Power Cable for Teaching, Its Fault Judgment Method and Intermediate Joint Manufacturing Method

Abstract

The present invention discloses a power cable for teaching, its fault judgment method and the manufacturing method of the intermediate joint, which includes phase A wire, phase B wire and phase C wire. The phase A wire, phase B wire and phase C wire are extruded together through an inner sheath, an outer sheath and an armor layer to form a power cable. The inner sheath is arranged on one side close to the phase A wire, phase B wire and phase C wire, and the outer sheath is arranged on one side far from the phase A wire, phase B wire and phase C wire. There is a filler between the inner sheath and the phase A wire, phase B wire and phase C wire, and there is an armor layer between the inner sheath and the outer sheath. The phase A wire, phase B wire and phase C wire at the left end of the cable are in the shape of cable terminals, and the phase A wire, phase B wire and phase C wire at the right end of the cable are cut open to show the internal structure of the cable. There is an intermediate joint in the middle part of the cable, and the phase A wire, phase B wire and phase C wire inside the intermediate joint are respectively set into fault structures to facilitate the teaching of cable fault nature judgment. The present invention is convenient for teaching, can be reused, and does not waste resources.

Description

Technical Field

[0001] The present invention belongs to the field of power cables, and particularly relates to a power cable for teaching, a method for judging cable faults, and a method for manufacturing intermediate joints thereof. Background Art

[0002] Power cables are cables used for transmitting and distributing electrical energy. Power cables are commonly used in urban underground power grids, outgoing lines of power stations, internal power supply of industrial and mining enterprises, and underwater power transmission lines across rivers and seas. In power lines, the proportion of cables is gradually increasing. Power cables are cable products used to transmit and distribute high-power electrical energy in the main lines of the power system. Understanding power cables and how to judge cable faults is an indispensable course in practical teaching. Power cables used for physical connection operations and judgments usually adopt national standard cables. However, in teaching, if national standard cables are directly used, the cost will be very high, and the waste phenomenon is serious. Moreover, in the teaching of judging the nature of cable faults with existing cables, it is not easy to realistically set various faults, which affects the teaching effect. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to overcome the deficiencies of the prior art and provide a power cable for teaching, a method for judging cable faults, and a method for manufacturing intermediate joints thereof, which can realistically demonstrate the judgment of cable faults.

[0004] The technical solution adopted by the present invention to solve the technical problem is as follows:

[0005] A power cable for teaching includes a phase A wire, a phase B wire, and a phase C wire. The phase A wire, the phase B wire, and the phase C wire are extruded together through an inner sheath, an outer sheath, and an armor layer to form a power cable. The inner sheath is disposed on one side close to the phase A wire, the phase B wire, and the phase C wire, and the outer sheath is disposed on one side far from the phase A wire, the phase B wire, and the phase C wire. A filler is disposed between the inner sheath and the phase A wire, the phase B wire, and the phase C wire, and an armor layer is disposed between the inner sheath and the outer sheath. The left ends of the phase A wire, the phase B wire, and the phase C wire of the cable are in the shape of cable terminals, and the right ends of the phase A wire, the phase B wire, and the phase C wire of the cable are cut open to show the internal structure of the cable. An intermediate joint is disposed in the middle part of the cable. The phase A wire, the phase B wire, and the phase C wire inside the intermediate joint are respectively arranged into fault structures to facilitate the teaching of judging the nature of cable faults. A cable model is disposed on the power cable to facilitate the teaching of cable models and technical parameters.

[0006] The structures arranged for the phase A, phase B, and phase C lines inside the intermediate joint, respectively and among themselves, are as follows: The phase A line is conducting, the phase B and phase C lines are disconnected. The phase A line is connected to the steel armor layer after being connected to a capacitor through a wire. The left end of the disconnected phase B line is directly connected to the steel armor layer through a wire, which is equivalent to direct grounding, and the right end is connected to the steel armor layer through a wire after being connected to a first resistor, which is equivalent to grounding through a resistor. The left end of the disconnected phase C line is connected to the steel armor layer through a wire after being connected to a second resistor, which is equivalent to grounding through a resistor, and the right end is connected to the phase B line through a wire after being connected to a third resistor, which is equivalent to phase - to - phase short - circuit. The first resistor, the second resistor, and the third resistor are low - value resistors or high - value resistors.

[0007] The phase A, phase B, and phase C lines all include a conductor core, an inner semiconductive layer, a main insulation layer, an outer semiconductive layer, and a copper shielding layer. The conductor core is first wrapped by the inner semiconductive layer. The main insulation layer and the outer semiconductive layer are sequentially arranged between the inner semiconductive layer and the copper shielding layer. The connections between the phase A, phase B, and phase C lines and the steel armor layer, as well as the connections between the phase A, phase B, and phase C lines among themselves, are all connections between the conductor core and the steel armor layer or connections between the conductor cores.

[0008] At the disconnected positions of the phase B and phase C lines, non - crimp connecting pipes are used and set with a certain gap. Copper - plastic wires are welded on both sides of the disconnected positions of the phase B and phase C lines. The copper - plastic wire welded on the left side of the phase B line at the disconnected position of the phase B line extends out of the outer layer of the inner sheath and is welded to the steel armor layer. The copper - plastic wire welded on the right side of the phase B line extends out of the outer layer of the inner sheath, is connected in series with the first resistor, and then is welded to the steel armor layer. The copper - plastic wire welded on the left side of the phase C line at the disconnected position of the phase C line extends out of the outer layer of the inner sheath, is connected in series with the second resistor, and then is welded to the steel armor layer. The copper - plastic wire welded on the right side of the phase C line extends out of the main insulation layer, is connected in series with the third resistor, and then is welded to the copper - plastic wire extending out of the right end of the disconnected position of the phase B line. A copper - plastic wire is led out from the phase A line. This copper - plastic wire extends out of the outer layer of the inner sheath, is connected in series with the capacitor, and then is welded to the steel armor layer. All the above structures are connected inside the outer sheath.

[0009] A method for judging power cable faults includes the following steps.

[0010] 1) A copper - plastic wire is respectively led out from both ends of the phase A, phase B, and phase C lines on the power cable and both ends of the steel armor layer.

[0011] 2) Short-circuit the A-phase wire, B-phase wire, C-phase wire, and steel armor layer at one end of the power cable in pairs using the drawn copper-plastic wire. At the other end of the power cable, measure the insulation resistance of the two short-circuited wires using an insulation resistance meter, record the insulation resistance value, and determine whether the A-phase wire, B-phase wire, and C-phase wire are broken through the recorded combined insulation resistance value.

[0012] 3) Remove the wires that short-circuit the A-phase wire, B-phase wire, C-phase wire, and steel armor layer at one end of the power cable in pairs using the drawn copper-plastic wire. Then, measure the insulation resistance value between the A-phase wire and the B-phase wire, between the A-phase wire and the C-phase wire, and between the B-phase wire and the C-phase wire at both ends of the power cable using an insulation resistance meter respectively, record the insulation resistance value, and determine phase-to-phase short-circuit or reduction of phase-to-phase insulation resistance value through the recorded combined insulation resistance value.

[0013] 4) Measure the insulation resistance value between the A-phase wire and the copper-plastic wire drawn from the steel armor layer, between the B-phase wire and the copper-plastic wire drawn from the steel armor layer, and between the C-phase wire and the copper-plastic wire drawn from the steel armor layer at both ends of the power cable using an insulation resistance meter respectively, record the insulation resistance value, and determine whether the insulation is good, high-resistance grounding, low-resistance grounding, or direct grounding through the magnitude of the recorded combined insulation resistance value.

[0014] In step 2), the recorded insulation resistance values are respectively the insulation resistance value between the A-phase wire and the B-phase wire, between the A-phase wire and the C-phase wire, between the B-phase wire and the C-phase wire, between the A-phase wire and the steel armor layer, between the B-phase wire and the steel armor layer, and between the C-phase wire and the steel armor layer. The recording results show that the insulation resistance values between the A-phase wire and the B-phase wire, between the A-phase wire and the C-phase wire, between the B-phase wire and the C-phase wire, between the B-phase wire and the steel armor layer, and between the C-phase wire and the steel armor layer are all infinite, and the insulation resistance value between the A-phase wire and the steel armor layer is very small, close to zero. It can be known that the A-phase wire and the steel armor layer are conducting, and the B-phase wire and the C-phase wire are disconnected.

[0015] In step 3), among the recorded insulation resistance values, the insulation resistance values between the A-phase wire and the B-phase wire at both ends of the power cable are all very large, the insulation resistance values between the A-phase wire and the C-phase wire at both ends of the power cable are also very large, the insulation resistance value between the B-phase wire and the C-phase wire at one end of the power cable is very large, and the insulation resistance value between the B-phase wire and the C-phase wire at the other end is reduced. Then, it is determined that there is a phase-to-phase short-circuit between the B-phase wire and the C-phase wire at the end where the insulation resistance value is reduced.

[0016] In step 4), among the recorded insulation resistance values, the insulation resistance values between both ends of phase A wire and the copper-plastic wire led out from the steel armor layer have been changing continuously, indicating that the insulation between both ends of phase A wire and the steel armor layer is good, and there is a capacitor between phase A wire and the steel armor layer, which is equivalent to a grounding capacitor. The absorption ratio can be calculated. Generally, the absorption ratio is the insulation resistance value at one minute divided by the insulation resistance value at fifteen seconds; the insulation resistance value between the left end of phase B wire and the steel armor layer is very small, approaching zero, indicating that the left end of phase B wire is directly connected to the steel armor layer, equivalent to direct grounding. The insulation resistance value between the right end of phase B wire and the steel armor layer decreases, indicating that the right end of phase B wire is connected to the steel armor layer through a resistor; the insulation resistance value between the left end of phase C wire and the steel armor layer decreases, indicating that the left end of phase C wire is connected to the steel armor layer through a resistor. The insulation resistance value between the right end of phase C wire and the steel armor layer is infinite, indicating that the insulation between the right end of phase C wire and the steel armor layer is good.

[0017] A method for manufacturing an intermediate joint of a power cable, comprising the following steps:

[0018] 1) Peel the power cable at the position where the intermediate joint is to be set to expose the inner phase A wire, phase B wire, and phase C wire, and cut phase B wire and phase C wire in the middle and cut off a small section.

[0019] 2) At the disconnection points of the phase B wire and the phase C wire, non-crimp connection pipes are used, and a certain gap is maintained. And on both sides of the disconnection points of the phase B wire and the phase C wire, copper-plastic wires led out are welded. After leading out the copper-plastic wires, the main insulation layer is shrunk. A copper-plastic wire is also led out on the phase A wire, but phase A wire is not cut off.

[0020] 3) The copper-plastic wire welded on the phase B wire at the left side of the disconnection point of the phase B wire is extended out of the outer layer of the inner sheath and then welded to the steel armor layer. The copper-plastic wire welded on the phase B wire at the right side is extended out of the outer layer of the inner sheath, then connected in series with the first resistor and welded to the steel armor layer.

[0021] 4) The copper-plastic wire welded on the phase C wire at the left side of the disconnection point of the phase C wire is extended out of the outer layer of the inner sheath, then connected in series with the second resistor and welded to the steel armor layer. The copper-plastic wire welded on the phase C wire at the right side is extended out of the main insulation layer, then connected in series with the third resistor and welded to the copper-plastic wire extended out of the phase B wire at the right end of the disconnection point.

[0022] 5) The copper-plastic wire led out on the phase A wire is extended out of the outer layer of the inner sheath, then connected in series with the capacitor and welded to the steel armor layer.

[0023] 6) After welding the above components, connect the steel armor layer, and finally shrink the outer sheath.

[0024] In step 2), a copper-plastic wire is also led out from the A-phase line, which means that by using the stripping method on the A-phase line, stripping to the wire core, welding a copper-plastic wire, leading it out of the A-phase line, and then respectively connecting and restoring the inner semiconductive layer, main insulation layer, outer semiconductive layer and copper shielding layer on the A-phase line.

[0025] The positive and beneficial effects of the present invention are:

[0026] In the present invention, the left end of the cable is set as a cable terminal shape part, which can facilitate the teaching of cable terminals; the A-phase line, B-phase line and C-phase line at the right end of the cable are stripped to show the internal structure part of the cable, which can facilitate the teaching of the cable structure composition and its functions; a middle joint is provided in the middle part of the cable, and the A-phase line, B-phase line and C-phase line inside the middle joint are respectively set as fault structures to facilitate the teaching of cable fault nature judgment. The cable faults include cable break, high-resistance grounding, low-resistance grounding, direct grounding and phase-to-phase short circuit; the absorption ratio can also be measured, and the cable model is set on the power cable to facilitate the teaching of cable models and technical parameters; all the teachings can be explained on the same power cable, which is convenient and practical, and can be reused without wasting resources; in addition, because various faults are set in the middle joint, when judging, various judgment results will be taught for various faults, which greatly improves the teaching effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 is the overall structure schematic diagram of the power cable for teaching in the present invention;

[0028] Figure 2 is Figure 1 the structure schematic diagram of the middle joint part;

[0029] Figure 3 is the connection structure diagram of the power cable at the left end of the middle joint part;

[0030] Figure 4 is the connection structure diagram of the power cable at the right end of the middle joint part. DETAILED DESCRIPTION OF THE INVENTION

[0031] The present invention will be further explained and described below with reference to the drawings and specific embodiments:

[0032] See Figure 1 , Figure 2 , Figure 3 and Figure 4, in the figure: 1 - Phase A line, 2 - Phase B line, 3 - Phase C line, 4 - inner sheath, 5 - outer sheath, 6 - power cable, 7 - filler, 8 - steel armor layer, 9 - cable terminal shape part, 10 - cable internal structure part, 11 - middle part, 12 - intermediate joint, 13 - first resistor, 14 - second resistor, 15 - third resistor, 16 - cable model, 17 - conductor core, 18 - inner semi-conductive layer, 19 - main insulation layer, 20 - outer semi-conductive layer, 21 - copper shielding layer, 22 - capacitor.

[0033] Embodiment: A power cable 6 for teaching purposes, comprising a Phase A line 1, a Phase B line 2 and a Phase C line 3. The Phase A line 1, Phase B line 2 and Phase C line 3 are extruded together through an inner sheath 4, an outer sheath 5 and a steel armor layer 8 to form a power cable 6. The inner sheath 4 is arranged on one side close to the Phase A line 1, Phase B line 2 and Phase C line 3, and the outer sheath 5 is arranged on one side far from the Phase A line 1, Phase B line 2 and Phase C line 3. A filler 7 is arranged between the inner sheath 4 and the Phase A line 1, Phase B line 2 and Phase C line 3, and a steel armor layer 8 is arranged between the inner sheath 4 and the outer sheath 5. The Phase A line 1, Phase B line 2 and Phase C line 3 at the left end of the cable are the cable terminal shape part 9, and the Phase A line 1, Phase B line 2 and Phase C line 3 at the right end of the cable are cut open to show the cable internal structure part 10. An intermediate joint 12 is arranged in the middle part 11 of the cable. The Phase A line 1, Phase B line 2 and Phase C line 3 inside the intermediate joint 12 are respectively set into a fault structure to facilitate the teaching of cable fault nature judgment. A cable model 16 is arranged on the power cable 6 to facilitate the teaching of the cable model 16 and technical parameters.

[0034] The structures arranged for the Phase A line 1, Phase B line 2 and Phase C line 3 inside the intermediate joint 12 respectively and mutually are as follows: The Phase A line 1 is conducting, the Phase B line 2 and Phase C line 3 are disconnected. The Phase A line 1 is connected to the steel armor layer 8 through a conductor after being connected to the capacitor 22. The left end of the disconnected Phase B line 2 is directly connected to the steel armor layer 8 through a conductor, which is equivalent to direct grounding, and the right end is connected to the steel armor layer 8 through a conductor after being connected to the first resistor 13, which is equivalent to grounding through a resistor; The left end of the disconnected Phase C line 3 is connected to the steel armor layer 8 through a conductor after being connected to the second resistor 14, which is equivalent to grounding through a resistor, and the right end is connected to the Phase B line 2 through a conductor after being connected to the third resistor 15, which is equivalent to phase-to-phase short circuit; The first resistor 13, the second resistor 14 and the third resistor 15 are low-value resistors or high-value resistors.

[0035] Phase A line 1, Phase B line 2 and Phase C line 3 each include a conductor core 17, an inner semiconductive layer 18, a main insulation layer 19, an outer semiconductive layer 20 and a copper shielding layer 21. The conductor core 17 is first wrapped by the inner semiconductive layer 18. Between the inner semiconductive layer 18 and the copper shielding layer 21, the main insulation layer 19 and the outer semiconductive layer 20 are sequentially arranged. The connections between Phase A line 1, Phase B line 2 and Phase C line 3 and the steel armor layer 8, as well as the connections between Phase A line 1, Phase B line 2 and Phase C line 3 to each other, are all the connections between the conductor core 17 and the steel armor layer 8 or the connections between the conductor core 17 and the conductor core 17.

[0036] At the disconnection points between Phase B line 2 and Phase C line 3, non-crimp connecting pipes are used, and a certain gap is maintained. Copper-plastic wires are welded on both sides of the disconnection points between Phase B line 2 and Phase C line 3. The copper-plastic wire welded on the left side of Phase B line 2 at the disconnection point extends out of the outer layer of the inner sheath 4 and is welded to the steel armor layer 8. The copper-plastic wire welded on the right side of Phase B line 2 extends out of the outer layer of the inner sheath 4 and is welded to the steel armor layer 8 after being in series with the first resistor 13; the copper-plastic wire welded on the left side of Phase C line 3 at the disconnection point extends out of the outer layer of the inner sheath 4 and is welded to the steel armor layer 8 after being in series with the second resistor 14. The copper-plastic wire welded on the right side of Phase C line 3 extends out of the main insulation layer 19 and is welded to the copper-plastic wire extending out of the right end of the disconnection point of Phase B line 2 after being in series with the third resistor 15; a copper-plastic wire is led out from Phase A line 1. This copper-plastic wire extends out of the outer layer of the inner sheath 4 and is welded to the steel armor layer 8 after being in series with the capacitor 22. All the above structures are connected inside the outer sheath 5.

[0037] A method for judging power cable faults includes the following steps.

[0038] 1) Lead out a copper-plastic wire from both ends of Phase A line 1, Phase B line 2, Phase C line 3 on the power cable 6 and both ends of the steel armor layer 8 respectively.

[0039] 2) Short-circuit Phase A line 1, Phase B line 2, Phase C line 3 and the steel armor layer 8 at one end of the power cable 6 in pairs by using the led-out copper-plastic wires. At the other end of the power cable 6, use an insulation resistance meter to measure the insulation resistance between the two short-circuited wires, and record the insulation resistance value. By the recorded combined insulation resistance value, judge whether Phase A line 1, Phase B line 2 and Phase C line 3 are broken.

[0040] 3) Remove the wires that short-circuit Phase A line 1, Phase B line 2, Phase C line 3 and the steel armor layer 8 in pairs at one end of the power cable 6. Then, use an insulation resistance meter to measure the insulation resistance value between Phase A line 1 and Phase B line 2, the insulation resistance value between Phase A line 1 and Phase C line 3, and the insulation resistance value between Phase B line 2 and Phase C line 3 at both ends of the power cable 6 respectively, and record the insulation resistance value. By the recorded combined insulation resistance value, judge the phase-to-phase short circuit or the reduction of the phase-to-phase insulation resistance value.

[0041] 4) At both ends of the power cable 6, use an insulation resistance meter to measure the insulation resistance values between the phase A wire 1 and the copper-plastic wire led out from the steel armor layer 8, between the phase B wire 2 and the copper-plastic wire led out from the steel armor layer 8, and between the phase C wire 3 and the copper-plastic wire led out from the steel armor layer 8, and record the insulation resistance values. Determine whether the insulation is good, high-resistance grounded, low-resistance grounded, or directly grounded based on the magnitudes of the recorded combined insulation resistance values.

[0042] In step 2), the recorded insulation resistance values are respectively the insulation resistance value between the phase A wire 1 and the phase B wire 2, the insulation resistance value between the phase A wire 1 and the phase C wire 3, the insulation resistance value between the phase B wire 2 and the phase C wire 3, the insulation resistance value between the phase A wire 1 and the steel armor layer 8, the insulation resistance value between the phase B wire 2 and the steel armor layer 8, and the insulation resistance value between the phase C wire 3 and the steel armor layer 8. The recording results show that the insulation resistance values between the phase A wire 1 and the phase B wire 2, between the phase A wire 1 and the phase C wire 3, between the phase B wire 2 and the phase C wire 3, between the phase B wire 2 and the steel armor layer 8, and between the phase C wire 3 and the steel armor layer 8 are all infinite, and the insulation resistance value between the phase A wire 1 and the steel armor layer 8 is very small, close to zero. It can be seen that the phase A wire 1 and the steel armor layer 8 are conducting, and the phase B wire 2 and the phase C wire 3 are disconnected.

[0043] In step 3), among the recorded insulation resistance values, the insulation resistance values between the phase A wire 1 and the phase B wire 2 at both ends of the power cable 6 are all very large, the insulation resistance values between the phase A wire 1 and the phase C wire 3 at both ends of the power cable 6 are also very large, the insulation resistance value between the phase B wire 2 and the phase C wire 3 at one end of the power cable 6 is large, and the insulation resistance value between the phase B wire 2 and the phase C wire 3 at the other end is reduced. Then, it is judged that there is an interphase short circuit between the phase B wire 2 and the phase C wire 3 at the end where the insulation resistance value is reduced.

[0044] In step 4), among the recorded insulation resistance values, the insulation resistance values between both ends of the phase A wire 1 and the copper-plastic wire led out from the steel armor layer 8 are constantly changing, indicating that the insulation between both ends of the phase A wire 1 and the steel armor layer 8 is good, and a capacitor 22 is provided between the phase A wire 1 and the steel armor layer 8, which is equivalent to a grounding capacitor 22. The absorption ratio can be calculated. Generally, the absorption ratio is the insulation resistance value at one minute divided by the insulation resistance value at fifteen seconds.

[0045] The insulation resistance value between the left end of Phase B wire 2 and the steel armor layer 8 is very small, approaching zero, indicating that the left end of Phase B wire 2 is directly connected to the steel armor layer 8, equivalent to direct grounding. The insulation resistance value between the right end of Phase B wire 2 and the steel armor layer 8 decreases, indicating that the right end of Phase B wire 2 is connected to the steel armor layer 8 through a resistor; the insulation resistance value between the left end of Phase C wire 3 and the steel armor layer 8 decreases, indicating that the left end of Phase C wire 3 is connected to the steel armor layer 8 through a resistor, and the insulation resistance value between the right end of Phase C wire 3 and the steel armor layer 8 is infinite, indicating that the insulation between the right end of Phase C wire 3 and the steel armor layer 8 is good.

[0046] To determine whether a resistor is a high-value resistor or a low-value resistor, it can be indicated according to the value measured by an insulation resistance meter. If the measured resistance value is greater than 100 megohms, it is a high-value resistor; if it is less than 100 megohms, it is a low-value resistor.

[0047] A method for manufacturing an intermediate joint of a power cable includes the following steps:

[0048] 1) Peel the power cable 6 at the location where the intermediate joint 12 is to be set, expose the inner Phase A wire 1, Phase B wire 2, and Phase C wire 3, and cut Phase B wire 2 and Phase C wire 3 in the middle and cut off a small section.

[0049] 2) At the disconnection points of Phase B wire 2 and Phase C wire 3, non-crimp connection tubes are used, with a certain gap maintained, and copper-plastic wires are welded on both sides of the disconnection points of Phase B wire 2 and Phase C wire 3. After the copper-plastic wires are led out, the main insulation layer 19 is shrunk. A copper-plastic wire is also led out on Phase A wire 1, but Phase A wire 1 is not cut off.

[0050] 3) The copper-plastic wire welded on the left side of Phase B wire 2 at the disconnection point extends out of the outer layer of the inner sheath 4 and is welded to the steel armor layer 8. The copper-plastic wire welded on the right side of Phase B wire 2 extends out of the outer layer of the inner sheath 4, is connected in series with the first resistor 13, and then is welded to the steel armor layer 8.

[0051] 4) The copper-plastic wire welded on the left side of Phase C wire 3 at the disconnection point extends out of the outer layer of the inner sheath 4, is connected in series with the second resistor 14, and then is welded to the steel armor layer 8. The copper-plastic wire welded on the right side of Phase C wire 3 extends out of the main insulation layer 19, is connected in series with the third resistor 15, and then is welded to the copper-plastic wire extending out of the right end of Phase B wire 2 at the disconnection point.

[0052] 5) The copper-plastic wire led out on Phase A wire 1 extends out of the outer layer of the inner sheath 4, is connected in series with the capacitor 22, and then is welded to the steel armor layer 8.

[0053] 6) After welding the above components, connect the steel armor layer 8, and finally shrink the outer sheath 5.

[0054] In step 2), a copper-plastic wire is also led out on phase A wire 1, which means that on phase A wire 1, the stripping method is adopted to strip to the wire core 17, weld a copper-plastic wire, lead it out of phase A wire 1, and then respectively connect and restore the inner semiconductive layer 18, main insulation layer 19, outer semiconductive layer 20 and copper shielding layer 21 on phase A wire 1.

[0055] During operation, the cable terminal shape part 9 at the left end of the power cable 6 is used for teaching the cable terminal; the stripped phase A wire 1, phase B wire 2 and phase C wire 3 at the right end of the power cable 6 are used for teaching the cable structure composition and composition functions; the fault structure in the intermediate joint 12 of the power cable 6 is used for teaching the judgment of the power cable fault nature, including cable breakage, high-resistance grounding, low-resistance grounding, direct grounding and phase-to-phase short circuit; the cable model 16 set on the power cable 6 is used for teaching the cable model 16 and technical parameters.

[0056] Certainly, the present invention is not limited to the above embodiments. Those skilled in the art can make equivalent deformations or substitutions without departing from the spirit of the present invention, and these equivalent deformations or substitutions are all included in the scope defined by the claims of this application.

Claims

1. A method for judging power cable faults, characterized in that, it includes the following steps: The teaching power cable includes phase A, phase B, and phase C conductors. The phase A, phase B, and phase C conductors are extruded together through an inner sheath, an outer sheath, and an armor layer to form a power cable. The inner sheath is arranged on one side close to the phase A, phase B, and phase C conductors, and the outer sheath is arranged on the side far from the phase A, phase B, and phase C conductors. There is a filler between the inner sheath and the phase A, phase B, and phase C conductors, and there is an armor layer between the inner sheath and the outer sheath. The phase A, phase B, and phase C conductors at the left end of the cable are in the shape of cable terminals, and the phase A, phase B, and phase C conductors at the right end of the cable are cut open to show the internal structure of the cable. There is an intermediate joint in the middle part of the cable. The phase A, phase B, and phase C conductors inside the intermediate joint are respectively set into fault structures to facilitate the teaching of judging the nature of cable faults. There is a cable model on the power cable to facilitate the teaching of cable models and technical parameters; Copper-plastic wires are welded on both sides of the disconnection between the phase B and phase C conductors; a copper-plastic wire is led out from the phase A conductor; 1) Lead out a copper-plastic wire from both ends of the phase A, phase B, and phase C conductors on the power cable and both ends of the armor layer respectively; 2) Short-circuit the phase A, phase B, and phase C conductors and the armor layer at one end of the power cable pairwise by using the led-out copper-plastic wires. Measure the insulation resistance of the two short-circuited wires at the other end of the power cable by using an insulation resistance meter, and record the insulation resistance value. Judge whether the phase A, phase B, and phase C conductors are broken by the recorded combined insulation resistance value; 3) Remove the wires that short-circuit the phase A, phase B, and phase C conductors and the armor layer at one end of the power cable pairwise by using the led-out copper-plastic wires. Then measure the insulation resistance value between the phase A and phase B conductors, the insulation resistance value between the phase A and phase C conductors, and the insulation resistance value between the phase B and phase C conductors at both ends of the power cable respectively by using an insulation resistance meter, and record the insulation resistance value. Judge the phase-to-phase short circuit or the reduction of the phase-to-phase insulation resistance by the recorded combined insulation resistance value; 4) Measure the insulation resistance value between the phase A conductor and the copper-plastic wire led out from the armor layer, the insulation resistance value between the phase B conductor and the copper-plastic wire led out from the armor layer, and the insulation resistance value between the phase C conductor and the copper-plastic wire led out from the armor layer at both ends of the power cable respectively by using an insulation resistance meter, and record the insulation resistance value. Judge whether it is good insulation, high-resistance grounding, low-resistance grounding, or direct grounding by the size of the recorded combined insulation resistance value.

2. The method for judging power cable faults according to claim 1, characterized in that: In step 2), the recorded insulation resistance values are respectively the insulation resistance value between the A-phase wire and the B-phase wire, the insulation resistance value between the A-phase wire and the C-phase wire, the insulation resistance value between the B-phase wire and the C-phase wire, the insulation resistance value between the A-phase wire and the steel armor layer, the insulation resistance value between the B-phase wire and the steel armor layer, and the insulation resistance value between the C-phase wire and the steel armor layer. The recording results show that the insulation resistance values between the A-phase wire and the B-phase wire, between the A-phase wire and the C-phase wire, between the B-phase wire and the C-phase wire, between the B-phase wire and the steel armor layer, and between the C-phase wire and the steel armor layer are all infinite, and the insulation resistance value between the A-phase wire and the steel armor layer is very small, approaching zero. It can be seen that the A-phase wire and the steel armor layer are conducting, and the B-phase wire and the C-phase wire are disconnected.

3. A method for judging power cable faults according to claim 1, characterized in that: In step 3), among the recorded insulation resistance values, the insulation resistance values between the A-phase wire and the B-phase wire at both ends of the power cable are both very large, the insulation resistance values between the A-phase wire and the C-phase wire at both ends of the power cable are also both very large, the insulation resistance value between the B-phase wire and the C-phase wire at one end of the power cable is very large, and the insulation resistance value between the B-phase wire and the C-phase wire at the other end is reduced. Then it is judged that there is a phase-to-phase short circuit between the B-phase wire and the C-phase wire at the end where the insulation resistance value is reduced.

4. A method for judging power cable faults according to claim 1, characterized in that: In step 4), among the recorded insulation resistance values, the insulation resistance values between the two ends of the A-phase wire and the copper-plastic wire led out from the steel armor layer have been changing all the time, indicating that the insulation between the two ends of the A-phase wire and the steel armor layer is good, and there is a capacitor between the A-phase wire and the steel armor layer, which is equivalent to a grounding capacitor, and the absorption ratio can be calculated. Generally, the absorption ratio is the insulation resistance value at one minute divided by the insulation resistance value at fifteen seconds; the insulation resistance value between the left end of the B-phase wire and the steel armor layer is very small, approaching zero, indicating that the left end of the B-phase wire is directly connected to the steel armor layer, which is equivalent to direct grounding, and the insulation resistance value between the right end of the B-phase wire and the steel armor layer is reduced, indicating that the right end of the B-phase wire is connected to the steel armor layer through a resistor; the insulation resistance value between the left end of the C-phase wire and the steel armor layer is reduced, indicating that the left end of the C-phase wire is connected to the steel armor layer through a resistor, and the insulation resistance value between the right end of the C-phase wire and the steel armor layer is infinite, indicating that the insulation between the right end of the C-phase wire and the steel armor layer is good.

5. A manufacturing method for an intermediate joint of a power cable based on the method according to any one of claims 1-4, characterized by including the following steps: 1) Peel the power cable at the position where the intermediate joint is to be set to expose the A-phase wire, B-phase wire, and C-phase wire inside, and cut off the B-phase wire and the C-phase wire from the middle and cut off a small section; 2) At the disconnection points of the B-phase line and the C-phase line, non-crimp connection pipes are used, with a certain gap maintained, and copper-plastic wires are welded on both sides of the disconnection points of the B-phase line and the C-phase line. After the copper-plastic wires are led out, the main insulation layer is shrunk. A copper-plastic wire is also led out on the A-phase line, but the A-phase line is not cut off; 3) The copper-plastic wire welded on the left B-phase line at the disconnection point of the B-phase line is extended out of the outer layer of the inner sheath and then welded to the steel armor layer. The copper-plastic wire welded on the right B-phase line is extended out of the outer layer of the inner sheath, connected in series with a first resistor, and then welded to the steel armor layer; 4) The copper-plastic wire welded on the left C-phase line at the disconnection point of the C-phase line is extended out of the outer layer of the inner sheath, connected in series with a second resistor, and then welded to the steel armor layer. The copper-plastic wire welded on the right C-phase line is extended out of the main insulation layer, connected in series with a third resistor, and then welded to the copper-plastic wire extended out of the B-phase line at the right end of the disconnection point; 5) The copper-plastic wire led out on the A-phase line is extended out of the outer layer of the inner sheath, connected in series with the capacitor, and then welded to the steel armor layer; 6) After the above components are welded, the steel armor layer is connected, and finally the outer sheath is shrunk.

6. According to the method for manufacturing an intermediate joint of a power cable as described in claim 5, in step 2), leading out a copper-plastic wire on the A-phase line means using a stripping method on the A-phase line to strip to the wire core, welding a copper-plastic wire, leading it out of the A-phase line, and then respectively connecting and restoring the inner semi-conductive layer, main insulation layer, outer semi-conductive layer, and copper shielding layer on the A-phase line.

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