A valve-side sleeve online monitoring device based on a capacitor voltage division principle

Abstract

The application discloses a valve-side bushing on-line monitoring device based on a capacitor voltage division principle, and belongs to the technical field of electric power, comprising a voltage divider FYQ and a monitor CJY, and solves the technical problem of real-time on-line collection of key insulation parameters such as leakage current and partial discharge in the operation process of the valve-side bushing. The application adopts the capacitor voltage division principle, and the output signal has no angle difference with the primary voltage, thereby significantly improving the measurement precision of dielectric loss and capacitance. The integrated current and high-frequency partial discharge signal collection can realize comprehensive evaluation of the insulation health state of the bushing. Through real-time monitoring of the leakage current and the partial discharge, insulation degradation and hidden danger development trends can be captured in time. The voltage divider is a passive device, has good insulation isolation capacity, and is additionally provided with a voltage-dependent resistor and a TVS protection at the end screen, so that abnormal voltage damage to equipment can be prevented. The monitoring device can be quickly connected to an existing electric power automation system through Ethernet / optical fiber communication, and supports remote data transmission and background analysis.

Description

Technical Field

[0001] This invention belongs to the field of power technology, and in particular relates to an online monitoring device for valve-side bushings based on the principle of capacitive voltage division. Background Technology

[0002] Converter transformer bushings are key equipment connecting ultra-high voltage / extra-high voltage direct current (UHVDC) transmission lines to AC transmission lines, and their safety and reliability directly affect the stable operation of the DC transmission system. In actual operation, the converter transformer valve-side bushings are subjected to multiple stresses, including electrical, thermal, and mechanical stresses, making them one of the components most prone to failure. Once an accident occurs, not only will a long-term shutdown for maintenance be required, resulting in huge economic losses, but in severe cases, it may also damage surrounding power equipment, expanding direct and indirect losses. Therefore, their safety and reliability have always been a focus of attention in the industry.

[0003] Structurally, there are two main types of main insulation structures for converter transformer valve-side bushings: epoxy sleeve SF6 gas insulation and epoxy core solid insulation. Among them, dry-type converter transformer bushings, due to their oil-free characteristics, better meet the oil-free requirements of valve halls and are widely used in many converter stations. Dry-type bushings typically use a capacitor core wound with dry-state corrugated paper as the main insulation. Aluminum foil is sandwiched between the layers of the capacitor core to form multiple capacitor screens. The core is impregnated with epoxy resin under vacuum drying conditions, cured, machined, and then surface-coated. This type of epoxy-impregnated paper bushing has advantages such as stable electrical performance, good explosion-proof performance, small size, and light weight.

[0004] In terms of operating environment, dry bushings used as converter transformer bushings must withstand both AC and DC components simultaneously. Under the combined AC and DC electric field, their insulation performance faces severe challenges. Currently, conventional valve-side bushing testing relies on offline tests under power-off conditions: voltage is applied to the bushing taps using experimental instruments to measure parameters such as leakage current, dielectric loss, capacitance, and partial discharge, thereby assessing the bushing condition.

[0005] The shortcomings of existing technology are:

[0006] Lack of effective online monitoring methods: There is no effective online monitoring technology for the operating status of valve-side bushings in the field, making it impossible to capture key characteristics of the insulation degradation process in real time and difficult to achieve early warning.

[0007] There are blind spots in the operational status assessment: Since the tap voltage of the valve side bushing cannot be directly measured during operation, its core status parameters (such as dielectric loss and partial discharge reflecting the insulation status) are difficult to obtain under energized conditions. Therefore, it is impossible to accurately assess the health status of the bushing under actual operating conditions. The assessment can only rely on the results of power outage tests, which results in an assessment lag. Summary of the Invention

[0008] The purpose of this invention is to provide an online monitoring device for valve side bushings based on the principle of capacitive voltage division, which solves the technical problem of real-time online acquisition of key insulation parameters such as leakage current and partial discharge during the operation of valve side bushings.

[0009] To achieve the above objectives, the present invention adopts the following technical solution:

[0010] An online monitoring device for valve-side bushings based on the principle of capacitive voltage division includes a voltage divider FYQ and a monitor CJY;

[0011] The voltage divider FYQ includes capacitor CZ, resistor R1, resistor RV1, TVS transistor GDT1, resistor R2, resistor RV2, TVS transistor GDT2, resistor R3, interface IN+, interface IN-, interface X1, and interface X4.

[0012] Pin 1 of capacitor CZ is connected to interface IN+ via resistor R1, and pin 2 is connected to interface IN-. The two ends of resistor RV1 are connected to interface IN+ and interface IN- respectively. TVS transistor GDT1 is connected in parallel with resistor RV1, and resistor R2 is connected in parallel with TVS transistor GDT1. The node where resistor R2 is connected to interface IN+ is connected to interface X1. One end of resistor R3 is connected to interface X4, and the other end is connected to interface IN-. TVS transistor GDT2 is connected in parallel with resistor R3, and resistor RV2 is connected in parallel with TVS transistor GDT2.

[0013] Interface IN+ and interface IN- are respectively connected to the end screen tap and end screen ground wire of the external valve side bushing;

[0014] The monitor CJY includes a current sensor T1, a partial discharge sensor T2, a first sampling resistor, a second sampling resistor, a first amplification circuit, a second amplification circuit, an AD chip, a main control chip, a power supply module, an Ethernet communication module, and an optical fiber communication module. The current sensor T1 is connected to the first sampling resistor, which is connected to the first amplification circuit. The partial discharge sensor T2 is connected to the second sampling resistor, which is connected to the second amplification circuit. Both the first and second amplification circuits are connected to the AD chip. The AD chip, the Ethernet communication module, and the optical fiber communication module are all connected to the main control chip.

[0015] The power supply module provides power to the current sensor T1, the partial discharge sensor T2, the first sampling resistor, the second sampling resistor, the first amplifier circuit, the second amplifier circuit, the AD chip, the main control chip, the Ethernet communication module, and the fiber optic communication module.

[0016] Current sensor T1 and partial discharge sensor T2 are used to collect the current signal and partial discharge signal output from the X1 interface and X4 interface of voltage divider FYQ, respectively.

[0017] Preferably, the current sensor T1 is a current transmitter, the partial discharge sensor T2 is a current transmitter, and both the current sensor T1 and the partial discharge sensor T2 are through-hole current transformers. The interface X1 of the voltage divider FYQ is connected to the interface X4 of the voltage divider FYQ by passing a wire through the primary wire hole of the current sensor T1 and the primary wire hole of the partial discharge sensor T2 in sequence.

[0018] Preferably, the capacitor CZ is a thin-film capacitor.

[0019] Preferably, both resistors RV1 and RV2 are varistors.

[0020] Preferably, the capacitor CZ is model B32671L8222K000; the current sensor T1 and the partial discharge sensor T2 are both model MIK-DJI-50A-K; the first amplifier circuit and the second amplifier circuit are both model AD822A and their peripheral circuits; the AD chip is model AD620; the main control chip is model STM32F407VGT6; the Ethernet communication module is model W5500; and the fiber optic communication module is model HFBR-2521Z / 1521Z fiber optic transceiver.

[0021] This invention discloses an online monitoring device for valve-side bushings based on the capacitive voltage divider principle. It solves the technical problem of real-time online acquisition of key insulation parameters such as leakage current and partial discharge during valve-side bushing operation. The invention employs the capacitive voltage divider principle, ensuring no angle difference between the output signal and the primary voltage, significantly improving the measurement accuracy of dielectric loss and capacitance. It integrates current and high-frequency partial discharge signal acquisition to achieve a comprehensive assessment of the bushing insulation health status. By monitoring leakage current and partial discharge in real time, it promptly detects insulation degradation and potential hazard development trends. The voltage divider is a passive device with excellent insulation isolation capabilities. Simultaneously, a varistor and TVS protection are added to the end screen to prevent damage to the equipment from abnormal voltage. The monitoring device can be quickly connected to existing power automation systems via Ethernet / fiber optic communication, supporting remote data transmission and backend analysis. Attached Figure Description

[0022] Figure 1 This is the circuit diagram of the voltage divider FYQ of the present invention;

[0023] Figure 2 This is a block diagram of the CJY monitor of the present invention;

[0024] Figure 3 This is a schematic diagram illustrating the principle of dielectric loss measurement in this invention;

[0025] Figure 4 This is a circuit diagram of the first sampling resistor, the first amplifier circuit, and the AD chip of the present invention. Detailed Implementation

[0026] Depend on Figures 1-4 The device shown is an online monitoring device for valve side bushing based on the principle of capacitive voltage division, including a voltage divider FYQ and a monitor CJY;

[0027] In this embodiment, a capacitor voltage divider FYQ is installed on the lead-out line of the bushing end screen on the converter valve side. The high-voltage signal is passively converted into a low-voltage signal according to the principle of capacitor voltage division, thereby extracting the AC component of the operating voltage inside the bushing. The monitor CJY collects and processes the output signal of the voltage divider, the current leakage signal and the partial discharge signal to realize real-time monitoring and early warning of the bushing insulation status.

[0028] The voltage divider FYQ includes capacitor CZ, resistor R1, resistor RV1, TVS transistor GDT1, resistor R2, resistor RV2, TVS transistor GDT2, resistor R3, interface IN+, interface IN-, interface X1, and interface X4.

[0029] The FYQ voltage divider is built on the principle of capacitive voltage division. It divides the voltage signal from the valve-side bushing end screen to ground through the high-voltage arm (bushing capacitor) and the low-voltage arm (capacitor CZ) and outputs it to interfaces X1 and X4. The entire voltage divider is a passive structure, does not rely on power supply, avoids introducing excitation errors, and effectively restores the true transient waveform of the primary voltage.

[0030] The capacitor CZ is a film capacitor. Pin 1 of the capacitor CZ is connected to interface IN+ through resistor R1, and pin 2 is connected to interface IN-. The two ends of resistor RV1 are connected to interface IN+ and interface IN- respectively. TVS diode GDT1 is connected in parallel with resistor RV1, and resistor R2 is connected in parallel with TVS diode GDT1. The node where resistor R2 is connected to interface IN+ is connected to interface X1. One end of resistor R3 is connected to interface X4, and the other end is connected to interface IN-. TVS diode GDT2 is connected in parallel with resistor R3, and resistor RV2 is connected in parallel with TVS diode GDT2.

[0031] Both resistors RV1 and RV2 are varistors.

[0032] In this embodiment, a varistor and a TVS diode are connected in parallel between the voltage divider's final screen and ground to effectively prevent surges caused by a broken final screen or induced high voltage during operation. The protection circuit is as follows: Figure 1 As shown in the diagram. According to the schematic diagram of the voltage divider, U1 is the tap voltage, i.e., Vin, X1 and X4 are the output terminals, and their output voltage is Vo. C1 is the equivalent capacitance of the bushing, and CZ is the voltage divider capacitor. According to the voltage divider principle of capacitors: Vo / Vin=C1 / (C1+CZ).

[0033] Capacitor CZ is a precision thin-film capacitor, whose low temperature drift and high linearity characteristics ensure the accuracy of capacitor voltage division. R1, R2, and R3 form an auxiliary impedance path, which, together with varistors RV1 and RV2 and gas discharge tubes GDT1 and GDT2, constitutes the protection circuit on the end screen side. It can effectively suppress overvoltage and protect the safe operation of the device in abnormal situations such as end screen disconnection and surge.

[0034] Varistors RV1 and RV2 are in a high-resistance state during normal operation. When an overvoltage transient occurs in the circuit, their resistance drops sharply, realizing the instantaneous discharge function, thereby protecting the output circuit of the voltage divider from damage by overvoltage impact.

[0035] Interface IN+ and interface IN- are respectively connected to the end screen tap and end screen ground wire of the external valve side bushing;

[0036] IN+ is connected to the tap at the end of the bushing screen, and IN- is connected to the ground wire of the end screen, forming a complete high- and low-voltage connection path for the voltage divider. This wiring method ensures accurate sampling of the bushing's operating voltage and forms a complete capacitive voltage divider network for voltage extraction.

[0037] In this embodiment, the voltage divider housing is made of aluminum, and a sealing strip is used between the upper and lower covers of the voltage divider. The overall protection level reaches IP66. The end screen tap and the voltage divider capacitor are connected in parallel by two 4mm² wires to ensure the reliability of the end screen connection while ensuring current flow. The voltage divider capacitor is a high-precision, low-temperature drift film capacitor to ensure the accuracy of voltage division.

[0038] The monitor CJY includes a current sensor T1, a partial discharge sensor T2, a first sampling resistor, a second sampling resistor, a first amplification circuit, a second amplification circuit, an AD chip, a main control chip, a power supply module, an Ethernet communication module, and an optical fiber communication module. The current sensor T1 is connected to the first sampling resistor, which is connected to the first amplification circuit. The partial discharge sensor T2 is connected to the second sampling resistor, which is connected to the second amplification circuit. Both the first and second amplification circuits are connected to the AD chip. The AD chip, the Ethernet communication module, and the optical fiber communication module are all connected to the main control chip.

[0039] The CJY monitor performs multi-channel synchronous acquisition of the voltage signal, leakage current, and partial discharge signal from the voltage divider output. T1 and T2 are through-hole current transformers, which acquire the operating frequency and high-frequency components through wire coupling; the sampling resistor converts the signal into voltage, which is then amplified by the AD620 amplifier with high common-mode rejection ratio, and then converted by the AD620 through high-speed multi-channel A / D conversion before being sent to the STM32 main control chip for processing and communication.

[0040] The current sensor T1 is a current transmitter, the partial discharge sensor T2 is a current transmitter, and both the current sensor T1 and the partial discharge sensor T2 are through-hole current transformers. The interface X1 of the voltage divider FYQ is connected to the interface X4 of the voltage divider FYQ by passing a wire through the primary wire hole of the current sensor T1 and the primary wire hole of the partial discharge sensor T2 in sequence.

[0041] By sequentially passing the wires from X1 to X4 through T1 and T2, simultaneous non-contact induction acquisition of leakage current (power frequency component) and partial discharge (high frequency component) is achieved. The through-hole structure simplifies the installation process, enhances the system's anti-interference capability, and ensures the synchronous acquisition and transmission of multiple parameters.

[0042] The power supply module provides power to the current sensor T1, the partial discharge sensor T2, the first sampling resistor, the second sampling resistor, the first amplifier circuit, the second amplifier circuit, the AD chip, the main control chip, the Ethernet communication module, and the fiber optic communication module.

[0043] The power module is model LDE02-23B05.

[0044] Current sensor T1 and partial discharge sensor T2 are used to collect the current signal and partial discharge signal output from the X1 interface and X4 interface of voltage divider FYQ, respectively.

[0045] In practical use, T1 is used to sense the power frequency leakage current (reflecting dielectric loss), and T2 is used to detect high-frequency pulses (reflecting partial discharge activity).

[0046] The system is powered by an industrial-grade DC-DC isolated power supply module, providing 5V or ±15V multiple outputs to drive the analog front-end sampling circuit, AD conversion module and main control communication module respectively, ensuring clean and stable power supply and that the signals of each channel are not affected by power supply noise.

[0047] The amplitude and direction of the leakage current reflect changes in the conductivity of the bushing medium, while the partial discharge signal reflects localized breakdown phenomena inside or on the surface of the insulation. By jointly analyzing the output signals of T1 and T2, the dielectric loss angle, the number and intensity of partial discharge pulses can be assessed, providing a basis for judging the trend of insulation degradation.

[0048] The capacitor CZ is model B32671L8222K000; the current sensor T1 and the partial discharge sensor T2 are both model MIK-DJI-50A-K; the first amplifier circuit and the second amplifier circuit are both model AD822A and their peripheral circuits; the AD chip is model AD620; the main control chip is model STM32F407VGT6; the Ethernet communication module is model W5500; and the fiber optic communication module is model HFBR-2521Z / 1521Z fiber optic transceiver.

[0049] In this embodiment, the signal collected by the current sensor T1 is input to the first amplification circuit through the first sampling resistor. After amplification, it is then input to the AD chip, such as... Figure 4 As shown, in this embodiment, the signal collected by the current sensor T1 is VOUT2. The first sampling resistor is a sampling resistor circuit composed of resistor R148, resistor R136 and capacitor C69. The signal after voltage division by resistors R148 and R136 is input to the first amplifier circuit. The first amplifier circuit is composed of amplifier U24A and amplifier U24B. The signal after voltage division is input to the positive input terminal of amplifier U24A. The negative input terminal of amplifier U24A is connected to the output terminal of amplifier U24A. The signal after voltage division is also sent to the positive input terminal of amplifier U24B. The negative input terminal of amplifier U24B is also connected to the output terminal of amplifier U24B.

[0050] After passing through a voltage divider circuit composed of resistors R144 and R147, the output terminal of amplifier U24A outputs a detection signal VOUT2_1. This signal is a spare signal used for debugging or user-defined purposes.

[0051] The AD chip is chip U26. The output terminal of amplifier U24B is connected to pin 3 of chip U26 through resistor R140. Pin 6 of chip U26 outputs the digital signal after AD conversion and inputs it into the main control chip.

[0052] The overall selection prioritizes high precision, anti-interference, and industrial-grade stability. The B32671L thin-film capacitor ensures voltage division linearity, the AD620 provides high-precision differential amplification, and the AD620 guarantees high-speed and high-precision sampling. The STM32 main controller has strong processing capabilities and supports multiple communication interfaces, enabling remote data upload and fault warning system access.

[0053] In this embodiment, under AC voltage, the current flowing in the dielectric inside the bushing consists of a capacitive component Ic and a resistive component Ir, where Ir is the component generated by the dielectric loss itself. This resistive current component causes a phase shift in the total current relative to the pure capacitive current; the shift angle is called the dielectric loss angle δ, and its tangent tanδ reflects the degree of insulation material loss. Furthermore, tanδ is an intrinsic parameter of the material and is independent of the equipment's geometry. Based on this principle, this invention uses a current sensor T1 to collect the leakage current signal in the voltage divider output circuit and combines it with the power frequency voltage signal for phase analysis. This can be used to approximately assess the change in the dielectric loss factor (tanδ), thereby determining the trend of insulation performance degradation.

[0054] Dielectrics always experience energy loss under voltage, including losses due to conductivity and polarization. The equivalent circuit and vector diagram of a dielectric under alternating current voltage are shown below. Figure 3As shown.

[0055] The equivalent circuit yields:

[0056] ;

[0057] ;

[0058] Where Ir is the active current component, Ic is the capacitive current component, ω is the power supply angular frequency, Cp is the equivalent capacitance of the dielectric, R is the equivalent parameter of the dielectric resistive loss, p is the dielectric loss power, and U is the effective value of the applied AC voltage.

[0059] From the above formulas, it can be seen that dielectric loss is directly proportional to the applied voltage, power supply frequency, dielectric capacitance C, and dielectric loss factor tanδ. When the applied voltage and frequency are constant, dielectric loss is only related to the equivalent capacitance of the dielectric and the dielectric loss factor. For the device under test, the equivalent capacitance is a constant value, therefore tanδ completely reflects the dielectric loss.

[0060] In a vector diagram, the complementary angle between the voltage and current is the dielectric loss angle. For a lossless, ideal dielectric, the dielectric loss angle δ is zero, and the angle between voltage and current is zero. Since actual operating capacitive devices are not ideal dielectrics, the phase difference between the current flowing through the end screen and the high-voltage terminal voltage of the capacitive device will be <π / 2, and the dielectric loss angle δ cannot be zero.

[0061] Meanwhile, the partial discharge sensor T2 is used to capture high-frequency pulse signals, which can effectively identify partial discharge activities in the insulation. Combined with the tanδ index, it can construct a more accurate insulation condition criterion, providing early warning and assessment basis for the operating status of the converter transformer bushing. The power frequency phase is obtained by coupling the reference phase voltage and passing it through a zero-crossing comparator.

[0062] This invention discloses an online monitoring device for valve-side bushings based on the capacitive voltage divider principle. It solves the technical problem of real-time online acquisition of key insulation parameters such as leakage current and partial discharge during valve-side bushing operation. The invention employs the capacitive voltage divider principle, ensuring no angle difference between the output signal and the primary voltage, significantly improving the measurement accuracy of dielectric loss and capacitance. It integrates current and high-frequency partial discharge signal acquisition to achieve a comprehensive assessment of the bushing insulation health status. By monitoring leakage current and partial discharge in real time, it promptly detects insulation degradation and potential hazard development trends. The voltage divider is a passive device with excellent insulation isolation capabilities. Simultaneously, a varistor and TVS protection are added to the end screen to prevent damage to the equipment from abnormal voltage. The monitoring device can be quickly connected to existing power automation systems via Ethernet / fiber optic communication, supporting remote data transmission and backend analysis.

Claims

1. An online monitoring device for valve-side bushings based on the principle of capacitive voltage division, characterized in that: Includes voltage divider FYQ and monitor CJY; The voltage divider FYQ includes capacitor CZ, resistor R1, resistor RV1, TVS transistor GDT1, resistor R2, resistor RV2, TVS transistor GDT2, resistor R3, interface IN+, interface IN-, interface X1, and interface X4. Pin 1 of capacitor CZ is connected to interface IN+ via resistor R1, and pin 2 is connected to interface IN-. The two ends of resistor RV1 are connected to interface IN+ and interface IN- respectively. TVS transistor GDT1 is connected in parallel with resistor RV1, and resistor R2 is connected in parallel with TVS transistor GDT1. The node where resistor R2 is connected to interface IN+ is connected to interface X1. One end of resistor R3 is connected to interface X4, and the other end is connected to interface IN-. TVS transistor GDT2 is connected in parallel with resistor R3, and resistor RV2 is connected in parallel with TVS transistor GDT2. Interface IN+ and interface IN- are respectively connected to the end screen tap and end screen ground wire of the external valve side bushing; The monitor CJY includes a current sensor T1, a partial discharge sensor T2, a first sampling resistor, a second sampling resistor, a first amplification circuit, a second amplification circuit, an AD chip, a main control chip, a power supply module, an Ethernet communication module, and an optical fiber communication module. The current sensor T1 is connected to the first sampling resistor, which is connected to the first amplification circuit. The partial discharge sensor T2 is connected to the second sampling resistor, which is connected to the second amplification circuit. Both the first and second amplification circuits are connected to the AD chip. The AD chip, the Ethernet communication module, and the optical fiber communication module are all connected to the main control chip. The power supply module provides power to the current sensor T1, the partial discharge sensor T2, the first sampling resistor, the second sampling resistor, the first amplifier circuit, the second amplifier circuit, the AD chip, the main control chip, the Ethernet communication module, and the fiber optic communication module. Current sensor T1 and partial discharge sensor T2 are used to collect the current signal and partial discharge signal output from the X1 interface and X4 interface of voltage divider FYQ, respectively.

2. The valve-side bushing online monitoring device based on the capacitive voltage division principle as described in claim 1, characterized in that: The current sensor T1 is a current transmitter, the partial discharge sensor T2 is a current transmitter, and both the current sensor T1 and the partial discharge sensor T2 are through-hole current transformers. The interface X1 of the voltage divider FYQ is connected to the interface X4 of the voltage divider FYQ by passing a wire through the primary wire hole of the current sensor T1 and the primary wire hole of the partial discharge sensor T2 in sequence.

3. The valve-side bushing online monitoring device based on the capacitive voltage division principle as described in claim 1, characterized in that: The capacitor CZ is a thin-film capacitor.

4. The valve-side bushing online monitoring device based on the capacitive voltage division principle as described in claim 1, characterized in that: Both resistors RV1 and RV2 are varistors.

5. The valve-side bushing online monitoring device based on the capacitive voltage division principle as described in claim 1, characterized in that: The capacitor CZ is model B32671L8222K000; the current sensor T1 and the partial discharge sensor T2 are both model MIK-DJI-50A-K; the first amplification circuit and the second amplification circuit are both composed of AD822A amplifier and its peripheral circuits; the AD chip is model AD620; the main control chip is model STM32F407VGT6; the Ethernet communication module is model W5500; and the fiber optic communication module is model HFBR-2521Z / 1521Z fiber optic transceiver.

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