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The Effect of Temperature on SF6 Gas Density Relays and Precautions in Operation

Ⅰ. Specific analysis of the impact of sunlight radiation on SF6 relays

Due to the strong sunlight radiation makes the density relay metal shell temperature is much higher than the ambient temperature, in the summer high temperature season, the shell surface temperature is expected to reach 60 ℃, so that the high temperature of the metal shell will make the density relay volume is very small gas chamber SF6 gas temperature rises a lot.

Compared with the larger volume of the gas chamber of the circuit breaker, the convection of the gas inside the gas chamber of the SF6 relay at the same pressure with the gas inside the gas chamber of the circuit breaker body through the slender connecting pipe is negligible.

Therefore, the temperature of SF6 gas inside the density relay is higher than the temperature of the gas chamber of the circuit breaker body, and there is a large error with the standard pressure of 20℃.

After eliminating the effect of sunlight radiation, the action pressure value of the density relay is qualified. It can be seen that the strong radiation of sunlight makes the temperature of the gas chamber of the density relay higher than the temperature of the gas chamber of the equipment body.

This will make the bimetallic compensation device inside the density relay in an over-compensated state, so that the action pressure of the density relay is higher than the normal action pressure at ambient temperature, which will cause false alarm or early blocking, affecting the normal operation of the equipment.

Therefore, in the installation of SF6 gas density relay must choose a suitable installation location, as far as possible to eliminate the impact of sunlight radiation.

For example, the density relay will be installed in a place weakened by sunlight radiation, and at the same time should be installed in its periphery can shade the enclosure to further block the sunlight, to ensure the reliability of its action.

Ⅱ. The SF6 relay operation considerations

1. The main role of the gas density relay is to monitor whether the SF6 gas leakage, only after the SF6 equipment out of operation, and in the equipment inside and outside the temperature balance, to accurately measure the density value of SF6 gas, in order to judge whether the change in density readings.

2. SF6 relay temperature compensation role of the bimetal, only able to compensate for changes in density (or pressure) value due to changes in ambient temperature, but not to compensate for changes in density (or pressure) value caused by the internal temperature rise of the equipment.

3. When the circuit breaker is put into operation, due to the circuit breaker load current through the conductor resistance and contact resistance of the conductive circuit so that the electrical power consumed will be fully converted to heat.

Heating SF6 gas and temperature rise, and then produce pressure increments, density (or pressure) table readings will be large, which is the normal phenomenon of this density (or pressure) table.

If the meter reading is small at this time, then the equipment should be judged because of gas leakage or its own gas filled with less mass in both cases.

4. According to the density relay (table) configuration in the circuit breaker location is different, its readings also have deviations, SF6 relay should be installed in the location of the weaker impact of sunlight radiation.

At the same time, it should be installed in its periphery a shell that can be shaded from the sun to ensure the reliability of its action, and should avoid the installation of density relays in the institution box where the heater is installed.

5. During the inspection tour in operation, it is necessary to record both the SF6 gas density (or pressure) value and ambient temperature, as well as the load current and temperature rise of SF6 electrical equipment.

Only through comparison with past records, you can probably determine whether the internal temperature is too high, whether it exceeds the standard temperature allowable value, and thus determine whether the grounding resistance of the conductive circuit exceeds the standard.

6. In the case of SF6 circuit breaker blackout, the corrected pressure value of the SF6 gas "pressure-temperature curve" can be used to determine whether the circuit breaker has a gas leak.

In order to make the SF6 gas density relay reflect the density value of electrical equipment gas, it is necessary to strengthen the management of SF6 gas density relay, so that the temperature sensor used in the SF6 gas density relay and the body of the circuit breaker is at the same ambient temperature.

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Lanso Instruments INC.
233 W 1st St #210, North Vancouver, Canada
233 W 1st St #210, North Vancouver, Canada