SF₆ is highly effective at insulating switchgears, transducers, and circuit breakers – but only if there is enough of the gas in the equipment. Knowing the density of SF₆ is the best way to make sure gas-filled components are not safety compromised.

SF6 Density Overview

Sulfur hexafluoride (SF₆) is an extremely effective electrical insulator used in a variety of applications, especially in medium- and high-voltage gas-insulated equipment (GIE) like switchgears, disconnectors, transducers, transformers, and ring main units. If GIE relied on air or N₂ alone to extinguish electric arcs, it would have to be almost three times as large. But to maintain proper insulation, the density of SF₆ inside the equipment must remain within certain levels.

What would cause the gas density to drop in the first place? There are two reasons, and they’re interrelated:

• Over time, GIE could develop tiny fissures that allow SF₆ to escape. Fugitive emissions means there’s less insulating gas inside the chamber. What’s more, as SF₆ is a powerful greenhouse gas, any leaks harm the environment.
  
  
• In the presence of fissures, air could enter the GIE. Ambient air is problematic because it contains water vapor, which combines with sulfur and fluorine molecules after an electrical discharge to produce a host of toxic decomposition products like sulfur dioxide (SO₂) and sulfuryl fluoride (SO₂F₂). These and other byproducts corrode gas compartments, leading to more leaks and even lower SF₆ density. What’s more, some decomposition products are neurotoxic.

Monitoring SF6 Density with Gas Density Indicators

For decades, the transmission and distribution (T&D) sector has relied on WIKA’s analog GDI-100 gas density indicators to detect leaks and maintain proper gas pressure. Hermetically sealed, robust, and temperature-compensated, this device remains the go-to gauge for monitoring SF₆ gas in closed-tank electrical switchgear. However, there are certain capabilities that only a digital instrument can offer. 

Because our SF₆ experts understand the evolving needs of the T&D industry, WIKA has designed the GDI-100-D. This state-of-the-art digital gas density indicator combines the simplicity of an analog device with the accuracy of a digital gauge.

GDI-100-D for Extreme Accuracy and Ease of Use

The GDI-100-D provides temporary or continuous monitoring of the density of SF₆ gas. To do so, it measures pressure inside the tank with the CPG1500 precision digital pressure gauge. There’s also a temperature sensor that compensates for temperature variations (referenced to 20°C). Using these measurements, the unit’s internal algorithm quickly calculates the density of SF₆ gas.

This gas density indicator is simple to operate. It has a user-friendly navigation menu and a lighted display with integral bar graphs and large text area. A data logger stores up to three measured values per second.

An exceptional 0.6% accuracy makes the GDI-100-D the ideal instrument for verifying and calibrating other gas density indicators, monitors, and sensors. It is also useful for checking the tightness of a tank after maintenance or repairs.

SF6 Gas Density Indicator with Digital Capabilities

Today’s connected systems call for smart devices. The GDI-100-D comes with Bluetooth for wireless communication between the gas density indicator and a user’s software for remote monitoring.

The myWIKA deviceapp, available on both Google Play and Apple’s App Store, offers additional flexibility for configuring the instrument and monitoring SF₆ gas. With this app, users can easily:

• Check gas density
• Check gas pressure
• Check the actual gas temperature
• See bar graphs
• See the mean value over time
• See logger data (initialization, configurations, stop)
• Retrieve historical data
• Change units
• Adjust zero, reading rate, and internal clock

The GDI-100 remains the gas density indicator of choice for the T&D world. But for a device with calibration-level accuracy, data logging, and other digital capabilities, the GDI-100-D is quickly becoming the industry standard. See this video for a quick introduction to the digital gas density indicator. For more information about this or other SF₆ gas solutions, contact WIKA’s SF₆ experts.