Three way valve renovation

What problem is being solved?

Some SF6 gas insulated switchgear with longer service life do not have an online calibration valve between the interface of the switchgear body and the density relay. This structure may cause the following inconvenience:
The gas circuit cannot be isolated from the main body. If the density meter needs to be replaced urgently, power can only be cut off for operation. If the interface of the main body is not a self sealing structure, gas recovery, purification and recharge treatment are even required, which brings great inconvenience to the maintenance work.
SF6 gas density relays need to be regularly calibrated according to preventive testing procedures. For gas chambers that do not have online calibration valves, they need to be removed from the equipment and sent to the laboratory for inspection in conjunction with power outages. Density relays may be affected by long-distance transportation bumps, which may affect their accuracy and stability. The on-site installation and maintenance time is generally tight, and it takes a long time to remove them from the equipment and send them to the laboratory for inspection.

Why provide this service?

The "18 Major Anti accident Measures of State Grid Corporation of China (2018)" and the "25 Key Requirements for Preventing Power Production Accidents" of the National Energy Administration both mention that the connection between SF6 density relays and switchgear bodies should meet the requirement of not disassembling and verifying density relays.
The switchgear chamber equipped with an online verification three-way valve structure can perform non disassembly verification of gas density relays, maintenance and replacement of density relays, replacement of air supply port seals, and other operations when the equipment is live, improving the safety and reliability of the power grid.

Related experience and operational procedures

1. Apply for a work permit and confirm that the equipment has been powered off.
2. Remove the rain cover and original density relay.
3. Install an online verification three-way valve and confirm that the valve is in the closed state before installation.
4. Install density relay.
5. Open the valve, charge the density relay, and the pointer is normal.
6. Perform leak detection at each interface.
7. Install rain cover.