Introduction: Pad Mounted Transformer, also known as a combined substation, is a complete power transformation and distribution unit that combines a transformer, the load switch and protective fuse devices on the high-voltage receiving side, and the low-voltage distribution wiring section. It is used in ring network power supply, dual power supply, or terminal power supply systems, and is suitable for factories, mines, oil fields, ports, airports, urban public buildings, residential communities, highways, underground facilities, and other locations. It offers advantages such as convenient switching of power supply modes, safe and reliable operation, compact size, fast installation, safe use, convenient operation, attractive appearance, and easy maintenance. Economically, it also has advantages such as a small footprint, short construction period, and reduced waste.
Pad Mounted Transformer is a compact power center suitable for utility, commercial, or industrial applications and is designed to withstand various types of environments. The product features a compact and miniaturized structure, fully insulated design, good sealing performance, strong corrosion resistance, and flexible configuration. These transformers can be located outside or inside buildings to provide energy-efficient and safer solutions. Fluid-filled transformers are available in various configurations and can be used with a variety of accessories to meet both basic and complex specifications. Pad Mounted Transformer has been widely used in many fields due to its unique advantages.
Pad-Mounted Transformer Manufactured by CHBEB
CHBEB GROUP has focused on transformer manufacturing for 60 years. Its products cover various types of transformers, including oil-immersed transformers, dry-type transformers, and various types of compact substations, meeting the needs of industrial, renewable energy, power distribution, and other application scenarios. Click the link to learn more about our Pad Mounted Transformer.
A pad-mounted transformer is also known as a combined transformer and was developed by relevant electrical companies in the United States. In this type of transformer, the fuses, multi-position loop-feed load switch, and de-energized tap changer are all installed inside the transformer oil tank as transformer components. The fuses can be easily replaced and the load switch can be operated from outside the tank to change the operating condition of the transformer.
On the high-voltage side, electrical power is supplied through loadbreak elbow cable connectors. A separate low-voltage outgoing compartment is installed outside the oil tank, with space available for additional protection devices and measuring instruments as required. All live parts are enclosed inside the cabinet, with no exposed energized parts.
Because the main components are installed inside the oil tank, it is called a combined transformer rather than a compact substation. However, the combined transformer also performs the functions of a compact substation. Six cable receptacles are installed on the high-voltage side, allowing the transformer to be connected to a loop-feed power supply system and to form a loop-feed distribution system together with a cabinet-type ring main unit or cable distribution box.
Therefore, combined transformer, pad-mounted transformer, and the commonly used term American-style compact transformer all refer to the same type of product. The main body is a transformer rather than a substation.
Pad-mounted transformers integrate traditional transformers into a box-type enclosure and feature compact size, light weight, low noise, low losses, and high reliability. They are widely used in residential communities, commercial centers, light rail stations, airports, factories and mines, enterprises, hospitals, schools, and other locations.
Pad-mounted transformers are installed inside enclosures with doors and locks, usually outdoors, and use dead-front medium-voltage terminals. Single-phase transformers are designed to operate on the primary side under a line-to-ground system to avoid ferroresonance effects.
These transformers are available in two basic configurations: radial feed and loop feed, which can be selected according to the type of circuit on which the transformer is installed.
Radial Feed Configuration
The transformer is connected to the primary supply line and does not allow the line to continue through the equipment.
Loop Feed Configuration
The transformer is connected to the primary supply line and allows other loads to be supplied through the equipment.
Scope of Supply
Manufactured in accordance with applicable NTC, IEC, and ANSI standards and/or specific customer requirements.
Ratings (kVA)
Single-phase: 15 kVA to 500 kVA.
|
Rated Capacity (kVA) |
HV | LV | Efficiency | |
|---|---|---|---|---|
| DOE(2016) | CSA(2023) | |||
| 15 |
34.5kV/19.92kV 13.8kV/7.96kV 13.2kV/7.62kV 12.47kV/7.20kV or others |
120–240V 240–480V 347V 600V or others |
98.82 | 99.73 |
| 25 | 98.95 | 98.87 | ||
| 37.5 | 99.05 | 98.97 | ||
| 50 | 99.11 | 99.04 | ||
| 75 | 99.19 | 99.13 | ||
| 100 | 99.25 | 99.19 | ||
| 167 | 99.33 | 99.28 | ||
Actual ratings can be selected according to project requirements and application conditions.
Three-phase: 30 kVA to 2500 kVA.
|
Rated Capacity (kVA) |
HV | LV | Efficiency | |
|---|---|---|---|---|
| DOE(2016) | CSA(2023) | |||
| 75 |
4.16kV 12.47kV 13.2kV 13.8kV 22.86kV 24.94kV 34.5kV or others |
240V 480V 480Y V 277V 600Y V 347V or others |
99.03 | 98.95 |
| 112.5 | 99.11 | 99.04 | ||
| 150 | 99.16 | 99.09 | ||
| 225 | 99.23 | 99.17 | ||
| 300 | 99.27 | 99.21 | ||
| 500 | 99.35 | 99.30 | ||
| 750 | 99.40 | 99.35 | ||
| 1000 | 99.43 | 99.38 | ||
| 1500 | 99.48 | 99.44 | ||
| 2000 | 99.51 | 99.47 | ||
| 2500 | 99.53 | 99.49 | ||
Actual ratings can be selected according to project requirements and application conditions.
Basic Insulation Level
Up to BIL 150 kV.
In terms of arrangement, the low-voltage compartment, transformer compartment, and high-voltage compartment of a pad-mounted transformer adopt a triangular layout rather than being arranged side by side in a straight line.
Structurally, a pad-mounted transformer is divided into front and rear sections. The front section contains the high- and low-voltage operating compartments, including the high- and low-voltage terminals, load switch operating handle, de-energized tap changer, bayonet fuse, oil level indicator, and other components. The rear section consists of the oil-filled tank and radiators. The transformer windings, core, high-voltage load switch, and fuses are installed inside the transformer oil tank.
The surge arrester also adopts an oil-immersed metal oxide design. The transformer does not use a conservator and instead adopts a sealed tank designed according to the principle of maintaining a constant combined volume of transformer oil and air space. The tank and radiators are exposed to the air, so there is no difficulty with heat dissipation.
Molded-case circuit breakers are used as the main circuit breaker and outgoing circuit breakers on the low-voltage side. Due to the simplified structure, the footprint and overall volume of this type of transformer are greatly reduced. Because of its compact size and single-side door design, the required footprint is only about one-quarter that of a Compact Substation, while its volume is only about one-fifth to one-third that of a Compact Substation of the same capacity.
The transformer typically consists of an active part including the core (magnetic circuit), coils (electrical circuit), and clamps. Its structure is determined according to the transformer type and is installed inside the tank to provide the equipment with the required characteristics for its specific application.
Coils
Rectangular cross-section with concentric copper or aluminum windings.
Insulation: High-quality insulating paper with epoxy resin coating.
Core
Shell-type or core-type structure, with wound and step-lapped construction for easy assembly and disassembly without affecting dimensional characteristics, while ensuring low losses and low excitation current.
Material: Cold-rolled grain-oriented electrical silicon steel sheets with insulating coatings on both sides, featuring low core loss and high permeability.
Clamps
Made of cold-rolled and hot-rolled steel and used to clamp the core. Individually bolted clamping plates allow easy disassembly for maintenance.
They provide high resistance to mechanical stresses caused by short circuits, as well as low noise levels and low excitation current.
Tank
The tank has a rectangular structure and is made of cold-rolled or hot-rolled steel sheets with reinforcing structures capable of withstanding internal pressure caused by temperature rise and mechanical stresses generated during equipment installation and handling.
Three-phase tanks are equipped with a separate cabinet fixed to the transformer by studs to protect the low- and medium-voltage circuits. A mechanical interlocking system is provided so that, for safety reasons, the medium-voltage compartment cannot be opened before the low-voltage compartment is opened.
Single-phase tanks are equipped with a separate cabinet hinged at the top, providing easy access to the terminals and transformer protection system.
Radiators are mounted on the tank and made of cold-rolled steel.
Accessories and Protection Devices
The medium-voltage accessories used in pad-mounted transformers are of the premolded elastomeric type, suitable for load operation except for 600 A versions, and adopt a dead-front design to ensure safe operation.
Power is supplied through an internal load-operating switch, together with bayonet fuse or canister fuse systems, forming a complete protection system.
Choosing the right power transformer supplier not only affects equipment performance, but also directly influences the safety and economic efficiency of the power system. So, how can you choose a truly reliable transformer manufacturer? As a transformer manufacturer with more than 60 years of production history, CHBEB GROUP has summarized the following criteria based on our experience and practice.
A reliable transformer manufacturer must first operate legally and compliantly and obtain recognition from authoritative certification systems. This is important evidence of the company’s strength and product quality, and it is also a prerequisite for participating in major project tenders.
CHBEB GROUP has advanced production and testing equipment, comprehensive testing processes, and a modern management system. We adhere to innovative development and have passed ISO9001 Quality Management System Certification, ISO14000 Environmental Management System Certification, ISO45001 Occupational Health and Safety Management System Certification, CE Conformity Report, Low Voltage Directive Conformity, and GOST Declaration of Conformity, to meet the requirements of different markets and projects.
The technical advancement of transformers is directly related to the operating efficiency and stability of a project over the coming decades. A reliable manufacturer must have solid technical expertise and advanced product support.
As a National High-Tech Enterprise, CHBEB GROUP has certification from the National Transformer Quality Supervision and Inspection Center, CCC certification, 5 invention patents, and more than 120 patent certifications.
We provide high-quality products and solutions for State Grid Corporation of China and industries around the world, including power, metallurgy, steel, petrochemical, machinery manufacturing, and pharmaceuticals.
During 60 years of development, CHBEB GROUP has established its Beijing headquarters as the center for technical research and development, with three major production industrial parks in Nanjing, Jiangsu and Yueqing, Zhejiang. The company specializes in the production of transformers, compact substations, wind power substations, solar photovoltaic substations, high- and low-voltage switchgear assemblies, ring main units, pole-mounted outdoor circuit breakers, outdoor vacuum circuit breakers, power transmission and distribution supporting equipment, as well as power engineering contracting and installation.
A high-quality transformer product depends not only on reliable raw materials, but also on strict control of every production process.
CHBEB has always attached great importance to quality control throughout the entire production process and insists on working with leading raw material suppliers in the industry. From silicon steel sheets, copper wire, and insulation materials to transformer electrical accessories, product quality and stability are ensured from the source.
In terms of manufacturing processes, automatic winding equipment is used for the windings, with strict control over winding dimensions and conductor arrangement. The double vacuum casting process can effectively remove air bubbles and moisture from the coils, greatly improving the insulation strength of the transformer. During assembly, the coils and core are fitted tightly, the silicon steel laminations are stacked evenly, and strict operating standards are applied to the connections of leads, bushings, and switches.
During final inspection, every CHBEB product undergoes rigorous quality testing. Key tests such as no-load and load tests, partial discharge tests, and lightning impulse tests are strictly controlled.
In the coming years, the pad-mounted transformer market will continue to benefit from renewable energy integration, grid intelligence, and infrastructure renewal demand. Product development will move from traditional distribution equipment toward more intelligent, digital, and high-efficiency solutions, including online monitoring, remote management, fault prediction, and designs with improved environmental performance. As the global energy structure changes and power systems continue to upgrade, renewable energy projects, data centers, industrial parks, and urban distribution construction will become important sources of growth. Market competition will also increasingly shift toward technical capabilities, regional service capabilities, and comprehensive solution capabilities.
If you are selecting a Pad-Mounted Transformer for your project, please contact CHBEB GROUP. Our technical team can provide suitable selection recommendations and solutions based on capacity, voltage level, power supply configuration, and actual application conditions.
The oil filled in the tank of a pad-mounted transformer is generally FR3 insulating oil. Its fire point can reach 312°C, and it has excellent electrical and thermal properties, high dielectric strength, good lubricity, strong arc-extinguishing capability, is non-toxic, and is biodegradable, thereby minimizing harm to the environment and human health. Unlike traditional mineral oil, FR3 insulating oil does not form deposits.
A pad-mounted transformer does not have oil temperature protection and only uses a thermometer to display the oil temperature. When the oil temperature becomes too high, protection is provided by the bayonet fuse. A pressure relief valve is also provided to release excessive pressure inside the tank. Therefore, the fuse should be checked regularly to ensure proper operation under these conditions, and the enclosure should also be inspected for oil leakage.
Because the tank of a pad-mounted transformer is exposed externally, it should be inspected regularly to prevent damage caused by external impact and resulting oil leakage.
