JP2654794B2 - Partial discharge detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a partial discharge detection device for detecting a partial discharge of a three-phase power specimen such as a power cable or a generator coil.

[Prior Art] Partial discharge measurement is one of the most widely used methods for testing high voltage insulation. With the spread of computer measurement technology in recent years, not only detection of partial discharge pulse,
Various important data analyzes are being performed by various data processing techniques. However, in the partial discharge measurement, since a weak pulse voltage of about several mV is detected and measured from the specimen during application of a high voltage, it is easily affected by various kinds of noise, and it is difficult to measure a small partial discharge. Therefore, noise removal technology is required to obtain sufficient measurement sensitivity and accuracy.

Noise is broadly divided into internal noise due to the measuring instrument itself and external noise that enters due to external environmental factors, but internal noise is mainly the thermal noise and corona noise of the measuring instrument and is avoided. It is extremely difficult. On the other hand, extraneous noise appears only when there is a noise source and an intrusion path as shown in the following equation. As a countermeasure, both or one of the right sides may be set to zero.

External noise = intrusion path x noise source However, in practice, it is appropriate to think that noise generation from other equipment cannot be avoided in factories and the like, and eventually, external noise is removed by blocking the intrusion path. Will be. Therefore, the intrusion path is cut off by providing a line filter, a blocking coil, etc. in the measurement circuit or by applying a single point grounding, but there is actually noise having a more complicated intrusion path. It is difficult to completely remove external noise.

Therefore, the total noise including the internal noise and the true partial discharge pulse must be discriminated by the measuring instrument.
There is a drawback that accurate discrimination cannot be easily performed with conventionally known measuring instruments and measuring methods. In other words, despite various noise elimination measures, measurement is not possible due to large noise, or the measurement result is extremely low in accuracy.

For example, as a method of measuring the partial discharge of the power cable, there are a method in which power transmission to the power cable is stopped and a method in which power is transmitted in a live state. Of these methods, the method of measuring the partial discharge by stopping the power transmission is performed by disconnecting the power cable from the power supply and newly connecting the test DC power supply to the measuring instrument. Therefore, every time a partial discharge is measured, the power transmission to the power cable must be stopped and the power cable must be disconnected from the power supply. There is a problem that the secondary effect of stopping the power transmission to the power supply is caused. Furthermore, since the measurement of the partial discharge is performed by applying a DC voltage, there is a disadvantage that the correlation with the AC voltage at the time of transmitting power to the power cable must be grasped.

FIG. 3 is a block diagram of a conventional apparatus for carrying out a method of performing partial discharge measurement in a live state of a power cable.
The conductors of the three-phase power cables Ca, Cb, Cc are grounded at the neutral point N via the secondary windings of the transformers Ta, Tb, Tc, respectively, and the primary windings of the transformers Ta, Tb, Tc are respectively One end is grounded, and the other end is connected to a 50 Hz or 60 Hz three-phase power supply 1. The shield layers of the three power cables Ca, Cb, and Cc are grounded via a ground line G, and the detection coil 2 is arranged so as to wind the ground line G. The output of the detection coil 2 is partially It is connected to a discharge measuring device 3.

In the device configured as described above, the three-phase power supply 1
Power cables Ca, Cb,
When a partial discharge occurs due to a void in any of Cc, a pulse current flows to the ground point via the shielding layer of the power cables Ca, Cb, and Cc where the partial discharge has occurred, and the ground line G. An induced voltage is generated in the detection coil 2 by electromagnetic induction of the pulse current flowing through the ground line G, and the induced voltage, that is, the pulse voltage is measured by the partial discharge measuring device 3. Then, the degree of insulation deterioration of the power cables Ca, Cb, and Cc can be measured by detecting the number of discharge pulses and the amount of discharge charge per unit time.

[Problems to be Solved by the Invention] However, when pulsed noise is externally applied to such a device, a pulse current flows through the power cables Ca, Cb, Cc and the ground wire G, and the power cables Ca, Cb, Cc The pulse current generated in the shielding layer and the ground line G flows integrally to the ground line G, and generates a pulse voltage in the detection coil 2 by electromagnetic induction. It is very difficult for the partial discharge measuring device 3 to accurately measure the partial discharge because it is difficult to distinguish between the pulse voltage generated by the external pulsed noise and the pulse voltage generated by the partial discharge. .

[Object of the Invention] An object of the present invention is to provide a partial discharge detection device capable of detecting a partial discharge occurring in a specimen with high accuracy while transmitting power to a three-phase power specimen such as a power cable. Is to do.

[Summary of the Invention] The gist of the present invention for achieving the above object is to form a discharge pulse obtained by connecting to each phase of a three-phase power specimen and removing an AC component together with information on its positive or negative polarity. Three discharge pulse detecting means for detecting, and a gate for outputting a gate pulse signal at a plurality of predetermined angles having different combinations of magnitudes of instantaneous voltage values of respective phases of the three-phase AC voltage applied to the three-phase power test specimen Pulse signal generating means, and synchronizing outputs of the three discharge pulse detecting means with the gate pulse signal;
There is an output pulse from all of the three discharge pulse detecting means, and when these polarities are the same, it is determined that there is noise, and when there is an output pulse from the discharge pulse detecting means under other conditions, a partial discharge is detected. A partial discharge detection device comprising: a determination unit for determining.

[Principle of the Invention] Considering measurement using a three-phase power cable as an example, a three-phase AC voltage as shown in FIG. 1 is applied to each of the power cables Ca, Cb, and Cc. The partial discharge pulse mainly occurs near the peak of the amplitude of the AC voltage near the partial discharge starting voltage, that is, at the phase angle where the instantaneous value of the applied voltage is large, and at the phase angle where the instantaneous value of the applied voltage is near zero. It is known not to. Further, the positive or negative polarity of the partial discharge pulse at that time corresponds to the positive or negative polarity of the applied voltage instantaneous value. Therefore, in each of the power cables Ca, Cb, and Cc whose phases are shifted from each other like a three-phase AC voltage, the partial discharge characteristics with respect to the reference phase angle R are different for each cable.

On the other hand, noise that is a problem during measurement penetrates equally into each power cable Ca, Cb, Cc regardless of the instantaneous value of the applied voltage, and all have a positive polarity, or all have a negative polarity. Become. Therefore, it is possible to discriminate the noise to some extent by such a difference in the characteristic regarding the polarity between the partial discharge pulse and the noise.

Further, for example, when the reference phase angle R is
Degrees, 150 degrees, ..., the instantaneous value of the voltage of each phase is always ±
1.0, .., There is a high possibility that the partial discharge pulse is generated only in the phase having an instantaneous value of ± 1.0. At this time, even if the instantaneous value is Even if a partial discharge pulse is generated in the two phases, the polarity is opposite to the ± 1.0 phase. When the reference phase angle R is 60
Degrees, 120 degrees, 180 degrees, ..., the instantaneous value of the voltage of each phase is always ± 0.86, 0, Therefore, the partial discharge pulse has an instantaneous value of ± 0.86 and , But the polarities are different from positive (or negative) and negative (or positive), respectively.

When the measurement of the partial discharge of each phase is performed at the point where the value of the reference phase angle R indicated by such an arrow and is taken,
Even if partial discharge pulses are detected from three phases at the same time, their polarities do not coincide with each other. on the other hand,
Since noise enters the three phases equally and has the same polarity,
When pulses having the same polarity are detected simultaneously from three phases, it can be discriminated as noise. Of course, the combination of the reference phase angles R for performing the partial discharge measurement is not limited to this, because some other combinations are possible. For example, when the arrow or the arrow is delayed 15 degrees or advanced, the instantaneous value of the voltage of each phase is ± 0.97, Which also occur regularly during each cycle.

Embodiment of the Invention The present invention will be described in detail based on the embodiment shown in FIG.

The embodiment shown in FIG. 2 is based on the measurement principle in the future, and a coupling capacitor Cka is connected to the power cable Ca.
Is connected to the measurement lead terminal la provided with the shielding layer. This measurement lead terminal la has a pulse transformer PT
The amplifier circuit 10a and the polarity discriminating circuit 11a are sequentially connected via a, and the output of the polarity discriminating circuit 11a is converted into binary circuits 12a and 13a.
Connected to each other. Further, the binarizing circuit 12a having the negative polarity is connected to the first discriminating circuit 14, and the binarizing circuit 13a having the positive polarity is connected to the second discriminating circuit 15.

In addition, a step-down converter 16, a phase shift circuit 17,
The gate signal generation circuit 18 is connected in sequence, and the outputs of the gate signal generation circuit 18, the first discrimination circuit 14, and the second discrimination circuit 15 are connected to an AND circuit 19, the output of which is a counting circuit serving as an observation circuit. Connected to 20.

Although not shown, the electric cables Cb and Cc have the same circuit configuration as the power cable Ca, and the first discriminating circuit 14, the second discriminating circuit 15, and the AND circuit 19 are shared. In addition, a step-down converter 16, a phase shift circuit 15, a gate signal generation circuit
As for 18, only the power cable Ca is installed.

From the power cable Ca, a discharge pulse is extracted from the applied AC voltage by the capacitor Cka, and the measurement lead terminal la
, The pulse component and the AC component are discriminated by the pulse transformer PTa, and only a weak pulse component is input to the amplifier circuit 10a and amplified. By selecting a high input resistance, the amplification circuit 10a can suppress the oscillation of the pulse component and give a polarity to the amplified signal.The amplified detection pulse is discriminated by the polarity discrimination circuit 11a for each polarity, and the amplified detection pulse is negative. Are input to the binarization circuit 12a, and the positive detection pulse is input to the binarization circuit 13a, and are converted into pulse signals of a fixed size.

The AC component causes a charging current to flow to the coupling capacitor Cka, which is detected by the voltage step-down device 16 and stepped down to a predetermined voltage.After the time difference from the pulse component processing system is corrected by the phase shift circuit 17, the gate signal generation circuit Entered in 18. The gate signal generating circuit 18 outputs a gate pulse signal S1 each time the phase angle of the applied AC voltage reaches a predetermined value. In this embodiment, as described above, the gate pulse signal S1 and the arrow shown in FIG. At the value of the reference phase angle R every 30 degrees,
Gate pulse signal S1 is output.

In the embodiment, the above-described circuit for generating the gate pulse signal S1 is installed only on the power cable Ca, but may be installed on all three phases, in which case the output from the three gate signal generation circuits 18 It is necessary to provide a gate for selecting one of the three gate pulse signals S1 and sending it to the AND circuit 19.

Phases of the negative side of the binarizing circuit 12a, 12b, the data pulse A output from 12c ^-, B ^-, C ^- are input to the first determination circuit 14. The first discriminating circuit 14 is a logic circuit for performing an ethical operation based on the truth table of Table 1 for discriminating between a partial discharge pulse and noise. For example, as described above, the data pulses A ⁻ , When all of B ^- and C ^- are high-level H pulse signals, it means that negative pulses are detected from all three phases at the same time. Therefore, the detected pulse is determined to be noise, and the low-level L pulse signal S2 is detected. Is output.

On the other hand, the data pulses A ⁺ , B ⁺ , and C ⁺ output from the positive-side binarization circuits 13a, 13b, and 13c of each phase are input to the second determination circuit 15. The second discriminating circuit 15 is also a logic circuit for discriminating between a partial discharge pulse and noise.
Is the same as For example, when the data pulses A ⁺ , B ⁺ , and C ⁺ are all high-level H pulse signals, it means that positive pulses have been detected simultaneously from all three phases. The level L pulse signal S3 is output.

Subsequently, the gate pulse signal S1, the output pulse S2 of the first determination circuit 14, and the output pulse S3 of the second determination circuit 15 are AND circuits.
Entered in 19. The AND circuit 19 outputs a count signal based on the timing of the gate pulse signal S1,
When the output pulse signals S2 and S3 from the first discriminating circuit 14 and the second discriminating circuit 15 are both at the high level H, since the detection pulse is due to partial discharge, 1 is added to the value of the counting circuit 20. Has become. Note that the configurations of these logic circuits vary depending on how the reference phase angle R for generating the gate pulse signal S1 is selected, and are not limited to the truth table of Table 1.

With this configuration, the partial discharge pulse can be distinguished from the noise with a considerable probability, and the coefficient circuit 20 displays the accurate partial discharge pulse as the number of pulses. Also, if the data pulses and the gate pulse signals S1 output from the binarization circuits 12a to 12c and 13a to 13c of each phase are monitored on a display or the like, the status of the partial discharge for each of the power cables Ca, Cb, and Cc can be monitored. It is also possible to know the relationship with the phase angle, which is useful for actual measurement.

[Effects of the Invention] As described above, the partial discharge detection device according to the present invention can detect a partial discharge by applying a three-phase AC voltage to the three-phase power specimen, and thus can be used under a hot-line condition. Can be detected. In addition, by utilizing characteristics such as the phase angle of the AC voltage and the polarity of the partial discharge pulse, noise can be accurately removed from the detected discharge pulse, so that a highly accurate partial discharge measurement can be performed. .

[Brief description of the drawings]

FIG. 1 is a waveform graph of a three-phase AC applied voltage, FIG. 2 is a block diagram of a partial discharge detecting device according to an embodiment of the present invention, and FIG. 3 is a diagram of a conventional example. Reference numeral 10 denotes an amplifying circuit, 11 denotes a polarity discriminating circuit, 12 and 13 denote a binarizing circuit, 14 denotes a first discriminating circuit, 15 denotes a second discriminating circuit, 16 denotes a step-down converter, 17 denotes a phase shift circuit, and 18 denotes a gate signal. A generating circuit, 19 is an AND circuit, and 20 is a counting circuit.

Claims (1)

(57) [Claims] 1. Three discharge pulse detecting means connected to each phase of a three-phase power test sample for detecting a discharge pulse obtained by removing an AC component together with information on its positive or negative polarity, and said three-phase power supply. Gate pulse signal generating means for outputting a gate pulse signal at a plurality of predetermined angles in which a combination of magnitudes of voltage instantaneous values of each phase of the three-phase AC voltage applied to the specimen is different,
The outputs of the three discharge pulse detectors are synchronized with the gate pulse signal, and when there are output pulses from all of the three discharge pulse detectors and their polarities are the same, it is determined that the output pulse is noise. A partial discharge detection device comprising: a determination unit configured to determine a partial discharge when there is an output pulse under other conditions from the pulse detection unit.