T&D World Magazine

New SF6 Leakage Test Unit for GIS Components

DILO Armaturen und Anlagen GmbH in Babenhausen (Germany) has developed a new SF6 leakage test unit allowing detection of even smallest leakages within a short period of time. Thus, conventional and time-consuming test procedures are a thing of the past. The new leakage test unit delivers the test result within a few minutes.

The SF6 leakage test system developed by DILO allows an integral and fully automatic leak measurement on gas-insulated medium or high voltage components and assemblies. The system’s core components are: a vacuum test chamber with diffusion accelerator, a highly sensitive leak measuring system as well as a vacuum pump for evacuation of the test chamber.

State-of-the-art control technology and a 17“ TFT screen make system operation easy and comfortable. All major system parameters are stored for further processing. Layout, size of vacuum test chamber and the conveying system can be widely realized acc. to customer’s specifications. As a standard, the vacuum chamber is feasible with a volume of up to 4 m³ allowing a large component or several smaller GIS components to be checked in one process. Upon request, however, larger chamber volumes can be configured, too.

The inert gas SF6 (sulphur hexafluoride) is used in component testing. As the gas cannot be found in ambient air, a highly precise and pure test result can be guaranteed. The new leak test unit virtually does “detective work” for it is able to trace smallest SF6 leakages. Even leakage rates down to 1*10-9 mbar l/s can be easily detected. The system’s detection limit is as low as < 1 ppb, and test time is short: As a rule, the test result is already indicated after 3 – 5 minutes, the total leakage rate being displayed on the screen in mbar l/s or other common measurement units.

For the test no high vacuum is needed. As a rule, an absolute test pressure of about 10 – 20 mbar is fully sufficient. Upon start of operation, the leakage test system carries out a preliminary leakage test and only in case of a positive result, the SF6-gas is filled in resp. the final precision test started. Pressure and vacuum are permanently monitored during the process.

As SF6 is used as quenching and insulating gas in the GIS assembly itself, it can stay in the test object when the test is completed. Therefore, the SF6 leak test method is a viable alternative to the well-established helium leak test as no test gas needs to be recovered upon completion of the process. Thus, with the SF6 test method, the handling time per test object is shorter.

Before the test starts, the test object is evacuated from air outside the test installation and is subsequently filled with SF6 up to the desired final pressure. For preparatory handling of GIS components before the SF6 leak test starts, DILO delivers special SF6 equipment allowing emission-free gas handling of GIS assemblies manufactured in series. For highly challenging test objects, such as medium voltage GIS components, the leak test system can be configured with recovery and filling functions to be carried out inside the vacuum chamber. With this option, the admissible pressure difference between chamber and internal pressure of the test object is permanently monitored via system control.

Part of DILO’s core business are SF6 gas service carts for maintenance of gas-insulated switchgear as well as measuring devices to determine SF6 quality. Hermetically sealing valves and couplings round off the specialist’s product range.

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