Hybrid Gas Insulated Switchgear (HGIS) 126kV for flexibility and lower cost solution

Switchgear (HGIS) 126kV

1. General Description

126kV Hybrid Gas Insulated Switchgear (HGIS) is an extra-high-voltage switching system that combines the compactness and reliability of Gas Insulated Switchgear (GIS) with the flexibility and lower cost of Air Insulated Switchgear (AIS).

The main switching equipment—including the circuit breaker, disconnectors, earthing switches, current transformers (CT), and voltage transformers (VT)—is installed inside sealed gas-insulated modules, while external connections such as busbars, overhead lines, and transformer connections may remain air-insulated.

The 126kV HGIS class is commonly applied in 110kV/115kV/132kV transmission and sub-transmission networks.

2. Typical Technical Specifications
·Equipment Type: Hybrid Gas Insulated Switchgear (HGIS)
·Rated Voltage: 126 kV
·System Voltage Class: 110 / 115 / 132 kV
·Rated Frequency: 50 / 60 Hz
·Rated Current: 2000 / 3150 / 4000 A
·Short-Time Withstand Current: 31.5 / 40 / 50 kA (3 s)
·Short-Circuit Breaking Current: 31.5–50 kA
·Peak Withstand Current: 80–125 kAp
·Power Frequency Withstand Voltage: Approx. 230 kV
·Lightning Impulse Withstand Voltage (BIL): 550 kVp
·Insulation Medium: SF6 or eco-friendly gas
·Circuit Breaker Type: SF6 or Vacuum Interrupter
·Installation: Outdoor / Indoor GIS hall
·Enclosure: Single-phase or three-phase encapsulated

3. Main Components

1.) High Voltage Circuit Breaker
·The HGIS circuit breaker is installed in a gas-insulated enclosure.
Functions:
·Interrupts short-circuit currents
·Switches transmission lines
·Protects transformers and generators
Typical technologies:
·SF6 self-blast interrupter
·Vacuum interrupter (for selected designs)

2.) Gas Insulated Disconnector
Provides:
·Electrical isolation
·Safe maintenance conditions
·Bus transfer operations
Features:
·Compact structure
·High mechanical reliability
·Low maintenance requirement

3.) Earthing Switch
·Provides grounding of isolated sections.
Types:
·Maintenance earthing switch
·High-speed earthing switch
Functions:
·Discharges trapped charge
·Ensures personnel safety
·Handles induced voltage grounding

4.) Current Transformer (CT)
Integrated CT units provide:
·Protection measurement
·Revenue metering
·Fault detection
Typical protection applications:
·Distance protection
·Differential protection
·Overcurrent protection

5.) Voltage Transformer (VT/CVT)
Provides voltage signals for:
·Protection relays
·Metering systems
·Synchronizing equipment

6.) AIS Connection Interface
The hybrid design allows connection to:
·Air-insulated busbars
·Overhead transmission lines
·Power transformers
·Cable systems

This makes HGIS suitable for upgrading existing substations.

4. Advantages of 126kV HGIS
* Reduced Substation Footprint
·Requires significantly less space than conventional AIS
·Suitable for urban and industrial sites
* High Reliability
Gas-insulated components are protected from:
·Dust
·Rain
·Salt pollution
·Industrial contamination
* Cost Optimization
Compared with full GIS:
·Less gas-insulated equipment
·Lower investment cost
·Easier installation
* Easier Retrofit
Ideal for:
·AIS replacement projects
·Substation expansion
·Capacity upgrades
* Lower Maintenance
·Sealed primary components
·Reduced cleaning requirements
·Stable insulation performance

5. Typical Applications
126kV HGIS is widely used for:
·110kV transmission substations
·132kV grid substations
·Renewable energy collector substations
·Hydropower plants
·Wind and solar power stations
·Industrial power networks
·Railway electrification systems
·Urban grid reinforcement projects

6. Common Arrangement Schemes
Single Busbar
·Economical configuration
·Suitable for smaller substations
Double Busbar
·Higher operational flexibility
·Allows maintenance without total shutdown
Ring Bus
·Improved supply continuity
Breaker-and-a-Half
·Used in important transmission substations

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 standards

Summary
126kV Hybrid Gas Insulated Switchgear (HGIS) is a 110/132kV-class high-voltage switching solution combining GIS reliability with AIS flexibility. It typically provides 2000–4000A continuous current capability and 31.5–50kA short-circuit interruption capacity, making it suitable for modern transmission substations, renewable energy projects, and substation modernization where space, reliability, and cost efficiency are important.