A New Approach for the Measurement of the Complex Value of Fault-Loop Impedance in Low-Voltage Electrical Installations

The primary method for verifying the safety of electrical installations is the measurement of fault-loop impedance. The most common approach involves measuring the voltage under no-load and load conditions and determining the difference between them. However, this method has several drawbacks, including the need for complex instrumentation and measurement uncertainty that depends on the magnitude and nature of the load in the tested electrical system. Additionally, most existing measurement systems allow only the determination of the impedance modulus. This paper introduces a novel, theoretically grounded method for measuring fault-loop impedance. The proposed approach is based on measuring the RMS no-load voltage, followed by three voltage measurements under different loading conditions using reference impedances with known phase angles (defined by the resistance-to-reactance ratio). The complex value of the fault-loop impedance is then obtained using a second-degree polynomial approximation. The main advantage of the proposed method is that it reduces the influence of slowly varying operating loads under quasi-stationary network conditions of the network on measurement accuracy. This property requires experimental verification. It should be noted that the presented analysis is of a theoretical nature and constitutes a basis for further research and discussion within the scientific community.