Pad Mounted Transformer – Compact, Safe, Reliable Urban Power Core.
01 General
1.1 Project Description
150 kVA three phase pad mounted transformer was delivered to USA in 2025. The rated power of the transformer is 150 kVA with ONAN cooling. The high voltage is 13.2D kV with ±2*2.5% tapping range (NLTC), the low voltage is 0.208GrdY/0.12 kV, they formed a vector group of Dyn1.
This pad-mounted transformer is a completely self-contained, subsurface-type distribution transformer designed for reliable, safe, and efficient power delivery in utility, commercial, and industrial applications. Engineered for direct installation on a concrete pad at ground level, it offers a robust and compact solution for stepping down medium voltage to usable low voltage, serving as a critical node in the electrical distribution network.
Constructed with a premium stainless steel tank, this unit provides exceptional corrosion resistance, ensuring long-term structural integrity and a maintenance-free exterior life even in harsh or coastal environments. Its superior high-efficiency performance is demonstrated by low loss figures, with an exceptionally low no-load loss of 373W and a full load loss of 1163W, translating directly into significant energy savings and reduced operating costs over the transformer’s lifecycle.
Beyond efficiency, this transformer is built for maximum protection and operational intelligence. It is equipped with an Internal Fault Detector (IFD), which provides early warning and protection against internal arcing faults, enhancing safety for both the equipment and the public. For comprehensive downstream circuit protection and convenient switching, an integrated Low-Voltage Circuit Breaker is included. Furthermore, to safeguard the transformer’s insulation from damaging voltage surges caused by lightning or switching events, High-Voltage Surge Arresters are standardly fitted on the primary side.
1.2 Technical Specification
150 kVA pad mounted transformer specifications type and data sheet
| Delivered to | USA |
| Year | 2025 |
| Type | Pad mounted transformer |
| Standard | ANSI/IEEE C57.12.00 |
| Rated Power | 150 kVA |
| Frequency | 60HZ |
| Phase | 3 |
| Feed | Loop |
| Front | Dead |
| Cooling Type | ONAN |
| Primary Voltage | 13.2D kV |
| Secondary Voltage | 0.208Y/0.12 kV |
| Winding Material | Aluminum |
| Vector Group | Dyn1 |
| Impedance | 3.5% (±7.5%) |
| Efficiency | 99.16% |
| Tap Changer | NLTC |
| Tapping Range | ±2*2.5% |
| No Load Loss | 0.373 kW |
| On Load Loss | 1.163 kW |
1.3 Drawings
150 kVA pad mounted transformer diagram drawing and size.
02 Manufacturing
2.1 circuit breaker
| The low-voltage circuit breaker for pad mounted transformers is installed on the transformer’s low-voltage side, serving as a critical protection and control component for the distribution system. It rapidly detects and interrupts overloads, short circuits, and other abnormal current conditions with high responsiveness, preventing damage to the transformer, downstream equipment, and the power grid. Featuring robust construction, reliable breaking capacity, and weather-resistant design to adapt to outdoor operating environments, it supports both manual and optional electric operation for convenient maintenance and system management. By ensuring safe current distribution and swift fault isolation, this circuit breaker enhances the overall stability and safety of the pad mounted transformer in urban, commercial, and industrial power distribution scenarios. |  |
2.2 IFD
 | The Integrated Fault Detector (IFD) in this pad-mounted transformer is a comprehensive monitoring system designed to enhance reliability and safety. It continuously monitors key operational parameters such as internal pressure, fluid level, and temperature. In the event of an internal electrical fault, it quickly detects the resulting pressure rise and activates a visible flag alarm on the exterior cabinet. This immediate, local indication allows for rapid fault identification and location. The IFD system provides critical early warning, enabling proactive maintenance decisions, helping to prevent catastrophic failures, minimize outage times, and extend the overall service life of the transformer. |
2.3 Non-PCB Label
| The “Non-PCB” label affixed to this pad-mounted transformer serves as a critical safety and environmental declaration. It clearly certifies that the transformer’s dielectric insulating fluid does not contain Polychlorinated Biphenyls (PCBs), hazardous chemicals once commonly used in older electrical equipment. This label provides immediate visual assurance to utility personnel, first responders, and environmental regulators that the unit complies with modern health and safety regulations (such as EPA guidelines and IEEE standard C57.12.29). It signifies a safer work environment, simplified handling and disposal procedures, and the manufacturer’s commitment to environmental stewardship and sustainable design. |  |
2.4 Final Assembly
 | The 200A 35kV class bushing well designed for terminating primary winding leads in oil-filled units. Externally mounted on the tank wall via stainless steel or zinc dichromate-plated 3-hole clamps, it fits a 65mm hole and uses a rubber gasket for secure, moisture-resistant sealing. Crafted from high-quality polymer with temperature stability and low moisture absorption, it features knurled copper studs (embedded or removable) for reliable conductivity, supporting 200A continuous current and short-time withstand capacities (10,000A/0.17s or 3,500A/3s). With voltage ratings up to 36.6kV phase-to-phase and 150kV BIL, it undergoes strict production tests to ensure durable, consistent performance in harsh outdoor environments. |
2.5 Elbow Arrester
Elbow arrester integrates a metal oxide varistor (MOV) module into a peroxide-cured insulating and semi-conducting rubber housing, meeting IEEE 386 standards for interchangeability with compatible industry products. Equipped with a #4AWG flexible copper stranded woven ground lead and a weatherproof stainless steel cap, it delivers reliable overvoltage protection by diverting surge currents to ground, safeguarding pad mounted transformers, entry cabinets, and underground distribution systems while extending cable life. Featuring precision-molded semiconducting shielding for corona-free performance, the arrester undergoes rigorous tests (including partial discharge, high-current discharge, and thermal stability checks) and is available in various voltage ratings to suit different system requirements, ensuring durable, consistent protection in harsh outdoor and underground operating environments.
03 Testing
The DC winding resistance measurement (Resistance Measurements) for the pad mounted transformer results in a value of 4.45 ohms, a key test to assess the integrity of the transformer’s windings and the reliability of internal electrical connections. This precise reading confirms consistent conductor quality, secure joint fastenings, and uniform current distribution across the windings, minimizing resistive losses during operation. Falling within the optimal operational range, the 4.45 ohm measurement ensures the transformer maintains stable electrical performance, efficient power transmission, and long-term reliability in urban distribution network applications.
04 Packing and Shipping
05 Site And Summary
In summary, this pad-mounted transformer delivers a robust and efficient power distribution solution. Its corrosion-resistant stainless steel tank ensures long-term durability, while the low losses (373W/1163W) contribute to significant energy savings. The integrated package-featuring the IFD for condition monitoring, the low-voltage breaker for safe operation, and the high-voltage arrester for surge protection-provides a comprehensive safeguard, resulting in a highly reliable, secure, and low-maintenance unit for modern electrical networks.
