KR-20260065777-A - CONTROL METHOD FOR PREVENTING MALFUNCTION OF DIGITAL PROTECTION RELAY FOR DETERMINING GROUND FAULT IN SELF-SECTION

Abstract

A control method for preventing malfunction of a protective relay for determining a self-section ground fault is disclosed. A control device for preventing malfunction of a protective relay for determining a self-section ground fault according to one aspect of the present invention includes a measurement module for measuring the current of each phase of a transformer, and a processor for calculating the zero-sequence current and the negative-sequence current of each phase based on the current of each phase measured through the measurement module, and for determining whether a self-section ground fault has occurred based on the zero-sequence current and the negative-sequence current of each phase.

Inventors

• 오세환

Assignees

• 한국전력공사

Dates

Publication Date

20260511

Application Date

20260424

Claims (1)

1. A step in which a processor measures the current of each phase of a transformer through a measurement module; The above processor calculates the zero-sequence current and the negative-sequence current of each phase based on the current of each phase of the transformer; and The above processor includes a step of determining whether a magnetic section ground fault has occurred based on the zero-sequence current and the negative-sequence current of each phase, and In the step of determining whether a ground fault has occurred in the above-mentioned section, The above processor determines whether a ground fault has occurred based on the zero-sequence current of each phase and determines whether an unbalanced fault has occurred based on the negative-sequence current of each phase, and determines whether a ground fault has occurred in its own section based on the ground fault occurrence and the unbalanced fault occurrence. The above processor determines that a self-section ground fault has occurred when a ground fault and an unbalanced fault occur, and If a ground fault occurs and no imbalance fault occurs, it is determined that a ground fault has occurred in another section, and In the above calculation step, The processor compensates for the magnitude of the current of each phase of the transformer, and calculates the zero-sequence current and the negative-sequence current of each phase based on the magnitude-compensated current of each phase, respectively. In the step of determining whether a ground fault has occurred in the above-mentioned section, The above processor compares the zero-sequence current of each phase with a preset first reference value, and determines that a ground fault has occurred in the phase where the zero-sequence current is greater than or equal to the reference value. The negative sequence current of each phase is compared with a preset second reference value, and it is determined that an unbalanced fault has occurred in a phase where the negative sequence current is greater than or equal to the second reference value. In the step of determining whether a ground fault has occurred in the above-mentioned section, A control method for preventing malfunction of a protective relay for determining a self-section ground fault, characterized in that the above processor outputs a trip signal when a self-section ground fault is determined, and outputs a ground fault alarm when a ground fault in another section is determined.

Description

Control Method for Preventing Malfunction of Digital Protection Relay for Determining Ground Fault in Self-Segment The present invention relates to a control method for preventing malfunction of a protective relay for determining a self-section ground fault, and more specifically, to a control method for preventing malfunction of a protective relay for determining a self-section ground fault that enables determining a self-section ground fault based on the zero-sequence current and the negative-sequence current of each phase of a transformer. Under the goal of carbon neutrality, the deployment of distributed power sources is continuously expanding, and research for stable supply and efficient demand is actively underway in various fields. Carbon neutrality aims to prevent global warming as much as possible by fixing carbon emissions at a specific point in time. Since carbon is emitted from fossil fuels, the new and renewable energy industry, which does not use fossil fuels, has begun to emerge worldwide. Various issues arise as we transition from conventional fossil fuel-powered synchronous generators to power generation using renewable energy sources. The most significant issue concerns distributed power generation. The shift is from the traditional method of constructing large-scale power complexes near the coast to bring electricity to consumers, to a new approach where small-scale distributed power sources are installed near consumers to be used internally and supplied to nearby areas. Countries with a high understanding of renewable energy, such as Europe, face no major difficulties in increasing the share of renewable energy generation to immediately achieve carbon neutrality; however, Korea is experiencing various issues. Consequently, standards for maintaining power grid reliability and electricity quality are continuously being revised, and recently, regulations known as Fault Ride Through (FRT) have even been introduced. In addition to these, there are various problems regarding grid protection, but the biggest issue is that all renewable energy distributed power sources are inverter-based. Inverter-based distributed power sources utilize IGBT devices to achieve micro-level control speeds. Since the inverter converts DC voltage according to the desired operating mode (power factor control, constant P output, constant Q output, Vac control, etc.) and supplies it to the AC grid, the fault current exhibits a form entirely different from that of conventional synchronous generators in the event of a power grid failure. Inverter control methods can take various forms, and since inverter control is performed in micro-time units, the value is significantly smaller than the minimum unit (1/16 Cycle) detected by the protection relay. Therefore, although a fault current may flow momentarily when a fault occurs, the time is in micro-units and is significantly smaller than the cycle unit that the protection relay can recognize, so it is sometimes considered that inverter-based power sources have no fault current contribution. However, in the event of a ground fault in another section, the ground fault current returns through the neutral point on the primary side of the interconnection transformer installed to connect the distributed power source to the power system. For example, as shown in Figure 1, the fault current supplied from the power system is A, but as this A current returns through the ground, some of it flows to the ground of the distributed power source connected transformer, so B current flows to the healthy line, which can cause the protective relay to malfunction. Directional ground fault overcurrent relays are applied to prevent healthy magnetic lines from tripping in the event of a fault in another line. However, in order to apply directional ground fault overcurrent relays, there is a problem in that existing non-directional OCGRs must be replaced with directional OCGRs. Furthermore, changes in the distribution system make it difficult to clearly manage which lines are connected to distributed power sources. Additionally, there is a risk of malfunction if not only the distributed power sources but also the customer transformers are grounded. Moreover, since distributed power lines must be connected via DOCGR during a line outage, there is a problem where power outages are impossible. For these reasons, all interconnection lines must use directional protection relays, regardless of whether distributed power sources are present or not. There are tens of thousands of distribution lines alone, and the cost of replacing all of them with directional overcurrent relays amounts to tens of billions of won. This is practically impossible, and ultimately, the only option is to purchase directional protection relays in bulk when replacing power facilities after their service life has expired, which will take more than 10 to 20 years. Therefore, there is a need for technology that can prevent malfunction