JP-7855152-B1 - Protective relay and method for controlling a protective relay

Abstract

The protective relay comprises a slope change detection relay that detects changes in the slope of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, and a command output unit that outputs an open command for a second circuit breaker located near the first circuit breaker when it is determined that the open command for the first circuit breaker continues and the slope change detection relay is not operating.

Inventors

• 浅井 ユリ
• 田中 俊哉

Assignees

• 三菱電機株式会社

Dates

Publication Date

20260507

Application Date

20250722

Claims (6)

1. A slope change detection relay that detects changes in the slope of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, A protective relay comprising: a command output unit that outputs an opening command for a second circuit breaker in the vicinity of the first circuit breaker when the opening command for the first circuit breaker continues and the tilt change detection relay determines that it has not detected a change in the tilt of the current magnitude .
2. The protective relay according to claim 1, wherein the command output unit outputs an open command for the second circuit breaker surrounding the first circuit breaker when the open command is continued and the slope change detection relay determines that no change in the slope of the current magnitude has been detected for a predetermined period of time.
3. The protective relay according to claim 1, wherein the command output unit outputs an open command for the second circuit breaker surrounding the first circuit breaker when the open command is continued and the slope change detection relay determines that the slope of the current magnitude does not change to a predetermined value within a predetermined period.
4. The system further includes an overcurrent detection relay that detects whether the magnitude of the current in the first circuit breaker is greater than or equal to a threshold, The protective relay according to claim 1, wherein the command output unit outputs an open command for a second circuit breaker near the first circuit breaker when the open command is continued, the slope of the current magnitude does not change to a predetermined value by the slope change detection relay during a predetermined period, and the overcurrent detection relay determines that the current magnitude is greater than or equal to a threshold.
5. The system further includes an overcurrent detection relay that detects whether the magnitude of the current in the first circuit breaker is greater than or equal to a threshold, The protective relay according to claim 1, wherein the command output unit outputs an open command for a second circuit breaker near the first circuit breaker when the open command is continued and the slope of the current magnitude does not change to a predetermined value by the slope change detection relay during a predetermined period, or when the overcurrent detection relay determines that the current magnitude is above a threshold.
6. A step of detecting a change in the gradient of the magnitude of the current flowing through a current transformer installed near a first circuit breaker in a DC power system, A control method for a protective relay, comprising the step of outputting an open command for a second circuit breaker in the vicinity of the first circuit breaker when it is determined that the open command for the first circuit breaker continues and no change in the slope of the magnitude of the current is detected.

Description

This disclosure relates to a circuit breaker malfunction prevention measure to be implemented in a protective relay installed in a DC power system. Generally, protective relays are provided that output an open command to the circuit breaker in order to eliminate a fault in a power transmission line (see Patent Documents 1 and 2). In this regard, even if a protective relay outputs an open command to the circuit breaker when a system fault occurs, the circuit breaker may not be able to properly perform its function due to a malfunction. When such a circuit breaker failure (CBF) occurs, it can lead to equipment damage due to fault current, expansion of the fault area, widening of the power outage area, decreased system stability, and the spread of the fault to the entire power system. Therefore, in order to quickly resolve the fault, a CBF countermeasure (circuit breaker malfunction countermeasure) function is provided that outputs an open command to the adjacent circuit breaker when a CBF is detected. Japanese Unexamined Patent Publication No. 64-8828Japanese Patent Publication No. 2021-136078 This figure schematically shows an example of the configuration of a DC power system in which a protective relay equipped with a CBF countermeasure function according to Embodiment 1 is installed.This block diagram shows the hardware configuration of a digital protection relay device that constitutes a protection relay system according to Embodiment 1.This is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 1.This figure illustrates the current change detected by the current transformer 7 according to Embodiment 1.This is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 2.This figure illustrates the current change detected by the current transformer 7 according to Embodiment 2.This is a block diagram showing the functional configuration of the CBF countermeasure function according to Embodiment 3. The following describes each embodiment in detail with reference to the drawings. Note that identical or corresponding parts are denoted by the same reference numerals, and their descriptions may not be repeated. Embodiment 1. [Power System Configuration] Figure 1 is a schematic diagram showing an example of the configuration of a DC power system equipped with a protective relay that has a CBF (Cold Breakdown Fever) countermeasure function according to Embodiment 1. Referring to Figure 1, in the DC power system, wire 1 is connected to busbar 2. Furthermore, circuit breakers 4 and 5 and a current transformer 7 are provided on wire 1. The power system in Figure 1 will be described in the case of a DC system. Also, a circuit breaker 6 is provided on busbar 2. The protective relay system 10 includes a main relay function 20 for detecting faults in the power system and a circuit breaker malfunction prevention function (CBF prevention function) 30. Normally, the main relay function 20 and the CBF (Cold Burden Fuel) countermeasure function 30 are calculated and processed by a common CPU implemented in the protective relay unit. The main relay function 20 detects the occurrence of a fault in the power system based on the current signal CS from the current transformer 7 installed on the power line 1. When a fault is detected, it outputs an open command TR1 to the circuit breaker 4 and an open command TR2 to the CBF countermeasure function 30. The fault determination method by the main relay function 20 is not particularly limited. The main relay function 20 may include, for example, a current differential relay element or a distance relay element. In the case of a current differential relay element, current signals from other current transformers (not shown) installed on the power line 1 are also input to the main relay function 20. In the case of a distance relay element, voltage signals from a voltage transformer (not shown) installed on the busbar 2 are also input to the main relay function 20. The CBF (Critical Base Fault) countermeasure function 30 includes a CBF detection element (for example, reference numeral 40 in Figure 3) for determining the presence or absence of fault current based on the current signal CS from the current transformer 7. If the CBF countermeasure function 30 receives an open command TR2 from the main relay function 20 and the open command TR2 persists even after the time required for the circuit breaker 4 to open has elapsed, it determines that the circuit breaker 4 is not operating and outputs an open command TR3 to trip the surrounding circuit breakers 5 and 6, respectively. The main relay function 20 and the CBF (Cold Burden Fever) countermeasure function 30 described above are configured by the digital protection relay device shown in Figure 2. [Hardware configuration of digital protection relay device] Figure 2 is a block diagram showing the hardware configuration of a digital