5 MVA Pad Mount Transformers-33/0.48 kV | USA 2025

The key to the smart grid, the three-phase pad mounted transformer empowers the future!

01 General

1.1 Project Description

5000 kVA three phase pad mounted transformer was delivered to America in 2025. The rated power of the transformer is 5000 kVA with ONAN cooling. The primary voltage is 33GrdY/19.053kV with ±2*2.5% tapping range (NLTC), the secondary voltage is 0.48Y/0.277kV, they formed a vector group of YNyn0.

A three-phase pad-mounted transformer is a widely used electrical power conversion device in urban and rural distribution systems. Its primary function is to convert high-voltage electricity into low-voltage electricity, enabling safe supply to commercial, industrial, and residential users. The pad mount transformers consist of a closed stainless steel tank designed to withstand various climatic conditions. The box contains a transformer, switching devices, protective equipment, and other necessary electrical components. The design of the three-phase pad-mounted transformer incorporates multiple safety measures, including overload protection, short-circuit protection, and grounding systems to ensure safe operation and maintenance. This 5000 kVA three-phase pad-mounted transformer, equipped with a four-position load switch, combines high power capacity with flexible load management, providing users with a safe, stable, and efficient power solution.

Due to the transformer’s exceptionally large capacity, standard bayonet fuses available on the market are not suitable for its protection. This challenge is fully addressed through our advanced internal design: windings reinforced with solidifying processes and a advanced cooling structure significantly enhance its inherent ability to withstand high inrush and fault currents; combined with high-impedance design and an integrated smart monitoring system, internal abnormalities are effectively suppressed and pre-warned. Consequently, the transformer achieves high durability and long-term reliable operation without relying on external fuse protection.

1.2 Technical Specification

5000kVA three phase pad mounted transformer specification and data sheet

1.3 Drawings

5000kVA pad mount transformers dimensions and weight details

02 Manufacturing

2.1 Transformer Bushing

Electrical cables serve as the link between low-voltage pad mount transformers bushings and various electrical loads: for lighter-load scenarios, a single cable connected to each bushing is usually enough to fulfill power supply demands. However, when dealing with higher-load equipment or systems, multiple cables need to be connected in parallel to the same bushing. These low-voltage bushings come pre-equipped with multiple wiring holes, which are specifically designed to support multi-cable connections. Notably, the exact number of holes provided for each low-voltage bushing is generally determined by the size and specifications of the corresponding padmount transformer.

2.2 Oil Level Guage

The oil level gauge is a vital sight glass, typically mounted on the side of the tank, providing a clear visual indication of the insulating liquid volume. Featuring a temperature-compensated scale, it allows for accurate monitoring to ensure the oil level remains within the safe operating range, which is critical for proper insulation, cooling, and the long-term reliability of the transformer.

2.3 Tank

The oil tank is made of steel and treated with anti-corrosive coatings to enhance its resistance to oxidation and corrosion, extending its service life. The design of the oil tank prevents moisture and dust from entering, protecting the quality of the insulating oil and preventing its degradation. The insulating oil inside the tank has excellent electrical insulating properties, effectively preventing electrical short circuits and leakage issues, thus protecting the transformer’s core components.

2.4 Tap Changer

The no-load tap changer (NLTC) of a pad mounted transformer is a key voltage regulation component on the high-voltage side. Operated only when the transformer is de-energized, it switches between different taps to compensate for grid voltage deviations and match load requirements, ensuring stable output voltage. Compact in structure, it’s fully adapted to the pad mounted transformer’s outdoor operation scenario.

03 Testing

Pressure Resistance Test (High Voltage Test):

• Apply high voltage to various parts of the transformer (such as windings and the casing, between different windings, etc.) to conduct a pressure resistance test. The purpose is to verify whether the transformer can maintain its insulation performance under electrical load conditions.
• There are two main forms of pressure resistance tests: DC withstand voltage test and AC withstand voltage test. The DC withstand voltage test is typically used to detect the polarity and strength of insulation, while the AC withstand voltage test is mainly used to simulate the electrical stress of the transformer in actual operation.

04 Packing and Shipping

05 Site And Summary

First, a concrete pedestal is pre-cast to match the unit’s dimensions and load-bearing specs, with pre-reserved channels to route cables through. Next, the transformer is lifted into position using suitable hoisting equipment (with careful attention to balance during lifting), then firmly secured to the pedestal with fastening bolts.

Subsequently, high-voltage and low-voltage cables are connected to their dedicated terminals-each connection is tightened properly, and insulation protection is verified to meet safety standards. After wiring, an internal check is carried out: confirming the load switch is in the correct (safe) position, inspecting the tightness of wiring terminals, and ensuring built-in meters/components are intact.

Finally, a pre-commissioning safety review is done to eliminate potential hazards, and the transformer is then ready for initial functional debugging.