JPS6150264B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an insulation diagnosis method and apparatus for easily diagnosing the function of an equipment insulation structure.

The insulation structure deteriorates due to the effects of various electrical, mechanical, thermal, and chemical stresses that occur during long-term operation of the equipment in use, and in extreme cases, it may not be able to fulfill its insulating function. This may lead to dielectric breakdown and cause a serious accident. Various insulation diagnostic methods have been proposed to prevent insulation breakdown accidents. However, there are various obstacles to performing reliable insulation diagnosis in a non-destructive manner at the site where equipment is installed. In particular, when using an alternating current voltage in an electrical test in which a relatively high voltage is applied for inspection, a large power supply capacity is required, which is often difficult. For this reason, a DC high voltage power supply is used. However, in general, the DC voltage application method provides insufficient judgment material compared to the AC voltage application method. In other words, when AC is applied, it is easy to generate partial discharges that sensitively indicate internal defects in the insulating structure, making it possible to detect partial discharges, but when DC is applied, partial discharges can only be seen during voltage step-up or step-down processes. . For this reason, conventional DC application methods have had to mainly measure insulation resistance. When measuring insulation resistance, it is often difficult to detect even serious defects such as peeling of the insulation structure unless there is moisture absorption.

The present invention was made in view of the drawbacks of the conventional method as described above, and uses a relatively lightweight device to apply a direct current high voltage in a linearly rising and falling manner, thereby generating a partial discharge. Thus, the present invention provides a rational insulation diagnosis method and apparatus for obtaining a wealth of deterioration determination data equivalent to or greater than that of the conventional AC voltage application method.

FIG. 1 is a block diagram showing the basic configuration of the present invention. In FIG. 1, a voltage converted into DC by a low voltage rectifier circuit 1 is converted into a high frequency low voltage of several kHz by a DC/AC converter circuit 2. The waveform that has become a high voltage through the small and small capacity high frequency step-up transformer 3 passes through the polarity switch 14 and the high voltage rectifier circuit 4 and is applied to the test object 8 as a forward/reverse direct current high voltage. The applied voltage waveform is divided by a voltage divider 7,
It is compared and verified with the output voltage waveform of the reference voltage generator 5 which has been programmed in advance by a comparison and verification device 6,
If there is an excess or deficiency, the output level of the low voltage rectifier circuit is controlled to be increased or decreased. Of the current flowing through the test object, the pulsed current caused by the discharge is detected by the pulse transformer 9, passes through the high frequency amplifier 10 and the waveform shaping circuit 11, and is counted by the pulse counter 13 to accumulate the number of pulses generated during the test. The number will be displayed. Further, the output waveform of the waveform shaping circuit 11 together with the applied voltage waveform supplied from the voltage divider 7 is led to the waveform recorder 12, and the time point at which the discharge occurs is displayed in relation to the applied voltage waveform. The reference voltage generator 5 issues instructions for linear step-up, constant voltage maintenance, and linear step-down, and after step-down, acts on the polarity switch 14 to reverse the polarity of the voltage. As a result, a DC high voltage that repeats linear changes in forward and reverse directions is generated according to a predetermined program, and is applied to the test object.

Furthermore, it is conceivable that the power source of the device is not alternating current but direct current such as a storage battery. This case can be easily realized by incorporating a DC/AC converter circuit before the low voltage rectifier circuit 1. Furthermore, by inserting a DC current detection circuit in series with the test object 8, it can also function as a conventional insulation resistance meter. The use of the above-mentioned insulation diagnostic device of the present invention provides the following advantages over conventional diagnostic devices. In other words, in the conventional applied voltage waveform, as shown in Figure 2A, little attention is paid to the step-up and step-down waveforms, and as a result, most of the applied voltage waveforms are based on the capacitance of the test object, the limiting resistance of the DC power source, and the step-up speed on the AC side. The waveform is as follows. Therefore, there are many examples of exponentially rising and falling curves. The discharge pulse phase that occurs at this time is as shown in FIG. 2B. That is, discharge pulses are generated in a concentrated manner at the initial stage when the voltage change rate is large, and as the voltage change becomes gradual, discharge pulses become less likely to occur. Therefore, if a discharge measurement is performed in a poor measurement environment and there is a lot of external noise, once the discharge concentration period is interrupted and the measurement fails, re-measurement cannot be easily performed. In theory, even if the voltage step-up process fails, it would be possible to re-measure the voltage during the step-down process, but in reality, due to the asymmetry of the electrode configuration, the accumulated charge is often not discharged during the step-down process. Even if the voltage is increased again, the accumulated charge is insufficiently discharged, so new discharge detection is impossible. This is the reason why it is difficult to detect discharge using DC voltage. Next, FIG. 3A shows an applied voltage waveform according to the present invention. According to this waveform, the above drawbacks can be eliminated. First, since the voltage step-up and step-down processes are intentionally linearly changed, there is no spacing between discharge occurrences, as shown in FIG. 3B, and detection failures are eliminated. Furthermore, since a DC voltage of the opposite polarity that increases at a constant speed is applied by reversing the polarity after stepping down, the applied DC voltage from the perspective of partial discharge detection is twice as large as that of the conventional method. This increases the detection ability. This bipolar application solves the problem of unipolar polarized charging, which is a drawback of the direct current application method. Of course, the conventional insulation resistance time characteristics can be measured by using the constant voltage holding period.

The waveform recorder displays the discharge pulse generation phase as shown in FIG. 3B in accordance with the applied DC waveform. This allows the degree of moisture absorption of the insulator to be estimated. In other words, research has revealed that in dry insulators, discharges easily occur only during changes in the applied voltage waveform, but when moisture is absorbed, discharges occur frequently even during constant voltage periods. Therefore, the pulse generation phase indicator is extremely effective for insulation diagnosis.

By displaying the cumulative number of pulses occurring during the test, the progress of deterioration can be easily quantified. In addition, partial discharge measurement may lead to erroneous judgments if it is not reproducible, but this method has the advantage that reproducibility can be easily checked because DC voltages of both positive and negative polarities can be applied repeatedly.

As explained above, according to the present invention, a relatively small device is used to apply a DC high voltage that alternately repeats linear voltage rises and falls in both forward and reverse polarities to an insulator. It is a rational method that eliminates the influence of cumulative charges, uniformizes the generation of partial discharge pulses, improves reproducibility and measurement accuracy, and allows the degree of insulation to be measured numerically by counting the generated pulses. An insulation diagnostic method and device can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the basic configuration of the insulation diagnosis device according to the present invention, FIGS. 2A and B are diagrams showing examples of test voltage waveforms and discharge pulses in the conventional insulation diagnosis method, and FIGS. 3A and B FIG. 2 is a diagram showing an example of a test voltage waveform and a discharge pulse in the present invention. 1...Low voltage rectifier circuit, 2...DC exchange circuit, 3...Step-up transformer, 4...High voltage rectifier circuit, 5
...Reference voltage generator, 6... Comparison verifier, 7...
Voltage divider, 8... Test object, 9... Pulse transformer, 10... High frequency amplifier, 11... Waveform shaping circuit, 12... Waveform recorder, 13... Pulse counter, 14... Polarity switcher .

Claims (1)

[Claims] 1. A high voltage applied to an insulator is linearly raised and lowered at a predetermined slope up to a predetermined forward and reverse voltage, and when each of the predetermined voltages is reached, the voltage is maintained for a predetermined period of time. An insulation diagnosis method characterized in that the partial discharge that occurs is measured in response to the applied voltage waveform by repeating the above steps. 2. A forward/reverse direct current high voltage generator that repeats linear voltage rise, constant voltage maintenance, and linear voltage fall according to a predetermined program, and a partial discharge that occurs in an insulator to which the high voltage is applied, corresponding to the applied voltage waveform. An insulation diagnostic device comprising: a display device for counting and displaying the measured values.