A power cable testing device based on low-noise short-time near power frequency high voltage excitation

Abstract

The application discloses a kind of power cable testing devices based on low-noise short-time near power frequency high voltage excitation, it is related to the field test of cable insulation, its composition includes multi-level DC power supply module, multi-level energy storage module, forward linear power amplifier module, reverse linear power amplifier module, inverter unit, host system, power amplifier drive module, inverter unit drive module, control module, sampling circuit, current-limiting resistance, resonant reactance.Charge to target voltage by multi-level DC power supply module to multi-level energy storage module and disconnect, so that multi-level energy storage module is as multi-level DC voltage source.Linear power amplifier mode is adopted, control drive circuit generates sinusoidal half-wave voltage, through hierarchical conduction circuit, control the switch device in forward linear power amplifier module and reverse linear power amplifier module output sinusoidal half-wave voltage, sinusoidal half-wave voltage is converted into sinusoidal voltage by inverter unit, the frequency of control sinusoidal voltage is between 30-300Hz, loop reaches natural resonant state.During testing process, all switch devices are in linear conduction state, the noise level of equipment itself is very low, the output duration is not greater than 1 second, and the short-time near power frequency voltage reaching specified test voltage, which has good application prospect in diagnostic test of cable insulation.

Description

Technical Field

[0001] This invention patent relates to cable insulation testing technology and its application fields, and is a cable testing device based on low-noise short-time near-power frequency high-voltage excitation. Background Technology

[0002] With the development of the economy and society, the importance of a stable and reliable power supply has become increasingly prominent. The power grid has increasingly stringent requirements for the safety and reliability of electrical equipment. As an important part of the power grid transmission and distribution network, the insulation condition of power cables is very important for the safe and stable operation of the power grid. In order to ensure the normal power supply of cable lines, it is necessary to conduct insulation tests on cables regularly to meet the performance requirements for long-term stable operation.

[0003] In 1998, Dutch scholars proposed and adopted a cable testing method called oscillating wave, which has been widely used in industry both domestically and internationally for the past two decades. However, this technology has a drawback: DC charging of the cable is required before generating the oscillating wave. This DC charging leads to space charge accumulation in the cable, posing a risk of insulation damage during the subsequent oscillating wave phase. In light of this, in 2021, the International Large Electric Systems Organization (Cirge) issued technical guidelines (TB 841) explicitly pointing out this problem and even no longer recommending DC oscillating waves for testing cross-linked polyethylene (XLPE) cables above 220kV. To address this, Chinese scholars proposed AC oscillating wave technology, using pulse width modulation (PWM) switching frequency converters to overcome the space charge accumulation problem associated with DC oscillating waves. However, PWM generates wideband voltage pulses, and this high-frequency electromagnetic noise highly overlaps with the partial discharge signal spectrum of the test object, severely interfering with the partial discharge measurement of electrical equipment. One proposed solution is to use LC filters and electromagnetic shielding, but high-voltage LC filters are costly and complicate the equipment. The second proposed solution is to use a PWM pause method, which involves pausing the switching action of the power electronic switching devices in the PWM inverter power supply when the voltage rises to its peak value, and completing the partial discharge measurement of the test sample during the subsequent oscillation wave phase. However, this method completely loses the partial discharge information during the voltage rise phase and cannot detect the partial discharge initiation voltage.

[0004] In summary, researching a power cable testing device that can output a short-time AC voltage and eliminate switching noise throughout the entire voltage application process is of significant value. Summary of the Invention

[0005] This invention discloses a power cable testing device based on low-noise, short-time, near-power frequency high-voltage excitation, which can realize partial discharge detection of capacitive test objects of power cables under near-power frequency voltage waveforms. The device has a strong load-carrying capacity, greatly reduces the noise level of the equipment itself, improves the sensitivity of partial discharge detection, and can easily obtain information such as the initiation voltage and extinction voltage of partial discharge.

[0006] This invention relates to a power cable testing device based on low-noise, short-time, near-power frequency high-voltage excitation. It includes a multi-level DC power supply module, a multi-level energy storage module, a forward linear power amplifier module, a reverse linear power amplifier module, an inverter unit, a main unit system, a power amplifier drive module, an inverter unit drive module, a control module, a sampling circuit, a current-limiting resistor, and a resonant reactance. The multi-level DC power supply module converts AC mains voltage into multiple levels of DC voltage to charge the multi-level energy storage module, stopping charging during cable testing. The multi-level energy storage module stores electrical energy and simultaneously acts as a DC voltage source of multiple voltage levels to power subsequent circuits during cable testing. The forward linear power amplifier module outputs a near-power frequency sinusoidal voltage when the output voltage and output current are in a correlated reference direction, improving output power and load capacity. The reverse linear power amplifier module outputs a near-power frequency sinusoidal voltage when the output voltage and output current are in a non-correlated reference direction and can utilize feedback current to charge the multi-level energy storage module, improving efficiency and output power. The inverter unit converts the AC mains voltage into multiple levels of DC voltage to charge the multi-level energy storage module, improving efficiency and output power. The sinusoidal half-wave DC voltage output from the forward and reverse linear power amplifier modules is inverted into a complete sinusoidal AC voltage. The host system monitors the sampled voltage and issues commands to the control and drive modules. The power amplifier drive module generates the drive voltage to control the switching transistors in the forward and reverse linear power amplifier modules. The inverter unit drive module generates the drive voltage to control the switching transistors in the inverter unit. The control module controls the drive modules and adjusts the control strategy based on the data from the sampling circuit. The sampling circuit collects the output voltage and current of the forward and reverse linear power amplifier modules. The current-limiting resistor limits the output circuit current. The resonant reactance forms a resonant circuit with the equivalent capacitance Cx of the cable load.

[0007] The multi-level DC power supply module consists of an isolation transformer, a rectifier circuit, a charging current-limiting resistor, a voltage-stabilizing capacitor, and 12 DC-DC converter circuits. The output voltage of the 12 DC-DC converter circuits is determined based on an immune genetic algorithm that comprehensively considers power efficiency and cost, resulting in 12 levels of DC voltage. The output voltage ratio of each DC-DC converter circuit is 78:42:33:30:26:24:21:20:18:15:13:10. This module can charge the multi-level energy storage module to the target voltage within 10s-20s through the current-limiting resistor.

[0008] The multilevel energy storage module consists of multiple large-capacity capacitors connected in series and parallel, providing 12 different levels of DC voltage nodes. The voltage of each voltage node is determined by the ratio of the output voltages of each DC-DC conversion circuit in the multilevel DC power supply module.

[0009] The positive linear power amplifier module consists of 12 emitter followers. Each emitter follower consists of an NPN channel IGBT and its auxiliary circuitry. The collector of each IGBT is connected to the corresponding DC voltage node in the multi-level energy storage module via an anti-backflow diode. The emitter of each IGBT is connected to the high-voltage terminal of the inverter unit.

[0010] The inverting linear power amplifier module consists of 12 emitter followers. Each emitter follower consists of a PNP channel MOSFET and its auxiliary circuit. The source of each MOSFET is connected to the corresponding DC voltage node in the multi-level energy storage module via an anti-backflow diode. The drain of each MOSFET is connected to the high-voltage terminal of the inverter unit.

[0011] The inverter unit is composed of an inverter full bridge consisting of 4 IGBTs. The high-voltage end is connected to the output ends of the forward linear power amplifier module and the reverse linear power amplifier module, and the low-voltage end is grounded.

[0012] The control module is implemented using an FPGA as the main control board. Combined with a driver board and a digital-to-analog converter, it generates adjustable sinusoidal half-wave power amplifier drive voltage signals to control the forward and reverse linear power amplifier modules, as well as inverter unit drive voltage signals with the same period as the sinusoidal half-wave. When each sinusoidal half-wave enters the next cycle, the inverter unit drive voltage signal controls the inverter full-bridge to switch the output voltage polarity. During the series resonant cable test, the frequency of the sinusoidal half-wave is equal to twice the natural resonant frequency of the load equivalent capacitance Cx and the resonant reactance L. The natural resonant frequency is equal to...

[0013] The power amplifier driver module consists of a digital-to-analog converter, a power amplifier circuit, an amplitude amplifier circuit, and a 12-channel hierarchical control circuit. It is divided into a forward linear power amplifier module hierarchical driver module and a reverse linear power amplifier module hierarchical driver module. The hierarchical control circuit in the forward linear power amplifier module hierarchical driver module consists of a PNP channel transistor and its auxiliary circuit, while the hierarchical control circuit in the reverse linear power amplifier module hierarchical driver module consists of an NPN channel transistor and its auxiliary circuit.

[0014] Compared with the prior art, the present invention has the following beneficial technical effects:

[0015] 1. The present invention provides a power cable testing device based on low-noise short-time near-power frequency high-voltage excitation. It adopts the principle of linear power amplifier circuit, which eliminates the problem of switching noise, greatly reduces the noise level of the power cable testing equipment with near-power frequency high-voltage excitation, and improves the sensitivity of partial discharge detection.

[0016] 2. The present invention provides a power cable testing device based on low-noise short-time near-power frequency high-voltage excitation. This device can output a near-power frequency voltage with a peak value of up to the specified test voltage within a short time of no more than 1 second. During the voltage rise phase, the partial discharge initiation voltage can be determined, and during the voltage fall phase, the partial discharge extinction voltage can be determined.

[0017] 3. The present invention provides a power cable testing device based on low-noise short-time near-power frequency high-voltage excitation. The device uses capacitor energy storage to ensure that the system no longer relies on large-capacity generators or external power sources.

[0018] 4. This invention designs a power cable testing device based on low-noise short-time near-power frequency high-voltage excitation. It uses IGBTs with a wide linear operating range as power amplification devices, which greatly improves the output power of the device. Furthermore, the output power of the device is further improved by parallel connection of IGBTs. It has strong scalability and is easy to modularize. Attached Figure Description

[0019] The above is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0020] Figure 1 This is a schematic diagram of the overall structure of a power cable testing device based on low-noise, short-time, near-power frequency high-voltage excitation according to the present invention.

[0021] Figure 2 This is a circuit diagram of a power cable testing device based on low-noise, short-time, near-power frequency high-voltage excitation according to the present invention.

[0022] Figure 3 This is the output voltage waveform diagram of a power cable testing device based on low-noise, short-time, near-power frequency high-voltage excitation according to the present invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to the accompanying drawings:

[0024] A power cable testing device based on low-noise, short-time, near-power frequency high-voltage excitation includes: a multi-level DC power supply module, a multi-level energy storage module, a forward linear power amplifier module, a reverse linear power amplifier module, an inverter unit, a host system, a power amplifier drive module, an inverter unit drive module, a control module, a sampling circuit, a current-limiting resistor R, and a resonant reactance L.

[0025] like Figure 2 As shown, the multilevel energy storage module consists of 12 capacitors C1 to C12 connected in series. Each capacitor is composed of multiple large-value capacitors connected in parallel to increase its capacitance. The capacitance of C1 to C12 is 7.5mF. One end of capacitor C1 is grounded. The node voltage between adjacent capacitors is determined by the multilevel DC power supply module, which is E1 to E12 respectively.

[0026] In the forward linear power amplifier module, NPN channel IGBT switches Sz1 to Sz12 are all connected in reverse parallel with diodes. The collectors of IGBT switches Sz1 to Sz12 are respectively connected to the negative terminals of anti-backflow diodes Dz1 to Dz12, and the positive terminals of anti-backflow diodes Dz1 to Dz12 are respectively connected to voltage nodes E1 to E12. The emitters of IGBT switches Sz1 to Sz12 are all connected to the collectors of IGBT switches Sn1 and Sn3 in the inverter unit, and the collectors of IGBT switches Sn1 and Sn3 are connected together. The gates of IGBT switches Sz1 to Sz12 are respectively connected to the PNP channel via gate drive resistors Rg1 to Rg12. The collectors and emitters of transistors Jz1 to Jz12 are all connected to the driving voltage Ut. The bases are connected to the anodes of current-limiting diodes Dx1 to Dx12 via current-limiting resistors Rz1 to Rz12. The anodes of current-limiting diodes Dx1 to Dx12 are connected to voltage nodes GND to E11. The cathodes of clamping diodes Dw1 to Dw12 are connected to the gates of IGBT switches Tp1 to Tp12, and the anodes are connected to the collectors of IGBT switches Sn1 and Sn3. The discharge resistors Rw1 to Rw12 are connected in parallel across the gate and collector of IGBT switches Sz1 to Sz12.

[0027] In the reverse linear power amplifier, PNP channel MOSFET switches Sf1-Sf12 are all connected in reverse parallel with diodes. The drains of MOSFET switches Sf1-Sf12 are connected to the anodes of anti-backflow diodes Df1-Df12, respectively, and the cathodes of anti-backflow diodes Df1-Df12 are connected to voltage nodes GND-E11. The sources of MOSFET switches Sf1-Sf12 are connected to the collectors of IGBT switches Sn1 and Sn3 in the inverter unit. The gates are connected to the collectors of NPN channel transistors Jf1-Jf12 via gate drive resistors Rg13-Rg24, respectively. The emitters of f1 to Jf12 are all connected to the driving voltage Ut, and their bases are connected to the negative terminals of current-limiting diodes Dx13 to Dx24 via transistor current-limiting resistors Rp13 to Rp24, respectively. The positive terminals of current-limiting diodes Dx13 to Dx24 are connected to voltage nodes E1 to E12, respectively. The positive terminals of clamping diodes Dw13 to Dw24 are connected to the gates of MOSFET switches Sf1 to Sf12, respectively, and their negative terminals are connected to the collectors of IGBT switches Sn1 and Sn3, respectively. The discharge resistors Rw13 to Rw24 are connected in parallel across the gate and collector terminals of MOSFET switches Sf1 to Sf12, respectively.

[0028] The specific models of IGBT switches Sz1-Sz12 and Sn1-Sn4 are all MG200HF12MRC2, which are IGBT modules with anti-parallel diodes, and the maximum output current reaches 300A. Each IGBT module consists of two IGBTs connected in series. Switches Sz1-Sz12 each use an independent IGBT module, and only one IGBT switch is used in the module. Switches Sn1 and Sn2 use one IGBT module, and switches Sn3 and Sn4 use another IGBT module. The specific models of MOSFET switches Sf1-Sf12 are all IXF. The N82N60P transistor features an anti-parallel diode with a maximum output current of 82A. Backflow prevention diodes Dz1-Dz12 and Df1-Df12 are all MF300C06F2, with a forward current of 300A. PNP channel transistors Jz1-Jz12 are STN9360, and NPN channel transistors Jf1-Jf12 are FJPF5027OTU. Clamping diodes Dw1-Dw24 are 15V Zener diodes (model 2EZ15D5), and current-limiting diodes Dx1-Dx24 are SFR12S20T. Discharge resistors Rw1-Rw24 are all 20kΩ, used to discharge stray capacitance voltage from the switching transistors. Transistor current-limiting resistors Rp1-Rp24 are all 20kΩ, and gate drive resistors Rg1-Rg24 are all 10Ω.

[0029] The FPGA is programmed to output a frequency-adjustable sinusoidal half-wave digital signal, which is then converted into a 0-5V sinusoidal half-wave analog voltage signal by a digital-to-analog converter. This analog voltage signal is amplified by a power amplifier circuit to increase its output power, and then amplified by an amplitude amplifier circuit to obtain the drive voltage Ut for the forward and reverse linear power amplifiers. Ut is a sinusoidal half-wave voltage with a maximum amplitude of 600V. The power amplifier circuit consists of the power amplifier chip OPA541 and its auxiliary circuits, while the amplitude amplifier circuit consists of the NPN channel transistor FJPF5027OTU and its auxiliary circuits. The drive signals Us and Ut of the inverter unit are kept synchronized, and their polarity is reversed when the sinusoidal half-wave Ut crosses zero.

[0030] A sinusoidal half-wave drive voltage Ut is connected in series with a 6V DC voltage source to offset the on-state voltage drop of the IGBT, so as to avoid crossover distortion in the output voltage.

[0031] The current-limiting diodes Dx1-Dx12, the current-limiting resistors Rz1-Rz12, the transistors Jz1-Jz12, and the gate drive resistors Rg1-Rg12 form a 12-channel hierarchical control circuit for the forward linear power amplifier. The current-limiting diodes Dx13-Dx24, the current-limiting resistors Rf1-Rf12, the transistors Jf1-Jf12, and the gate drive resistors Rg13-Rg24 form a 12-channel hierarchical control circuit for the reverse linear power amplifier. For the forward linear power amplifier, as the voltage Ut increases, when it exceeds voltages GND to E11 respectively, transistors Jz1-Jz12 conduct sequentially, and IGBT switches Sz1-Sz12 enter the linear conduction region sequentially. However, only the last IGBT switch to enter the linear conduction region has current flowing through it. For the reverse linear power amplifier, the switching states are the same as in the forward power amplifier, but it only functions when the output voltage and output current are in non-associated reference directions.

[0032] The DC voltage provided by the multilevel energy storage module, together with the positive linear power amplifier and its driving signal Ut, forms an emitter follower. Therefore, the power amplifier emitter output voltage is the same as Ut. After being inverted by the inverter unit, the output voltage is a sinusoidal near-power frequency voltage with the same amplitude as Ut.

[0033] During cable testing, a multi-level DC power supply module is first used to charge the multi-level energy storage module until the target voltage is reached, at which point the preceding multi-level DC power supply module is disconnected. At this time, the FPGA-controlled drive circuit generates drive voltages Ut for the forward and reverse linear power amplifiers with small amplitudes, as well as drive voltage Us for the inverter unit. Due to the presence of the reverse linear power amplifier, the device provides a reverse current path when driving non-purely resistive loads, exhibiting a strong ability to drive such loads. The sinusoidal half-wave drive voltage Ut, with a frequency of 2f, can generate a sinusoidal voltage with a frequency of f on the load, where f is close to the power frequency. The frequency f is continuously adjusted to equal the resonant frequency of the load circuit. At this time, the amplitude of the driving voltage Ut is increased to induce a near-power frequency high voltage on the load cable. During the charging process, the voltage across the capacitors that are in the power supply state in the multi-level energy storage module keeps decreasing. When E(i-1)<Ut<Ei (i=1,2...12), capacitors C1 to Ci are all in the power supply state, and the node potentials E1 to Ei are all in a decreasing state. Only when the highest potential E12 in the multi-level energy storage module is less than Ut, the device cannot maintain the sinusoidal voltage output with the amplitude of Ut, and a saturation phenomenon begins to occur. Therefore, in order to avoid the occurrence of the saturation phenomenon, the amplitude of the driving voltage Ut is controlled to gradually decrease as the highest potential E12 in the multi-level energy storage module decreases, so that the amplitude of the driving voltage Ut is always less than E12. At this time, the device can output a near-power frequency high voltage excitation for cable testing for a short time.

[0034] According to the capacity of the multi-level energy storage module, it can output a near-power frequency sinusoidal voltage with a duration of about 1s, an amplitude of no less than 311V, and a frequency between 30 and 300Hz, as shown in Figure 3 the figure. Since IGBT, which has multiple advantages such as strong current-carrying capacity, good heat dissipation performance, and wide linear operating region, is used as the power amplification device, the output power can reach hundreds of kilowatts, which can meet the high-voltage test requirements of power cables.

Claims

1. A power cable testing device based on low-noise, short-time, near-power frequency high-voltage excitation, characterized in that... The entire device consists of a multi-level DC power supply module, a multi-level energy storage module, a forward linear power amplifier module, a reverse linear power amplifier module, an inverter unit, a host system, a power amplifier drive module, an inverter unit drive module, a control module, a sampling circuit, a current limiting resistor, and a resonant reactance. The multi-level DC power supply module is used to convert AC mains voltage into DC voltage of multiple levels to charge the multi-level energy storage module, and stops charging during cable testing. The multi-level energy storage module is used to store electrical energy and also serves as a DC voltage source of multiple voltage levels to power subsequent circuits during cable testing. The positive linear power amplifier module is used to output a near-power frequency sinusoidal voltage when the output voltage and output current are in the associated reference direction, thereby improving the output power and load capacity. The reverse linear power amplifier module is used to output a near-power frequency sinusoidal voltage when the output voltage and output current are in non-associated reference directions, and can use the feedback current to charge the multi-level energy storage module, thereby improving efficiency and output power. The inverter unit is used to invert the sinusoidal half-wave DC voltage output from the forward linear power amplifier module and the reverse linear power amplifier module into a complete sinusoidal AC voltage. The host system is used to monitor the sampling voltage and issue commands to the control module and drive module; The power amplifier driver module is used to generate the drive voltage that controls the switching transistors in the forward linear power amplifier module and the reverse linear power amplifier module to turn on and off. The inverter unit drive module is used to generate the drive voltage that controls the switching transistors in the inverter unit to turn on and off. The control module is used to control the drive module and adjust the control strategy according to the data from the sampling circuit. The sampling circuit is used to collect the output voltage and current of the forward linear power amplifier module and the reverse linear power amplifier module. The current-limiting resistor is used to limit the output circuit current; The resonant reactance is used to form a resonant circuit with the equivalent capacitance Cx of the cable load.

2. The power cable testing device based on low-noise, short-time near-power frequency high-voltage excitation according to claim 1, characterized in that... The multi-level DC power supply module consists of an isolation transformer, a rectifier circuit, a charging current-limiting resistor, a voltage-stabilizing capacitor, and 12 DC-DC converter circuits. The output voltage of the 12 DC-DC converter circuits is determined based on an immune genetic algorithm that comprehensively considers power efficiency and cost, resulting in 12 levels of DC voltage. The output voltage ratio of each DC-DC converter circuit is 78:42:33:30:26:24:21:20:18:15:13:

10. This module can charge the multi-level energy storage module to the target voltage within 10s-20s through the current-limiting resistor.

3. The power cable testing device based on low-noise, short-time near-power frequency high-voltage excitation according to claim 1, characterized in that... The multilevel energy storage module consists of multiple large-capacity capacitors connected in series and parallel, providing 12 different levels of DC voltage nodes. The voltage of each voltage node is determined by the ratio of the output voltages of each DC-DC conversion circuit in the multilevel DC power supply module.

4. The power cable testing device based on low-noise, short-time near-power frequency high-voltage excitation according to claim 1, characterized in that... The positive linear power amplifier module consists of 12 emitter followers. Each emitter follower consists of an NPN channel IGBT and its auxiliary circuitry. The collector of each IGBT is connected to the corresponding DC voltage node in the multi-level energy storage module via an anti-backflow diode. The emitter of each IGBT is connected to the high-voltage terminal of the inverter unit.

5. The power cable testing device based on low-noise, short-time near-power frequency high-voltage excitation according to claim 1, characterized in that... The inverting linear power amplifier module consists of 12 emitter followers. Each emitter follower consists of a PNP channel MOSFET and its auxiliary circuit. The source of each MOSFET is connected to the corresponding DC voltage node in the multi-level energy storage module via an anti-backflow diode. The drain of each MOSFET is connected to the high-voltage terminal of the inverter unit.

6. The power cable testing device based on low-noise short-time near-power frequency high-voltage excitation according to claim 1, characterized in that... The inverter unit is composed of an inverter full bridge consisting of 4 IGBTs. The high-voltage end is connected to the output ends of the forward linear power amplifier module and the reverse linear power amplifier module, and the low-voltage end is grounded.

7. The power cable testing device based on low-noise, short-time near-power frequency high-voltage excitation according to claim 1, characterized in that... The control module is implemented using an FPGA as the main control board. Combined with a driver board and a digital-to-analog converter, it generates adjustable sinusoidal half-wave power amplifier drive voltage signals to control the forward and reverse linear power amplifier modules, as well as inverter unit drive voltage signals with the same period as the sinusoidal half-wave. When each sinusoidal half-wave enters the next cycle, the inverter unit drive voltage signal controls the inverter full-bridge to switch the output voltage polarity. During the series resonant cable test, the frequency of the sinusoidal half-wave is equal to twice the natural resonant frequency of the load equivalent capacitance Cx and the resonant reactance L. The natural resonant frequency is equal to...

8. The power cable testing device based on low-noise short-time near-power frequency high-voltage excitation according to claim 1, characterized in that... The power amplifier driver module consists of a digital-to-analog converter, a power amplifier circuit, an amplitude amplifier circuit, and a 12-channel hierarchical control circuit. It is divided into a forward linear power amplifier module hierarchical driver module and a reverse linear power amplifier module hierarchical driver module. The hierarchical control circuit in the forward linear power amplifier module hierarchical driver module consists of a PNP channel transistor and its auxiliary circuit, while the hierarchical control circuit in the reverse linear power amplifier module hierarchical driver module consists of an NPN channel transistor and its auxiliary circuit.

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