Verification of busbar loss calculation according to Russian National Standard 35224

Verification of a Web-Based Busbar Loss and Heating Calculator According to GOST 35224

This web application for calculating losses in low-voltage switchgear (LVSG) busbars uses a client-server architecture. The JavaScript frontend handles input of cabinet, busbar, and device parameters, visualization of results, and a 2D thermogram of temperature distribution. The Python backend implements the physical calculation algorithms.

Users input parameters and instantly receive: power losses for busbars and devices, internal cabinet temperature, step-by-step calculations, and a color thermogram.

Physical Calculation Model

Heat Generation Accounting for Temperature

Joule-Lenz power is adjusted for the temperature dependence of resistance:

R(T) = R₂₀ × [1 + α × (T - 20°C)]

where α = 0.00393 1/°C for copper. This accounts for feedback: heating increases R, which in turn increases heat generation.

Alternating Current Effects

Skin effect and proximity effect are modeled with coefficients:

• k_skin: 1.0 for thickness ≤10 mm, up to 1.2–1.3 for greater thicknesses;
• k_prox: 1.1–1.6 depending on busbar arrangement.

Effective resistance: R_EFF = R₂₀ × (1 + αΔT) × k_skin × k_prox.

Heat Exchange Area

For a single busbar: A = 2 × (w × l + h × l + w × h).

In a busbar pack:

• Gap ≥ thickness: sum of individual areas;
• Tightly packed: external surfaces with a coefficient of 0.7.

Heat Dissipation Mechanisms

Convection: 6.5 W/(m²·K) vertically, 5.0 horizontally; +20–50% with ventilation. Radiation: +15% to the coefficient. This approach ensures accuracy for preliminary assessments, complementing IEC 60890.

Verification Conditions

Testing according to GOST 35224-2024 (IEC TR 60890:2022, Annex E):

| Parameter | Value |

|-----------|-------|

| T_air | 55°C |

| T_busbar | 70°C |

| Material | Copper |

| Shape | Rectangular |

| Orientation | Horizontal |

| Busbars/phase | 1–2 |

| Frequency | 50 Hz |

| Length | 1 m |

42 tests (21 per configuration) for cross-sections of 24–1200 mm².

Metrics: MAPE, RMSE, R².

Results for a Single Busbar

• MAPE: 4.3%;
• RMSE: 1.0 W/m;
• R²: 0.979.

Deviation ≤7%, physical dependency accurately reproduced. Suitable for GOST-based calculations.

Results for Two Busbars

• MAPE: 6.7%;
• RMSE: 1.1 W/m;
• R²: 0.987.

Conservative bias, maximum at medium cross-sections. Proximity effect modeling is correct.

Application Areas

The tool is useful for:

• Layout analysis;
• Assessing the impact of cross-section, material, orientation;
• Non-standard conditions (vertical busbars, aluminum, different ambient temperatures);
• Preliminary calculations with GOST-level accuracy.

Key Takeaways

• R² 0.979–0.987 confirms the physical adequacy of the model.
• MAPE 4–7% allows for engineering estimates without full simulation.
• Accounting for skin effect, proximity, and heat exchange extends applicability beyond GOST tables.
• Web-based format ensures speed and accessibility without software installation.
• Conservative results enhance selection safety.

— Editorial Team