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GIS Testing

GIS or Gas-Insulated Switchgear is an electrically powered device utilized in various high-voltage power stations and substations. Its body is enclosed by solid metal and includes equipments like circuit breakers, switches and disconnectors. The GIS chamber is usually filled with an inert gas, Sulfur Hexafluoride (SF6), which has insulation properties.

The Working Principle of GIS

The GIS switchgear filled with an insulated gas, SF6, protects the distribution and supply of electrical power when necessary. The breaker contacts are closed normally. 

During a failure in the electrical system, these breakers get disconnected, forming an arc between them. These movements of breakers allow the high-pressure SF6 to enter the chamber while the arc is occurring. The characteristics of SF6 gas help the arc to get extinguished. 

As the arc extinguishes, the pressure of the SF6 gas also decreases, and it is stored in a low-pressure tank and then in a high-pressure tank when it is ready for reuse. The insulation of SF6 makes GIS much more reliable for medium and high-voltage powered substations.6

Types Of Tests Involved In GIS Testing

The usual test procedures according to IEC are as follows:

    • An AC voltage test
    • The Partial discharge measurement test
    • The Lightning Surge test

Laxmi Associates assist you with the following GIS testing procedures

GIS testing involves the following procedures:

  • Pre-test Preparations: Proper safety precautions and necessary equipment are arranged in this step to ensure a smooth testing procedure. The GIS system is also switched off for testing.
  • Insulation Resistance Test: It helps measure the resistance between the conductors and the ground. The test aims to detect any insulation deterioration or contamination that could result in a potential fault or failure.
  • Gas Leakage Test: The test ensures your GIS system has no leakages. If not done correctly, the whole switchgear system might fail or break down. The GIS system is pressurized with gas in this process.
  • Partial Discharge Test: The test detects voids, gaps, or insulation defects, which can lead to an eventual insulation breakdown. A high voltage is applied to the GIS system to detect and measure partial discharges.
  • Dielectric test: It tests the electrical strength of the GIS system by using high voltage for a specified period. This helps the GIS to prepare for high-voltage operations.
  • Mechanical Operation Test: This test checks the accuracy of GIS’s mechanical operations by operating the circuit breaker multiple times to ensure smooth working.

After GIS testing, a report is generated based on the issues identified. 

During GIS testing, it is mandatory to perform a voltage withstand test according to IEC’s standards. Laxmi Associates has experience of more than 15years in testing, with a large team of engineers and technicians.


GIS is designed to be reliable and compact with the working principle based on SF6. To fully utilize the functions of GIS, proper testing must be done. It ensures the reliability and security of the equipment. Moreover, the estimated service life of a gas-insulated switchgear is approximately 35 – 50 years, during which its insulation system has to withstand all voltage loads without maintenance; therefore, it should be tested regularly.


1. What are the different types of Substations?  

Electrical Substations are classified into several types depending on various factors:

Based on insulation

Based on services rendered

  • Transformer substation
  • Switching substation
  • Converting substation

2. What are the different  types of switchgears available in the market?

The different types of Switchgear available commonly are:

  • HV: High Voltage Switchgear
  • LV: Low Voltage Switchgear
  • MV: Medium Voltage Switchgear

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