Earth fault distance protection

Abstract

Earth fault compensated networks improve power reliability, due to the reason that most of the earth faults extinguish without interferences of the grid operation, thus allowing uninterrupted power supply during the fault situation. However, in compensated networks earth faults can cause big problems, because sometimes they do not extinguish themselves (permanent earth faults). To find the fault point is from high interest also in combination with network expansion (see paper "Earth fault resonant grounded grids -Quo vadis?) .

Single Phase Earth Fault Location in the Medium Voltage Distribution Networks

“…In this paper we are presented the most popular single phase earth fault location methods, which are operated by using a current and voltage of the fundamental frequency, and by analyzing of the transient processes and the higher harmonics during the earth faults [4,5]. The classification of the single phase earth fault location methods is shown in figure 1.…”

“…In the medium voltage networks this method gives good results in the case of the low ohmic faults, but is not reliable in the case of the high ohmic faults [4]. The medium voltage radial network circuit is shown in Figure 3.…”

“…During single phase earth fault the grounding impedance drown three times. It is neglected to use classical method network capacitances [4].…”

“…Using the classical fault distance calculation method the some parameters are neglected [4]: 1. network capacitances are neglected because in the solid grounded neutral networks the earth fault current at the faulted place is similar to the measured current at the measuring point; 2. the classic method does not consider the fault impedance and earth fault current therefore the resistance at the faulted place is very small in the solid grounded neutral and low impedance grounded networks; 3. for the calculation the distance to the single phase earth fault have used only the reactive part of calculated impedance; 4. the grounding impedance and current which goes through compensation coil. With the assumptions above, equation (1) can be simplified to equation (4): As mentioned above, the calculation of the distance to the single phase earth fault have used only the reactive part of the calculated impedance [4]. Dividing the imaginary part of the impedance by the specific positive sequence line impedance we will get the fault distance:…”

“…To increase estimation of accuracy, fault current I z , fault impedance Z z , grounding impedance Z E , and current during through compensation coil I komp must be considered [4].…”