JPS6031268B2 - Cable insulation defect detection method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a cable insulation defect detection method for detecting the direction in which an insulation defect exists by passing a current through the metal shielding layer of a power cable having a metal shielding layer from the middle of the route. It is.

Conventionally, as a method for detecting the direction in which a corrosion protection layer insulation failure point exists, for example, as shown in Fig. 1, two locations are determined at a predetermined distance apart in the middle of the cable installation route, and a corrosion protection layer 1 is applied at each of these two locations. The metal shielding layer 2 is removed and the metal shielding layer 2 is exposed, terminals are attached as necessary to points a and b on one of the exposed metal shielding layers 2, and terminals are attached to points c and d on the other metal shielding layer 2. After connecting the terminals to the terminals B and C, a measuring power source 4 is connected between the terminals B and C via a switchgear 5, and a galvanometer is connected between each of the terminals A and D and the ground as a means for measuring minute currents. A method has been proposed in which galvanometers 6 and 6' are connected in sequence, and the direction in which the anti-corrosion layer insulation defect exists is detected by observing the presence or absence of deflection of the pointers of the galvanometers 6 and 6'. If there is a corrosion protection layer insulation failure resistor 7 that shows insulation failure points only on the left side of the observation position, the measurement power source 4 is connected when the galvanometer 6 is connected between the d terminal and the ground. A closed circuit including the anti-corrosion layer insulation failure resistor 7 and the galvanometer 6 is formed between the b and c terminals, and the pointer of the galvanometer 6 swings due to the minute current flowing in the closed circuit, so the c terminal It can be determined that the anti-corrosion layer insulation failure resistor 7 exists on the left side.

Also, when galvanometer 6' is connected between terminal a and earth,
Since the closed circuit including the galvanometer 6' and the anti-corrosion layer insulation failure resistor 7 is connected only to one terminal b to which the measurement power source 4 is connected, no current flows in that closed circuit. . Therefore, since the pointer of the galvanometer 6' does not swing, it can be determined that there is no defective point in the anticorrosive layer insulation at the right end of the b terminal. Based on this judgment, when we next set the observation position to the left of the above observation position and perform the detection work as described above, if the relationship between the presence and absence of deflection of the galvanometer pointer is the same as above. , it can be determined that there is a defective point in the corrosion protection layer insulation on the left side of the observation position, and the relationship between the presence or absence of deflection of the galvanometer pointer is the opposite of the above, that is, the galvanometer 6 If the pointer does not swing and the pointer of the galvanometer 6' swings, it can be determined that there is a defective point in the anticorrosive layer insulation to the right of the observation position. In this way, by narrowing the range in which the corrosion protection layer insulation failure point exists, it is possible to detect the position where the corrosion protection layer insulation failure point exists. Note that when the direction in which the corrosion protection layer insulation defect point exists is detected in this way, it is not necessary to ground the conductor terminal 3. Furthermore, as shown in Fig. 2, by grounding the conductor terminal 3, it is possible to detect the direction in which an insulation defect exists in the insulation body. If there is a main body insulation failure resistance 8 that indicates an insulation failure point, when the galvanometer 6 is connected between the d terminal and the ground, there is a resistance between the b and c terminals to which the measurement power source 4 is connected. A closed circuit including the main body insulating resistor 8 and the galvanometer 6 is formed, and a current from the measurement power source 4 flows through the closed circuit.

Therefore, since the pointer of the galvanometer 6 swings, it can be determined that the main body insulation failure resistance 8 exists on the left side of the c terminal. In addition, when the galvanometer 6' is connected between the a terminal and the ground, the galvanometer is A total of 6' pointers do not swing. Accordingly, it can be determined that there is no defective insulation point on the main body on the right side of the b terminal. Below, two parts are separated by a predetermined interval according to the case explained in Fig. 1.
This involves sequentially determining the locations and performing detection work to detect defects in the main body insulation. However, the conventional cable insulation defect detection method explained in FIGS.
Since the metal shielding layer 2 between terminals b and c is connected in parallel between the terminals of
Most of the current from the measurement power source 4 flows through the metal shielding layer 2 between the terminals, and only a small amount of current flows through the galvanometer 6 through the poorly insulated resistor, and there is particularly high insulation resistance where insulation deterioration has not progressed much. In this case, it becomes difficult to detect minute currents, and therefore it becomes extremely difficult to detect the direction in which a defective point exists.

Furthermore, if the distance between terminals b and c is increased, the amount of current flowing through the galvanometer 6 through the poorly insulated resistor will increase, but on the other hand,
The two locations where the anti-corrosion layer 1 is removed are separated, making removal and repair work of the anti-corrosion layer 1, the work of observing the galvanometers 6 and 6', and other tasks cumbersome. The present invention is a novel invention that improves the conventional drawbacks as described above, and its purpose is to allow most of the current from the measurement power supply to flow to the defective insulation point, making it easy to detect the direction in which the defective insulation point exists. It is to make it.

Examples will be described in detail below. FIG. 3 is an explanatory diagram of the detection method according to the embodiment of the present invention, and as shown in the figure,
The corrosion protection layer 1 is removed at one point along the cable installation route to expose the metal shielding layer 2, and the exposed metal shielding layer 2 is cut at the center to form a slit 9, and the metal shielding on the left and right sides of the metal shielding layer 2 is cut at the center of the exposed metal shielding layer 2. Layer 2 is electrically isolated. However, since the semiconductive layer existing under the metal shielding layer 2 has a low conductivity, it is not necessarily necessary to cut it. Then, the measurement power source 4 is connected via the switch 5 between the metal shielding layers 2 on the left and right of the slit 9, that is, between terminals b and c, and between the metal shielding layers on the left and right of the slit 9 and the ground, that is, the terminal a. Galvanometers 6 and 6' serving as minute current measuring means are successively connected between each of the terminals 1 and d and the ground to detect the direction in which a defective point in the anticorrosive layer insulation exists. Note that grounding of the conductor woven portion 3 is not necessary. For example, if there is a corrosion protection layer insulation failure resistor 7 that indicates the position of the insulation failure point only on the left side of the observation position where the slit 9 is formed as shown in the figure, a galvanometer 6 is placed between the d terminal and the ground. When connected, a closed circuit including the anti-corrosion layer insulation failure resistor and the galvanometer 6 is formed between terminals b and c to which the measurement power source 4 is connected, and current from the measurement power source 4 flows through the closed circuit. Since the pointer of the galvanometer 6 swings, it can be determined that the anti-corrosion layer insulation failure resistor 7 exists on the left side of the c terminal.

Also, when a galvanometer 6' is connected between the a terminal and the ground,
Since the closed circuit including the galvanometer 6' and the anti-corrosion layer insulation failure resistor 7 is connected only to one terminal b to which the measurement power source is connected, the current from the measurement power source 4 flows through the closed circuit. Therefore, the pointer of the galvanometer 6' does not swing. As a result, it can be determined that there is no corrosion-protective layer insulation defect on the right side of the b terminal. For this reason, the observation position where the metal shielding layer 2 is next cut to form a slit and the detection work is performed is to the left of the initial observation position where the slit 9 is formed, and the detection work is performed as described above. It will be a good thing if you do it. If the deflection of the galvanometer has the above-mentioned relationship at the observation position where the next slit is formed, it can be determined that the anticorrosive layer insulation failure resistance 7 exists further to the left of that position, and If the deflection of the galvanometer is in the opposite relationship to the above-mentioned relationship, that is, the pointer of galvanometer 6 does not swing, but the pointer of galvanometer 6' swings, an anti-corrosion layer insulation is placed on the right side of that position. This means that it can be determined that a defective point exists. In this way, by narrowing the range in which the corrosion protection layer insulation failure points exist, it is possible to detect the position where the corrosion protection layer insulation failure points exist. Also, by grounding the conductor end 3 as shown in Figure 4,
It is possible to detect the direction in which an insulation defect exists. For example, if there is a main body insulation failure resistor 8 that indicates the position of the insulation failure point only on the left side of the measurement position as shown in the figure,
When galvanometer 6 is connected between the d terminal and the ground,
A closed circuit including the main body insulation failure resistor 8 and the galvanometer 6 is formed between terminals b and c to which the measurement power source 4 is connected, and the current from the measurement power source 4 flows through the closed circuit, causing the pointer of the galvanometer 6 to flow. Since the voltage swings, it can be determined that the main body insulation failure resistance 8 exists on the left side of the c terminal. In addition, when the galvanometer 6' is connected between the a terminal and the ground, an open circuit including the main body insulation failure resistance 8 and the galvanometer 6' is connected to the one b terminal to which the measurement power source 4 is connected. Since the current from the measuring power source 4 does not flow through the closed circuit, the pointer of the galvanometer 6' does not swing. Accordingly, it can be determined that there is no defective insulation point on the main body on the right side of the b terminal. By sequentially performing detection operations by cutting the metal shielding layer 2 in accordance with the case explained in FIG. 3, the position where the main body insulation defect exists can be detected. As mentioned above, by connecting the measurement power source 4 between the b and c terminals corresponding to the metal shielding layer 2 whose left and right sides are electrically separated by the slit 9, the b and c terminals to which the measurement power source 4 is connected are connected. When a closed circuit including a poorly insulated resistor and a galvanometer is formed between them, the metal shielding layer 2 between terminals b and c is
are never connected in parallel. Therefore, the current flowing through the galvanometer through the poorly insulated resistor has a magnitude of approximately V/R, which is the voltage V of the measurement power source 4 divided by the poorly insulated resistor R. Therefore, the amount of current flowing through the galvanometer increases dramatically. FIG. 5 is an explanatory diagram of a detection method according to another embodiment of the present invention, and is an explanatory diagram for detecting the direction in which a corrosion protection layer insulation defect point exists under a live wire.

As shown in the figure, when the circuit breaker 11 is closed and the conductor terminal 3 is under a live wire connected to a high voltage bus bar, etc., as shown in the figure, the connection between the metal shielding layer 2 and the ground at both ends of the cable is made in advance. After connecting a large capacity capacitor 10, 10' to the metal shielding layer 2, the original grounding of the metal shielding layer 2 is removed. Next, a measurement position is arbitrarily selected along the cable installation route, and at this measurement position, the corrosion protection layer 1 is removed at only one location to expose the metal shielding layer 2. The capacitors 10 and 10' may be connected between the metal shielding layer 2 on the left and right of the planned slit 9 position and the ground, respectively, and the original grounding of the metal shielding layer 2 may be connected. The removal can also be done after the slits 9 are formed. In short, the connection positions of the capacitors 10 and 10' can be any position as long as the left and right metal shielding layers 2 sandwiching the portion where the slit 9 is planned to be formed are connected to the ground, respectively. That means it's good. By connecting the capacitors 10 and 10' in this way, the metal shielding layer 2 can be brought to a potential close to ground in terms of alternating current. Therefore, the formation of the slit 9, the removal of the original grounding of the metal shielding layer 2, and other operations can be performed safely. After forming the slit 9, the procedure is the same as that described in Fig. 3, but since the measurement is carried out under live cables, the alternating current enters the galvanometers 6 and 6', causing vibrations in the pointers. , there may be cases where observation becomes difficult.

In such a case, it is preferable to install the capacitors 10, 10' near both sides of the slit 9, rather than at both ends of the cable, in order to reduce the AC voltage applied to the galvanometer. It is also a good idea to connect an AC blocker in series to 6'. Although the case where the metal shielding layer 2 is newly cut to form the slit 9 at an arbitrarily selected measurement position along the cable installation route has been exemplified, the present invention is not limited thereto, and the cable installation route is not limited to this. Detection work can also be performed using a location where the left and right metal shielding layers in the longitudinal direction of the cable are electrically separated, such as an existing insulated connection part that is appropriately provided along the route, as a measurement position.

For example, as shown in FIG. 6, an insulating junction box 12 has a structure in which the left and right metal shielding layers 2 are electrically separated by an insulating part 13.
In this case, the left and right terminals of the insulated junction box 12 can be used as connection terminals for the measurement power source 4 and the galvanometers 6, 6'. That is, since the insulating part 13 corresponds to the slits shown in FIGS. 3 to 5, one of the terminals provided on both sides of the insulating part 13 corresponds to the a terminal and the b terminal, and the other one corresponds to the c terminal. Corresponds to the terminal and d terminal. Therefore, the measuring power source 4 is connected through the switch 5 between the terminals on both sides with the insulating part 13 in between.
Subsequently, galvanometers 6 and 6' are successively connected between each of the terminals on both sides thereof and the ground, thereby making it possible to detect the direction in which the anti-corrosion layer insulation failure resistor 7 exists. Although not shown, the direction in which the main body insulation defect point exists can be detected using the insulation junction box 12. In this case,
If either one of the conductor terminals of the cable is grounded, the same as the case explained in FIG. 4 will be obtained. Furthermore, if an insulated junction box is used in this way, there is no need to newly cut out the metal shielding layer, so it is easy to implement even in the case of an internal pressure type aluminum sheathed OF cable. In addition, when connecting the measurement power source 4 and the galvanometer 6, the lead wires should be those that were used for cross bonding connection, those that were used for connection to ground, or those that were used for left and right short circuits. It is possible to disconnect the parts as appropriate and connect them as shown in FIG. As explained above, the present invention connects a measurement power source between the left and right metal shielding layers at electrically separated positions on the left and right sides in the longitudinal direction of the cable, and connects the left and right metal shielding layers to the ground. Since the microcurrent measuring means is connected in sequence between The metal shielding layers between the terminals of the metal shielding layers are not connected in parallel. Therefore, most of the current from the measurement power source will flow to the insulation defect point. Therefore, even if there is a high insulation resistance where insulation deterioration has not progressed much, the direction in which the defective point exists can be easily detected. Moreover, in order to increase the amount of current flowing through the microcurrent measurement power supply, there is no need to increase the range in which both terminals of the measurement power supply are connected.
This facilitates the removal of the anti-corrosion layer and its repair work, the observation work of the microcurrent measuring means, and other works.

[Brief explanation of the drawing]

1 and 2 are explanatory diagrams of a conventional detection method, and FIGS. 3 to 6 are explanatory diagrams of a detection method according to an embodiment of the present invention. Fig. 4 is an explanatory diagram for detecting the direction in which the main body insulation defect exists, and Fig. 5 is an explanatory diagram for detecting the direction in which the corrosion protection layer insulation defect exists under live wires. FIG. 6 is an explanatory diagram of a case where the direction in which an insulation defect exists is detected using an existing insulated connection part. 1 is a corrosion protection layer, 2 is a metal shielding layer, 3 is a conductor terminal, 4 is a measurement power source, 5 is a switch, 6 and 6' are galvanometers as means for measuring minute currents, 7 is a resistance with poor insulation in the corrosion protection layer, 8 9 is a main body insulation failure resistance, 9 is a slit, 10 and 10' are capacitors, 11 is a circuit breaker, 12 is an insulated junction box, and 13 is an insulating part. Figure 6 Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1. In a method for detecting insulation defects in a power cable having a metal shielding layer, the corrosion protection layer is removed at one point along the power cable installation route to expose the metal shielding layer, and the exposed metal shielding layer is One slit is formed by cutting the center part, a measurement power source is connected between the metal shielding layers on the left and right of the slit, and a minute current measuring means is connected between the metal shielding layers on the left and right of the one slit and the ground. The conductor ends of the power cables are connected in sequence, and the conductor ends of the power cables are floated or connected to the ground, and depending on whether or not the microcurrent is detected by the microcurrent measuring means,
A cable insulation defect detection method comprising detecting a direction in which an insulation defect exists from the slit position.