What is Gas Insulated Substation?
A Gas Insulated Substation (GIS) is an advanced type of electrical substation where major electrical equipment, such as circuit breakers, bus bars, and disconnectors, are encapsulated in a metal enclosure filled with SF₆ gas. The gas acts as an insulating and arc-extinguishing medium.
Diagram Explanation
Figure 1.
The figure 1 illustrates a GIS system, highlighting components such as:
- Gas bushing for high-voltage connections.
- SF₆ gas breakers for circuit protection.
- Bus bars (Bus A and Bus B) for power transfer.
- Grounding switches, disconnectors, and high-duty arresters for enhanced functionality.
Construction of Gas Insulated Substation (GIS)
The main components of a GIS include:
| Component | Description |
|---|---|
| SF₆ Gas | Primary insulating medium with high dielectric strength and arc-quenching properties. |
| Gas Bushing | Connects the GIS to high-voltage lines, ensuring proper insulation and support. |
| Circuit Breaker | Encased in SF₆ gas for fault interruption and circuit protection. |
| Disconnector and Grounding Switch | Ensures safe isolation and grounding for maintenance operations. |
| Bus Bars | Conduct power between different GIS sections, insulated by SF₆ gas. |
| Current Transformer (CT) | Measures current for protection and metering purposes. |
| Voltage Transformer (VT) | Provides voltage measurement for control and monitoring. |
| Spacer | Maintains physical separation between GIS components. |
| High-Duty Arrester | Protects GIS components from lightning and switching surges. |
| Enclosures | Metal enclosures (aluminum or stainless steel) protect components and prevent gas leakage. |
Working of Gas Insulated Substation (GIS)
GIS operates on the same principle as a conventional substation but utilizes SF₆ gas for insulation and arc extinction. Key steps include:
- Insulation: SF₆ gas surrounds the live components, providing high dielectric strength and preventing electrical breakdown.
- Current Flow: Electrical power is transmitted through bus bars, switchgear, and transformers enclosed in the GIS.
- Fault Protection: Circuit breakers, protected by SF₆ gas, interrupt current flow during faults.
- Switching: Disconnectors isolate parts of the GIS, and grounding switches ensure maintenance safety.
Types of Gas Insulated Substation (GIS)
- Isolated Phase GIS: Each phase is enclosed in a separate compartment.
- Integrated 3-Phase GIS: All three phases share a single enclosure.
- Hybrid GIS: Combines air-insulated and gas-insulated technology.
- Compact GIS: Designed for limited spaces, with reduced dimensions.
Difference between Air Insulated Substation (AIS) and Gas Insulated Substation (GIS)
| Feature | Air Insulated Substation (AIS) | Gas Insulated Substation (GIS) |
|---|---|---|
| Insulation Medium | Uses air as the primary insulation medium. | Uses SF₆ gas as the primary insulation medium. |
| Space Requirement | Requires large space due to open-air design. | Compact design requires significantly less space. |
| Cost | Lower initial cost. | Higher initial cost due to equipment and gas handling. |
| Maintenance | Higher maintenance due to exposure to environmental factors. | Low maintenance due to enclosed design. |
| Reliability | Less reliable in extreme weather conditions. | Highly reliable in harsh environments. |
| Environmental Impact | No significant environmental concerns. | SF₆ gas is a potent greenhouse gas. |
| Application | Suitable for rural and less space-constrained areas. | Ideal for urban areas and space-constrained locations. |
Advantages of Gas Insulated Substation (GIS)
- Space-Saving Design: Ideal for urban areas and indoor installations.
- High Reliability: SF₆ insulation minimizes the risk of faults.
- Low Maintenance: Enclosed components reduce exposure to environmental conditions.
- Safety: Gas enclosure prevents electrical hazards.
- Environmental Resistance: Performs well in extreme weather conditions.
Disadvantages of Gas Insulated Substation (GIS)
- High Cost: Initial setup and SF₆ gas handling increase expenses.
- Environmental Concerns: SF₆ is a potent greenhouse gas.
- Complex Repairs: Specialized knowledge and equipment are needed.
- Gas Leakage Risks: Leaks can lead to system inefficiencies and safety issues.
Applications of Gas Insulated Substation (GIS)
- Urban Substations: Compact design suits dense city environments.
- Power Transmission: Efficient in transmitting high-voltage power over long distances.
- Industrial Facilities: Serves industries requiring high reliability.
- Renewable Energy: Integrates seamlessly with wind and solar farms.
- Critical Installations: Used in airports, railways, and data centers where downtime is not an option.