VPI Dry-Type Transformers: The Safer, More Reliable Power.
01 General
1.1 Project Description
The 315 kVA vpi dry type transformer was delivered to South Africa in 2025. The rated power of the dry type transformer is 315 kVA with AN/AF cooling, the primary voltage is 11 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 0.55kV, they formed a vector group of Dyn11.
This product is an open-type, Class H dry-type transformer manufactured with advanced Vacuum Pressure Impregnation (VPI) technology, specifically engineered for demanding industrial environments. Its windings undergo multiple VPI treatments to form a dense Class H insulation layer, providing exceptional resistance to moisture, dust, and corrosion. Designed with Class H insulation materials and a 100K temperature rise, it offers substantial thermal margin, ensuring extended service life and superior overload capacity even under high-temperature conditions. The unique open-style construction, combined with efficient cooling fans, enables automatic temperature-controlled forced air cooling, significantly enhancing short-term overload capability and enabling reliable performance under impact loads. Featuring an oil-free, flame-retardant design, it delivers maximum safety and reliability, is optimized for 110V power systems, and is widely used in industrial plants, data centers, rail transportation, and other applications requiring high safety and reliability in power distribution.
1.2 Technical Specification
315 kVA VPI dry type transformer specification and data sheet
| Delivered to | South Africa |
| Year | 2025 |
| Type | Open winding dry type transformer |
| Core material | Grain oriented silicon steel sheet |
| Standard | IEC60076 |
| Rated Power | 315kVA |
| Frequency | 50HZ |
| Vector group | Dyn11 |
| Phase | 3 |
| Cooling Type | ONAN/ONAF |
| Primary Voltage | 11 kV |
| Secondary Voltage | 0.55 kV |
| Winding Material | Aluminum |
| Impedance | 4% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5%@primary side by tapping links |
| No Load Loss | 1.1KW |
| On Load Loss | 4.1KW |
| Insulation level | H |
| Winding temperature rise @rated service side | 100K |
1.3 Drawings
315 kVA VPI dry type transformer diagram drawing and size.
02 Manufacturing
2.1 Core
The core is constructed from high-quality grain-oriented silicon steel sheet. This specialized material is meticulously laminated and wound to minimize core losses and maximize magnetic efficiency. Its grain-oriented structure significantly reduces hysteresis and eddy current losses, ensuring excellent magnetic permeability and low no-load power consumption. The core’s precise engineering contributes to the transformer’s high efficiency, low noise operation, and overall energy-saving performance.
2.2 Winding
 | The coils utilize high-purity aluminum conductors, vacuum-pressure impregnated (VPI) with high-grade insulating varnish. This process creates a solid, moisture-resistant insulation system that ensures excellent thermal stability, mechanical strength, and reliable performance under demanding conditions. |
2.3 Final Assembly
| The final assembly of the VPI dry type transformer integrates the impregnated core and coils into a robust mechanical structure, securely mounted with vibration-resistant fasteners. Electrical connections are precision-terminated with high-strength connectors, while cooling fans and protective shields are installed to ensure optimal thermal management and operational safety. |  |
03 Testing
The test of VPI dry type transformer (315kVA-11/0.55kV) on 2024/12/5, per IEC standards, covered winding resistance (qualified unbalance), voltage ratio/phase (tiny deviation, Dyn11), short-circuit/no-load parameters, voltage withstand (no collapse) and partial discharge (≤10pC). All results met requirements, qualified.
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion | |
| 1 | Measurement of winding resistance | / | Maximum resistance unbalance rate Line resistance:≤2% | HV (line) | LV (line) | Pass |
| 0.37% | 0.58% | |||||
| 2 | Measurement of voltage ratio and check of phase displacement | / | The tolerance of voltage ratio on the principal tapping: ±1/10 Connection symbol: Dyn11 | 0.02% ~ 0.18% Dyn11 | Pass | |
| 3 | Measurement of Short-circuit Impedance and Load Loss | / kW kW | t:120℃ Z%: measured value Pk: measured value Pt: measured value | 4.27% 2.390 3.329 | Pass | |
| 4 | Measurement of No-load Loss and Current at 90% and 110% of rated voltage | / kW | I0 :: provide measured value P0: provide measured value | 90% Ur | 0.81 0.9198 | Pass |
| 100% Ur | 0.90 1.022 | |||||
| 110% Ur | 0.99 1.124 | |||||
| 5 | Applied Voltage Test | / | HV: 35kV 60s LV: 3kV 60s | No collapse of the test voltage occurs | Pass | |
| 6 | Induced Voltage Withstand Test | / | Applied voltage (KV): 2 Ur Induced voltage (KV): 1.1 Duration(s):40 Frequency (HZ): 150 | No collapse of the test voltage occurs | Pass | |
| 7 | Partial Discharge Test | pC | The maximum level of partial discharges shall be 10 pC | ＜10 | Pass | |
04 Packing and Shipping
4.1 Packing
The VPI dry type transformer is securely packaged using weather-resistant and shock-absorbing materials. The transformer is firmly mounted within a custom wooden crate, with additional protective padding to prevent movement during transit. Critical components are covered with moisture-proof barriers, and the entire package is clearly labeled with handling instructions and technical specifications to ensure safe and efficient logistics.
4.2 Shipping
Under CIF (Cost, Insurance, and Freight) terms, the VPI dry type transformer will be shipped to the port of Durban, South Africa. The supplier handles sea freight and marine insurance coverage, ensuring protected transit in weather-resistant, maritime-grade packaging. All necessary shipping documents (bill of lading, insurance certificate, commercial invoice) are provided for efficient customs clearance at destination. Risk transfers to the buyer upon unloading at Durban port.
05 Site And Summary
The VPI dry type transformer stands as a cornerstone of modern power systems, combining unparalleled reliability with cutting-edge engineering. Through Vacuum Pressure Impregnation (VPI) technology, Class H insulation, and intelligent thermal management, it delivers exceptional efficiency, flame-resistant safety, and robust performance in the most demanding environments. From industrial power distribution and renewable energy integration to critical infrastructure applications, the VPI dry-type transformer operates with silent resilience, ensuring clean and stable power delivery worldwide. Choosing this transformer means investing in sustained energy security and operational excellence for the future.
