JP2654792B2 - Partial discharge detection device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention 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 pulses, but Various important data analyzes have been performed by various data processing techniques. However, in partial discharge measurement, a weak pulse voltage of about several mV is detected and measured from the specimen during application of high voltage,
It is susceptible to various kinds of noise, making it difficult to measure small partial discharges. 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 formula. As a countermeasure, both or one of the right sides may be made zero.

External noise = Intrusion path x Noise source However, it is reasonable to think that noise generation from other equipment cannot be avoided in a factory or the like.
Eventually, blocking the intrusion path will remove extraneous noise. 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. However, in reality, there is noise with a more complicated intrusion path. It is difficult to remove extraneous noise.

Therefore, the total noise including the internal noise and the true partial discharge pulse must be discriminated by the measuring instrument. However, it is not possible to easily perform the appropriate discrimination by the conventionally known measuring instrument and measuring method. There are drawbacks. That is, despite various noise removal measures, the noise is large and measurement cannot be performed, or the measurement result becomes 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 to the power cable is performed by disconnecting the power cable from the power supply and newly connecting the test DC power supply and 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 stopping power transmission to the power supply causes secondary effects. 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. 4 is a block diagram of a conventional apparatus for carrying out a method of performing a partial discharge measurement in a live state of a power cable.
The conductors of the three-phase power cables Ca, Cb, and Cc are grounded at the neutral point N via the secondary coils of the transformers Ta, Tb, and Tc, respectively, and the primary coils of the transformers Ta, Tb, and Tc have one ends respectively. It is grounded, and the other end is connected to a three-phase power supply 1 of 50 Hz or 60 Hz. 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 Connect to the 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 a 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. By detecting the number of discharge pulses and the amount of charge discharged per unit time, the power cable
The degree of insulation deterioration of Ca, Cb, and Cc can be measured.

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

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

[Summary of the Invention] The gist of the present invention for achieving the above object is to provide three discharge pulse detecting means connected to each phase of a three-phase power specimen and detecting a generated discharge pulse, and the three-phase power supply. A gate pulse signal generating unit that outputs a gate pulse signal at a plurality of phase angles in which a combination of magnitudes of the instantaneous values of the phases of the three-phase AC voltage applied to the specimen is different; The output is determined in synchronization with the gate pulse signal, and when there is an output pulse from all of the three discharge pulse detecting means, it is determined that the output pulse is noise, and there is an output pulse from one or two of the discharge pulse detecting means. And a determination means for determining a partial discharge in a case.

[Principle of the Invention] Considering a measurement using a three-phase power cable as an example, each power cable Ca, Cb, and Cc has 120
Three-phase AC voltages that are shifted by degrees are applied. 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. Therefore,
Each power cable whose three-phase AC voltage is out of phase with each other
For Ca, Cb, and Cc, the partial discharge characteristics with respect to the reference phase angle R differ for each cable. On the other hand, it is considered that noise which is a problem at the time of measurement enters the power cables Ca, Cb, and Cc equally regardless of the instantaneous value of the applied voltage. Therefore, the noise can be discriminated and removed due to the difference between the characteristics of the partial discharge pulse and the noise.

For example, when the reference phase angle R is 30 degrees, 90 degrees, as indicated by arrows,
At 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. When the reference phase angle R is 60 degrees, 120 degrees, 180 degrees,... As shown by the arrows, the instantaneous value of the voltage of each phase is always ± 0.86, 0, … The instantaneous value of the partial discharge pulse is ±
0.86 and There is a great possibility that the two phases will occur.

Therefore, when the measurement of the partial discharge of each phase is performed where the value of the reference phase angle R indicated by such an arrow and is taken,
Although partial discharge pulses may be detected from one or two phases, the probability that partial discharge pulses are simultaneously detected in three phases is extremely low. On the other hand, since noise penetrates equally into the three phases, if the discharge pulses are detected simultaneously in the three phases, these pulses can be discriminated as noise.

Of course, some other combinations of the reference phase angle R for performing the partial discharge measurement are conceivable, and the combination is not limited to the above phase angle. 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. Therefore, if at least three reference phase angles R are set in one cycle, a high voltage instantaneous value is obtained at least once for each phase.

Embodiments of the Invention The present invention will be described in detail based on the embodiments shown in FIGS.

The embodiment shown in FIG. 2 is configured to implement the above-described measurement principle, and the power cable Ca is connected to a coupling capacitor.
The measurement lead terminal la provided with the shielding layer is connected via Cka. Amplifying circuits 10a and binarizing circuits 11a of which the degree of amplification is variable are sequentially connected to the measuring lead terminal la via a pulse transformer PTa, and the output of the binarizing circuit 11a is the first.
The determination circuit 12 and the second determination circuit 13 are connected to each other. In addition, the step-down converter 14a and the phase shift circuit 1
5a, the gate signal generation circuit 16a is connected in sequence, and the output of the gate signal generation circuit 16a is connected via the gate 17 to the first determination circuit 12 and the monitor terminal 18s of the monitor (not shown). The output of the first determination circuit 12 is connected to the second determination circuit 13, and the output of the second determination circuit 13 is connected to the counting circuit 19 and the monitor terminal 18a.

The power cables Cb and Cc have the same circuit configuration as the power cable Ca, and include a gate 17, a first determination circuit 12, a second
The discrimination circuit 13 is commonly used.

From power cable Ca, coupling capacitor Cka and lead l
Only weak pulse components due to discharge in accordance with the applied AC voltage are taken out through a and the pulse transformer PTa, amplified by the amplifier circuit 10a, and converted into a pulse signal of a fixed size by the binarization circuit 11a. . On the other hand, the AC voltage applied to the power cable Ca causes a charging current to flow through the coupling capacitor Cka, which is detected by the step-down converter 14a and stepped down to a predetermined voltage, and a time difference from the pulse component processing system in the phase shift circuit 15a. Is corrected, the gate signal generation circuit 16a
Is input to The gate signal generating circuit 16a outputs a gate pulse signal each time the phase angle R of the applied AC voltage reaches a predetermined value. In the embodiment, as described above, the gate pulse signal shown in FIG. , A gate pulse signal is output at a value of the reference phase angle R every 30 degrees. Note that these operations are described in the power cables Cb and Cc.
The same applies to.

The pulse outputs A, B, and C obtained by the binarization circuits 11a, 11b, and 11c of the respective phases are input in parallel to the first determination circuit 12 and the second determination circuit 13, respectively, and the gate signal generation circuits 16a, 16
The outputs of b and 16c are input to the first determination circuit 12 via the gate 17. The gate 17 is connected to each gate signal generation circuit 16a, 1
Although the output gates 6b and 16c are selected and the gate pulse signal S1 is sent to the first discriminating circuit 12, in the three-phase AC, the AC voltages applied to the respective phases have a fixed relationship.
Even if the gate pulse signal is generated from only one phase, there is no problem in the operation. Therefore, the gate signal generation circuit 16 does not necessarily need to be provided for each phase, and in this case, the gate 17 does not need to be provided.

The first discriminating circuit 12 is a logic circuit for discriminating between the partial discharge pulse and the noise, and discriminates the output pulses A, B, C based on the output pulses A, B, C from each phase and the gate pulse signal S1. When the output pulses A, B, and C are due to partial discharge, the high-level H pulse signal S2 is used. When the output pulses A, B, and C are due to noise, the low-level L pulse signal S2 is used. Output to the determination circuit 13.

The method for discrimination from noise is as described in the above [Principle of the Invention]. In the embodiment, the gate pulse signal S1 becomes high level H when the reference phase angle R is an arrow as shown in FIG. It is set as follows. Therefore, as described above, when the gate pulse signal S1 is at the high level H, if the one-phase or two-phase output pulses A, B, and C are at the high level, it is determined to be a partial discharge pulse, and the three-phase output is performed simultaneously. If the pulses A, B, and C are at the high level H, the logic circuit may be configured to judge it as noise, and a truth table of the operation is shown in Table 1.

Note that the operation of the logic circuit forming the first determination circuit 12 changes depending on how the value of the reference phase angle R for generating the gate pulse signal S1 is selected.
The present invention is not limited to the truth table shown in the table.

On the other hand, the second discriminating circuit 13 includes three AND circuits 13a, 13b, 13c and one OR circuit 1 as shown by the logic circuit in FIG.
If the discrimination signal S2 from the first discriminating circuit 12 is at the high level H, a discharge pulse is generated. Therefore, the phase in which the discharge has occurred is determined based on which output pulse is at the high level H. Thus, 1 is added to the value of the counting circuit 19 as a discharge pulse. Further, even if the first determination circuit 12 determines that the discharge pulse is a discharge pulse, if a high-level output pulse is obtained in a phase in which the instantaneous value of the voltage at the reference phase angle R is low in this case, this output pulse is Can be determined to be low.

In this manner, the partial discharge pulse can be distinguished from the noise with a considerable probability, and the counting circuit 19 displays the number of partial discharge pulses with high accuracy. Further, by monitoring the pulse outputs A, B, C of each phase and the gate pulse signal S1 on a display or the like, it is possible to know the relationship between the partial discharge status and the phase angle of each of the power cables Ca, Cb, Cc. Therefore, it is useful in actual measurement.

[Effects of the Invention] As described above, the partial discharge detection device according to the present invention provides a three-phase power test specimen in which a three-phase AC voltage is applied to a live line in which the phase angle of the AC voltage and the partial discharge pulse are different. Utilizing the characteristics, the discharge pulse and noise can be accurately separated,
It is possible to detect a partial discharge with high accuracy.

[Brief description of the drawings]

FIG. 1 is a graph showing a waveform of a three-phase AC applied voltage, and FIG.
FIGS. 3 and 3 show an embodiment of a partial discharge detecting device according to the present invention. FIG. 2 is a block diagram of a block circuit, FIG. 3 is a block diagram of a second discriminating circuit, and FIG. It is a block diagram. Reference numeral 10 denotes an amplifying circuit, 11 denotes a binarizing circuit, 12 denotes a first discriminating circuit, 13 denotes a second discriminating circuit, 14 denotes a step-down converter, 15 denotes a phase shift circuit, 16
Is a gate signal generation circuit, 17 is a gate, and 19 is a counting circuit.

Claims (1)

(57) [Claims] 1. Three discharge pulse detecting means connected to each phase of a three-phase power specimen to detect a generated discharge pulse, and voltages of each phase of a three-phase AC voltage applied to the three-phase power specimen. A gate pulse signal generating unit that outputs a gate pulse signal at a plurality of phase angles having different combinations of magnitudes of instantaneous values, and an output of each phase discharge pulse detecting unit is determined in synchronization with the gate pulse signal; Discriminating means for judging noise when there is an output pulse from all three discharge pulse detecting means, and judging partial discharge when there is an output pulse from one or two of the discharge pulse detecting means; A partial discharge detection device characterized by the above-mentioned.