SF6 Gas Insulated Equipment

​Monitor quality of SF6 with online dew point and pressure measurement

The electric power industry uses SF6 to insulate switchgears, circuit breakers and other equipment used in electricity transmission and distribution. To ensure the integrity of SF6 gas as an insulator, the amount of water vapor in SF6 gas should be kept to a minimum. Moisture may also increase the formation of unwanted secondary decomposition products, which can lead to arcing and equipment failure.

Online monitoring of SF6 is convenient with Vaisala's Multiparameter Transmitter DPT145. The DPT145 is a unique innovation that not only monitors dewpoint online but also pressure and temperature. In addition the instrument calculates four other values, including gas density and ppm. The DPT145 provides an excellent assessment of the SF6 insulation. Both sudden and minor leaks are detected by the direct normalized pressure measurement, while online dew point measurement alerts the user to moisture issues, which can weaken the insulation properties of SF6 and cause rapid deterioration. Integrating the DPT145 into a condition based monitoring system minimizes the need for on-site visits and helps to ensure that no SF6 is released into the atmosphere.

Spot-checking is easy with Vaisala's hand-held dew point meter DM70 which is a lightweight, battery-powered instrument for measuring the dew point in SF6. It provides fast response time and internal datalogging to optimize the field technician's time. A unique sample cell allows dew point measurement at both in gas pressure and in ambient atmospheric pressure. The cell meets and even exceeds environmental regulations by ensuring protection against accidental discharge of SF6, requiring minimal amount of SF6 for sampling, and enabling collection and recycling of SF6.

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