Compact Substation 101: All You Need to Know

Nowadays, the demand for electricity is growing rapidly, and various types of power stations have come into being, such as hydroelectric, atomic, and thermal power stations. Substations are being built at different locations, depending on the accessibility of various power sources. However, these locations may not be close to the load center. Therefore, it is crucial to transmit electricity from the substation to the load center location. To achieve this function, a long-distance, high-speed transmission network is required.

The need for efficient and space-saving solutions has led to the development of compact substations. A compact substation is a self-contained unit that integrates all the essential components of a traditional substation into a smaller space. These substations play a vital role in stepping down high-voltage electricity from the transmission grid to lower voltage levels suitable for distribution. In this article, we will learn in detail about the working components of a compact substation, how it works, and what are the benefits it brings.

1. What is a compact substation?

A compact substation, also known as a prefabricated substation, is a kind of indoor and outdoor compact power distribution equipment. It combines high-voltage switchgear, distribution transformer, and low-voltage distribution equipment according to a certain wiring scheme and is installed in a moisture-proof, rust-proof, dust-proof, rodent-proof, fire-proof, anti-theft, heat-insulating, fully enclosed and movable steel structure building.

It can be understood as a group of electrical equipment assembled on a trailer or platform. To ensure that the compact substation is fully energized when it is transported to the required location, it is integrated and thoroughly tested in a factory environment. Compared with traditional substations, compact substations have more advantages, such as shortened construction time, reduced space requirements, and improved safety.

2. What components does a compact substation include?

The integrated substation is not just a transformer, it is equivalent to a small substation, which directly provides electricity to users. It mainly includes a high-voltage room, a transformer room, and a low-voltage room. The high-voltage room is the power supply side, generally 35kV or 10kV incoming line, including high-voltage bus, high-voltage circuit breaker or fuse, voltage transformer, lightning arrester, etc. The transformer in the transformer room is the main equipment of the integrated substation. The low-voltage room has low-voltage bus, low-voltage circuit breaker, metering device, lightning arrester, etc. The electric energy passes through the power supply side of the high-voltage room, changes the voltage through the transformer, and finally leads out from the low-voltage bus to supply power to users.

High-voltage input section: This section is responsible for receiving high-voltage power from the transmission grid. It includes high-voltage circuit breakers, disconnect switches, and lightning arresters. Circuit breakers are protective devices that interrupt current flow in the event of a fault, while disconnect switches can safely isolate the substation during maintenance or emergencies.
Power Transformer: Power transformers are one of the key components of compact substations. They step down the high voltage electricity received from the grid to lower voltage levels suitable for distribution. Transformers consist of primary and secondary windings, and the turns ratio of these windings determines the voltage transformation.
Low voltage section: This section of the compact substation includes low voltage switchgear for distributing power to various feeders and consumers. It includes low voltage circuit breakers, fuses and other protective devices to protect the distribution network from overload and short circuit.
LV and HV Busbars: Busbars are the conductive bars or rails that carry electrical current within a substation. Low voltage (LV) busbars distribute power at lower voltage levels within a substation, while high voltage (HV) busbars handle incoming high voltage power and distribute it to transformers.
Control and protection system: The control and protection system is the brain of the compact substation. It consists of various relays, sensors, and monitoring equipment to continuously monitor the operating status and performance of the substation. The system detects faults, and abnormal conditions and operates necessary protection devices to ensure the safety and reliability of the substation.

3. How does a compact substation work?

When electricity enters the compact substation from the transmission grid, the incoming high-voltage section ensures that it is safely connected to the high-voltage busbar. The power transformer then steps down the voltage to a distribution level suitable for local consumers.

Control and protection systems continuously monitor parameters such as voltage, current, frequency, and temperature. If any abnormal conditions are detected, such as faults or overloads, the system triggers the appropriate protection mechanisms. For example, in the event of a fault, a circuit breaker opens, isolating the faulty section from the rest of the network and preventing further damage.

The low voltage section distributes the stepped-down power to different feeders to supply residential, commercial, and industrial areas. Distribution transformers are also used to further reduce the voltage level before delivering the power to the consumer premises.

4. What are the advantages of compact substations?

The reason why a compact substation is preferred over a conventional substation is that it is a complete solution and can be easily adapted to any configuration as per the customer’s requirement.

Compact substations have the advantages of small size, flexible combination, and reliable technology. They are widely used in 11kV to 33kV three-phase distribution systems for power distribution. The protection level reaches IP55, and they can be installed outdoors with a small footprint.

The power capacity of the prefabricated substation is usually designed to be less than 2500kva, which depends on the capacity of the distribution transformer.

The compact substation is compact and its components are easily accessible through simple interfaces. Due to its small size, it takes up less space. It reduces installation space, cost, and time. The compact substation requires minimal on-site work to ensure maximum safety for operators. A maximum amount of mobility can be achieved when it comes to transportation and relocation. It can resist harsh environmental conditions to replace a fast and reliable power supply. To give you a better understanding, some of the advantages of compact substation are listed below:

The internal structure of the compact substation is more reasonable and occupies less space. Compared with the traditional transformer, the compact substation adopts a scientific and reasonable way to install the high-voltage distribution equipment in a sealed steel box. Its internal structure is very compact and the gaps between the components are quite small, so the compact substation occupies relatively less space.
The compact substation is very easy to operate and can be assembled quickly. Professional designers, through understanding the requirements of power engineering construction, separate the main wiring and supporting equipment outside the box according to different requirements, which is easy to operate and quick to assemble.
Compact substations have high application benefits. Compact substations typically cost between 40,000 and 80,000 dollars to construct from the perspective of construction costs. From the perspective of operating costs, even under full load operation, compact substations consume about 1 million kWh less electricity per year than ordinary transformers, and even if problems occur, the maintenance cost is also lower. Therefore, compact substations have high application benefits.
Compact substations are flexible in combination. Since compact substations have the characteristics of a compact and simple structure, each part is an independent system. In this way, compact substations have considerable flexibility in combination.
Compact substations are highly safe and stable. Since the shell of the compact substation is made of metal with strong corrosion resistance, the interfaces between the internal equipment are all made of insulating materials, and it is also equipped with air conditioning and dehumidification equipment, the compact substation’s resistance to the external environment is greatly improved, and its operation safety and reliability are improved.
Compact substations have less harm to the environment. Traditional substations require digging the ground, which affects natural drainage, but this does not exist in compact substations. Since tamper-proof metal containers are used to house equipment, it helps eliminate multiple environmental threats such as exposed grounding conductors and fences.

5. Operation and maintenance of compact substations

The following are the operation and maintenance of compact substations.

1). Basic requirements for compact substation operation

The base plate of compact substation equipment should be placed at a higher place, not in a low-lying place, to prevent rainwater from entering the box and affecting operation. When pouring the concrete platform, a gap should be left to facilitate the laying of cables in and out.
Between the box and the grounding grid, two reliable connections must be made. The grounding grids can be connected together. The grounding grids are generally grounded at the four corners of the foundation and then connected into a whole.
No items should be randomly piled or placed around the box equipment to ensure ventilation and inspection of electrical equipment. It is recommended that the transformer room door not be blocked to allow natural air circulation in the box.
Equipment in high-voltage distribution devices should be inspected and maintained regularly, including ring network switches, transformers, lightning arresters, etc. Any defects should be repaired in time, insulation preventive tests should be carried out regularly, and mechanical linkage devices should be disconnected correctly and operated with insulating rods.

2). Inspection and maintenance

The transformer should be inspected regularly according to the inspection and maintenance cycle (no less than once a month), the temperature of the cable terminal connection should be tested, the equipment operation should be checked, and tests should be carried out when necessary.

Make sure the foundation is solid, the holes are blocked, and there is no moisture in the cabinet.
Check whether the grounding device is complete and well connected and whether the grounding resistance meets the requirements.
Has the outdoor environment changed? Does it affect traffic and pedestrian safety?
Check the load of each feeder, whether the three-phase load is balanced, whether there is any overload, whether the switch position and instrument indication are correct, and whether the control device is working normally.
The transformer room should be dusted once every year. The surface of the high-voltage room and low-voltage room cabinet and the surface of the air box can be wiped with a wet cloth. The transformer room can be dusted by blowing or vacuuming.
Daily maintenance and inspection of the fan. Check the operation of the fan. If the fan does not operate, use the temperature and humidity controller, set it below the current temperature, and start the fan for inspection.
Maintain and repair the operating mechanism of high-voltage and low-voltage switches. Check the pressure gauge pointer to ensure it is in the green area. Lubricate mechanical parts and conduct separate and combined operation tests. Conduct insulation tests and leakage current tests on cables and lightning arresters.
Routine test of temperature and humidity controller; routine test of smoke alarm device; terminal block tightening and inspection: standard parts tightening and inspection.
Terminal block maintenance. The terminal block may become loose due to thermal expansion and contraction. All terminals in the terminal room should be checked and re-tightened every year. Note: Before re-tightening, make sure that both the primary AC circuit and the secondary control circuit are powered off to avoid electric shock!

The above maintenance and inspection measures should be carried out under the condition of ensuring personal safety. If necessary, please seek help from professionals to improve maintenance efficiency and reduce unnecessary time and property losses.

6. Conclusion

Compact substations have revolutionized the power distribution industry by providing space-saving and efficient solutions. Reliable and easy to maintain, these systems feature an integrated design and advanced control systems. These substations play a key role in ensuring a stable and safe supply of electricity from the high-voltage transmission grid to homes and businesses. As technology continues to advance, compact substations will undoubtedly develop further to meet the growing energy needs of the future.