How Dry-type Transformers Are Cooled？

The heat dissipation efficiency of dry-type transformer coils directly determines their load capacity and service life. Based on convection heat dissipation theory and numerical simulations, optimizing airflow state (laminar vs. turbulent) and cooling structure can significantly improve heat dissipation, but practical applications must balance efficiency with noise and system capacity constraints. Below is a detailed breakdown of the core principles, structural optimizations, and CHH Power’s targeted solutions.

Contents hide

1 1. Coil Convection Heat Dissipation Mechanism: Laminar vs. Turbulent Flow

2 2. Optimized Cooling Structure Based on Numerical Simulations

3 3. Practical Application Constraints: Balancing Efficiency, Noise & Capacity

4 4. CHH Power’s Balanced Solution: Efficiency + Low Noise

5 OUR CERTIFICATE

6 OUR PROJECTS

1. Coil Convection Heat Dissipation Mechanism: Laminar vs. Turbulent Flow

The heat dissipation efficiency of the coil surface depends on the airflow state (laminar or turbulent) and the thickness of the thermal boundary layer—this is the core of convection heat dissipation theory.

(1) Laminar Flow State (Low Air Velocity)

Key Relationship: When air near the coil surface is in laminar flow, the local heat dissipation efficiency is inversely proportional to the thickness of the thermal boundary layer (a static air layer attached to the coil surface that hinders heat transfer).
Velocity Impact: The thermal boundary layer thickness decreases as the main airflow velocity increases—thus, local heat dissipation efficiency increases with higher main airflow velocity (e.g., a 2x increase in velocity reduces the boundary layer by ~30%, improving heat dissipation by ~25%).

(2) Turbulent Flow State (High Air Velocity, “Mixed Flow” in Original Text)

Key Advantage: When airflow transitions to turbulent flow, the air layer near the coil surface is disturbed, breaking the thick thermal boundary layer. Local heat dissipation efficiency is significantly higher than in laminar flow (up to 50% improvement).
Velocity Independence: Once turbulent flow is formed, heat dissipation efficiency is basically independent of further increases in main airflow velocity—this means continuing to boost wind speed will not bring proportional efficiency gains.

2. Optimized Cooling Structure Based on Numerical Simulations

To maximize coil surface airflow velocity and promote turbulent flow, CHH Power summarizes a set of targeted cooling structures based on transformer-specific designs (verified via large-scale numerical simulations):

Component	Installation Position	Core Function
Damper	Upper part of the coil	Guides airflow to concentrate on the coil’s high-temperature upper area, avoiding airflow short-circuiting.
Baffle	Above the large horizontal airway	Blocks useless airflow paths, forcing air to pass through the coil surface at a higher velocity.
Insulating Cylinder	Low-voltage coil (outer circumference)	Creates a constrained airflow channel between the low-voltage and high-voltage coils, increasing local wind speed.
Buffer	Low-voltage coil (end part)	Reduces airflow turbulence loss at the coil ends, ensuring stable high-velocity airflow over the coil surface.

Core Goal of Structure Design

Increase the coil surface airflow velocity to ~2–3 m/s (the critical threshold for transitioning from laminar to turbulent flow).
Ensure uniform airflow distribution across the coil surface (avoiding “dead zones” with low velocity and poor heat dissipation).

3. Practical Application Constraints: Balancing Efficiency, Noise & Capacity

While higher wind speed and turbulent flow improve heat dissipation (and thus the transformer’s off-nameplate load capacity), two key constraints limit their application in real scenarios:

(1) System Capacity Restrictions

Most dry-type transformer systems have fixed off-nameplate capacity limits (e.g., 120% of rated load for 2 hours) due to grid load planning or downstream equipment constraints. Even if cooling efficiency is improved, the transformer cannot operate beyond this system-defined limit—making excessive wind speed upgrades unnecessary.

(2) Fan Noise Limitations

Fan noise increases sharply with wind speed (noise level follows the “5th power law” of wind speed: a 2x increase in speed raises noise by ~15 dB). For indoor scenarios (e.g., residential basements, data centers), user noise limits (usually ≤55 dB for 200kVA transformers) restrict wind speed to ~3 m/s—exceeding this will cause noise violations.

4. CHH Power’s Balanced Solution: Efficiency + Low Noise

To address the above contradictions, CHH Power adopts a “precision design” approach instead of simply increasing wind speed:

Optimized Fan Selection: Use backward-curved centrifugal fans (instead of axial fans). They generate higher static pressure (promoting turbulent flow) at lower noise levels (10–15 dB quieter than axial fans at the same wind speed).
Airflow Duct Optimization: Combine the cooling structure (damper + baffle + insulating cylinder) with a streamlined duct design to achieve turbulent flow at a lower wind speed (~2.5 m/s), balancing heat dissipation and noise.
Intelligent Speed Control: Equip fans with stepless speed regulation (instead of on/off control). The fan speed automatically adjusts based on coil temperature—low speed for normal operation (low noise) and high speed only during overload (temporary, short-duration noise increase).