Method for measuring oil gap insulation characteristics of on-load tap-changer under high frequency

Abstract

The invention discloses a method for measuring the oil gap insulation characteristic of an on-load tap-changer under high frequency, and belongs to the technical field of electrical equipment monitoring and fault diagnosis. Comprising the following steps: arranging an on-load tap-changer between a high-voltage winding and a neutral point or between a network side winding and the neutral point; building an ultrahigh frequency monitoring system, and carrying out on-load tap-changer switching discharge monitoring and contact gap insulating oil partial discharge monitoring; a partial discharge detector is used for carrying out partial discharge monitoring on insulation oil degradation of the on-load tap-changer; and two-dimensional electric field measurement is carried out through a Kerr effect method. The on-load tap-changer main contact switching discharge process is monitored, the time domain waveform is obtained, and an effective monitoring means is provided for analyzing the discharge phenomenon in the switching process.

Description

Technical Field

[0001] This invention relates to the field of electrical equipment monitoring and fault diagnosis technology, and in particular to a method for measuring the oil gap insulation characteristics of on-load tap changers at high frequencies. Background Technology

[0002] With the rapid development of my country's power industry and its continuous transformation, the structure of the power system has become increasingly complex, and the voltage levels, equipment capacity, and grid scale of power equipment have also increased accordingly. Under this new development context, the safety and stability of the power system have become increasingly prominent, and faults in power equipment themselves have caused serious economic losses and negative social impacts. Therefore, adopting effective measures for online monitoring and fault diagnosis of the operating status of power equipment is of great significance for improving the safety and reliability of the power system.

[0003] In recent years, OLTCs have become widely used in power systems. Developed countries have adopted on-load tap changers for transformers with a capacity of 10MVA and above. Currently, many 110kV and above transformers in my country have also installed OLTCs. As of July 2022, my country had put into operation 16 UHVDC projects, with over 1,600 converter transformer OLTCs in operation and over 40,000 OLTCs on 110kV and above power transformers. With the significant increase in voltage regulation frequency, the number of faults has also increased accordingly. OLTC faults mainly include mechanical and electrical faults. Electrical faults include local overheating and discharge caused by poor contact, oil gap breakdown caused by foreign objects carried by oil flow to high field strength areas, and partial discharge caused by deterioration of insulating oil. Mechanical faults include drive shaft breakage, insufficient spring energy storage (wear or breakage), loose drive disc, switch slippage caused by operating mechanism failure, drive mechanism jamming, and loose fasteners. In past statistics, OLTC faults accounted for approximately 20% of transformer faults in my country. On the one hand, OLTCs have a precise and complex mechanical structure. Switching requires the precise coordination of multiple mechanical components, including drive mechanisms, transmission mechanisms, tap selectors, and switching switches. During operation, they are simultaneously subjected to the combined effects of multiple factors such as electricity, heat, and magnetism. Furthermore, their switching actions are frequent, occurring approximately 10-20 times per day. This harsh operating environment makes their mechanical parts prone to wear, jamming, breakage, and other malfunctions. On the other hand, although OLTCs have passed rigorous type and factory tests, potential quality issues in manufacturing, transportation, installation, and handover processes can still pose hidden dangers to their operation.

[0004] In addition, engineering practice shows that conductive particles and moisture are important causes of the deterioration of the insulating oil in the OLTC switching chamber. Conductive particles mainly include metal particles generated during manufacturing, transportation, and installation due to long-term switching wear and ablation of the OLTC contacts, as well as carbide particles generated by the cracking of the insulating oil, with metal particles being the predominant component. Excessive moisture is mainly due to insufficient drying or poor sealing of the OLTC on-site. Conductive particles carried by the oil flow into the strong field area of ​​the switching chamber contacts, as well as severe moisture in the insulating oil, will cause partial discharge in the OLTC switching chamber, and may even cause breakdown leading to inter-stage short circuit faults.

[0005] Therefore, a method for measuring the oil gap insulation characteristics of on-load tap changers at high frequencies is needed to quickly detect internal faults in the tap changers and improve the safety and efficiency of tap changer operation. Summary of the Invention

[0006] The purpose of this invention is to provide a method for measuring the oil gap insulation characteristics of on-load tap changers at high frequencies, comprising the following steps:

[0007] A load tap changer is installed between the high-voltage winding and the neutral point or between the grid-side winding and the neutral point.

[0008] A high-frequency monitoring system was established to monitor discharge during on-load tap changer switching and partial discharge of insulating oil in contact gaps.

[0009] Partial discharge monitoring of on-load tap changer insulating oil deterioration using a partial discharge detector;

[0010] Two-dimensional electric field measurement was performed using the Kerr effect method.

[0011] Furthermore, the detection sensitivity of the partial discharge detector is 0.01 pC.

[0012] Furthermore, the two-dimensional electric field measurement specifically involves applying a modulated electric field while simultaneously applying a DC electric field.

[0013] Furthermore, the on-load tap changer includes a drive and transmission mechanism, a switching switch, and a tap selector.

[0014] Furthermore, the phase difference generated by the combined action of the DC electric field and the modulation electric field is:

[0015] Δθ=2πBL(E dc +E ac sinωt) 2 ,

[0016] Where B is the Kerr constant, L is the length of the electric field region through which the beam passes, and E dc It is a direct current electric field, E ac It is the modulated electric field, ω is the angular frequency, and t is the time.

[0017] The beneficial effects of this invention are as follows:

[0018] 1. An ultra-high frequency monitoring system (including ultra-high frequency sensors, radio frequency amplifiers, and other components) was constructed, and the monitoring of the discharge process of the main contact switching of the on-load tap changer was realized through experiments. The time-domain waveform was obtained, providing an effective monitoring method for analyzing the discharge phenomenon during the switching process.

[0019] 2. The partial discharge characteristics (phase distribution of ultra-high frequency and pulse current, pulse amplitude, etc.) of insulating oil containing metal particles and dampness at different deterioration stages (initiation, development, and severe) have been mastered, providing a basis for judging the degree of deterioration and discharge stage of insulating oil and helping to provide early warning of potential faults.

[0020] 3. Based on the two-dimensional electric field measurement principle of the Kerr effect method, the relationship and calculation formula between the phase difference and electric field strength of transformer oil under an applied electric field were clarified. The measurement sensitivity was improved by AC modulation electric field measurement technology, providing theoretical and technical support for the accurate measurement of electric field in transformer oil. Attached Figure Description

[0021] Figure 1 This is a flowchart of the method for measuring the oil gap insulation characteristics of on-load tap changers under high frequency according to the present invention.

[0022] Figure 2 This is a schematic diagram of an on-load tap changer switching.

[0023] Figure 3 This is a structural diagram of an on-load tap changer.

[0024] Figure 4 This is for the on-load tap changer switching discharge monitoring circuit.

[0025] Figure 5 This is the time-domain waveform diagram of the first group of UHF switching signals.

[0026] Figure 6 This is the time-domain waveform diagram of the second group of UHF switching signals.

[0027] Figure 7 This is a schematic diagram of the Kerr effect. Detailed Implementation

[0028] This invention proposes a method for measuring the oil gap insulation characteristics of on-load tap changers under high frequency. The invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] Figure 1 This is a flowchart of the method for measuring the oil gap insulation characteristics of on-load tap changers under high frequency according to the present invention.

[0030] 1. An on-load tap changer is installed between the high-voltage winding and the neutral point or between the grid-side winding and the neutral point.

[0031] Figure 2 This is a schematic diagram of an on-load tap changer. The on-load tap changer is located between the high-voltage winding or grid-side winding and the neutral point. It typically has several taps leading from the high-voltage winding or grid-side winding of the power transformer. When a load current is applied, adjusting the tap position of the winding changes the transformer's turns ratio, thus achieving voltage regulation. Its structure mainly includes three parts: a drive and transmission mechanism, a switching switch, and a tap selector. The structure of an on-load tap changer is shown below. Figure 3 As shown.

[0032] 2. Establish an ultra-high frequency monitoring system to monitor discharge during on-load tap changer switching and partial discharge of insulating oil in contact gaps.

[0033] The UHF monitoring system includes components such as UHF sensors, radio frequency transmission lines, radio frequency amplifiers, and oscilloscopes. The UHF sensors and radio frequency amplifiers are both from Beijing Huadian Zhicheng Co., Ltd. The radio frequency amplifier has the functions of amplifying and detecting the monitoring signal, and the frequency of the detected signal is within 20MHz.

[0034] The ultra-high frequency signal is acquired by the sensor, transmitted to the amplifier through the transmission line, and then displayed on the oscilloscope after being filtered and regulated.

[0035] In the on-load tap changer switching experiment, ultra-high frequency sensors were used to monitor the switching process of the main contacts. The monitoring circuit was as follows: Figure 4 As shown.

[0036] Based on the on-load tap changer switching experimental chamber, ultra-high frequency sensors were arranged in the observation window of the top cover of the experimental chamber, and two sets of ultra-high frequency switching signals were set to monitor the discharge signal during the switching process. Figure 5 This is the time-domain waveform diagram of the first group of UHF switching signals. Figure 6 This is the time-domain waveform diagram of the second group of UHF switching signals.

[0037] 3. Use a partial discharge detector to monitor the partial discharge of the insulating oil in on-load tap changers to detect deterioration.

[0038] Partial discharge spectrum testing of pure insulating oil under the influence of various factors was conducted using the LDS-6 partial discharge detector manufactured by Doble GmbH, Germany. The detector achieved a sensitivity of 0.01 pC, conforming to the IEC 60270:2000 standard. The software includes a built-in data analysis and storage program, capable of storing discharge characteristic information such as discharge quantity and number of discharges in TXT format.

[0039] The method of use is to connect the detection impedance and the coupling capacitor in series to ground, and then connect the detection impedance to the LDS-6 partial discharge instrument through two BNC coaxial cables. The LDS-6 partial discharge instrument and the laptop are connected through a network cable. The monitoring results are displayed through computer software.

[0040] 4. Two-dimensional electric field measurement using the Kerr effect method.

[0041] Transformer oil and other Kerr media, under the influence of an applied electric field, exhibit different refractive indices for two components of a light beam: one parallel to the electric field direction and the other perpendicular to it. This creates a phase difference between the two beam components, which is proportional to the square of the applied electric field—a phenomenon known as the Kerr effect. Figure 7 As shown.

[0042] The phase difference produced by the Kerr effect can be expressed by the formula:

[0043]

[0044] If the electric field is uniform along the direction of beam propagation, the formula can be simplified to Δθ=2πBLE 2 Where B is the Kerr constant, L is the length of the electric field region through which the beam passes, and E is the applied electric field strength. Since the Kerr constant of transformer oil is very low, approximately 3.0 × 10⁻¹⁵ m / V, an AC-modulated electric field measurement technique is used to improve the sensitivity of the measurement system: in addition to applying the DC electric field E to be measured to the test sample... dc Simultaneously apply a modulated electric field E ac sinωt, where ω is the angular frequency and t is time. The phase difference resulting from their combined effect is:

[0045] Δθ=2πBL(E dc +E ac sinωt) 2 .

[0046] In summary, the technical solution of this invention constructs an ultra-high frequency monitoring system containing ultra-high frequency sensors, radio frequency amplifiers, and other components. Through experiments, it realizes the monitoring of the discharge process of the main contact switching of the on-load tap changer, and obtains the time-domain waveform, providing an effective monitoring means for analyzing the discharge phenomenon during the switching process.

[0047] This invention provides insights into the partial discharge characteristics of insulating oil containing metal particles and dampness at different deterioration stages, including the phase distribution and pulse amplitude of ultra-high frequency and pulse currents. This provides a basis for judging the degree of deterioration and discharge stage of insulating oil, and helps to provide early warning of potential faults.

[0048] In addition, based on the two-dimensional electric field measurement principle of the Kerr effect method, this invention clarifies the relationship and calculation formula between the phase difference and electric field strength of transformer oil under an applied electric field, and improves the measurement sensitivity through AC modulation electric field measurement technology, providing theoretical and technical support for the accurate measurement of electric field in transformer oil.

Claims

1. A method for measuring the oil gap insulation characteristics of an on-load tap changer at high frequency, characterized in that, Includes the following steps: A load tap changer is installed between the high-voltage winding and the neutral point or between the grid-side winding and the neutral point. A high-frequency monitoring system was established to monitor discharge during on-load tap changer switching and partial discharge of insulating oil in contact gaps. Partial discharge monitoring of on-load tap changer insulating oil deterioration using a partial discharge detector; Two-dimensional electric field measurement was performed using the Kerr effect method.

2. The method for measuring the oil gap insulation characteristics of a high-frequency on-load tap changer according to claim 1, characterized in that, The detection sensitivity of the partial discharge detector is 0.01 pC.

3. The method for measuring the oil gap insulation characteristics of a high-frequency on-load tap changer according to claim 1, characterized in that, Two-dimensional electric field measurement specifically involves applying a modulated electric field while simultaneously applying a DC electric field.

4. The method for measuring the oil gap insulation characteristics of a high-frequency on-load tap changer according to claim 1, characterized in that, The on-load tap changer includes a drive and transmission mechanism, a switching switch, and a tap selector.

5. The method for measuring the oil gap insulation characteristics of a high-frequency on-load tap changer according to claim 3, characterized in that, The phase difference generated by the combined action of the DC electric field and the modulating electric field is: Δθ=2πBL(E dc +E ac sinωt) 2 , Where B is the Kerr constant, L is the length of the electric field region through which the beam passes, and E dc It is a direct current electric field, E ac It is the modulated electric field, ω is the angular frequency, and t is the time.

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