CN114034963A - Distribution line single-phase earth fault section identification method based on phase current variable quantity - Google Patents
Distribution line single-phase earth fault section identification method based on phase current variable quantity Download PDFInfo
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- G—PHYSICS
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/08—Locating faults in cables, transmission lines, or networks
- G01R31/081—Locating faults in cables, transmission lines, or networks according to type of conductors
- G01R31/085—Locating faults in cables, transmission lines, or networks according to type of conductors in power transmission or distribution lines, e.g. overhead
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
- G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
- G01R31/52—Testing for short-circuits, leakage current or ground faults
Abstract
The invention provides a distribution line single-phase earth fault section identification method based on phase current variation, which comprises the following steps: when a single-phase earth fault occurs in the line, the amplitude and the phase of the variable quantity of the three-phase current of the same measuring point before and after the fault are compared. If the amplitude and the phase of the three-phase current variation are basically the same, determining that the measuring point is on the load side of the fault point; and if one phase in the three-phase current variation is significantly larger in amplitude than the other two phases and is opposite in phase to the other two phases, judging that the measuring point is on the power supply side of the fault point. And uploading the judgment results of each measuring point to the master station, and sequentially comparing the judgment results of two adjacent measuring points by the master station. If two adjacent measurement points are respectively on the power supply side and the load side of the fault point, the fault is judged to occur between the two measurement points. By the technical scheme, the accurate identification of the single-phase earth fault section of the distribution line is realized, and the single-phase earth fault is quickly and selectively cut off from two ends of the line.
Description
Technical Field
The invention relates to the technical field of power system protection and control, in particular to a distribution line single-phase earth fault section identification method based on phase current variable quantity.
Background
Single-phase earth faults are the main type of fault in power distribution networks, accounting for over 80%. To improve the reliability of the power supply, medium voltage distribution systems typically employ a non-effective grounding of the neutral point. In this manner, industry standards specify that operation is allowed to continue for 2 hours after a single-phase ground fault of the system occurs. The method avoids frequent power failure caused by frequent occurrence of the single-phase earth fault, and also leaves enough time for processing the single-phase earth fault. However, the single-phase earth fault can cause overvoltage, which causes great threat to the personal, life and property safety of residents near the earth point. Therefore, the traditional way of handling the single-phase earth fault of the distribution line is fault line selection, that is, a fault line is selected from a plurality of outgoing lines of a substation. The 20 th century and 80 th era proposed single-phase earth fault line selection technology. This technology has developed greatly over thirty years. And respectively deriving a steady state method, a transient state method and a traveling wave method based on the steady state characteristics, the transient state characteristics and the traveling wave characteristics after the fault. The signal injection method detects a faulty line by introducing an external signal.
The four methods are the existing main fault line selection methods. The steady-state method and the transient-state method are used for selecting fault lines by utilizing the difference of steady-state characteristics and transient-state characteristics of different feeder lines after a single-phase earth fault occurs. The steady state method comprises a population amplitude-to-amplitude ratio phase method, a zero sequence admittance method and other classical methods. The transient method includes a first half wave method, a transient characteristic frequency band method and the like. However, under the influence of arc suppression coils and complex operation conditions, the steady-state method and the transient-state method are difficult to meet the field requirements. The signal injection method is to artificially inject signals at the bus of the fault distribution network, and to select lines by a method for detecting signal changes of different lines by analyzing the influence of the signals on fault lines and non-fault lines. The method needs to change or operate the primary-side device, and the signal injection may affect the safe and stable operation of the power system. The traveling wave line selection method is a method for selecting a grounded line based on traveling waves generated by a single-phase ground fault. The method compares the amplitude and polarity of the initial current traveling wave on different feeder lines to select the fault line. Therefore, the traveling wave line selection method comprises an amplitude comparison method, a polarity comparison method and an amplitude and polarity comparison method. The existing traveling wave line selection method is successfully applied to a distribution network, and the traveling wave line selection method and a device developed according to the method are tested on site, so that the requirements on site can be met under most conditions. However, the traveling wave line selection method has certain defects, mainly including that the standards of the current transformers are not uniform and the accuracy of the current transformers to branch lines is not achieved.
The current transformer is an instrument for measuring by converting a large primary side current into a small secondary side current according to the electromagnetic induction principle. A 10kV feeder current transformer configuration is typically required to take into account the load level of the line and the requirements of conventional overcurrent protection. Different load levels and short circuit capacities require different current transformers. Meanwhile, in the process of the expanded construction of the distribution line, the feeder lines accessed by the same transformer substation at different periods use different batches of current transformers, so that the types of the current transformers are different, and the standard of the current transformers which are not unified, so that the difference of transformation ratio and saturation degree is mainly reflected. The traveling wave line selection technology based on the amplitude needs to collect and compare initial current traveling wave amplitudes of all feeder lines of the same transformer substation. The current transformers with different transformation ratios lead to the fact that the conversion of the traveling wave amplitude received by the line selection device is not uniform, and therefore a functional module needs to be added in the device to convert the transformation ratios of the transformers. This increases the complexity of the engineering and reduces reliability. The difference of the saturation is reflected in that the current transformers with different saturation degrees have different transmission characteristics to the initial current traveling wave. The current transformer with lower saturation can cause larger distortion to the initial traveling wave band, so that the amplitude of the initial current traveling wave is attenuated. This can cause errors in the amplitude-based traveling wave line selection technique.
Distribution lines are typically segmented to install circuit breakers or load switches for selective isolation of faults. The traditional line selection strategy can only select a fault line, and cannot realize the identification of a fault section.
Disclosure of Invention
The present invention is directed to solving at least one of the problems of the prior art or the related art.
To this end, an aspect of the present invention is to provide a method for identifying a single-phase ground fault section of a distribution line based on a phase current variation.
In view of this, the present invention provides a method for identifying a single-phase ground fault section of a distribution line based on a phase current variation. It includes: when a single-phase earth fault occurs in the line, the amplitude and the phase of the variable quantity of the three-phase current of the same measuring point before and after the fault are compared. If the amplitude and the phase of the three-phase current variation are basically the same, determining that the measuring point is on the load side of the fault point; and if one phase in the three-phase current variation is significantly larger in amplitude than the other two phases and is opposite in phase to the other two phases, judging that the measuring point is on the power supply side of the fault point. And uploading the judgment results of each measuring point to the master station, and sequentially comparing the judgment results of two adjacent measuring points by the master station. If two adjacent measurement points are respectively on the power supply side and the load side of the fault point, the fault is judged to occur between the two measurement points.
By the technical scheme, the distribution line single-phase earth fault section is accurately identified, a foundation is laid for rapidly and selectively cutting off single-phase earth faults from two ends of the line, conditions are provided for rapidly recovering normal line power supply, the operation reliability of the power line is improved, and the method has good economy and practicability.
The phase current on the distribution line comprises three parts of load current, interphase coupling capacitance current and capacitance current to ground. The head end of the power distribution system is the low-voltage side of a 110kV transformer, and the three phases are usually in angle connection and can be equivalent to a three-phase angle-connected power supply; the tail end is the high-voltage side of distribution transformation, and the three phases are also connected in an angle mode generally and can be equivalent to three-phase angle connection loads. For a distribution system with an ungrounded neutral point, after a single-phase grounding fault occurs, the symmetry between a three-phase load and a three-phase power supply is not changed, so that the load current of the system is not changed under the condition of neglecting the impedance and the line loss of the system.
The distribution line is a three-phase coupled system. The inter-phase coupling capacitance is only related to the wire diameter of the wires, the relative position between the three-phase wires and the dielectric constant of a substance between the wires, and is not related to whether the system is grounded or not. Meanwhile, after the single-phase earth fault occurs, the phase voltage of the system is not changed, so that the current of the inter-phase coupling capacitor of the system is not changed.
The capacitance-to-ground current of the distribution line is determined by the small voltage-to-ground and the ground-to-ground capacitance. When the single-phase earth fault occurs to the distribution line, the earth capacitance of the earth phase is short-circuited, so that the earth capacitance is reduced to 0. The voltage to ground of the non-faulty phase rises and the capacitance to ground does not change, so the capacitance to ground current increases.
From the above, it can be concluded that the change of the current on the line after the single-phase ground fault occurs depends on the change of the capacitance-to-ground current.
After the single-phase earth fault occurs, the phase current is changed by charging and discharging the line-to-earth distributed capacitor. Taking phase a grounding as an example, when phase a grounding fault occurs in the system, phase a is shorted to the grounding capacitor, and the charges stored at both ends of the capacitor are discharged through the grounding point and flow into the ground. On a non-fault line, the direction of the A-phase capacitive current appears to flow from the line to the bus; on the fault line, the power supply side of the grounding point and the load side of the grounding point have the same capacitance current flowing direction. On the power supply side of the grounding point, the relative capacitance current A flows from the bus to the line; on the load side of the ground point, a relative capacitance current flows from the line to the bus, and to ground at the ground point.
For non-failed phases B-phase and C-phase, the capacitance to ground will be charged to ground as the phase voltages are raised. After charging is complete, the B, C phase capacitance-to-ground current will increase, with these increased portions flowing to the bus either through the line head end. The portion of BC that increases relative to the point capacitance can be considered to be flowing from the line to the bus.
In order to realize the section identification of the single-phase earth fault, the characteristic difference between the fault point power supply side and the fault point load side in the fault line needs to be analyzed. In order to describe the phase current variation after the single-phase earth fault, a steady-state phasor analysis method is adopted, namely three-phase earth currents before and after the single-phase earth fault are respectively analyzed, and the corresponding earth current difference value is calculated, so that the three-phase current variation can be obtained.
Firstly, the power supply side of the fault line is analyzed. Fig. 1(a), 1(b) and 1(c) show graphs of voltage/current-to-ground phasors and current-to-ground phasors before and after a fault at the head end of a fault line, respectively.
In the context of figure 1(a),
respectively showing the three-phase voltage of the head end of the fault line before the fault,
respectively represent the relative ground currents of the three phases; before a fault occurs, the three-phase capacitance-to-ground current can be expressed as:
in the above formula, Xc represents a lumped parameter of any relative capacitance to ground.
In the context of FIG. 1(b),
indicating the electricity of the B phase and C phase at the head end of the fault line after the faultThe pressure is applied to the inner wall of the cylinder,
phase B and phase C phase ground currents respectively,
is the current flowing through the fault point to earth; after the phase a ground fault occurs, the capacitance to ground of the phase B and the phase C does not change, so the current to ground of the phase BC can be expressed as:
the BC two-phase voltage after the fault is as follows:
in the case of FIG. 1(c),
respectively, represent the amount of change in the phase-to-ground current of the three phases. According to the phasor diagram, the variation of the relative ground current of the BC two phases is obtained as follows:
at this time, the fault current flowing into the ground through the fault point is the sum of the two relative ground capacitance currents BC after the fault, that is:
the phase a current variation is:
the relationship of the capacitance-to-ground current variation of the power supply side of the fault point can be obtained in the following steps:
that is, on the power supply side of the fault point, the fault phase current variation is opposite to the non-fault phase, and the amplitude is four times of the non-fault phase current variation.
The change conditions of the phase-to-ground currents of the load side, the phase B and the phase C of the fault point are similar to those of the power supply side of the fault line, so that the change conditions are not analyzed. However, for the phase a, since the capacitance to ground of the phase a is shorted by the fault point at this time, the capacitance to ground current on the line is 0 at this time, and the relationship of the change amount of the capacitance to ground current is as follows:
therefore, the conclusion can be obtained that the three-phase current variation quantity directions are the same and the amplitudes are the same on the load side of the fault point of the fault line.
In summary, the difference between the phase current variation before and after the single-phase ground fault is shown in the following table:
through the principle analysis, the three-phase current variable quantity before and after the single-phase earth fault detected at the observation point of the fault point power supply side is known, and the fault phase is obviously larger than the non-fault phase and has opposite phase; the three-phase current variable quantity before and after the single-phase earth fault detected by the load side of the fault point is equal in amplitude and polarity between the fault phase and the non-fault phase.
Using the above principles, measurement points can be placed at the segments of the distribution line. And the measuring points detect and store the three-phase current waveforms within a certain time range in real time. When the zero sequence voltage is detected to be larger than the setting value and the three-phase current has no overcurrent, the system is indicated to have single-phase earth fault. At the moment, the measuring point avoids the transient state of two cycles, and the stable waveform of the three-phase current after the fault is obtained. And subtracting the steady-state waveform before the fault from the steady-state waveform after the fault to obtain the waveform of the phase current variable quantity, and further calculating the amplitude and the phase. And comparing the amplitude and the phase of the three-phase current variation. If the amplitude and the phase of the three-phase current variation are basically the same, determining that the measuring point is on the load side of the fault point; and if one phase in the three-phase current variation is significantly larger in amplitude than the other two phases and is opposite in phase to the other two phases, judging that the measuring point is on the power supply side of the fault point.
After judgment is finished, each measuring point uploads a judgment result to the main station, and the main station comprehensively researches and judges. And the master station compares the judgment results of two adjacent measurement points of the same line in sequence. If two adjacent measuring points are respectively arranged on the power supply side and the load side of the fault point, judging that the fault occurs between the two measuring points; if the judgment results of two adjacent measurements are both on the power supply side or the load side, the fault is not between the two measurement points.
After the determination is completed, the master station may perform further processing. The main station can remotely control the circuit breakers at two ends of the fault section to be tripped off, so that the single-phase earth fault can be quickly isolated. And the attendant is informed to carry out timely treatment.
Drawings
Fig. 1(a), 1(b) and 1(c) show a voltage/ground current phasor diagram and a ground current phasor variation before and after a fault at the head end of a fault line, respectively;
fig. 2 is a flow chart of a proposed phase current variation-based single-phase ground fault section identification algorithm of a distribution line according to the present invention;
figure 3 shows a schematic diagram of the present invention applied to a four-segment distribution line.
Detailed Description
In order that the above objects, features and advantages of the present invention can be more clearly understood, a more particular description of the invention will be rendered by reference to the appended drawings. It should be noted that the embodiments and features of the embodiments of the present application may be combined with each other without conflict.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, however, the present invention may be practiced otherwise than as specifically described herein, and thus the scope of the present invention is not limited by the specific embodiments disclosed below.
Referring to fig. 2 and 3, according to an embodiment of the present invention, a method for identifying a single-phase ground fault section of a distribution line based on a phase current variation is provided, where the method includes:
(1) as shown in fig. 3, measurement points M1, M2, M3, and M4 are arranged at substation outlets and segments of one line.
(2) Each measurement point samples the three-phase current waveform in real time. The sampling frequency was 1 kHz. While storing the pre-fault waveform.
(3) The algorithm starts up by means of zero sequence voltage. And step 202, when the zero sequence voltage is detected to be greater than the setting value and the three-phase current has no overcurrent, indicating that the system has a single-phase earth fault. And step 204, the transient state of the two cycles is avoided at the measuring point, and the steady-state waveform of the three-phase current after the fault is obtained and stored.
(4) And step 206, subtracting the steady state waveform before the fault from the steady state waveform after the fault to obtain the waveform of the phase current variable quantity, and further calculating the amplitude and the phase.
(5) And step 208, comparing the amplitude and the phase of the three-phase current variation. If the amplitude and the phase of the three-phase current variation are basically the same, determining that the measuring point is on the load side of the fault point; and if one phase in the three-phase current variation is significantly larger in amplitude than the other two phases and is opposite in phase to the other two phases, judging that the measuring point is on the power supply side of the fault point. And uploading the judgment results of the measurement points to a master station, and sequentially comparing the judgment results of two adjacent measurement points of the same line by the master station. If two adjacent measuring points are respectively arranged on the power supply side and the load side of the fault point, judging that the fault occurs between the two measuring points; if the judgment results of two adjacent measurements are both on the power supply side or the load side, the fault is not between the two measurement points.
(6) And step 210, the master station can remotely control the circuit breakers at the two ends of the fault section to be tripped off, so that the single-phase earth fault is quickly isolated. And the attendant is informed to carry out timely treatment.
The above is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and various modifications and changes will occur to those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (7)
1. A distribution line single-phase earth fault section identification method based on phase current variation is characterized by comprising the following steps:
when a single-phase earth fault occurs in a line, comparing the amplitude and the phase of the variation of the three-phase current of the same measuring point before and after the fault, and if the amplitude and the phase of the variation of the three-phase current are basically the same, judging that the measuring point is on the load side of the fault point; if one phase amplitude in the three-phase current variation is obviously larger than the other two phases and the phase is opposite to the other two phases, the measuring point is judged to be on the power supply side of the fault point, each measuring point uploads the judgment result to the master station, the master station compares the judgment results of the two adjacent measuring points in sequence, and if the two adjacent measuring points are on the power supply side and the load side of the fault point respectively, the fault is judged to occur between the two measuring points.
2. The method of claim 1, wherein the phase current variance is a phasor value obtained by subtracting the steady-state phase current before the fault from the steady-state phase current after the fault, and comprises an amplitude and a phase.
3. The method for identifying the distribution line single-phase earth fault section based on the phase current variation as claimed in claim 1, wherein the three-phase current variation at the same measurement point is compared to determine the relative relationship between the measurement point and the fault point, and if the amplitude and the phase of the three-phase current variation are substantially the same, the measurement point is determined to be on the load side of the fault point; and if one phase in the three-phase current variation is significantly larger in amplitude than the other two phases and is opposite in phase to the other two phases, judging that the measuring point is on the power supply side of the fault point.
4. The method for identifying the distribution line single-phase ground fault section based on the phase current variation as claimed in claim 1, wherein the master station needs to perform comprehensive judgment on data, the master station sequentially compares the judgment results of two adjacent measurement points, and if the two adjacent measurement points are respectively on the power supply side and the load side of the fault point, the fault is judged to occur between the two measurement points.
5. The method for identifying the distribution line single-phase ground fault section based on the phase current variation amount as recited in claim 1, wherein the measuring device is required to communicate with a master station, the master station is a master terminal during communication, the measuring point is a slave terminal, and information is transmitted from the slave terminal to the master terminal during communication.
6. The method for identifying the distribution line single-phase earth fault section based on the phase current variation amount as claimed in claim 2, wherein the three-phase current is sampled and stored, the sampling frequency is selected to be 1kHz, and the waveforms to be stored are steady-state current waveforms before and after the fault.
7. The method for identifying the single-phase ground fault section of the distribution line based on the phase current variation according to claim 2, wherein transformation ratios and polarities of three-phase current transformers at the same measuring point are consistent.
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| CN112436481A (en) * | 2020-11-12 | 2021-03-02 | 贵州电网有限责任公司 | Self-adaptive protection method for distribution line of neutral point non-effective grounding system |
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