CN113219369B - Test method for testing cross-connection performance of cables in laying site - Google Patents
Test method for testing cross-connection performance of cables in laying site Download PDFInfo
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- CN113219369B CN113219369B CN202110520742.7A CN202110520742A CN113219369B CN 113219369 B CN113219369 B CN 113219369B CN 202110520742 A CN202110520742 A CN 202110520742A CN 113219369 B CN113219369 B CN 113219369B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/66—Testing of connections, e.g. of plugs or non-disconnectable joints
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/66—Testing of connections, e.g. of plugs or non-disconnectable joints
- G01R31/67—Testing the correctness of wire connections in electric apparatus or circuits
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Abstract
The invention provides a test method for cross interconnection performance test of cables laid on site, which comprises the steps of arranging a test power supply, wherein the test power supply is used as a power supply for performance test and loop resistance measurement of a cable metal sheath cross interconnection grounding system; applying three-phase power frequency alternating current to a cable core of the cable metal sheath cross interconnection grounding system by using three-phase alternating voltage output by the test power supply, measuring induced voltage and circulating current of the metal sheath in the cable metal sheath cross interconnection grounding system, and realizing the performance inspection of the cable metal sheath cross interconnection grounding system; and applying the direct-current voltage output by the test power supply to two ends of the cable metal sheath cross-connection grounding system, and measuring the loop resistance of the cable metal sheath cross-connection grounding system. The invention solves the problem that the test for testing the cross interconnection performance of the cable lines of 110kV and above is difficult to implement on the laying site, can carry out site test on the system performance and ensures stable, reliable and safe power supply.
Description
Technical Field
The invention relates to the technical field of power equipment inspection, in particular to a test method for inspecting cross interconnection performance of cables in a laying field.
Background
With the rapid development of the power industry in China, especially the development and the transformation of urban power grids, high-voltage and ultrahigh-voltage power cables are widely applied. At present, in the ultra-high voltage cable of 110kV and above, the metal sheath of the cable is usually connected to ground in a cross-connection manner.
The cable metal sheath cross-connection grounding system is very important, and the cable breakdown can be caused by the defects of wrong connection or poor contact and the like. Therefore, it is necessary to effectively check the performance of the cable metal sheath cross-connect grounding system. However, in the current power equipment, inspectors lack appropriate test power sources and test methods when inspecting the performance of the cable metal sheath cross-connection grounding system, especially in a construction site, so that the performance of the cable metal sheath cross-connection grounding system is difficult to inspect in the cable application, and the reliability and the safety of power supply are affected. In addition, the cable metal sheath cross interconnection grounding system has a plurality of connections, and the measurement of loop resistance can prevent the sheath from being misconnected or poor in welding and connection, but the field construction has no proper power supply and cannot be implemented all the time.
Therefore, a test method for testing the cross interconnection performance of the cable is needed, which is very important for ensuring the economic and stable operation of a power grid and has important value and significance for the development of an intelligent power grid.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provide a test method for testing the cross-connection performance of cables laid on site; the test method can solve the problem that the test of the cross interconnection performance test of the cable line of 110kV and above is difficult to implement in the laying field, can carry out field test on the performance of the cable metal sheath cross interconnection grounding system, and ensures stable, reliable and safe power supply, thereby realizing the effective test of the cross interconnection performance of the cable.
In order to achieve the purpose, the invention is realized by the following technical scheme: a test method for testing cross-connection performance of cables laid on site is characterized by comprising the following steps: setting a test power supply as a power supply for performance test and loop resistance measurement of a cable metal sheath cross-connection grounding system;
applying three-phase power frequency alternating current to a cable core of the cable metal sheath cross interconnection grounding system by using three-phase alternating voltage output by a test power supply, measuring induced voltage and circulating current of the metal sheath in the cable metal sheath cross interconnection grounding system, and realizing laying field inspection on the performance of the cable metal sheath cross interconnection grounding system;
and applying the direct-current voltage output by the test power supply to the grounding end of the cable metal sheath cross-connection grounding system, and carrying out laying field measurement on the loop resistance of the cable metal sheath cross-connection grounding system.
In the scheme, the test method can solve the problem that the test is difficult to implement on the laying site due to the lack of a proper test power supply in the test for testing the cross interconnection performance of the cable lines of 110kV and above, and can ensure stable, reliable and safe power supply for the performance detection of the cable metal sheath cross interconnection grounding system. In addition, the cable metal sheath cross interconnection grounding system has a plurality of connections, the measurement of loop resistance can prevent sheath misconnection or poor welding and connection, and measurement requirements exist, but the measurement cannot be implemented all the time due to the fact that a proper power supply is not available. The test method can adopt the direct current voltage output by the test power supply as the power supply of the cable metal sheath cross interconnection grounding system so as to meet the requirement of measuring the loop resistance of the cable metal sheath cross interconnection grounding system on the laying site.
The cable metal sheath cross interconnection grounding system comprises a plurality of large-section cables, each large-section cable is composed of three small-section cable units with equal length, and each small-section cable unit is connected with each other by adopting an insulating joint; the three-phase cable cores in the metal sheath at the insulating joint are connected in a transposition mode through a cross interconnection grounding box by adopting coaxial cores, a group of sheath protectors is arranged in the cross interconnection grounding box, and two ends of each large section of cable are respectively connected in an interconnection mode and are grounded.
The three-phase alternating voltage output by the test power supply is applied to the cable cores of the cable metal sheath cross interconnection grounding system to form three-phase power frequency alternating current, which means that: the three-phase alternating current output ends A, B and C of the test power supply are respectively connected with one end of a cable core of any one large section of cable, the other end of the cable core is in short circuit, and the test power supply applies three-phase power frequency alternating current to the cable core through the three-phase alternating current output ends A, B and C;
the application of the direct-current voltage output by the test power supply to the two ends of the cable metal sheath cross interconnection grounding system means that: the DC voltage output end of the test power supply is connected with the grounding ends of two large-section cables.
The test power supply is formed by connecting an alternating current-direct current alternating frequency power supply module and an LC filter; the alternating-current, direct-current and alternating-current variable frequency power supply module is formed by connecting an input end, a direct-current voltage output end, three-phase alternating-current voltage output ends U, V and W, a three-phase half-controlled full-bridge rectifying circuit, a direct-current capacitor and an inverter circuit through a peripheral circuit; the input end of the AC-DC alternating-frequency power supply module is connected with a three-phase half-controlled full-bridge rectifying circuit, the three-phase half-controlled full-bridge rectifying circuit is connected with a DC capacitor in parallel and then outputs DC voltage, the output DC voltage is connected with a DC voltage output end, the output DC voltage is connected with an inverter circuit and then outputs three-phase AC voltage, and the output three-phase AC voltage is connected with three-phase AC voltage output ends U, V and W;
the three-phase alternating voltage output ends U, V and W are connected with an LC filter; and the direct-current voltage output end is connected with the grounding end of the cable metal sheath cross interconnection grounding system.
The direct current capacitor can stabilize direct current voltage and can also compensate reactive power. The direct-current voltage outputs three-phase alternating-current voltage with stable frequency through an inverter circuit controlled by software, and the phase difference is 120 degrees.
The AC-DC-AC frequency conversion power supply module also comprises a DC adjustable constant current source, and the output DC voltage is connected with a DC voltage output end through the DC adjustable constant current source. The invention is connected with a direct current adjustable constant current source in series on the direct current voltage, and can output the stable and adjustable direct current voltage, thereby outputting the constant current on the load for measuring the loop resistance of the cable metal sheath cross interconnection grounding system.
The input end is provided with three input terminals, and the input voltage of the input end is 220V voltage, two-phase 380V voltage, three-phase 380V voltage or direct current voltage. The input of the test power supply has strong compatibility, and the power frequency single-phase voltage, the two-phase voltage, the three-phase voltage and the direct-current voltage can be compatible, so that the common 220V voltage of a construction site can be adopted when the cable line is short and the required power is small, and the three-phase 380V voltage is adopted when the line is long and the required power is large.
The inverter circuit is a three-phase inverter bridge formed by IGBTs. The inverter circuit is a three-phase inverter bridge formed by six IGBTs and is used for inverting the direct current obtained by the three-phase half-control full-bridge rectifier circuit to obtain alternating current.
The LC filter is formed by sequentially connecting an input end U, an input end V, an input end W, an inductor, an alternating current capacitor and three-phase alternating current output ends A, B and C; the input ends U, V and W are connected with the three-phase alternating voltage output ends U, V and W, and the three-phase alternating voltage output ends A, B and C output three-phase alternating voltage and are connected with the cable cores of the cable metal sheath cross interconnection grounding system.
The alternating-current-direct-current-alternating-frequency power supply module outputs three-phase alternating-current voltage which is not a true sine wave, but is a square wave (high-frequency square wave) with the conduction time changed discontinuously under the condition of keeping the absolute value of the voltage unchanged, so that the performance inspection of the cable metal sheath cross-connection grounding system is extremely unfavorable, and the measurement errors of sheath induction voltage and sheath circulation current in the cable metal sheath cross-connection grounding system can be caused. The main function of the LC filter is to smooth and link the discontinuous high-frequency square wave, and the waveform of the three-phase alternating voltage output by the LC filter is very close to a sine wave.
The induced voltage and the circulation of the metal sheath in the measurement cable metal sheath cross-connection grounding system realize that the performance of the cable metal sheath cross-connection grounding system is paved by the field test: the three-phase alternating-current voltage output by the three-phase alternating-current voltage output ends A, B and C is adjusted by controlling the switching frequency of the IGBT and/or the negative feedback parameter of the three-phase power frequency alternating current and/or the frequency of alternating current output, and the induced voltage and the circulating current of the metal sheath in the cable metal sheath cross-connection grounding system are measured and judged, so that the performance of the cable metal sheath cross-connection grounding system is tested.
Through the switching frequency of control IGBT and/or the frequency of negative feedback parameter and/or the interchange output of three-phase power frequency alternating current, realize adjusting the three-phase alternating voltage of three-phase alternating voltage output A, B, C output to measure and judge the induced voltage and the circulation of the metal sheath in the cable metal sheath cross-connection grounding system, the realization is to lay on-the-spot inspection to the performance of cable metal sheath cross-connection grounding system and is to mean: the method comprises the following steps:
firstly, a connecting sheet of a cross interconnection grounding box in a cable metal sheath cross interconnection grounding system is positioned at a correct connecting position, and the switching frequency of an IGBT (insulated gate bipolar translator) and/or the negative feedback parameter of three-phase power frequency alternating current and/or the frequency of alternating current output are controlled according to the negative feedback numerical value change of the three-phase power frequency alternating current, so that the three-phase alternating voltage output by three-phase alternating voltage output ends A, B and C is adjusted, and a cable core passes through balanced current I to be used as test current;
second, measuring the metal sheath current I at the cross-connected grounding box1And a voltage V to earth1(ii) a After the measurement is finished, the three-phase alternating voltages output by the three-phase alternating voltage output ends A, B and C are simultaneously adjusted according to the negative feedback numerical value change of the three-phase power frequency alternating current, so that the test current is reduced to zero, and a test power supply is cut off;
thirdly, connecting pieces of a cross interconnection grounding box in the cable metal sheath cross interconnection grounding system in a simulated error connecting mode, controlling the switching frequency of the IGBT and/or the negative feedback parameter of the three-phase power frequency alternating current and/or the frequency of alternating current output according to the negative feedback numerical value change of the three-phase power frequency alternating current, and realizing adjustment of the three-phase alternating current voltage output by the three-phase alternating voltage output ends A, B and C so that a cable core passes through a balanced current I to serve as a test current;
fourthly, measuring the current I of the metal sleeve at the position of the cross-connection grounding box2And a voltage V to ground2(ii) a After the measurement is finished, the outputs A, B and C of the three-phase alternating-current voltage output end are simultaneously adjusted according to the negative feedback numerical value change of the three-phase power-frequency alternating currentThe output three-phase alternating voltage reduces the test current to zero and cuts off the test power supply;
fifthly, restoring the connecting sheet of the cross interconnection grounding box in the cable metal sheath cross interconnection grounding system to a correct connecting position, controlling the switching frequency of the IGBT and/or the negative feedback parameter of the three-phase power frequency alternating current and/or the frequency of the alternating current output according to the negative feedback numerical value change of the three-phase power frequency alternating current, realizing the adjustment of the three-phase alternating current voltage output by the three-phase alternating voltage output ends A, B and C, leading the cable core to pass through the balanced current I to be used as a test current, and measuring the metal sleeve current I at other cross interconnection grounding boxes3And a voltage V to ground3；
And sixthly, if the following judgment conditions are met, the performance of the cable metal sheath cross-connection grounding system is considered to meet the use requirement:
(1) Current of metal jacket I1And metal sheath current I3Same and not more than 3% of the test current I;
(2) Current of metal sheath I3Less than the current of the metal sleeve is less than I2；
(3) When protective measures are taken, the voltage kV1And kV3The same is lower than 200V; otherwise, voltage kV1And kV3Same, all lower than 50V; wherein, the first and the second end of the pipe are connected with each other,
I4the rated current of the wire core.
The test power supply has a simple structure and is divided into two modules, and the test power supply can effectively, quickly and reliably test the performance of the cable metal sheath cross interconnection grounding system, so that the reliability and safety of power supply are ensured.
The test method of the invention has the advantages that:
1. the input compatibility of the test power supply is strong, and the power frequency single-phase, two-phase, three-phase and direct-current voltage can be compatible, so that a 220V power supply which is common in a construction site can be adopted when a cable line on the laying site is short and the required power is small, and when a line on the laying site is long and the required power is large, the three-phase 380V input is adopted.
2. The two ends of the direct-current voltage of the test power supply are connected with the direct-current capacitors with enough size in parallel, so that the reactive power of the line during measurement is compensated, and the capacity of the input power supply and the weight of the instrument are greatly reduced.
3. The method firstly provides the loop resistance measurement of a cable metal sheath cross interconnection grounding system on the laying site, develops corresponding direct current voltage output, and can reach 100A after the load with the cross interconnection loop.
4. A test power supply for cross interconnection performance test is provided for the first time in an alternating-current, direct-current and alternating-current frequency conversion mode, and three-phase alternating current output by the power supply meets test requirements.
5. In a laying site, the power supply outputs two voltages, namely 100A power frequency alternating current can be applied to a cable core, and the induced voltage and the circulating current of the metal protective layer are measured; and can output direct current voltage for measuring the loop resistance of the cable metal sheath cross interconnection grounding system.
6. The system with feedback is arranged inside the circuit, and stable alternating current and direct current can be output.
7. The power control system adopts self-programming software, has high intelligence, can modify internal parameters of the system (such as parameters of IGBT switching frequency, current negative feedback, alternating current output frequency and the like), and can set output alternating current and direct current parameters.
8. And the power control system has a fault self-checking function, if an instrument has a fault, the power control system can carry out self-checking, and the fault reason is displayed on a display screen in a code form.
9. And an industrial LED display screen is adopted, so that the performance is stable and reliable.
Compared with the prior art, the invention has the following advantages and beneficial effects: the test method can solve the problem that the test laying site for testing the cross interconnection performance of the cable lines of 110kV and above is difficult to implement, can carry out site test on the performance of the cable metal sheath cross interconnection grounding system, and ensures stable, reliable and safe power supply, thereby realizing the effective test of the cross interconnection performance of the cable.
Drawings
FIG. 1 is a schematic diagram of an AC-DC-AC frequency conversion power supply module in the test power supply of the present invention;
FIG. 2 is a schematic diagram of an LC filter in a test power supply of the present invention;
FIG. 3 is a schematic diagram of the connections of the test power supply of the present invention for performance testing;
FIG. 4 is a schematic diagram of the connections of the test power supply of the present invention for loop resistance measurement;
wherein, the first and the second end of the pipe are connected with each other, the power supply comprises a cable core 1, a cross interconnection grounding box 2, an alternating current-direct current alternating frequency power supply module 3, an LC filter 4, a three-phase half-control full-bridge rectifying circuit 5, a direct current capacitor 6, an inverter circuit 7, a direct current adjustable constant current source 8, a large-section cable 9 and a small-section cable unit 10.
Detailed Description
The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.
Examples
As shown in fig. 1 to 4, a test method for testing the cross-connection performance of cables in a laying site according to the present invention is as follows: setting a test power supply as a power supply for performance test and loop resistance measurement of a cable metal sheath cross-connection grounding system;
applying three-phase power frequency alternating current to a cable core 1 of the cable metal sheath cross-connection grounding system by using three-phase alternating voltage output by a test power supply, measuring induced voltage and circulating current of the metal sheath in the cable metal sheath cross-connection grounding system, and realizing laying field inspection on the performance of the cable metal sheath cross-connection grounding system;
and applying the direct-current voltage output by the test power supply to the grounding end of the cable metal sheath cross-connection grounding system, and carrying out laying field measurement on the loop resistance of the cable metal sheath cross-connection grounding system.
Specifically, the cable metal sheath cross-connection grounding system comprises three large-section cables 9, each large-section cable 9 is composed of three small-section cable units 10 with the same length, and each small-section cable unit 10 is connected through an insulating joint; adopt coaxial core to replace the connection through alternately interconnected grounding box 2 between the three-phase cable core in the metal sheath of insulating joint department, set up a set of sheath protector in alternately interconnected grounding box 2, the both ends of every major segment cable are interconnected and ground connection respectively. The cross-connect grounding box 2 is a prior art product, for example: cross-connection grounding box produced by Zhejiang high-quality electrical appliances.
The three-phase power frequency alternating current applied to the cable core 1 of the cable metal sheath cross-connection grounding system by the three-phase alternating voltage output by the test power supply means that: the three-phase alternating current output ends A, B and C of the test power supply are respectively connected with one end of the cable core 1 of any one large-section cable 9, the other end of the cable core 1 is in short circuit, and the test power supply applies three-phase power frequency alternating current to the cable core 1 through the three-phase alternating current output ends A, B and C. The application of the dc voltage output by the test power supply to the two ends of the cable metal sheath cross-connection grounding system means: and a direct-current voltage output end of the test power supply is connected with grounding ends of two large-section cables.
The test power supply is formed by connecting an AC-DC-AC frequency conversion power supply module 3 and an LC filter 4, wherein the AC-DC frequency conversion power supply module 3 comprises an input end and a DC voltage output end A+And A-Three-phase alternating voltage output end U, V, W, three-phase half-control full-bridge rectifier circuit 5, direct current capacitor 6 and inverter circuit 7 are connected through peripheral circuit and constitute, wherein, the input of alternating current-direct current alternating frequency power module 3 is provided with three input terminal L1, L2 and L3, input terminal L1, L2 and L3 are connected with three-phase half-control full-bridge rectifier circuit 5, three-phase half-control full-bridge rectifier circuit 5 and direct current capacitor 6 output direct current voltage after connecting in parallel, the direct current voltage of output connects direct current voltage output end A+And A-The output direct-current voltage is connected with the inverter circuit 7 and then outputs three-phase alternating-current voltage, and the output three-phase alternating-current voltage is connected with the output ends U, V and W of the three-phase alternating-current voltage; three-phase AC voltage output ends U, V and W are connected with LC filter 4, and DC voltage output end A+And A-And is connected with the grounding end of the cable metal sheath cross interconnection grounding system.
The AC-DC-AC frequency conversion power supply module 3 also comprises a DC adjustable constant currentA source 8, the output DC voltage passes through the DC adjustable constant current source 8 and the DC voltage output end A+And A-And (4) connecting. The invention is connected with a direct current adjustable constant current source 8 in series on the direct current voltage, and can output stable and adjustable direct current voltage, thereby outputting constant current on a load and being used for measuring the loop resistance of a cable metal sheath cross interconnection grounding system. And the input voltage of the input end is 220V voltage, two-phase 380V voltage, three-phase 380V voltage or direct current voltage. The input of the test power supply has strong compatibility, and the power frequency single-phase voltage, the two-phase voltage, the three-phase voltage and the direct-current voltage can be compatible, so that the common 220V voltage in a construction site can be adopted when the cable line is short and the power is low, and the three-phase 380V voltage is adopted when the line is long and the power is high. The inverter circuit 7 is a three-phase inverter bridge formed by IGBTs. The inverter circuit 7 of the present embodiment is a three-phase inverter bridge composed of six IGBTs, and is configured to invert the direct current obtained by the three-phase half-controlled full-bridge rectifier circuit 5 to obtain an alternating current.
The LC filter 4 is formed by sequentially connecting input ends U, V and W, an inductor, an alternating current capacitor and three-phase alternating current output ends A, B and C, wherein the input ends U, V and W are connected with the three-phase alternating voltage output ends U, V and W, and the three-phase alternating current output ends A, B and C output three-phase alternating current voltages and are connected with a cable core 1 of a cable metal sheath cross interconnection grounding system. The three-phase alternating voltage output by the alternating current-direct current-alternating frequency power supply module 3 is not a true sine wave, but is a square wave (high-frequency square wave) with the conduction time changed discontinuously under the condition of keeping the absolute value of the voltage unchanged, which is extremely unfavorable for the performance inspection of the cable metal sheath cross-connection grounding system and can cause the measurement error of sheath induction voltage and sheath circulation current in the cable metal sheath cross-connection grounding system. The main function of the LC filter 4 is to smooth and make the discontinuous high-frequency square wave continuous, and the waveform of the three-phase ac voltage output by the LC filter 4 is very close to a sine wave.
The invention is used in the test method of the cable cross-connection performance test, measures the induced voltage and the circulation current of the metal sheath in the cable metal sheath cross-connection grounding system, and realizes the performance test of the cable metal sheath cross-connection grounding system, which means that: the three-phase alternating-current voltage output by the three-phase alternating-current voltage output ends A, B and C is adjusted by controlling the switching frequency of the IGBT and/or the negative feedback parameter of the three-phase power frequency alternating current and/or the frequency of alternating current output, and the induced voltage and the circulating current of the metal sheath in the cable metal sheath cross-connection grounding system are measured and judged, so that the performance of the cable metal sheath cross-connection grounding system is tested.
The method specifically comprises the following steps:
firstly, a connecting sheet of a cross interconnection grounding box in a cable metal sheath cross interconnection grounding system is positioned at a correct connecting position, and the switching frequency of an IGBT and/or the negative feedback parameter of three-phase power frequency alternating current and/or the frequency of alternating current output are controlled according to the negative feedback numerical value change of the three-phase power frequency alternating current, so that the three-phase alternating voltage output by three-phase alternating voltage output ends A, B and C is adjusted, and a cable core 1 passes through a balanced current I to be used as a test current;
second, measuring the metal sheath current I at the cross-connected grounding box1And a voltage V to ground1(ii) a After the measurement is finished, the three-phase alternating voltages output by the three-phase alternating voltage output ends A, B and C are simultaneously adjusted according to the negative feedback numerical value change of the three-phase power frequency alternating current, so that the test current is reduced to zero, and a test power supply is cut off;
thirdly, connecting pieces of a cross interconnection grounding box 2 in the cable metal sheath cross interconnection grounding system in a simulated wrong connection mode, controlling the switching frequency of the IGBT and/or the negative feedback parameter of the three-phase power frequency alternating current and/or the frequency of alternating current output according to the negative feedback numerical value change of the three-phase power frequency alternating current, and realizing adjustment of the three-phase alternating voltage output by the three-phase alternating voltage output ends A, B and C, so that the cable core 1 passes through the balanced current I to be used as test current;
the fourth step, measuring the metal sheath current I at the cross-connected grounding box 22And a voltage V to ground2(ii) a After the measurement is finished, the three phases are simultaneously adjusted according to the negative feedback value change of the three-phase power frequency alternating currentThree-phase alternating-current voltages output by the alternating-current voltage output ends A, B and C enable the test current to be reduced to zero, and a test power supply is cut off;
fifthly, restoring the connecting sheet of the cross interconnection grounding box 2 in the cable metal sheath cross interconnection grounding system to a correct connecting position, controlling the switching frequency of the IGBT and/or the negative feedback parameter of the three-phase power frequency alternating current and/or the frequency of alternating current output according to the negative feedback numerical value change of the three-phase power frequency alternating current, realizing the adjustment of the three-phase alternating current voltage output by the three-phase alternating voltage output ends A, B and C, leading the cable core 1 to pass through the balanced current I to be used as a test current, and measuring the metal sleeve current I at other cross interconnection grounding boxes 23And a voltage V to ground3；
And sixthly, if the following judgment conditions are met, the performance of the cable metal sheath cross interconnection grounding system is considered to be good:
(1) Current of metal jacket I1And metal sheath current I3Same and not more than 3% of the test current I;
(2) Current of metal sheath I3Less than the metal jacket current is less than I2；
(3) If protective measures are taken, the voltage is kV1And kV3The same, all are lower than 200V; otherwise, voltage
kV1And kV3The same, all are lower than 50V; wherein the content of the first and second substances,
I4the rated current of the wire core.
The test method can solve the problem that the test is difficult to implement due to the lack of a proper test power supply in the test of the cross interconnection performance test of the cable lines of 110kV and above, and can ensure stable, reliable and safe power supply for the performance test of the cable metal sheath cross interconnection grounding system. In addition, the cable metal sheath cross-connection grounding system has a plurality of connections, the measurement of loop resistance can prevent sheath misconnection or poor welding and connection, and the operation department also has measurement requirements, but the measurement cannot be implemented all the time because no proper power supply is available. The test method can adopt the direct-current voltage output by the test power supply as the power supply of the cable metal sheath cross-connection grounding system so as to meet the requirement of measuring the loop resistance of the cable metal sheath cross-connection grounding system.
The test power supply of this embodiment still includes feedback system, power control system and the LED display screen that can feed back and stabilize alternating current and direct current, and wherein, feedback system and power control system all are connected with alternating current-direct current alternating frequency power module, and the LED display screen is connected with power control system. The power control system can modify internal parameters of the system (such as parameters of IGBT switching frequency, current negative feedback, AC output frequency and the like), and can set output AC current and DC current parameters. The power control system has a fault self-checking function, if an instrument fault occurs, the power control system can perform self-checking, and the fault reason is displayed on an LED display screen in a code form.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Claims (6)
1. A test method for testing cross-connection performance of cables in a laying site is characterized by comprising the following steps: setting a test power supply as a power supply for performance test and loop resistance measurement of a cable metal sheath cross-connection grounding system;
applying three-phase power frequency alternating current to a cable core of the cable metal sheath cross interconnection grounding system by using three-phase alternating voltage output by the test power supply, measuring induced voltage and circulating current of the metal sheath in the cable metal sheath cross interconnection grounding system, and realizing laying field inspection on the performance of the cable metal sheath cross interconnection grounding system;
applying direct-current voltage output by a test power supply to two ends of the cable metal sheath cross-connection grounding system, and carrying out laying field measurement on loop resistance of the cable metal sheath cross-connection grounding system;
the test power supply is formed by connecting an alternating current-direct current alternating frequency power supply module and an LC filter; the AC-DC-AC variable frequency power supply module is formed by connecting an input end, a DC voltage output end, a three-phase AC voltage output end U, V and W, a three-phase half-controlled full-bridge rectifying circuit, a DC capacitor and an inverter circuit through a peripheral circuit; the input end of the alternating-current and direct-current alternating-frequency power supply module is connected with a three-phase half-controlled full-bridge rectifying circuit, the three-phase half-controlled full-bridge rectifying circuit is connected with a direct-current capacitor in parallel and then outputs direct-current voltage, the output direct-current voltage is connected with a direct-current voltage output end, the output direct-current voltage is connected with an inverter circuit and then outputs three-phase alternating-current voltage, and the output three-phase alternating-current voltage is connected with three-phase alternating-current voltage output ends U, V and W;
the three-phase alternating voltage output ends U, V and W are connected with an LC filter; the direct-current voltage output end is connected with the grounding end of the cable metal sheath cross interconnection grounding system;
the inverter circuit is a three-phase inverter bridge formed by IGBT;
the LC filter is formed by sequentially connecting input ends U, V and W, an inductor, an alternating current capacitor and three-phase alternating current output ends A, B and C; the input ends U, V and W are connected with three-phase alternating voltage output ends U, V and W, and the three-phase alternating voltage output ends A, B and C output three-phase alternating voltages and are connected with cable cores of a cable metal sheath cross interconnection grounding system;
the induced voltage and the circulation of the metal sheath in the measurement cable metal sheath cross-connection grounding system realize that the performance of the cable metal sheath cross-connection grounding system is paved by the field test: by controlling the switching frequency of the IGBT and/or the negative feedback parameters of the three-phase power frequency alternating current and/or the frequency of alternating current output, the three-phase alternating current voltage output by the three-phase alternating voltage output ends A, B and C is adjusted, the induced voltage and the circulating current of the metal sheath in the cable metal sheath cross-connection grounding system are measured and judged, and the performance of the cable metal sheath cross-connection grounding system is subjected to paving field inspection.
2. The test method for cross-connection performance inspection of cables laid in site according to claim 1, wherein: the cable metal sheath cross interconnection grounding system comprises a plurality of large-section cables, each large-section cable is composed of three small-section cable units with equal length, and each small-section cable unit is connected with each other by adopting an insulating joint; the three-phase cable cores in the metal sheath at the insulating joint are connected in a transposition mode through a cross interconnection grounding box by adopting coaxial cores, a group of sheath protectors is arranged in the cross interconnection grounding box, and two ends of each large section of cable are respectively connected in an interconnection mode and are grounded.
3. Test method for the cross-connection performance inspection of cables laid in the field according to claim 2, characterized in that: the three-phase alternating voltage output by the test power supply is applied to the cable cores of the cable metal sheath cross interconnection grounding system to form three-phase power frequency alternating current, which means that: the three-phase alternating current output ends A, B and C of the test power supply are respectively connected with one end of a cable core of any one large-section cable, the other end of the cable core is in short circuit, and the test power supply applies three-phase power frequency alternating current to the cable core through the three-phase alternating current output ends A, B and C;
the application of the direct-current voltage output by the test power supply to the two ends of the cable metal sheath cross interconnection grounding system is as follows: the DC voltage output end of the test power supply is connected with the grounding ends of two large-section cables.
4. The test method for cross-connection performance inspection of cables laid in site according to claim 1, wherein: the alternating current-direct current alternating frequency power supply module further comprises a direct current adjustable constant current source, and the output direct current voltage is connected with the direct current voltage output end through the direct current adjustable constant current source.
5. Test method for the cross-connection performance inspection of cables laid in the field according to claim 1, characterized in that: the input end is provided with three input terminals, and the input voltage of the input end is 220V voltage, two-phase 380V voltage, three-phase 380V voltage or direct current voltage.
6. Test method for the cross-connection performance inspection of cables laid in the field according to claim 1, characterized in that: through the switching frequency of control IGBT and/or the frequency of negative feedback parameter and/or the interchange output of three-phase power frequency alternating current, realize adjusting the three-phase alternating voltage of three-phase alternating voltage output A, B, C output to measure and judge the induced voltage and the circulation of the metal sheath in the cable metal sheath cross-connection grounding system, the realization is to lay on-the-spot inspection to the performance of cable metal sheath cross-connection grounding system and is to mean: the method comprises the following steps:
firstly, a connecting sheet of a cross interconnection grounding box in a cable metal sheath cross interconnection grounding system is positioned at a correct connecting position, and the switching frequency of an IGBT and/or the negative feedback parameter of three-phase power frequency alternating current and/or the frequency of alternating current output are controlled according to the negative feedback numerical value change of the three-phase power frequency alternating current, so that the three-phase alternating voltage output by three-phase alternating voltage output ends A, B and C is adjusted, and a cable core passes through a balanced current I to be used as a test current;
second, measuring the metal sheath current I at the cross-connected grounding box1And a voltage V to earth1(ii) a After the measurement is finished, the three-phase alternating current voltage output by the three-phase alternating voltage output ends A, B and C is simultaneously adjusted according to the negative feedback numerical value change of the three-phase power frequency alternating current, so that the test current is reduced to zero, and the test power supply is cut off;
thirdly, connecting pieces of a cross interconnection grounding box in the cable metal protective layer cross interconnection grounding system in a simulated wrong connection mode, controlling the switching frequency of the IGBT and/or the negative feedback parameters of the three-phase power frequency alternating current and/or the frequency of alternating current output according to the negative feedback numerical value change of the three-phase power frequency alternating current, and realizing adjustment of three-phase alternating current voltage output by three-phase alternating voltage output ends A, B and C so that a cable core passes through balanced current I to serve as test current;
fourthly, measuring the current I of the metal sleeve at the position of the cross-connection grounding box2And a voltage V to ground2(ii) a After the measurement is finished, the method is carried out according to the negative feedback numerical value change of the three-phase power frequency alternating currentAdjusting the three-phase alternating-current voltages output by the three-phase alternating-current voltage output ends A, B and C to reduce the test current to zero and cut off the test power supply;
fifthly, restoring the connecting sheet of the cross interconnection grounding box in the cable metal sheath cross interconnection grounding system to a correct connecting position, controlling the switching frequency of the IGBT and/or the negative feedback parameter of the three-phase power frequency alternating current and/or the frequency of alternating current output according to the negative feedback numerical value change of the three-phase power frequency alternating current, realizing the adjustment of the three-phase alternating current voltage output by the three-phase alternating voltage output ends A, B and C, leading the cable core to pass through the balanced current I to be used as a test current, and measuring the metal sleeve current I at other cross interconnection grounding boxes3And a voltage V to ground3；
And sixthly, if the following judgment conditions are met, the performance of the cable metal sheath cross-connection grounding system is considered to meet the use requirement:
(1) Current of metal jacket I1And metal sheath current I3The same, and not more than 3% of the test current I;
(2) Current of metal jacket I3Less than the metal jacket current is less than I2；
(3) When protective measures are taken, the voltage kV1And kV3The same is lower than 200V; otherwise, voltage kV1And kV3The same, all are lower than 50V; wherein, the first and the second end of the pipe are connected with each other,
I4the rated current of the wire core.
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