CN117741343A - Single-phase earth fault transition resistance calculation method, fault judgment method and system - Google Patents
Single-phase earth fault transition resistance calculation method, fault judgment method and system Download PDFInfo
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Abstract
The invention discloses a single-phase grounding fault transition resistance calculation method, a fault judgment method and a system, which are used for judging whether the operation mode of a power grid is changed when the power grid does not have faults in a power distribution area, if so, withdrawing an arc suppression coil, measuring the voltage and the capacitance current of a neutral point once, and putting the arc suppression coil into the power grid again after the measurement; if not, continuously monitoring the three-phase voltage and the bus zero sequence voltage of the arc suppression coil grounding system; when the zero sequence voltage of the bus is greater than a zero sequence voltage threshold, selecting a grounding circuit and a grounding phase, acquiring the voltage of the fault phase in normal operation, measuring the neutral point voltage and the detuning degree, adjusting the gear of the arc suppression coil after a preset time interval, and re-measuring the neutral point voltage and the detuning degree to obtain the neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gears after grounding; and calculating the grounding transition resistance according to the voltage and the capacitance current of the fault phase in normal operation and the neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gears after grounding.
Description
Technical Field
The invention belongs to the technical field of single-phase earth fault processing of a power distribution network, and particularly relates to a single-phase earth fault transition resistance calculation method, a fault judgment method and a system.
Background
The urban power grid mainly adopts a small-current grounding mode, and has the main advantage that the urban power grid can still run for 1-2 hours when single-phase grounding faults occur. However, if a fault occurs in the cable pit, fire is extremely easy to be caused due to low position of the cable pit, easy water accumulation, heavy moisture in the pipeline and poor heat dissipation performance, and even fire is connected to cause a great number of vicious events of burning of cables in the same pit, so that tripping measures should be taken for single-phase grounding occurring in the cable. However, the existing power distribution network cannot correctly distinguish whether faults occur in a cable section or an overhead section, and once faults occur, the faults are not tripped selectively, so that the power supply reliability is poor.
In the distribution network, the overhead line is often contacted with branches, cement, sandy soil and the like to form a grounding fault, the grounding resistance of the overhead line is hundreds of ohms or thousands of ohms, and the cable line is usually mainly characterized by faults such as cable insulation damage, aging, tap loosening and the like and generally has low-resistance characteristics. Research shows that the single-phase grounding occurs on the cable, and the transition resistance is small and is generally not more than 300-500 omega. Therefore, it is contemplated to employ a determination of the transition resistance magnitude to effect the selective tripping.
Disclosure of Invention
The invention aims to provide a single-phase grounding fault transition resistance calculation method, a fault judgment method and a system, so as to solve the problems in the prior art.
In order to achieve the above purpose, the invention adopts the following technical scheme:
the single-phase earth fault transition resistance calculation method comprises the following steps:
judging whether the operation mode of the power grid is changed when the power grid does not have faults in the power distribution area, if so, exiting the arc suppression coil, measuring the voltage and the capacitance current of a neutral point once, and putting the arc suppression coil again after the measurement; if not, continuously monitoring the three-phase voltage and the bus zero sequence voltage of the arc suppression coil grounding system;
judging whether the zero sequence voltage of the bus is greater than a zero sequence voltage threshold value, if not, executing the previous step; if yes, executing the next step;
selecting a grounding circuit and grounding phase;
the method comprises the steps of obtaining voltage of a fault phase in normal operation, measuring neutral point voltage and detuning degree, adjusting arc suppression coil gear after a preset time interval, and re-measuring the neutral point voltage and the detuning degree to obtain neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gear after grounding;
and calculating the grounding transition resistance according to the voltage and the capacitance current of the fault phase in normal operation and the neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gears after grounding.
Further, the selected grounding circuit and the grounding phase are specifically: and selecting a grounding circuit and a grounding phase by adopting a low-current grounding line selecting device.
Further, the calculation formula of the grounding transition resistance is as follows:
wherein R is g In order to ground the transition resistance,for the voltage at normal operation of the faulty phase, I C The capacitive current, v and v' are the detuning degrees corresponding to two groups of different arc suppression coil gear positions after being grounded, u 0,f And u' 0,f Neutral point voltages corresponding to different arc suppression coil gear positions after being grounded are respectively +.>Per unit value as reference value, u 00 The unbalanced voltage per unit value is caused by the asymmetry of three-phase parameters of the arc suppression coil grounding system.
Further, the calculation formula of the unbalanced voltage per unit value caused by the asymmetry of the three-phase parameters of the arc suppression coil grounding system is as follows:
wherein U is n And d is the damping rate of the arc suppression coil grounding system in order to exit the primary neutral point voltage measured by the arc suppression coil.
Further, the zero sequence voltage threshold U 0,set 600-900V.
Further, the preset time interval is 1-3 s.
The single-phase earth fault transition resistance calculation system comprises a first measurement module, a judgment module, a line selection module, a second measurement module and a calculation module:
a first measurement module: when the power grid does not have faults in the power distribution area, judging whether the operation mode of the power grid is changed, if so, exiting the arc suppression coil, measuring the voltage and the capacitance current of a primary neutral point, and putting the arc suppression coil again after the measurement; if not, continuously monitoring the three-phase voltage and the bus zero sequence voltage of the arc suppression coil grounding system;
and a judging module: the method comprises the steps of judging whether the zero sequence voltage of a bus is greater than a zero sequence voltage threshold value, and if not, entering a first measurement module; if yes, entering a line selection module;
and a line selection module: the grounding circuit is used for selecting a grounding circuit and the grounding phase;
and a second measurement module: the method comprises the steps of obtaining voltage of a fault phase in normal operation, measuring neutral point voltage and detuning degree, adjusting arc suppression coil gear after a preset time interval, and re-measuring the neutral point voltage and the detuning degree to obtain neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gear after grounding;
the calculation module: the method is used for calculating the grounding transition resistance according to the voltage, the capacitance current and the neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gears after grounding when the fault phase normally operates.
A fault determination method, comprising:
obtaining a single-phase grounding fault transition resistance calculated by a calculation method;
judging the relation between the grounding transition resistance and a preset threshold value, and judging that the fault is a high-resistance fault and occurs in the overhead section of the line when the grounding transition resistance is greater than or equal to the preset threshold value; and when the transition resistance is smaller than a preset threshold value, judging that the fault is a low-resistance fault, and the fault occurs to the line cable section.
The method is characterized in that the preset threshold value is 500 omega.
A fault determination system, comprising:
the grounding transition resistance acquisition module: the method is used for obtaining the grounding transition resistance calculated by the single-phase grounding fault transition resistance calculation method;
and a judging module: the method comprises the steps of judging the relation between the grounding transition resistance and a preset threshold value, and judging that the fault is a high-resistance fault and occurs in an overhead section of the line when the grounding transition resistance is larger than or equal to the preset threshold value; and when the transition resistance is smaller than a preset threshold value, judging that the fault is a low-resistance fault, and the fault occurs to the line cable section.
Compared with the prior art, the invention has the following beneficial technical effects:
the invention provides a single-phase grounding fault transition resistance calculation method, which realizes the on-line calculation of the grounding transition resistance by utilizing the neutral point voltage after the arc suppression coil exits at normal time, the two groups of neutral point voltages after the grounding and the detuning degree, and the support data required by calculation can be obtained from an arc suppression coil controller without adding new equipment, so that the economy is better. And the arc suppression coil is adopted to obtain two groups of neutral point voltages and detuning degree after faults in an online shift mode to calculate the grounding transition resistance, so that the influence of the damping rate of the system can be effectively eliminated, and the calculation accuracy is high.
The invention also provides a fault judging method, which can preliminarily judge the fault property and the fault position in the mixed circuit by the size of the grounding transition resistor, and effectively prevent the condition that the fault exists and worsens in the cable circuit for a long time.
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The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention.
FIG. 1 is a flow chart of a single-phase earth fault transition resistance calculation method of the invention.
Detailed Description
In order that those skilled in the art will better understand the present invention, a technical solution in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in which it is apparent that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present invention without making any inventive effort, shall fall within the scope of the present invention.
It should be noted that the terms "first," "second," and the like in the description and the claims of the present invention and the above figures are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used may be interchanged where appropriate such that the embodiments of the invention described herein may be implemented in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.
Example 1
Referring to fig. 1, the invention provides a single-phase earth fault transition resistance calculation method based on arc suppression coil gear shifting, which comprises the following steps:
when the power grid does not have faults in the power distribution area, judging whether the power grid operation mode is changed, if so, exiting the arc suppression coil and measuring the primary neutral point voltage U n And capacitive current I C After the measurement, the arc suppression coil is put into again, if not, the three-phase voltage of the arc suppression coil grounding system is measuredAnd bus zero sequence voltage.
Judging whether the zero sequence voltage of the bus is greater than a zero sequence voltage threshold value, and when the zero sequence voltage of the bus exceeds a zero sequence voltage threshold value U 0,set During the process, the grounding circuit and the grounding phase are selected through the low-current grounding line selecting device.
Obtaining voltage of fault phase in normal operationAnd measure neutral point voltage U 0,f And detuning v; after a preset time interval delta t, adjusting the gear of the arc suppression coil, and measuring the neutral point voltage U 'again' 0,f And detuning v'.
Wherein,u is the voltage at which the fault phase operates normally 0,f And u' 0,f Neutral point voltages corresponding to different arc suppression coil gear positions after being grounded are respectively +.>As per unit value of the reference value.
Calculating the grounding transition resistance R through the obtained parameters g 。
In this embodiment, the zero sequence voltage threshold U 0,set 600-900V, and deltat is 1-3 s.
Ground transition resistance R g The calculation formula is as follows:
for the arc suppression coil grounding system, the per unit value of neutral point offset voltage in normal operation is as follows:
wherein u is 0,N For the neutral point offset voltage per unit value in normal operation, expressed as the phase voltage per unit value, u 00 The method is characterized in that the method is that the per unit value of unbalanced voltage caused by the asymmetry of three-phase parameters of the arc suppression coil grounding system is represented by v, the detuning degree is represented by v, and the damping rate of the arc suppression coil grounding system is represented by d. V=1 when the arc suppression coil is out of operation, u 00 Approximately equal to u 0,N 。
The per unit value of the neutral point offset voltage after the occurrence of the single phase grounding can be expressed as:
wherein d g For the ground transition resistance R g The resulting additional damping rate is calculated as:
from the above three formulas, we know that u 0,N 、I C 、u 0,F Specific values of v and d can be calculated as R g However, in general, the damping rate d of the arc suppression coil grounding system is difficult to accurately know. Therefore, two groups of neutral point voltages corresponding to different detuning degrees are acquired under the fault state, and d in the formula is eliminated. Specifically, the detuning degree of the phase control pre-preset arc suppression coil is adjusted from v to v', and the per-unit value u of the neutral point voltage before adjustment 0,f The method comprises the following steps:
the per unit value u 'of the adjusted neutral point voltage' 0,f The method comprises the following steps:
the two simultaneous solutions can be obtained:
carry the above to d g In the calculation formula, the estimated value of the grounding transition resistance can be obtained:
wherein,for the voltage at normal operation of the faulty phase, I C Is capacitance current, v and v' are the detuning degree corresponding to different arc suppression coil gear after fault, u 0,f And u' 0,f Neutral point voltages corresponding to different arc suppression coil gear positions after faults are respectively +.>As a standard per unit value, the neutral point voltage can be divided by +.>And (5) calculating to obtain the product.
Example two
The invention provides a single-phase ground fault transition resistance calculation system which comprises a first measurement module, a judgment module, a line selection module, a second measurement module and a calculation module, wherein the first measurement module is used for measuring the transition resistance of a single-phase ground fault:
a first measurement module: when the power grid does not have faults in the power distribution area, judging whether the operation mode of the power grid is changed, if so, exiting the arc suppression coil, measuring the voltage and the capacitance current of a primary neutral point, and putting the arc suppression coil again after the measurement; if not, continuously monitoring the three-phase voltage and the bus zero sequence voltage of the arc suppression coil grounding system;
and a judging module: the method comprises the steps of judging whether the zero sequence voltage of a bus is greater than a zero sequence voltage threshold value, and if not, entering a first measurement module; if yes, entering a line selection module;
and a line selection module: the grounding circuit is used for selecting a grounding circuit and the grounding phase;
and a second measurement module: the method comprises the steps of obtaining voltage of a fault phase in normal operation, measuring neutral point voltage and detuning degree, adjusting arc suppression coil gear after a preset time interval, and re-measuring the neutral point voltage and the detuning degree to obtain neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gear after grounding;
the calculation module: the method is used for calculating the grounding transition resistance according to the voltage, the capacitance current and the neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gears after grounding when the fault phase normally operates.
Example III
The invention provides a fault judging method, which comprises the following steps:
and obtaining the grounding transition resistance calculated by the single-phase grounding fault transition resistance calculation method in the first embodiment.
According to the fault statistics rule, the grounding transition resistance is larger when the fault occurs in the overhead section, the grounding transition resistance is smaller when the fault occurs in the cable section, and the fault is mostly a permanent fault.
Thus, the initial judgment of the fault property and the fault position can be carried out: when the calculated grounding transition resistance is larger (not smaller than 500 omega), most of faults are high-resistance faults, and the faults are generally in an overhead section of the line; when the calculated ground transition resistance is small (less than 500 Ω), the fault is mostly a low-resistance fault, typically a line cable segment.
Example IV
The invention provides a fault judging system, comprising:
the grounding transition resistance acquisition module: the method is used for obtaining the grounding transition resistance calculated by the single-phase grounding fault transition resistance calculation method;
and a judging module: the method comprises the steps of judging the relation between the grounding transition resistance and a preset threshold value, and judging that the fault is a high-resistance fault and occurs in an overhead section of the line when the grounding transition resistance is larger than or equal to the preset threshold value; and when the transition resistance is smaller than a preset threshold value, judging that the fault is a low-resistance fault, and the fault occurs to the line cable section.
It will be appreciated by those skilled in the art that embodiments of the present invention may be provided as a method, system, or computer program product. Accordingly, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.
The present invention is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the invention. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.
These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.
Finally, it should be noted that: the foregoing embodiments are merely for illustrating the technical aspects of the present invention and not for limiting the scope thereof, and although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that various changes, modifications or equivalents may be made to the specific embodiments of the present invention after reading the present invention, and these changes, modifications or equivalents are within the scope of the invention as defined in the appended claims.
Claims (10)
1. The single-phase earth fault transition resistance calculation method is characterized by comprising the following steps of:
judging whether the operation mode of the power grid is changed when the power grid does not have faults in the power distribution area, if so, exiting the arc suppression coil, measuring the voltage and the capacitance current of a neutral point once, and putting the arc suppression coil again after the measurement; if not, continuously monitoring the three-phase voltage and the bus zero sequence voltage of the arc suppression coil grounding system;
judging whether the zero sequence voltage of the bus is greater than a zero sequence voltage threshold value, if not, executing the previous step; if yes, executing the next step;
selecting a grounding circuit and grounding phase;
the method comprises the steps of obtaining voltage of a fault phase in normal operation, measuring neutral point voltage and detuning degree, adjusting arc suppression coil gear after a preset time interval, and re-measuring the neutral point voltage and the detuning degree to obtain neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gear after grounding;
and calculating the grounding transition resistance according to the voltage and the capacitance current of the fault phase in normal operation and the neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gears after grounding.
2. The method for calculating the transition resistance of the single-phase earth fault according to claim 1, wherein the selected earth line and the earth phase are specifically: and selecting a grounding circuit and a grounding phase by adopting a low-current grounding line selecting device.
3. The method for calculating the single-phase earth fault transition resistance according to claim 1, wherein the calculation formula of the earth transition resistance is as follows:
wherein R is g In order to ground the transition resistance,for the voltage at normal operation of the faulty phase, I C The capacitive current, v and v' are the detuning degrees corresponding to two groups of different arc suppression coil gear positions after being grounded, u 0,f And u' 0,f Neutral point voltages corresponding to different arc suppression coil gear positions after being grounded are respectively +.>Per unit value as reference value, u 00 The unbalanced voltage per unit value is caused by the asymmetry of three-phase parameters of the arc suppression coil grounding system.
4. The method for calculating the transition resistance of the single-phase earth fault according to claim 3, wherein the calculation formula of the unbalanced voltage per unit value caused by the asymmetry of the three-phase parameters of the arc suppression coil grounding system is as follows:
wherein U is n And d is the damping rate of the arc suppression coil grounding system in order to exit the primary neutral point voltage measured by the arc suppression coil.
5. The single-phase earth fault transition resistance calculation method according to claim 1, characterized in that the zero sequence voltage threshold U 0,set 600-900V.
6. The method for calculating the single-phase earth fault transition resistance according to claim 1, wherein the preset time interval is 1-3 s.
7. The single-phase earth fault transition resistance calculation system is characterized by comprising a first measurement module, a judgment module, a line selection module, a second measurement module and a calculation module:
a first measurement module: when the power grid does not have faults in the power distribution area, judging whether the operation mode of the power grid is changed, if so, exiting the arc suppression coil, measuring the voltage and the capacitance current of a primary neutral point, and putting the arc suppression coil again after the measurement; if not, continuously monitoring the three-phase voltage and the bus zero sequence voltage of the arc suppression coil grounding system;
and a judging module: the method comprises the steps of judging whether the zero sequence voltage of a bus is greater than a zero sequence voltage threshold value, and if not, entering a first measurement module; if yes, entering a line selection module;
and a line selection module: the grounding circuit is used for selecting a grounding circuit and the grounding phase;
and a second measurement module: the method comprises the steps of obtaining voltage of a fault phase in normal operation, measuring neutral point voltage and detuning degree, adjusting arc suppression coil gear after a preset time interval, and re-measuring the neutral point voltage and the detuning degree to obtain neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gear after grounding;
the calculation module: the method is used for calculating the grounding transition resistance according to the voltage, the capacitance current and the neutral point voltage and the detuning degree corresponding to two groups of different arc suppression coil gears after grounding when the fault phase normally operates.
8. A fault determination method, comprising:
obtaining the calculated grounding transition resistance of the single-phase grounding fault transition resistance calculation method according to any one of claims 1-6;
judging the relation between the grounding transition resistance and a preset threshold value, and judging that the fault is a high-resistance fault and occurs in the overhead section of the line when the grounding transition resistance is greater than or equal to the preset threshold value; and when the transition resistance is smaller than a preset threshold value, judging that the fault is a low-resistance fault, and the fault occurs to the line cable section.
9. The method according to claim 8, wherein the predetermined threshold is 500Ω.
10. A fault determination system, comprising:
the grounding transition resistance acquisition module: a single-phase earth fault transition resistance calculation method for obtaining the calculated earth transition resistance of any one of claims 1-6;
and a judging module: the method comprises the steps of judging the relation between the grounding transition resistance and a preset threshold value, and judging that the fault is a high-resistance fault and occurs in an overhead section of the line when the grounding transition resistance is larger than or equal to the preset threshold value; and when the transition resistance is smaller than a preset threshold value, judging that the fault is a low-resistance fault, and the fault occurs to the line cable section.
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| CN117973097A (en) * | 2024-04-02 | 2024-05-03 | 国网四川省电力公司电力科学研究院 | Method for acquiring resistance interval corresponding to starting fixed value under arc suppression coil grounding system |
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN117973097A (en) * | 2024-04-02 | 2024-05-03 | 国网四川省电力公司电力科学研究院 | Method for acquiring resistance interval corresponding to starting fixed value under arc suppression coil grounding system |
| CN117973097B (en) * | 2024-04-02 | 2024-06-11 | 国网四川省电力公司电力科学研究院 | Method for acquiring resistance interval corresponding to starting fixed value under arc suppression coil grounding system |
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