Prefabricated Substation

All the prefabricated substations which manufactured by Cotenele are fully type-tested in accordance with international and national standards prior to delivery. This can ensure compliance with performance and safety requirements. Prefabricated substations represent a significant evolution from traditional brick-and-mortar substations, offering substantial reductions in installation time—up to 70%—and overall project costs of 20-30% for applications up to 35kV. They are designed for three-phase AC power distribution systems with rated voltages typically ranging from 6kV to 35kV on the high-voltage side and 0.4kV on the low-voltage side.

What is a prefabricated substation?

1. Definition

A prefabricated substation is a complete electrical assembly in which a transformer, medium-voltage switchgear and control equipment, low-voltage switchgear and control equipment, internal wiring (cables, busbars, etc.), metering devices, power factor correction equipment, and surge arresters are housed within a common enclosure (cabinet) or multiple interconnected enclosures. The unit is designed, manufactured, assembled, wired, tested, and inspected at the factory before being transported to the project site as an integrated system.

2. Working Principle

The working principle of a prefabricated substation is a simple power conversion and distribution sequence actually:

• Medium-Voltage Input: Medium-voltage electricity is usually received from the public grid through an incoming feeder line, with voltage levels generally between 6kV and 35kV. The feeder line can be configured as a terminal type or a ring-network type, with the terminal type being a single feeder line and the ring-network type being a double feeder line to achieve redundancy.
• Switching and Protection: The incoming power enters the medium-voltage switchgear compartment to transmit power. The medium-voltage switchgear compartment contains load isolation switches, circuit breakers, fuses, and protective relays. These devices provide isolation, switching, fault protection such as overcurrent, short circuit, and ground fault, and control functions.
• Voltage Transformation: Medium-voltage power is reduced to low voltage such as 400V, 415V, or 433V, through a power transformer, which can be either an oil-immersed transformer or a dry-type transformer.
• Low-Voltage Distribution: The reduced 400V or 415V low-voltage power enters the low-voltage switchgear compartment and distributes power to downstream loads through circuit breakers, busbars, metering equipment, and surge protection devices.
• Monitoring and Control: Advanced units incorporate intelligent electronic devices (IEDs), microcomputer-based protection relays, and communication interfaces that enable "three-remote" functions—telemetry, telesignaling, and remote control—for integration with SCADA and distribution automation systems.

3. Internal Structure

The internal structure of a prefabricated substation usually contains three functional compartments:

(1) Medium-Voltage Compartment

• Used for installing medium-voltage switchgear, including segmented circuit breakers, vacuum or sulfur hexafluoride (SF6) circuit breakers, fuses, and lightning arresters.
• Contains busbars, current transformers (CTs), and potential transformers (PTs).
• Can be equipped with Ring Main Unit (RMU) for ring network configuration.
• Equipped with protective relays and interlocking mechanisms.

(2) Transformer Compartment

• Contains the power transformer, such as oil-immersed transformer or dry-type transformer.
• Includes cooling systems which can be natural ventilation or forced-air cooling.
• Features temperature monitoring devices and pressure relief mechanisms.
• May incorporate oil-level indicators and Buchholz relays for oil-immersed units.

(3) Low-Voltage Compartment

• Installs low-voltage switchgear, including molded case circuit breakers (MCCBs), air circuit breakers (ACBs), and busbars.
• Contains metering equipment, power factor correction capacitors, and surge protection devices.
• Includes control wiring, auxiliary power supplies, and communication interfaces.

Operating Conditions

Prefabricated substations are designed to operate under specific environmental conditions. Typical operating parameters include:

For applications in harsh climates, units may be equipped with additional climate control systems, including heating, ventilation, and air conditioning (HVAC) for extreme temperature environments.

Main Technical Parameters

Key technical parameters for prefabricated substations typically include:

What are power transformers classifications?

Key Differentiators

1. European-Style prefabricated substation are the most technologically mature substation products, but their disadvantages include a large footprint and high investment costs, but they have the highest reliability and scalability. Its modular and partitioned structure is particularly suitable for application scenarios that require extremely high power supply reliability.
2. American-Style pad-mounted transformer advantages are their emphasis on compactness and cost-effectiveness, integrated fuel tank design, minimal footprint and lowest cost, and fully enclosed structure that can effectively resist the impact of environmental factors. But the disadvantage is poor maintenance convenience and scalability.
3. Chinese-Style compact substation represents an optimized compromise that combines the compactness of American designs with the automation capabilities and maintenance convenience of European designs. It eliminates the dedicated transformer compartment found in European units, reducing overall footprint while maintaining independent HV and LV compartments. The design is particularly well-suited for renewable energy applications, including photovoltaic and wind power projects.

Application Scenarios

Prefabricated substations are widely deployed across diverse sectors:

• Urban Power Distribution: Residential communities, commercial centers, multi-story buildings, and public utilities
• Industrial Facilities: Industrial parks, factories, mines, and oil and gas fields
• Renewable Energy Projects: Photovoltaic power stations, wind farms (step-up from 690V or 315V to 35kV), and energy storage systems
• Transportation Infrastructure: Subways, airports, expressways, and railways
• Temporary Power Supply: Construction sites, large-scale events, and emergency response
• Infrastructure Projects: Urban renovation, rail transit, and bridges
• Data Centers: High-reliability power distribution for critical IT infrastructure
• Rural Electrification: Grid renovation and remote area power supply