Novosibirsk State Technical University (NSTU) has developed a method that can be used to locate single-phase short circuits on overhead power transmission lines. It allows you to determine the location of damage to the phase insulation without installing expensive equipment and increase the reliability of the power supply by quickly detecting damaged areas.
According to Vladimir Kachesov, Associate Professor of the Department of High Voltage Engineering and Electrophysics at NSTU-NETI, Doctor of Technical Sciences, the most common damage in electrical networks (ES) with an inefficiently grounded neutral (in Russia, this is a 6-35 kV ES) is a single-phase earth fault.
When a single-phase earth fault occurs in such electrical systems, the fault current is limited only by the capacity of the electrical network and is too small for the relay protection to operate. The line continues to work, but the OPC significantly increases the voltage at other phases. This creates a risk of breakdown of the insulation of healthy phases, occurrence of phase-to-phase short circuits and may eventually lead to an emergency shutdown of consumers. In case of an OPR, it is not enough to identify the damaged transmission line, an important task is to determine the location (zone) of the damage so that an operational field team can localize and eliminate the malfunction.
Scientists at NSTU-NETI have proposed a method for determining a single-phase ground fault on a power transmission line based on measurement results from several high-frequency sensors located along the power line and connected to the phase wires of the line.
"The method is based on the excitation of high-frequency oscillations in simple RCL sensors. The amplitude of the oscillations is determined by the steepness of the voltage wave front that occurs during a short circuit, and decreases significantly with increasing distance from the fault site. The analysis of telemetry data by constructing a polynomial dependence of the voltages measured on the storage capacitors of the sensors and finding its maximum allows us to determine the fault zone," said Vladimir Kachesov.
The operability of the method of localization of the damage zone was tested on an existing 10 kV overhead power line. During the experiment, the sensors demonstrated the necessary sensitivity, and the recorded signals confirmed the effectiveness of the proposed solution for accurately determining the location of damage.
The relative error of the method depends on various factors, namely, the ways in which RF sensors are positioned along the line, their number, the length of the line itself, and the resistivity of the earth. Based on the simulation, the scientists concluded that in order to minimize the error, it is advisable to place the sensors at an equal distance along the overhead line.
The method proposed by NSTU-NETI scientists can be used to locate single-phase short circuits on overhead power lines, especially where it is not possible to install zero-sequence current measuring transformers.