The value of SF6 gas density is expressed by the pressure after temperature compensation of SF6 gas, that is to be expressed as a standard pressure value when it is 20°C.
The SF6 density meter works under the rated pressure. When the ambient temperature changes, the pressure of the SF6 gas in the gas chamber also changes. The temperature compensation unit inside the SF6 relay compensates for pressure changes caused by temperature changes, so that the display value of the meter does not change. When the SF6 gas leaks, the pressure drops, and when it drops to the alarm setting value, the alarm contact of the density relay will act and output an alarm signal. At this time, the user is required to add air to the device. When the pressure continues to drop and drops to the blocking set value, the blocking contact of the SF6 relay will act, output a blocking signal. Then the control system of the equipment will be locked to ensure the safe operation of electrical equipment.
The SF6 gas of the SF6 circuit breaker is sealed in a gas chamber with a certain volume. Within the allowable operation ranges of the circuit breaker, the pressure of the SF6 gas changes according to the temperature, but the SF6 gas density value is always the same.
Since the insulation and arc extinguishing performance of SF6 circuit breakers largely depend on the purity and density of SF6 gas, purity detection and density monitoring of SF6 gas are particularly important. SF6 relay plays a role of monitoring, control and protection.
In actual situations, if the SF6 gas density value is too large in the circuit breaker, it is considered to be able to prevent the alarm and blocking signals from appearing. Indeed, if the gas pressure is high, the probability of generating the alarm and blocking signals is reduced, but the burden on each sealing part of the device becomes larger. Therefore, the supplementary air volume should be strictly controlled within the standard range.