The symbol of density is expressed by ρ, and the unit symbol is kg/m3 or g/L. According to the definition of density, the indication value of SF6 gas density metre should be the unit of density. According to the ideal gas equation of state pv=nRT, it can be seen that the pressure p is linearly related to the temperature, and when the gas temperature changes in SF6 equipment, the pressure gauge value changes with it, so the pressure gauge cannot accurately reflect the state of the equipment.
1. Structure principles of SF6 relay
SF6 relay is an indispensable and important accessory for sulfur hexafluoride circuit breaker and sulfur hexafluoride combination apparatus (GIS). Its basic role is to monitor the sealing condition of the operating SF6 electrical chamber, whether there is gas leakage phenomenon.
SF6 gas density relay is mainly composed of C-type metal spring tube, gear mechanism and pointer, double-layer metal belt and other parts, in fact, on the basis of the spring tube type pressure gauge structure principle, plus a double-layer metal belt in accordance with changes in ambient temperature and expansion as a temperature compensation device, so that the spring tube and double-layer metal belt with temperature changes and expansion of the increment equal and reverse iteration, so that the density (pressure) readings do not change with the change in ambient temperature.
2. Structure temperature compensation principle of SF6 relay
SF6 relay is actually a pressure relay with temperature compensation, are expressed in terms of the corresponding pressure value of 20 ℃ to its density value. When the temperature changes, the elastic Boden tube and the double layer of metal belt change at the same time, thus making the pointer display unchanged. Any pressure change due to temperature change alone is compensated by the simultaneous corresponding change in the elastic boden tube and the double metal band, while the volume remains unchanged, thus causing no deflection of the pointer and ensuring the accuracy of the pressure indication.
The response of the pressure element to any pressure change not caused by a temperature change is translated into a gas density relay pointer action and reflected on the dial, and can monitor pressure values beyond the minimum or maximum pressure allowed by the system.
Requirements on the structure of the sulfur hexafluoride density relay: The density relay should be installed in a position where the monitored gas chamber is at the same operating ambient temperature. If different operating ambient temperatures, resulting in inconsistent compensation temperatures, can lead to inaccurate gauge indications.
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