High efficiency, low noise—Three-phase pad-mounted transformers safeguard your power solutions!
01 General
1.1 Project Description
The buyer of the transformer for this project is Dovey. 250 kVA pad mounted transformer was delivered to Chile in 2024. The rated power of the transformer is 250 kVA with ONAN cooling. The primary voltage is 23 kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 0.4 kV, they formed a vector group of Dyn1, and it is a radial feed and dead front transformer. Pad mounted transformer is a compact outdoor pre-installed transformer, mainly used in the power distribution system to convert medium-voltage electrical energy into low-voltage electrical energy, suitable for residential communities, commercial centers, industrial parks and other places that need centralized power supply. pad mounted transformer is factory prefabricated, users only need to access the high-voltage power supply and load cable can be used, greatly simplifying the installation project. It can be customized according to user requirements to meet the load and operation requirements of different scenarios. Protection devices such as circuit breakers and fuses can be equipped according to customer requirements to protect equipment and the power grid in case of overload or short circuit.
1.2 Technical Specification
250 kVA pad mounted transformer specifications type and data sheet
| Delivered to | Chile |
| Year | 2024 |
| Type | Pad mounted transformer |
| Standard | IEEE Std C57.12.34-2022 |
| Rated Power | 250KVA |
| Frequency | 50HZ |
| Phase | 3 |
| Cooling Type | KNAN |
| Primary Voltage | 23 KV |
| Secondary Voltage | 0.4 KV |
| Winding Material | Copper |
| Angular displacement | Dyn1 |
| Impedance | 4% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | ＜0.5KW |
| On Load Loss | ＜3.705KW |
| Accessories | Standard Configuration |
1.3 Drawings
250 kVA pad mounted transformer diagram drawing and size.
02 Manufacturing
2.1 Core
The magnetic flux of each phase of the three-column core forms a closed magnetic circuit through the adjacent columns, and no additional external circuit of the core is required, greatly reducing the phenomenon of magnetic leakage. Through reasonable design, the magnetic flux of the three adjacent columns offset each other’s leakage part, so that the magnetic circuit is more balanced and the vibration and noise in operation are reduced. The design of the core magnetic circuit is reasonable, the distribution of magnetic flux density is uniform, and the iron loss (including hysteresis loss and eddy current loss) is effectively reduced. In the three-column design, the magnetic circuit is evenly distributed and the heat concentration is low, which is conducive to the overall heat dissipation. The structure of the three-column iron core is strong, and it can maintain good mechanical strength under the impact of short circuit current, and is not easy to deformation. Because of the good balance of the magnetic circuit, it can cope with short-term voltage fluctuations and current shocks in the power grid more stably.
2.2 Winding
 | The low-voltage foil is wrapped around the inner layer, and the high-voltage wire is wrapped around the outer layer, and the electric field intensity inside and outside the winding is reasonably distributed to avoid the insulation damage caused by excessive local electric field. The foil-wound structure of the low-voltage winding can uniformly carry the leakage magnetic field generated by the high-voltage winding, thus reducing the inductance loss of the low-voltage winding. The foil-wound and wire-wound combined design reduces the axial size between the windings, makes the overall structure of the transformer more compact, and reduces the volume and cost. The foil winding structure of low-voltage winding helps to form a smooth flux distribution, which can effectively reduce leakage induction and improve transformer efficiency when combined with high-voltage wire winding. The foil-wound low-voltage winding has high mechanical strength and can withstand the impact of high short-circuit current. The high voltage wire winding structure has good insulation and can withstand high voltage shock, and the combination of the two further improves the reliability of the transformer. |
2.3 Tank
| The tank structure is made of high-strength steel plate and treated with anti-corrosion coating, which can withstand harsh environmental conditions such as high humidity, high salt spray or high temperature difference. Automatic processes such as laser cutting and numerical control welding are used to ensure stable product quality and reduce labor costs. The KNAN-cooled fuel tank from SCOTECH operates entirely on natural convection (natural circulation of oil + natural cooling of air), avoiding the noise generated by fan or pump operation, especially in noise-sensitive applications. |  |
2.4 Final Assembly
 | Component Preparation: Inspect the transformer core, enclosure, electrical terminals, and protective devices. Transformer Installation: Assemble the transformer core with the windings and perform oil immersion treatment. Enclosure Assembly: Assemble the metal enclosure and apply anti-corrosive coating, ensuring tight seals at all joints. Electrical Connections: Connect high and low voltage terminals and install the grounding system. Cooling System: Install cooling devices to ensure proper operating temperature. Sealing and Testing: Ensure all joints are sealed and perform dielectric and grounding tests. |
03 Testing
| No. | Test Item | Unit | Acceptance Values | Measured Values | Conclusion |
| 1 | Resistance Measurements | % | Maximun resistance unbalance rate≤5% | 0.87 | Pass |
| 2 | Ratio Tests | % | The deviation of voltage ratio on the principal tapping: ≤0.5% Connection symbol: Dyn1 | -0.06% ~ -0.05% | Pass |
| 3 | phase-relation tests | / | Dyn1 | Dyn1 | Pass |
| 4 | No-load losses and excitation current | / | I0 :: provide measured value | 0.93% | Pass |
| P0: provide measured value(t:20℃) | 0.505kW | ||||
| the tolerance for no load loss is +10% | / | ||||
| 5 | Load losses impedance voltage and efficiency | / | t:85℃ the tolerance for impedance is ±7.5% the tolerance for total load loss is +6% | / | Pass |
| Z%: measured value | 4.21% | ||||
| Pk: measured value | 3.443kW | ||||
| Pt: measured value | 3.948 kW | ||||
| Efficiency not less than 98.94% | 98.98% | ||||
| 6 | Applied Voltage Test | kV | HV: 40kV 60s LV: 10kV 60s | No collapse of the test voltage occurs | Pass |
| 7 | Induced Voltage Withstand Test | kV | Applied voltage (KV):2Ur | No collapse of the test voltage occurs | Pass |
| Induced voltage(KV):46 | |||||
| Duration(s):40 | |||||
| Frequency (HZ): 150 | |||||
| 8 | Leakage Test | kPa | Applied pressure：20kPA | No leakage and no Damage | Pass |
| Duration：12h | |||||
| 9 | Insulation Resistance Measurement | GΩ | HV-LV to Ground : | 5.62 | / |
| LV-HV to Ground: | 5.72 | ||||
| HV&LV to Ground: | 3.68 | ||||
| 10 | Oil Dielectric Test | kV | ≥45 | 54.86 | Pass |
04 Packing and Shipping
05 Site And Summary
In the rapidly evolving power industry, the three-phase pad-mounted transformer stands out as an ideal choice for modern power distribution, thanks to its exceptional performance and reliability. It not only offers excellent electrical safety and energy efficiency but also ensures a stable power supply and flexible installation options. Whether for industrial, commercial, or residential applications, the three-phase pad-mounted transformer provides users with high-quality power solutions. By choosing our product, you will experience efficient, stable, and safe power services. Let us work together to create a better future!
