电感性本质安全电路L/R的选择原则

基于电感性本质安全电路放电电流线性衰减模型,引入最小建弧电压的概念,得到了放电时间不含未知参数的表达式,利用电感电路的本质安全性能判别式,确定了电感电阻比L/R的选取原则.

THE PRINCIPLE FOR CHOICE OF THE INDUCTANCE TO RESISTANCE L/R RATIO IN INTRINSICALLY SAFE INDUCTIVE CIRCUIT

The paper is aimed at discussing the principle for choosing L/R ratio by strictly comparing IEC to the actual situation. Based on the current linear attenuation model and the idea of minimum arcing voltage in inductive intrinsically safe circuit, the authors establish the principle for choosing L/R ratio assuredly by using the intrinsic safety discriminant of inductive circuit and express the discharge time with known circuit parameters. The circuits for transferring such safe signal to the intrinsically safe electrical devices through the long cable are widely used for the intrinsically safe system where explosives are used. It is necessary to regulate the ratio of inductance to resistance L/R of the cable to ensure the due safety of the safe system. The ratio of L/R has been regulated in the standard IEC 60079 11 of International Electric Committee (IEC), which can make sure the safety of the system. Nevertheless, it is still necessary to take the deposited energy LI 2/2 of inductance into full account in the whole process of arc discharge and ignore the energy EIT/6 supplied by power source. However, it is found that the energy supplied by electrical source can't be ignored in the whole arc discharge if the value of inductance is uncertain by experimentation. Since the value of the minimum arcing voltage assessed in the literature is 11 V to cadmium and 15 V to tungsten,it is necessary to do some spark test by using the spark test apparatus for some inductive circuits for this purpose and it is found that it can't ignite the explosive mixture of firedamp and air under regulated test condition. This proves the validity of L/R ratio determined in the present paper.