Application of Pad-Mounted Transformers in Distribution Systems

I. Design Principles of Pad-mounted Transformers

With the upgrading of power infrastructure, pad-mounted transformers are widely used in various scenarios due to their light weight, small size, low loss, low noise and high reliability. Studies show that when the power supply voltage is increased from 380V to 10kV, line loss is reduced by 60%, and copper consumption and investment are each reduced by 52%, with remarkable economic and social benefits. As a product of modern economic and social development, it is an efficient and economical power distribution equipment, promoting high voltage to penetrate deep into the load center. This paper expounds its design principles, analyzes its applications in power distribution systems, and prospects its future development.

Pad-mounted transformers are integrated power distribution devices combining high and low voltage electrical equipment with transformers. Currently, they have become a key part of modern urban power grid construction, commonly used for secondary power distribution in new areas, residential districts, factories and temporary power sites, enhancing the flexibility and reliability of power distribution. Figures 1 and 2 below show the appearance of oil-immersed transformers and the internal structure of dry-type transformers respectively.

Based on the design principles and structural features, the advantages of pad-mounted transformers are as follows:

• High integration: Integrating high/low-voltage electrical equipment and transformers, it facilitates unified management and improves operation efficiency.

• Compact structure and space - saving: Occupying only 1/10 to 1/5 of the land area of traditional substation, it reduces construction costs, ensures equipment safety, and enables easy mobility and maintenance. It can be applied to ring network, radial terminal, and dual - power distribution systems.

II. Application of Pad-mounted Transformers in Distribution Systems
(1) Application Standards and Environmental Requirements

Pad-mounted transformers must comply with High/Low Voltage Prefabricated Substations (GB/T 17467 - 1998). Suitable environments include: altitude ≤ 1km, temperature range - 30℃ to 40℃, and no severe pollution, fire, corrosion, explosion risks, or intense vibration. Key technical issues to address include: reliability of closed cable connectors, flashover discharge under high/low voltage, heat dissipation affecting transformer output, and shell explosion prevention.

(2) Case Study

A power plant construction site adopted a ring network distribution system combining prefabricated and combined transformers. It deployed 3 ZBW combined transformers (1600kVA) and 5 prefabricated transformers (1000kVA) in living and construction areas. Prefabricated transformers were chosen for construction power due to their smaller size, while combined transformers supplied stable loads for offices and living areas. The system was powered by two switchgears (A and B), with switch C normally open to restore power quickly in case of cable faults, enhancing reliability.

Practical applications show that fully enclosed pad-mounted transformers:

• Prevent corrosive gases (e.g., salt mist) from damaging equipment, extending service life;

• Adapt to tight construction spaces with compact design;

• Eliminate bare live parts through cable connections, ensuring electrical safety.

III. Prospect of Pad-mounted Transformers

With the acceleration of urbanization and socioeconomic development, urban-rural land resources are increasingly strained, power load density continues to rise, and the transition of urban distribution networks to cable systems is accelerating. In this context, traditional pole-mounted distribution transformers can no longer meet modern social needs, while pad-mounted transformers are gaining market favor for their unique advantages, showing a trend of deep penetration into user load centers. Practical applications have proven that pad-mounted transformers not only enhance power supply safety but also integrate with the surrounding environment through aesthetic designs, playing a role in urban landscape beautification. It can be predicted that pad-mounted transformers will demonstrate enormous development potential and broad market space in future distribution systems.

Conclusion

As an important achievement of modern socioeconomic development, pad-mounted transformers highly meet the current social needs. Their fully enclosed structure effectively resists corrosion from corrosive liquids and gases, significantly extending the service life of electrical equipment. The shells made of anti-rust aluminum alloy or hot-dip galvanized color steel plates with special anti-corrosion treatment have excellent waterproof, anti-corrosion, and dust-proof properties, enabling them to withstand long-term outdoor operation. Meanwhile, pad-mounted transformers integrate environmental beautification and safe power supply, providing strong support for urban construction and power supply.

It is emphasized that to ensure the stable and reliable operation of pad-mounted transformers in residential areas, industrial parks, high-tech development zones, urban high-rise buildings, and other scenarios, their design, manufacturing, and use must strictly comply with the standards and specifications of High/Low Voltage Prefabricated Substations (GB/T 17467-1998). Only in this way can the technical advantages of pad-mounted transformers be fully leveraged to continuously provide safe and efficient power support for social development.