CN114280415A - Power distribution network ground fault processing method based on parallel resistors of arc suppression coils - Google Patents
Power distribution network ground fault processing method based on parallel resistors of arc suppression coils Download PDFInfo
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Abstract
The invention provides a power distribution network ground fault processing method based on arc suppression coil parallel resistors, which comprises the following steps of: when the power distribution network has a single-phase short-circuit earth fault, judging whether the fault is an intermittent fault; if the fault is not an intermittent fault, arc extinction is carried out in the compensation time through the arc extinction coil; if the fault of the power distribution network does not disappear after the arc extinction, the permanent fault is judged to occur; when the intermittent fault or the permanent fault occurs in the power distribution network, estimating the resistance value of a transition resistor of a fault point, and evaluating the reliability of a line selection result; and controlling the access of the parallel resistor of the arc suppression coil and the removal of the fault line according to the transition resistor resistance value of the fault point and the reliability of the line selection result. The invention can sensitively remove the fault and avoid frequent tripping due to transient fault, thereby greatly improving the reliability of the operation of the power distribution network system.
Description
Technical Field
The invention relates to the technical field of power distribution network ground protection of a power system, in particular to a power distribution network ground fault processing method based on arc suppression coil parallel resistors.
Background
The neutral point grounding mode mainly comprises three modes of ungrounded mode, resonant grounding mode and small resistance grounding mode, the single-phase grounding fault processing strategy is limited by different grounding modes, and the single-phase grounding fault processing modes of different grounding modes have certain difference. In 10kV power distribution networks in China, most of the power distribution networks adopt a mode of resonant grounding, namely grounding of a neutral point through an arc suppression coil, and along with the continuous development of the power distribution networks, places adopting a low-resistance grounding mode are gradually increased.
When single-phase earth fault occurs, the arc suppression coil generates inductive current to compensate earth capacitance current, so that the current passing through the earth point is lower than the current value needed for generating intermittent arc or maintaining stable arc, the influence caused by system arc grounding can be eliminated, and the non-fault phase is prevented from generating too high voltage value. Meanwhile, transient earth faults can be eliminated by self, and permanent earth faults can continue to operate for two hours in a charged mode, so that the stability of the power distribution network can be improved. However, when a single-phase earth fault occurs in the power distribution system, the generated fault current is small, a fault line is not easy to be found, the relay protection device is not easy to act, and the fault cannot be eliminated sensitively, particularly when a high-impedance earth fault occurs.
The grounding mode of the neutral point through the small resistor is generally applied to the field with high cabling degree and high automation level requirement of a power distribution network line, when a single-phase grounding short circuit fault occurs in a power distribution system, the neutral point is connected with the ground through the small resistor, so that zero-sequence current generated by the line where the fault is located is rapidly increased, and the magnitude of the zero-sequence current is related to the magnitude of capacitance current, the resistance value of the neutral point small resistor and the resistance value of a grounding resistor of the system. If the zero sequence current exceeds the setting value of the relay protection, the fault line can be cut off rapidly by the relay protection device. However, the small-resistance grounding method still has certain disadvantages, a fault line is cut off once the zero-sequence current exceeds a setting value, when transient faults occur, frequent tripping of the line is inevitably caused, and the tripping is usually unnecessary, so that the operation reliability of the system is not high.
Disclosure of Invention
The invention aims to solve the technical problems and provides a power distribution network ground fault processing method based on arc suppression coil parallel resistors, which can be used for flexibly eliminating faults and avoiding frequent tripping due to transient faults, so that the reliability of the operation of a power distribution network system is greatly improved.
The technical scheme adopted by the invention is as follows:
a power distribution network ground fault processing method based on arc suppression coil parallel resistors comprises the following steps: when the power distribution network has a single-phase short-circuit earth fault, judging whether the fault is an intermittent fault; if the fault is not an intermittent fault, arc extinction is carried out in the compensation time through the arc extinction coil; if the fault of the power distribution network does not disappear after the arc extinction, the permanent fault is judged to occur; when the intermittent fault or the permanent fault occurs in the power distribution network, estimating the resistance value of a transition resistor of a fault point, and evaluating the reliability of a line selection result; and controlling the access of the parallel resistor of the arc suppression coil and the removal of the fault line according to the transition resistor resistance value of the fault point and the reliability of the line selection result.
Controlling the access of the parallel resistor of the arc suppression coil and the removal of the fault line according to the transition resistor resistance value of the fault point and the reliability of the line selection result, and specifically comprising the following steps: judging whether the reliability of the line selection result is higher than a reliability threshold value; if the reliability of the line selection result is higher than the reliability threshold value, the fault line is cut off; if the reliability of the line selection result is not higher than the reliability threshold, further judging whether the transition resistance value of the fault point is higher than the transition resistance setting value; if the transition resistance value of the fault point is higher than the transition resistance setting value, sending alarm information; if the transition resistance value of the fault point is not higher than the transition resistance setting value, the parallel resistor is accessed after delaying for a first preset time; if the zero sequence current protection is started to cut off the fault line within a second preset time after the parallel resistor is connected, the parallel resistor is disconnected; and if the zero sequence current protection is not started within a second preset time after the parallel resistor is connected, sending alarm information and disconnecting the parallel resistor.
And setting the transition resistance setting value by combining the setting value of the zero sequence overcurrent protection of the actual line of the power distribution network.
The power distribution network is a 10kV power distribution network, and whether the power distribution network has a single-phase short circuit grounding fault or not and whether the fault disappears or not are judged, wherein 15V is used as a zero sequence voltage threshold value.
And the compensation time of the arc suppression coil is 3-10 s.
The first preset time is greater than 2 power frequency cycles.
And the second preset time is set according to the maximum action time limit of zero-sequence current protection.
The invention has the beneficial effects that:
the invention firstly tries to eliminate the fault by utilizing the arc suppression coil, secondly integrates the transition resistance value of the fault point and the reliability of the line selection result, and accesses the grounding resistance connected with the arc suppression coil in parallel at a proper time, thereby ensuring the zero sequence current protection to accurately act, cutting off the fault line, avoiding frequent tripping when encountering intermittent fault by timely disconnecting the parallel resistance to influence the stability of the power system, and timely and accurately tripping when facing high-resistance grounding fault of about 500 omega. Therefore, faults can be removed sensitively, and frequent tripping caused by transient faults can be avoided, so that the running reliability of the power distribution network system is greatly improved.
Drawings
Fig. 1 is a schematic structural diagram of parallel resistors of arc suppression coils in a power distribution network according to an embodiment of the present invention;
fig. 2 is a flowchart of a power distribution network ground fault processing method based on arc suppression coil parallel resistors according to an embodiment of the invention;
fig. 3 is a flowchart of a method for processing a ground fault of a power distribution network based on parallel resistors of arc suppression coils according to an embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
As shown in fig. 1, in the embodiment of the present invention, the neutral point of the grounding transformer of the power distribution network is grounded through the arc suppression coil, and the arc suppression coil may be connected in parallel with a resistor (hereinafter, referred to as a parallel resistor), and the parallel resistor may be controlled to be opened or closed by controlling the opening and closing of the switch through the controller.
As shown in fig. 2, the method for processing the ground fault of the power distribution network based on the parallel resistors of the arc suppression coils in the embodiment of the invention includes the following steps:
and S1, judging whether the power distribution network has an intermittent fault when the power distribution network has a single-phase short-circuit grounding fault.
In an embodiment of the present invention, whether a single-phase short-circuit ground fault occurs in the power distribution network may be determined according to a zero-sequence voltage threshold, for example, 15V may be taken as the zero-sequence voltage threshold for a 10kV power distribution network.
In one embodiment of the invention, an intermittent fault is determined if the multiple faults in a short time all last for less than the compensation time Ts of the arc suppression coil. That is, if the fault can be eliminated by itself without active control or operation, but occurs frequently, the fault is an intermittent fault.
And S2, if the fault is not an intermittent fault, arc extinction is carried out through the arc extinction coil within the compensation time of the fault.
If the fault can not be eliminated by itself, the arc suppression coil can fully extinguish the arc within the compensation time Ts, and a better arc suppression effect can be achieved by injecting current from the neutral point so as to avoid causing larger influence on a power distribution network system.
In one embodiment of the invention, the compensation time Ts of the arc suppression coil can be 3-10 s.
And S3, if the fault of the power distribution network does not disappear after arc extinction, determining that a permanent fault occurs.
In an embodiment of the present invention, whether the power distribution network fault disappears may also be determined according to a zero sequence voltage threshold, and if the zero sequence voltage after arc extinction in step S2 is not higher than the threshold, the fault disappears, the power distribution network system recovers to normal operation and continues to monitor whether the power distribution network has a single-phase short-circuit ground fault, otherwise, a permanent fault occurs.
And S4, when the power distribution network has intermittent faults or permanent faults, estimating the resistance value of the transition resistor of the fault point, and evaluating the reliability of the line selection result.
In one embodiment of the present invention, the estimation of the transition resistance of the fault point may be performed by using a phase current variation method, or may be performed by calculating the capacitance to ground of each line according to the line current and voltage variation, so as to estimate the transition resistance. For the evaluation of the reliability of the line selection result, an algorithm using the waveform polarity comparison result as the line selection basis, such as judging the relationship between the transient zero-mode voltage derivative and the zero-mode current polarity, may be selected, or an algorithm using the fault component amplitude comparison result as the line selection basis, such as a transient current amplitude comparison method, may be selected. And selecting a proper algorithm according to the actual situation to obtain the reliability evaluation result.
And S5, controlling the access of the parallel resistor of the arc suppression coil and the cutting of the fault line according to the transition resistor resistance value of the fault point and the reliability of the line selection result.
Specifically, whether the reliability of the line selection result is higher than a reliability threshold value or not can be judged, and if the reliability of the line selection result is higher than the reliability threshold value, namely the line selection result is reliable, the result is directly acted on protection tripping, a fault line is cut off, and the processing flow is ended; and if the reliability of the line selection result is not higher than the reliability threshold value, namely the line selection result is not reliable, further judging whether the resistance value of the transition resistor of the fault point is higher than the setting value of the transition resistor. The setting value of the transition resistance can be set by combining with the actual setting current value of the power distribution network protection, namely the setting value of the zero-sequence overcurrent protection of the actual line of the power distribution network, different power distribution lines are different, for example, if the parallel resistance is 300 Ω, when the setting value of the zero-sequence overcurrent protection is 10A, the fault judgment of the transition resistance below 500 Ω can be completed, and the setting value of the transition resistance can be set to 500 Ω.
If the transition resistance value of the fault point is higher than the transition resistance setting value, sending alarm information and ending the processing flow; if the transition resistance value of the fault point is not higher than the setting value of the transition resistance, the parallel resistance is connected after the first preset time t1 is delayed, and the fault current parameter is amplified so as to cut off the fault line through the action of the zero sequence current protection device.
If the zero-sequence current protection is started to cut off the fault line within a second preset time t2 after the parallel resistor is switched in, the parallel resistor is switched off; if the zero sequence current protection is not started within a second preset time t2 after the parallel resistor is connected, namely the fault line is not successfully cut off, an alarm message is sent, and the parallel resistor is disconnected. It should be understood that after the parallel resistor is connected, if the zero-sequence fault current value is large enough, the relay protection device responsible for zero-sequence current protection will act in time to cut off the fault line, and the ground fault disappears instantly. However, under the condition of high impedance grounding, the zero sequence fault current may not reach the setting value of the relay protection device, so that the relay protection device cannot act, and at the moment, the part can be used as the backup protection of the system, find out the line with the short circuit grounding fault, and send out an alarm prompt to ensure that the power system can safely and stably operate.
Fig. 3 is a flowchart of a method for processing a ground fault of a power distribution network based on parallel resistors of arc suppression coils according to an embodiment of the present invention, which can be understood by referring to fig. 3.
In one embodiment of the present invention, whether zero sequence current protection is enabled or not can be judged by the neutral point voltage. If the neutral point voltage recovers to be normal, the action is normal, and the fault line is tripped, the parallel resistor is automatically disconnected by the controller, and the power distribution network system recovers to be in a normal operation state. If the neutral point voltage is still high, after a second preset time t2, the system tripping device is considered to be abnormal, the fault line is not tripped, and at the moment, in order to protect the parallel resistor, the controller automatically disconnects the parallel resistor and simultaneously sends out an abnormal tripping alarm.
In summary, in the embodiment of the present invention, when the power distribution network is in normal operation, the ground resistor, i.e., the parallel resistor, is not put into operation, and only when a fault that cannot be solved by the arc suppression coil occurs in the power distribution network system, the ground resistor is put into operation in a short time to remove the fault line. After the fault line is cut off, the controller can automatically disconnect the grounding resistor according to the setting time, and the power distribution network system recovers to a normal operation state.
In one embodiment of the invention, the parallel resistors are chosen to comply with the following principle: on the premise of not generating large fault residual current (about 10A), the parallel resistor can provide enough fault amount information for line selection, and a fault line can be accurately selected within a certain range of the grounding transition resistor. In general, the detuning degree of a neutral point in a system grounded through an arc suppression coil is 5% -10%, the neutral point adopts a parallel resistor of 300 ohms, and the residual current of a fault point is less than 10A, so that the principle can be met; when the absolute value of the detuning degree is close to 20%, a parallel resistor of 300 omega is selected, and when a metallic grounding fault occurs or a grounding transition resistor is smaller than a fault of 100 omega, the amplitude of the residual current of the single-phase grounding point fault of the power grid slightly exceeds 10A; when the grounding transition resistance is larger than 100 omega, the residual current of the single-phase grounding point can be smaller than 10A. In an actual power grid, a current-carrying part of electrical equipment discharges due to insulation damage caused by mechanical damage, insulation pollution aging, lightning stroke and the like, or branches, birds, beasts and the like are bridged on a power transmission line to cause certain transition resistance. Therefore, it is appropriate to select the 300 Ω ground resistance even in the case where the degree of detuning is 20%. Therefore, it is appropriate to connect a 300 Ω ground resistance in parallel to the neutral point in a 10kV neutral point arc suppression coil grounding system. By analyzing and calculating the residual current of the fault point when the system has single-phase earth fault when the metal earth fault and the transition resistance of the arc suppression coil are 100 omega and 300 omega under the condition of different detuning degrees and different parallel resistance values, the method can know that when the neutral point has single-phase earth fault through the arc suppression coil earth system, after the neutral point puts about 300 omega parallel earth resistance, the active component of the zero-sequence current flowing through the fault circuit is far larger than the active component of the zero-sequence current flowing through the normal circuit, and the direction of the active component is opposite to the voltage of the zero-sequence current flowing through the normal circuit, even if the grounding transition resistance is up to 500 omega, the value of the active component of the zero-sequence current flowing through the fault circuit is also larger than 1A, the measurement requirement of a line selection device can be met, and the grounding resistance of the neutral point parallel 300 omega can meet the requirement of line selection.
The first preset time t1 is determined as follows: in 1-2 cycles after single-phase grounding, zero sequence transient current of the system can be basically attenuated, and the larger the transition resistance value is, the faster the attenuation of the zero sequence transient current of the system is. Therefore, when the single-phase earth fault occurs in the power distribution network system, after 2 power frequency cycles of the fault, the neutral point is put into parallel connection with the ground resistor, and at the moment, the fault line selection of the system can be basically not influenced by the transient process of the earth connection, and the best line selection effect can be achieved. Therefore, the first preset time t1 in the embodiment of the present invention may be greater than 2 power frequency cycles, for example, may be 2.5 to 3.5 power frequency cycles.
The second preset time t2 is determined as follows: the second preset time t2 is a period of time from the time when the parallel resistor is connected to the time when the fault line resistor is cut off, the value of the second preset time t2 is greater than the maximum action time limit of the zero sequence overcurrent protection of the system, and after the parallel resistor is connected to the time when the second preset time t2 is reached, the zero sequence current does not reach the starting threshold value of the zero sequence overcurrent protection of the system, the fault processing is not successful, and the parallel resistor is forcibly cut off at this time. In the case that the fault processing is not successfully executed, the second preset time t2 should be set according to the maximum action time limit of zero sequence overcurrent protection of the actual distribution line, and different lines are different and can be generally set to be 3-5 s.
According to the power distribution network ground fault processing method based on the parallel resistors of the arc suppression coils, firstly, fault elimination by the arc suppression coils is tried, secondly, the transition resistance values of fault points and the reliability of line selection results are synthesized, the ground resistors connected with the arc suppression coils in parallel are connected in due time, zero sequence current protection can accurately act, fault lines are cut off, frequent tripping can be avoided when intermittent faults occur through timely disconnection of the parallel resistors, the stability of a power system is influenced, and timely and accurate tripping can also be realized when high-resistance ground faults of about 500 ohms face. Therefore, faults can be removed sensitively, and frequent tripping caused by transient faults can be avoided, so that the running reliability of the power distribution network system is greatly improved.
In the description of the present invention, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. The meaning of "plurality" is two or more unless specifically limited otherwise.
In the present invention, unless otherwise expressly stated or limited, the terms "mounted," "connected," "secured," and the like are to be construed broadly and can, for example, be fixedly connected, detachably connected, or integrally formed; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood by those skilled in the art according to specific situations.
In the present invention, unless otherwise expressly stated or limited, the first feature "on" or "under" the second feature may be directly contacting the first and second features or indirectly contacting the first and second features through an intermediate. Also, a first feature "on," "over," and "above" a second feature may be directly or diagonally above the second feature, or may simply indicate that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature may be directly under or obliquely under the first feature, or may simply mean that the first feature is at a lesser elevation than the second feature.
In the description herein, references to the description of the term "one embodiment," "some embodiments," "an example," "a specific example," or "some examples," etc., mean that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the schematic representations of the terms used above are not necessarily intended to refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Furthermore, various embodiments or examples and features of different embodiments or examples described in this specification can be combined and combined by one skilled in the art without contradiction.
Any process or method descriptions in flow charts or otherwise described herein may be understood as representing modules, segments, or portions of code which include one or more executable instructions for implementing specific logical functions or steps of the process, and alternate implementations are included within the scope of the preferred embodiment of the present invention in which functions may be executed out of order from that shown or discussed, including substantially concurrently or in reverse order, depending on the functionality involved, as would be understood by those reasonably skilled in the art of the present invention.
The logic and/or steps represented in the flowcharts or otherwise described herein, e.g., an ordered listing of executable instructions that can be considered to implement logical functions, can be embodied in any computer-readable medium for use by or in connection with an instruction execution system, apparatus, or device, such as a computer-based system, processor-containing system, or other system that can fetch the instructions from the instruction execution system, apparatus, or device and execute the instructions. For the purposes of this description, a "computer-readable medium" can be any means that can contain, store, communicate, propagate, or transport the program for use by or in connection with the instruction execution system, apparatus, or device. More specific examples (a non-exhaustive list) of the computer-readable medium would include the following: an electrical connection (electronic device) having one or more wires, a portable computer diskette (magnetic device), a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber device, and a portable compact disc read-only memory (CDROM). Additionally, the computer-readable medium could even be paper or another suitable medium upon which the program is printed, as the program can be electronically captured, via for instance optical scanning of the paper or other medium, then compiled, interpreted or otherwise processed in a suitable manner if necessary, and then stored in a computer memory.
It should be understood that portions of the present invention may be implemented in hardware, software, firmware, or a combination thereof. In the above embodiments, the various steps or methods may be implemented in software or firmware stored in memory and executed by a suitable instruction execution system. For example, if implemented in hardware, as in another embodiment, any one or combination of the following techniques, which are known in the art, may be used: a discrete logic circuit having a logic gate circuit for implementing a logic function on a data signal, an application specific integrated circuit having an appropriate combinational logic gate circuit, a Programmable Gate Array (PGA), a Field Programmable Gate Array (FPGA), or the like.
It will be understood by those skilled in the art that all or part of the steps carried by the method for implementing the above embodiments may be implemented by hardware related to instructions of a program, which may be stored in a computer readable storage medium, and when the program is executed, the program includes one or a combination of the steps of the method embodiments.
In addition, functional units in the embodiments of the present invention may be integrated into one processing module, or each unit may exist alone physically, or two or more units are integrated into one module. The integrated module can be realized in a hardware mode, and can also be realized in a software functional module mode. The integrated module, if implemented in the form of a software functional module and sold or used as a stand-alone product, may also be stored in a computer readable storage medium.
Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.
Claims (7)
1. A power distribution network ground fault processing method based on arc suppression coil parallel resistors is characterized by comprising the following steps:
when the power distribution network has a single-phase short-circuit earth fault, judging whether the fault is an intermittent fault;
if the fault is not an intermittent fault, arc extinction is carried out in the compensation time through the arc extinction coil;
if the fault of the power distribution network does not disappear after the arc extinction, the permanent fault is judged to occur;
when the intermittent fault or the permanent fault occurs in the power distribution network, estimating the resistance value of a transition resistor of a fault point, and evaluating the reliability of a line selection result;
and controlling the access of the parallel resistor of the arc suppression coil and the removal of the fault line according to the transition resistor resistance value of the fault point and the reliability of the line selection result.
2. The method for processing the ground fault of the power distribution network based on the parallel resistors of the arc suppression coils as claimed in claim 1, wherein the method for controlling the access of the parallel resistors of the arc suppression coils and the removal of the fault line according to the transition resistor resistance value of the fault point and the reliability of the line selection result specifically comprises the following steps:
judging whether the reliability of the line selection result is higher than a reliability threshold value;
if the reliability of the line selection result is higher than the reliability threshold value, the fault line is cut off;
if the reliability of the line selection result is not higher than the reliability threshold, further judging whether the transition resistance value of the fault point is higher than the transition resistance setting value;
if the transition resistance value of the fault point is higher than the transition resistance setting value, sending alarm information;
if the transition resistance value of the fault point is not higher than the transition resistance setting value, the parallel resistor is accessed after delaying for a first preset time;
if the zero sequence current protection is started to cut off the fault line within a second preset time after the parallel resistor is connected, the parallel resistor is disconnected;
and if the zero sequence current protection is not started within a second preset time after the parallel resistor is connected, sending alarm information and disconnecting the parallel resistor.
3. The method for processing the ground fault of the power distribution network based on the arc suppression coil parallel resistor as recited in claim 2, wherein the transition resistor setting value is set in combination with a setting value of zero-sequence overcurrent protection of an actual line of the power distribution network.
4. The method for processing the ground fault of the power distribution network based on the arc suppression coil parallel resistor is characterized in that the power distribution network is a 10kV power distribution network, and the zero-sequence voltage threshold value of 15V is used for judging whether the power distribution network has a single-phase short circuit ground fault or not and whether the fault disappears.
5. A method for handling a ground fault in a power distribution network based on parallel resistors with arc suppression coils as set forth in claim 4, wherein the compensation time of the arc suppression coils is 3-10 s.
6. The method for processing the ground fault of the power distribution network based on the arc suppression coil parallel resistor as recited in claim 2, wherein the first preset time is more than 2 power frequency periods.
7. The method for processing the ground fault of the power distribution network based on the arc suppression coil parallel resistor as recited in claim 2, wherein the second preset time is set according to a zero-sequence current protection maximum action time limit.
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| CN115184729A (en) * | 2022-07-20 | 2022-10-14 | 国网辽宁省电力有限公司电力科学研究院 | Simulation system and method for automatically detecting and processing intermittent arc grounding fault |
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