JPH0729691A - Method for eliminating space charge of insulator - Google Patents

Abstract

PURPOSE:To eliminate the space charge of an insulator in a short time, and improve the quality by applying an AC voltage to the insulator, implanting a new charge thereto, and extracting the space charge. CONSTITUTION:When a switch 7 is connected to a DC voltage power source 8a side, and a prescribed high voltage is applied to an internal conductor 2, a charge is accumulated in the conductor 2. A cable insulator 4 is cut, a mixture of sulfur and red lead is sprayed on the section, and the space charge distribution is measured by the distributed state of the mixture. In the cable insulator 4, a negative charge of the same pole as the charge generated in an internal semiconductor layer 3 is generated in its protruding top end part, and a positive charge is generated around it. The switch 7 is connected to an AC voltage power source 8b, and a voltage is applied from the power source 8b to the conductor 2. In the insulator 4, then, the negative charge around the projection of the conductive layer 3 is eliminated, and the insulator 4 is uniformly charged with the positive charge. Thus, the space charge of the insulator 4 can be eliminated, and working property is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of removing space charges formed in an insulator used for insulation of a power cable when a DC voltage is applied to the insulator.

[0002]

2. Description of the Related Art As is well known, a power cable has a structure in which an outer circumference of a conductor is sequentially covered with an inner semiconductive layer, an insulating layer, an outer semiconductive layer, a shielding layer, a sheath and the like. A direct current voltage is applied to the insulator made of resin such as cross-linked polyethylene used for the insulating layer of this power cable by applying a super high voltage direct current to the conductor, and space charge is generated inside the insulator. May be formed. When this space charge is generated, the electric field around the current flowing through the conductor is distorted, which may cause the insulation performance of the power cable to deteriorate and the reliability of the power cable to be impaired. For this reason, conventionally, in order to maintain the quality of the insulator, a method of maintaining the quality of the insulator by grounding the insulator at the temperature of the atmosphere and removing the space charge of the insulator has been implemented. It had been.

[0003]

However, since the space charge formed inside the insulator has a very long life,
There is a drawback in that it takes a long time to remove the space charges simply by grounding the insulator. Therefore, there is a problem that the quality of the insulator cannot be sufficiently maintained. In addition, in recent years, with the increase in size and the increase in voltage of power cables, it has been desired to improve the quality of the insulator.

The present invention effectively solves the above problems, and an object of the present invention is to provide a method of removing space charges of an insulator, which can remove the space charges formed inside the insulator in a short time.

[0005]

The invention according to claim 1 is
In order to solve the above problems, an AC voltage is applied to the insulator to remove the space charges generated in the insulator. In order to solve the above-mentioned problems, the invention according to claim 2 is solved by grounding the insulator at a high temperature to remove the space charge generated in the insulator.
In order to solve the above problems, the invention according to claim 3 is solved by applying an AC voltage to the insulator at a high temperature to remove the space charges generated in the insulator.

[0006]

According to the invention described in claim 1, by applying an AC voltage to the insulator, a new charge is injected into the space charge generated in the insulator or the space charge of the insulator is extracted. , The space charge in the insulator is removed.
According to the second aspect of the present invention, by grounding the insulator at a high temperature, the space charge in the insulator becomes easy to move, the space moves at high speed, and the space charge in the insulator is removed. In the invention according to claim 3, by applying an AC voltage to the insulator at a high temperature, the space charge of the insulator is made to move easily, new charges are injected into the space charge, or the space in the insulator is injected. The space charge is removed by extracting the charge.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a configuration of an apparatus for removing space charges of a cable insulator used when carrying out the method of the present invention. Sample cable 1 to be measured
In this example (power cable, etc.), as shown in FIG.
The inner conductor 2, the inner semiconductive layer 3, the cable insulator (insulator) 4, the outer semiconductive layer 5, the shield layer 6, and the PVC sheath 7 are coaxially arranged in order from the center. As shown in FIG. 1, to one end of the inner conductor 2 of the sample cable 1, a DC voltage power supply 8a and an AC voltage power supply 8b are selectively connected through a switch 7 via a resistor 6, and with this configuration. A DC voltage or an AC voltage can be selectively applied to the inner conductor 2. The other end of the inner conductor 2 is grounded.

Next, a method of removing the space charge distribution of the cable insulator 1 will be described. First, the switch 7 is connected to the DC voltage power supply 8a side, and the internal conductor 2 is connected to, for example, 40
When a high voltage of kV is applied, charges are accumulated in the inner conductor 2. The Dustfiger method is known for measuring the space charge distribution of the cable insulator 4 in this state. This Dust-figer method cuts the cable insulator 1 to which a DC voltage is applied, sprinkles a mixture powder of sulfur and lead on the cross section of the cable insulator 1, and depending on the distribution state of the mixture powder, the space charge It is to measure the distribution. Here, sulfur is colored yellow and has a property of adhering to the electric charge of the positive electrode, and red lead is colored red and has a property of adhering to the electric charge of the negative electrode.

The results of measuring the space charge distribution of the cable insulator 4 by using this Dustfiger method are shown in FIGS. FIG. 3 shows a cross-sectional view of the sample cable 1 which is almost half-divided, and FIG. 4 is an enlarged view of the vicinity of the protrusion 3 a formed on the inner semiconductive layer 3 of the sample cable 1. As shown in FIG. 4, in the cable insulator 4, a charge (negative charge) having the same polarity as the charge generated in the inner semiconductive layer 3 is generated around the tip portion of the protrusion 3a, and the charge is generated around the negative charge. Charges of different polarity (positive charges) are generated.

After that, the switch 7 is connected to the AC voltage power supply 8b. Here, the AC voltage power supply 8b has a frequency of 1 to
It is preferable to set 1 kHz and the AC voltage to 100 to 50 kV. If the frequency exceeds 1 kHz, the charge does not follow, which is not preferable, and if it is less than 1 Hz,
Space charges are formed, which is not preferable. If the AC voltage exceeds 50 kV, dielectric breakdown may occur, which is not preferable. In this way, an AC voltage is applied to the inner conductor 2. Here, the application time of the AC voltage is 10 to 60.
It is preferable to apply for 2 seconds. When the application time exceeds 60 seconds, it is not preferable because of deterioration of the insulator. As a result, the cable insulator 4 has, as shown in FIG.
Negative charges around the protrusions 3a of the internal semiconductive layer 3 are removed.
The cable insulator 4 around the protrusion is uniformly charged with a positive charge.

According to such a method for removing the space charge of the insulator, when the ultrahigh voltage DC voltage is transmitted to the sample cable 1, the DC voltage is applied to the cable insulator 4 and the cable insulator 4 is applied. Space charge is generated. Then, by applying an AC voltage to the inner conductor 2, the cable insulator 4
Since an AC voltage is applied to the cable insulator 4, a new charge is injected into the space charge generated in the cable insulator 4, or the space charge in the cable insulator 4 is extracted. For this reason,
Compared with the method of grounding the cable insulator 4 and removing the space charge of the cable insulator 4 for a long period of time, the space charge of the cable insulator 4 can be removed in an extremely short time, and the space charge of the cable insulator 4 can be removed. Workability can be improved. Since the space charge can be easily removed from the cable insulator 4 in this manner, the insulation performance of the cable insulator 4 can be maintained, and thus the quality of the cable insulator 4 can be maintained. It should be noted that, in the above-described embodiment, the space charge is likely to be generated in the peripheral portion of the protrusion 3a, so the method of removing the space charge around the protrusion 3a has been described. However, this embodiment can be applied.

(Experimental example) Next, using the above apparatus, an insulator sample (length 80 mm, width 80 m) made of cross-linked polyethylene using dicumyl peroxide (DCP) as a cross-linking agent.
m, thickness 3 mm) space charge distribution was measured. here,
As a dust figure, a color copying toner containing lead oxide, sulfur, etc. was used, and the space charge distribution around the protrusions of the insulator sample was measured. As a result, a charge distribution equivalent to that shown in FIGS. 3 to 5 was obtained. It was 3 and 4 show charge distributions as a result of connecting the switch 7 to the DC voltage power supply 8a and applying a DC voltage of 40 kV to the inner conductor 2. And FIG.
4 shows the charge distribution as a result of connecting the switch 7 to the AC voltage power supply 8b and applying the AC voltage of 20 kV to the inner conductor 2 for 30 seconds after showing the charge distribution of FIG. As shown in FIG. 4, a negative charge distribution appeared near the tip of the protrusion of the insulator sample, and a positive charge distribution appeared around this negative charge. Then, by applying an AC voltage, as shown in FIG. 5, the negative charge distribution disappeared from the insulator sample near the tip of the protrusion.

<Other Embodiments> In the above embodiments, the space charge is removed from the cable insulator 4 by using the device capable of applying the AC voltage to the sample cable 1. However, the cable insulator 4 is grounded by a lead wire or the like. With this cable insulator 4
It is also possible to wind a heater around and heat the cable insulator 4 to a high temperature with this heater to remove the space charge. That is, by heating the cable insulator 4 on which the space charge is formed to a high temperature, the space charge of the cable insulator 4 easily moves, and this space charge moves along the lead wire or the like, so that the space charge is reduced. It can be removed from the cable insulator 4 at a fast rate. Here, for example, when the cable insulator 4 is made of polyethylene, the temperature of the cable insulator 4 may be set to 80 ° C. or lower which is the heat resistant temperature of polyethylene and lower than or equal to the heat resistant temperature of the sample cable. preferable.

<Modification> The apparatus used in the above embodiment may be provided with a sample cable around which a heater is wound to remove space charges. That is, the heater is a cable insulator 4
Alternatively, an AC voltage may be applied to the cable insulator 4 while heating the. At this time, the cable insulator 4 may be grounded. By applying an AC voltage to the cable insulator 4 at a high temperature in this way, an AC voltage is applied to the space charges that are easy to move, so this space charge can be easily extracted or can be applied to the space charges that are easy to move. Can inject various charges. Therefore, the space charge in the cable insulator 4 can be easily removed, the removal speed of this space charge can be improved, and the space charge can be removed easily and in a short time. Can be maintained.

[0015]

As described above, according to the method of the present invention, even when a space charge is generated in an insulator of a power cable or the like when a DC voltage is applied to the power cable or the like, the insulator When an AC voltage is applied to the space charge, a new charge is injected into the space charge of the insulator or the space charge of the insulator is extracted, and the space charge in the insulator is removed. Therefore, compared with the conventional method of grounding the insulator and removing the space charge of the insulator over a long period of time, the space charge of the insulator can be removed in an extremely short time, and the workability of removing the space charge of the insulator is improved. Can be made. In this way, the space charge can be easily removed from the insulator, so that the quality of the insulator can be maintained.

Further, since the space charge is removed by grounding the insulator at a high temperature, the space charge easily moves in a high temperature state as compared with the case where the insulator is simply grounded at the atmospheric temperature, and the space charge The removal rate can be increased. On the other hand, by applying an AC voltage to the insulator at a high temperature, this space charge can be removed to extract the space charge with enhanced mobility, and a new charge is injected into the space charge with enhanced mobility. Therefore, the space charge removal efficiency can be improved.

[Brief description of drawings]

FIG. 1 is a side view showing an example of an apparatus used for carrying out the method of the present invention.

FIG. 2 is a cross-sectional view of the power cable used in FIG.

FIG. 3 is a diagram showing a charge distribution state of an insulator sample before carrying out the method of the present invention.

FIG. 4 is a diagram showing a charge distribution state of a protruding portion of the inner semiconductive layer of FIG.

FIG. 5 is a view showing a charge distribution state of an insulator sample after the method of the present invention is carried out.

[Explanation of symbols]

 1 Sample cable (power cable) 4 Cable insulator (insulator)

Claims (3)

[Claims] 1. A method for removing space charges generated in an insulator used in a power cable or the like when a DC voltage is applied to the insulator, which comprises applying an AC voltage to the insulator. A method of removing space charges in an insulator, characterized by removing the space charges generated in the insulator. 2. A method of removing space charges generated in an insulator used for a power cable or the like when a direct current voltage is applied to the insulator, which is obtained by grounding the insulator at a high temperature. A method for removing space charges in an insulator, comprising removing space charges generated in the insulator. 3. A method of removing space charges generated in an insulator used in a power cable or the like when a DC voltage is applied to the insulator, which comprises applying an AC voltage to the insulator at a high temperature. The method for removing space charges in an insulator is characterized by removing the space charges generated in the insulator.