1. Importance of Accurate Transformer Sizing
10kV/0.4kV dry type transformers are key components of industrial and commercial power distribution systems. Improper sizing causes unstable power supply, energy waste, and shortened service life. Three common selection errors lead to most site risks:
Oversizing: Higher upfront cost and continuous no-load power loss.
Undersizing: Frequent tripping, over-temperature alarms and accelerated insulation aging under peak loads.
Improper IP Rating: Mismatched protection grades for humid, dusty or corrosive environments accelerate transformer failure.
This IEC-standard guide simplifies dry type transformer sizing, covering load calculation, capacity selection and core technical specifications.
2. 3-Step Dry Type Transformer Sizing Formula
Accurate capacity calculation relies on the Demand Factor (Kd) and compensated power factor, instead of simple equipment power summation.
Step 1: Calculate Active Power
P = ΣPe × Kd
Pe = Total installed power; Kd = 0.6–0.8 (standard factory load)
Step 2: Calculate Apparent Power
S = P / cosφ
Standard compensated power factor: 0.9
Step 3: Confirm Rated Capacity
Reserve capacity for future expansion and optimal 60%–80% load rate: continuous load is limited to 85% of rated capacity.
Se ≥ S / 0.85
Note: 85% limit for continuous operation only; short-time overload complies with IEC 60076.
Calculation Example
800kW total load, 0.7 demand factor, 0.9 power factor
Active Power = 560kW | Apparent Power ≈ 622.2kVA | Min. Capacity ≈ 732kVA
Final Selection: 800kVA standard dry type transformer
3. Core Technical Specifications
Insulation Class F / H
Class F (155°C): Cost-effective for standard indoor substations. Class H (180°C): Higher thermal stability, suitable for heavy-load and high-temperature working scenarios.
IP Protection Grade
IP00: Open type for internal switchgear installation IP20: Clean dry indoor substations IP23: Covered semi-outdoor environments Note: IP23 is not for direct open-air outdoor use.
Dyn11 Vector Group
Industry-standard connection with superior harmonic suppression and voltage balance. Standard design supports 75% neutral current; customized winding available for 100% full neutral current output.
PT100 Temperature Monitoring System
Equipped with high-precision PT100 RTD sensors for real-time winding temperature monitoring. Optional terminal hot-spot detection, automatic fan control and dual pre-alarm/alarm thresholds ensure safe operation.
4. Product Advantages
◆ Low Energy Loss: High-permeability silicon steel core and pure copper windings reduce no-load and load losses for long-term energy savings.
◆ High Safety: Resin cast and VPI dry type transformers adopt flame-retardant, moisture-resistant materials, ideal for indoor and dense-area power supply.
◆ Full Customization: Custom voltage ratios, tapping ranges, dimensions and enclosures for various harsh working environments.
5. Get Custom Quote & Support
We provide professional 10kV/400V dry type transformer sizing, drawing documents and customized solutions for global industrial and EPC projects. Contact us for competitive quotations and technical datasheets.
6. Standard Classification
This guide applies to ≤35kV distribution transformers for end-user power supply. ≥66kV high-voltage power transformers follow independent grid design standards.
