A method for locating multi-point discharge of capacitor units in a capacitor and detecting discharge amount

Abstract

The present disclosure discloses a method for locating and detecting the discharge amount of a capacitor unit in a capacitor at multiple points of discharge, including the following steps: collecting a first current signal of each capacitor unit in the capacitor during partial discharge; filtering the collected first current signal to obtain a second current signal; extracting and analyzing the amplitude and phase of the second current signal, and locating the faulty capacitor unit in the capacitor according to the analysis result; detecting the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor. The present disclosure can combine online monitoring of capacitors with fault location to achieve the location of partial discharge signals in capacitors and the detection of discharge amount.

Description

Technical Field

[0001] The present invention belongs to the field of discharge detection of power capacitors, and in particular relates to a method for locating multi-point discharge of capacitor units in a capacitor and detecting the discharge amount. Background Art

[0002] Due to the uneven distribution of energy centers and population centers in my country, high-voltage direct current transmission, an efficient and clean way of power transmission, is needed to undertake long-distance, large-capacity power transmission tasks. The converter is the core equipment of the direct current transmission system, which will generate 12k (k=1, 2, 3...) harmonics during operation. Harmonics will cause resonance, overvoltage and accelerated equipment aging. Therefore, a DC filter needs to be installed between the DC bus and the neutral point to eliminate harmonics.

[0003] High-voltage capacitors play the role of isolating DC voltage and bearing DC voltage in DC filters. They are easily affected by voltage fluctuations on the DC bus and fail. Actual operation shows that high-voltage capacitors are the devices with the highest failure rate in DC filters. The interior of high-voltage capacitors is formed by capacitor units connected in series and parallel. After a failure occurs, the method of manually measuring the capacitance value of the capacitor unit by maintenance personnel to locate the fault has the phenomenon of inaccurate positioning and low efficiency. Therefore, a more sensitive and reliable capacitor internal defect warning and positioning method is needed.

[0004] Partial discharge detection is an important means to discover potential insulation defects of high-voltage power equipment and conduct quality control. Partial discharge has an important impact on the insulation reliability and service life of capacitors. In order to ensure the factory quality of capacitors, domestic and foreign manufacturers have taken partial discharge as a key item in capacitor factory inspection. Partial discharge monitoring of operating capacitors can detect insulation defects inside the capacitor before a serious failure occurs in the equipment, avoid serious damage to the equipment and avoid major failures such as shutdown of the DC transmission system. In addition, using the characteristics of partial discharge pulse current for fault location can help maintenance personnel determine which parallel branch of the capacitor with weak insulation is located, which helps to reduce the workload of maintenance personnel. Although there are technologies for online monitoring of electrical parameters such as capacitor voltage and capacitance, as well as defect location methods for capacitor short circuit and open circuit failures, there is no method that combines online monitoring with fault location to achieve a location method for partial discharge signals in capacitors. Summary of the invention

[0005] In view of the deficiencies in the prior art, the purpose of the present invention is to provide a method for locating multi-point discharge of capacitor units in a capacitor and detecting the discharge amount, which can combine online monitoring of the capacitor with fault location to achieve the positioning of partial discharge signals in the capacitor and the detection of the discharge amount.

[0006] To achieve the above objectives, the present disclosure provides the following technical solutions:

[0007] A method for locating multi-point discharge of a capacitor unit in a capacitor and detecting the discharge amount, comprising the following steps:

[0008] S100: collecting a first current signal of each capacitor unit in the capacitor during partial discharge;

[0009] S200: filtering the collected first current signal to obtain a second current signal;

[0010] S300: extracting and analyzing the amplitude and phase of the second current signal, and locating the faulty capacitor unit in the capacitor according to the analysis result;

[0011] S400: Detect the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor.

[0012] Preferably, the frequency of the second current signal is 100 kHz to 1 MHz.

[0013] Preferably, step S300 includes the following steps:

[0014] S301: extracting the amplitude of the second current signal, and determining the row where the faulty capacitor unit is located according to the amplitude variation degree;

[0015] S302: Analyze phase changes of all capacitor units in the row where the faulty capacitor unit is located to determine the column where the faulty capacitor unit is located.

[0016] The present disclosure also provides a device for discharging and locating a capacitor unit in a capacitor and detecting a discharge amount, comprising:

[0017] A collection unit, used for collecting a first current signal of each capacitor unit in the capacitor during partial discharge;

[0018] A filtering unit, used for filtering the collected first current signal to obtain a second current signal;

[0019] A positioning unit, used for extracting the amplitude and phase of the second current signal and analyzing it to locate the faulty capacitor unit in the capacitor;

[0020] The detection unit is used to detect the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor.

[0021] Preferably, the positioning unit comprises:

[0022] A first extraction module, used for extracting the amplitude of the second current signal;

[0023] A second extraction module, used for extracting the phase of the second current signal;

[0024] A first analysis module, used for analyzing the amplitude change of the second current signal;

[0025] The second analysis module is used to analyze the phase change of the second current signal.

[0026] Preferably, the positioning unit further includes:

[0027] A first positioning module, used to determine the row where the faulty capacitor unit in the capacitor is located according to the amplitude change of the second current signal;

[0028] The second positioning module is used to determine the column where the faulty capacitor unit is located according to the phase change of the second current signal.

[0029] Preferably, the device further comprises a storage unit for storing the location of the faulty capacitor unit in the capacitor, the number of faults and the fault time, and the discharge amount information of the partial discharge of the capacitor.

[0030] The present disclosure also provides a device for locating multi-point discharge of a capacitor unit in a capacitor and detecting discharge amount, comprising:

[0031] Memory for storing computer programs;

[0032] The processor is used to execute a computer program to: collect a first current signal of each capacitor unit in the capacitor during partial discharge; filter the collected first current signal to obtain a second current signal; extract the amplitude and phase of the second current signal and analyze it, and locate the faulty capacitor unit in the capacitor according to the analysis result; detect the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor.

[0033] Compared with the prior art, the beneficial effects brought about by the present disclosure are: the present disclosure can accurately locate and monitor the local discharge of the capacitor unit in the power capacitor to prevent major failures, and help operation and maintenance personnel to quickly locate the faulty capacitor unit after a failure occurs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a flow chart of a method for locating multi-point discharge of a capacitor unit and detecting discharge amount in a capacitor provided by an embodiment of the present disclosure;

[0035] Figure 2 is a schematic diagram of a capacitor structure provided by another embodiment of the present disclosure;

[0036] Figure 3 is a schematic diagram of an equivalent structure of a capacitor provided by another embodiment of the present disclosure;

[0037] Figure 4 is a schematic diagram of the direction of a discharge pulse in a capacitor when a fault occurs, provided by another embodiment of the present disclosure;

[0038] Figure 5 is a circuit diagram of a single capacitor unit failure provided by another embodiment of the present disclosure;

[0039] Figure 6 is a current waveform diagram of a single faulty capacitor unit and a normal group provided by another embodiment of the present disclosure;

[0040] Figure 7 is a current waveform diagram of a single faulty capacitor unit and a faulty group provided by another embodiment of the present disclosure;

[0041] Figure 8 is a circuit diagram of two capacitor units failing according to another embodiment of the present disclosure;

[0042] Fig. 9 is a current waveform diagram of fault group 2 provided by another embodiment of the present disclosure;

[0043] Fig.10 is a current waveform diagram of fault group 4 provided by another embodiment of the present disclosure;

[0044] Fig.11 is a current waveform diagram of a normal group provided by another embodiment of the present disclosure. DETAILED DESCRIPTION

[0045] The following will refer to the accompanying drawings Figures 1 to 11 Specific embodiments of the present disclosure are described in detail. Although specific embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art.

[0046] It should be noted that certain words are used in the specification and claims to refer to specific components. Those skilled in the art should understand that technicians may use different nouns to refer to the same component. This specification and claims do not use the difference in nouns as a way to distinguish components, but use the difference in the functions of the components as the criterion for distinction. As mentioned throughout the specification and claims, "including" or "comprising" is an open term, so it should be interpreted as "including but not limited to". The subsequent description of the specification is a preferred embodiment of the present disclosure, but the description is based on the general principles of the specification and is not used to limit the scope of the present disclosure. The scope of protection of the present disclosure shall be determined by the attached claims.

[0047] To facilitate understanding of the embodiments of the present disclosure, further explanation will be given below using specific embodiments as examples in conjunction with the accompanying drawings, and each of the accompanying drawings does not constitute a limitation on the embodiments of the present disclosure.

[0048] like Figure 1 As shown, the present disclosure provides a method for locating multi-point discharge of a capacitor unit in a capacitor and detecting the discharge amount, comprising the following steps:

[0049] S100: collecting a first current signal of each capacitor unit in the capacitor during partial discharge;

[0050] S200: filtering the collected first current signal to obtain a second current signal;

[0051] S300: extracting and analyzing the amplitude and phase of the second current signal, and locating the faulty capacitor unit in the capacitor according to the analysis result;

[0052] S400: Detect the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor.

[0053] The above embodiments constitute a complete technical solution of the present disclosure. The method proposed in the above embodiments can accurately locate the faulty capacitor unit in the capacitor and detect the discharge amount when the capacitor is partially discharged, thereby overcoming the situation in the prior art where either the discharge can only be monitored but the fault cannot be located or the fault can only be located but the discharge monitoring cannot be realized. Therefore, it can greatly help operation and maintenance personnel to locate the fault and detect the weak insulation area inside the capacitor before a serious fault occurs.

[0054] In another embodiment, the frequency of the second current signal is 100 kHz to 1 MHz.

[0055] In this embodiment, since the current of the industrial frequency and low-order harmonics is very large, the high-frequency current transformer coil will reach magnetic saturation and the high-frequency current signal cannot be measured. Therefore, by filtering the first current signal and making the frequency of the second current signal fall within the range of 100kHz to 1MHz, the high-frequency current transformer will not reach magnetic saturation, thereby obtaining a discharge pulse signal that meets the detection needs.

[0056] In another embodiment, step S300 includes the following steps:

[0057] S301: extracting the amplitude of the second current signal, and determining the row where the faulty capacitor unit is located according to the amplitude variation degree;

[0058] The structure of the capacitor is as follows Figure 2As shown in the figure, it is composed of m rows and n columns of capacitor units connected in parallel, and each row of capacitor units is connected in parallel with a voltage-equalizing resistor, and each capacitor unit is connected in series with a fuse. When there is no short circuit fault in the capacitor unit, the fuse will not be triggered to blow, so the fuse can be regarded as a wire; in addition, since the resistance of the voltage-equalizing resistor is very large, it can be regarded as an open circuit for partial discharge pulses. For the convenience of subsequent analysis, the simplified circuit is shown below after ignoring the fuse and the voltage-equalizing resistor. Figure 3 shown.

[0059] When a capacitor unit in the capacitor fails, resulting in weak insulation and thus partial discharge, the voltage on the faulty capacitor unit will be lower than the voltage of the capacitor unit in normal operation. At the moment of the fault, the voltage on other normal capacitor units connected in parallel with the faulty capacitor unit will not have time to change suddenly, resulting in a voltage difference ΔU between the normal capacitor unit and the faulty capacitor unit. At this time, the current will flow from the normal capacitor unit to the faulty capacitor unit, such as Figure 4 As shown. For the entire capacitor, since the discharge pulse forms a closed loop in the row where the faulty capacitor unit is located, the effect of the discharge pulse on the normal capacitor unit can be ignored, and the discharge current detected thereon is very weak. The discharge current detected on the faulty capacitor unit will undergo a step change compared to the normal capacitor unit. The step change of the discharge current indicates that the amplitude of the high-frequency component in the current is large during the fault. Therefore, the row where the faulty capacitor unit in the capacitor is located can be determined by the change in the amplitude of the mid-high frequency component of the second current signal.

[0060] S302: Analyze phase changes of all capacitor units in the row where the faulty capacitor unit is located to determine the column where the faulty capacitor unit is located.

[0061] After determining the row where the faulty capacitor is located, it is necessary to further analyze the column where the faulty capacitor unit is located. For the row where the faulty capacitor unit is located, when partial discharge occurs, it can be equivalent to charging the faulty capacitor unit from the normal capacitor unit, so that the phase of the discharge current signal of the normal capacitor unit and the discharge current signal of the faulty capacitor unit are opposite. Therefore, the column where the faulty capacitor unit is located can be determined by detecting the phase of the discharge current signal of the capacitor unit.

[0062] Through the above analysis of the discharge current amplitude and phase, the faulty capacitor unit in the capacitor can be accurately located.

[0063] Below, the present disclosure combines Figures 5 to 11 The method disclosed in the present invention is further introduced.

[0064] A capacitor matrix was constructed using PSCAD simulation software, in which capacitor units electrically connected in parallel were constructed into a capacitor group, the group where the faulty capacitor unit was located was defined as the faulty group, and the other groups were defined as normal groups.

[0065] The capacitance value of the normal capacitor unit is set to 1μF, and the faulty capacitor unit is set to consist of two 1μF capacitors connected in series, that is, the capacitance value before the fault is 0.5μF. The fault is set to short-circuit one of the capacitors at 0.2 seconds, that is, the capacitance value of the faulty capacitor unit suddenly changes to 1μF at 0.2 seconds. A current matrix is ​​formed by measuring the current flowing through each capacitor unit, and the amplitude and phase of the current in the current matrix are analyzed to locate the faulty capacitor unit.

[0066] First, in Figure 5 A single fault point is set in the circuit shown, and the fault capacitor is connected in series with the current coil No. 33.

[0067] By measurement, Figure 6 As can be seen from the waveform diagram, when Figure 5 When the No. 33 capacitor unit in the group has a discharge fault, the current of the capacitor unit in the normal group has almost no change ( Figure 6 In the figure, the numbers 13, 23, 33, 43, and 53 represent the current signals of the capacitor units in the normal group and the faulty group. The current of each capacitor unit in the faulty group is as follows: Figure 7 The step change shown ( Figure 7 In the figure, the signals measured by each faulty capacitor unit in the fault group are represented by numbers 31, 32, 33, 34, and 35). The step change of the current indicates that the high-frequency component of the current has a large amplitude during the fault. Therefore, by judging the magnitude of the current, the fault can be located in the third group. Further analysis of the direction of the current of each capacitor unit in the fault group shows that the current direction of the faulty capacitor unit is opposite to that of the other capacitor units. Therefore, it can be judged that the capacitor unit whose current direction in the faulty group is opposite to that of the other capacitor units in the group when a discharge fault occurs is the capacitor unit with the faulty fault, that is, capacitor unit No. 33 has a discharge fault.

[0068] Secondly, in Figure 8 In the circuit shown, two faulty capacitor units, No. 25 and No. 41, are provided. The fault is set such that at 0.2 seconds, one capacitor in the faulty capacitor unit is short-circuited for 20ms.

[0069] After measurement, it is found that only the fault group detected a step-change current (i.e., the current has a high high-frequency content) when a fault occurred. The current waveforms of fault group 2 and fault group 4 are shown in Figures 9 and 10 respectively; Figure 11 shows the current waveform of the capacitor unit in the normal group. It can be seen that the current change of the capacitor unit in the normal group is very small when a fault occurs. Therefore, by judging the magnitude of the high-frequency current amplitude, it can be known that the discharge occurred in fault group 2 and fault group 4. Continuing to analyze the current signals of fault group 2 and fault group 4, at the moment of the fault, the current direction of the faulty capacitor unit in the fault group is opposite to that of the normal capacitor unit in the fault group. For example, in Figure 9, the current of capacitor unit No. 25 is opposite to the current of capacitor units No. 21, 22, 23, and 24. Fig.10 The current of capacitor unit No. 41 is opposite to the current of capacitor units No. 42, 43, 44, and 45, so it can be determined that capacitor unit No. 25 in fault group 2 and capacitor unit No. 41 in fault group 4 have discharge faults.

[0070] Through the above specific embodiments, it can be seen that the multi-point discharge positioning method of the power capacitor proposed in the present disclosure is feasible.

[0071] In another embodiment, in step S400, detecting the peak voltage of the high-frequency current transformer on the faulty capacitor unit comprises the following steps:

[0072] S401: connect a pulse calibration source in parallel to both ends of the capacitor unit to be calibrated, use the pulse calibration source to emit a pulse signal with a constant discharge amount, record the discharge amount at this time, recorded as Q1, and simultaneously measure the peak voltage of the high-frequency current transformer on the faulty capacitor unit, recorded as V1;

[0073] S402: When the faulty capacitor unit discharges, measure the peak voltage of the high-frequency current transformer on it, recorded as V2, and the discharge amount of the capacitor when partial discharge occurs can be recorded as

[0074] .

[0075] In another embodiment, the present disclosure further provides a device for locating multi-point discharge of a capacitor unit in a capacitor and detecting discharge amount, comprising:

[0076] A collection unit, used for collecting a first current signal of each capacitor unit in the capacitor during partial discharge;

[0077] A filtering unit, used for filtering the collected first current signal to obtain a second current signal;

[0078] A positioning unit, used for extracting the amplitude and phase of the second current signal and analyzing it to locate the faulty capacitor unit in the capacitor;

[0079] The detection unit is used to detect the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor.

[0080] In another embodiment, the positioning unit includes:

[0081] A first extraction module, used for extracting the amplitude of the second current signal;

[0082] A second extraction module, used for extracting the phase of the second current signal;

[0083] A first analysis module, used for analyzing the amplitude change of the second current signal;

[0084] The second analysis module is used to analyze the phase change of the second current signal.

[0085] In another embodiment, the positioning unit further includes:

[0086] A first positioning module, used to determine the row where the faulty capacitor unit is located according to the amplitude change of the second current signal;

[0087] The second positioning module is used to determine the column where the faulty capacitor unit is located according to the phase change of the second current signal.

[0088] In another embodiment, the device further comprises a storage unit for storing the location of the faulty capacitor unit in the capacitor, the number of faults and the fault time, and the discharge amount information of the partial discharge of the capacitor.

[0089] In another embodiment, the present disclosure further provides a device for locating multi-point discharge of a capacitor unit in a capacitor and detecting discharge amount, comprising:

[0090] Memory for storing computer programs;

[0091] A processor is used to execute a computer program to: collect a first current signal of each capacitor unit in a capacitor during partial discharge; filter the collected first current signal to obtain a second current signal; extract and analyze the amplitude and phase of the second current signal, and locate the faulty capacitor unit in the capacitor according to the analysis result; and detect the peak voltage of a high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor.

[0092] The above specific embodiments are used to illustrate the present disclosure, which is only used to help understand the present disclosure and is not used to limit the present disclosure. Any local modification or replacement within the technical scope disclosed by any technician familiar with the technology should be included in the scope of the present disclosure.

Claims

1. A method for locating multi-point discharge of a capacitor unit and detecting discharge amount in a capacitor, comprising the following steps: S100: collecting a first current signal of each capacitor unit in the capacitor during partial discharge; S200: filtering the collected first current signal to obtain a second current signal; S300: extracting and analyzing the amplitude and phase of the second current signal, and locating the faulty capacitor unit in the capacitor according to the analysis result; Step S300 includes the following steps: S301: extracting the amplitude of the second current signal, and judging the row where the faulty capacitor unit in the capacitor is located according to the degree of amplitude change; the capacitor is composed of m rows and n columns of capacitor units connected in parallel. When a capacitor unit in the capacitor has a fault, resulting in weak insulation and thus partial discharge, the voltage on the faulty capacitor unit will be lower than the voltage of the capacitor unit in the normal operating state. At the moment of the fault, since the voltage on other normal capacitor units connected in parallel with the faulty capacitor unit has no time to change suddenly, a voltage difference ΔU will be generated between the normal capacitor unit and the faulty capacitor unit. At this time, the current will flow from the normal capacitor unit to the faulty capacitor unit. For the entire capacitor, since the discharge pulse forms a closed loop in the row where the faulty capacitor unit is located, the influence of the discharge pulse on the normal capacitor unit can be ignored, and the discharge current detected thereon is very weak, while the discharge current detected on the faulty capacitor unit will have a step change compared to the normal capacitor unit. The step change of the discharge current indicates that the amplitude of the high-frequency component in the current is large during the fault. Therefore, the row where the faulty capacitor unit in the capacitor is located can be judged by the change in the amplitude of the medium and high-frequency components of the second current signal; S302: Analyze the phase changes of all capacitor units in the row where the faulty capacitor unit is located to determine the column where the faulty capacitor unit is located; for the row where the faulty capacitor unit is located, when partial discharge occurs, it can be equivalent to charging the faulty capacitor unit from the normal capacitor unit, so that the phases of the discharge current signals of the normal capacitor units and the discharge current signals of the faulty capacitor units are opposite, therefore, the column where the faulty capacitor unit is located can be determined by detecting the phases of the discharge current signals of the capacitor units; S400: Detect the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor, including: S401: connect a pulse calibration source in parallel to both ends of the capacitor unit to be calibrated, use the pulse calibration source to emit a pulse signal with a constant discharge amount, record the discharge amount at this time, recorded as Q1, and simultaneously measure the peak voltage of the high-frequency current transformer on the faulty capacitor unit, recorded as V1; S402: When the faulty capacitor unit discharges, measure the peak voltage of the high-frequency current transformer on it, recorded as V2, and the discharge amount of the capacitor when partial discharge occurs can be recorded as 。 2. The method according to claim 1, wherein: The frequency of the second current signal is 100 kHz to 1 MHz.

3. A device for locating multi-point discharge of capacitor units in a capacitor and detecting discharge amount for implementing the method as claimed in claim 1, comprising: A collection unit, used for collecting a first current signal of each capacitor unit in the capacitor during partial discharge; A filtering unit, used for filtering the collected first current signal to obtain a second current signal; A positioning unit, used for extracting the amplitude and phase of the second current signal and analyzing it to locate the faulty capacitor unit in the capacitor; The detection unit is used to detect the peak voltage of the high-frequency current transformer on the faulty capacitor unit to obtain the discharge amount of the partial discharge of the capacitor.

4. The device according to claim 3, wherein: The positioning unit comprises: A first extraction module, used for extracting the amplitude of the second current signal; A second extraction module, used for extracting the phase of the second current signal; A first analysis module, used for analyzing the amplitude change of the second current signal; The second analysis module is used to analyze the phase change of the second current signal.

5. The device according to claim 3 or 4, wherein: The positioning unit also includes: A first positioning module, used to determine the row where the faulty capacitor unit is located according to the amplitude change of the second current signal; The second positioning module is used to determine the column where the faulty capacitor unit is located according to the phase change of the second current signal.

6. The device according to claim 3, wherein: The device also includes a storage unit for storing the location of a faulty capacitor unit in the capacitor, the number of faults and the fault time, and the discharge amount information of the partial discharge of the capacitor.

7. A device for locating multi-point discharge of capacitor units in a capacitor and detecting discharge amount for implementing the method as claimed in claim 1, comprising: Memory for storing computer programs; A processor, configured to execute a computer program to: collect a first current signal of each capacitor unit in the capacitor during partial discharge; filtering the collected first current signal to obtain a second current signal; Extracting and analyzing the amplitude and phase of the second current signal, and locating the faulty capacitor unit in the capacitor according to the analysis result; The peak voltage of the high-frequency current transformer on the faulty capacitor unit is detected to obtain the discharge amount of the partial discharge of the capacitor.

Images