Gas insulated substation is employed

Question

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Option A: Where there is less space available

Explanation & Concepts:
Gas Insulated Substations (GIS) utilize Sulfur Hexafluoride ($SF_6$) gas as an insulating medium, which has a significantly higher dielectric strength than air. Because of this, the physical dimensions of the substation components can be reduced by 70% to 90% compared to conventional Air Insulated Substations (AIS), making GIS ideal for installations where land space is scarce or expensive.

Working Principle: The GIS uses a metal-enclosed design where live conductors are supported by spacers within a grounded metal enclosure filled with pressurized $SF_6$ gas. The superior ionization potential of $SF_6$ allows for much smaller clearance distances ($d_{min} \propto \frac{V}{E_{breakdown}}$) between phases and between phases and ground. This compact, encapsulated design protects the insulation from environmental factors like pollution, humidity, and salt spray.

Key Formulas: $E_b = k \cdot p$; $V_{flashover} \approx d \cdot E_b$

Key Points: SF6 is an electronegative gas with high dielectric strength and excellent arc-quenching properties.; GIS components are modular, facilitating faster assembly and minimal site maintenance.; The sealed enclosure renders the substation immune to external atmospheric pollution.; Reduced land acquisition costs significantly offset the higher equipment costs of GIS.

Advantages: Requires significantly less space (compact footprint).; High reliability and lower maintenance requirements.; Immune to environmental pollution and salt deposits.; Safe to touch as all high voltage parts are enclosed in earthed metal.

Disadvantages: High initial investment cost compared to AIS.; Complex installation process requiring specialized tools.; SF6 is a potent greenhouse gas, necessitating strict leakage control.

Applications: Urban city centers where land is extremely expensive.; Underground substations.; Offshore platforms and ships.; Industrial plants with limited space.

Additional Info: SF6 gas is chemically inert, non-toxic, and non-flammable.. GIS is generally used for voltage levels ranging from 66kV up to 800kV and beyond.. Option B (high altitude) can be a factor, but the primary universal driver is space constraint; Option C is incorrect as terrain does not mandate GIS over AIS.

Answer: A is correct — Gas Insulated Substations are primarily deployed in space-constrained areas due to the high dielectric strength of $SF_6$ gas allowing for significantly reduced clearance requirements.

Exam Tip: Always remember that while AIS is cost-effective for rural areas, GIS is the standard for urban planning; look for keywords like 'footprint' or 'enclosure' in exams to identify GIS questions.

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Option B: For high altitude locations

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Option C: In terrain region

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Option D: All of above

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