JPH04235360A - Partial-discharge detecting circuit of electric apparatus - Google Patents

Abstract

PURPOSE:To perform the detection of internal partial discharge and the specification of the apparatus wherein the discharge occur noiselessly without a special capacitor voltage divider and the like by monitoring a plurality of transforming apparatuses which are connected to the bus of the same system with the minimum number of sensors at the same time. CONSTITUTION:Discharge detecting sensors 3a, 3b and 3c are inserted in the grounding lines of (three or more) transforming apparatuses to be monitored 2a, 2b and 2c which are connected the same system bus 1. The rise-up polarities of the output signals are discriminated with a polarity-discriminating circuit 8. When the polarity of only one unit is different from the other signals, it is judged that there is the internal partial discharge in this apparatus. The analog switch of a signal selecting circuit 9 is changed by the signal outputted from a logic circuit, and this apparatus and the output of the sensor are displayed. When all signals indicate the same polarity, the indication is judged as the noise.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a partial discharge detection circuit used in a monitoring device for predicting the maintenance of substation equipment during operation, and in particular, to monitor multiple substation equipment simultaneously using a minimum number of sensors. The present invention relates to a partial discharge detection circuit that detects partial discharge and identifies a device that generates the partial discharge.

0002

[Prior Art] As a method for detecting partial discharge generated inside an electrical device by distinguishing it from noise, a bridge circuit including the device under test is constructed, and two wires are inserted on both sides of the bridge.
A method that compares the output signal polarities of two discharge sensors, and if the polarities are opposite to each other, it is determined that there is an internal partial discharge, and if the polarities are the same, it is determined to be noise.
Symp. I. 3, 2-02 (1975).
A. Black, known for ``Pulse Discrimination System for Detecting Electric Discharges in Noisy Environments''.

Furthermore, in the method and apparatus described in Japanese Patent Publication No. 60-29075, the outputs of two sensors inserted on the two sides of the bridge are respectively introduced into a tuned circuit to create a vibration waveform, and each The signal is input to an amplitude limiter circuit, converted into a pulse train with a constant amplitude, and the difference between the two pulses is taken to discriminate between a signal and noise. That is, in the case of noise, both pulses have the same polarity, so the difference is zero, but in the case of partial discharge, since both pulses have opposite polarities, when the difference is taken, an output twice as large as the input is obtained. By turning on the gate circuit at this double output and turning it off when the output is zero, it is possible to distinguish between signals and noise.

[0004] In all of the above techniques, in order to detect partial discharge inside a single substation device, a device that is certain that partial discharge will not occur (for example, a coupling capacitor whose rated voltage is sufficiently higher than the system voltage, etc.) is used. ) are connected in parallel in the same system to form a bridge circuit, and a discharge current sensor is inserted on each side.

FIG. 6 is a block diagram showing an example of a conventional partial discharge detection circuit for electrical equipment. In the figure, reference numeral 61 denotes a system bus, to which substation equipment to be monitored 62a, 62b, and 62c are connected in parallel, and a discharge detection sensor 63 is connected to each ground wire to detect internal partial discharge.
a, 63b, and 63c are attached. In the figure, 64 is a coupling capacitor such as an ND, and a discharge detection sensor 63d is similarly attached thereto. Sensors 63a, 63b
, 63c are the noise discrimination circuits 65a, 63c for each target device.
65b and 65c, and the output of the sensor 63d becomes a noise discrimination signal that is commonly superimposed on them. The noise discrimination circuits 65a, 65b, and 65c discriminate noise on the sensor output signal and pass only the partial discharge signal to the partial discharge level meters 66a, 66b, and 66c. It consists of a circuit 69. The polarity determination circuit 68 is a logic circuit that compares the polarity of the sensor output signal of each target device and the sensor output signal of the coupling capacitor 64, and if the polarity is the same, it is determined as noise.
If the polarity is reversed, it is determined that it is a true partial discharge, and the signal opening/closing circuit 69 is opened/closed for each sensor output signal. The partial discharge level meters 66a, 66b, and 66c measure the level of the signal determined to be a true discharge, count the number of occurrences, and output an alarm.

[0006]

[Problems to be Solved by the Invention] In order to monitor a plurality of substation equipment using the above-mentioned conventional method, it is necessary to have the same number of monitoring circuits as the equipment to be monitored in principle. becomes larger and costs increase. In addition, it is necessary to provide a coupling capacitor to obtain a noise discrimination signal, and if an internal partial discharge occurs in this capacitor itself, the polarity will be opposite to the sensor output of the normal monitored equipment, making it appear as if there was a partial discharge. It will be determined as if there was a problem, resulting in a malfunction. In order to prevent this, the quality of the coupling capacitor must be made stricter to improve its reliability, which also increases costs. Furthermore, with this method, it is not possible to distinguish between the location where the partial discharge occurs and whether it is the equipment to be monitored or the coupling capacitor, so some kind of target must be taken.

The present invention was devised in view of the above-mentioned problems, and is capable of detecting partial discharge and its occurrence by simultaneously monitoring a plurality of substation equipment connected to the same bus using a minimum number of sensors. The purpose of the present invention is to provide a partial discharge detection circuit that can identify a device without noise and does not require a special capacitor voltage divider.

[0008]

[Means for Solving the Problems] The means for solving the above problems in the present invention are as shown in FIG. In a partial discharge detection circuit 4 that simultaneously monitors partial discharges in devices 2a, 2b, and 2c online, discharge sensors 3a, 3b, and
A polarity discrimination circuit 8 that discriminates the rising polarity of the output signal 3c.
and a signal selection circuit 9 that determines that there is an internal partial discharge in the corresponding device when the polarity of only one device is different from other signals, the polarity determination circuit 8 is It is preferable to select the device in which partial discharge is occurring by switching an analog switch based on the output of the circuit, and the polarity determining circuit 8 branches the output signal of one discharge sensor, and the polarity determining circuit 8 branches the output signal of one discharge sensor, It is preferable to separately compare the positive polarity and negative polarity using two comparators, and to discriminate the rising polarity of the signal using a monostable multivibrator connected to each comparator.

[0009]

[Operation] The present invention is a partial discharge detection circuit that connects three or more substation devices to the same bus and simultaneously monitors them online to determine which device has caused a partial discharge.

The first rise of the sensor output is shown in FIG.
), two types of polarity are generated randomly: one with positive polarity as shown in (b) of the same figure, and one with negative polarity as shown in (b) of the same figure. For example, Figure 3
As shown in the figure, three substation equipment (A), (B), and (C) are
sensors (CT-A), (CT-B), (CT-C)
When monitoring with
The polarity of the output signal of each sensor (CT-A), (CT-B), (CT-C) corresponds to the positive or negative polarity of the discharge.
The result will be as shown in the table below.

[0011]

[Table 1]

That is, for example, if a positive (or negative) partial discharge Dh occurs inside the substation equipment (A), the output polarity of the sensors (CT-B) and (CT-C) will be negative. (or positive polarity). In other words, when a partial discharge occurs in one of the substation devices, the sensor outputs of the other two devices have opposite polarities to the sensor output of the discharge generating device. As is clear from Fig. 3, when a partial discharge Dh occurs in the substation equipment (A) connected to the same system bus, the flow of partial discharge current circulates as shown by the arrow in Fig. 3, and the sensor (CT -A
) The direction of the current is sensor (CT-B) and sensor (CT-B).
-The direction of the current is opposite to that in C). On the other hand, the noise current riding on the bus passes through all the sensors to the ground side, so the direction of the current flowing through each sensor is the same, and the polarity of the output signal of all the sensors is also the same.

By utilizing this characteristic, it is easy to use the polarity discrimination circuit of the present invention as a logic circuit to identify the device that generates the partial discharge.If the polarity of all sensor outputs is the same, it is noise. If only one difference exists, the device can be distinguished from the generating device. It cannot be said that there is a possibility that internal partial discharges occur in two substation devices at the exact same time, and in that case, the location of occurrence cannot be identified using the above logic circuit, but partial discharges do not occur only once. Therefore, when the occurrence time of the two devices deviates the next time the problem occurs, there is an opportunity for the logic circuit to operate correctly, and the problem is solved.

In the present invention, a polarity discrimination circuit discriminates the rising polarity of the output signal of the discharge sensor inserted into the grounding wire of the monitored equipment, and when only one signal has a different polarity from the other signals, the It is determined that there is a partial discharge inside the device. The polarity determination circuit is preferably configured with a logic circuit, and its output selects the device in which the partial discharge is occurring by switching an analog switch. In addition, the polarity discrimination circuit branches the output signal of one discharge detection sensor, inputs it to two comparators, and compares the positive polarity and negative polarity separately,
The rising polarity of the signal may be determined by using a monostable multivibrator for the output of each comparator.

[0015]

Embodiments Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an embodiment of the present invention, which also serves as a basic configuration diagram of the present invention.
Monitored substation equipment (e.g. transformer) 2a, 2b, 2
c is monitored by three discharge detection sensors 3a, 3b, and 3c inserted into each ground wire, and noise discrimination and discharge generating equipment are oriented.The configuration and operation of these are almost the same as the conventional example. The same is true. In the figure, 4 is a partial discharge detection circuit of the present invention that simultaneously monitors the above three devices, 5 is a display, 6 is a partial discharge level meter, and display 5 is the number of the device selected by the partial discharge detection circuit 4. The partial discharge level meter 6 receives the sensor output, and instructs the level, counts the number of pulses, and stores the waveform.

The partial discharge detection circuit 4 includes a buffer amplifier 7
, a polarity discrimination circuit 8 , and a signal selection circuit 9 . The outputs of the discharge detection sensors 3a, 3b, 3c are sent to respective buffer amplifiers 7a, 7b, 7 within the partial discharge detection circuit 4.
c and is also input to the polarity discrimination circuit 8. The buffer amplifier 7 performs signal amplification and signal delay of approximately 1 μsec. The polarity determination circuit 8 identifies the device in which partial discharge has occurred, and selects the selection switch Sw in the signal selection circuit 9.
Turn on in accordance with the device that generates partial discharge.

FIG. 4 is a block diagram showing an example of a partial discharge detection circuit using a logic circuit. In the same figure, the logic circuit is connected to the three sensors (CT-A), (CT-B), (C
This is to determine the output polarity of T-C) and locate the equipment where partial discharge has occurred.

[0018] Discharge detection sensor (CT-A), (CT-B
), (CT-C) are each branched into two, and the comparator (CP-C) operates with a positive input signal.
P) 41a, 41b, 41c and comparators (CPN) 42a, 42b, 42c that operate with negative polarity input signals.
is input to. A monostable multivibrator (MMP or MMN) 43 is connected to each comparator, and the Q output of the monostable multivibrator (MMP) on the positive polarity side is collected in one AND gate 44p, and the The Q output of the vibrator (MMN) is collected at the other AND gate 44n. These and gates 4
Either of the outputs of 4p or 44n is inputted from the OR gate 45 to the latch circuit 46 and also to the signal selection circuit 47.
is input to. The Q outputs of one monostable multivibrator (MMP or MMN) belonging to the same sensor are mutually connected to the CLR terminal of the other monostable multivibrator (MMN or MMP).

FIG. 5 is a waveform diagram at each part of the logic circuit. For example, if a positive partial discharge occurs in substation equipment A shown in Figure 3, sensors (CT-A), (C
The outputs of T-B) and (CT-C) are as shown in Fig. 5(a), and the output of the sensor (CT-A) is divided into two comparators that are input, and operate with the input of the positive polarity. The one (CPP-A) outputs a pulse as shown in the upper part of Figure 5(b), and the one (CPN-A) that operates with negative polarity input outputs the second pulse.
Outputs stage-like pulses. In the monostable multivibrator, the one (MMP-A) to which the input signal comes first from the comparator (CPP-A or CPN-A) outputs a pulse with a predetermined width tw, as shown in the third stage. At this time, by inputting the negative logic output Q to the other CLR terminal,
Monostable multivibrator (MMP-A) that starts up later
) is suppressed to zero as shown in the fourth stage.

In this way, when the rising edge of the signal is negative as in the case of sensors (CT-B) and (CT-C), the other monostable multivibrator is A pulse with a predetermined width tw is obtained from (MMN).

Here, the predetermined pulse width tw is determined by the values of the external capacitor C and the resistor R of the monostable multivibrator, and becomes tw=C×R (sec), and the signal output from the sensor with one partial discharge. determined by the time constant of
It is usually 20 to 100 μsec, and is adjusted by the external capacitor C and resistor R depending on the characteristics of the sensor. When the output of the monostable multivibrator as described above is configured into a logic IC based on the classification shown in Table 1 above, the AND gate 44 and OR gate 45 shown in FIG. , B or C is obtained with a predetermined pulse width tw, and by inputting this to the analog switch of the signal selection circuit 47, the sensor output can be selected. The latch circuit 46 is for outputting the output A, B, or C to a display device or a host computer where the output is generated.

Although this embodiment has been explained assuming that there are three devices to be monitored, the same applies to four or more devices, and the algorithm for noise discrimination is also the same. Just by matching the number of sensors, the logic circuit can be left as is. It can be extended by simply extending it. If the number of devices to be monitored is one or two, the same effect can be achieved by replacing the device to be monitored with another device connected to the same system, such as a reactor or switch, to form three devices to be detected. algorithm can be used.

The following effects are evident in this example.

(1) A plurality of substation devices connected to the same bus can be monitored simultaneously with a minimum number of monitoring circuits.

(2) It is possible to identify equipment in which partial discharge is occurring.

(3) For standard use, there is no need for a capacitor voltage divider or the like which itself is required to be free from partial discharge.

(4) It has expandability and can easily monitor a desired number of devices, including three or more.

(5) Even if there is one or two monitored devices, if two or one other device is connected to the same system,
The detection circuit of the present invention can be applied.

[0029]

[Effects of the Invention] As explained above, according to the present invention, multiple substation equipment connected to the same bus can be simultaneously monitored using a minimum number of sensors, and partial discharge can be detected and the equipment generating it can be identified. It is possible to provide a partial discharge detection circuit that is resistant to noise and does not require a special capacitor voltage divider or the like.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is an output waveform diagram of a discharge detection sensor.

FIG. 3 is a configuration diagram of charge flow.

FIG. 4 is a configuration diagram of a partial discharge detection circuit using a logic circuit.

FIG. 5 is a waveform diagram of a logic circuit.

FIG. 6 is a configuration diagram of a conventional example.

[Explanation of symbols]

1,61...System bus line 2,62...Monitored substation equipment 3,63...Detection sensor 4...Partial discharge detection circuit 5...Indicator 6,66...partial discharge level meter 7, 67...buffer amplifier 8, 68...Polarity discrimination circuit 9, 69...Signal selection circuit 64...Coupling capacitor 65...Noise discrimination circuit

Claims (3)

[Claims] Claim 1: In a partial discharge detection circuit that simultaneously monitors partial discharges in three or more substation devices connected to a bus in the same system, the rising polarity of the output signal of a discharge sensor inserted into the ground wire of each device to be monitored. 1. A partial discharge detection circuit for electrical equipment, comprising: a polarity discrimination circuit for determining the polarity; and a signal selection circuit for determining that there is an internal partial discharge in the corresponding equipment when the polarity of the polarity differs from other signals for only one device. . [Claim 2] An electric device characterized in that the polarity discrimination circuit according to claim (1) is configured with a logic circuit, and the device in which partial discharge is occurring is selected by switching an analog switch using the output thereof. partial discharge detection circuit. [Claim 3] The output signal of one discharge sensor is branched, the positive polarity and the negative polarity are compared separately by two comparators, and the rising polarity of the signal is determined by a monostable multivibrator connected to each comparator. 2. The polarity discrimination circuit according to claim 1, wherein the polarity discrimination circuit discriminates .