JP2006014400A - Differential current monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a differential current monitor in which a differential current monitoring logic is standardized by substantially eliminating the need for setting a timer at each site. <P>SOLUTION: The differential current monitor comprises: a differential current detection circuit 1 for comparing a current flowing into a power facility apparatus with a current flowing out therefrom, and detecting the differential current of unbalance component corresponding to a fault current at the time of tripping a circuit breaker by outputting a trip signal upon occurrence of fault in the apparatus; and a differential current monitoring timer 4 for locking output of the trip signal until the differential current of unbalance component sustains for a predetermined time or longer. The monitor is further provided with: a circuit 2 for detecting the second harmonic from a current signal; and a gate circuit 3 for stopping output from the differential current detection circuit 1 to the differential current monitoring timer 4 when the detected second harmonic is not lower than a predetermined level. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a differential current monitoring device in a digital type protective relay device of a power system facility, and more particularly to a means for making it unnecessary to set a timer circuit on-site so as not to malfunction when a magnetizing inrush current occurs.

  FIG. 4 is a block diagram showing an example of the control logic of the differential current monitoring device in the conventional digital type protective relay device.

  In the differential current monitoring device in the digital type protective relay device, in order to detect the magnetizing inrush current flowing through the power equipment when the circuit breaker is turned on as a difference current abnormality and not to operate the circuit breaker instantaneously, for example, 10 seconds. Alternatively, a 20-second monitoring timer 4A is provided.

  However, depending on the characteristics of the power equipment, the magnetizing inrush current may continue for a long time. At that time, the duration of the magnetizing inrush current is estimated in advance by simulation or the like, and the timer set value is lengthened so that the magnetizing inrush current is not unnecessarily detected as a difference current abnormality.

Japanese Patent Laid-Open No. 8-13165 (pages 3-4, FIGS. 1-2)

  In the above prior art, it is necessary to set a timer according to the power equipment at each site, and the differential current monitoring logic cannot be standardized.

  Also, depending on the characteristics of the power equipment, the inrush current may continue for a long time, so if the timer setting time is increased accordingly, the inrush current will not flow and the time that should be taken for the original failure detection will be extended. There was a problem that the original protection operation was delayed.

  It is an object of the present invention to provide a differential current monitoring device in which timer setting for each site is substantially unnecessary and the differential current monitoring logic is standardized.

  In order to achieve the above object, the present invention compares the current flowing into the power system equipment with the current flowing out of the equipment, and outputs a trip signal when an accident occurs in the equipment to trip the circuit breaker. A differential current detection circuit for detecting an unbalanced difference current corresponding to an accident current, and a differential current monitoring timer for locking an output of a trip signal until the unbalanced difference current continues for a predetermined time or more. In the monitoring device, the second harmonic detection circuit for detecting the second harmonic from the current signal and the output from the difference current detection circuit to the difference current monitoring timer are stopped when the detected second harmonic is a predetermined value or more. A differential current monitoring device including a gate circuit is proposed.

  The current signal analog filter and A / D converter are included as monitoring targets, and a twelfth harmonic detection circuit for monitoring changes in the analog filter characteristics is provided, and outputs of the second harmonic detection circuit and the twelfth harmonic detection circuit An abnormality in the analog filter and the A / D converter may be determined based on whether or not there is.

  According to the present invention, it is not necessary to set a timer according to the power equipment for each site, and the differential current monitoring logic can be standardized.

Further, even if the excitation inrush current continues for a long time due to the characteristics of the power equipment, the second harmonic wave f ₂ associated therewith is detected, so it is not necessary to lengthen the timer setting time, and the original failure in which the excitation inrush current does not flow Can be detected quickly and the protection operation is not delayed.

  As a result, a timer setting for each site is substantially unnecessary, and a differential current monitoring device with a standardized differential current monitoring logic can be obtained.

  Next, an embodiment of the differential current monitoring apparatus according to the present invention will be described with reference to FIGS.

  FIG. 1 is a block diagram showing a control logic of an embodiment of a differential current monitoring device in a digital protection relay device according to the present invention.

  FIG. 2 is a block diagram illustrating an example of a configuration of a power system to which the differential current monitoring device of FIG. 1 is applied. The monitoring target range of the differential current monitoring is a portion indicated by 7.

In the present embodiment, the second harmonic f ₂ detection circuit 2 is used together with the difference current detection circuit 1 provided in the conventional difference current monitoring device of FIG.

Since the second harmonic f ₂ detection circuit 2 is already installed for the trip signal lock of the differential relay, the sequence logic is not complicated even if the differential current monitoring logic of the present invention is adopted. Absent.

In the present embodiment, normally, since the output signal of the second harmonic f ₂ detection circuit 2 is off, the AND gate circuit 3 is open. Therefore, as in the conventional differential current monitoring logic configuration, if the differential current continues for a predetermined time or longer of the monitoring timer 4, it is detected as a differential current monitoring abnormality, and a trip signal is output to the circuit breaker 6 in FIG. To.

When the magnetizing inrush current is generated, the output signal of the second harmonic f ₂ detection circuit 2 is turned on and the AND gate circuit 3 is closed. Therefore, it is not erroneously detected as a difference current monitoring abnormality.

When the magnetizing inrush current ends, the output signal of the second harmonic f ₂ detection circuit 2 is turned off and the AND gate circuit 3 is opened, so that the normal state is restored.

In the present embodiment, when detecting the second harmonic f _2, since locking the differential current monitoring, it can not be detected when an abnormality with the second harmonic wave f ₂ that is to be detected originally was the case and continues occurred afraid There is.

Therefore, a part and a case where an abnormality with the second harmonic f ₂ occurs are examined separately.

  FIG. 3 is a chart showing the relationship between normal / abnormal parts A, B, and C in the power system of FIG. 2 and the presence or absence of harmonic components.

  The monitoring target range 7 is divided into three parts A, B, and C for examination.

Site A is the main circuit, to the site of the second harmonic wave f ₂ is generated, it is mainly during inrush current occurs. In this case, there is no problem even if the differential current monitoring is locked in order to avoid the influence of the magnetizing inrush current.

The part B is a CT and an input converter, and wire and cable disconnection and contact failure are considered. However, never second harmonic f ₂ is generated.

Site C is an analog filter and A / D converter, in this embodiment, in order to monitor changes in the filter characteristics, since monitoring the superposition of the first 12 harmonics f _12, inrush site A The abnormality of this part C can be identified by distinguishing from the event at the time of current generation.

Or as, even when abnormality occurs with the second harmonic wave f ₂ of in the differential current monitoring scope 7, the abnormality can be reliably detected, there is no problem in locking the differential current monitoring.

  Therefore, regardless of the duration of the magnetizing inrush current, it is not necessary to set a timer in the field according to the transformer, and the timer setting of the differential current monitoring device can be standardized to, for example, the shorter one of 10 seconds.

In this differential current monitoring device, the second harmonic f ₂ detection signal is used. If the second harmonic f ₂ does not occur, it can detect abnormalities in the standard monitoring timer time.

Further, since the second harmonic f ₂ detection signal has already been captured, the sequence logic is not complicated.

Further, even when abnormality occurs with the second harmonic wave f ₂ in the difference current monitored range is reliably detectable abnormalities, there is no problem in locking the differential current monitoring.

It is a block diagram which shows the control logic of one Embodiment of the differential current monitoring apparatus in the digital type protective relay apparatus by this invention. It is a block diagram which shows an example of a structure of the electric power system which should apply the difference current monitoring apparatus of FIG. 3 is a chart showing a relationship between normal / abnormality of parts A, B, and C in the power system of FIG. 2 and the presence or absence of harmonic components. It is a block diagram which shows an example of the control logic of the differential current monitoring apparatus in the conventional digital type protective relay apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Difference current detection circuit 2 2nd harmonic f ₂ Detection circuit 3 AND gate circuit 4 Difference current monitoring timer 4A of the present invention 4A Conventional difference current monitoring timer 5 AND gate circuit 6 Breaker 7 Range to be monitored A Main circuit B CT and Input converter C Analog filter and A / D converter

Claims (2)

Compare the current flowing into the power system equipment with the current flowing out of the equipment, and output a trip signal when an accident occurs in the equipment and when the circuit breaker is tripped, the difference between the unbalanced parts corresponding to the accident current In a difference current monitoring device having a difference current detection circuit for detecting a current and a difference current monitoring timer for locking the output of a trip signal until the difference current for the unbalanced portion continues for a predetermined time or more,
A second harmonic detection circuit for detecting a second harmonic from the current signal;
A differential current monitoring apparatus comprising: a gate circuit that stops output from the differential current detection circuit to the differential current monitoring timer when the detected second harmonic is equal to or greater than a predetermined value. In the differential current monitoring apparatus according to claim 1,
Including the analog filter and A / D converter of the current signal as monitoring targets,
A twelfth harmonic detection circuit for monitoring a change in the analog filter characteristic;
An apparatus for monitoring a difference current, wherein an abnormality of the analog filter and the A / D converter is determined based on presence / absence of outputs of the second harmonic detection circuit and the twelfth harmonic detection circuit.

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