Integrated test and service valve for gas density monitors

Direct access to the gas compartment of the switchgear is required for the maintenance and inspection of gas density monitors in gas-insulated high-voltage switchgear. For this purpose, additional valves are often installed between the system and the gas density monitor. The main disadvantages of these separate valves, apart from the costs, are the additional connection points, which can lead to leakage, and the increased space requirement.

As the importance of maintenance and testing is increasing and at the same time network operators are expecting ever greater efficiency, Trafag offers optional integrated valves for the current gas density monitors and hybrid gas density monitors: Test valves to check the compartment switching points of the gas density monitor as well as service valves for sampling and refilling the insulating gas and filling valves with a large cross-section to quickly fill or empty the entire insulating gas. The test valve and the service or filling valve can also be integrated into the gas density monitor in combination.

Simple, safe and efficient maintenance processes thanks to integrated valves

Without a test valve, the gas density monitor would have to be removed from the system to check the switching points. Every disassembly and assembly process involves the risk of components being mixed up, incorrectly connected or damaged during transportation to the test equipment. All these risks are eliminated by integrating the valve directly into the gas density monitor. The more compact design of the integrated valves not only saves space in installation and makes access easier, but the shorter overall length also reduces the distance between the mass of the gas density monitor and the mounting point. A short lever arm to the vibrating masses is particularly important for switching operations that can cause strong vibrations. The compact design of the integrated valve reduces the load on the gas density monitor caused by vibrations, thereby reducing the risk of wear, damage and malfunctions such as contact bounce.

In addition to the insulating gas SF₆, more environmentally friendly alternative gases are increasingly being used on high-voltage switchgear, as the use of SF₆ on new systems is being increasingly restricted and will be completely banned throughout the EU in the next few years. To prevent confusion, the cover caps of the valves integrated in the Trafag gas density monitors are marked in the usual colors: Orange for SF₆ , green for alternative insulating gases C₄FN and blue for air mixtures. Just like the gas density monitor itself, the valves are also designed for a specific gas, both in terms of pressure resistance (alternative insulating gases require a significantly higher pressure than SF₆ for equivalent insulating properties) and the sealing materials used.

Trafag offers a safe and elegant solution for the reliable operation and efficient maintenance of high-voltage switchgear with the patented direct integration of valves in the gas density monitor for checking the switching points, for sampling, for refilling insulating gas and for emptying and filling the gas compartments.

Integrated DN8 test valve

The integrated test valve enables the switching points of the gas density monitor to be checked while being installed. An external test device can be connected via a standardized DN8 connection. For the test procedure, the valve closes the opening to the gas compartment and opens the connection to the DN8 connection. Once the test of the switching points of the gas density monitor and, if applicable, the signal of the gas density sensor installed in the hybrid gas density monitor has been completed, the valve is switched back to the normal position and the line to the DN8 connection is closed again. The test device can now be removed.

Function of the test valve for periodically checking the switching points of the density monitor:

Normal operation

Monitor test mode

Integrated service valve DN8

If samples of the insulating gas need to be taken for maintenance purposes, the sampling devices can be connected to the DN8 connection of the service and refill valve. By opening the valve, the connection to the gas compartment is established while the connection to the gas density monitor is maintained. Gas can be refilled via the DN8 connection. Once the maintenance work has been completed, the valve is reset to its normal operating state and the external modules can be disconnected.

Functionality of the service valve, which enables a direct connection to the compartment gas: In normal operation, the valve is closed (left); in monitor test mode, the valve is open (right) for gas sampling and refilling.

Normal operation

Monitor test mode

Integrated filling valve DN20

In contrast to the refill valve described above, the integrated filling valve offers a massively larger flow cross-section and thus enables both initial filling when the system is commissioned and the replacement of the entire insulating gas in the corresponding gas compartment within a short time. The connection to the filling system is made via a DN20 connection, which can usually be connected directly to the system. All other functions of the filling and maintenance valve are identical to those of the service and refilling valve.

Combined variants of service and filling valve

In addition to the individual valve variants, Trafag also offers the combined integration of test valve and filling or refill valve. This is because most systems not only require refilling or complete filling of the gas tank and maintenance work in connection with the insulating gas, but the gas density monitors must also be checked. The combined valves integrated directly into the connection of the gas density monitor even eliminate the need for additional connection points.

Both the individual valves and the combinations can be ordered in different arrangements to ensure optimum access to the connections and to the gas density monitor itself for every installation position.

Integrated valves for all Trafag density monitors

The integrated valves, individually or as combination valves, are available for all Trafag density monitors and hybrid density monitors. On the one hand, this includes the new 87x9 generation with the 8719 density monitor, the 8729 hybrid density monitor with analog output signal and the 8739 hybrid density monitor with digital Modbus output signal. On the other hand, integrated valves are also optionally available on all models of the previous generation 87x6/87x8 (density monitor), 878x (hybrid density monitor with analog output signal) and 879x (hybrid density monitor with digital Modbus output signal).

Why are test and maintenance valves used in gas-insulated high-voltage switchgear?

Gas density monitors are used to monitor insulating gas such as sulphur hexafluoride (SF₆) or more environmentally friendly alternative gases (C₄FN-based insulating gases such as EconiQ or g³ and air mixtures such as CleanAir*) in high-voltage switchgear. These are either gas density monitors with electromechanical switching elements, gas density sensors with continuous electronic density measurement or hybrid gas density monitors, a combination of gas density monitor and sensor. These devices are attached to the gas compartment of the switchgear either directly or via additional valves. Monitoring the gas density alone is not enough to ensure safe operation of the system: Samples must occasionally be taken from the system gas in order to analyze the gas quality offline. If the density falls below a certain value due to leaks, insulation gas must be refilled. Furthermore, the correct switching of the gas density monitor must be checked regularly due to regulatory requirements (F-Gas regulation). The regular functional check of the switches is particularly important because they are set to alarm values and it is therefore not possible to check their function during regular operation. Refilling insulating gas is particularly relevant for older systems, whereas modern systems from leading manufacturers are usually installed so tightly that refilling is not or only very rarely necessary.

* EconiQ is a trademark of Hitachi Energy
g³ is a trademark of General Electric Company
CleanAir (Clean Air) is a term used by Siemens Energy

Product details

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