Hybrid Gas Insulated Switchgear (HGIS) 72.5kV for 66kV-class transmission and sub-transmission substations

Switchgear (HGIS) 72.5kV

1. General Description

72.5kV Hybrid Gas Insulated Switchgear (HGIS) is a high-voltage switchgear solution that combines the advantages of Gas Insulated Switchgear (GIS) and Air Insulated Switchgear (AIS). It integrates major switching components such as the circuit breaker, disconnectors, earthing switches, current transformers, and voltage transformers into a compact gas-insulated module, while maintaining external air-insulated connections for busbars or line interfaces.

HGIS is designed for 66kV-class transmission and sub-transmission substations, where reduced footprint, high reliability, and easier expansion are required.

2. Typical Technical Specifications
·Equipment Type: Hybrid Gas Insulated Switchgear (HGIS)
·Rated Voltage: 72.5 kV
·System Voltage Class: 66 kV
·Rated Frequency: 50 / 60 Hz
·Rated Current: 1250 / 2000 / 3150 A
·Short-Time Withstand Current: 25 / 31.5 / 40 kA (3 s)
·Short-Circuit Breaking Current: 25–40 kA
·Peak Withstand Current: 63–100 kAp
·Power Frequency Withstand Voltage: 140 kV (typical)
·Lightning Impulse Withstand Voltage (BIL): 325 kVp
·Insulation Medium: SF6 / alternative insulating gas
·Circuit Breaker Type: SF6 or Vacuum Interrupter
·Installation: Outdoor / Indoor GIS building
·Protection Class: Metal enclosed, sealed gas compartments

3. Main Components

1.) Gas Insulated Circuit Breaker Module
·Located inside a sealed gas enclosure
·Provides fault interruption and load switching
Available with:
·SF6 interrupter technology
·Vacuum interrupter technology
Functions:
·Short-circuit clearing
·Transformer switching
·Line switching
·System protection

2.) Disconnect Switches
·Gas-insulated disconnectors provide reliable isolation
Used for:
·Maintenance
·Equipment separation
·Bus transfer operations

3.) Earthing Switches
Types:
·Standard earthing switch
·High-speed earthing switch
Functions:
·Grounds isolated sections
·Improves operator safety
·Removes induced voltages

4.) Current Transformer (CT)
Integrated CTs provide:
·Protection signals
·Metering measurement
·Fault monitoring
Common applications:
·Overcurrent protection
·Differential protection
·Distance protection

5.) Voltage Transformer (VT/CVT)
Used for:
·Voltage measurement
·Synchronization
·Protection relay input

6.) Air-Insulated Connection Section
HGIS typically connects to:
·AIS busbars
·Overhead lines
·Power transformers
·Cable terminations
·This allows easier integration with existing substations.

4. Advantages of 72.5kV HGIS
* Compact Design
·Requires less space than conventional AIS
·Smaller substation layout
* Higher Reliability
·Critical switching equipment is protected inside gas compartments
Less affected by:
·Dust
·Humidity
·Pollution
·Salt contamination
* Easier Expansion
·Compatible with existing AIS substations
·Simplifies retrofit projects
* Lower Cost Compared with Full GIS
·Uses fewer gas-insulated sections
·Reduces investment while maintaining GIS benefits
* Reduced Maintenance
·Sealed modules require less cleaning and inspection

5. Typical Applications
72.5kV HGIS is widely used in:
·66kV transmission substations
·Renewable energy substations
·Wind power collection systems
·Solar power plants
·Industrial substations
·Urban substations
·Railway traction substations
·Substation modernization and expansion projects

6. Typical Busbar Arrangements
Common configurations:
Single Busbar
·Simple and economical
·Used for smaller substations
Double Busbar
·Provides operational flexibility
·Allows maintenance without full shutdown
Ring Bus
·Improves supply reliability
Breaker-and-a-Half
·Used for important transmission nodes

7. Applicable Standards
·IEC 62271-1 — High-voltage switchgear common requirements
·IEC 62271-100 — High-voltage AC circuit breakers
·IEC 62271-102 — Disconnectors and earthing switches
·IEC 62271-203 — Gas-insulated metal-enclosed switchgear above 52kV
·IEEE C37 series — High-voltage switchgear requirements

Summary
72.5kV Hybrid Gas Insulated Switchgear (HGIS) is a 66kV-class compact high-voltage switching system combining GIS-protected primary equipment with AIS connections. It typically supports 1250–3150A rated current and 25–40kA short-circuit capability, offering a balance of compact size, reliability, cost efficiency, and easy integration for modern transmission and industrial substations.