Prefabricated Substation: A Full Guide

Substations are places where voltage is changed. In order to transmit electricity from power plants to distant places, the voltage must be increased to high voltage and then reduced as needed near the user. The work of increasing and reducing voltage is done by substations. Prefabricated substations are rapidly becoming an important part of the power system. These substations can increase and decrease voltage to achieve efficient power transmission over long distances and help distribute power to consumer areas.

Compared with traditional on-site built substations, prefabricated substations have the advantages of faster deployment, lower cost, smaller footprint and flexibility. Since most of them have been manufactured, they are quick and easy to assemble, saving users a lot of time and cost.

This guide will introduce in detail the composition and working principle of the prefabricated substation, as well as its installation and maintenance precautions.

1. What is a prefabricated substation?

Substations are located within the electric power system and step up or down the voltage depending on whether the power is going to consumers or other stations. Substations can be either transmission or distribution substations. Transmission substations step up the voltage to enter the grid, while distribution substations step down the voltage for consumers. Prefabricated substations can be used as distribution substations but can also set the voltage when needed.

Prefabricated substations are similar to electrical substations and are usually located in cities and urban areas. We might find these substations on the side of a road, near a business, in a neighborhood, or near a park. They are usually built like a house. With a prefabricated substation, the manufacturer builds most of the components. Once you receive it, you will assemble it according to the manufacturer’s instructions.

This is different from traditional substations, which are custom-designed and built from scratch according to the final site location. Prefabricated units offer a simplified manufacturing, transportation, permitting, installation, and commissioning process compared to site-built substations.

Most electrical equipment suppliers offer prefabricated substations in standard designs. If required, they can be customized to specific voltage, capacity, functionality, and layout requirements. Both indoor and outdoor designs are commonly constructed with metal cladding and concrete enclosures.

2. Components of prefabricated substation

Prefabricated container substations typically consist of three main components: enclosure, transformer, and switchgear. The enclosure is the substation housing, designed to protect the components from environmental hazards such as rain, wind, and dust.

A transformer is a component that converts incoming high-voltage electricity to a lower voltage suitable for distribution. It is usually located inside an enclosure and can be customized to meet specific power requirements.

Switchgear is the component that controls the power distribution in the substation. It includes circuit breakers, switches, and other protective devices used to control and protect high-voltage line connections to ensure safe and reliable power distribution.

A complete prefabricated substation should also include the following components:

Low-voltage power distribution is used to distribute and control low-voltage electricity to end users.
Monitor and control devices such as instruments, sensors, automation systems, and HMI interfaces
Auxiliary systems for ventilation, heating, fire extinguishing, security and lighting
Structural frames, walls, roofs, and foundations that support and contain components
Safety systems such as arc barriers, insulated busbars, and physical access controls

3. Working principle of prefabricated substation

Prefabricated substations operate similarly to traditional substations, but the components are integrated into a prefabricated enclosure. Their core purpose is to convert higher transmission voltages to lower distribution voltages for commercial, industrial and residential end users.

The transmission line from the power plant delivers high voltage power such as 115kV or 230kV to the input of the prefabricated substation. This high voltage feed is connected to the primary side of the step-down power transformer through switchgear that provides overcurrent protection and disconnection functions.

Input voltages of 12kV and 34kV are converted to medium voltage distribution voltages by transformers. These lower medium voltages are interconnected to the low voltage switchboards through additional protection devices.

The distribution board then steps down the voltage further to 120/240V or 480V for delivery to the end-use loads through outgoing distribution lines and feeders.

Monitoring, controlling, and protecting downstream networks and substation equipment are accomplished with the help of a variety of switchgear, relay devices, sensors, and automation systems. Operators interact with the substation locally or remotely through the HMI to control operations and respond to changes in demand.

4. Functions of prefabricated substation

In any power distribution system, the voltage needs to be stepped up or down at some point. The electricity passes through a substation to change the voltage. While substations typically manage smaller voltages, using transformers to step down the voltage, prefabricated substations can handle larger voltages and perform both step-up and step-down.

Prefabricated substations convert electricity from AC to DC and back again. It allows for higher currents when the power station and the consumer are far apart. Many substations can convert AC to DC to get a high voltage, thus preventing power loss.

These substations save energy, which is good for the environment and consumers. Most prefabricated substations are high voltage stations that manage medium voltage or lower levels of high voltage current.

Prefabricated substations are easy to transport and assemble. When installing the substation, choose a safe location for the concrete pad. Avoid any nearby flammable materials and areas where explosions may occur. Substations should be located on the windward side of main buildings. Finally, avoid crowded areas and consider other factors such as weather, environment, and wildlife.

5. Advantages of prefabricated substations

Prefabricated substations have significant advantages over traditional on-site construction designs:

Faster deployment: Parallel manufacturing of substations off-site can significantly reduce installation time.
Reduced costs: Standardized designs enable economies of scale, reducing costs by 15-30%.
Smaller Footprint: Integrating all equipment into a single compact housing minimizes the required land area.
Flexibility: Prefabricated units can be easily relocated as needs change; standardized design allows for incremental capacity increases.
Testing: Components and assemblies can be factory tested and commissioned prior to final on-site installation.
Permitting: Offsite construction avoids the complexity and restrictions of onsite permitting.
Reduced risk: Manufacturing in a controlled environment enhances quality control and safety.
Environmental: Prefabricated enclosures provide noise reduction and containment options for sensitive areas.

In summary, prefabricated substations facilitate faster and lower-cost deployment in space-constrained areas, temporary applications, disaster recovery, and flexible growth scenarios. Their integrated off-site construction allows for better quality control while reducing on-site issues and permitting hurdles.

6. Types of prefabricated substations

There are two main types of prefabricated substations: integrated substations (also known as pad-mounted transformers) and combined substations (also known as compact transformers). Each type has slightly different uses, and you can choose the best type for your situation.

In a comprehensive substation, the transformer forms the main structure. Its housing houses the load switches and fuses. The housing is sealed and insulated, requiring little maintenance. Before building a substation, you need to prepare a pad. It tends to be smaller than other substations.

(1). Pad-mounted substation

A integration substation is divided into two parts, the front part is the high and low voltage terminals. The high voltage terminal has bushings and voltage regulating load switches, the low voltage terminal has oil filling valves, thermometers, nameplates, grounding copper bars, etc. The rear part is the radiator, transformer oil tank, etc.

(2). Compact substation

A compact substation has the same components – transformer, high voltage switchgear and low voltage distribution system. Each component is housed in its own substation room, unlike an integrated substation. They come in the more convenient mu form, or the more compact pin form.

Compact substations are usually pin-type when using multiple transformers. One of the biggest advantages of compact substations is that you can rearrange the components to suit different situations. Enclosures are available in both metallic and non-metallic materials, providing different levels of protection and aesthetics.

(3). Key differences

High voltage configuration: Pad-type transformers integrate the high voltage components within the transformer tank, while compact transformers require a separate high voltage cabinet.
Customization Flexibility: Compact transformers offer more customization options for high-voltage, transformer, and low-voltage configurations than pad-mounted transformers.
Transformer Type: Pad-mounted transformers usually use oil-immersed transformers, while compact transformers can accommodate both oil-immersed transformers and dry-type transformers.
Size and Cost: Compared to compact transformers, pad-mounted transformers are more compact and cost-effective and are suitable for various urban applications.

7. Application of prefabricated substation

Prefabricated box substations are widely used in the following fields due to their small size, complete functions, and convenient operation and maintenance:

Industrial production: Box-type substations can be used in industrial parks, manufacturing enterprises, and other places to provide stable and reliable power supply for production equipment.
Urban construction: Prefabricated box-type substations can be used for urban infrastructure construction to provide power services for residential areas, commercial plazas, etc.
Rural electricity use: European-style box transformers can be used in rural areas to meet farmers’ production and living electricity needs.
Other fields: Prefabricated container substations can also be used in oil and gas exploration, transportation, and other fields to provide power guarantees for various scenarios.

8. Installation of prefabricated substation

The installation of prefabricated substations must strictly comply with electrical safety and related regulations. Please seek help from professional electricians when necessary. The following are common installation steps for reference.

(1). Design planning

Determine the model, specification, and layout of the box-type substation according to actual needs and site conditions. Consider factors such as power supply load, power equipment, and environmental requirements, and make reasonable design planning.

(2). Site preparation

Select a suitable site for installation, and ensure that the site is flat and stable, and meets relevant safety requirements. For earthwork, infrastructure, drainage, and other treatments, carry out corresponding preparations according to design requirements.

(3). Box installation

After the box-type substation is transported to the designated site, the box is hoisted and placed according to the design drawings and the reserved foundation. Ensure that the connection between the box and the foundation is stable and reliable and meets relevant safety requirements.

(4). Equipment installation

After the cabinet is installed, proceed with the equipment installation. Install the transformer, switchgear, protection device, etc. one by one to the designated location. Pay attention to the technical requirements of the equipment such as connection method, insulation treatment, and fixed installation.

(5). Grounding and wiring

Effectively ground the box-type substation to ensure a safe and reliable electrical connection. At the same time, carry out wiring work between equipment to ensure smooth and stable power transmission.

(6). Debugging and acceptance

After the installation is completed, the system is debugged and accepted. The normal operation of the box-type substation is ensured by checking the operating status of the equipment and measuring parameters such as current and voltage. Corresponding tests and inspections are carried out to verify that the box-type substation meets relevant standards and requirements.

(7). Safety protection and training

During the installation process, pay attention to safety protection measures, construction workers should wear personal protective equipment that meets the requirements and comply with relevant safety operating procedures. After the installation is completed, relevant personnel will be trained, including knowledge on equipment operation, maintenance and emergency response.

9. Maintenance of prefabricated substation

Correct and regular maintenance of prefabricated substations can extend their service life and improve performance. It is also helpful to discover potential electrical risks in daily use and reduce losses. Common maintenance measures are listed below.

(1). Daily inspection

Inspection personnel should regularly inspect the substation to check whether all components are intact and whether there are any abnormal sounds or vibrations. At the same time, pay attention to checking the temperature of the equipment to prevent malfunctions caused by overheating.
Regularly clean the dust and debris in the substation to keep the equipment clean and dry to prevent the normal operation of the equipment from being affected by the accumulation of dirt.
Regularly check the circuit breakers, isolating switches, load switches, and other electrical components to ensure that they are flexible and in good contact. For aging or damaged components, they should be replaced or repaired in time.
Regularly check the working status of cooling fans, radiators, and other components to ensure they are operating normally. If there is a fault in the cooling system, it should be repaired in time to prevent the equipment temperature from being too high due to poor heat dissipation.
The insulation performance of the equipment should be tested regularly, including the measurement of insulation resistance, dielectric loss, and other indicators. Equipment with degraded insulation performance should be handled in a timely manner to prevent accidents caused by insulation failure.
Check the lightning protection device regularly to ensure that it performs well and is effectively grounded. At the same time, check the connection of the grounding grid to ensure that the grounding resistance meets the requirements. Any problems found should be dealt with in a timely manner to prevent equipment damage or safety accidents caused by lightning strikes or poor grounding.

(2). Establish maintenance and care files

In order to better manage the maintenance and maintenance of prefabricated substations, maintenance and maintenance files should be established. The files should record in detail the time, content, personnel, problems found, and handling of each maintenance and maintenance. Through the establishment and management of files, the operating status of the equipment can be easily tracked and analyzed, providing a reference for subsequent maintenance and maintenance work.

In summary, the installation and maintenance of prefabricated substations is a complex and important task. By strictly following the installation process and strengthening daily maintenance and care work, the safe and stable operation of box-type substations can be ensured, providing a strong guarantee for the reliable power supply of the power system.

10. Conclusion

In summary, prefabricated substations are a modern and efficient solution for power distribution. A number of advantages are available over traditional substations, including compactness, flexibility, and durability. They are suitable for a variety of applications, including commercial and industrial buildings, construction sites, and remote locations. Fast and easy installation makes it a reliable solution for power distribution.