A device and method for testing high voltage cable grounding connection defects under voltage

Abstract

The present invention discloses a live testing device and method for a high-voltage cable ground connection defect. The present invention uses a direct current source to charge the cable tail pipe (i.e., injects direct current). After charging twice, the resistance value between the tail pipe of each phase and the corresponding grounding terminal can be obtained according to the current measured by a current measuring device and the voltage measured by a voltage measuring device. Whether there is a defect between the tail pipe of the cable and the corresponding grounding terminal can be judged according to the resistance value, thereby reducing the number of charging times, shortening the test time, and improving the test efficiency. The present invention is efficient and flexible, and has good application prospects.

Description

Technical Field

[0001] The invention relates to a device and method for testing ground connection defects of a high-voltage cable under voltage conditions, belonging to the technical field of power transmission and transformation equipment. Background Art

[0002] Defects in the grounding connection of high-voltage cables can easily cause the failure of the cable metal shield grounding, which can easily cause the metal sheath and insulation shield to discharge and damage the insulation, leading to cable failure. There is a live loop resistance test method on site, which requires testing three times of current charging. The test efficiency is low and cannot meet the needs of rapid on-site testing. Summary of the invention

[0003] The present invention provides a device and method for testing ground connection defects of high-voltage cables, which solves the problems of complex algorithms, low testing efficiency and inability to meet the needs of rapid on-site testing in existing testing methods.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0005] A live testing device for high-voltage cable grounding connection defects, comprising a DC charging circuit, a voltage measuring device and a switching switch;

[0006] The DC charging circuit includes a DC source and a current measuring device connected in series; the two ends of the DC charging circuit are respectively connected to the two-phase tail pipes at the local end; the current measuring device is used to measure the current of the tail pipe connected to the DC charging circuit;

[0007] One end of the voltage measuring device is externally connected to the remaining tail pipe of one phase at this end, and the other end of the voltage measuring device is connected to the DC charging circuit through a switching switch; by switching the switching switch, the voltage measuring device measures the voltage between each tail pipe connected to the DC charging circuit and the corresponding ground terminal.

[0008] Both ends of the DC charging circuit and the voltage measuring device are connected to the tail pipe through a current limiting device.

[0009] The voltage measured by the voltage measuring device is equal to the voltage of the current limiting device plus the voltage between the tail pipe connected to the current limiting device and the corresponding ground terminal.

[0010] The switching switch is a single-pole double-throw switch, the moving end of the single-pole double-throw switch is connected to the voltage measuring device, and the two static ends of the single-pole double-throw switch are respectively connected to the two ends of the DC charging circuit.

[0011] The current limiting device is a metal coil or a resistor.

[0012] The DC source is a battery power source or a constant current source with an output current ripple factor not exceeding 0.1%.

[0013] The accuracy of the current measuring device and the voltage measuring device shall not be less than Class 0.2.

[0014] A method for testing a high voltage cable ground connection defect live device, comprising:

[0015] The high-voltage cable grounding connection defect live testing device is connected to the three-phase tail pipe at the local end, and the DC source of the DC charging circuit outputs DC power;

[0016] Calculate the resistance between each tail pipe connected to the DC charging circuit and the corresponding ground terminal according to the current measured by the current measuring device and the voltage measured by the voltage measuring device;

[0017] Adjust the two-phase tail pipes connected to the DC charging circuit so that the tail pipes connected this time are different from the tail pipes connected the first time;

[0018] Calculate the resistance between the remaining one-phase tail pipe at this end and the corresponding grounding terminal according to the current measured by the current measuring device and the voltage measured by the voltage measuring device;

[0019] In response to the resistance between any single-phase tail pipe and the corresponding grounding terminal being greater than a first threshold, or the ratio of the resistance between any two-phase tail pipes and the corresponding grounding terminals exceeding a second threshold and the resistance between the largest single-phase tail pipe and the corresponding grounding terminal being greater than a third threshold, it is determined that the high-voltage cable grounding connection is defective.

[0020] In response to both ends of the DC charging circuit being connected to the tail pipe through the current limiting device, the total resistance between the current limiting device and the corresponding ground terminal is calculated according to the current measured by the current measuring device and the voltage measured by the voltage measuring device, and the resistance between the tail pipe connected to the current limiting device and the corresponding ground terminal is calculated according to the total resistance and the resistance of the current limiting device.

[0021] The first threshold is 1Ω, the second threshold is 2, and the third threshold is 100mΩ.

[0022] The beneficial effects achieved by the present invention are as follows: the present invention uses a DC source to charge the cable tail tube (i.e., injects DC current), and after charging twice, the resistance between the tail tube of each phase and the corresponding grounding terminal can be obtained according to the current measured by the current measuring device and the voltage measured by the voltage measuring device, and whether there is a defect between the cable tail tube and the corresponding grounding terminal can be judged according to the resistance value, thereby reducing the number of charging times, shortening the test time, and improving the test efficiency. The present invention is efficient and flexible, and has good application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of the cable grounding system;

[0024] Figure 2 This is the connection diagram of the cable grounding system;

[0025] Figure 3 It is the equivalent circuit diagram of the cable grounding system;

[0026] Figure 4 It is a schematic diagram of the structure of the device of the present invention. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0028] like Figure 1 , 2 As shown in Figure 3, the cable grounding system includes a three-phase tail pipe at this end, a three-phase metal sheath, a three-phase tail pipe at the opposite end, and a three-phase copper busbar; wherein, the A-phase tail pipe at this end, the A-phase metal sheath, the A-phase tail pipe at the opposite end, and the A-phase copper busbar are connected in series in sequence, and the end of the A-phase copper busbar is the grounding end, which is directly grounded; the B-phase tail pipe at this end, the B-phase metal sheath, the B-phase tail pipe at the opposite end, and the B-phase copper busbar are connected in series in sequence, and the end of the B-phase copper busbar is the grounding end, which is directly grounded; the C-phase tail pipe at this end, the C-phase metal sheath, the C-phase tail pipe at the opposite end, and the C-phase copper busbar are connected in series in sequence, and the end of the C-phase copper busbar is the grounding end, which is directly grounded.

[0029] To test the grounding connection defects of the high-voltage cable, it is sufficient to measure whether the resistance between the tail pipe of each phase and the corresponding grounding terminal is abnormal; therefore, the high-voltage cable grounding connection defect live testing device used includes a DC charging circuit, a voltage measuring device and a switching switch.

[0030] The DC charging circuit includes a DC source and a current measuring device connected in series; two ends of the DC charging circuit are respectively connected to the two-phase tail pipes at the local end; the current measuring device is used to measure the current of the tail pipe connected to the DC charging circuit; one end of the voltage measuring device is externally connected to the remaining one-phase tail pipe at the local end, and the other end of the voltage measuring device is connected to the DC charging circuit through a switching switch; by switching the switching switch, the voltage measuring device measures the voltage between each tail pipe connected to the DC charging circuit and the corresponding ground terminal.

[0031] The specific structure of the above device is as follows Figure 4 As shown, it includes a DC charging circuit, a voltage measuring device, a switching switch, two current limiting devices and three clamps.

[0032] Among them, the DC source and the current measuring device are connected in series to form a DC charging circuit; in order to limit the influence of the tail pipe induced voltage on the test equipment (i.e., the voltage measuring device and the current measuring device), both ends of the DC charging circuit and the voltage measuring device are connected to the tail pipe through a current limiting device, the current limiting device is externally connected to the tail pipe through a clamp, and the other end of the voltage measuring device is connected to the two ends of the DC charging circuit through a switching switch. The voltage measured by the voltage measuring device is equal to the voltage of the current limiting device plus the voltage between the tail pipe connected to the current limiting device and the corresponding grounding terminal (i.e., the current limiting device voltage + the corresponding single-phase tail pipe voltage + the corresponding metal sheath voltage + the corresponding copper busbar voltage).

[0033] The DC source adopts a battery power supply or a constant current source with an output current ripple factor not exceeding 0.1%; the current limiting device adopts a metal coil or a resistor with a resistance value of not less than 1kΩ; the accuracy of the current measuring device and the voltage measuring device are not less than level 0.2, and the current measuring device and the voltage measuring device adopt an ammeter and a voltmeter respectively; the switching switch is a single-pole double-throw switch, the moving end of the single-pole double-throw switch is connected to the voltage measuring device, and the two static ends of the single-pole double-throw switch are respectively connected to the two ends of the DC charging circuit. Of course, other switches can also be used as long as the switching purpose is achieved.

[0034] The current limiting device is defined as a first current limiting device, a second current limiting device and a third current limiting device, and the three clamps are defined as a first clamp, a second clamp and a third clamp. The specific structure of the above devices is as follows:

[0035] The first clamp, the first current limiting device, the current measuring device, the DC source, the second current limiting device and the second clamp are connected in series in sequence (of course, the positions of the current measuring device and the DC source can be interchanged), the switching switch adopts the simplest single-pole double-throw switch, one end of the voltage measuring device is connected to the remaining one-phase tail pipe through the third current limiting device and the third clamp in sequence, the other end of the voltage measuring device is connected to the moving end of the single-pole double-throw switch, and the two static ends of the single-pole double-throw switch are respectively connected to the first current limiting device and the second current limiting device. Through the switching of the single-pole double-throw switch, the voltage measuring device measures the total voltage of the first current limiting device, the corresponding tail pipe, the corresponding metal sheath and the corresponding copper bus, or the total voltage of the second current limiting device, the corresponding tail pipe, the corresponding metal sheath and the corresponding copper bus. For example, the first clamp and the second clamp are connected to the A-phase and B-phase tail pipes respectively, so the voltage measuring device measures the sum of the A-phase tail pipe voltage at this end, the A-phase metal sheath voltage, the A-phase tail pipe voltage at the opposite end, and the A-phase copper busbar voltage, or the sum of the B-phase tail pipe voltage at this end, the B-phase metal sheath voltage, the B-phase tail pipe voltage at the opposite end, and the B-phase copper busbar voltage.

[0036] The process of testing the cable ground connection with the above device is as follows:

[0037] Step 1: Connect the high-voltage cable grounding connection defect live test device to the three-phase tail pipe at this end, and the DC source of the DC charging circuit outputs DC power.

[0038] Connect the DC charging circuit to any two-phase tail pipes, connect the voltage measuring device to the remaining one-phase tail pipe, and apply a DC stable current.

[0039] Step 2: Calculate the resistance between each tail pipe connected to the DC charging circuit and the corresponding ground terminal according to the current measured by the current measuring device and the voltage measured by the voltage measuring device.

[0040] During measurement, the resistance of the current measuring device is equivalent to 0, and the resistance measured by the voltage measuring device is equivalent to infinity. Therefore, by switching the switch, the voltage measuring device measures the voltage between each tail pipe connected to the DC charging circuit and the corresponding ground terminal. According to the voltage and current, using Ohm's law, the resistance between each tail pipe and the corresponding ground terminal can be obtained.

[0041] Step 3, adjusting the two-phase tail pipes connected to the DC charging circuit so that the tail pipes connected this time are different from the tail pipes connected for the first time.

[0042] Step 4: Calculate the resistance between the remaining one-phase tail pipe at this end and the corresponding ground terminal according to the current measured by the current measuring device and the voltage measured by the voltage measuring device.

[0043] Step 5, in response to the resistance between any single-phase tail pipe and the corresponding grounding terminal being greater than the first threshold, or the ratio of the resistance between any two-phase tail pipes and the corresponding grounding terminal exceeding the second threshold and the resistance between the largest single-phase tail pipe and the corresponding grounding terminal being greater than the third threshold, it is determined that the high-voltage cable grounding connection is defective; wherein the first threshold is 1Ω, the second threshold is 2, and the third threshold is 100mΩ.

[0044] If both ends of the DC charging circuit are connected to the single-phase tail pipe (i.e. Figure 4 In the structure), the total resistance between the current limiting device and the corresponding grounding terminal is calculated according to the current measured by the current measuring device and the voltage measured by the voltage measuring device, and the resistance between the tail pipe connected to the current limiting device and the corresponding grounding terminal is calculated according to the total resistance and the resistance of the current limiting device.

[0045] To further illustrate the above method, an example is given below:

[0046] S1) Select the A and B phase tail pipes to connect to the DC charging circuit. Figure 4 The first and second clamps in the apparatus are connected to the two-phase copper bars or tail pipes on the protective grounding side of the high-voltage cable, and the third clamp connected to the voltage measuring device is connected to the C-phase tail pipe to apply a DC stable current.

[0047] S2) According to the current measured by the current measuring device and the voltage measured by the voltage measuring device, the resistance between the tail pipe of phase A and the grounding terminal of phase A (i.e., the end of the copper busbar of phase A) and the resistance between the tail pipe of phase B and the grounding terminal of phase B (i.e., the end of the copper busbar of phase B) are calculated.

[0048] The current measuring device measures the current in the entire circuit, that is, the current flowing through phases A and B is the same. The single-pole double-throw switch is actuated to connect the first current limiting device to the voltage measuring device. Since the resistance measured by the voltage measuring device is equivalent to infinity, there is no current from the C phase tail pipe to the C phase copper. Therefore, the voltage measuring device is equivalent to measuring the voltage of the first current limiting device + the voltage from the A phase tail pipe to the A phase grounding terminal. The voltage divided by the current can obtain the total resistance from the first current limiting device to the A phase grounding terminal, and then subtract the previously known resistance of the first current limiting device to obtain the resistance from the A phase tail pipe to the A phase grounding terminal.

[0049] Similarly, the single-pole double-throw switch is actuated to connect the second current limiting device to the voltage measuring device, and the resistance value from the tail pipe of phase B to the ground terminal of phase B can be obtained.

[0050] If there is no current limiting device, the resistance from the tail pipe to the corresponding ground terminal can be directly obtained by dividing the voltage by the current.

[0051] S3) Adjust the two-phase tail pipe connected to the DC charging circuit so that the tail pipe connected this time is different from the first connected tail pipe. It can be the A and C two-phase tail pipe connected to the DC charging circuit, or it can be the B and C two-phase tail pipe connected to the DC charging circuit, which can be selected arbitrarily.

[0052] S4) Calculate the resistance from the C phase tail pipe to the C phase ground terminal according to the current measured by the current measuring device and the voltage measured by the voltage measuring device. The calculation principle is the same as that in step S2.

[0053] S5) In response to the resistance between any single-phase tail pipe and the corresponding grounding terminal being greater than 1Ω, or the ratio of the resistance between any two-phase tail pipes and the corresponding grounding terminals being greater than 2 and the largest resistance between the single-phase tail pipe and the corresponding grounding terminal being greater than 100mΩ, it is determined that the high-voltage cable grounding connection is defective.

[0054] The present invention uses a DC source to charge the cable tail tube (i.e., injects DC current). After charging twice, the resistance value between the tail tube of each phase and the corresponding grounding terminal can be obtained according to the current measured by the current measuring device and the voltage measured by the voltage measuring device. Whether there is a defect between the cable tail tube and the corresponding grounding terminal can be judged according to the resistance value, thereby reducing the number of charging times, shortening the test time, and improving the test efficiency. The invention is efficient and flexible, and has good application prospects.

[0055] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A testing method for a high voltage cable grounding connection defect live testing device, characterized in that: The device comprises a DC charging circuit, a voltage measuring device and a switching switch; the DC charging circuit comprises a DC source and a current measuring device connected in series; two ends of the DC charging circuit are respectively connected to two-phase tail pipes at the local end; the current measuring device is used to measure the current of the tail pipe connected to the DC charging circuit; one end of the voltage measuring device is connected to the remaining one-phase tail pipe at the local end, and the other end of the voltage measuring device is connected to the DC charging circuit through the switching switch; By switching the switch, the voltage measuring device measures the voltage between each tail pipe connected to the DC charging circuit and the corresponding ground terminal; The method comprises: The high-voltage cable grounding connection defect live testing device is connected to the three-phase tail pipe at the local end, and the DC source of the DC charging circuit outputs DC power; Calculate the resistance between each tail pipe connected to the DC charging circuit and the corresponding ground terminal according to the current measured by the current measuring device and the voltage measured by the voltage measuring device; Adjust the two-phase tail pipes connected to the DC charging circuit so that the tail pipes connected this time are different from the tail pipes connected the first time; Calculate the resistance between the remaining one-phase tail pipe at this end and the corresponding ground terminal according to the current measured by the current measuring device and the voltage measured by the voltage measuring device; In response to the resistance between any single-phase tail pipe and the corresponding grounding terminal being greater than a first threshold, or the ratio of the resistance between any two-phase tail pipes and the corresponding grounding terminals exceeding a second threshold and the resistance between the largest single-phase tail pipe and the corresponding grounding terminal being greater than a third threshold, it is determined that the high-voltage cable grounding connection is defective.

2. The testing method of a high-voltage cable grounding connection defect live testing device according to claim 1 is characterized in that: In response to both ends of the DC charging circuit being connected to the tail pipe through the current limiting device, the total resistance between the current limiting device and the corresponding ground terminal is calculated according to the current measured by the current measuring device and the voltage measured by the voltage measuring device, and the resistance between the tail pipe connected to the current limiting device and the corresponding ground terminal is calculated according to the total resistance and the resistance of the current limiting device.

3. The testing method of a high-voltage cable grounding connection defect live testing device according to claim 1 is characterized in that: The first threshold is 1Ω, the second threshold is 2, and the third threshold is 100mΩ.

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