A short-time AC voltage generator for power cable testing

Abstract

This invention discloses a short-time AC voltage generator for power cable testing, applied in the field of high-voltage testing technology. It consists of a high-voltage staged charging unit, a staged energy storage unit, a cascaded inverter unit, an inverter-driven isolated power supply unit, a reactor unit, and a cable test specimen. This device can generate a short-time AC high voltage on the cable test specimen, comprising three stages: an AC high voltage with increasing amplitude, a constant-amplitude sinusoidal current voltage, and an amplitude-decreasing oscillating wave voltage. The duration of the entire short-time AC voltage is no more than 1 second, enabling various tests such as cable withstand voltage, partial discharge, and overall insulation diagnosis. The device is characterized by its small size, light weight, low loss, and high load-carrying capacity, meeting the current industry's needs for voltage sources for on-site power cable testing, and has broad application prospects in the power industry, as well as in petroleum, chemical, and steel industries.

Description

Technical Field

[0001] This invention relates to the fields of electrical material testing and high voltage testing technology, and more specifically to a short-time AC voltage generating device for power cable testing. Background Technology

[0002] Power cables are widely used in power transmission and distribution systems, and their safe and stable operation is a key factor in ensuring the reliability of the power system. For many years, extensive research has been conducted both domestically and internationally to detect and evaluate the insulation condition of cables. The main methods commonly used for cable insulation condition testing fall into three categories: withstand voltage testing, partial discharge testing, and diagnostic testing reflecting the overall insulation condition. Currently, the testing method that integrates these three functions is the oscillating wave test method (DAC). This method uses a high-voltage DC voltage to charge the cable, forming an oscillating wave high voltage with a frequency between 20Hz and 500Hz acting on the cable, used to measure partial discharge and dielectric loss. Since its invention in the 1990s, the DAC method has gained high recognition in industry and has been widely used in the handover testing and routine maintenance testing of distribution cables. However, the DAC testing method has encountered serious technical problems in its application to transmission cables. In September 2021, the International Large Electric Systems Organization (ILEO) released the CIGRETB 841 standard, which clearly states that the existing DAC test method is no longer recommended for the large number of XLPE high-voltage cables. This is because the electric field generated by the space charge accumulated in the insulation (especially cross-linked polyethylene insulation) during the DC charging phase will be superimposed on the electric field generated in the cable during the subsequent DAC voltage oscillation process, thus damaging the cable insulation.

[0003] Therefore, proposing a short-time AC voltage generating device for power cable testing, and overcoming the technical problem that existing oscillating wave high voltage testing devices damage cable insulation during testing, is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0004] In view of this, the present invention provides a short-time AC voltage generator for power cable testing, which improves the ability to drive loads, slows down the attenuation of oscillating high voltage waves, and can output a short-time AC voltage with a duration of no more than 1 second, thereby enabling various tests such as cable withstand voltage, partial discharge, and overall insulation diagnosis.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A short-time AC voltage generating device for power cable testing includes: a voltage-level charging unit, a voltage-level energy storage unit, a cascaded inverter unit, an inverter drive isolation power supply unit, and a high-voltage reactor unit; the voltage-level charging unit is connected to the cascaded inverter unit through the voltage-level energy storage unit, the cascaded inverter unit is connected to the cable test specimen through the high-voltage reactor unit, and the cascaded inverter unit is also connected to the inverter drive isolation power supply unit.

[0007] Optionally, the high-voltage graded charging unit includes: a multi-tap isolation transformer and n rectifier charging circuits; the multi-tap isolation transformer is connected to the n rectifier charging circuits connected in parallel.

[0008] Optionally, the cascaded inverter unit includes n IGBT inverter bridges, which are connected in a cascaded manner.

[0009] Optionally, the graded energy storage unit consists of n capacitors, and the n capacitors are respectively connected to the n IGBT inverter bridges.

[0010] Optionally, the n capacitors are metallized film capacitors.

[0011] Optionally, the inverter drive isolation power supply unit consists of a rectifier circuit, transformers T1 to Tn, MOSFETs, and a power factor correction circuit. The input AC power is rectified and output as DC. The control and drive signals are fed back to the PFC control and drive circuit, and the MOSFETs are controlled to generate n-coulomb output through the transformers T1 to Tn.

[0012] Specifically, the inverter drive isolation power supply unit controls the magnetic induction intensity in the core of transformers T1 to Tn by controlling the switching of MOSFET M1, thereby generating voltage in the secondary side of T1 to Tn.

[0013] The primary winding of the transformer T1 is wound around the magnetic core in the form of a wire, and the secondary load is wound on the magnetic core of T1 to Tn with insulated wire, with one or several turns.

[0014] The MOSFET M1 control chip is an L6561 chip, which adopts a frequency conversion critical control mode. When the secondary circuit current drops to zero, the switch M1 is turned on.

[0015] The inverter drive isolation power supply unit adopts a power factor correction (PFC) circuit. The PFC circuit encapsulates the peak primary current into the half-sinusoidal rectified output voltage waveform, thereby reducing odd harmonics.

[0016] Optionally, the high-voltage graded charging unit and the inverter drive isolation power supply unit are powered by 220V AC.

[0017] As can be seen from the above technical solution, compared with the prior art, the present invention discloses a short-time AC voltage generating device for power cable testing. Compared with the prior art, the above technical solution has the following technical effects:

[0018] 1. The short-time AC voltage generating device for power cable testing of the present invention avoids the DC charging process in the existing oscillating wave test, thus completely avoiding cable damage caused by the accumulation of space charge in DC oscillating wave cable testing; at the same time, it completely solves the problem that the cable insulation may deteriorate and thus cannot be pressurized or that the charging time is too long in DC charging.

[0019] 2. The short-time AC voltage generating device for power cable testing according to the present invention features optimized circuitry, low system loss, high load capacity, and the ability to meet the testing requirements of longer cables with the same volume and weight.

[0020] 3. The short-time AC voltage generator for power cable testing of the present invention generates a short-time AC voltage with a smaller attenuation coefficient and a slower attenuation rate in the oscillation wave stage, and a longer high voltage maintenance time, which meets the requirements for measuring partial discharge over a longer period of time. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 A structural diagram of a short-time AC voltage generator for power cable testing provided by the present invention;

[0023] Figure 2 This is a structural diagram of the high-voltage graded charging unit provided by the present invention;

[0024] Figure 3 A structural diagram of the hierarchical energy storage unit and cascaded inverter unit provided by the present invention;

[0025] Figure 4 This is a structural diagram of the inverter drive isolation power supply unit provided by the present invention;

[0026] Figure 5 This is a short-time AC voltage waveform generated in a specific embodiment of the present invention. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] like Figure 1 As shown, this embodiment of the invention discloses a short-time AC voltage generating device for power cable testing, comprising: a high-voltage graded charging unit 1, a graded energy storage unit 2, a cascaded inverter unit 3, an inverter drive isolation power supply unit 4, and a high-voltage reactor unit 5; the high-voltage graded charging unit 1 is connected to the cascaded inverter unit 3 through the graded energy storage unit 2, the cascaded inverter unit 3 is connected to the cable test specimen 6 through the high-voltage reactor unit 5, and the cascaded inverter unit 3 is also connected to the inverter drive isolation power supply unit 4.

[0029] Further, see Figure 2 As shown, the high-voltage graded charging unit 1 includes: a multi-tap isolation transformer and n rectifier charging circuits; the multi-tap isolation transformer is connected to the n rectifier charging circuits connected in parallel.

[0030] Further, see Figure 3 As shown, the cascaded inverter unit 3 includes n IGBT inverter bridges, which are connected in a cascaded manner.

[0031] Further, see Figure 3 As shown, the graded energy storage unit 2 consists of n capacitors, which are connected to n IGBT inverter bridges respectively.

[0032] Furthermore, the n capacitors are metallized film capacitors.

[0033] Further, see Figure 4 As shown, the inverter drive isolation power supply unit 4 consists of a rectifier circuit, transformers T1 to Tn, MOSFETs, and a power factor correction circuit. The input AC power is rectified and output as DC. The control and drive signals are fed back to the PFC control and drive circuit, and the MOSFETs are controlled to generate n-coulomb output through the transformers T1 to Tn.

[0034] Specifically, the inverter drive isolation power supply unit 4 controls the magnetic induction intensity in the core of transformers T1 to Tn by controlling the switching of MOSFET M1, thereby generating voltage in the secondary side of T1 to Tn.

[0035] The primary winding of transformer T1 is wound around the magnetic core in the form of a wire, while the secondary load is wound on the magnetic core of T1 to Tn with insulated wire, with one or several turns.

[0036] The MOSFETM1 control chip uses the L6561 chip and adopts the frequency conversion critical control mode. When the secondary circuit current drops to zero, the switch M1 is turned on.

[0037] The inverter drive isolation power supply unit 4 adopts a power factor correction (PFC) circuit. The PFC circuit encapsulates the peak primary current into the half-sinusoidal rectified output voltage waveform, reducing odd harmonics.

[0038] Furthermore, the high-voltage graded charging unit 1 and the inverter drive isolation power supply unit 4 are powered by 220V AC power.

[0039] Specifically, the short-time AC voltage generating device for power cable testing according to the present invention mainly consists of a high-voltage graded charging unit 1, a graded energy storage unit 2, a cascaded inverter unit 3, an inverter drive isolation power supply unit 4, a high-voltage reactor unit 5, and a cable test specimen 6. The high-voltage graded charging unit 1 provides charging power to the graded energy storage unit 2, storing electrical energy in the energy storage unit. Then, the cascaded inverter unit 3 operates under the drive circuit, cooperating with the high-voltage reactor to generate a short-time AC voltage on the cable test specimen 6.

[0040] The high-voltage graded charging unit 1 consists of an apparent power of 2kVA, a voltage ratio of 220:1700, a four-tap transformer, a 1kΩ charging resistor, a 5kV 10A rectifier bridge, and a mechanical switch on the secondary side.

[0041] The graded energy storage unit 2 consists of four metallized film capacitors with a rated voltage of 2.5kV and a rated capacitance of 10mF.

[0042] The cascaded inverter unit 3 is composed of four cascaded H-bridges consisting of IGBTs with a rated collector-emitter voltage of 3300V and a continuous collector DC current of 200A.

[0043] The inverter drive isolation power supply unit 4 has a secondary side output voltage of 4 channels of 15V DC voltage.

[0044] When the above parameters are used, by controlling the inverter, the short-time AC voltage generator can generate and apply a short-time AC voltage to the cable for a duration of no more than 1 second. The constant-amplitude oscillating AC voltage phase lasts for 5-10 cycles. Figure 5 As shown.

[0045] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0046] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A short-time AC voltage generating device for testing power cables, characterized in that, include: The high-voltage graded charging unit (1), graded energy storage unit (2), cascaded inverter unit (3), inverter drive isolation power supply unit (4), and high-voltage reactor unit (5) are connected. The high-voltage graded charging unit (1) is connected to the cascaded inverter unit (3) through the graded energy storage unit (2), and the cascaded inverter unit (3) is connected to the cable test specimen (6) through the high-voltage reactor unit (5). The cascaded inverter unit (3) is also connected to the inverter drive isolation power supply unit (4). The inverter drive isolation power supply unit (4) consists of a rectifier circuit, transformers T1~Tn, MOSFETs, and a power factor correction circuit. The mains power input is rectified and output as DC. The control and drive signals are fed back to the PFC control and drive circuit, and n outputs are generated by controlling the MOSFETs through the transformers T1~Tn. The high-voltage graded charging unit (1) includes: a multi-tap isolation transformer and n rectifier charging circuits; the multi-tap isolation transformer is connected to the n rectifier charging circuits connected in parallel; The cascaded inverter unit (3) includes n IGBT inverter bridges, which are connected in a cascaded manner. The graded energy storage unit (2) consists of n capacitors, and the n capacitors are respectively connected to the n IGBT inverter bridges; The n capacitors are metallized film capacitors; The high-voltage graded charging unit (1) and the inverter drive isolation power supply unit (4) are powered by 220V AC power.

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