Improved Procedure for Earth Fault Loop Impedance Measurement in TN Low-Voltage Network

Liviu Neamt,Olivian Chiver,Alina Neamt

doi:10.3390/en14010205

Abstract

The difficulties and uncertainties related to earth fault loop impedance measurement are addressed in this paper. Based on the presentation of the measurement procedure implemented in the test equipment (diagrams and measured quantities, respectively, interpretation of results), the shortcomings and errors that accompany it are highlighted. The position in the power system, the influence of power transformers, and the use of effective quantities instead of phasors are important sources of errors, but, as will be seen, the switching of loads at the consumer sides and/or the occurrence of fault regimes during measurements can lead to the most serious impairment of the accuracy in the impedance assessment. The clarification of these aspects is achieved, both starting from the equivalent diagrams of the measurement circuits and the analytical interpretation of the phenomena associated with the measurements, as well as based on the modeling and simulation of TN low-voltage electrical distribution networks, in a specialized program, Eaton xSpider, which allows the complete and complex analysis of a large number of scenarios. Thus, essential conclusions were drawn regarding the level of errors and their causes, obviously, with the research coming with solutions to be implemented at the level of the measurement protocols of the devices used.

Highlights

The energy dependence of human society is indisputable
Low-voltage distribution network equipped with protective devices, circuit breaker (CB) or general-purpose fuse, the maximum measured tective breaker (CB) or general-purpose fusethe, the maximum valuesdevices, of earthcircuit fault loop impedance should not exceed values specified measured in Table 2 values of earth fault loop impedance should not exceed the values specified in°C
Not taking into account the switching of some loads during the impedance measurement, the errors increased over 30%, maximum allowable error only in the case of networks fed by low-power transformers and for measuring p close to it

Summary

Introduction

The energy dependence of human society is indisputable. In the current context of the energy crisis and the problems related to global warming, electricity is the bridge to the new energy era of the planet. Due to the lack of accessible technology solutions for storing significant amounts of electricity, it is consumed simultaneously with production, which implies the need for the existence of power systems, the most complex and extensive man-made systems Their exploitation must be safe and as simple as possible from the consumers’ perspective. Zloop is the earth fault loop impedance and Ia is the tripping current for safe disconnection time. According to [4], in TN low-voltage distribution network equipped with protective devices, circuit breaker (CB) or general-purpose fuse (gG), the maximum measured tective breaker (CB) or general-purpose fusethe (gG), the maximum valuesdevices, of earthcircuit fault loop impedance should not exceed values specified measured in Table 2 values of earth fault loop impedance should not exceed the values specified in°C. The earth fault loop impedance measurement method, implemented in most testers, is based on the simplified equivalent scheme, shown in Figure 2 [4], in which the voltages are measured between the live and PE (earth) conductors, through a known resistor, Ri, or in no-load (from points a and b perspective) condition

B Normal Operating Unknown

Source of Errors

Suggested Procedure

Validation

Findings

Conclusions