings (DLRs), which adjust for real-time wind speed, wind direction, and solar radiation, providing a complete assessment of conductor thermal limits.

IEEE 738 Heat Balance Assumptions

The core thermal calculations in TREX are based on the IEEE 738 standard. The steady-state and transient models determine capacity by balancing the heat generated (Joule heating from electrical current and solar heat gain) against the heat dissipated (convective cooling from wind and radiative cooling). TREX allows users to interactively adjust these assumptions, such as surface emissivity, solar absorptivity, and conductor azimuth, to observe their immediate impact on the line's carrying capacity in MVA.

Rust WebAssembly Implementation

To ensure high-performance, real-time calculations directly in the browser, the physics engine driving TREX is implemented in Rust and compiled to WebAssembly (WASM). By executing the rigorous IEEE 738 steady-state and differential equations at near-native speeds client-side, the application avoids the latency of server round-trips. This modern architecture guarantees instant feedback when adjusting parameters, providing a fluid and highly responsive analytical dashboard to explore and learn.