Fault full sensing terminal and its accurate positioning method for small current single-phase grounding

Abstract

The present invention proposes a fault full-sensing terminal and a method for accurately locating a small current single-phase grounding thereof, which is characterized in that it includes: an electronic voltage transformer, an electronic current transformer, a protection line loss board and a main board; the electronic voltage transformer is used to collect the voltages of the A phase, B phase and C phase of the ring network cabinet; the electronic current transformer is used to collect the currents of the A phase, B phase and C phase of each interval of the ring network cabinet; the electronic voltage transformer and the electronic current transformer are respectively connected to the main board via the protection line loss board; the electronic voltage and electronic current transformers are integrated with an integrator and a filter, and are resistor-capacitor type transformers; the protection line loss board is used to perform analog-to-digital conversion on the voltage and current signals. Through the acquisition of various types of signals, the cable operation status can be depicted in real time, and the faulty equipment can be eliminated in advance. At the same time, various types of faults can be accurately located in a short time when a fault occurs.

Description

Technical Field

[0001] The present invention belongs to the technical field of distribution network operation and maintenance, and in particular relates to a full-fault sensing terminal and a method for accurately locating a small-current single-phase grounding thereof. Background Art

[0002] In the power industry, existing DTUs lack the ability to diagnose small current grounding faults and do not describe the hidden dangers of old cables. Especially in scenarios where the cabling rate is high and cable faults account for a relatively high proportion, the 10kV distribution network system uses arc suppression coil grounding. The actual operation and maintenance process has the following difficulties:

[0003] 1. Difficulty in troubleshooting cable fault points. Cables are buried underground and cannot be directly observed. In addition, there is a lack of ground fault analysis and judgment methods, and the cable network fault location is inaccurate, which makes it difficult to find the cable fault point, resulting in a long time for fault repair, which has a great impact on power outage users and cannot meet the requirements for improving the quality of power supply services.

[0004] 2. The distribution network is prone to secondary faults. Due to the lack of cable operation monitoring means, when the distribution network grounds, the phase voltage is raised to the line voltage. In addition, the hidden dangers of old cables have not been discovered and eliminated in time, resulting in the weak links of the line (such as cable heads) being easily broken down. In recent years, it has caused multiple secondary faults. The occurrence of secondary faults also shows that there are indeed weak points in the cable network in Shishi area. Realizing real-time monitoring of cable operation is an urgent problem to be solved at this stage.

[0005] As of March 2020, a certain province has put into operation 11,661 sets of primary and secondary equipment, covering 5,018 lines and forming 288 standard automated feeders. The accuracy rate of fault analysis of primary and secondary equipment in the province in February was only 11.74%.

[0006] After analyzing the waveform characteristics, it was found that only 9 waveforms can actually be used for research and judgment, and the remaining 120 waveforms (accounting for 93.02%) have serious noise, no zero-sequence current, no zero-sequence voltage, unbalanced phase current and other phenomena. Such phenomena are the main reasons for misjudgment.

[0007] In summary, it is currently an urgent need to develop a full-sensing terminal that uses the key technology of locating small current grounding faults in medium-voltage distribution networks as the longitude, and non-electrical quantity monitoring such as partial discharge and temperature as the latitude, to deeply analyze the characteristics of old faulty cables, achieve accurate positioning of single-phase grounding faults, and eliminate hidden dangers of cables in advance. Summary of the invention

[0008] In view of the defects and shortcomings of the existing solutions, the present invention provides a fault full-sensing terminal and a small current single-phase grounding accurate positioning method thereof, which specifically adopts the following technical solutions:

[0009] A full fault sensing terminal, characterized in that it includes: an electronic voltage transformer, an electronic current transformer, a line loss protection board and a main board; the electronic voltage transformer is used to collect the A-phase, B-phase and C-phase voltages of the ring network cabinet; the electronic current transformer is used to collect the A-phase, B-phase and C-phase currents of each interval of the ring network cabinet; the electronic voltage transformer and the electronic current transformer are respectively connected to the main board via the line loss protection board; the electronic voltage and electronic current transformers are integrated with integrators and filters and are resistor-capacitor type transformers; the line loss protection board is used to perform analog-to-digital conversion on voltage and current signals.

[0010] Preferably, the main board and the line loss protection board are arranged in a terminal cabinet.

[0011] Preferably, the voltages of phase A, phase B and phase C of the ring main unit are collected by setting two electronic voltage transformers at the incoming line intervals, and the leads of the direct voltage sensor used are fixed on the ABC three-phase copper busbar of the ring main unit and are electrically connected to the copper busbar.

[0012] Preferably, the electronic current transformer is used to collect the A-phase, B-phase and C-phase currents of each interval of the ring network cabinet according to a transformation ratio of 600A / 1V and is snap-mounted on the cable; the electronic voltage transformer converts the 10kV voltage of the line into a 3.25V voltage.

[0013] Preferably, the electronic voltage transformer and the electronic current transformer are connected to a line loss protection board via a secondary line assembly control system.

[0014] Preferably, it also includes: an ultrasonic / TEV / UHF three-in-one cable partial discharge sensing sensor installed on the inner wall of the lower cabinet of the ring network cabinet, a temperature sensor installed on the cable head, and a harmful gas detection device installed on the lower part of the lower cabinet of the ring network cabinet, and a wireless receiving module connected to the mainboard through wireless communication.

[0015] Preferably, it also includes: a leakage current transformer installed at the cable grounding wire of the ring network cabinet; the leakage current transformer is connected to the main board via a line loss protection board.

[0016] And the small current single-phase grounding accurate positioning method based on the above fault full sensing terminal is characterized by:

[0017] The formation of secondary noise is suppressed by the integrator and filter integrated in the electronic voltage and electronic current transformers, and the line loss protection board converts the voltage and current signals into analog-to-digital signals and transmits them to the main board; the main board realizes the precise positioning of small current single-phase grounding based on the voltage and current signals and the preset small current single-phase grounding criteria.

[0018] Preferably, the preset small current single-phase grounding criterion is:

[0019] When a line grounding fault occurs, if one line meets the following conditions, it is located as a small current single-phase grounding fault:

[0020] The zero-sequence voltage leads the zero-sequence current by 60° to 120° and the zero-sequence voltage in the switching state is greater than 0;

[0021] At least one of the following conditions is met: the ratio of the two-phase voltage increase to the one-phase voltage decrease is greater than the first set value, and the zero-sequence voltage is greater than the second set value;

[0022] Zero sequence current> third set value;

[0023] At least two phase voltages are greater than 4kV.

[0024] Preferably, when the preset small current single-phase grounding locates a small current single-phase grounding fault, it is determined whether the grounding alarm enable is turned on, and if it is turned on, the grounding alarm is started.

[0025] Compared with the prior art, the present invention and its preferred solution have the following main features and advantages:

[0026] 1. It adopts advanced ground fault analysis technology. The selected voltage and current sensors are more accurate and safer. The resistor-capacitor type electronic sensors are not saturated, have a wide frequency response range, a large measurement range, good linearity, no ferromagnetic resonance, and no short-circuit overvoltage risk. Therefore, it can use advanced algorithms that comprehensively analyze transient, steady-state, and direction.

[0027] 2. Install cable operation status monitoring sensors: Use advanced three-in-one cable partial discharge sensing sensors, which do not require subsequent operation and maintenance charging. At the same time, install temperature sensors at the cable joints and gas monitoring devices. Through partial discharge and temperature measurement and harmful gas detection devices and leakage current monitoring, early warning of cable insulation hazards and potential failures can be provided, thereby improving the operating environment of old cables and reducing the occurrence of secondary failures.

[0028] 3. Existing terminals are maintenance-free: The terminal has low power consumption, and a high-performance maintenance-free backup power supply can be used to reduce the terminal operation and maintenance. Lithium iron phosphate batteries with an 8-year warranty can be used as backup power supplies. They have low power consumption and low heat dissipation, stable operation at 0-70 degrees, a service life of not less than 8 years, a capacity of not less than 25Ah, and a capacity attenuation rate of not more than 10% / year.

[0029] 4. Support the distribution network operation and maintenance services such as synchronous line loss: It has automatic data collection of electricity, and collects data such as three-phase voltage, three-phase current, zero-sequence voltage, zero-sequence current, active / reactive power and electricity according to the measurement accuracy, which is convenient for line loss assessment. At the same time, it has the function of automatic phase verification to reduce the burden of manual operation, and realizes the forced locking of the loop of the line with inconsistent phase sequence, which improves the intrinsic safety.

[0030] The present invention and its preferred solution realize real-time depiction of the cable operation status through various signal collections, provide early warning and eliminate faulty equipment, and can accurately locate various faults (especially small current grounding) in a short time when a fault occurs, thereby reducing the duration of fault power outages and taking a big step towards zero power outage perception. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments:

[0032] Figure 1 Schematic diagram of the installation position of each sensor in the ring network cabinet according to an embodiment of the present invention;

[0033] Figure 2 Schematic diagram of a line loss protection board and a main board in a terminal cabinet according to an embodiment of the present invention;

[0034] Figure 3 This is a schematic diagram of a small current single-phase grounding criterion according to an embodiment of the present invention;

[0035] Figure 4 It is a schematic diagram of the fault within the boundary;

[0036] Figure 5 It is a schematic diagram of an out-of-bounds fault;

[0037] Figure 6 It is a schematic diagram of the waveform outside the single-phase grounding boundary;

[0038] Figure 7 This is a schematic diagram of a single-phase disconnection waveform;

[0039] Figure 8 It is a schematic diagram of three-phase disconnection waveform;

[0040] Fig. 9 This is a waveform diagram of poor contact of aviation connectors;

[0041] Fig.10 It is a schematic diagram of the startup process of the device according to the embodiment of the present invention;

[0042] Fig.11 is a schematic diagram of an active analog integrator according to an embodiment of the present invention;

[0043] In the figure: 1-electronic voltage transformer; 2-electronic current transformer; 3-line loss protection board; 4-main board; 5-three-in-one cable partial discharge sensing sensor; 6-temperature sensor; 7-harmful gas detection device; 8-leakage current transformer. DETAILED DESCRIPTION

[0044] In order to make the features and advantages of this patent more obvious and easy to understand, the following embodiments are specifically described in detail as follows:

[0045] like Figure 1 , Figure 2 As shown, in order to realize the function of accurate positioning of small current single-phase grounding, the full fault sensing terminal provided by the device of this embodiment includes: an electronic voltage transformer 1, an electronic current transformer 2, a line loss protection board 3 and a main board 4.

[0046] Among them, the electronic voltage transformer 1 is used to collect the voltage of phase A, phase B, and phase C of the ring network cabinet, and convert the 10kV voltage of the line into a 3.25V voltage available to the terminal. Since the ring network cabinet is the same as the busbar, the power transfer path is not determined. Therefore, as long as two transformers are installed in the incoming line interval, the three-phase voltage of the line can be collected regardless of which side the power is supplied from, and the corresponding voltage can be shared with other outgoing line intervals (for functionality and cost requirements, the voltage of two intervals is collected). Therefore, in this embodiment, the electronic voltage transformer 1 with two incoming line intervals is set to collect the voltage of phase A, phase B, and phase C of the ring network cabinet, and the lead of the direct voltage sensor used is fixed on the ABC three-phase copper busbar of the ring network cabinet and is electrically connected to the copper busbar. In terms of installation, the copper nose screws of the ABC three-phase copper busbar can be loosened after the power outage, and the lead of the direct voltage sensor can be locked on the corresponding copper busbar. The base is fixed to the bottom plate of the cabinet with self-tapping screws and connected to the ground wire.

[0047] In this embodiment, the electronic current transformer 2 is used to collect the A-phase, B-phase and C-phase currents of each interval of the ring network cabinet according to a 600A / 1V transformation ratio, and is snap-fitted onto the cable after a power outage.

[0048] The electronic voltage transformer 1 and the electronic current transformer 2 are connected to the main board 4 via the line loss protection board 3 respectively; the electronic voltage and electronic current transformers 2 are integrated with integrators and filters, and are resistance-capacitance type transformers; the line loss protection board 3 is used to perform analog-to-digital conversion on voltage and current signals. The main board 4 and the line loss protection board 3 are arranged in the terminal cabinet.

[0049] The integrator and filter integrated in the electronic voltage transformer 1 and the electronic current transformer 2 are used to suppress the formation of secondary noise, and then the corresponding secondary lines of current and voltage are integrated into a control system to transmit the corresponding voltage and current signals to the protection line loss board 3. Figure 2 As shown, the analog-to-digital conversion is realized, and then the corresponding digital signal is transmitted to the main board 4 through J1, and the collected current and voltage are processed in the main board 4 according to the following Figure 3 The algorithm logic of the traditional primary and secondary switch set is optimized as shown, current starting criteria and power analysis criteria are added to avoid the interference range of clutter and achieve accurate positioning of small current single-phase grounding.

[0050] like Figure 3 As shown, the small current single-phase grounding criterion used in this embodiment is:

[0051] When a line grounding fault occurs, if one line meets the following conditions, it is located as a small current single-phase grounding fault:

[0052] The zero-sequence voltage leads the zero-sequence current by 60° to 120° and the zero-sequence voltage in the switching state is greater than 0;

[0053] At least one of the following conditions is met: the ratio of the two-phase voltage increase to the one-phase voltage decrease is greater than the first set value, and the zero-sequence voltage is greater than the second set value;

[0054] Zero sequence current> third set value;

[0055] At least two phase voltages are greater than 4kV.

[0056] When the preset small current single-phase grounding locates the small current single-phase grounding fault, it is determined whether the grounding alarm enable is turned on. If it is turned on, the grounding alarm is started.

[0057] In addition, if Figure 1 , Figure 2 As shown in the figure, in order to realize the function of cable operation status monitoring, the "ultrasound / TEV / UHF" three-in-one cable partial discharge sensing sensor 5 is used and installed on the inner wall of the lower cabinet of the ring network cabinet; the temperature sensor 6 is installed on the cable head; considering the high density of SF6 and other gases, the harmful gas detection device 7 is installed at the lower part of the lower cabinet of the ring network cabinet to monitor the operation status of the cable; the above sensor modules are connected to the Figure 2 The wireless receiving module of the full-sensing terminal mainboard 4 performs matching communication, and then transmits it to the mainboard 4 after analog-to-digital processing.

[0058] At the same time, a leakage current transformer 8 for accurately measuring small currents is installed at the cable grounding wire to monitor the leakage current, and the corresponding current signal is collected by hard wiring and transmitted to the Figure 2 The protection line loss board 3, finally sets the over-limit alarm function on the main board 4, and uploads the corresponding fault signal to the main station, so as to formulate relevant maintenance plans, replace old cables and branch boxes, analyze the characteristic status of old cables before failure, and realize early warning to eliminate hidden dangers of old cables.

[0059] The following is a specific analysis of the principles of the design of this embodiment:

[0060] 1 Analysis of the reasons for the low accuracy of the fault diagnosis of primary and secondary equipment

[0061] 1.1 Logic for judging small current grounding of primary and secondary integrated switchgear

[0062] Traditional steady-state zero-sequence overcurrent requires offline setting of various protection quantities. However, when a multi-loop same-phase complex grounding fault occurs in a low-resistance grounding system, it is easy for the traditional zero-sequence current protection to refuse to operate or malfunction due to unreasonable setting of protection quantities, which cannot meet the power grid's requirements for the selectivity of protection devices.

[0063] like Figure 4 As shown, it is an internal fault. Figure 5 As shown, it is an out-of-bounds fault.

[0064] Due to the complexity of the clutter on the line, in order to prevent false alarms of out-of-bounds faults, it is recommended to set the voltage start threshold to more than 20% of the rated value. The specific reasons are as follows:

[0065] The traditional method of judging small current is as follows:

[0066] When the Nth effective sampling point of zero-sequence voltage is greater than the zero-crossing point:

[0067] If the zero-sequence voltage N+1th valid sampling point is greater than the Nth valid sampling point, it returns 1 and the trend is upward, otherwise it returns 0

[0068] When the Nth effective sampling point of zero-sequence voltage is less than the zero-crossing point:

[0069] If the zero-sequence voltage N+1th valid sampling point is less than the Nth valid sampling point, it returns -1, indicating a downward trend; otherwise, it returns 0.

[0070] When the Nth effective sampling point of zero-sequence current is greater than the zero-crossing point:

[0071] If the zero-sequence current N+1th valid sampling point is greater than the Nth valid sampling point, it returns 1 and the trend is upward, otherwise it returns 0

[0072] When the Nth effective sampling point of zero-sequence current is less than the zero-crossing point:

[0073] If the zero-sequence current N+1th valid sampling point is less than the Nth valid sampling point, it returns -1, indicating a downward trend; otherwise, it returns 0.

[0074] C=iN(return value)*uN(return value) (N=0,1,2,3,4,……)

[0075] The small current grounding is judged by starting with zero voltage, and the small current grounding fault range is judged by the zero voltage and zero current angle.

[0076] 1.2 Analysis of misjudgment of small current grounding in primary and secondary integrated switchgear

[0077] The waveform before the on-site fault is as follows Figure 6 The single-phase grounding out-of-bounds waveform is shown. It can be found that at about 78ms, a voltage has reached the voltage threshold, and the later change characteristics have met the above logic requirements.

[0078] like Figure 7-Figure 9 As shown, they are: single-phase disconnection waveform, three-phase disconnection waveform and aviation connector poor contact waveform

[0079] 129 samples of false alarms of complete sets of switches were selected. After analyzing the waveform characteristics, it was found that only 9 waveforms were actually usable for research and judgment, and the remaining 120 waveforms (accounting for 93.02%) had serious noise, no zero-sequence current, no zero-sequence voltage, and phase current imbalance, which were the main reasons for misjudgment.

[0080]

[0081] 1.3 Causes of misjudgment of small current grounding in primary and secondary integrated switchgear

[0082] The above abnormal waveforms have the following characteristics: 1. The amplitude (effective value) of the clutter is relatively small, and is most likely lower than 1A. 2. The positive and negative clutter are relatively symmetrical and the frequency of change is relatively fast.

[0083] According to the above characteristics, three main directions are determined: 1. Based on the characteristics of small amplitude of clutter, but because the unbalanced current interferes with the simple current judgment, the voltage judgment is more reliable in characterizing small current grounding. Therefore, it is possible to consider revising the current startup logic to a voltage and current combined startup judgment to avoid the clutter influence interval. 2. Use high-precision voltage and current transformers, filter circuits, integrators, etc. to filter out the influence of clutter 3. Use the power increase judgment to achieve "software filtering" through the integration effect to offset the influence of high-frequency clutter.

[0084] This embodiment is based on the fact that the traditional primary and secondary integrated switch relies on a fixed installation method to realize the analysis of small current grounding, optimize the algorithm logic and related hardware, and realize the development of an adaptive fault full-perception terminal.

[0085] 2 Research on the joint start-up criterion of voltage and current of fault-sensing terminal

[0086] 2.1 Theoretical analysis of current starting criteria

[0087] Compare the sampling signal with the start threshold value. When the amplitude of two of the three consecutive sampling points in the sampling window is greater than the threshold value for device start, the device starts and records fault data; otherwise, the device does not upload data to the master station and continues to sample the zero-mode current signal in the system. The specific implementation process is as follows: Fig.10 shown.

[0088] 2.2 Summary of voltage and current combined start-up criteria

[0089] Due to the steady-state characteristics of small current grounding faults at the boundary switch, the boundary switch is generally installed at the end of the branch line or line. The length of its downstream (user side) line is much smaller than the sum of the lengths of other lines in the system. Correspondingly, the distributed capacitance of the downstream line to the ground is much smaller than the distributed capacitance of other lines to the ground, and the current of the distributed capacitance of the downstream line to the ground is also much smaller than the current of the distributed capacitance of the upstream (system side) line to the ground.

[0090] If the grounding point is located upstream of the boundary switch, no matter the system is ungrounded or grounded via an arc suppression coil, the fault power frequency zero-sequence current detected by the boundary switch is the distributed capacitance current of the downstream line to the ground. According to the capacitance current of 30 mA for a 10kV overhead line with a length of 1 km and 600 mA for a 10 kV cable line with a length of 1 km, the amplitude generally does not exceed 1A.

[0091] In summary, increasing the steady-state current by 1A to form a voltage-current joint starting criterion can effectively ensure the correctness of the boundary switch action while suppressing the interference of high-frequency and low-amplitude clutter.

[0092] 3 Research on Fault-Sensing Terminal Voltage and Current Transformer

[0093] 3.1 Research background and significance of RC transformer

[0094] The traditional electromagnetic PT power supply is currently used by most automation equipment and switch operating mechanisms. Due to the limitations of the technical principle itself, the failure rate of the electromagnetic PT device is very high. It is the component with the highest failure rate on site. In addition, there are safety issues such as overcurrent and electromagnetic resonance caused by short circuit on the secondary side of the voltage. In addition, the secondary rated voltage of the voltage sensor is 100V or 100 / 3V, which is not convenient for direct interface with modern microcomputer protection and measurement equipment, and it is difficult to adapt to the requirements of automation and digitization of power systems. The RC voltage divider voltage sensor has the advantages of high measurement accuracy, large linear range, and wide bandwidth. It eliminates the safety hazards caused by ferromagnetic resonance and secondary side short circuit, and better overcomes the various problems of electromagnetic PT from the working principle.

[0095] 3.2 Selection of Filter and Integrator for Fault-Sensing Terminal Voltage and Current Transformer

[0096] 1) Design of low-pass filter

[0097] In order to improve the measurement accuracy, the measured input signal needs to pass through a low-pass anti-aliasing filter to filter out the influence of noise. There are three most commonly used low-pass filters, namely Butterworth filter, Chebychev filter and Bessel filter. Among them, the amplitude-frequency response of the Butterworth filter has the maximum flatness in the passband, but the attenuation from the passband to the stopband is slow. The Chebychev filter can decay quickly, but the error value will change with ripples in the passband. The Bessel filter only meets the phase-frequency characteristics and does not care about the amplitude-frequency characteristics, and can obtain a waveform with less phase distortion. At the same time, the order of the selected filter should not be too high, otherwise it will easily lead to an increase in the phase shift error of the voltage and current channels. The selection of the filter must be able to meet certain bandwidth characteristics to ensure that its phase offset value is within the accuracy range that meets the measurement error. Chebychev or Butterworth second-order low-pass filters are common choices in actual processing.

[0098] 2) Principle and design of integrator

[0099] The integrator is a key part of the sensor signal processing link, and its integration accuracy is directly related to the accuracy of the sensor output. From the previous analysis, it can be seen that analog integration and digital integration, as two commonly used integration methods, each has its own advantages and disadvantages. The analog integrator has the advantages of simple structure, fast response speed, large input dynamic range, and the technology is relatively mature. When using analog devices to implement the integration process, its performance and temperature stability are determined by the analog components. However, since the actual op amp device is not an ideal device, the op amp offset, the leakage and loss of the capacitor, the time drift and temperature drift of the op amp and other analog devices will affect the result of the integration, causing integration errors. In addition, the feedback and compensation design of the analog integrator is not flexible enough, and the compensation link may introduce new errors. For electronic transformers, the integrator must work stably for a long time, and it is difficult to completely overcome the errors caused by these factors.

[0100] The digital integrator has simple hardware circuit, good temperature stability, flexible design, and has the advantages of high reliability and repeatability. The integral algorithm is used to calculate the amplitude and phase data of the original signal, and its accuracy is only affected by the accuracy of A / D conversion, the number of sampling points and the calculation accuracy. However, the digital integrator needs to solve the algorithm problem of digital integration after high-speed A / D conversion, and this process must be as short as possible to achieve the purpose of fast sampling integration. Therefore, the microprocessor's computing speed is very high. At the same time, in practical use, factors such as speed and accuracy must be comprehensively considered to select the appropriate number of sampling points. In addition, in the design of the digital integrator, it is also necessary to solve the influencing factors such as DC offset, initial value of integration and input saturation, and by adding compensation links, the accuracy and stability of the digital integrator are guaranteed.

[0101] Active analog integrators are selected to realize the integration function. Combining the two improved integration circuits, the integrator circuit is as follows Fig.11 In addition to the reasonable selection of capacitor and resistor parameters, fine-tuning devices are added to the circuit to ensure the accuracy of the transmitted signal.

[0102] In summary, the full-fault sensing terminal voltage and current transformer uses a resistor-capacitor transformer to ensure accuracy while suppressing the formation of secondary noise.

[0103] 3.3 Fault-sensing terminal transient reactive power direction method

[0104] Since the transient current amplitude is generally several to dozens of times the power frequency and is not affected by arc suppression coil compensation and unstable arcs, it provides a reliable basis for locating distribution network faults and is widely used in my country's distribution networks.

[0105] Transient reactive power is defined as the Hilbert transform value of the transient voltage signal and the average power of the transient current signal during the transient period. The calculation formula is as follows:

[0106] (1-5)

[0107] Where: is the Hilbert transform of the transient voltage signal.

[0108] After a single-phase grounding fault occurs in a low-current grounding system, the zero-sequence network of the system can be regarded as a simple uniform line with an open end at the downstream of the fault point and the sound line. Its input impedance is not affected by the arc suppression coil and is capacitive before the first series resonance. The input impedance of the measurement point from the upstream of the fault point to the busbar is equal to the parallel connection of the impedance of each sound line and then in series with the impedance between each measurement point and the busbar. Its input impedance is also capacitive at the first series resonance. When the frequency is greater than 150Hz, the compensation effect of the arc suppression coil can be ignored. Therefore, the input impedance between 3 times the power frequency and the first series resonance is equivalent to capacitive, and the low-frequency band where all lines are capacitive is selected as the characteristic frequency band. In the characteristic frequency band, the transient reactive power of all measurement points upstream of the fault point of the fault line is less than 0, while the transient reactive power of the downstream of the fault point and the sound line is greater than 0. This characteristic is used for positioning.

[0109] In summary, the power method realizes the integration effect of the product of voltage and current, can achieve the effect of "algorithm filtering", and can be used as a starting criterion for adaptive judgment. It automatically corrects the current angle and its own power calculation according to the positive and negative power, and realizes adaptive judgment of small current grounding.

[0110] This patent is not limited to the above-mentioned optimal implementation mode. Anyone can derive other forms of full-fault sensing terminals and their small-current single-phase grounding precise positioning methods under the inspiration of this patent. All equal changes and modifications made according to the scope of the patent application of the present invention should be covered by this patent.

Claims

1. A fully fault-aware terminal, characterized in that: include: Electronic voltage transformer, electronic current transformer, line loss protection board and main board; The electronic voltage transformer is used to collect the voltages of phase A, phase B and phase C of the ring main unit; The electronic current transformer is used to collect the currents of phase A, phase B and phase C of each interval of the ring network cabinet; the electronic voltage transformer and the electronic current transformer are respectively connected to the main board via the line loss protection board; the electronic voltage and electronic current transformers are integrated with integrators and filters, and are resistance-capacitance type transformers; The line loss protection board is used to perform analog-to-digital conversion on voltage and current signals; The method for accurately locating a small current single-phase grounding is as follows: the integrator and filter integrated in the electronic voltage and electronic current transformers are used to suppress the formation of secondary clutter; the line loss protection board converts the voltage and current signals into analog-to-digital signals and transmits them to the main board; the main board realizes accurate positioning of the small current single-phase grounding according to the voltage and current signals and the preset small current single-phase grounding criterion; The preset small current single-phase grounding criterion is: When a line grounding fault occurs, if one line meets the following conditions, it is located as a small current single-phase grounding fault: The zero-sequence voltage leads the zero-sequence current by 60° to 120° and the zero-sequence voltage in the switching state is greater than 0; At least one of the following conditions is met: the ratio of the two-phase voltage increase to the one-phase voltage decrease is greater than the first set value, and the zero-sequence voltage is greater than the second set value; Zero sequence current> third set value; At least two phase voltages are greater than 4kV.

2. The fault-sensing terminal according to claim 1, characterized in that: The main board and the line loss protection board are arranged in the terminal cabinet.

3. The fault-sensing terminal according to claim 1, characterized in that: The voltages of phase A, phase B and phase C of the ring main unit are collected by setting two electronic voltage transformers at the incoming line intervals. The leads of the direct voltage sensor used are fixed on the ABC three-phase copper busbar of the ring main unit and are electrically connected to the copper busbar.

4. The fault-sensing terminal according to claim 1, characterized in that: The electronic current transformer is used to collect the A-phase, B-phase and C-phase currents of each interval of the ring network cabinet according to the transformation ratio of 600A / 1V and is snap-fitted onto the cable; the electronic voltage transformer converts the 10kV voltage of the line into a 3.25V voltage.

5. The fault-sensing terminal according to claim 1, characterized in that: The electronic voltage transformer and the electronic current transformer are connected to a line loss protection board via a secondary line assembly control system.

6. The full fault sensing terminal according to claim 1, characterized in that: Also includes: The ultrasonic / TEV / UHF three-in-one cable partial discharge sensing sensor installed on the inner wall of the lower cabinet of the ring network cabinet, the temperature sensor installed on the cable head and the harmful gas detection device installed on the lower part of the lower cabinet of the ring network cabinet are connected to the wireless receiving module of the mainboard through wireless communication.

7. The full fault sensing terminal according to claim 1, characterized in that: Also includes: Leakage current transformer installed at the cable grounding wire of the ring main unit; The leakage current transformer is connected to the main board via the line loss protection board.

8. The full fault sensing terminal according to claim 1, characterized in that: When the preset small current single-phase grounding locates a small current single-phase grounding fault, it is determined whether the grounding alarm enable is turned on. If it is turned on, the grounding alarm is started.

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