New gas density monitor 8719: reliable monitoring of all insulating gases

Advanced reference chamber measuring system

Trafag has over 40 years of experience in the development and manufacture of instruments for gas density monitoring in highvoltage switchgear and has established itself as a leading supplier on the market.

The core of the Trafag gas density monitor is the unique reference chamber principle, which has been tried and tested for over 35 years. This has also been been used in the new generation, as it offers vibration resistance and reliability unmatched on the market. In addition, the Trafag measuring system has the best switching point accuracy over the entire temperature range. The measuring system of the 8719 gas density monitor is based on an advanced reference chamber. It is suitable for monitoring both SF₆ and the more environmentally friendly alternative gases. Alternative gases must be used at a significantly higher pressure in order to achieve the same insulation effect as SF₆. For this reason, the measuring system has been improved so that it can monitor absolute pressures of up to 13bar.

Easier to read thanks to large display

The most striking of all the innovative new features of the 8719 gas density monitor is certainly the large display: it offers the best readability across the entire measuring range of all reference chamber system-based gas density monitors on the market. Although the design of the full-range display is based on traditional pressure gauge systems, it offers a much higher resolution in the key ranges and therefore better readability: the display range is not scaled linearly, but divided into different areas. These are more or less finely resolved according to their importance in operation and for reading. This means that the operating range, which is crucial for system safety, has the largest proportion of the scale, while the low-pressure and intermediate ranges appear correspondingly reduced.

Operating range

The operating range of the display covers the gas density range in which the system is operated. The reading scale offers a particularly high resolution and reading accuracy here: it ranges from just below the lowest alarm switching point to just above the overpressure alarm switching point.

The maximum difference between the highest and lowest switching points has been significantly increased compared to previous models and other systems on the market thanks to the advanced reference chamber system. It is now up to 250kPa.

Low pressure range

The low pressure range extends from vacuum to an absolute pressure of around 4bar. The scale enables good readability in those low pressure measuring ranges that are relevant for transportation and storage pressure — usually between 1.5 and 2bar absolute pressure — as well as for evacuating the gas tank.

Intermediate range

The range between the operating and low-pressure ranges is neither important for operation nor for maintenance. It has therefore been reduced to the technically necessary minimum on the display scale in order to achieve the highest possible resolution in the operating and the low pressure ranges.

As pressure monitoring is not always necessary during transportation and storage, the display of the low pressure range can be omitted in these cases. Instead of the full range display, a partial range display is used, which is limited to the operating range and is therefore simpler. For further simplification, the scaling of the display can be omitted completely, so that a distinction is only made between the green marked operating range and the red marked range outside. For systems that never require a display, it can of course be omitted completely, e.g. to optimise costs.

Optimum integration into the switchgear

Modern, gas-insulated high-voltage switchgear is becoming increasingly compact. The installation position of the gas density monitor must therefore comply with many different requirements. To ensure reliable readability, simple installation and cabling as well as good accessibility for reading and maintenance, the gas density monitor must be able to be installed and connected in a wide variety of positions. The flexible, modular concept of the new 8719 gas density monitor allows it to be optimally integrated into the overall system, even where space is limited.

Thanks to the design of the housing, the gas connection can be axial or radial. On the other hand, the positioning of the electrical connection can be freely selected in the angles 0°, 90°, 180° and 270°. The combination of these options minimises the space required and simplifies the installation of the wiring. This also simplifies any maintenance and makes it more efficient.

Integrated valves: testing, service and filling in situ

The test, service and filling valves offer an important option for maintenance, testing and commissioning. The valves integrated in the gas density monitor enable the direct connection of test devices for regular, compliant checking of the switching points and for taking gas samples. The initial filling of the system with process gas and refilling after years of operation can also be carried out easily via these valves. The valves are available in the angle positions 0°, 90°, 180° and 270° to ensure optimum accessibility.

Integrated plugs for simple cabling

In addition to the user-friendly connections already described, particular attention was paid to ease of installation and cabling when developing the 8719 gas density monitor. The cable connection — connection variants with one or two cables are available — has been optimised for maximum flexibility and modularity: The cable no longer has to follow the gas density monitor; instead, the connection configuration on the gas density monitor is selected which allows the cables to be laid ideally in the respective installation situation.

Unlike conventional devices, the connection is no longer made in the gas density monitor itself, but via a separate connector housing, which can be pre-assembled and only needs to be plugged into and screwed onto the gas density monitor. If it is discovered on site that the cables need to be routed differently than planned, the connector housing can simply be removed and turned into the desired position. The connector housing is available in many configurations and is made of robust die-cast aluminum as standard. A more cost-effective version made of polyamide is also available for simple indoor installations.

Hybrid variants for continuous gas density measurement

The new 8719 gas density monitor will be complemented by the 8729 and 8739 hybrid versions in the coming months. The 8729 hybrid gas density monitor has the same reference chamber system as the 8719 gas density monitor and also features an integrated gas density sensor with a 4... 20mA analogue output signal for the gas density. In addition to the measured values for the gas density, the 8739 hybrid gas density monitor with digital Modbus output signal also supplies the temperature and the calculated pressure of the process gas normalised to 20°C. The three device types 8719, 8729 and 8739 form the new generation of insulating gas density monitoring in the Trafag product portfolio, which is characterized by high operational safety, great reliability, optimum ease of installation, ease of maintenance, high modularity and simple configurability. The new 8719 gas density monitor and the two hybrid gas density monitors 8729 and 8739 are not only ideal for the efficient monitoring of existing and new SF₆ switchgear, but are also ready for the challenges of the future thanks to their full compatibility with alternative insulating gases.

If you are not sure which Trafag product is best suited for your application, please contact us. Our specialists will be happy to provide you with competent advice.

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If you are not sure which gas density monitor is best suited for your application, please contact us. Our specialists will be happy to provide you with competent advice.