Analysis of the Influence of the Insulation Parameters of Medium Voltage Electrical Networks and of the Petersen Coil on the Single-Phase-to-Ground Fault Current

Dumitru Toader,Maria Vintan,Marian Greconici,Claudiu Solea,Daniela Vesa

doi:10.3390/en14051330

Abstract

Settings of protection are essential to ensure the sensitivity and selectivity needed to detect defects. Making the correct settings requires the calculation of the fault currents with as little error as possible. Fault currents are influenced by the parameters of the electrical networks, including the state of the insulation and the Petersen coil, which changes during their operation electrical networks. This paper analyzes how the insulation parameters of medium voltage power lines, the parameters of the Petersen coil used to treat the neutral of the medium voltage electrical network and the value of the resistance at the fault location influence the fault current in the case of a single-phase fault. The large number of single-phase faults that occur in medium voltage electrical networks justifies this analysis. The symmetrical components method was used to calculate the fault current. The results obtained by calculation were verified experimentally by causing a single-phase-to-ground fault in a real medium voltage network. The paper presents the situations in which the analytical calculation of the single-phase-to-ground fault current can lead to inadmissibly large errors, even over 50%, but also the situations in which the errors fall below 3%.

Highlights

Single-phase-to-ground faults are most commonly encountered in the operation of medium voltage electrical networks [1–3], which is why it is necessary to develop protection systems that allow for the selective detection of these faults [4–11]
This paper analyzes the influence of the insulation state of medium voltage networks, and the characteristics of the Petersen coil on the single-phase-to-ground fault current
The mathematical model for calculating the single-phase fault current is presented in the literature, but the insulation of the medium voltage network is usually considered to be ideal, i.e., the losses of active power in the insulation are neglected, and in the equivalent scheme it is considered that the electrical resistance of the insulation (Riz ) has infinite value

Summary

Introduction

Single-phase-to-ground faults are most commonly encountered in the operation of medium voltage electrical networks [1–3], which is why it is necessary to develop protection systems that allow for the selective detection of these faults [4–11]. This paper analyzes the influence of the insulation state of medium voltage networks, and the characteristics of the Petersen coil on the single-phase-to-ground fault current. The mathematical model for calculating the single-phase fault current is presented in the literature, but the insulation of the medium voltage network is usually considered to be ideal, i.e., the losses of active power in the insulation are neglected, and in the equivalent scheme it is considered that the electrical resistance of the insulation (Riz ) has infinite value. The phase difference between the zero-sequence voltage of the medium voltage bus bars in the transformer substation (u0 ) and the total capacitive current of electrical networks is denoted by φc. This paper analyzes the influence of the resistance at the fault location Rt on the single-phase fault current For this parameter, the values 8 Ω, 100 Ω, 268 Ω, 575 Ω and

Results

Discussion

Conclusion