KR102249186B1 - System for measuring volume electricla resistivity of DC cable - Google Patents

Abstract

In the system for measuring volume resistance of a DC cable according to the present invention, in the system for measuring the volume resistance of a DC cable including a conductor, an inner semiconducting layer, an insulating layer, and an outer semiconducting layer, the outer periphery of the exposed insulating layer of the DC cable A measuring electrode part provided along the line, a resistance terminal part connected to a conductor exposed at both ends of the DC cable and surrounding the exposed insulating layer, a reinforcing insulating layer surrounding the exposed insulating layer of the DC cable, a conductor of the DC cable It characterized in that it comprises a voltage supply unit for applying a voltage to and an ammeter connected to the measuring electrode unit to measure a current.

Description

System for measuring volume electricla resistivity of DC cable

The present invention relates to a system for measuring volume resistance of a DC cable.

In general, it is important to understand the electric field distribution when designing a cable. In particular, in the case of a DC electric field applied to a DC (direct current) cable, a resistive electric field in which the electric field is distributed according to the volume intrinsic resistance of the insulating material of the DC cable. Indicate distribution characteristics. Therefore, in order to design the DC cable, it is necessary to know the volume intrinsic resistance of the insulating layer of the DC cable.

Although the volume intrinsic resistance of the raw material constituting the insulating layer of the DC cable is measured, the volume intrinsic resistance is measured by preparing a thin plate-shaped measurement specimen before being applied to the product of the DC cable. Therefore, when the raw material is actually applied to a DC cable, it is necessary to measure the volume intrinsic resistance value.

6 shows an apparatus for measuring volume resistance of a cable according to a conventional method.

As described above, in the case of manufacturing and measuring a measurement specimen, since it is manufactured in a thin plate shape, it is possible to measure even in a high electric field by applying a DC voltage. However, in the case of an actual DC cable, since the thickness of the insulating layer is significantly thicker than that of the specimen for measurement, a configuration for applying voltage is essential in order to apply a high electric field.

6, the conventional cable volume resistance measuring device 10 removes a part of the external semiconducting layer (not shown) of the DC cable and the insulation layer 14 is exposed, the voltage is applied to the conductor 15 of the cable. A voltage is applied by connecting the supply unit 12. Meanwhile, an electrode unit 16 is provided on the exposed surface of the insulating layer 14, and an ammeter 18 is connected to the electrode unit 16. In the above configuration, the voltage V applied by the voltage supply unit 12 can be known, and the current I flowing by the ammeter 18 can be measured.

Meanwhile, the volume intrinsic resistance (ρ) of the DC cable to be measured can be calculated by the following [Equation 1].

In the [Equation 1], the voltage (V) and the current (I) can be measured by the voltage supply unit 12 and the ammeter 18, respectively. Furthermore, since'A' represents the effective area of the insulating layer of the DC cable for which the volume intrinsic resistance is to be measured, it can be determined by measuring the area of the insulating layer of the actual DC cable. In addition, since the'l' represents the insulation thickness of the insulation layer, it can be determined by measuring the thickness of the insulation layer of the actual DC cable.

However, in the conventional configuration as described above, since the measurement is performed in the presence of air, that is, air, in order to secure the creepage distance, the external semiconducting layer must be removed by a relatively long distance or more according to the voltage applied to the conductor. there was. In addition, in the conventional configuration as described above, since the electric field is concentrated at the end of the outer semiconducting layer (not shown) and the end of the conductor 15 that have been removed, it is difficult to apply the desired target electric field. This entails a problem that the experiment is difficult.

An object of the present invention is to provide a volume resistance measurement system capable of reducing the hassle of removing the external semiconducting layer of the DC cable when measuring the volume resistance of the DC cable in order to solve the above problems.

Furthermore, the present invention provides a volume resistance measurement system that enables high electric field application by preventing the electric field from being concentrated at the end of the outer semiconducting layer and the end of the conductor of the DC cable when measuring the volume resistance of the DC cable. It aims to do.

An object of the present invention as described above is a system for measuring the volume resistance of a DC cable including a conductor, an inner semiconducting layer, an insulating layer and an outer semiconducting layer, provided along the outer periphery of the exposed insulating layer of the DC cable. Measuring electrode part, a resistance terminal part connected to the conductor exposed at both ends of the DC cable and surrounding the exposed insulating layer, a reinforcing insulating layer surrounding the exposed insulating layer of the DC cable, and applying a voltage to the conductor of the DC cable It is achieved by a volume resistance measurement system of a DC cable, comprising: a voltage supply unit and an ammeter connected to the measurement electrode unit to measure a current.

Here, it is possible to further include at least one guard electrode unit spaced apart from the measurement electrode unit by a predetermined distance along the outer periphery of the exposed insulating layer.

Meanwhile, the reinforcing insulating layer may be provided to surround the exposed insulating layer between the measuring electrode part, the guard electrode part, and the resistance terminal part.

In addition, the measuring electrode part and the guard electrode part may be formed of an outer semiconducting layer of the DC cable.

According to the configuration of the present invention having the above configuration, when measuring the volume resistance of the DC cable, it is troublesome to remove the external semiconducting layer by using the outer semiconducting layer of the DC cable as a measuring electrode part or a guard electrode part. Can be reduced.

Furthermore, the present invention provides a resistance terminal for electrically connecting the conductor of the DC cable and the outer semiconducting layer when measuring the volume resistance of the DC cable, so that the electric field is concentrated at the end of the outer semiconducting layer and the end of the conductor. To prevent high electric field application.

1 is a view showing the configuration of a DC cable according to an embodiment,
2 is a schematic diagram showing a circuit diagram of a system for measuring volume resistance of a DC cable according to the present invention;
3 is a cross-sectional view showing a cross-sectional configuration of a DC cable in the system for measuring volume resistance of a DC cable according to the present invention;
4 is a diagram showing an equipotential distribution of the DC cable in the volume resistance measurement system of a DC cable according to the present invention and an equipotential distribution in a conventional measuring device;
5 is a view showing the electric field distribution of the DC cable in the volume resistance measurement system of the DC cable according to the present invention and the electric field distribution in a conventional measuring device.
6 is a schematic diagram showing a conventional device for measuring volume resistance of a DC cable.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided so that the disclosed content may be thorough and complete, and the spirit of the present invention may be sufficiently conveyed to those skilled in the art. The same reference numbers throughout the specification indicate the same elements.

1 is a diagram showing the configuration of a DC cable according to an embodiment.

Referring to FIG. 1, the DC cable 110 includes a conductor 112 along the center. The conductor 112 serves as a passage through which current flows, and may be made of, for example, copper or aluminum. The conductor 112 is formed by twisting a plurality of wires.

However, the conductor 112 may have a non-uniform electric field because its surface is not smooth, and corona discharge is likely to occur partially. In addition, if a void is formed between the surface of the conductor 112 and the insulating layer 120 to be described later, the insulating performance may be deteriorated. In order to solve the above problems, the outside of the conductor 112 is wrapped with a semiconductive material such as semiconductive carbon paper, and a layer formed of the semiconductive material is defined as the inner semiconducting layer 114.

The inner semiconducting layer 114 evenly distributes electric charges on the conductor surface to make the electric field uniform, thereby improving the dielectric strength of the insulating layer 120 to be described later. Furthermore, by preventing the formation of a gap between the conductor 112 and the insulating layer 120, corona discharge and ionization are prevented. In addition, the inner semiconducting layer 114 also serves to prevent penetration of the insulating layer 120 into the conductor 112 when the DC cable 110 is manufactured.

An insulating layer 120 is provided outside the inner semiconducting layer 114. The insulating layer 120 electrically insulates the conductor 112 from the outside. In general, the insulating layer 120 has a high breakdown voltage and must be able to stably maintain the insulating performance for a long period of time. Furthermore, it should have low dielectric loss and have resistance to heat such as heat resistance. Therefore, as the insulating layer 120, polyolefin resins such as polyethylene and polypropylene are used, and polyethylene resins are preferred. The polyethylene resin may be a crosslinking resin and may be prepared by silane or an organic peroxide, for example, dicumyl peroxide (DCP) as a crosslinking agent.

However, when a high DC voltage is applied to the power cable, the insulating layer 120 is injected with electric charges from the conductor 112 to the inner semiconducting layer 114, the insulating layer 120, etc. Space charge can be formed. The formed space charge is accumulated in the insulating layer 120 according to the use time of the cable, and the accumulated space charge is in the vicinity of the conductor 112 when the impulse voltage is applied to the cable or the polarity of the DC voltage applied to the cable is rapidly reversed. It causes the problem of lowering the insulation breakdown voltage of the power cable by rapidly increasing the electric field strength.

Accordingly, the insulating layer 120 may include inorganic particles in addition to the crosslinking resin. The inorganic particles may be nano-sized aluminum silicate, calcium silicate, calcium carbonate, magnesium oxide, or the like. However, in terms of the impulse strength of the insulating layer, magnesium oxide is preferable as the inorganic particle. Although the magnesium oxide can be obtained from natural magnesium ore, it can also be prepared from artificial synthetic raw materials using magnesium salt in seawater, and has the advantage that it can be supplied as a material with stable quality and properties with high purity.

The magnesium oxide basically has a crystal structure of a face-centered cubic structure, but may have various forms, purity, crystallinity, physical properties, etc. depending on the synthesis method. Specifically, the magnesium oxide is classified into a cubic, a terrace, a rod, a porous, and a spherical shape, and may be used in various ways according to each specific physical property. Inorganic particles, including magnesium oxide, form a potential well at the boundary between the base resin and the inorganic particles when an electric field is applied to the cable, thereby exhibiting the effect of inhibiting the movement of electric charges and accumulation of space charges.

However, when a large amount of inorganic particles added to the insulating layer 120 is added, it acts as an impurity, and even when used in a small amount, there is a problem of lowering the impulse strength, which is another important characteristic required in a power cable, It is preferable to add 0.2 to 5 parts by weight, since the accumulated space charge cannot be sufficiently reduced with only the inorganic particles.

Meanwhile, the insulating layer 120 may be formed through a ground insulating process in which insulating paper is wound around the surface of the inner semiconducting layer 114. In this case, in order to improve the insulating properties, the insulating paper is wound around the surface of the conductor 112 and impregnated with insulating oil. The insulating oil is absorbed into the insulating paper through the impregnation process, and can be classified into an'oil filled (OF) cable' and a'mass impregnated (MI) cable' according to the viscosity of the insulating oil.

OF cable is impregnated with insulating paper using relatively low viscosity insulating oil, and the length of extension is limited because it must be operated while maintaining the hydraulic pressure at a certain level by pressurizing the insulating oil. On the contrary, since the insulating paper is impregnated with insulating oil of relatively high viscosity, the MI cable has the advantage of having a long extension length since there is little flow of insulating oil in the insulating paper, so there is no need to maintain hydraulic pressure.

The insulating layer 120 is formed by wrapping a plurality of insulating papers, and may be formed by repeatedly wrapping a thermoplastic resin such as kraft paper or kraft paper and polypropylene resin.

Specifically, the insulating layer may be formed by winding only kraft paper, but preferably, an insulating layer is formed by winding an insulating paper having a structure in which kraft paper is stacked on the upper and lower surfaces of a composite insulating paper, such as polypropylene resin. can do.

In the case of a MI cable that is wound with only kraft and impregnated with insulating oil, when the cable is operated (when energized), the current flowing through the cable conductor causes the inner side in the radial direction, that is, the outer side in the radial direction from the part of the insulating layer in the direction of the inner semiconducting layer. That is, a temperature difference occurs in the portion of the insulating layer in the direction of the outer semiconducting layer, which will be described later. Therefore, the insulating oil of the insulating layer on the side of the inner semiconducting layer, which is higher temperature, has a lower viscosity and thermally expands to move to the insulating layer on the side of the outer semiconducting layer. As it does not return, bubbles are generated in the radial direction inward, that is, in the insulating layer portion on the inner semiconducting layer side, resulting in deterioration of the insulating performance.

However, when the insulating layer is formed with a composite insulating paper as described above, a thermoplastic resin such as polypropylene resin, which is not impregnated with oil during cable operation, thermally expands to suppress the flow of insulating oil, and the polypropylene resin is Since the insulation resistance is greater than that of kraft paper, even if bubbles are generated, the voltage shared by the bubbles can be reduced.

In addition, since the polypropylene resin is not impregnated with the insulating oil, it is possible to suppress the flow of the insulating oil in the diameter direction of the cable due to gravity. Since the surface pressure is applied to the kraft paper by thermal expansion, the flow of insulating oil can be further suppressed.

Composite insulating paper is laminated of kraft paper on one side of a thermoplastic resin such as polypropylene resin, a thermoplastic resin such as polypropylene resin is laminated on the top and bottom of kraft paper, or four layers of thermoplastic resin such as kraft paper and polypropylene resin are alternately stacked The above laminated ones can be used, and the effects and effects in this case are the same as in the case of insulating paper having a structure in which kraft paper is laminated on the upper and lower surfaces of the polypropylene resin described above.

In addition, the insulating layer 120 is formed by winding the composite insulating paper, but any one or both surfaces of the surface in contact with the inner semiconducting layer 114 and the surface in contact with the outer semiconducting layer 125 may be formed of kraft paper. , Preferably, both the surface in contact with the inner semiconducting layer 114 and the surface in contact with the outer semiconducting layer 125 may be formed by winding kraft paper.

In this case, since kraft paper having a lower resistivity than composite insulating paper is formed on one or both surfaces of the surface in contact with the inner semiconducting layer 114 of the insulating layer or the surface in contact with the outer semiconducting layer 125, the insulating layer, which is the starting point of impulse destruction, and Even if bubbles are generated in a portion where the inner semiconducting layer contacts or the portion where the insulating layer and the outer semiconducting layer come in contact, the impulse breakdown characteristic can be prevented from deteriorating due to the electric field relaxation effect of the kraft paper layer. Further, since kraft paper has little polarity effect on impulse destruction, the impulse polarity effect generated by using plastic laminate paper can be reduced.

On the other hand, if the outside as well as the inside of the insulation layer 120 is not shielded, a part of the electric field is absorbed by the insulation layer 120, but most of the electric field is discharged to the outside. In this case, when the electric field becomes larger than a predetermined value, the insulation layer 120 and the outer shell of the DC cable 110 may be damaged by the electric field. Accordingly, a semiconducting layer is provided outside the insulating layer 120 again, and is defined as an outer semiconducting layer 125 to distinguish it from the above-described inner semiconducting layer 114. As a result, the outer semiconducting layer 125 is grounded to make the distribution of electric field lines between the above-described inner semiconducting layer 114 at equipotential, thereby improving the dielectric strength of the insulating layer 120. In addition, the outer semiconducting layer 125 may smooth the surface of the insulating layer 120 in the cable to mitigate electric field concentration, thereby preventing corona discharge.

A shielding layer 127 made of a metal sheath or a neutral wire is provided outside the outer semiconducting layer 125 according to the type of cable. The shielding layer 127 is provided for electrical shielding and return of short-circuit current.

The outer shell 129 is provided on the outside of the DC cable 110. The outer shell 129 is provided on the outer periphery of the DC cable 110 and serves to protect the internal configuration of the DC cable 110. Accordingly, the shell 129 has excellent chemical resistance and mechanical strength to withstand weather resistance, chemicals such as chemicals, etc. that can withstand natural environments including various climates such as light, wind and rain, moisture, and gases in the air. In general, the outer shell is made of PVC (polyvinyl chloride) or PE (polyethylene). Hereinafter, a system for measuring the volume resistance of a DC cable having the above configuration will be described with reference to the drawings.

2 is a schematic diagram showing a circuit diagram of a system for measuring volume resistance of a DC cable according to the present invention, and FIG. 3 is a cross-sectional view showing a cross-sectional configuration of a DC cable in the system for measuring volume resistance of a DC cable according to the present invention.

2 and 3, the volume resistance measurement system 100 of the DC cable includes a measurement electrode unit 130 provided along the outer periphery of the exposed insulating layer 120 of the DC cable 110, the A resistance terminal unit 150 connected to the conductor 112 exposed at both ends of the DC cable 110 and surrounding the exposed insulating layer 120, and surrounding the exposed insulating layer 120 of the DC cable 110 A reinforcing insulating layer 140, a voltage supply unit 160 for applying a voltage to the conductor 112 of the DC cable, and an ammeter 170 connected to the measuring electrode unit 130 to measure a current. Furthermore, the volume resistance measurement system 100 of the DC cable includes at least one guard electrode unit 132 spaced apart from the measurement electrode unit 130 by a predetermined distance along the outer periphery of the exposed insulating layer 120. ) May be further provided.

When the volume resistance measurement system 100 of the DC cable measures the volume resistance of the DC cable 110, the outer semiconducting layer 125 of the DC cable is exposed so that at least a part of the insulating layer 120 is exposed. Reference). However, in the present invention, since the outer semiconducting layer 125 of the DC cable is used as the measuring electrode unit 130 and the guard electrode unit 132, the length of removing the outer semiconducting layer is reduced, compared to the prior art. It can save the trouble of removing the outer semiconducting layer.

Specifically, the outer semiconducting layer 125 of the DC cable 110 is removed so that at least a part of the insulating layer 120 of the DC cable 110 is exposed, and conductors ( 112) is exposed to protrude by a predetermined length. A voltage supply unit 160 is connected to the conductor 112. The voltage supply unit 160 applies a predetermined voltage to the conductor 112. Accordingly, the conductor 112 of the DC cable 110 serves as a high voltage electrode part in the volume resistance measurement system 100 of the DC cable.

A measurement electrode part 130 is provided on the outer periphery of the exposed insulating layer 120 of the DC cable 110. Although it is possible to add a separate component to the measuring electrode unit 130, in the present invention, it is configured by utilizing the outer semiconducting layer 125 of the DC cable. That is, when the external semiconductor layer is removed, an external semiconductor layer having a predetermined width is left at an approximately intermediate portion of the exposed insulating layer 120, so that the remaining external semiconductor layer is used as the measurement electrode part 130. It is done. According to this configuration, it is possible to avoid the hassle of manufacturing and installing a separate measuring electrode unit. Further, in the above configuration, it is possible to reduce the trouble of removing the outer semiconducting layer by a relatively long distance.

An ammeter 170 is connected to the measuring electrode unit 130. The ammeter 170 is connected to the measuring electrode unit 130 to measure the current flowing by the voltage applied to the conductor 112.

Meanwhile, the guard electrode part 132 is spaced apart from the measuring electrode part 130 by a predetermined distance and is provided along the outer periphery of the exposed insulating layer 120. The guard electrode part 132 is configured by utilizing the outer semiconducting layer 125 of the DC cable, like the measuring electrode part 130. Further, the guard electrode part 132 may be preferably provided with a pair of the measuring electrode part 130 interposed therebetween. The guard electrode part 132 is provided to be spaced apart from the measuring electrode part 130 to remove a leakage current flowing along the surface of the insulating layer 120 to enable more accurate current measurement.

Meanwhile, the volume resistance measurement system 100 of the DC cable is provided with a reinforcing insulating layer 140 surrounding the exposed insulating layer 120 of the DC cable. The reinforcing insulating layer 140 surrounds the exposed insulating layer 120 of the DC cable 110. That is, in the present embodiment, the reinforcing insulating layer 140 is provided to surround the exposed insulating layer 120 between the measuring electrode part 130, the guard electrode part 132, and the resistance terminal part 150. . The reinforcing insulating layer 140 may be formed by winding an insulating tape or the like having a high dielectric strength compared to external air.

Meanwhile, in the present invention, a resistance terminal 150 electrically connected to the exposed conductor 112 is provided. The resistance terminal 150 has one end connected to the exposed conductor 112 and the other end connected to the guard electrode part 132. Since the guard electrode part 132 is configured by utilizing the outer semiconducting layer 125 of the DC cable 110 as described above, the conductor 112 and the outer semiconducting layer are formed by the resistance terminal unit 150 as described above. When the guard electrode unit 132 is connected, the distribution of equipotential lines of the DC cable is not concentrated and an even distance can be maintained compared to the prior art.

Meanwhile, the resistance terminal 150 may be configured to have a volume resistance value of approximately 1.0*10 ⁸ to 1.0*10 ¹² (Ω·cm), for example,'SCTM'of'Raychem'. Can be configured using

Since the method of measuring the volume resistance of the DC cable in the system for measuring the volume resistance of the DC cable according to the present invention having the above configuration is similar to the method using [Equation 1] of the prior art described above, a repetitive description will be provided. Omit it.

4 is a diagram showing an equipotential distribution of the DC cable 110 and an equipotential distribution in a conventional measuring apparatus in the system for measuring volume resistance of a DC cable according to the present invention. In FIG. 4, the diagram of FIG. 4(A) shows the distribution of equipotentials of the DC cable 110 in the volume resistance measurement system of the DC cable according to the present invention, and the drawing of FIG. 4(B) shows the equipotentiality of the conventional measuring device. The distribution is shown.

Referring to FIG. 4, as in the system for measuring volume resistance of a DC cable according to the present invention, when a resistance terminal unit 150 connecting a conductor 112 and an external semiconductor layer 125 is provided, the external semiconductor layer 125 It can be seen that the equipotential lines are not concentrated at the end of) and the equipotential lines are distributed at approximately uniform intervals along the resistance terminal 150 as shown in FIG. 4(a). Reference numeral '200', which is not described in FIG. 4A, denotes air.

On the other hand, in the conventional device without the resistance terminal unit 150 of the present invention, it can be seen that the equipotential lines are not distributed at uniform intervals, but the equipotential lines are concentrated at the ends of the outer semiconducting layer 125.

The above results can also be confirmed in FIG. 5. 5 is a view showing the electric field distribution of the DC cable 110 and the electric field distribution in a conventional measuring device in the system for measuring the volume resistance of a DC cable according to the present invention. In FIG. 5, the diagram of FIG. 5(A) shows the electric field distribution of the DC cable in the volume resistance measurement system of the DC cable according to the present invention, and the drawing of FIG. 5(B) shows the electric field distribution in the conventional measuring device. do.

Referring to FIG. 5, when the resistance terminal unit 150 connecting the conductor 112 and the outer semiconducting layer 125 is provided as in the system for measuring the volume resistance of a DC cable according to the present invention, the outer semiconducting layer 125 It can be seen that the electric field is not concentrated at the end of) and the electric field is spread and distributed along the inside of the insulating layer 120 as shown in FIG. 5(a).

On the other hand, in the conventional device without the resistance terminal unit 150 of the present invention, it can be seen that the electric field is concentrated at the end of the outer semiconducting layer 125.

Although the present specification has been described with reference to preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention within the scope not departing from the spirit and scope of the present invention described in the claims described below. You will be able to do it. Therefore, if the modified implementation basically includes the elements of the claims of the present invention, it should be seen that all are included in the technical scope of the present invention.

Volume resistance measurement system for 100...DC cables
112... conductor
120...insulation layer
130...measuring electrode part
132...guard electrode part
140... reinforced insulating layer
150... resistance terminal

Claims (4)

In a system for measuring the volume resistance of a DC cable including a conductor, an inner semiconducting layer, an insulating layer and an outer semiconducting layer,
A measuring electrode part provided along an outer circumference in a circumferential direction from the center of the exposed insulating layer of the DC cable;
A resistance terminal connected to each of the exposed conductors at both ends of the DC cable and surrounding the exposed insulating layer to a position spaced apart from the measurement electrode part in the length direction of the DC cable;
A pair of reinforcing insulating layers surrounding the exposed insulating layer in a circumferential direction while being in contact with both sides of the measuring electrode part in the length direction of the DC cable;
A pair of guard electrode portions connecting the reinforcing insulating layer and the resistance terminal portion and surrounding the outer circumference of the insulating layer in a circumferential direction at a position spaced apart from the measuring electrode portion by a predetermined distance in the length direction of the DC cable;
A voltage supply unit for applying a voltage to a conductor of the DC cable; And
A volume resistance measurement system of a DC cable, comprising: an ammeter connected to the measurement electrode unit to measure a current. delete delete The method of claim 1,
The volume resistance measurement system of a DC cable, wherein the measuring electrode part and the guard electrode part are made of an outer semiconducting layer of the DC cable.

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