Notes on Instructions for SF6 Relay and Gas Density Meter Operation

1. Sf6 relay and gas density meter can accurately measure the sf6 gas density (or pressure) value only after the sf6 equipment is out of operation and the internal and external temperatures of the equipment reach equilibrium.

2. The sf6 relay and the double-layer metal belt of the gas density meter can only compensate the change of density (or pressure) value caused by the change of ambient temperature, but not the change of density (or pressure) value caused by the temperature rise inside the equipment.

3. The main function of sf6 relay and gas density meter is to monitor whether sf6 gas leaks. Only after the equipment is out of operation and the temperature inside and outside the equipment reaches equilibrium, can we judge whether there is gas leakage according to the change of density (or pressure) reading.

4. When the circuit breaker is put into operation, as the load current of the circuit breaker passes through the conductor resistance and contact resistance of the conductive circuit, all the consumed electric power will be converted into heat energy. When sf6 gas is heated to produce temperature rise and pressure increment, the reading of density (or pressure) gauge will be too large, which is a normal phenomenon of this gas density gauge. If the reading of the meter is too small at this time, it is necessary to judge whether the equipment is due to air leakage or less gas filling quality.

5. According to the configuration of sf6 relay and gas density meter in different positions of circuit breaker, their readings also have deviation. The so-called ambient temperature generally refers to the air temperature without sunlight. If the density (or pressure) gauge is installed on the back sunlight side of the circuit breaker, the density (or pressure) reading will be larger; If the density (or pressure) gauge is installed on the sunny side of the circuit breaker, the temperature will be higher and the density (or pressure) reading will be lower after being exposed to the sun. The deviation depends on the temperature difference.

6. When the circuit breaker is in operation, the reading error of sf6 relay and gas density meter depends on the temperature rise caused by the load current and loop resistance of the circuit breaker, and the error is independent of the ambient temperature. Strictly speaking, this reading can neither represent the actual pressure value of sf6 gas nor the actual density value of sf6 gas. According to DL/T728-2013 "Technical Guidelines for Ordering Gas-insulated Metal-enclosed Switchgear", the temperature rise of the GIS shell that is easily accessible to operators should not exceed 40K; for parts that are not touched by operators, the allowable temperature rise can be increased by 65K .

7. When using sf6 relays and gas density meters, specific analysis should be made according to their structure, principles, and conditions of use. For example, in a typical temperate continental climate, the average daily temperature difference between winter and summer is about 10-15°C. It cannot be because of sf6 monitor. If the actual density of the gas does not change with temperature changes, it is considered that the reading of the density (or pressure) meter does not change with temperature changes. In actual work, when there is a temperature difference between the ambient temperature and the air chamber temperature, the indication will also fluctuate.

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