Why Keep Gas Moisture Below 15 ppm in Eco-Friendly Switchgear?

Moisture is a small number on a test report, but it can have a direct effect on the insulation performance of gas-insulated switchgear. This is why gas moisture is usually controlled to a very low level during manufacturing and gas filling.

For some eco-friendly switchgear designs, the moisture requirement may be specified below 15 ppm. But why 15 ppm? And what can happen if the moisture level is too high?

Moisture Can Affect Insulation Performance

Gas-insulated switchgear relies on the insulation system to maintain the required dielectric strength between live parts and between live parts and ground. The insulation system is not determined by the insulating gas alone. Gas pressure, temperature, solid insulation, surface condition and moisture level can all have an influence.

When the gas contains excessive moisture, the insulation conditions can become less stable, especially when the equipment operates under temperature changes. Moisture may also accumulate on internal insulating surfaces if local conditions allow condensation to occur.

That is why moisture control is part of the overall quality control for eco-friendly gas-insulated switchgear.

What Does “Below 15 ppm” Mean?

A moisture level below 15 ppm by volume means that the amount of water contained in the insulating gas is very low. Such a requirement is not simply a number used for marketing. It normally reflects the gas quality and insulation requirements of a specific product design.

It is also important to note that 15 ppm should not be treated as a universal limit for every type of gas-insulated switchgear. The appropriate moisture value depends on the insulating medium, gas pressure, equipment design, operating temperature and applicable technical requirements, such as IEC 62271-1 and relevant national standards. In practice, moisture content is typically verified by dew point measurement or Karl Fischer titration.

In other words, the moisture requirement should be considered together with the complete insulation system rather than viewed separately.

How Is Low Moisture Achieved During Manufacturing?

Keeping moisture below the specified level requires more than using dry gas during final filling. Moisture can come from different parts of the manufacturing process, including insulating materials, internal surfaces, assembly conditions and storage.

Manufacturers normally pay attention to several points:

l Internal parts and insulating materials should be properly dried before assembly.

l The assembly environment should be controlled to reduce moisture entering the equipment.

l The gas filling process should use gas with controlled moisture content.

l Vacuum evacuation can help remove residual air and moisture before gas filling.

l Sealing performance is important because the equipment is designed as a closed insulation system.

l Moisture testing can be carried out during production or before delivery according to the applicable inspection requirements.

These details may not be visible after the switchgear is assembled, but they can have a significant effect on its long-term insulation performance.

Why Is Moisture Control Important for SF₆-Free Switchgear?

The move toward SF₆-free and lower-environmental-impact insulation solutions has brought more attention to gas properties and insulation design. Different eco-friendly gas-insulated switchgear technologies may use dry air, nitrogen-based mixtures, vacuum insulation combined with solid insulation, or other insulation media.

Each solution has its own electrical and physical characteristics. Therefore, moisture control should be considered together with the selected insulation medium and the actual construction of the switchgear.

For sealed equipment, keeping the internal environment stable from the factory is particularly important. Good moisture control at the manufacturing stage provides a better starting condition for subsequent operation.

Moisture Control Is Part of Product Quality

A gas moisture value on a test report may look like a very small detail, but it reflects several aspects of manufacturing quality: material preparation, assembly conditions, gas handling, vacuum treatment and sealing.

For eco-friendly gas-insulated switchgear, these processes work together with the insulation design to provide reliable electrical performance.

This is why manufacturers pay close attention to moisture during production instead of treating it as a final inspection item only.

Conclusion

Keeping gas moisture below 15 ppm can help maintain stable insulation conditions and reduce the possibility of moisture-related problems inside sealed switchgear. However, the exact moisture requirement should always be considered according to the gas type, equipment design and applicable technical specifications.

For manufacturers of eco-friendly gas-insulated switchgear, moisture control is therefore not an isolated parameter. It is one part of the overall manufacturing process that supports the reliability and service performance of the finished product.

About TAILI Electric

TAILI Electric manufactures eco-friendly gas-insulated switchgear for medium-voltage distribution. Moisture control is integrated into our manufacturing process—from drying internal components and controlling assembly humidity to vacuum evacuation and gas filling. Each gas compartment is tested before delivery to verify the specified moisture level and insulation performance.

For project-specific requirements, please contact our technical team for gas system information, testing documentation, and configuration recommendations.