150 kVA transformer box electrical delivering compact, reliable, and efficient power for auxiliary distribution systems.
01 General
1.1 Project Description
As part of the same American electrical infrastructure project delivered in 2025, the customer also ordered a 150 kVA three phase pad mounted transformer designed to support auxiliary electrical loads within the distribution system, providing localized power conversion while maintaining compatibility with the medium-voltage network supplied by the main transformer.
Within this project, the customer also installed a 2660 kVA 22.8/0.8 KV three phase pad mounted transformer as the primary power conversion unit, responsible for handling the main distribution load of the facility (see the related project case: 2660 kVA outdoor transformer box). The 150 kVA unit therefore operates as a supplementary transformer box electrical solution, supplying reliable voltage transformation for smaller electrical loads such as control systems, facility services, and auxiliary equipment.
The transformer is rated 150 kVA, with a primary voltage of 22.8 kV and a secondary voltage of 0.48 kV. It uses the Dyn1 vector group, which provides appropriate grounding characteristics and voltage phase relationships required for reliable operation within three-phase distribution systems.
Although the transformer capacity is relatively small, it is designed in accordance with IEEE Std C57.12.34-2022, ensuring that this small pad-mounted transformer meets the same safety and performance standards as larger distribution transformers used in medium-voltage networks.
1.2 Technical Specification
150kVA three phase pad mounted transformer specification and data sheet
| Delivered to | America |
| Year | 2025 |
| Type | Three phase pad mount transformer |
| Standard | IEEE Std C57.12.34-2022 |
| Rated Power | 150KVA |
| Frequency | 60HZ |
| Feed | Loop |
| Front | Dead |
| Phase | three |
| Cooling Type | KNAN |
| Liquid insulant | FR3 Oil |
| Primary Voltage | 22.8 kV |
| Secondary Voltage | 0.48 kV |
| Vector Group | Dyn1 |
| Winding Material | Aluminum |
| Impedance | 3.5% |
| Efficiency | DOE |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 0.373 kV |
| On Load Loss | 1.163 kV |
| Accessories | Grounded shield |
1.3 Drawings
2500kVA three phase pad mounted transformer drawing and nameplate
02 Manufacturing
2.1 Three-Phase Three-Limb Core
The transformer adopts a three-phase three-limb magnetic core made from cold-rolled grain-oriented silicon steel laminations. Precision stacking reduces core loss, vibration, and noise while improving efficiency during continuous operation. A stable magnetic flux distribution is essential for the long-term reliability of transformer box electrical equipment operating in medium-voltage distribution systems. |  |
2.2 Aluminum Winding
 | The winding system uses aluminum conductors with high-temperature insulation, designed for the 22.8 kV / 0.48 kV voltage conversion. Aluminum windings provide a good balance of conductivity, strength, and weight-suitable for compact transformer box electrical assemblies in pad-mounted cabinets. Vacuum processing and mechanical reinforcement improve insulation reliability and resistance to short-circuit forces. |
2.3 FR3 Insulation
The transformer uses FR3 natural ester insulating fluid, offering higher fire safety and better moisture tolerance than mineral oil. The KNAN cooling method relies on natural oil circulation and natural air cooling to maintain stable operating temperature. Reliable cooling is essential. Even for small transformers.
2.4 Transformer Tank
 | The transformer adopts a compact pad-mounted enclosure structure, forming a transformer box electrical unit that combines transformer components, switching equipment, and protection devices within a secure outdoor enclosure suitable for utility or industrial installation. The small pad mounted transformer uses a dead-front design, which protects maintenance personnel by preventing accidental contact with energized parts during operation and servicing. The enclosure also supports loop feed configuration, allowing the transformer to be installed within ring distribution systems where power continuity and flexible network configuration are required. Despite its smaller capacity, the transformer is built to provide the same reliability standards expected from larger three phase distribution transformer equipment. |
2.5 Protection and Monitoring
The transformer includes essential monitoring instruments that allow operators to track internal conditions during operation.
Additional protection components include: |  |
03 Testing
04 Site And Summary
Within the overall project infrastructure, the 150 kVA transformer box electrical unit operates together with the larger 2660 kVA outdoor transformer box, forming a coordinated power distribution arrangement in which the main transformer carries the majority of the electrical load, while the smaller unit provides localized power supply for auxiliary systems and service equipment across the facility.
The large transformer handles bulk power conversion.
The small unit supports auxiliary loads.
Together, these transformer box electrical units create a stable medium-voltage distribution structure capable of supporting continuous operation while allowing flexible power allocation within the project.
