GIS Circuit Breaker Testing Without Disconnecting the Ground Connection – Is It Possible?

Gas-insulated substations (GIS) are among the most compact and reliable solutions in high-voltage power systems. However, when it comes to maintenance and testing, they present a unique challenge – one that has complicated the work of testing personnel for years.

The Problem with Conventional Testing

In a GIS substation, all high-voltage components – circuit breaker interrupters, disconnectors, grounding switches, current transformers – are encapsulated within SF6 gas inside grounded metal enclosures. This means direct access to the circuit breaker’s main circuit terminals is not possible.

To perform timing or contact resistance measurements using conventional methods, testing personnel must first disconnect the ground connection on one side of the breaker. This step is necessary to eliminate the parallel circuit formed through the enclosure and grounding path – but it comes at a cost. It reduces the safety of the test procedure and makes the entire maintenance process significantly more time-consuming compared to other substation types.

A New Approach – Both Sides Grounded (BSG)

DV Power developed the Both Sides Grounded (BSG) method specifically to address these shortcomings. Instead of requiring ground disconnection, the method is based on high DC current injection through the parallel connection of the main circuit and grounding path, while simultaneously measuring the current signal response – either on the secondary of the current transformers (CT) or at the primary circuit terminals – during circuit breaker operation.

The result: accurate timing and contact resistance measurements, with both sides of the breaker remaining grounded throughout the test.

How It Works in the Field

The BSG method is performed using the GIS Test Module in combination with the CAT500 circuit breaker analyzer. The GIS Test Module contains three battery-based current sources, each capable of generating 400 A DC, connected to the GIS circuit breaker access points via test cables.

Test terminals (detachable shunts) at the GIS enclosure

For timing, the current response signal is recorded through the primary circuit at the test terminals (detachable shunts) where available, using AC current probes. If primary detachable shunts are not accessible, as an alternative to record the current response signal during breaker operation the CT secondary terminals (wires) can be used.

For contact resistance measurement, the method follows automatic steps based on the Kelvin four-point method and Ohm’s law:

• Measurement of the open circuit resistance (R_gr) of the grounding path and GIS enclosure
• Measurement of the closed circuit resistance (R_p) of the parallel connection of the main circuit and grounding path
• Automatic calculation of the main circuit resistance (R_c)

The CAT500 handles all calculations automatically, with the option to measure all three phases simultaneously or each phase individually.

Connection setup for GIS timing measurement using the GIS Test Module and CAT500

Why It Matters

The BSG method represents a significant step forward in GIS substation maintenance. By eliminating the need to disconnect the ground, it:

• Reduces safety risks during the test procedure
• Shortens maintenance time
• Simplifies the overall testing workflow
• Enables non-invasive condition assessment of GIS circuit breakers

As GIS installations continue to grow globally, the demand for safer and more efficient test methods will only increase. The Both Sides Grounded approach offers a practical, field-proven solution that meets that demand.

Learn More

For full technical details on connection setup, measurement procedure, and device configuration, download our Application Note:
Test Method for Timing and Contact Resistance Measurement of GIS Circuit Breaker with Both Sides Grounded.

July 31, 2026