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(1) SF6 gas density relay is mainly used to monitor and control the density of SF6 gas in the sealed container. Generally used in high voltage switch, medium voltage switch, gas insulated equipment (GIS), high voltage cables, transformers and transformers (CT and PT).
(2) The most used SF6 gas density relay is actually a pressure gauge with electric contacts and temperature compensation.
(3) This type of SF6 monitor outputs two or three sets of contacts and sends out alarm and blocking control signals.
(4) Principle of SF6 density relay: The density of SF6 gas in SF6 electrical equipment is expressed by the pressure of SF6 gas after temperature compensation, that is, the pressure value at 20°C. The relay works under the rated pressure. When the ambient temperature changes, the pressure of SF6 gas will also change. The measurement system inside the relay should also consider the temperature while measuring the pressure, that is, the internal temperature compensation unit automatically adjusts the pressure for the changed pressure. Compensate so that the indicated value of the rated pressure remains unchanged. When the SF6 gas leaks for some reason, the pressure will drop after temperature compensation, and when it drops to the alarm pressure value, the relay will output a pair of contacts (alarm signal), and the user is required to replenish the gas to the equipment, and If the pressure continues to drop and reaches the locking action pressure value, the relay will output another pair of contacts (locking signal) to lock the corresponding control system of the equipment, thus realizing the safe operation protection of electrical equipment. When the equipment is filled with SF6 gas, when the excess exceeds the rated value, some density relays can also send out an overpressure alarm signal.
(5) Most of them are directly used outdoors, so they need to be suitable for the harsh external conditions outdoors. It is mainly used for SF6 combined electrical appliances (GIS) indoors.
(6) According to the principle of compensation, it is divided into relative cavity compensation and bimetal tie rod compensation.
Suppose the temperature of the gas rises suddenly, what will happen to the indicated value of the gas density meter? The ambient temperature of the gas density meter must be consistent with the SF6 gas temperature of the equipment body to accurately reflect the gas density. If the ambient temperature of the density meter is higher than the SF6 gas temperature of the equipment body, the density meter will indicate a low value at this time, and vice versa. If the temperature of the gas rises suddenly, if the temperature at the density gauge rises synchronously, the indicated value will remain unchanged; otherwise, if the temperature at the density gauge does not rise synchronously, the reading will increase.
In addition, can the alarm and blocking values be set according to the use environment and place? For absolute pressure density gauges, after inflated operation, the reading has nothing to do with the altitude, but when there is no air, the zero position is related to the altitude, where the altitude is high, the reading is small, otherwise the reading is large. For the relative pressure type gas density meter, after inflated operation, the reading is related to the altitude, where the altitude is high, the reading is large, otherwise the reading is small. And when there is no gas, its zero position has nothing to do with altitude. In addition, the alarm and blocking values generally cannot be set according to the use environment and place, and cannot be adjusted after they are done.
