The appendix of the HZSF-702 instruction manual specifically lists the requirements for measuring the moisture content of SF6 circuit breakers, which is the direct basis for determining whether the measurement results are qualified on site. Only by interpreting the content of this appendix clearly can correct judgments be made in actual testing.

Limit values for four occasions

According to the regulations of the power industry, the appendix provides four different moisture content limits for SF6 in different situations (unit: μ l/l, i.e. ppm, measured at a reference temperature of 20 ℃):

During factory and major repairs (before overall reassembly): The disconnect unit and support unit should be measured separately, with a limit value of ≤ 150 μ l/l. This is the strictest standard, which applies to the state of the equipment before manufacturing, maintenance, and sealing, during which the gas should be the driest.

During handover: Measure the moisture content of the circuit breaker at the lower inflation interface of the pillar, with a limit of ≤ 150 μ l/l. The handover acceptance is the same as the factory standard and is the final checkpoint before the equipment is put into operation.

During operation: measured by the lower inflation interface of the pillar, the limit value is ≤ 200 μ l/l. After long-term operation, it is normal for the equipment in operation to absorb a small amount of moisture. The standard is slightly relaxed, but it cannot exceed 200 μ l/l.

Individual measurement of the disconnecting unit during operation (if necessary): When the disconnecting unit leaks or needs to be disassembled, it should be measured separately from the self sealing joint inside the header, with a limit value of ≤ 300 μ l/l. Due to frequent arcing, the disconnection unit is listed separately in the standard and has a wide limit.

How to correspond to dew point temperature

The above μ l/l limit corresponds to the dew point temperature. 150 μ l/l is approximately equivalent to a dew point of around -36 ℃, and 200 μ l/l is approximately equivalent to around -30 ℃ (approximately converted at rated pressure, subject to instrument display). HZSF-702 displays two units simultaneously, allowing for direct judgment based on the standard without the need for additional conversion.