JP4708949B2 - Tracking detector - Google Patents

Description

  The present invention relates to a tracking detection device that detects generation of tracking generated in an outlet or a plug.

If the plug is connected to an outlet installed on the wall or the like for a long time, dust or the like adheres between the plug blades. If dew condensation occurs on such a plug due to temperature changes, etc., a discharge may occur between the plug's blades. As a result, discharge is always generated. As a result, there is a problem that a large current eventually flows and a fire occurs in the worst case.
As an apparatus for detecting the generation of tracking by detecting such a small tracking discharge that occurs before a tracking short circuit occurs, there is a technique disclosed in Patent Document 1. This makes it possible to detect a phenomenon peculiar to tracking discharge by obtaining the charge amount, generation frequency, and frequency-specific level of the high-frequency current from the waveform of the circuit current flowing through the plug. By using this device, the electric circuit can be interrupted before the tracking short circuit occurs.

JP 2004-279205 A

However, in the case of the technique disclosed in Patent Document 1, detection before reaching the tracking short circuit is possible, but it is insufficient in terms of early detection, and it is difficult to detect the carbonization phenomenon at an early stage.
In view of the above problems, an object of the present invention is to provide a tracking detection apparatus capable of detecting tracking generation at an early stage.

In order to solve the above-mentioned problem, the invention described in claim 1 is characterized in that current detection means for detecting a circuit current and at least three types of frequencies of a fundamental wave, a third harmonic, and a fifth harmonic from the detected current waveform possess a harmonic extracting means for extracting a component, the fundamental wave of the path current, third harmonic, a tracking decision circuit peak value of each of the fifth harmonic is determined that tracking discharge generation After satisfies a predetermined relationship The tracking determination circuit performs tracking when the sum of the peak value of the third harmonic and the peak value of the fifth harmonic exceeds the peak value of the fundamental wave when the load electrically connected to the electric circuit is not operating. It is determined that a discharge has occurred .
With this configuration, it is possible to detect a discharge phenomenon that occurs only when there is moisture between the plug blades, and it is possible to detect the generation of tracking at an early stage.

And tracking discharge can be detected reliably.

According to a second aspect of the invention, in the invention described in claim 1, before Symbol tracking decision circuit, said peak value in a state where path to the load is connected to the electrical is not running third harmonic and the fifth When the number of times that the sum of the peak values of the harmonics exceeds the peak value of the fundamental wave reaches a predetermined number within a specific time, it is determined that tracking is generated.
With this configuration , generation of tracking can be reliably detected.

According to a third aspect of the present invention, in the first or second aspect of the present invention, a low-pass filter for eliminating a harmonic component exceeding the fifth harmonic is provided between the current detection unit and the harmonic extraction unit. It is characterized by comprising.
With this configuration, the third and fifth harmonics become prominent, and tracking determination becomes easy.

  According to the present invention, it is possible to detect a discharge phenomenon that occurs only when there is moisture between both plug blades, and it is possible to detect the generation of tracking at an early stage.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments of the invention will be described in detail with reference to the drawings. FIG. 1 is a circuit block diagram showing an example of an embodiment of a tracking detection apparatus according to the present invention, and shows a circuit breaker that interrupts an electric circuit when tracking is generated. In the figure, 1 is a current transformer as a current detecting means for detecting the current of the electric circuit 5, 2 is a filter circuit having a low-pass filter (LPF) that removes a high frequency of 10 kHz or more, and 3 is a detection of tracking generation. The tracking detection unit 4 is a blocking means for cutting off the electric circuit.

  The tracking detection unit 3 includes a fast Fourier transform circuit (hereinafter referred to as FFT) 10 as a harmonic extraction means for frequency-resolving the detected circuit current, and an A / D conversion circuit (converter) for converting the frequency-resolved current waveform into digital data. First A / D conversion circuit) 11, discharge detection circuit 12 for extracting a discharge current waveform, A / D conversion circuit (second A / D conversion circuit) 13 for converting the extracted discharge current waveform into digital data, and a tracking determination circuit Are provided, a register circuit 15 for storing various determination elements and calculation values, and a determination output circuit 16 for outputting an operation signal of the blocking means 4. The arithmetic circuit 14 is constituted by a CPU.

  The operation of the tracking detection unit configured as described above will be described with reference to the flowchart of FIG. First, the present invention pays attention to the discharge between the blades generated when moisture is present between the blades of the plug due to condensation as a method for detecting the generation of tracking at an early stage. The discharge phenomenon that occurs at this time is configured to detect the tracking discharge at an early stage by detecting the change since the discharge current waveform greatly changes due to evaporation of water accompanying the discharge. It has been found that this discharge waveform has a peak value below 10 kHz.

  FIG. 3 shows an example of a current waveform (upper) and a frequency decomposition diagram (lower) of a tracking discharge current generated under such conditions. (A) shows a state in which 4 minutes and 52 seconds elapse after the discharge occurs ( b) is current data after 6 minutes 19 seconds. In the figure, P1 is the waveform of the fundamental wave, P2 is the third harmonic, and P3 is the fifth harmonic. In this discharge waveform, water droplets are dropped on both blades of a plug connected to an outlet to artificially create a dew condensation state and generate a tracking discharge. From this data, it can be seen that in the tracking discharge, the third and fifth harmonics increase when 6 minutes or more have elapsed from the occurrence of the discharge. Based on such changes, the present invention detects the initial tracking discharge. Here, the frequency of the electric circuit is 60 Hz, the fundamental frequency is 60 Hz, the third harmonic is 180 Hz, and the fifth harmonic is 300 Hz.

  In order to detect such a characteristic, the fundamental wave, the third harmonic wave, and the fifth harmonic wave component are extracted from the current waveform detected by the current transformer 1 (S1) (S2) by the FFT 10 (S2). A comparison operation is performed (S3). The arithmetic circuit 14 compares the peak value of the fundamental wave with the sum of the peak values of the third harmonic and the fifth harmonic, and the sum of the peak value of the third harmonic and the peak value of the fifth harmonic is the fundamental wave. If the peak value is exceeded, that is, if [fundamental wave <(third harmonic + fifth harmonic)], it is determined that tracking discharge has occurred.

  When this tracking discharge occurs a predetermined number of times within a predetermined time, it is determined that tracking is generated and the plug has deteriorated (S4), and a tracking generation signal is output (S5). As a specific example, FFT analysis is performed every 100 mS, and if a discharge (tracking discharge) satisfying the above condition is generated 5 times or more in 2 seconds, it is determined that tracking is generated and a tracking generation signal is output. In response to this output signal, the determination output circuit 16 outputs a drive signal for the blocking means 4 and the electric circuit 5 is blocked.

In this way, by detecting the discharge phenomenon that occurs only when there is moisture between both plug blades, it becomes possible to detect the generation of tracking at an early stage, by performing an operation to shut off the electric circuit at an early stage, Treatment can be performed before the plug or the like is greatly deteriorated.
However, in this embodiment, the harmonic information is input to the arithmetic circuit 14, and at the same time, the discharge current information extracted by the discharge detection circuit 12 is converted into digital data and input. In response to this signal, the arithmetic circuit 14 is configured to detect a relatively small discharge (tracking discharge) that occurs even when the tracking progresses and the air is dry. By detecting the tracking discharge in this state as well, the state in which deterioration has progressed can be reliably detected.

As an example, a condition is shown in which a tracking discharge is determined to occur when the tracking discharge occurs, for example, 5 times within a specific time (2 seconds). However, even if a tracking generation signal is output only by detecting the tracking discharge once. Alternatively, the tracking generation signal may be output by setting a larger number of occurrences.
Further, in the case of [fundamental wave <(third harmonic wave + fifth harmonic wave)], detection is made as a tracking occurrence, but as [fundamental wave <(third harmonic wave or fifth harmonic wave)] Tracking discharge can be detected. Although the third and fifth harmonics can be extracted without the filter circuit 2, the discharge waveform can be detected with higher accuracy if the frequency component of 10 kHz or higher is deleted.

  The circuit block diagram of FIG. 4 shows another form of the tracking detection circuit of the present invention. The filter circuit 18 is different from the above embodiment, and is configured by combining LPF and HPF. For example, if an elimination filter is formed by combining an LPF that passes a waveform of 300 Hz or less and a high-pass filter (HPF) that passes 1 kHz or more in the filter circuit, the third and fifth harmonics (fundamental waves) (In the case of 60 Hz) can be effectively extracted, and a waveform of 1 kHz or more, which is a feature of the micro spark discharge that occurs during tracking progress, can be extracted, and the generation of tracking can be detected effectively from both data. It becomes possible.

  In addition, if a bandpass filter that passes the third harmonic and the fifth harmonic is configured by LPF and HPF, it is easy to extract and compare the third harmonic and the fifth harmonic. In the case of tracking discharge generated in the presence of moisture, it has been confirmed that the third harmonic and the fifth harmonic have specific properties. Therefore, it is possible to know the occurrence of tracking discharge only by comparing the third harmonic and the fifth harmonic. For example, it is possible to determine that a tracking discharge has occurred when a waveform satisfying [third harmonic> fifth harmonic] is detected immediately after [third harmonic <fifth harmonic] is detected.

It is a circuit block diagram which shows an example of embodiment of the tracking detection apparatus which concerns on this invention. It is a flowchart which shows the flow of the tracking detection operation | movement of FIG. An example of a frequency decomposition diagram of the tracking discharge current is shown. (A) is data after 4 minutes and 52 seconds have elapsed since the occurrence of tracking discharge, and (b) is data after 6 minutes and 19 seconds have elapsed. It is a circuit block diagram which shows the other example of this invention.

Explanation of symbols

  1 .... Current transformer (current detection means) 2 .... Filter circuit (low-pass filter) 3 .... Tracking detector 10 .... Fast Fourier transform circuit (harmonic extraction means) 14 .... Operation circuit (Tracking judgment circuit), 18 ..filter circuit.

Claims (3)

Current detection means for detecting a circuit current, harmonic extraction means for extracting at least three types of frequency components of a fundamental wave, a third harmonic, and a fifth harmonic from the detected current waveform; third harmonic, the peak value of each of the fifth harmonic will have a tracking determining circuit for determining a tracking discharge generation After satisfies a predetermined relation,
The tracking determination circuit performs tracking discharge when the sum of the peak value of the third harmonic and the peak value of the fifth harmonic exceeds the peak value of the fundamental wave when the load electrically connected to the electric circuit is not operating. A tracking detection apparatus characterized by determining occurrence . Before Symbol tracking decision circuit, the sum of the third harmonic of the peak value and the peak value of the fifth harmonic in a state where electrical and has load connected to is not running exceeds the peak value of the fundamental wave to said path The tracking detection apparatus according to claim 1 , wherein when the number of times reaches a predetermined number of times within a specific time, it is determined that tracking is generated. The tracking detection apparatus according to claim 1 or 2, further comprising a low-pass filter for eliminating a harmonic component exceeding the fifth harmonic between the current detection means and the harmonic extraction means.

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