Nuova Via di Piano Comprensorio Vulcano
Sesto San Giovanni, MI 20099 Italy
Tel. 02-24105.001
IS 2653 GB
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CAUTION:
The refilling action must be performed by qualified operators. Periodical inspection and
maintenance of the gas filling station must be accurate to prevent damages to the valves and the equipment
installed inside or to the connecting pipe to the bushing.
CAUTION:
Always use equipment certified for SF6 gas. This will avoid mistakes, safety issues and risk for the
environment and the equipment.
7
Gas density monitor
The bushing is equipped with one or more gas density monitors.
This device ensures a great accuracy in the measurement, as it is based on the continuous and direct
comparison between the gas density inside the bushing and the gas density of a built-in reference chamber
filled with the same gas.
This system is different and it is more accurate than the normal gas density monitors, which estimate the gas
density by correcting the gas pressure measurement with the ambient temperature.
The
Figure 9
shows an example of the instrument and its graduated scale.
Figure 9 – Example of gas density monitor
The indication on the scale is expressed in MPa absolute, referred to a gas temperature of 20°C. This means
that the instrument converts the gas density into a value of pressure referred to 20°C, independently for the
effective temperature of the gas.
The instrument reading practically does not change with the gas temperature that is a function of the bushing
loading condition and ambient temperature. Changing of reading during the bushing normal operation is an
indication of gas leakages or malfunction of the instrument.
NOTE:
Due to the instrument principle of operation, the replacement of bushing gas from SF6 to a gas mixture
SF6 N2 is not allowed without replacing the gas density monitors with the proper type. In this case contact GE
Grid Solutions RPV for support, instructions and approval.
Each gas monitoring device is equipped with four change-over micro switches for alarm and tripping signals.
For further information regarding alarm pressure values, see the electrical scheme document.
Each gas density monitor device is installed on a DN 20 DILO Type valve for easy disassembly, without the
need to completely empty the bushing from the gas.
In addition, the electrical cables of all devices can be wired in a junction box provided with DIN type terminal
boards for easy assembly and maintenance; see the electrical scheme document for details.
