Circuit three-phase short-circuit fault current control method

Abstract

The invention provides a circuit three-phase short-circuit fault current control method, which relates to the technical field of circuit three-phase power, and comprises the following steps: S1, fault detection; s2, fault isolation; s3, fault positioning; s4, fault processing; s5, recovering the system; and S6, data recording and analysis: after the SOP is connected to the power distribution network, the fault current characteristics of the power distribution network can be obviously changed, the power distribution network connected with the SOP is analyzed, the fault occurring at the moment is a three-phase symmetric fault, and a control system of the SOP comprises a Vf control method to carry out power supply recovery, so that Vf control of the SOP can be utilized to generate a characteristic voltage reference, and the power supply recovery efficiency is improved. The characteristic voltage signal is generated through PWM modulation to carry out fault positioning, the fault position can be positioned more accurately by detecting and analyzing the characteristic voltage signal, the accuracy of fault positioning is improved, and the operation efficiency and stability of the power distribution network are improved.

Description

Technical Field

[0001] The invention relates to the field of three-phase line electricity technology, and in particular to a three-phase line short-circuit fault current control method. Background Art

[0002] Line three-phase refers to the line in the three-phase AC system, which consists of three AC wires with a phase difference of 120 degrees and is used to transmit electricity. Three-phase AC is widely used in industrial, commercial and residential power systems because it can provide a more efficient and stable power supply.

[0003] At present, it is difficult to install voltage transformers in distribution lines, and the problem of misconnection of voltage transformer polarity is also common on site. At the same time, directional elements are not suitable for new energy access scenarios. The threshold-based fault location method is simple in principle, but it limits the access capacity of DG and cannot be applied to distribution networks with a high proportion of DG access. The two-terminal traveling wave method can solve the fault location problem of active distribution networks by analyzing the difference in traveling wave signals at both ends of the line, but it has high requirements for two-terminal communication and detection devices need to be configured in each branch, which has poor economic efficiency. The fault detection method based on multi-terminal information can use the current amplitude and phase angle, current polarity, three-phase voltage / current synchronous phasor data on both sides of the line, energy function of the fault leading phase, waveform correlation, etc. to realize fault location of active distribution networks, but they all rely on the communication system. If data loss occurs during a fault, the fault detection will be inaccurate, resulting in reduced accuracy in locating the fault location and reducing the accuracy of fault location.

[0004] Therefore, it is necessary to provide a new line three-phase short-circuit fault current control method to solve the above technical problems. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a method for controlling a three-phase short-circuit fault current of a line.

[0006] A three-phase short-circuit fault current control method provided by the present invention comprises the following steps:

[0007] S1, Fault detection, by monitoring the voltage and current electrical parameters of the line, usually achieved through current transformers, voltage transformers and relay protection devices;

[0008] S2, Fault isolation: When a short circuit fault is found, the fault line is quickly cut off through the circuit breaker to isolate the fault point;

[0009] S3, fault location. After SOP is connected to the distribution network, the fault current characteristics of the distribution network will be significantly changed. The distribution network connected to SOP is analyzed. The fault at this time is a three-phase symmetrical fault. The control system of SOP includes a Vf control method for power supply recovery. Therefore, the Vf control of SOP can be used to generate a characteristic voltage reference, and then the characteristic voltage signal is generated through PWM modulation to locate the fault.

[0010] S4. Fault handling: Take appropriate measures according to the nature and severity of the fault. For minor faults, replace the damaged parts; for serious faults, replace the entire equipment or perform large-scale repairs;

[0011] S5, system recovery: after the fault is resolved, the system is inspected and tested to ensure that all equipment is back to normal working condition, and then power supply is gradually restored;

[0012] S6. Data recording and analysis: record the time, type, handling process and results of the fault for subsequent analysis and improvement.

[0013] Preferably, by directly giving the inner loop output voltage reference value and the synchronous phase in the Vf control, a set of three-phase symmetrical characteristic voltage signals is generated, and then the required characteristic voltage signal is superimposed on the voltage reference generated by the original current inner loop. After PWM modulation, the corresponding characteristic voltage component can be generated. The expression of the three-phase composite voltage modulation wave is:

[0014]

[0015] Where V is the original power frequency phase voltage modulation amplitude, is the additional characteristic phase voltage modulation wave amplitude, f, f tz are the power frequency and the frequency of the additional characteristic voltage signal respectively.

[0016] Preferably, when selecting the characteristic signal amplitude, the sensitivity of the detection device, the tolerance of the power electronic device and the system impact requirements need to be comprehensively considered. The larger the amplitude of the characteristic signal, the more conducive it is for the detection device to detect the signal, but the device tolerance and system stability requirements must be balanced.

[0017] Preferably, the characteristic current signal is extracted by fast Fourier transform.

[0018] Preferably, when judging the characteristic current signal, the characteristic current upstream of the fault point and the characteristic current downstream have obvious amplitude difference, but the difference is greatly affected by the position of the fault point and the size of the transition resistance. If only the characteristic current amplitude is used as the fault judgment criterion, its tolerance to the transition resistance is poor. When a three-phase high-resistance grounding fault occurs, it may be difficult to reliably distinguish the fault section. Therefore, the power frequency fault current amplitude is introduced for judgment. After the power frequency fault current amplitude is introduced, the characteristic current signal value is selected as:

[0019]

[0020] Among them, I tz / 50,min K is the ratio of the characteristic current amplitude on the SOP side to the power frequency current amplitude when a three-phase metallic short circuit occurs at the head end of the line. sen is the sensitivity coefficient, which can be taken as 1.25~1.3.

[0021] Preferably, the specific process of fault location includes the following steps:

[0022] S10, first turn on the FTU current monitoring system, and the FTU monitors the current;

[0023] S20, the fault current I monitored by FTU is greater than the fault current setting value I of the original distribution network fault location solution set When , proceed to the next step, otherwise go to step S40;

[0024] S30, first set the current unbalance criterion constant to I und,set , the characteristic current signal criterion value is set to I tz / 50,set , FTU reports fault information according to the fault information reporting logic shown in the figure. If a two-phase short circuit fault occurs, the system power supply side line current imbalance I und Greater than the current unbalance setting value I und,set , report fault information 1, otherwise the SOP side uploads no fault information 0;

[0025] S40, if a three-phase short circuit occurs, the characteristic current I tz / 50 Less than the characteristic current signal setting value I tz / 50,set , upload fault information 1, otherwise the SOP side uploads fault information 0;

[0026] S50. Based on the fault information uploaded by each FTU, the master station collects and analyzes the information and locates the faulty section.

[0027] Preferably, the various information described in step S6 includes time, type, processing process and result. The time when the fault occurs is usually recorded by the monitoring system and protection device of the power system, and the timestamp is recorded immediately when a three-phase short circuit fault is detected. The type of fault is recorded through the electrical quantity data such as current and voltage collected by the monitoring system.

[0028] Compared with the related art, the three-phase short-circuit fault current control method provided by the present invention has the following beneficial effects:

[0029] By connecting the SOP to the distribution network, the fault current characteristics of the distribution network will be significantly changed. The distribution network connected to the SOP is analyzed. The fault at this time is a three-phase symmetrical fault. The control system of the SOP includes a Vf control method for power supply restoration. Therefore, the Vf control of the SOP can be used to generate a characteristic voltage reference, and then the characteristic voltage signal is generated through PWM modulation to locate the fault. By detecting and analyzing this characteristic voltage signal, the fault position can be located more accurately, which improves the accuracy of fault location and improves the operating efficiency and stability of the distribution network. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A flow chart of a method for controlling a three-phase short-circuit fault current of a line provided by the present invention;

[0031] Figure 2 for Figure 1 The flowchart of fault location is shown in FIG. DETAILED DESCRIPTION

[0032] The present invention will be further described below in conjunction with the accompanying drawings and implementation modes.

[0033] Please refer to Figure 1 as well as Figure 2 ,in, Figure 1 A flow chart of a method for controlling a three-phase short-circuit fault current of a line provided by the present invention; Figure 2 for Figure 1 The fault location flow box is shown.

[0034] In the specific implementation process, Figure 1 as well as Figure 2 As shown, the following steps are included:

[0035] S1. Fault detection: abnormal changes are detected by monitoring the voltage and current electrical parameters of the line;

[0036] S2, Fault isolation: When a short circuit fault is found, the fault line is quickly cut off through the circuit breaker to isolate the fault point;

[0037] S3, fault location. After SOP is connected to the distribution network, the fault current characteristics of the distribution network will be significantly changed. The distribution network connected to SOP is analyzed. The fault at this time is a three-phase symmetrical fault. The control system of SOP includes a Vf control method for power supply recovery. Therefore, the Vf control of SOP can be used to generate a characteristic voltage reference, and then the characteristic voltage signal is generated through PWM modulation to locate the fault.

[0038] It should be noted that SOP is a standard operating procedure, which is a description of the standard operating steps and requirements of an event in a unified format to guide and standardize daily work. The Vf control method, also known as V / F control or variable frequency control, is a common method widely used in the field of motor control. Its core idea is to achieve precise control of the motor speed by adjusting the proportional relationship between the motor voltage (V) and frequency (f). PWM is pulse width modulation, which is an analog control technology. It is an electronic technology that equivalently obtains the required waveform (including shape and amplitude) by adjusting the duty cycle of the pulse signal (that is, the ratio of the pulse signal duration to the period in one cycle);

[0039] By directly giving the inner loop output voltage reference value and synchronous phase in Vf control, a set of three-phase symmetrical characteristic voltage signals is generated, and then the required characteristic voltage signal is superimposed on the voltage reference generated by the original current inner loop: After PWM modulation, the corresponding characteristic voltage component can be generated. The expression of the three-phase composite voltage modulation wave is:

[0040]

[0041] Where V is the original power frequency phase voltage modulation amplitude, is the additional characteristic phase voltage modulation wave amplitude, f, f tz are the power frequency and the frequency of the additional characteristic voltage signal respectively;

[0042] Among them, the frequency of the characteristic signal is mainly affected by the following aspects:

[0043] 1. The frequency of the characteristic signal should be lower than the carrier frequency of the VSC. In actual projects, the carrier frequency of the VSC is usually 1-2kHz.

[0044] VSC usually has multiple meanings, but in the field of electrical and automation, VSC most often refers to Voltage Source Converter;

[0045] 2. The characteristic signal frequency should avoid the resonant frequency of the filter at the converter outlet and be less than the cut-off frequency of the filter. The resonant frequency of the LCL filter is usually greater than 10 times the grid frequency and less than 1 / 2 of the switching frequency, which satisfies:

[0046]

[0047] Among them, f n is the rated frequency of the power grid, f w0 is the filter resonant frequency, f sw The switching frequency should avoid the resonant frequency of the filter, and the characteristic frequency should not be too high, which will cause the characteristic signal to be too strongly reduced by the filter and affect the fault location effect. Therefore, the selected characteristic signal frequency should be less than 10 times the rated frequency of the grid, that is, it meets the following requirements:

[0048] f tz <10f n

[0049] Among them, f tz is the characteristic frequency;

[0050] 3. The greater the difference between the upstream and downstream characteristic currents of the fault point, the more conducive it is to the accurate positioning of the fault. The difference between the upstream and downstream characteristic currents mainly depends on the upstream impedance of the fault point and the transition resistance of the fault point. The expression of the upstream and downstream characteristic current signals is:

[0051]

[0052] Among them, I sy is the characteristic current upstream of the fault point, I xy is the characteristic current downstream of the fault point, Z sy is the upstream equivalent impedance of the fault point. As the frequency of the characteristic signal increases, its upstream equivalent impedance Z sy The larger the value, the smaller the ratio of the upstream and downstream characteristic currents, which is helpful for distinguishing the characteristic currents upstream and downstream of the fault point and also helps to correctly report the fault information.

[0053] When selecting the characteristic signal amplitude, the sensitivity of the detection device, the tolerance of the power electronic device and the requirements of the system impact need to be comprehensively considered. The larger the amplitude of the characteristic signal, the more conducive it is for the detection device to detect the signal, but the requirements of the device tolerance and system stability must be balanced;

[0054] For the characteristic current signal, fast Fourier transform is used to extract it. The basic steps of extracting the characteristic current signal include the following steps:

[0055] Step 1: Signal acquisition: using appropriate sensors to collect current signals from the power system;

[0056] Step 2: Signal preprocessing: perform necessary conditioning on the collected current signal. In order to reduce spectrum leakage, the signal will be windowed.

[0057] Step 3: Fast Fourier transform, using the FFT algorithm to calculate the discrete Fourier transform of the signal;

[0058] It should be noted that the FFT algorithm, namely the Fast Fourier Transform, is an efficient algorithm for calculating the Discrete Fourier Transform (DFT) and its inverse transform. The introduction of the FFT algorithm greatly reduces the number of multiplications required to calculate the DFT, especially when the number of sample points N to be transformed is large, the calculation amount of the FFT algorithm is particularly significant.

[0059] When judging the characteristic current signal, the characteristic current upstream of the fault point and the characteristic current downstream have obvious amplitude differences, but the difference is greatly affected by the position of the fault point and the size of the transition resistance. If only the characteristic current amplitude is used as the fault judgment criterion, its tolerance to the transition resistance is poor. When a three-phase high-resistance grounding fault occurs, it may be difficult to reliably distinguish the fault section. Therefore, the power frequency fault current amplitude is introduced for judgment. After the power frequency fault current amplitude is introduced, the characteristic current signal value is selected as:

[0060]

[0061] Among them, I tz / 50,min K is the ratio of the characteristic current amplitude on the SOP side to the power frequency current amplitude when a three-phase metallic short circuit occurs at the head end of the line. sen is the sensitivity coefficient, which can be 1.25 to 1.3;

[0062] The specific process of fault location includes the following steps:

[0063] S10, first turn on the FTU current monitoring system, and the FTU monitors the current;

[0064] S20, the fault current I monitored by FTU is greater than the fault current setting value I of the original distribution network fault location solution set When , proceed to the next step, otherwise go to step S40;

[0065] S30, first set the current unbalance criterion constant to I und,set , the characteristic current signal criterion value is set to I tz / 50,set , FTU reports fault information according to the fault information reporting logic shown in the figure. If a two-phase short circuit fault occurs, the system power supply side line current imbalance I und Greater than the current unbalance setting value I und,set , report fault information 1, otherwise the SOP side uploads no fault information 0;

[0066] FTU (Fault-Tolerant Unit) current monitoring system is an advanced power equipment, which integrates the monitoring, control and protection functions of the power system, and plays an important role in current monitoring.

[0067] Current unbalance values ​​that need to be explained:

[0068] I unb =I n / I p

[0069] I unb,set =K rel I nub

[0070] Among them, I p is the positive sequence current amplitude, I n is the negative sequence current amplitude, I nub It can be taken as 4% (according to the standards of my country, the normal voltage imbalance at the public connection point of the power system shall not exceed 4%), K rel is the reliability coefficient, which can be 1.25 to 1.3. When the transition resistance is large, the amplitude of the positive sequence fault current on the power supply side will decrease. At this time, the current unbalance can better highlight its fault characteristics;

[0071] S40, if a three-phase short circuit occurs, the characteristic current I tz / 50 Less than the characteristic current signal setting value I tz / 50,set , upload fault information 1, otherwise the SOP side uploads fault information 0;

[0072] S50, based on the fault information uploaded by each FTU, the master station collects and analyzes the information and locates the fault section;

[0073] S4. Fault handling: take appropriate measures according to the nature and severity of the fault;

[0074] S5, system recovery: after the fault is resolved, the system is inspected and tested to ensure that all equipment is back to normal working condition, and then power supply is gradually restored;

[0075] S6. Data recording and analysis: record all the information of the fault for subsequent analysis and improvement;

[0076] It should be noted that the information in step S6 includes the time, type, processing process and result. The time of the fault occurrence is usually recorded by the monitoring system and protection device of the power system. When a three-phase short-circuit fault is detected, the timestamp is recorded immediately. The type of fault is recorded by analyzing the electrical characteristics when the fault occurs through the electrical quantity data such as current and voltage collected by the monitoring system. During the fault filtering process, the steps of fault repair, the tools and equipment used, the problems encountered in the repair process and the solutions are recorded in detail. The specific steps and measures for fault repair need to be recorded when the fault is processed, such as replacing damaged equipment and repairing damaged lines. At the same time, the difficulties and challenges encountered in the repair process and the solutions are recorded.

[0077] The circuits and controls involved in the present invention are all prior art and will not be described in detail here.

[0078] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for controlling a three-phase short-circuit fault current in a line, characterized in that: The following steps are involved: S1, fault detection, by monitoring the voltage and current electrical parameters of the line; S2, Fault isolation: When a short circuit fault is found, the fault line is quickly cut off through the circuit breaker to isolate the fault point; S3, fault location. After SOP is connected to the distribution network, the fault current characteristics of the distribution network will be significantly changed. The distribution network connected to SOP is analyzed. The fault at this time is a three-phase symmetrical fault. The control system of SOP includes a Vf control method for power supply recovery. The Vf control of SOP is used to generate a characteristic voltage reference, and then the characteristic voltage signal is generated through PWM modulation to locate the fault. S4. Fault handling: take appropriate measures according to the nature and severity of the fault; S5, system recovery: after the fault is resolved, the system is inspected and tested to ensure that all equipment is back to normal working condition, and then power supply is gradually restored; S6. Data recording and analysis: record all information about the failure for subsequent analysis and improvement.

2. The line three-phase short-circuit fault current control method according to claim 1, characterized in that: By directly giving the inner loop output voltage reference value and synchronous phase in Vf control, a set of three-phase symmetrical characteristic voltage signals is generated, and then the required characteristic voltage signal is superimposed on the voltage reference generated by the original current inner loop: After PWM modulation, the corresponding characteristic voltage component can be generated.

3. The line three-phase short-circuit fault current control method according to claim 2 is characterized in that: When selecting the characteristic signal amplitude, it is necessary to comprehensively consider the sensitivity of the detection device, the tolerance of the power electronic device and the system impact requirements. The larger the amplitude of the characteristic signal, the more conducive it is for the detection device to detect the signal, but the device tolerance and system stability requirements must be balanced.

4. The line three-phase short-circuit fault current control method according to claim 3 is characterized in that: The characteristic current signal is extracted by fast Fourier transform.

5. The line three-phase short-circuit fault current control method according to claim 4, characterized in that: When judging the characteristic current signal, the characteristic current upstream of the fault point and the characteristic current downstream have obvious amplitude differences, but the difference is greatly affected by the position of the fault point and the size of the transition resistance. If only the characteristic current amplitude is used as the fault judgment criterion, its tolerance to the transition resistance is poor. When a three-phase high-resistance grounding fault occurs, it may be difficult to reliably distinguish the fault section. Therefore, the power frequency fault current amplitude is introduced for judgment. After the power frequency fault current amplitude is introduced, the characteristic current signal value is selected as: Among them, I tz / 50,min K is the ratio of the characteristic current amplitude on the SOP side to the power frequency current amplitude when a three-phase metallic short circuit occurs at the head end of the line. sen is the sensitivity coefficient.

6. The line three-phase short-circuit fault current control method according to claim 5, characterized in that: The specific process of fault location includes the following steps: S10, first turn on the FTU current monitoring system, and the FTU monitors the current; S20, the fault current I monitored by FTU is greater than the fault current setting value I of the original distribution network fault location solution set When , proceed to the next step, otherwise go to step S40; S30, first set the current unbalance criterion constant to I und,set , the characteristic current signal criterion value is set to I tz / 50,set , FTU reports fault information according to the fault information reporting logic shown in the figure. If a two-phase short circuit fault occurs, the system power supply side line current imbalance I und Greater than the current unbalance setting value I und,set , report fault information 1, otherwise the SOP side uploads no fault information 0; S40, if a three-phase short circuit occurs, the characteristic current I tz / 50 Less than the characteristic current signal setting value I tz / 50,set , upload fault information 1, otherwise the SOP side uploads fault information 0; S50. Based on the fault information uploaded by each FTU, the master station collects and analyzes the information and locates the faulty section.

7. The line three-phase short-circuit fault current control method according to claim 6, characterized in that: The information described in step S6 includes the time, type, processing process and result. The time when the fault occurs is recorded by the monitoring system and protection device of the power system. When a three-phase short circuit fault is detected, the timestamp is recorded immediately. The type of fault is recorded through the electrical quantity data such as current and voltage collected by the monitoring system.

Images