In the realm of modern electricity distribution, Gas Insulated Switchgear (GIS) Substations represent
a pivotal advancement. These sophisticated systems play a crucial role by enhancing the efficiency, reliability, and safety of power transmission across various applications.
Table of Contents
A gas-insulated switchgear substation is a compact, metal-enclosed structure that houses high-voltage switchgear, busbars, and other electrical equipment. Unlike conventional Air Insulated Switchgear (AIS) Substations, which use open-air configurations, GIS substations utilize sulfur hexafluoride (SF6) gas as an insulating medium within metal-enclosed units. This design not only reduces the space requirement of substations but also enhances operational reliability and safety.
Enclosure
The common enclosure material is an aluminum alloy which is chosen for an enhanced combination of mechanical strength, electrical conductivity, resistance to atmospheric corrosion, and reasonable price. Casting, extrusion, and wrought production methods are used to manufacture the enclosures, depending upon their application. For example, the enclosure of a complex heavy duty switch may be cast aluminum and a bus enclosure may be extruded. Enclosure parts are also welded together sometimes.
COMPARTMENTALIZATION REQUIREMENTS
The components of the GIS substations come directly fitted in modules from the factory or the manufacturer. The assembly consists of separate modular compartments filled with gas and in a gas-tight partition so that maintenance in one feeder can be done without de-energizing the adjacent feeder. The compartmentalization is done to isolate the faulty section.
Phase segregation
All three phases can be assembled in a common metal enclosure or can be segregated in a separate metal enclosure depending upon cost consideration and three-phase fault rating value. In common practice, it is seen that up to 170 KV GIS no phase segregation is preferred.
Functionally the performance does not differ between three enclosures and a single enclosure.
GAS BARRIERS
To reduce the damaged area by a fault and to improve maintenance flexibility the GIS enclosure is subdivided into several compartments and the enclosure, gas barriers are used and are shown in orange or yellow color.
The Gas barrier is also called a resistant spacer which divides the bay into separate gas compartments that are sealed off from each other.
Acceessories
Flange joints that connect separate modules contain gaskets to prevent the leakage of gas. Therefore gas monitoring devices are installed for each compartment of the GIS enclosure.
For non switching compartments like CT, 1 Partial Discharge sensor is normally used at every 20meter distance.
For Switching compartments like disconnectors, circuit breakers etc 1 PD sensor is used for each module.
For each isolated gas compartment, 1 Gas density monitor is used, which indicates the density of the gas.
Space heaters are used in LCC panels and other cubicles.
In every gas compartment, 1 pressure relief device is installed. This device is installed to protect the main gas enclosure under the worst operating conditions and abnormal pressure rise which may be generated due to internal fault arcs. Although a protection system will interrupt the fault before a dangerous pressure is reached, PRD is used as a backup enclosure protection.
Each gas chamber is equipped with an absorber to remove the moisture and decomposed products from the gas chamber.
Advantages
The adoption of Gas Insulated Switchgear substations brings several compelling advantages:
Low area requirement Of GIS. Gis substations take a fraction of space as the same specification Ais substation will take. The fraction can be ranging from 1/10 to 1/25. The height of the substation is also reduced compared to the AIS substation’s switchyard.
Environmental adaptability of GIS. Gas Insulated Switchgear is suitable for installation almost anywhere in or out of doors, even underground, near the sea, in mountainous areas, in regions with heavy snowfall, etc.
High-margin safety of GIS. The high-voltage conductors are safely and securely enclosed in a grounded metal enclosure which enhances the margin of safety.
High reliability of GIS. The chemically inert SF6 enveloping the conductors and insulators preserves them for years of trouble-free operation.
Long maintenance intervals of GIS. SF6 gas’s arc-quenching properties reduce contact wear. Technological advancements over the years have seen Gas Insulated Switchgear continue to grow smaller and lighter.
Low Maintenance Cost of GIS: Gas Insulated Switchgear is highly reliable and maintenance-free. No inspection is required before ten years.
Long Life of GIS: The operating life of Gas Insulated Switchgear is 40 to 50 years compared to 25 to 30 years of conventional outdoor grid stations.
Personnel Safety in GIS: Gas Insulated Switchgear causes no risk of injury to operating personnel.
Short Circuits by Wildlife: Fully encapsulated enclosures reduce the risk of outages caused by lizards and vandalism.
Unbeatable Performance: Factory-assembled and tested units offer unbeatable performance in terms of reliability and continuity of power supply.
Unaffected by Environmental Conditions: Gas Insulated Switchgear is unaffected by environmental factors. It is most suitable for rough environmental conditions i.e. humid, saline, polluted atmospheric air where industrial exhausts are maximum.
Economical: GIS plants are more economical than conventional counterparts despite the high cost of Gas-insulated switchgear.
Applications and Deployment
Gas Insulated Switchgear substations find wide-ranging applications across various sectors:
Utility Sector: Integral to high voltage transmission and distribution networks, Gas Insulated Switchgear substations optimize grid efficiency and reliability.
Industrial Sector: Deployed in industrial complexes and critical facilities, Gas Insulated Switchgear substations ensure uninterrupted power supply and operational continuity.
Maintenance and Operational Considerations
Routine maintenance of Gas Insulated Switchgear substations involves periodic inspections, SF6 gas monitoring, and adherence to safety protocols. Emergency response procedures are meticulously planned to address any gas leaks or operational faults promptly, ensuring minimal disruption to the power supply.
Future Trends and Innovations
As technology evolves, GIS substations are poised to evolve as well:
Eco-friendly Alternatives: Ongoing research focuses on developing environmentally sustainable alternatives to SF6 gas, aligning with global initiatives for reducing greenhouse gas emissions.
Smart Grid Integration: Integration with smart grid technologies enhances the flexibility and efficiency of GIS substations, paving the way for real-time monitoring and grid management.
Conclusion:
GIS substations represent a paradigm shift in the field of power distribution, offering compactness, reliability, and safety unparalleled by traditional substations. As demands on electricity infrastructure grow, GIS technology continues to play a pivotal role in advancing the reliability and efficiency of power networks worldwide. Embracing GIS substations not only addresses current challenges but also positions us favorably for a sustainable and resilient energy future.
