Dry-type transformers are widely used in high-rise buildings, subways, industrial plants, hospitals, and other applications due to their safety, eco-friendliness, and maintenance-free features. When planning equipment layouts, accurately determining the size of a dry-type transformer is crucial. It impacts not only proper installation but also ventilation, safety clearance, and long-term maintenance.
This guide explains how to determine the transformer size from multiple aspects, including capacity selection, physical dimensions, installation space, and ventilation requirements, offering a practical reference for engineers and designers.
1. Identify the Application and Requirements
Before determining the size, consider the following key factors:
1. Application scenario: Is it used for commercial buildings, industrial machinery, or underground tunnels? Each scenario has different size and structure requirements.
2. Installation location: Is there sufficient room for setup? Will it be placed in an indoor substation, compact substation, or suspended from brackets?
3. Cooling conditions: Is there good natural ventilation? Is forced-air cooling required? These factors affect enclosure design and heat dissipation area.
2. Determine Transformer Capacity Based on Load
The transformer's capacity, measured in kVA, should be selected based on the total downstream load. Use the following formula for estimation:
Formula: Transformer Capacity (kVA) = Total Load Power (kW) ÷ Power Factor (cosφ)
Example: If the total equipment load is 120kW and the power factor is 0.9, the required transformer capacity is about 134kVA. A 160kVA model is recommended to allow for a margin.
3. Refer to Standard Model Dimensions
Although model naming may vary slightly between manufacturers, most dry-type transformers are produced in accordance with national or industry standards. For instance, the commonly used SCB10, SCB11, and SCB12 series have typical dimensions such as:
| Rated Capacity (kVA) | Dimensions (L × W × H, mm) | Weight (kg) |
|---|---|---|
| 100 | 900 × 750 × 1100 | 600 |
| 250 | 1150 × 850 × 1200 | 980 |
| 630 | 1450 × 1050 × 1350 | 1800 |
| 1000 | 1650 × 1200 × 1450 | 2800 |
| 1600 | 1850 × 1450 × 1600 | 4100 |
Since transformer size varies significantly by capacity, always consult manufacturer data sheets or technical support after confirming the capacity.
4. Allow Enough Space for Installation and Maintenance
Though dry-type transformers don't require oil tanks or explosion protection, proper clearance is still necessary for the following reasons:
1. Front and side access: Ensure enough space for cable connections and inspections. Typically, allow at least 1.2m at the front and 0.8m on the sides.
2. Top clearance: Required for lifting or ventilation fans; leave at least 0.8m of vertical space.
3. Ventilation pathway: Avoid placing the transformer directly against walls; allow airflow at the sides or base.
4. Dust protection: In dusty environments, add mesh or covers to protect windings from contamination.
5. Consider Cooling and Ventilation Requirements
The main heat sources in dry-type transformers are the windings and core. Typical cooling methods include natural air cooling (AN) and forced air cooling (AF). For forced-air models (with fans), additional space must be reserved for airflow ducts or components.
High-capacity transformers (e.g., above 2000kVA) may include top and bottom air ducts or smart cooling systems. Design the airflow path accordingly to avoid heat buildup.
6. Account for Transportation and Site Constraints
Large transformers are often transported as whole units or lifted into place on site. When choosing the size, consider:
1. Maximum doorway or hoist openings
2. Elevator or corridor turning radius
3. Whether disassembly and reassembly are allowed on site
This is particularly important in high-rise buildings or hospital facilities with tight access restrictions.
7. Use Manufacturer Technical Support
When finalizing the size, it’s recommended to consult the manufacturer for detailed technical drawings and application advice. Provide details like load conditions, layout constraints, and installation environment.
Leading brands such as CHINT, TBEA, Delixi, and Siemens can provide custom solutions for narrow spaces or low-noise environments.
The size of a dry-type transformer is more than a physical measurement — it affects safety, cooling, and future maintenance. Begin by determining the required capacity, then evaluate physical dimensions based on the site and environment step by step.
We recommend involving manufacturers or engineers early in the design phase to avoid misjudgment and ensure safe, efficient operation.
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