A Methodology for Assessing the Thermal Condition of Wires and Cables to Ensure Fire Safety of Protected Facilities

The relevance of the study is determined by the fact that in 0,4 kV distribution networks, the current in the neutral conductor is formed by two components: the zero-sequence current at the fundamental frequency, caused by load asymmetry, and the sum of higher harmonics that are multiples of three, generated by single-phase nonlinear consumers. Under conditions of a high density of nonlinear loads, the effective value of the current in the neutral conductor may exceed the phase currents, creating a risk of unacceptable insulation heating and the formation of potential ignition sources. Existing protection and monitoring systems typically either detect only exceedances of the current setpoint or a break in the neutral conductor. The thermal state of the insulation is assessed indirectly and with significant error, since the equivalent resistance of the conductor increases at higher harmonics, rendering the permissible current load, standardized for sinusoidal conditions, inaccurate. At the same time, temperature values for different types of insulation are strictly standardized, allowing for an assessment of the actual insulation condition based on an analysis of current loads. This article presents a methodology for assessing the thermal state of wires and cables based on the analysis of phase current parameters, which allows for the determining influence of operating modes on the fire hazard of protected facilities. The methodology utilizes phase current parameters to indirectly assess thermal processes in wiring, enabling monitoring of the current network state without the need for direct temperature measurements. The scientific novelty of the obtained results lies in the systematization of the calculated dependencies into a unified methodology adapted for assessing the fire hazard of protected facilities during a current overload. Practical recommendations for using the developed algorithm include its integration into existing automated electricity metering systems for analyzing the thermal state of cable lines and wiring in the absence of dedicated monitoring systems.