Elimination of the methodological error in measuring linear parameters of electric cables for intrinsically safe systems

The necessity of monitoring of the linear electric parameters of cables for intrinsically safe applications is justified and it is indicated that the manufacturer or supplier of the cables must guarantee that the parameters of supplied cable comply with the currently existing standards. The problem of inefficient consumption of cable products for the purposes of their control is analyzed. It is indicated that the standard measurement methods are correct for measuring, e.g., a parameter of linear inductance when using cable samples whose length is much smaller than the construction lengths. We investigate an analytic model of a cable line as an electric facility with distributed parameters. The reason for introducing a restriction for the cable length is explained. This is connected with the transition from the complete model to a simplified model traditionally used in some standards.

We propose systematic method for measuring the linear parameters of cables. It is based on a nonstandard (reverse) solution based on the transition from the measured secondary parameters to the evaluation of the primary parameters. In this case, the secondary parameters are measured according to the well-known standardized idling–short-circuit method. The proposed method is almost free of restrictions imposed on the length of cable samples, which enables one to monitor all finished cable products without cutting samples for measurements. The errors of measurements of the linear parameters of the cables do not exceed the limit specified by the standards and equal to 1%. The obtained results guarantee the possibility of nondestructive testing in the course of acceptance tests of cable products intended for intrinsically safe systems.