Air-insulated switchgear (AIS) is essential in various electrical systems due to its specific advantages and suitability for different applications. But there are still many people don’t know if they need to choose AIS. So, here is the ultimate guide for you.
Air-insulated switchgear (AIS) is a type of switchgear where air is used as the primary insulation medium to separate electrical components within the system. This is in contrast to gas-insulated switchgear (GIS), which uses a gas such as sulfur hexafluoride (SF6) for insulation.
AIS has gained widespread acceptance due to its simplicity, reliability, and cost-effectiveness. This article explores the various aspects of air-insulated switchgear, including its standards, components, benefits, limitations, comparison with other types of switchgear, applications, installation, and maintenance.
Table of Contents
Electrical Standards Relevant to AIS
Several international standards govern the design, testing, and operation of AIS to ensure safety, reliability, and interoperability. Key standards include:
- IEC 62271 Series: International standards for high-voltage switchgear and controlgear, including specifications for AIS.
- IEEE C37 Series: Standards by the Institute of Electrical and Electronics Engineers covering various aspects of switchgear, including AIS.
- ANSI C37 Series: American National Standards Institute standards that align with IEEE but may have regional specificities.
The classification of Air Insulated Switchgears
1. Based on Voltage Level:
- Low Voltage Switchgear (LV): Typically used for voltages up to 1 kV.
- Medium Voltage Switchgear (MV): Used for voltages ranging from 1 kV to 36 kV.
- High Voltage Switchgear (HV): Used for voltages above 36 kV. High voltage air-insulated switchgear is less common than medium voltage due to the larger space required for insulation.
2. Based on Application:
- Indoor Switchgear:
- Designed for installation inside buildings.
- Common in industries and commercial buildings.
- Provides protection against environmental conditions like rain, dust, and pollutants.
- Outdoor Switchgear:
- Designed for installation outside, exposed to environmental conditions.
- Typically used in substations or open switchyards.
- Requires weatherproof enclosures or shelters.
3. Based on Configuration:
- Fixed Type Switchgear:
- Components such as circuit breakers, relays, and meters are fixed and not removable without significant disassembly.
- More economical but requires more time and effort for maintenance.
- Withdrawable Type Switchgear:
- Components, especially circuit breakers, are mounted on carriages and can be easily removed for maintenance or replacement.
- Offers better flexibility and safety during maintenance activities.
4. Based on Design:
- Metal-Clad Switchgear:
- Components are enclosed in metal compartments, providing a high degree of safety.
- Each functional unit is separated by earthed metal partitions.
- Metal-Enclosed Switchgear:
- All live parts are enclosed in a metal enclosure, but the compartments are not fully partitioned like in metal-clad switchgear.
- Compartmentalized Switchgear:
- Similar to metal-clad, but each compartment may not be as strictly isolated. Offers a balance between cost and safety.
5. Based on Functionality:
- Switchboards:
- Used mainly in LV and MV applications for distributing electricity to different circuits.
- Ring Main Units (RMU):
- Typically used in MV networks to ensure the continuity of supply and the protection of downstream equipment.
- Control Gear:
- Includes switchgear that provides control functions, such as motor control centers (MCC).
6. Based on Interrupting Medium:
- Air Circuit Breakers (ACB):
- Uses air as the interrupting medium, commonly used in low voltage applications.
- Vacuum Circuit Breakers (VCB):
- Uses a vacuum as the interrupting medium but is housed within an air-insulated switchgear. Common in medium voltage applications.
- SF6 Circuit Breakers:
- While SF6 is the interrupting medium, the overall switchgear may still be air-insulated. These are typically used in higher voltage applications.
7. Based on Standard Compliance:
- IEC Standard Compliant Switchgear:
- Designed and tested according to International Electrotechnical Commission (IEC) standards.
- ANSI Standard Compliant Switchgear:
- Designed according to American National Standards Institute (ANSI) standards.
- Local Standards Compliant Switchgear:
- Designed to meet specific local standards, which may vary by region or country.
8. Based on Operational Features:
- Manual Operation:
- Operated manually by an operator using physical switches and controls.
- Motorized Operation:
- Equipped with motorized actuators for remote or automated operation.
Key Components of Air Insulated Switchgear
1. Circuit Breaker (CB)
- Function: Interrupts and isolates faults in the electrical circuit to protect the system.
- Types: Vacuum Circuit Breakers (VCB) and SF6 Circuit Breakers.
- Components: Moving contacts, fixed contacts, operating mechanism, arc chute.
2. Busbars
- Function: Conducts electrical power within the switchgear from incoming to outgoing feeders.
- Material: Typically made of copper or aluminum, coated to prevent oxidation.
- Arrangement: Can be single busbar, double busbar, or sectionalized busbar.
3. Disconnectors (Isolators)
- Function: Isolates parts of the switchgear for maintenance, ensuring that sections are de-energized.
- Components: Blades, operating mechanism, interlocking system.
4. Instrument Transformers
- Types:
- Current Transformers (CTs): Measure current for metering and protection.
- Voltage Transformers (VTs): Step down voltage for metering and protection.
- Function: Provide accurate readings for control, protection, and metering systems.
5. Earthing Switches
- Function: Safely discharge residual electrical energy to the earth, ensuring safety during maintenance.
- Components: Contacts, operating mechanism, interlocking system.
6. Protection Relays
- Function: Monitor the electrical system and trigger circuit breakers in case of faults (overcurrent, earth fault, etc.).
- Types: Numerical relays, electromechanical relays.
- Components: Sensing elements, processing units, tripping circuits.
7. Operating Mechanism
- Function: Mechanically operates the circuit breakers and disconnectors.
- Types: Spring-operated, motor-operated, or pneumatic mechanisms.
- Components: Motors, springs, cams, linkages.
8. Control Panels
- Function: Interface for the operator to control, monitor, and configure the switchgear.
- Components: Switches, indicators, meters, pushbuttons, HMI (Human-Machine Interface).
9. Enclosures
- Function: Provides physical protection for the internal components and ensures safety by preventing access to live parts.
- Material: Usually made of metal (steel or aluminum) with an insulated coating.
- Types: Indoor or outdoor, IP rated for environmental protection.
10. Busbar Supports and Insulators
- Function: Physically support and electrically isolate the busbars.
- Material: Made of epoxy resin, porcelain, or other insulating materials.
11. Cable Termination and Connections
- Function: Connects external cables to the switchgear, ensuring a secure electrical connection.
- Types: Heat shrink terminations, cold shrink terminations.
- Components: Connectors, bushings, sealing materials.
12. Arc Chutes
- Function: Extinguishes the arc formed when a circuit breaker interrupts a fault current.
- Material: Insulating materials with high thermal resistance, often ceramic or composites.
13. Surge Arresters
- Function: Protects the switchgear and connected equipment from voltage surges due to lightning or switching operations.
- Components: Non-linear resistors, spark gaps.
14. Interlocking System
- Function: Prevents unsafe operations by ensuring a correct sequence of actions (e.g., ensuring a breaker cannot be closed if the disconnector is open).
- Types: Mechanical, electrical, or electromechanical interlocks.
15. Ventilation System
- Function: Dissipates heat generated by electrical losses, maintaining optimal operating temperatures.
- Components: Fans, louvers, filters.
How Air Insulated Switchgear Works
AIS operates by using air as the insulating medium between live parts and grounded components. When a fault occurs, such as a short circuit, the circuit breaker opens to interrupt the current flow. The arc generated during this process is extinguished in the air, typically aided by the design of the interrupter, which cools and stretches the arc until it is extinguished.
Advantages of Air Insulated Switchgear
- Cost-Effective: Generally less expensive compared to Gas Insulated Switchgear (GIS) due to simpler construction and lower material costs.
- Ease of Installation and Maintenance: AIS systems are modular and easier to assemble on-site. Maintenance is straightforward since components are more accessible.
- Flexibility: Suitable for a wide range of applications and can be easily expanded or modified.
- Proven Technology: AIS has been widely used for many decades, ensuring reliability and a wealth of operational experience.
Disdvantages of Air Insulated Switchgear
- Space Requirements: AIS typically requires more physical space compared to GIS, making it less suitable for areas with limited space.
- Environmental Sensitivity: Air-based insulation can be affected by environmental conditions such as pollution, humidity, and temperature, potentially impacting performance.
- Higher Maintenance Needs: Although maintenance is easier, AIS may require more frequent inspections and upkeep compared to GIS.
Applications of Air Insulated Switchgear
- Utility Power Distribution: Used in substations for distributing electrical power at medium and high voltages.
- Industrial Facilities: Provides reliable power control and protection in manufacturing plants, refineries, and other industrial settings.
- Commercial Buildings: Ensures safe and efficient power distribution within large commercial complexes.
- Renewable Energy Plants: Integrates with wind farms, solar power installations, and other renewable energy sources for grid connection.
Comparison Between Air Insulated and Gas Insulated Switchgear
While AIS uses air for insulation, Gas Insulated Switchgear (GIS) employs insulating gases, typically Sulfur Hexafluoride (SF₆), to provide higher insulation levels in a more compact space. Here’s a brief comparison:
| Feature | AIS | GIS |
|---|---|---|
| Insulating Medium | Air | SF₆ Gas |
| Size | Larger footprint | Compact and space-saving |
| Cost | Generally lower initial cost | Higher initial investment |
| Installation | Easier to install in open environments | Suitable for confined or limited spaces |
| Maintenance | More accessible for maintenance | Requires specialized handling due to SF₆ |
| Environmental Impact | Less environmental risk (no SF₆) | SF₆ is a potent greenhouse gas |
| Application | Ideal for open substations and areas with ample space | Preferred in urban areas, indoor installations |
Choosing AIS for Your Needs
When selecting switchgear for a specific application, several factors need to be considered:
- Space Availability: AIS is suitable when ample space is available, whereas GIS is better for space-constrained environments.
- Budget Constraints: AIS offers a cost-effective solution with lower initial investment.
- Environmental Conditions: AIS may be preferred in cleaner environments to minimize insulation issues.
- Maintenance Capabilities: AIS allows easier access for routine maintenance and inspections.
- Future Expansion: AIS offers greater flexibility for system expansions or modifications.
Installation of Air Insulated Switchgear
Site Preparation:
- Ensure the site is dry, clean, and free from dust and moisture.
- Maintain a stable temperature environment to prevent condensation.
- Adequate ventilation must be ensured to prevent overheating of the switchgear.
Foundation and Mounting:
- The switchgear should be installed on a level, vibration-free foundation.
- Use suitable mounting hardware to securely anchor the switchgear to the foundation.
- Ensure proper alignment of all switchgear panels and sections to facilitate easy interconnection.
Cable Connection:
- Use appropriate cable lugs and terminals to connect the cables.
- Ensure that the cable connections are tight and secure to avoid any loose connections that could lead to arcing.
- Route cables carefully to avoid sharp bends and excessive strain on terminals.
Grounding:
- Ensure that the switchgear is properly grounded to prevent electric shock and equipment damage.
- Use grounding cables of adequate size, and ensure they are securely connected to the switchgear and the ground grid.
Busbar Connection:
- Ensure all busbar connections are clean and free from any oxidation or contamination.
- Tighten the busbar connections according to the manufacturer’s torque specifications.
Testing:
- Perform insulation resistance tests on the switchgear components before energizing.
- Conduct functional tests, such as checking the operation of circuit breakers, relays, and control systems.
- Verify the operation of protective devices and settings.
Commissioning:
- Once installation and testing are completed, the switchgear can be energized.
- Monitor the switchgear for any abnormal conditions during the initial energization phase.
Maintenance of Air Insulated Switchgear
Routine Inspection:
- Conduct regular visual inspections for signs of wear, corrosion, or damage to the switchgear components.
- Check for any abnormal noise, smell, or signs of overheating during operation.
Cleaning:
- Keep the switchgear clean and free from dust, dirt, and moisture.
- Use a vacuum cleaner or dry cloth to remove dust; avoid using water or any cleaning agents that may cause corrosion.
Lubrication:
- Lubricate moving parts such as circuit breaker mechanisms, hinge points, and operating handles according to the manufacturer’s recommendations.
- Use only the recommended lubricants to avoid contamination or damage to components.
Tightening Connections:
- Periodically check and retighten all electrical connections, including busbars, terminals, and grounding points.
- Ensure that the connections are within the specified torque settings to prevent loose connections and arcing.
Testing and Calibration:
- Perform regular insulation resistance tests to ensure the integrity of the insulation.
- Test and calibrate protective relays and devices to ensure they operate correctly and within the desired parameters.
- Conduct contact resistance measurements to check the condition of contacts in circuit breakers and disconnect switches.
Component Replacement:
- Replace worn or damaged components such as circuit breakers, fuses, or relays as needed.
- Use only manufacturer-approved parts to maintain the performance and safety of the switchgear.
Periodic Shutdown and Detailed Inspection:
- Schedule periodic shutdowns for detailed inspections and maintenance of internal components.
- Inspect and clean the busbars, insulation barriers, and switchgear housing.
- Verify the condition of the arc quenching medium (if applicable) and replace it if necessary.
Record Keeping:
- Maintain detailed records of all maintenance activities, including tests, inspections, and component replacements.
- Use these records to track the performance of the switchgear and to plan future maintenance activities.
Safety Precautions:
- Always follow proper lockout/tagout procedures before performing any maintenance or inspection.
- Use appropriate personal protective equipment (PPE) such as insulated gloves, safety glasses, and flame-resistant clothing.
- Ensure that all personnel working on the switchgear are adequately trained and aware of the safety procedures.
Recent Developments and Trends in Air Insulated Switchgear
In recent years, there has been a focus on enhancing the eco-efficiency of AIS by developing more sustainable materials and designs. The continuous improvement in AIS technology aims to reduce environmental impact, particularly by minimizing the use of materials with high carbon footprints.
Summary
Air Insulated Switchgear is a reliable, cost-effective solution widely used in various electrical power distribution applications. Its simplicity, ease of maintenance, and proven performance make it a preferred choice for many utilities and industries. However, considerations such as space constraints and environmental factors may lead to the selection of alternative solutions like Gas Insulated Switchgear in certain scenarios.
