JPS61180154A - Detecting method of partial discharging occurrence state of cable connection part - Google Patents

Abstract

PURPOSE:To grasp accurately the occurrence state of partial discharging at a cable connection part only by performing electric measuring operation without damaging a cable by applying a voltage between a conductor and a metallic shield layer in states wherein the insulating coating part of the cable connection part is pressed and not pressed and comparing measurement data with each other. CONSTITUTION:The cable connection part 1 is constituted by providing an internal semiconductor layer 4, the insulating coating part 5, an external semiconductor layer 6, and the metallic shield layer 7 on the periphery of a conductor connection part 3 where cables 2 and 2' after insulating coating layers 22 and 22' are peeled off stepwise are connected by a conductor connection pipe 31. Then, partial discharging data measured by applying the voltage between the conductors 26 and 26' and shield layer 7 while the coating part 5 of the connection part 1 is pressed is compared with partial discharging data measured by applying voltage while the coating part 5 is not pressed. In this case, the coating part is pressed locally to detect which part of the connection part partial discharging occurs.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for detecting the occurrence of partial discharge in a cable connection portion of a power cable such as a rubber/plastic insulated cable.

(Prior technology) The connection part of an electric cable whose insulator is rubber or plastic is made of a layer of wrapped rubber or plastic insulating tape, a molded product of insulating rubber or plastic, or a laminate of heat-shrinkable insulating plastic tubes. It has an insulating coating formed of a body or a combination thereof. If the cable connection section is used for a long period of time, thermal expansion and contraction due to energization and interruption may cause peeling and deterioration inside the insulation coating or at the interface between the insulation coating and its upper or lower layer. Partial discharge is likely to occur. Therefore, conventionally, when it is thought that a partial discharge is occurring in an existing cable line, etc., the occurrence situation has been detected using a normal method. That is, first, instruments for measuring partial discharge are connected to the middle of the grounding lead wire drawn out from the metal shielding layer on the periphery of the insulation coating of the cable connection part. Next, a voltage is applied between the cable conductor and the metal shielding layer, and the discharge starting voltage, its magnitude, etc. are observed using the instruments. If the existence of partial discharge is confirmed as a result of this observation, the cable connection where partial discharge is most likely to occur is actually dismantled and the location where it occurs is searched, and if no defect is found in the cable connection, the cable connection is sequentially started from the end of the cable. A method has been adopted in which the cables are dismantled.

(Problem to be solved by the invention) When using the conventional measurement method, it is possible to check whether or not partial discharge has occurred, but since the metal shielding layer of the cable connection part and the metal shielding layer of the cable body are electrically connected, It was not only possible to detect the exact location where the discharge occurred, but also to determine whether the partial discharge was occurring at the cable connection or in the cable itself. Therefore, there is a drawback that the occurrence of partial discharge cannot be determined unless the expensive objects to be measured, such as the cable connection section and the cable body, are actually dismantled one by one.

(Means for Solving the Problems) The present invention has been made in view of the above points, and its first purpose is to reduce the occurrence of partial discharge in the cable connection portion by reducing the partial discharge in the cable main body. The second purpose is to provide a method that can detect where in a cable connection part partial discharge is occurring. That is, the outline of the present invention is as follows.

(1) Partial discharge measured by applying voltage between the conductor and the metal shielding layer while applying pressure to the insulation coating of a cable connection part that has a metal shielding layer on the circumference of the conductor connection part via the insulation coating part. A method of detecting the occurrence of partial discharge in the insulating coating by comparing the data with data measured by applying a voltage between the conductor and the metal shielding layer while the insulating coating is not pressurized.

(2) Measurement by applying voltage between the conductor and the metal shielding layer while applying local pressure to the insulation part of the cable connection part that has a metal shielding layer on the circumference of the conductor connection part via the insulation coating part. By comparing the partial discharge data measured with the partial discharge data measured by applying a voltage between the conductor and the metal shielding layer in a state where the insulation coating is not pressurized, A method for detecting the occurrence of electrical discharge.

(Function) When the insulation coating is pressurized, the shape of the inner window of the insulation coating changes as voids generated due to peeling and wrinkles on the inner and outer surfaces are compressed. For example, if there is a void at the laminated interface of an insulating coating made of a laminated body, the interface will be brought into close contact with each other by applying pressure, and the void will disappear.

Therefore, the discharge starting voltage when pressure is applied to a portion having such a defect is significantly increased compared to when no pressure is applied.

In other words, if such an increase in discharge starting voltage is observed by pressurizing the insulating coating, it can be determined that a defective portion exists in that portion.

(Example) A first example of partial discharge occurrence situation detection based on the present invention will be described with reference to the drawings. The first embodiment uses the method of the invention to determine whether a partial discharge is occurring in the cable connection 1 or in the cable 2.2'. In the figure, the cable connection 1 has its own sheath 21, 21', a metal shielding layer 22.22', an outer semiconducting layer 23.23', an insulating covering layer 24.24' and an inner semiconducting layer 25.25'. Both cables 2, 2 to be connected are made by sequentially stripping the ends over a predetermined section.
The inner semiconducting layer 4,
It is constructed by providing an insulating coating section 5 made of a laminate of heat-shrinkable tubes, an outer semiconducting layer 6, and a metal shielding layer 7. Originally, the cable connection part 1 has an external protective layer on the periphery of the metal shielding layer 7, but this is not particularly shown because it is removed in advance when measuring partial discharge. Next, referring to the measuring instruments connected to such a cable connection part, a grounding lead wire 8 is drawn out from the metal shielding layer 7, and a known partial discharge detector 9 is connected to it.
and further connect a known partial discharge measuring device 10 via this.
and attach the observation device 11. A broadband type or narrow band acid type differential bridge or the like is used as the partial discharge measuring device 10, and the observation device 11
Use a cathode ray tube oscilloscope, synchroscope, etc. In addition, a recording instrument 12 is attached if necessary. Next, to explain the procedure for detecting the occurrence of partial discharge based on the above configuration, first, as in the conventional measurement method, a voltage is applied to the cable conductor in a state where the insulation coating is not pressurized, that is, in a natural state, and the measurement is performed. The discharge starting voltage, magnitude, number of occurrences, frequency of occurrence, etc. are measured using a device 10, an observation device 11, etc. The presence or absence of partial discharge can be easily determined by this measurement, but since the metal shielding layer 7 of the cable connection part and the metal shielding layer 22, 22' of the cable body are electrically connected as shown in J Heta earlier,
It cannot be determined from this measurement alone whether the partial discharge is occurring in the cable connection portion 1 or in the cables 2 and 2'. Therefore, as a result of the measurement, cable connection 1 or cable 2, 2'
If it is confirmed that partial discharge has occurred,
Record the measurement data. Next, an elastic body such as a vulcanized rubber tape is wrapped around the entire circumference of the metal shielding layer 7 of the cable connection part, and sufficient pressure is applied to the insulation coating part 5 through the metal shielding layer 7 to seal the insulation coating part. In a pressurized state, a voltage is applied between the conductor and the metal shielding layer, and various data on partial discharge are measured. Note that when applying pressure to the insulating coating portion 5 by wrapping the tape, the pressurizing effect can be further increased by using conductor heat generation due to conductor energization or external heating. Furthermore, as a pressurizing means for the insulating coating portion 5, instead of using the above-mentioned method of wrapping the elastic tape, a pressurizing method using pressurized fluid may be adopted. By the way, it is possible to determine whether a partial discharge is occurring in the cable connection part 1 or in the cable 2.2' by using the two types of measurement data mentioned above, that is, the data in a state where no pressure is applied to the insulation coating part 5. This is done by comparing the data with the data when pressure is applied, but if there is a defective part in the cable connection part 1 that causes partial discharge, the void will disappear by applying pressure, so The electrical characteristics when pressurized are significantly improved compared to those when no pressure is applied. On the other hand, if there is no defective part in the cable connection part and the defective part exists in the cable main body, the measurement results are not affected by whether the insulation coating part 5 is in a pressurized state or in a non-pressurized state. Therefore, as a result of comparing the measurement data, if the partial discharge data with the insulation coating 5 being pressurized is electrically improved, that is, if the discharge starting voltage is increasing, the partial discharge will occur at the cable connection. 1, and if no special change is observed in the discharge starting voltage, it can be determined that the problem is occurring in the cable body.

Next, the present invention will be explained in detail. In the second embodiment, the method for detecting the occurrence of partial discharge according to the present invention is applied as a means for detecting the exact position of occurrence of partial discharge. Used when it is judged or estimated. The main difference from the first embodiment is that the measurement is performed by locally pressurizing the insulating coating 5.

First, in view of the structure of the cable connection part 1, the insulation coating layer 5
Several locations where it is estimated that partial discharge is likely to occur are selected, and each location is sequentially locally pressurized and measured. Local pressure is applied to each part by tightening the insulating coating layer 5 of the part from around the upper metal shielding layer 7 with a metal band, ring, etc. in solder. Comparing the measurement data for each part that was sequentially pressurized and measured in this way with the measurement data when no pressure was applied, there were areas where the discharge starting voltage was clearly higher than when no pressure was applied, indicating that partial discharge It can be determined that the occurrence position is located in a portion where the discharge starting voltage has increased. On the other hand, if any increase in partial discharge inception voltage is observed in each pre-selected portion, measurements are sequentially performed on portions other than those portions while applying local pressure in the same manner. or,
If it is thought that partial discharges exist in several locations, two or three locations in each of the locations may be sequentially measured by applying local pressure at the same time while changing the combination. Although the embodiments of the present invention have been described in detail above, the scope of application of the present invention is wide, and can be used, for example, to detect the occurrence of partial discharge in a cable body.

(Effects of the Invention) In order to examine the effects of the method for detecting the occurrence of partial discharge based on the present invention, the present inventors actually produced a prototype cable connection part for a 15KV cross-linked polyethylene insulated electrical cable and conducted a confirmation test. I have done so, and I will present the results next. In addition, parts A, 8, 0, and D in the table below are respectively designated as A in the attached drawings.
The defective parts of the sample are artificially set in advance for measurement.

As described above, according to the method for detecting the occurrence of partial discharge of the present invention, the occurrence of partial discharge at the connection can be detected by only electrical measurement without unnecessary damage to the cable connection or the cable body. Because it can be accurately measured, it not only makes it possible to repair quickly and economically in the event of an accident occurring on an existing cable line, but also allows the measurement data to be reflected in the structural design of cable connections. effective.

[Brief explanation of drawings]

The figure is an explanatory diagram of an embodiment of the method for detecting the occurrence of partial discharge based on the present invention. 1; Cable connection part, 2, 2': Cable 3; Cable conductor connection part, 4; Inner semiconducting layer, 5; Insulating coating part, 6: Outer semiconducting layer, 7; Metal shielding layer, 8; Grounding lead Line, 9; Partial discharge detector, 10; Partial discharge measuring device, 11; Partial discharge observation device, 12: Recorder, 21.21': Sheath, 22.22': Metal shielding layer 23.23': External half Conductive layer 24.24': Insulating coating layer 25.25': Internal semiconductive layer 26.26': Conductor 31; Conductor connection tube

Claims (3)

[Claims] (1) Partial discharge measured by applying voltage between the conductor and the metal shielding layer while applying pressure to the insulation coating of a cable connection part that has a metal shielding layer on the circumference of the conductor connection part via the insulation coating part. By comparing the data with partial discharge data measured by applying a voltage between the conductor and the metal shielding layer in a state where the insulation coating is not pressurized, it is possible to determine the occurrence of partial discharge in the insulation coating. 1. A method for detecting partial discharge occurrence at a cable connection portion. (2) Measurement by applying a voltage between the conductor and the metal shielding layer while applying local pressure to the insulation coating of a cable connection part that has a metal shielding layer on the circumference of the conductor connection via the insulation coating. By comparing the partial discharge data measured with the partial discharge data measured by applying a voltage between the conductor and the metal shielding layer in a state where the insulation coating part is not pressurized, it is possible to determine the A method for detecting the occurrence of partial discharge at a cable connection portion, the method comprising detecting the occurrence of partial discharge. (3) Occurrence of partial discharge in the cable connection section according to claim 1 or 2, characterized in that heating the insulating coating section is also used when the insulating coating section is brought into a pressurized state. Detection method.