JPH05149993A - Measuring method for partial discharge - Google Patents

Abstract

PURPOSE:To easily measure a partial discharge with a high accuracy. CONSTITUTION:In this apparatus, a cable 1, a drum 19, a measuring device 8 and the like which are easily affected by noises from outside are coated with conductive sheets 16, 18, 20, 21. The conductive sheet is a net or a plastic film to which a conductive film is attached. By way of example, the drum 19 is coated with the conductive sheet 20 in the shape of a mosquito net. Accordingly, in order to shut the noises from outside, it is enough to wind or coat the necessary points with the conductive sheet and it is easy to wind or coat the sheet. Moreover, the space to store the sheet of this kind is small because the sheet can be folded.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partial discharge measuring method used for conducting an electric test on a power cable.

[0002]

2. Description of the Related Art In order to measure the insulation characteristics of a power cable, a high voltage is applied to the power cable and the partial discharge is measured. FIG. 2 shows a schematic diagram of a conventional partial discharge measuring method. In the illustrated example, the cable 1 is wound around a drum (not shown), one end of which is terminated inside the termination box 2 and the other end of which is raised and terminated inside the bushing 3. The conductor of this cable 1 includes a power source 4 to a coil 5
A high voltage is applied via. The coil 5 is a filter for removing external noise. The sheath of the cable 1 is divided into two in the longitudinal direction as shown in the figure, and is electrically divided into a sheath 6A on the power source side and a sheath 6B on the cable body side. Further, both of these sheaths 6A and 6B are electrically edged at their terminal ends. Here, the sheath 6A is connected to the measuring instrument 8 via the detection resistor 7A. The sheath 6B is connected to the measuring instrument 8 via the detection resistor 7B. The measuring device 8 has detection resistors 7A and 7B.
This is a device for comparing the signals input from to extract the partial discharge signal. The filter 9 is a circuit for supplying electric power to the measuring instrument 8 after removing external noise from an external power source (not shown).

FIG. 3 shows an equivalent circuit in the case of FIG. In the figure, in the cable 1 shown in FIG. 2, a high voltage is applied to its conductor, and the capacitor 1 is formed by the conductor and the sheath 6B.
0B is formed. Further, the sheath 6A on the power source side of the cable 1 shown in FIG. 2 constitutes the capacitor 10A shown in FIG. 3 together with the conductor. In this state, for example, the capacitor 10
Assuming that A is normal and partial discharge occurs inside the capacitor 10B, the capacitor 1 shown in FIG.
The partial discharge signal can be extracted by comparing the current passing through 0A and the detection resistor 7A with the current passing through the capacitor 10B and the detection resistor 7B.

FIG. 4 shows a schematic diagram of another conventional partial discharge measuring method. In the illustrated example, one end of the cable 1 is terminated in the termination box 2 and the other end is terminated inside the bushing 3A. The sheath of the cable 1 is trimmed only at both ends and is connected to the measuring instrument 8 via the detection resistor 7B. On the other hand, a high voltage is applied to the bushing 3A from the power supply 4 via the coil 5 and the lead cable 11. In addition to this, the high-voltage capacitor 3B is a detection resistor 7A.
Is inserted between the power supply 4 and the power supply 4, and the output of the detection resistor 7A is connected to the measuring instrument 8. The equivalent circuit and operation in this case are exactly the same as those shown in FIG. In the case of FIG. 2, a part of the cable 1 is used as a standard capacitor, and in FIG. 4, a high voltage capacitor 3B is separately prepared, which is the only difference. In any of the above cases, the weak partial discharge signal in the insulator of the cable 1 is extracted by the measuring instrument 8.

[0005]

By the way, the partial discharge measuring method as described above extracts an extremely weak partial discharge signal generated inside the cable insulator. Therefore, it is necessary to sufficiently reduce external noise. As this method, there is a method in which the entire measuring device is housed in a shielded room for measurement. There is also a method of performing measurement during a time period when there is little external noise, such as at night on a holiday. Further, there is a method in which the cable is housed in a metal pipe for shielding to perform measurement.

However, the above method has the following problems to be solved. First, when accommodating a device in a shield room, this kind of device becomes extremely large, so that a large shield room is required, and there is a problem that equipment cost increases. Further, the method of measuring at night on a holiday requires workers to work on holidays, which is problematic in terms of working conditions. Further, in the method of shielding the cable by accommodating it in a metal pipe or the like, it is not easy to adopt, for example, a long cable wound around a drum. The present invention has been made focusing on the above points,
It is an object of the present invention to provide a partial discharge measuring method capable of performing high-accuracy measurement with simple and sufficient shielding using equipment of relatively low cost.

[0007]

The method for measuring partial discharge according to the present invention is applied to a case where a high voltage is applied to one end of a cable wound around a drum to measure a partial discharge signal generated in the cable insulator. The cable and the drum are covered with a conductive sheet.

[0008]

According to this method, the cable 1, the drum 19, the measuring instrument 8 and the like, which are averse to external noise, are electrically conductive sheets 16, 18, and 2.
Cover with 0,21. This conductive sheet is composed of a plastic film to which a net or a conductive film is attached. Then, for example, the drum 19 is covered with a conductive sheet 20 configured like a mosquito net. As a result, the work of shielding the external noise only needs to be performed by winding or covering the sheet at a necessary place, and the installation is easy. Further, this type of sheet has a small storage space by being folded. Therefore, highly accurate partial discharge measurement can be performed easily.

[0009]

The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is a schematic view showing an embodiment of the partial discharge measuring method of the present invention. In the figure, cable 1 is shown as termination boxes 2 and 1.
It is terminated inside 5. The terminal box 15 is formed in an L shape, and one end thereof is incorporated in the bottom of the bushing 3. A standard capacitor (not shown) is incorporated in the terminal box 15, and the detection resistors 7A and 7B are connected thereto and connected to the measuring instrument 8. Therefore, this portion has the same configuration as that in FIG. 4, and its equivalent circuit is as described above with reference to FIG.

In the partial discharge measuring method of the present invention, in order to shield the cable 1, for example, a wire mesh 16 having a relatively fine mesh, for example, a mesh of about 10 mm on a side is used.
Wrap around. Further, although the cable 1 is wound around the drum 19, a similar wire net 18 is laid like a rug under the drum 19. And processed from the top into a bag with no bottom,
A so-called mosquito net-shaped wire net 20 is put on. And, the wire nets used for these shields are grounded by using lead wires (not shown). In this way, cable 1 and drum 1
The conductive sheet that covers 9 is not limited to a metal mesh, and for example, a plastic sheet or a metal foil having a conductive film attached thereto can be used. The measuring device 8, the filter 9, the detection resistors 7A, 7B, etc. are similarly covered with a conductive sheet such as a wire net 21. Since the conductive sheet is used in the partial discharge measuring method of the present invention having the above configuration, the work for blocking is extremely simple. Moreover, this causes the partial discharge noise propagating in the air to be 10
It can be attenuated to 1/0 or less.

FIG. 5 shows the noise level in the conventional partial discharge measuring method, with the vertical axis representing the noise level and the horizontal axis representing the time. Further, FIG. 6 shows the noise level by the partial discharge measuring method of the present invention in the same graph. As shown in the figure, according to the experiment, when the noise level is represented by the discharge charge amount, it is about 200 pc (pico coulomb) in the related art without any shielding.
It was confirmed that it was 0 pc or less. Therefore, 50 pc
It becomes possible to detect a partial discharge signal of a small degree without being disturbed by noise.

FIG. 7 is a schematic view of the case where the present invention is applied to the conventional device shown in FIG. As shown by the broken line in the figure, in this device, for example, the conductive sheet 22 such as a wire mesh or a metal foil is directly used for the cable 1 and the detection resistors 7A and 7B.
Etc. In this case, it is effective when the drum around which the cable 1 is wound is relatively small, or when the cable 1 is relatively short and simply bundled. The conductive sheet 22 only needs to be selected to have a size enough to cover the main part of the measuring device. In order to complete the shielding, a conductive sheet is previously laid on the floor surface in the same manner as the embodiment shown in FIG. 1, and the cable 1 and the detection resistor 7A,
7B or the like may be placed, and another conductive sheet may be covered from above. FIG. 8 shows an example in which the present invention is applied to the conventional device shown in FIG. Also in this example, the conductive sheet 2 covers the cable 1 and the detection resistors 7A and 7B.
Wrap or cover 2.

In any of the embodiments shown in FIGS. 7 and 8, the conductive sheet 22 is electrically connected to the shield such as the terminal box 2 and the bushing 3 and grounded. The present invention is not limited to the above embodiments. The material, shape and the like of the conductive sheet may be freely deformed within a range that does not impair the ease of handling and the shielding property. Further, if the measuring instrument or the like has a sufficiently shielded structure, it is not necessary to cover it with a conductive sheet, and only the portion that needs to be shielded may be covered with a conductive sheet.

[0014]

According to the partial discharge measuring method of the present invention described above, since the conductive sheet is arranged so as to cover the cable, the drum and the measuring instrument as a whole, a large shielded room unlike the conventional case is not required. In addition, it is possible to perform an electrical test of a long cable as it is wound around a drum regardless of the measurement time.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of a partial discharge measuring method of the present invention.

FIG. 2 is a schematic diagram of a conventional partial discharge measuring method.

FIG. 3 is a wiring diagram showing an equivalent circuit in the case of FIG.

FIG. 4 is a schematic view showing another example of a conventional partial discharge measuring method.

FIG. 5 is a graph showing a noise level of a conventional partial discharge measuring method.

FIG. 6 is a graph showing the noise level of the partial discharge measuring method of the present invention.

FIG. 7 is a schematic view showing a modification of the partial discharge measuring method of the present invention.

FIG. 8 is a schematic diagram showing another modification of the partial discharge measuring method of the present invention.

[Explanation of symbols]

 1 Cable 2 Termination Box 3 Bushing 4 Power Supply 7A, 7B Detecting Resistance 8 Measuring Instrument 19 Drum 16, 18, 20, 21 Wire Mesh (Conductive Sheet)

Claims (1)

[Claims] 1. When a high voltage is applied to one end of a cable wound around a drum to measure a partial discharge signal generated in the cable insulator, the cable and the drum are covered with a conductive sheet. Characteristic partial discharge measurement method.