JPH03170878A - Partial discharge detector - Google Patents

Abstract

PURPOSE:To facilitate the mounting of a detector and to detect partial discharge with high accuracy by mounting a pulse current detection element and a high- pass filter. CONSTITUTION:A high voltage bushing 5 is connected to high voltage winding 2a at one end thereof and a transmission line 20 at the other end thereof while the low voltage bushing 21 provided on the side part of a tank 1 is connected to low voltage winding 2b at one end thereof and a shielded power cable 22 at the other end thereof. The shield of the cable 22 is connected to the ground by a shield ground wire 23. An electric pulse detector 7 detects the pulse current flowing out to the ground through the ground wire 23 and outputs an electric pulse signal to a discharge level measuring device 8 and also outputs an acoustic signal delay time measuring start order to a delay time measuring device 10. The detector 7 is constituted of a pulse current detection element 7a, a high-pass filter 7b and a waveform rectifying circuit 7c. The greater part of the pulse current generated by partial discharge flows out through the shield of the cable 22 to be detected by the elements 7a. The low frequency noise penetrating from the cable 22 is removed by filter 7b.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a part that detects a pulse current due to a partial discharge generated inside an electrical equipment whose main body is housed in a container, such as an oil-immersed transformer. This relates to a discharge detection device. [Prior art] Figure 5 shows a method for detecting partial discharge occurring in an oil-immersed transformer.
It is a block diagram showing a conventional partial discharge detection device that also locates the location where partial discharge occurs. In the figure, (1) is a tank that houses the main body of an oil-immersed transformer, which consists of windings (self), iron core (3), etc., which are the power-carrying parts of an oil-immersed transformer, along with insulating oil (4). It is insulated. (5l is the high pressure bushing installed at the top of the tank (1), (6)
is the tank grounding wire for grounding the tank (1) at one point. (71 is an electric pulse detector that detects the pulse current generated by the partial discharge generated in winding m (2) etc. from the tank grounding wire (6), and (8) is detected by the electric pulse detector (7). (9a) to (9c) are acoustic pulse detectors that detect ultrasonic pulses generated with partial discharge; (1) are installed at different positions. flo+ is a delay time measuring device that measures the delay time from the time of pulse current detection to the time of acoustic signal detection, and (11) is the acoustic signal measured by the delay time measuring device QOI. (12) is a calculation device that calculates the position of partial discharge occurrence using signal delay time, and (12) is a discharge level measuring device (8
) and the arithmetic device <11)
This is an output unit that uses the calculation results to determine abnormalities in the oil-immersed transformer and outputs alarms and calculation results. In addition, the solid lines connecting the device components in the figure indicate the signal paths, and the arrows indicate the flow of the signals. FIG. 6 is a waveform diagram for explaining the operation of the conventional partial discharge detection device shown in FIG. Next, the operation of the conventional partial discharge detection device shown in Fig. 5 will be explained with reference to Fig. 6. The winding inside the tank (1) (
2) When a partial discharge occurs, minute pulse current and ultrasonic pulse are generated along with the partial discharge. First, the minute pulse current flows from the winding (2) to the ground through the tank (1) and the tank ground wire (6). An electric pulse detector (7) detects the pulse current flowing through this tank ground wire (6).
6 (A)), and further waveform shaping to detect the same figure (B).
) is converted into an electrical pulse signal as shown in (). When the peak value of this electric pulse signal exceeds a preset reference level, an acoustic signal delay time measurement start command is output to the delay time measuring device α0), and the electric pulse signal is sent to the discharge level measuring device (a). The ultrasonic pulse generated during the partial discharge is transmitted to the insulating oil (1) in the tank (1). 4) is propagated to the tank wall as a medium, and is detected after different delay times from the time of occurrence of partial discharge by a plurality of acoustic pulse detectors (9a) to (9C) installed at different positions of the tank (1). In acoustic pulse detection 5 (9a) to (9c), the detected signals indicate that there is some low frequency such as steady excitation vibration of the oil-immersed transformer, or that rain, sand, etc. hit the tank (1). Acoustic noise etc. that occur in Figure 6 (C) (
E) Only the discharge sound is extracted as in (G). The extracted acoustic signal is compared with a preset reference level, and if it exceeds the reference level, the sound signal shown in Fig. 6 (D) (F
) (H ). The delay time measuring device 00) starts an internal counter circuit in response to an acoustic signal delay time measurement start command from the electric pulse detector (7), and measures the electric pulses output from the acoustic pulse detectors (9a) to (9C), respectively. It gets stuck in the signal and stops the counter circuit. These count values are calculated as the acoustic signal delay time (ta
) (tb) (tc) and output to the arithmetic unit (1l). The arithmetic unit (11) calculates these acoustic signal delay times (
ta) (tb) Determine whether or not a partial discharge has occurred inside the tank (1) from (tc), and if it is determined that it has occurred inside, find the location of occurrence from the simultaneous equations of conditional expression (■) shown below. , and outputs the result to the output section (12). The output unit (l2) determines whether there is an abnormality in the oil-immersed transformer based on the magnitude of partial discharge, frequency of occurrence, etc. input from the discharge level measuring device, outputs an alarm signal, and outputs the determination result and the calculation unit? I! Display or print out the calculation result of (11). Here, (Xo, Yo, Zo) are the coordinate points of the partial discharge occurrence position, (Xa, Ya. Za), (Xb, Yb, Zb), .
(Xc, Yc, Zc) are acoustic pulse detectors (9a>~
(9C) Tank [coordinate point indicating the installation position to 11,
(ta), (tb), and (tc) indicate the respective acoustic signal delay times measured by the delay time measuring instrument (IO), and ■ indicates the propagation speed of the acoustic signal in the insulating medium. [Problem to be solved by the invention] Since the conventional partial discharge detection device is configured as described above, in order to detect the pulse current caused by the partial discharge, the tank (1) and therefore the entire oil-immersed transformer are insulated from the ground. However, the installation mechanism of the transformer is complicated and the construction work is complicated, and it cannot be applied to existing products where the tank (1) is installed directly on the ground. A method is known in which a so-called capacitor-type bushing is used for detecting partial discharge by using its capacitance.However, this type of bushing is only used for large-capacity, high-voltage equipment.
The price of the detection device is generally high, and it is not suitable for detecting partial discharge relatively easily and inexpensively.
Of course, this detection was impossible with equipment not equipped with these capacitor type bushings.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a partial discharge detection device that is easy to install and can be easily installed on existing products.

[Means to solve the problem]

The partial discharge detection device according to the present invention utilizes a shielded cable connected to a terminal that draws out the energized part of the electrical equipment body to the outside of the container, and detects a pulse current flowing from the shield of this cable to the ground. The sensor is equipped with a high-pass filter that removes low-frequency noise that propagates through the shielded cable and enters from the output of the pulse current detection element. [Function] Part of the pulse current generated by the partial discharge inside the container flows out from the container to the ground, but most of it flows out through the shield of the shielded cable and is detected by the pulse current detection element. Detected. Low-frequency noise that enters from the cable is removed by a high-pass filter, and a pulsed current output based on partial discharge is obtained.

〔Example〕

An embodiment of this invention will be explained below with reference to the drawings. No.l
In the figure, the same or equivalent parts as in FIG. 5 are designated by the same reference numerals and their explanation will be omitted. In the figure, one end of the high voltage bushing (51) is connected to the high voltage winding (2a), and the other end is connected to the power transmission line (20).

<21> is a low voltage bushing provided on the side of the tank (1), one end of which is connected to the low voltage winding (2b), and the other end connected to the shielded power cable (22). The shield of this shielded power cable (22) is connected to the ground by a shield grounding wire (23). (7) detects the pulse current flowing to the ground via the shield grounding wire (23), and the discharge level measuring device (8)
An electric pulse detector that outputs an electric pulse signal to the delay time measuring device and an acoustic signal to the delay time measurement start command.
It consists of a pulse current detection element (7a) such as a high-frequency CT, a high-pass filter (7b), and a waveform shaping circuit (7c).The partial discharge is generated from the pulse current generated by the partial discharge and the ultrasonic pulse. The overall configuration and operation for detecting the pulse current and its generation location are the same as conventional ones, so the explanation will be omitted.Hereinafter, the configuration for determining the above-mentioned pulse current and its operation will be explained in detail.First, the winding The behavior of this pulse current will be explained from the equivalent circuit of (2). Figure 2 shows an equivalent circuit in which the high voltage winding (2a) of an oil-immersed transformer is expressed as a distributed constant circuit.
Tl and T2 are the terminals at both ends of the winding, L is the series self-inductance, Cs is the capacitance between the coils, and Cg is the capacitance between the coil and the ground. Then, when a partial discharge occurs inside the winding, the low frequency component of the resulting pulse current, which is lower than the critical frequency ωC shown by the following formula (■), propagates through the series self-inductance L of the first winding, and ，
It flows out from T2 onto the power transmission line (20) and the ground.

On the other hand, in a high frequency region higher than the critical frequency ωC, the impedance of the series self-inductance L increases, and in fact, the inter-coil capacitance C as shown in FIG.
s and the coil-to-ground capacitance Cg.

Therefore, the high frequency part of the pulse current flows through the circuit shown in Figure 3 and also transfers to other windings via the capacitance. This is an equivalent circuit diagram of winding (2) of an oil-immersed transformer expressed in terms of capacitance.
Of course, this corresponds to a certain high frequency of the pulse current.
Note that the critical frequency ωC shown by equation (2) has a value of about 200 KHz in the case of a general oil-immersed transformer. In the figure,
H is high voltage winding (2a), L is low voltage winding (2b), CHK
is the equivalent capacitance between the power transmission line (20) connected to the high voltage bushing (51) and the ground, CHg is the high voltage winding (2a)
and the equivalent capacitance between the tank (1) and the iron core (3),
CHL is the equivalent capacitance between the high voltage winding (2a) and the low voltage winding (2b), and CLg is the equivalent capacitance between the low voltage winding (2b) and the tank (1
) and iron core G), and CLK is the equivalent capacitance between the shielded power cable (22) connected to the low-voltage pusher (21) and the ground. Here, since the equivalent capacitance CLK of the shielded power cable (22nd generation) has a very large value, the following formula (■) generally holds true: CLK>CHg, CLg>CHK... ...
・ ■As a result, most of the high-frequency signal of the pulse current due to partial discharge will flow out from the shield of the shielded power cable (22) to the ground. Therefore, by detecting this with the pulse current detection element {7a) and correcting the detection sensitivity based on the above-mentioned capacitances, etc., an accurate pulse current can be obtained. However, in this case, the shielded power cable (22) is often connected to devices such as inverters that have built-in power semiconductor elements as a load, and the so-called low frequency of several KHz caused by the switching operation of these semiconductor elements is generated. Noise propagates through the shielded power cable (22) and enters the pulse current detection element (7a), causing a detection error. The high pass filter (7b) is, for example, 200
This high-bass filter (7
b) enables highly accurate detection of pulse current based on partial discharge.

Connecting a shielded power cable (22) to the terminals of an oil-immersed transformer is a relatively simple matter;
Since there is no need to insulate the tank (1) from the ground, and there is no need to use a capacitor type bushing, the partial discharge detection device according to the present invention can be easily applied to existing products that do not specifically consider partial discharge detection. The device is simple and the installation process is simple. In the above embodiment, the high-pass filter (7b) was provided after the pulse current detection element (7a), but it may also be arranged before the pulse current detection element (7a).
7a) Output {Anything that removes low-frequency noise that may be included is sufficient. In addition, the shielded power cable (22) is not limited to the low-voltage bushing <2l>, but also uses a high-voltage bushing (51) or one connected to the extraction terminal from another winding to prevent the current flowing from the shield of the cable to the ground. Furthermore, the present invention can be widely applied not only to oil-to-air transformers but also to various other electrical equipment such as transformers and actuators, and the same effect can be achieved. [Effects of the Invention] As shown in the figure, the present invention uses a shielded cable connected to a terminal and is equipped with a predetermined pulse current detection element and a high-pass filter, making it easy to install a detection device and detect partial discharge with high accuracy. In addition, it can be easily installed on existing products that do not take this detection into consideration, making it possible to detect partial discharges.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a partial discharge detection device according to an embodiment of the present invention, FIGS. 2 to 4 are equivalent circuit diagrams of a transformer for explaining the behavior of pulse current generated by partial discharge, and FIG. FIG. 5 is a block diagram showing a conventional partial discharge detection device, and FIG. 6 is a waveform diagram for explaining the operation of the partial discharge detection device. In the figure, (1) is a tank as a container, (2) is a winding as a power supply part of the electrical equipment body, (7a) is a pulse current detection element, (7b) is a high-pass filter, (2I)
is a low-voltage bushing as an extraction terminal, and <22) is a shielded power cable as a shielded cable. The same symbols in each figure indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] In an electrical device whose main body is housed in a container, a pulse current due to a partial discharge generated in the container is detected outside the container, a terminal for drawing out the energized part of the main body to the outside of the container. A pulse current detection element that detects the pulse current flowing from the shield of the shielded cable connected to the ground to the ground, and a high pass that removes low frequency noise that propagates and enters the shielded cable from the output of this pulse current detection element. A partial discharge detection device characterized by comprising a filter.