Monitoring GIS Compartment and Gas Cylinder Pressure During SF6 Topping-Up
GIS SF6 Topping-Up Technical Series — Part 2 of 5
In Part 1, we introduced how an automatic SF6 topping-up system monitors a GIS compartment, starts gas admission and stops at a configured pressure.
Two measurements support this process: supply cylinder pressure P1 and GIS compartment pressure P2. They serve different purposes and must be interpreted according to their positions in the gas circuit.
P1 — Monitoring the Gas Supply
In the illustrated arrangement, P1 is measured on the supply side, before the pressure regulator. It helps the controller identify whether the available supply pressure is approaching the configured cylinder replacement warning level.
A low-pressure warning gives maintenance personnel time to check the supply and arrange cylinder replacement.
P1 is a pressure reading, not a direct measurement of the mass of SF6 remaining in the cylinder. It should therefore be used for supply-pressure monitoring rather than presented as an exact remaining-gas percentage.
P2 — Monitoring the GIS Compartment
P2 measures pressure at the compartment-side connection and provides feedback for topping-up control.
The controller compares this reading with two configured values:
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Start pressure: The condition at which automatic topping-up may begin.
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Stop pressure: The target at which the controller closes the filling valve.
The start pressure is set below the stop pressure, creating an operating band between starting and stopping.
[Insert the system diagram from Part 1, highlighting P1 and P2.]
Figure 1. P1 monitors supply pressure before regulation; P2 provides compartment-side pressure feedback.
Three Settings with Different Roles
| Setting | Purpose |
|---|---|
| Topping-up start pressure | Defines when the compartment requires replenishment |
| Topping-up stop pressure | Defines when gas admission should stop |
| Cylinder low-pressure warning | Alerts personnel that the gas supply requires attention |
These settings should be selected for the connected GIS equipment and the approved filling arrangement. A cylinder warning threshold must also account for the supply pressure needed to carry out replenishment.
Use a Consistent Pressure Reference
A pressure value is meaningful only when its reference is clear. The sensor reading and configured threshold must use a consistent basis, including whether the values are gauge pressure or absolute pressure.
Temperature also needs consideration. A raw pressure reading should not be treated as equivalent to a temperature-compensated density indication. Where compensation is used, its reference conditions and calculation method must be defined.
The topping-up settings should therefore be established using the GIS manufacturer’s requirements and the agreed control method, rather than copied from another installation.
Keep a Useful Record
For each topping-up event, recording the pressure before and after filling, start and stop times, equipment identifier and any supply warnings creates a useful maintenance history.
This allows operators to review both the compartment response and the supply conditions associated with the operation.
Next in the Series
Pressure measurements provide the feedback, while the gas circuit carries out the filling operation.
Part 3 — Pressure Control and Safety Protection in Automatic SF6 Topping-Up will examine the roles of pressure regulation, the solenoid valve, the check valve and protective functions.
Previous: Part 1 — How an Automatic SF6 Gas Topping-Up System Works for GIS
Planning an SF6 topping-up application? Share your GIS pressure requirements and gas supply arrangement with KSTONE.
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