What Is an Electrical Substation and How Does It Work?

In modern power transmission and distribution systems, electrical substations serve as core hubs. They connect power generation and end users. Substations handle voltage transformation, power flow control, fault isolation, and system protection.

Definition and Core Functions of Substations

According to IEC 61936-1 and GB/T 50062, a substation is defined as:

“A power facility consisting of transformers, switchgear, busbars, protection and control devices, grounding systems, and auxiliary facilities, used to realize the reception, transformation, distribution, and control of electrical energy.”

Refer to the table below to understand its core functions.

Function Category	Technical Implementation	Engineering Significance
Voltage Transformation	Power transformers realize high voltage and medium voltage/low voltage conversion	Reduce transmission losses and match load requirements
System Sectionalization and Isolation	Circuit breakers (CB), disconnectors (DS), earthing switches (ES)	Support maintenance and limit fault scope
Relay Protection and Automation	Microcomputer protection devices, SCADA, IEDs (Intelligent Electronic Devices)	Quickly clear faults and improve N-1/N-2 reliability
Reactive Power Compensation and Power Quality Management	Shunt capacitor banks, SVG, filters	Meet the requirement of power factor ≥ 0.9 (GB/T 12325)
Earthing and Lightning Protection	Ground grids (Ground Grid), surge arresters (Surge Arrester)	Ensure personal safety and suppress switching overvoltage

Electrical Principles Behind Voltage Transformation

Why are Multi-Stage Voltage Transformation Needed?

Power systems employ a “high-voltage long-distance transmission + step-down distribution” architecture, theoretically based on Joule’s law( Ploss=I2RPloss​=I2R)

When the transmitted power P  is fixed, increasing the voltage V can significantly reduce the current I/, thereby reducing line losses.

Transformer Working Principle: Electromagnetic Induction and Flux Coupling

The main transformer operates based on Faraday’s law of electromagnetic induction:

V1/V2=N1/N2V1​/V2​=N1​/N2​

where N1​,N2​  are the number of turns in the primary/secondary windings. Energy is efficiently transferred through the core magnetic circuit (efficiency typically >99%).

Typical Substation Architecture and Key Points for Equipment Selection

Substation Types Classified by Function

Type	Voltage Level	Typical Configuration	EPC Focus Points
Transmission Substation	220 kV and above	GIS/HGIS, large-capacity power transformers (≥ 180 MVA)	System short-circuit capacity, N-1 verification, footprint optimization
Regional Distribution Substation	110/35 kV	AIS or compact GIS, double busbar with sectionalization	Load forecasting, expansion reservation, automation interface
Customer-Specific Substation	10/20 kV	Compact substations (Compact Substation) or indoor substations	Power supply agreement (PCC point), harmonic assessment, metering accuracy
New Energy Collection Station	35 kV (Wind/PV)	SVG + collection lines + step-up transformers	Low Voltage Ride-Through (LVRT), reactive power response time

Key Equipment Selection Technical Parameters

Taking 110 kV GIS as an example

Equipment	Key Parameters	Standard Reference
SF₆ Circuit Breaker	Rated breaking current ≥ 40 kA, mechanical life ≥ 10,000 operations	IEC 62271-100
Current Transformer (CT)	Accuracy class 0.2S/5P20, transient coefficient ≥ 2.0	GB/T 20840.2
Voltage Transformer (VT)	Accuracy class 0.2/3P, residual voltage winding	IEC 61869-3
Power Transformer	Impedance voltage 10–12%, ONAN/ONAF cooling	GB/T 6451

Key Technical Challenges in Project Implementation

Grounding System Design

• Grounding resistance must meet the requirement R≤2000IgR≤Ig​2000 (GB/T 50065), Where IgIg​  is the ground fault current
• Step voltage and contact voltage simulation is required (e.g., using CDEGS software)
• In areas with high soil resistivity, resistance-reducing agents or deep well grounding are required

Relay Protection Setting Coordination

• Main transformer differential protection, backup overcurrent, and zero-sequence protection must be coordinated with the time-current characteristics (TCC) of the upstream/downstream protection
• New energy access requires the addition of frequency/voltage anomaly protection logic

Digitalization and Intelligentization Trends

• Promote the IEC 61850 standard and achieve GOOSE/SV communication
• Deploy online monitoring systems (DGA, partial discharge, iron core grounding current)
• Support remote operation and maintenance and digital twin integration

Substation application scenarios

Application Type	Typical Scenarios	Voltage Level (Common)	Main Function
Regional Substation	Urban power supply, industrial parks	110/220 kV → 10/35 kV	Step down high voltage to medium voltage for distribution network
Terminal Substation	Malls, hospitals, residential areas	10/35 kV → 400 V	Provide low-voltage power to end users
PV/Wind Step-up Station	Wind farms, photovoltaic power stations	0.69/35 kV → 110 kV	Collect renewable energy and step up for grid connection
Rail Transit Substation	Metro, high-speed rail traction systems	110/35 kV → 750 V DC / 25 kV AC	Supply dedicated traction power for trains

Conclusion

Driven by the “dual carbon” goal, substations are evolving from traditional power nodes to energy routers. For engineers and EPC teams, it is not only necessary to master classic electrical design but also to integrate power electronics, communication protocols, and system simulation capabilities.

In the future, substations will deeply integrate new technologies such as energy storage, flexible DC transmission, and virtual power plants, becoming a key carrier for building new power systems.

Appendix: Commonly Used Standards and Specifications

IEC 61936-1:2020: Design of AC Installations for High Voltage Substations

GB 50059-201: Design Specification for 35kV～110kV Substations

IEEE C37.118: Standard for Synchronous Phasor Measurement

DL/T 5103-2019: Design Code for 35kV～110kV Unmanned Substations

Frequently Asked Questions (FAQ)

1. What does a substation do?

Its main functions are to transform voltage, distribute electrical energy, and provide protection in the event of grid failures.

2. Are substations dangerous?

Substations are very safe when designed, constructed, and maintained according to regulations. There are strict national safety standards and protective measures.

3. Can substations explode?

Extremely rare. Modern protection systems effectively prevent serious accidents. Most accidents are caused by external factors such as extreme weather or traffic accidents.

4. How far should a residence or building be from a substation?

Regulations vary by region, but a safe distance of 3–10 meters is generally required. Consult your local power supply department or planning agency for specific advice.

5. Does a substation produce radiation?

It produces extremely low-frequency electromagnetic fields (EMF), but the intensity is comparable to that of household appliances. Authoritative organizations such as the World Health Organization confirm that there is no health risk at normal exposure levels.

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