Power cable withstand voltage test method
By employing vehicle-mounted resonance and interference suppression technology, the adaptability and accuracy issues of high-voltage cable withstand voltage testing have been resolved, enabling efficient and safe cable testing that adapts to complex terrain and length variations, thereby improving equipment utilization.
Patent Information
- Application Number
- CN202511776993.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-28
- Publication Date
- 2026-01-23
AI Technical Summary
Existing high-voltage cable withstand voltage testing methods have poor adaptability, are difficult to adapt to complex scenarios, have low testing efficiency, insufficient equipment capacity, weak anti-interference ability, and insufficient diagnostic accuracy. Moreover, existing devices are cumbersome to transport and cannot meet the needs of complex terrain.
The vehicle-mounted resonant method is adopted, which combines an on-board oil-immersed iron-core reactor, a partial discharge-free frequency converter, an excitation transformer, and a capacitor voltage divider to form a series resonant circuit. By combining hardware and software interference suppression, flexible parameter adjustment and high-precision partial discharge detection can be achieved, making it suitable for withstand voltage tests of cables of different lengths.
It improves the adaptability and accuracy of withstand voltage testing, increases equipment utilization, shortens the construction period, reduces the testing cost per cable, and ensures the flexibility and safety of testing.
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Figure CN121385571A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the technical field of power equipment detection, and in particular to a power cable withstand voltage test method. BACKGROUND
[0002] With the acceleration of urbanization and the wide construction of new energy projects (such as photovoltaic and wind power projects), as the core carrier of power transmission, the application scenarios of high-voltage power cables are increasingly complex. On the one hand, the laying length of high-voltage cables in urban power grids is increasing, and the length of some lines can reach more than 15 kilometers, and often needs to pass through complex terrains such as fish ponds and mudflats; on the other hand, the cable connection mode in new energy power collection lines is various, and the working conditions such as the "hand-in-hand" connection of box-type transformers are common. At the same time, the cable-to-ground capacitance increases significantly with the length, resulting in a continuous increase in the demand for equipment capacity for cable transfer withstand voltage test. Therefore, the insulation performance of high-voltage cables directly determines the safety of the power system, and the accuracy and applicability of the withstand voltage test as a key means to verify the insulation quality of the cable become the core requirement of engineering implementation.
[0003] However, there are many technical defects in the field of high-voltage cable withstand voltage test and partial discharge detection in the prior art, which are difficult to meet the actual engineering requirements, mainly in the following aspects: first, the adaptability of the traditional test method is poor. The direct current withstand voltage method is easy to accelerate the aging of the accumulated space charge of cross-linked polyethylene cables, the ultra-low frequency method is only suitable for low voltage grades and has poor equivalence with power frequency, and the power frequency resonance method cannot meet the needs of long-distance cables due to the limited inductance adjustment range; second, most of the existing devices are fixed, which are cumbersome to move and have a long construction period, and are difficult to adapt to complex terrains; third, the partial discharge detection is seriously disturbed, and the on-site noise and the device's own partial discharge (usually more than 10 pC) easily mix the signals, resulting in "sick operation" of the defective cable; fourth, there is a lack of flexible parameter adjustment mechanism, and different length cables need to be re-built circuits, resulting in low equipment utilization.
[0004] Therefore, there is an urgent need for a withstand voltage test method that can adapt to complex scenarios, improve test efficiency and accuracy, improve equipment capacity, anti-interference ability, operation adaptability and diagnostic accuracy, and perform power cable withstand voltage test more professionally, efficiently and safely. SUMMARY
[0005] The present application aims to provide a power cable withstand voltage test method to adapt to complex scenarios, improve test efficiency and accuracy, improve equipment capacity, anti-interference ability, operation adaptability and diagnostic accuracy, and perform power cable withstand voltage test more professionally, efficiently and safely.
[0006] To achieve the above-mentioned purpose, the present application adopts the following technical solution: a power cable withstand voltage test method, comprising the following steps: S1, test parameter acquisition and reactor combination matching; The rated voltage, length and capacitance parameters of the subject high-voltage cable are acquired, and the inductance value required by the test loop is calculated according to the formula The inductance value required by the test loop is calculated, wherein f is the resonance frequency, which is 30HZ-300Hz; L is the total inductance of the reactor; and C is the capacitance of the test sample; a single reactor, multiple reactors in series or parallel combination is selected from multiple vehicle-mounted oil-immersed core reactors to make the total inductance of the reactor meet the resonance frequency requirement; S2, vehicle-mounted test device building and interference pretreatment; The selected combination of vehicle-mounted oil-immersed core reactors, non-partial discharge variable frequency power supply, excitation transformer and capacitance divider are installed on the vehicle-mounted platform to form a series resonance loop; a voltage equalizing ring is arranged at the top of the reactor and the capacitance divider; an oxide film shielding wire is used for high-voltage lead, and the shielding layer is isolated from the center conductor; a self-made reactor is connected in series to complete the hardware interference suppression pretreatment; S3, resonance debugging and withstand voltage test execution; The non-partial discharge variable frequency power supply is started, and the output frequency is adjusted to the resonance frequency calculated in step S1, so that the loop power factor A standard test voltage is applied, and the withstand voltage is maintained for 60 minutes; the test current is calculated according to the formula , wherein U is the test voltage and ω is the angular frequency; at the same time of calculating the test current, the temperature rise of the device is monitored to ensure that the temperature rise is not greater than 65K; S4, partial discharge signal detection and interference suppression; During the withstand voltage test, the partial discharge detection module is started, the partial discharge signal is collected by using the pulse current method and the high-frequency current sensing method, the GATE value is set through the partial discharge detection system to filter out the fixed phase interference, the high-pass filter is connected in series to extract the effective signal of 25MHz-30MHz, and the software interference suppression is completed; S5, partial discharge signal analysis and test result determination; The filtered partial discharge signal is subjected to frequency spectrum classification, phase discrimination (judging whether it has the 180° phase characteristic with the test power supply), polarity discrimination (confirming whether the cable grounding line channel signal has the same polarity with the power supply and whether the divider grounding line channel signal has the opposite polarity with the power supply) and amplitude calculation; if the partial discharge quantity is not greater than 10pC, the cable is determined to be qualified, otherwise it is determined to be unqualified; a test report is generated and stored in the management database; S6, reuse of the vehicle-mounted test device and parameter adjustment; if different length cables need to be tested, steps S1-S5 are repeated; Further, the vehicle-mounted oil-immersed core reactor in step S1 is 6, the rated inductance of a single reactor is not greater than 38.04H, the rated current is not less than 23.62A, the total inductance of the 6 vehicle-mounted oil-immersed core reactors in parallel is not greater than 6.34H, the total current is not less than 180A, and it is suitable for 15km 110kV / 220kV high-voltage cable test.
[0007] Further, the no-partial discharge variable frequency power supply in step S2 has a rated capacity of no less than 437.1 kVA, an output frequency adjustment resolution of 0.02 Hz, a partial discharge amount of no more than 10 pC, and overcurrent, overvoltage and discharge protection functions, and the partial discharge interference signals at 0° and 180° phases of a PWM square wave inverse variable blanking sinusoidal wave form are eliminated.
[0008] Further, the excitation transformer in step S3 adopts a YD-500 / 3.3, 6.6 type oil-immersed iron shell structure, two groups of independent windings on the high-voltage side can be connected in series or parallel, and the output voltage is no less than 3.1 kV, and an electrostatic shielding layer is arranged between the high-voltage and low-voltage windings to eliminate electrical contact interference.
[0009] Further, the partial discharge detection module in step S4 has a signal capture rate of no less than 95%, a sensitivity that meets a minimum detectable partial discharge amount of no more than 5 pC, and is pre-calibrated through a discharge model; the discharge model is built and divided into intensity levels, each intensity level discharge intensity is applied, and the minimum discharge intensity value of the detected signal is recorded to ensure that the sensitivity meets the requirements.
[0010] Further, in step S5, the amplitude is calculated by comparing the detected partial discharge signal amplitude with the preset calibration signal amplitude according to the formula to calculate the actual partial discharge amount, wherein is the actual partial discharge amount, is the calibration signal partial discharge amount, is the detection signal amplitude, is the calibration signal amplitude.
[0011] Further, in step S6, when repeating steps S1-S5, only the combination mode of the reactor is adjusted, and the overall loop does not need to be rebuilt, wherein two reactors are connected in parallel to adapt to no more than 5.99 kilometers of 220 kV cables, and six reactors are connected in parallel to adapt to no more than 17.96 kilometers of 220 kV cables.
[0012] The beneficial effects of the present scheme are: step standardization, parameter matching, interference suppression and detection analysis are realized through a fixed process to avoid differences in manual operation; strong adaptability, flexible combination of multiple reactors, adaptation to 1-18 kilometers of 110 kV / 220 kV cables, vehicle-mounted structure to cope with complex terrain, and mobile convenience; accurate detection, double interference suppression of software and hardware, high accuracy of partial discharge detection, and avoidance of defect omission; economic advantage, high reuse rate of devices, adjustment of reactor combination for different cable tests, reduction of single cable test cost, and shortening of construction period. BRIEF DESCRIPTION OF DRAWINGS
[0013] Figure 1 is a flowchart of the present application; Figure 2 is a schematic diagram of the amplitude and phase in Example Two. Figure 3 A schematic diagram of the partial discharge signal waveform in Example 2.
[0014] Further details are described below through a specific embodiment: DETAILED DESCRIPTION The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application.
[0015] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.
[0016] The embodiment is basically as shown in the accompanying Figures 1-3 As shown in the accompanying Figure 1 A power cable withstand voltage test method, the vehicle-mounted test device used includes: A vehicle-mounted platform equipped with a damping device and a balance weight for carrying test equipment; 6 vehicle-mounted oil-immersed core reactors, each with a rated voltage of 250kV and a rated capacity of 6500kVA, supporting series or parallel combination; A partial discharge-free frequency conversion power supply with an input voltage of 400V three-phase and an output voltage of 550V effective value and an output frequency of 30-300Hz; An excitation transformer with two groups of windings on the high-voltage side that can be connected in series or parallel, with an output voltage of 3.3kV or 6.6kV; A capacitor voltage divider with a rated voltage of 250kV and a capacitance of 0.001uF, with a constant voltage division ratio in the range of 30Hz-300Hz; A partial discharge detector integrated with a pulse current sensor and a high-frequency current sensor, supporting phase windowing and frequency spectrum analysis; A control terminal connected to the above-mentioned devices for parameter calculation, test control and result determination.
[0017] As shown in the accompanying Figure 1 The power cable withstand voltage test method provided by the present application uses vehicle-mounted resonance, with "parameter matching-circuit building-resonance debugging-partial discharge detection-result determination" as the core process, balancing flexibility and accuracy, and each step is as follows: Step S1: Test parameter acquisition and reactor combination matching First, the key parameters of the test cable are obtained: rated voltage (such as 110 kV / 220 kV), cable length and unit length capacitance (0.296 μF / km for 110 kV cable and 0.232 μF / km for 220 kV cable), and the total capacitance is calculated . According to the series resonance frequency requirement (30-300 Hz), the formula is used to calculate the required inductance value L. From the six on-board oil-immersed core reactors (36H for single reactor), the combination mode is selected: for example, 15 kilometers of 110 kV cable (C=4.44 μF), f=30 Hz is taken, and L≈6.34H is calculated. Since the resonance frequency of the withstand voltage test circuit is inversely proportional to the square root of inductance and capacitance, that is, when the capacitance is large, the inductance of the test circuit must be small enough to ensure that the resonance frequency of the circuit is greater than 30 Hz (to ensure that the resonance frequency is within the range of 30-300 Hz in step S1), therefore, six reactors are connected in parallel (total inductance 6H), which meets the resonance frequency requirement. This step avoids manual experience errors by accurately calculating the matching reactor combination, and the modular design of the six reactors can adapt to different lengths of cables without the need for additional equipment.
[0018] Step S2: Vehicle-mounted test device setup and interference preprocessing The selected reactors, variable frequency power supply without partial discharge, excitation transformer and capacitor divider are installed on the vehicle-mounted platform, which is equipped with damping devices to ensure the stability of the equipment during transportation. When connecting the circuit, the following hardware interference suppression measures are adopted: A voltage equalizing ring is installed at the top of the reactor and the capacitor divider to eliminate the sharp end corona; The high-voltage lead uses an oxide film shielding wire, and the shielding layer is isolated from the center conductor to avoid the transmission of corona noise; A self-made reactor is connected between the high-voltage lead and the pressurizing point to suppress high-frequency interference.
[0019] At the same time, the control terminal reads the preset device parameters (such as reactor rated current and variable frequency power supply capacity) in the management database to ensure that the circuit connection meets the safety specifications. This step can preliminarily reduce the background noise to less than 5 pC.
[0020] Step S3: Resonance debugging and withstand voltage test execution Start the no-partial discharge variable frequency power supply, adjust the output frequency from 30 Hz, monitor the loop current and voltage phase difference in real time, when the phase difference is 0 (cosφ = 1), the loop reaches the resonance state, record the frequency at this time as the resonance frequency. According to the existing GB50150-2006 standard, apply a test voltage: 128 kV for 110 kV cables, 216 kV for 220 kV cables, and maintain the voltage for 60 minutes. During the test, the control terminal monitors the actual current and compares it with the theoretical current. If the deviation is greater than 5%, an automatic alarm is triggered. At the same time, the reactor and variable frequency power supply temperature rise are monitored to ensure that the temperature rise does not exceed 65K within 180 minutes of full load operation, ensuring the safety of the equipment.
[0021] Step S4: Partial discharge signal detection and interference suppression Start the partial discharge detector simultaneously with the withstand voltage test. Use pulse current method and high-frequency current sensing method to collect signals in double mode. The pulse current method collects loop pulse signals through a series resistor, with a capture rate of not less than 95%. The high-frequency current sensing method (HFCT) is set in the cable grounding line to detect high-frequency partial discharge signals.
[0022] To further filter out interference, execute software suppression measures and set the GATE value (phase window) to filter out fixed phase signals corresponding to 50 Hz power frequency interference. A 15 MHz high-pass filter (HPF) is connected in series to extract effective partial discharge signals in the 25-30 MHz frequency band, which has the least noise in the field and a signal-to-noise ratio of more than 20:1.
[0023] Step S5: Partial discharge signal analysis and test result determination. Analyze the filtered signals according to the following process: Frequency spectrum classification: divide the signals by frequency band, and only keep the signals in the 25-30 MHz frequency band to exclude narrowband interference. Phase discrimination: draw a partial discharge signal phase map. If the signal and the test power source have a 180° characteristic and are concentrated in a specific phase width (such as 0°-30°, 180°-210°), it is determined to be an effective partial discharge signal. Polarity discrimination: compare the signals of the cable grounding line channel (Zml) and the divider grounding line channel (Zm2). If Zml signal and power source have the same polarity, and Zm2 signal and power source have opposite polarity, it is confirmed that the signal comes from the cable itself. Amplitude calculation: calibrate through a pre-set calibration signal, and calculate the actual partial discharge amount (Q) according to the formula Q = K * I * t where K is the calibration signal partial discharge amount, I is the current, and t is the time. If Q < 0.5 * K then the cable is qualified, otherwise it is not qualified. The control terminal automatically generates a test report and stores it.
[0024] Step S6: Test device reuse and parameter adjustment If different length of cable test is needed, the overall loop does not need to be re-built, only the step S1 is repeated to adjust the combination of the reactor to meet the resonant frequency requirement, and then the steps S2-S5 are repeated.
[0025] Example One 110kV high voltage cable test (length 4.99km) Step S1: 110kV cable unit capacitance 0.296μF / km, total capacitance C=4.99x0.296≈1.48μF, take f=30Hz, calculate L≈15H, select 3 reactors in parallel (total inductance 12H); Step S2: build the loop, install the grading ring, use the shielded wire with oxide film, and connect the self-made reactor in series; Step S3: adjust the frequency of the variable frequency power supply to 32Hz (resonant frequency), apply 128kV voltage, last for 60 minutes, monitor the current not more than 90A and the temperature rise not more than 45K; Step S4: start the partial discharge detector, set the GATE value to filter out 50Hz interference, connect 15MHz HPF in series, and extract 25-30MHz signal; Step S5: analyze the signal phase showing 180° characteristics, the polarity meets the requirements, calculate the partial discharge≈5pC, and determine qualified; Example Two 110kV high voltage cable defect detection (length 1.3km) Step S1: 220kV cable total capacitance C=1.3x0.232≈0.30μF, calculate L≈90H, select 2 reactors in series (total inductance 72H); Steps S2-S4: same as example 1; Step S5: when the voltage rises to 50kV, partial discharge signal is detected, as shown in the attached Figure 2 and Figure 3 , the phase shows 180° characteristics, calculate the partial discharge≈9500pC, which is far more than the requirement that the partial discharge of the cable should be less than 10pC when leaving the factory, and is determined unqualified.
[0026] After the unqualified condition occurs, check whether there is discharge trace on the surface of the cable in time, if there is discharge trace, check whether the discharge part appears flat (i.e. judge the roundness of the cable) to cause the air gap to form on the interface between the sleeve inside and the cable insulation layer, and the partial discharge occurs under the action of voltage. Or check other reasons that cause discharge trace in time. The partial discharge test under voltage can effectively detect the possible partial damage and destruction in the voltage test process, and can avoid the operation of the cable with damage.
[0027] The above-mentioned are only embodiments of the present application, and common technical solutions and / or common knowledge of the scheme are not described in detail. It should be pointed out that, for those skilled in the art, without departing from the technical solutions of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, and these will not affect the effect and practicality of the patent. The protection scope claimed in the present application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.
Claims
1. A method of power cable withstand voltage test, characterized by, Comprising the following steps: S1, test parameter collection and reactor combination matching; The rated voltage, length and capacitance of the high-voltage cable of the subject are acquired, and the formula The inductance value required by the test loop is calculated, wherein f is the resonance frequency, and is 30HZ-300Hz; L is the total inductance of the reactor; C is the capacitance of the test sample; a combination mode of single reactor, multiple reactors in series or parallel is selected from multiple vehicle-mounted oil-immersed core reactors, so that the total inductance of the reactor meets the resonance frequency requirement; S2, vehicle-mounted test device building and interference pretreatment; The selected combination of vehicle-mounted oil-immersed core reactors, no partial discharge variable frequency power supply, excitation transformer and capacitor divider is installed on the vehicle-mounted platform, connected to form a series resonant circuit; A voltage grading ring is installed at the top of the reactor and the capacitor divider, the high-voltage lead uses an oxide film shielding line, and the shielding layer is isolated from the center conductor, the self-made reactor is connected in series, and the hardware interference suppression pretreatment is completed; S3, resonance debugging and withstand voltage test execution; Start the no-arcing variable frequency power supply, adjust the output frequency to the resonant frequency calculated in step S1, make the loop power factor , apply a standard test voltage, and continue for 60 minutes of voltage endurance. Monitor in real time and calculate the test current according to the formula , where U is the test voltage and ω is the angular frequency. At the same time, monitor the temperature rise of the device to ensure that the temperature rise is not greater than 65 K. S4, partial discharge signal detection and interference suppression; During the withstand voltage test, start the partial discharge detection module, collect the partial discharge signal by pulse current method and high-frequency current sensing method, filter out the fixed phase interference by setting the GATE value of the partial discharge detection system, extract the effective signal of 25MHz-30MHz by series high-pass filter, and complete the software interference suppression. S5, partial discharge signal analysis and test result determination; The filtered partial discharge signal is classified by frequency spectrum, phase discrimination (judging whether it is 180° phase characteristic with the test power supply), polarity discrimination (confirming that the cable ground line channel signal is of the same polarity with the power supply, and the divider ground line channel signal is of the opposite polarity with the power supply), and amplitude calculation. If the partial discharge is not greater than 10pC, the cable is determined to be qualified, otherwise it is determined to be unqualified, a test report is generated and stored in the management database; S6, reuse of vehicle-mounted test device and parameter adjustment. If different length cables need to be tested, repeat steps S1-S5.
2. The power cable withstand voltage test method using on-vehicle resonance according to claim 1, characterized by: The vehicle-mounted oil-immersed core reactor in step S1 is 6 units, with a single unit rated inductance not greater than 38.04H and a rated current not less than 23.62A. When the 6 units are connected in parallel, the total inductance is not greater than 6.34H and the total current is not less than 180A, which is suitable for 15km 110kV / 220kV high-voltage cable test.
3. The power cable withstand voltage test method using on-vehicle resonance according to claim 1, characterized by: The no partial discharge variable frequency power supply in step S2 has a rated capacity not less than 437.1kVA, an output frequency adjustment resolution of 0.02Hz, a partial discharge not greater than 10pC, and overcurrent, overvoltage and discharge protection functions. The PWM square wave inversion eliminates the partial discharge interference signal at 0° and 180° phase of the sine wave form.
4. A power cable withstand voltage test method according to claim 1, characterized by: The excitation transformer in step S3 adopts YD-500 / 3.3,6.6 type oil-immersed iron core structure, two groups of independent windings on the high-voltage side can be connected in series or parallel, the output voltage is not less than 3.1kV, and the static shielding layer between the high and low voltage windings is set to eliminate the electrical contact interference.
5. A power cable withstand voltage test method according to claim 1, characterized by: The signal capture rate of the partial discharge detection module in step S4 is not less than 95%, the sensitivity meets the minimum detection partial discharge not greater than 5pC, and is pre-calibrated by discharge model; Build a discharge model and divide the intensity level, apply each intensity discharge intensity, record the minimum discharge intensity value of the detected signal, and ensure that the sensitivity meets the requirements.
6. A power cable withstand voltage test method according to claim 1, characterized by: The amplitude calculation in step S5 is: comparing the detected partial discharge signal amplitude with the preset calibration signal amplitude, according to the formula calculating the actual partial discharge amount, wherein is the actual partial discharge amount, is the calibration signal partial discharge amount, is the detected signal amplitude, is the calibration signal amplitude.
7. A method of testing the voltage resistance of a power cable according to claim 1, characterized in that: In step S6, when repeating steps S1-S5, only the reactor combination method needs to be adjusted, and the overall circuit does not need to be rebuilt. Two reactors in parallel are suitable for not more than 5.99km of 220kV cable, and six in parallel are suitable for not more than 17.96km of 220kV cable.