JP4142608B2 - Tree contact monitoring device for distribution lines - Google Patents

Description

  The present invention relates to a tree contact monitoring device for a distribution line.

  Distribution line ground faults are caused by lightning strikes, cable degradation, tree contact, bird contact. It is known that if a ground fault occurs due to any cause, the zero phase voltage Vo and the zero phase current Io change. Generally, these voltage and current changes and abnormalities are measured, and protection is provided by a combination with a ground fault relay or a ground fault direction relay.

  As described in Patent Document 1 (Japanese Patent Application Laid-Open No. 8-265959), when a ground fault occurs, it is known to estimate the cause of the ground fault from the ground fault current waveform. Further, Patent Document 2 (Japanese Patent Laid-Open No. 2002-78188) proposes that a fine ground fault line is specified by observing a fine ground fault phenomenon.

  Normally, it is known that a ground fault phenomenon does not occur suddenly except for a large lightning strike, but a micro ground fault phenomenon in which a slight leakage current flows before that occurs. Therefore, if the condition of the line is monitored at the stage of the micro ground fault phenomenon and the lightning strike, the contact between the line and the tree, the insulation deterioration of the distribution line, etc. can be grasped, a large ground fault phenomenon that will occur in the future can be predicted, and measures are taken early. It is possible.

  However, since conventional micro ground fault detection is based on whether or not an abnormal signal exceeds a threshold value, it is difficult to detect contact of trees, insulation deterioration of distribution lines, etc. at an early stage. It was. In particular, maintenance related to tree contact of distribution lines takes measures such as cutting trees when it is doubtful that distribution lines and trees are in contact, or taking post-conservation measures after a ground fault occurs. This was a very expensive and inefficient maintenance.

JP-A-8-265959

JP 2002-78188 A

  In a fine grounding state before the occurrence of a ground fault, a pulse signal is generated in a cable or the like, whereas in a tree contact, a high resistance contact is made before reaching the ground fault. However, the leakage current signal due to tree contact is not weak and does not have a pulse waveform, but a sine wave waveform of the same commercial frequency as that of the power supply (for example, 50 Hz). For this reason, it is difficult to detect and determine a tree contact signal by discriminating from the residual zero-phase current Io and the residual zero-phase voltage Vo existing in the distribution system, and it has not been realized. A large amount of maintenance costs are incurred due to planned logging of places where trees are in contact with distribution lines. When efficient predictive maintenance and maintenance inspection are considered, it is necessary to detect accurately at the stage of micro ground fault.

  The present invention is intended for initial abnormality monitoring of distribution lines, particularly monitoring of initial lightning strike, tree contact, insulation deterioration, etc., and zero phase voltage Vo, zero phase current Io, phase difference between zero phase voltage and zero phase current. It is acquired at a set cycle, and the amount of change in time-series data is monitored.

  Since the fine ground fault due to the contact of the tree is a leaky phenomenon, both the zero-phase voltage Vo and the zero-phase current Io are measured as waveforms that are relatively small. Further, the magnitude of the zero-phase current Io or the phase with respect to the zero-phase voltage Vo changes on the order of several minutes to several tens of minutes. Therefore, by monitoring the amount of change in the magnitude of the zero-phase voltage Vo and the zero-phase current Io (monitoring the time change) and monitoring the amount of change in the phase difference between the zero-phase voltage Vo and the zero-phase current Io, The presence or absence can be detected.

  In the tree contact monitoring device for a distribution line according to the present invention, it is possible to detect a tree contact that has led to a ground fault without detecting a sign in the prior art, thereby enabling efficient predictive maintenance. In other words, costly maintenance such as planned tree cutting is unnecessary, and efficient maintenance such as taking measures immediately before an abnormality is possible by monitoring the state of tree contact.

  Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a distribution line tree contact monitoring device. The output of the transformer 1 is sent to each distribution system through the main circuit breaker 20 and the sub circuit breakers 21, 22, and 23. A plurality of system loads 5 are connected to each distribution system.

  Since the tree contact becomes a leaky current due to a high-resistance ground fault, the waveforms of the zero-phase voltage Vo and the zero-phase current Io are close to a sine wave. Its absolute value is very small compared to other ground fault accidents, and its progress is relatively slow. In FIG. 1, the zero-phase voltage Vo, the zero-phase current Io, the zero-phase voltage Vo, and the zero-phase current Io at the plurality of slave stations 112, 114, 116, 118 arranged at appropriate locations in the distribution substation and the distribution line. Measure the phase difference. Details of the measurement units in the slave stations 112 to 118 are shown in FIG.

  As an example of the measurement sensor, the zero-phase voltage Vo is measured by voltage measurement sensors 31 to 36 including voltage dividers PD (potential dividers) provided in the slave stations 112 to 118 to create the zero-phase voltage Vo. Each of the voltage measurement sensors 31 to 36 includes a ground resistance R and a ground potential transformer GPT.

  The zero phase current Io is measured by a zero phase current measuring sensor 41, 42, 43, 44, 45, 46 such as a ZCT (Zero phase Current Transformer). The zero-phase voltage Vo and the zero-phase current Io are A / D converted inside the slave station, and the effective value is calculated, and the phase difference between the zero-phase voltage Vo and the zero-phase current Io is also calculated.

  The measured zero-phase voltage Vo, zero-phase current Io, and the phase difference between the zero-phase voltage Vo and the zero-phase current Io are transmitted to the central monitoring system 12 of the monitoring station by optical network communication, for example. 1 and FIG. 2 are configured to perform data communication to the monitoring station and determine the abnormality at the monitoring station, but may be configured to perform the determination within the detection slave stations 112 to 118.

  FIG. 3 shows, as an example at the time of tree contact, the time change of the zero phase voltage Vo, the zero phase current Io, and the phase difference between the zero phase voltage Vo and the zero phase current Io. FIG. 3 shows a time change of about 30 minutes after the trees come into contact with each other, and it can be seen that the time constant increases with time in about 10 minutes. This change is a value smaller than a conventional ground fault detection threshold, for example, a zero-phase current magnitude of 200 mA.

  In other words, even if there is no abnormality, there is about 100 mA in a system with a large zero-phase current Io resulting from three-phase imbalance, and if only the magnitude is judged, it will be buried in the size of the residual, so it will be several tens of orders It is necessary to capture the amount of change. If there is no abnormality such as tree contact, even if a phenomenon such as system switching, load switching, etc. occurs, instantaneous changes and step value fluctuations are observed, but since there are no subsequent fluctuations, the increase or decrease of the change is Can be excluded by judgment.

  Also, single pulses such as lightning and random pulses generated by other devices are not measured with a change in the order of several minutes. That is, paying attention to the fact that there are few fluctuations in the residual zero phase voltage Vo and residual zero phase current Io remaining in the system, the phase difference between the zero phase voltage Vo, the zero phase current Io, and the zero phase voltage Vo and the zero phase current Io. The amount of change (change amount) is monitored.

  Further, the phase of the residual zero-phase current Io and the zero-phase current Io due to the tree contact do not always match. 4 to 6 show waveforms of the synthesized zero-phase current Io actually measured by the phase relationship generated by the residual zero-phase current Io and the tree contact. In FIG. 4, the residual zero-phase current Io and the tree contact zero-phase current Io are in the same phase, and the measured zero-phase current Io increases as the tree contact zero-phase current Io increases. When the time-series data measured in the case of FIG. 4 is plotted, as shown in FIG. 3, the phase difference between the zero-phase voltage Vo, the zero-phase current Io, and the zero-phase voltage Vo and the zero-phase current Io monotonously increases. Therefore, the tree contact can be detected by monitoring the time change.

FIG. 5 shows the case of the reverse phase, and the combined zero-phase current Io becomes smaller. An example of the time change in the case of FIG. 5 is shown in FIG. As can be seen from FIG. 7, even if the generated Vo and Io due to the tree contact increase, the observed Vo and Io monotonously decrease. Therefore, the time change of the measurement data may not only increase monotonously but also decrease monotonously.
Further, FIG. 6 shows a case where the angle is shifted by about 100 degrees. At this time, even if the tree contact zero-phase current Io increases, the magnitude of the measured composite zero-phase current Io does not change. 6 is plotted as shown in FIG. 8. In this case, even if only the magnitudes of the zero-phase voltage Vo and the zero-phase current Io are monitored, the magnitude varies depending on the phase relationship with the residual zero-phase current Io. Does not appear. Besides the magnitudes of the zero-phase voltage Vo and the zero-phase current Io, it is necessary to determine the phase difference between the zero-phase voltage Vo and the zero-phase current Io. As shown in FIG. 2, the zero-phase voltage Vo and the zero-phase current Io It is also effective to monitor the phase difference.

It is the block diagram which showed embodiment of the tree contact monitoring apparatus of the distribution line of this invention. It is the block diagram which showed the sensor part and detection part of the tree contact monitoring apparatus of the distribution line of this invention. It is the figure which showed the time change (monotonous increase) of the phase difference of the zero phase voltage Vo, the zero phase current Io, and the zero phase voltage Vo and the zero phase current Io when a tree contact occurs. It is the figure which showed the time change of the synthetic | combination zero phase current Io by the residual zero phase current Io and the tree contact zero phase current Io. It is the figure which showed the time change of the synthetic | combination zero phase current Io by the residual zero phase current Io and the tree contact zero phase current Io. It is the figure which showed the time change of the synthetic | combination zero phase current Io by the residual zero phase current Io and the tree contact zero phase current Io. It is the figure which showed the time change (monotonic decrease) of the phase difference of zero phase voltage Vo, zero phase current Io, zero phase voltage Vo, and zero phase current Io when a tree contact generate | occur | produces. It is the figure which showed the time change (only a phase difference increases) of the phase difference of zero phase voltage Vo, zero phase current Io, zero phase voltage Vo, and zero phase current Io when a tree contact generate | occur | produces.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Transformer, 20 ... Main circuit breaker, 21, 22, 23 ... Sub circuit breaker, 31, 32, 33, 34, 35, 36 ... Voltage sensor, 41, 42, 43, 44, 45, 46 ... Current sensor 5 ... System load, R ... Ground resistance, GPT ... Ground potential transformer, 112, 114, 116, 118 ... Slave station, 12 ... Central monitoring system.

Claims (2)

Obtains the magnitude of the zero-phase voltage of the distribution line, the magnitude of the zero-phase current, and the phase difference between the zero-phase voltage and the zero-phase current for each set period, and the magnitude of the zero-phase voltage , zero-phase Tree contact monitoring of a distribution line characterized by determining tree contact of a distribution line when there is a temporal change due to a magnitude of current and a monotonic increase or decrease in monotonous time between several minutes to several tens of minutes of the phase difference apparatus. Oite to claim 1, the magnitude of the zero-phase voltage, if not observed the temporal change in the magnitude of the zero-phase current, when there is the temporal change in the phase difference trees contact distribution line A tree contact monitoring device for a distribution line, characterized by determining.

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