Millisecond-level fault interruption! Hardcore full disassembly diagram of GIS equipment

In the intricate and interconnected power system, components like busbars, transmission lines, and transformers form a complex network. Any short circuit or overload at any point can trigger cascading failures, potentially leading to a grid collapse. In this issue, we delve straight into the "core" of GIS equipment! Through a series of "principle-level" dynamic schematic diagrams, combined with a precise structural breakdown, we vividly illustrate its core technical chain in ensuring grid safety under fully sealed conditions—from the powerful arc quenching of SF₆ gas and the clear isolation of disconnect switches, to the precise logic interlock of five-protection mechanisms and the reliable locking of grounding protection, all the way to the insulation guarantee provided by gas chamber sealing.

Technical Analysis and Application Research of SF₆ Gas-Insulated Metal-Enclosed Switchgear (GIS)

This paper takes CNKEEYA ELECTRIC’s GIS-220kV/145kV equipment as an example and analyzes it from four dimensions: technical principles, structural composition, installation and maintenance, and application scenarios, revealing the core advantages of gas-insulated metal-enclosed switchgear (GIS) in high-voltage power transmission. Through SF₆ gas insulation and a metal-enclosed structure, GIS achieves high reliability, compact design, and safe maintenance characteristics, making it suitable for critical power nodes such as grid hubs and substations. It provides technical support for the stable operation of modern power systems.

1. Introduction

With the increasing voltage levels of power systems and stricter requirements for power supply reliability, gas-insulated metal-enclosed switchgear (GIS) has become a core component in high-voltage/ultra-high-voltage power transmission due to its advantages such as high insulation strength, small footprint, and easy maintenance. Based on the technical diagram of CNKEEYA ELECTRIC’s GIS-220kV/145kV equipment, this paper systematically analyzes its technical principles, structural design, installation and maintenance, and application scenarios, providing theoretical and practical references for the selection, installation, and maintenance of GIS.

2. Technical Principles and Core Features

2.1 Working Principle: The "Open-Close" Logic of Circuit Breakers

The core operational unit of GIS is the circuit breaker (CB), whose "opening-closing" process relies on the insulation and arc-extinguishing properties of SF₆ gas:

Closing process: After receiving instructions from the control cabinet (Control System), the circuit breaker contacts close, allowing current to flow from the high-voltage source (High Voltage Source) through the main circuit to the low-voltage load (Low Voltage Load), completing power transmission.

Opening process: When the system detects a fault (e.g., a short circuit), a control signal triggers the separation of the circuit breaker contacts. The SF₆ gas decomposes under the high temperature of the arc, generating arc-extinguishing media to quickly quench the arc and cut off the fault current, ensuring grid safety.

Additionally, the disconnect switch (DS) provides visible breaking points, achieving electrical isolation during maintenance, while the earthing switch (ES) grounds the circuit during equipment maintenance to prevent injury from induced electricity.

2.2 Technical Parameters: Defining Performance Boundaries

Taking GIS-220kV/145kV as an example, the core technical parameters are as follows:

Rated voltage: 220kV / 145kV (adaptable to grids of different voltage levels);

Rated current: 3150A / 2500A (meeting high-power transmission requirements);

Rated frequency: 50Hz (matching the power frequency system);

Rated short-circuit current: 50kA (withstanding high-current impact during short-circuit faults);

SF₆ gas pressure: 0.35 MPa (20℃), ensuring insulation and arc-extinguishing performance;

Peak withstand current: 125kA (peak value of short-term short-circuit current withstand);

Lightning impulse withstand voltage: 1050kV (withstanding the damage caused by lightning overvoltage to the equipment).

These parameters collectively define GIS’s insulation level, current-carrying capacity, and fault tolerance limits, serving as the key basis for equipment selection and grid compatibility.

3. Structural Composition: Precision of Modular Design

GIS achieves high integration through "functional modules + metal enclosure + SF₆ gas insulation". The core structural components include:

Circuit breaker interrupter chamber (CB Interrupter Chamber): Carries the arc-extinguishing and breaking functions, with precise internal contact design to ensure the reliability of opening and closing operations;

Disconnect switch contact system (Disconnect Switch Contact System): Provides "visible breaking points" and achieves circuit isolation through mechanical linkage;

Basin insulator (Basin Insulator): Supports conductors and provides insulation between gas chambers, filled with SF₆ gas to ensure air tightness and insulation performance;

Epoxy insulator (Epoxy Insulator): Provides auxiliary insulation and mechanical support, with strong weather resistance to adapt to complex operating environments;

Current transformer (CT) and voltage transformer (PT): Realize power metering and protective signal acquisition;

Surge arrester (SA): Limits the amplitude of overvoltage, protecting equipment from damage caused by lightning or switching overvoltages;

Local control cabinet (LCCC): Integrates control, monitoring, and communication functions, enabling localized operation and status feedback of the equipment.

4. Installation and Maintenance: Balancing Safety and Efficiency

4.1 Installation Process: Precision Operations Ensure Reliability

The installation of GIS must follow the process of "hoisting, docking, and air-tightness testing":

Hoisting (Hoisting): Precisely hoist GIS modules to the predetermined position using lifting equipment to avoid collisions or deformation;

Docking (Docking): Connect modules through precise mechanical interfaces to ensure gas chamber sealing and reliable electrical connections;

Air-tightness testing: After filling with SF₆ gas, monitor pressure changes in the gas chambers to confirm no leakage (protective measures must be taken in case of SF₆ gas leakage, as per safety warnings).

During installation, it is essential to strictly control spatial positioning, torque calibration, and sealing tests to ensure the long-term stable operation of the equipment after commissioning.

4.2 Maintenance Focus: Condition Monitoring and Preventive Maintenance

GIS maintenance focuses on "visible status and defect pre-control":

Pressure monitoring: Monitor SF₆ gas pressure in real-time via pressure gauges. If abnormal pressure is detected (e.g., below 0.35 MPa), investigate and repair leaks, and replenish the gas;

Visual inspection: Regularly inspect equipment casings, contacts, and insulators to ensure no rust, looseness, or discharge traces;

Functional testing: Simulate opening and closing operations via the local control cabinet (LCCC) to verify the operational reliability of circuit breakers and disconnect switches.

The core of maintenance is "prevention first", identifying potential defects in advance through regular inspections to prevent fault escalation.

5. Application Scenarios: Adaptability to Critical Grid Nodes

GIS is suitable for scenarios with stringent requirements for "small footprint, high reliability, and low electromagnetic interference", such as:

Urban substations: GIS’s compact design significantly reduces the footprint of substations, adapting to the limited land resources in urban core areas;

Hub substations: High voltage levels (220kV) and strong short-circuit withstand capability (50kA) ensure regional grid power transmission and fault isolation;

Renewable energy grid integration: Low electromagnetic radiation and high reliability meet the "weak grid integration" requirements of wind and photovoltaic power stations, enhancing grid stability.

SF₆ gas-insulated metal-enclosed switchgear (GIS) achieves miniaturization, intelligence, and high reliability in high-voltage power systems through its innovative architecture of "gas insulation + metal enclosure + modular design". Technologically, the arc-extinguishing and insulation properties of SF₆ gas support the efficient opening and closing of circuit breakers. Structurally, modular design enhances maintainability and scalability. In practical applications, the widespread adaptability of GIS in urban grids, hub substations, and other scenarios demonstrates its core value in modern power systems. In the future, with the development of eco-friendly gases (e.g., dry air, fluorinated nitrogen) and advancements in digital maintenance technologies, GIS will further evolve toward "low-carbon, intelligent" development, continuing to safeguard grid security.