JPH0252992B2 - - Google Patents

Description

[Detailed description of the invention] [Technical field to which the invention pertains] The present invention relates to a partial discharge detection device used for internal partial discharge testing of oil-immersed transformers, etc., or periodic abnormality diagnosis of oil-immersed transformers during energization. In particular, it relates to a device that acoustically detects partial discharge.

[Prior art and its problems]

This type of acoustic partial discharge detection device uses a microphone to receive acoustic waves such as ultrasonic waves accompanying partial discharges generated inside a transformer, etc., and converts this received signal into an appropriate audio frequency. There is a known method in which the tester converts the signal into an electrical signal and listens to it using a receiver, etc. Since this method converts signals into audible sounds, it contains stationary audio noise such as mechanical vibration even when internal partial discharge has not occurred, and testers are able to detect sudden sudden sounds in this noise. The presence or absence of internal discharge is determined by listening to the magnitude of the change. Therefore, when external induction noise etc. enters the detection circuit or the received sound of internal discharge is small, it is difficult to judge whether partial discharge sound is detected inside the transformer due to the influence of the internal noise level of the detection circuit etc. The reality is that it is quite difficult, and even experienced examiners have to make judgments based on their intuition.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned situation, and is capable of confirming the presence or absence of partial discharge without being affected by externally induced noise, etc., and without requiring sophisticated testing techniques. The purpose is to provide a detection device.

[Key points of the invention]

According to the present invention, the above-mentioned object is to amplify the output electrical signal of the acoustic detector by focusing on the fact that the duration of the acoustic detection waveform of the internal partial discharge of the oil-filled electrical appliance is longer than that of the externally induced noise. A waveform converter that converts the output voltage waveform of the detector to be detected into a rectangular wave pulse that lasts for a period exceeding a threshold determined by the stationary noise level, and the output rectangular wave pulse of this waveform converter. A pulse generator is provided which emits a one-shot pulse with a narrow pulse width after a predetermined time delay from the trigger point. If an overlap is detected and an output is sent to the judgment unit, it is determined that an internal partial discharge of a stationary appliance with a long duration has occurred, and the judgment result is displayed.If the square wave pulse does not overlap, the duration is short. This was achieved by configuring the determination unit to determine that it is externally induced noise and block the output.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram of a partial discharge detection device showing an embodiment of the present invention. In the figure, an ultrasonic detector 1 is magnetically attracted to the outer wall of a tank 102 of an oil-immersed transformer 101. When a partial discharge occurs inside the transformer, an ultrasonic pulse generated along with the partial discharge is converted from mechanical vibration to an electrical vibration signal by the ultrasonic detector 1 and output. This detection signal is amplified by an amplifier 2 and passed through a cable 3 to a detector 4.
The signal is rectified and detected. The signal detected by this detector 4 is converted into a rectangular shape with a constant voltage value by the pulse converter 5 from the time when the detected signal exceeds a preset voltage value until it drops below a preset voltage value. converted into wave pulses. The pulse generator 6 is configured to generate a one-shot pulse with a delay of a preset time Ta from the time when the pulse converter 5 receives the output. The determining unit 7, which is an AND circuit, is configured to produce an output only when both the pulse converter 5 and the pulse generator 6 output simultaneously. The output of the determining section 7 is inputted to a pulse counter 9, a meter (not shown), etc., via an output terminal 8, for example. With this configuration, the output is digitally output only when transformer internal discharge is detected, and when there is no partial discharge, no external induction noise is output.

When induced noise enters the detection circuit, the induced noise is generally of a pulse nature and is quite small compared to the duration of the ultrasonic pulse signal (usually 0.2 msec or more). Even if it occurs, its duration is short, and by setting the delay time Ta until the pulse generator 6 generates a one-shot pulse longer than the duration of the induced noise, the one-shot pulse can be generated in the AND circuit. The rectangular wave pulse due to induced noise disappears before it is input. Therefore, there is no output from the AND circuit, and it is possible to reliably prevent induction noise from being mistakenly determined to be internal partial discharge.

Figures 2 and 3 are time charts for the embodiment shown in Figure 1, with Figure 2 showing the case where an internal partial discharge of a stationary appliance is detected, and Figure 3 showing the case where induced noise is detected. ing. In Figure 2, waveform V ₂ is the output ultrasonic pulse waveform of amplifier 2, and waveform V ₄ is the output voltage waveform of detector 4.
_P5 is the output rectangular wave pulse waveform of the pulse converter 5,
Waveform P ₆ is the output one-shot pulse waveform of the pulse generator 6, waveform P ₇ is the output pulse waveform of the judgment unit 7, and the waveform P ₇ is input to the pulse counter 9 etc. via the output terminal 8 to generate an internal partial discharge. It is configured to display. As is clear from the figure, the internal partial discharge pulse detected by the acoustic detector 1 has a high frequency damped oscillation waveform, but the waveform detected by the acoustic detector 4
It is converted into a unipolar attenuated voltage such as a rectified and detected waveform V ₄ by the pulse converter 5, and converted into a rectangular wave pulse P ₅ that lasts for a period Tw exceeding a predetermined threshold value V ₀ . Furthermore, a one-shot pulse is triggered by the rectangular wave pulse _P5 and is output from the pulse generator 6 with a delay of a predetermined time Ta.
P ₆ is input to the judgment unit 7 consisting of an AND circuit together with the rectangular wave pulse P ₅ , and the two pulse voltages P ₅
By detecting the overlap between P ₆ and P 6 , the determination unit 7 outputs a pulse P ₇ .

On the other hand, when induced noise is detected, as shown in the time chart of FIG. 3, since the duration of the waveform V ₂ is short, the pulse width Tw of the output rectangular wave pulse P ₅ of the pulse converter 5 is also short. Thus, from Pulse P ₅
By the time the one-shot pulse P ₆ output from the pulse generator 6 is input to the AND circuit 7 after a Ta time delay, the rectangular wave pulse P ₅ has already become zero, and the judgment unit 7 determines that the two pulse voltages are _P5 and
No overlap occurs on P ₆ . Therefore, the induced noise is blocked by the determination unit 7, and erroneous determination of the induced noise as internal partial discharge is avoided.

The partial discharge detection device of the present invention is not only effective as a partial discharge test and partial discharge monitoring device for oil-immersed electric appliances such as oil-immersed transformers and oil-immersed reactors, but also for detecting the electric field of conductive foreign objects in gas-insulated sealed electric appliances. As a levitation detection device, it can be expected to have the same function as the above-mentioned embodiment.

〔Effect of the invention〕

As described above, the present invention first converts the received signal of the acoustic detector into a rectangular wave pulse, and determines whether or not the pulse width of the rectangular wave pulse has a duration sufficient to determine that it is an internal partial discharge. The device is configured to discriminate between internal partial discharge and induced noise by making a decision using a decision section consisting of a pulse generator that outputs a one-shot pulse after a time delay of 1, and an AND circuit. As a result, even if the received signal level of internal partial discharge and the received signal level of induced noise are equal in magnitude, it is possible to reliably discriminate between the two. Further, the pulse width of the rectangular wave pulse is determined in accordance with the period in which the magnitude of the received signal exceeds a predetermined threshold value. As a result, by setting the threshold value to a value that exceeds the stationary noise level, the influence of stationary noise can be eliminated. Therefore, the effects of externally induced noise and internal noise, which have traditionally been obstacles to determining internal partial discharges, are eliminated, and the presence or absence of internal partial discharges can be confirmed without relying on the intuitive judgments of experienced testers. It is possible to provide a partial discharge detection device that can

[Brief explanation of drawings]

Fig. 1 is a block diagram of a partial discharge detection device showing an embodiment of the present invention, Fig. 2 is a time chart when internal partial discharge is detected in the embodiment of Fig. 1, and Fig. 3 is an externally induced noise This is a time chart when it was detected. In the figure, 1...acoustic detector, 2...amplifier, 4...detector, 5...pulse converter, 6...
Pulse generator, 7... Judgment section, 8... Output terminal,
9... Pulse counter, 101... Stationary electric appliance (oil-immersed transformer), 102... Sealed metal container (tank wall).

Claims (1)

[Claims] 1. In a device for detecting an internal partial discharge of a stationary electric appliance housed in a grounded closed metal container by converting it into an electric signal by an acoustic detector attached to a key point on the wall of the metal container, the acoustic detector a waveform converter that converts the output voltage waveform of the waveform detector into a rectangular wave pulse that lasts for a period in which the output voltage waveform exceeds a predetermined threshold; It is equipped with a pulse generator that is triggered by a pulse and generates a one-shot pulse after a predetermined time delay from the trigger point, and a judgment section that inputs the output rectangular wave pulse and the one-shot pulse. A partial discharge detection device characterized in that only the partial discharge is determined to have occurred inside the sealed metal container, and the determination result is displayed.