Detection and Location of Earth Fault in MV Feeders Using Screen Earthing Current Measurements

Abstract

The paper analyzes the utilization of cable screen currents for earth fault identification and location. Attention is paid on cable and mixed feeders—cable and overhead lines. The principle of operation is based on utilization of 3 criterion values: Ratio of cable screen earthing current and zero sequence cable core current—RF110/15, phase shift between cable screen earthing current and zero sequence cable core current—α and cable screen admittance defined as a ratio of cable screen earthing current and zero sequence voltage—Y0cs. Earth fault location is possible thanks to discovered relation between RF110/15 and α, whereas Y0cs allows for reliable detection of earth faults. Detection and identification are very important because it allows to increase the reliability of supply—reduce downtime and number of consumers affected by the fault. The article presents a phase to ground fault current flow for different power system configurations. At the end solution, which improves location capabilities is proposed. The solution is analyzed in PSCAD software and verified by network experiment.

Monitoring of MV Cable Screens, Cable Joints and Earthing Systems Using Cable Screen Current Measurements

“…Earthing screen current sources marked with blue color are presented in the following paragraph, whereas other screen current sources are presented in previous papers [16][17][18]. Papers [16,17] present the earthing screen current sources under earth fault conditions-marked with red and green color in Figure 1. Paper [18] presents earthing screen current sources under load and no-load conditions-marked with yellow and grey color.…”

“…According to the theory presented in previous papers [16,17], the amplitude of screen earthing current depends on:…”

“…cable laying formation, -parameters of cable line, in particular cable screen cross section, -earthing system resistance, -length of the cable line. According to the theory presented in previous papers [16,17], the amplitude of screen earthing current depends on:…”

“…The Ircs is bigger in cables laid in the flat formation and smaller in cables laid in trefoil formation. The non-intuitional relation According to the theory presented in previous papers [16,17], the amplitude of screen earthing current depends on:…”

“…An alternative for conventional monitoring of the earthing systems is to measure and analyze residual cable screen earthing system current-I rcs . Utilization of I rcs allows for simultaneous monitoring of many earthing systems in remote locations, and what is most important is that the proposed system utilizes exactly the same hardware as the system for detection and location of earth faults [16][17][18]. It is possible to detect degradation, mechanical damage, or theft of earthing systems.…”