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From the existing experience and theoretical analysis, such structure SF6 relay is adopted on the basis of the following.
(1) Although the pure SF6 gas pressure-temperature curve is more complicated, the relationship between the pressure of SF6 gas and the absolute temperature change within a certain temperature range is still linear. Therefore, each equipment manufacturer adopts the part of SF6 gas pressure-temperature curve actually used, that is, the pressure of SF6 gas changes with the change of temperature, but in a fixed container, the density value of SF6 gas is always the same as long as there is no gas leakage, and if there is gas leakage, the density value of SF6 gas changes proportionally as a function of the pressure value. Therefore, it is theoretically feasible to use the pressure value to monitor whether the equipment is leaking or not.
(2) Spring tube type pressure gauge has simple structure, mature manufacturing process and technical standards, accurate measurement, low cost and other characteristics, suitable for large-scale manufacturing and use. When the circuit breaker is filled with sulfur hexafluoride gas, generally 24 hours later, the SF6 circuit breaker internal temperature rises to reach equilibrium with the external ambient temperature, regardless of whether the SF6 gas is affected by the ambient temperature so that its pressure increases or decreases, due to the double-layer metal belt temperature compensation role, the pointer of the gas density meter should always point to the actual density (pressure) value of SF6 gas at 20 ℃ is unchanged. When SF6 equipment due to gas leakage or test taking gas and other reasons, so that the quality of SF6 gas is reduced, the pressure becomes smaller, the pointer to the density (or pressure) to indicate the direction of reduced value, the result is that the pointer indicates the density (or pressure) value becomes smaller.
(1) The SF6 relay can only accurately measure the density (or pressure) value of SF6 gas after the SF6 equipment has been withdrawn from operation and after the temperature inside and outside the equipment has reached equilibrium.
(2) SF6 relay plays the role of temperature compensation of the double-layer metal belt, only able to compensate for changes in density (or pressure) value due to changes in ambient temperature, but not for changes in density (or pressure) value due to internal temperature rise of the equipment.
(3) The main function of SF6 relay and gas density meter is to monitor whether the SF6 gas is leaking, and when the temperature difference between inside and outside of the equipment reaches equilibrium, the change in density (pressure) reading can be used to determine whether the gas is leaking.
(4) When the circuit breaker is put into operation, due to the load current of the circuit breaker through the conductor resistance and contact resistance of the conductive circuit, so that the electrical power consumed will all be converted into heat energy, heating SF6 gas and temperature rise, and then produce pressure increment, the density meter reading will be large, which is the normal phenomenon of this gas density meter. 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.
