CN114759530A - Small resistance grounding system fault differential protection method, system, medium and equipment - Google Patents
Small resistance grounding system fault differential protection method, system, medium and equipment Download PDFInfo
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- CN114759530A CN114759530A CN202111432485.8A CN202111432485A CN114759530A CN 114759530 A CN114759530 A CN 114759530A CN 202111432485 A CN202111432485 A CN 202111432485A CN 114759530 A CN114759530 A CN 114759530A
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
Abstract
The invention provides a fault differential protection method, a system, a medium and equipment for a small-resistance grounding system, which are used for detecting the effective value of the sudden change of zero-sequence current according to set intervals; acquiring three-phase current according to a preset period; calculating three-phase current phase quantity differences between the current terminal and the adjacent terminal, calculating the maximum value of effective values of the three-phase current phase quantity differences by using the three-phase current phase quantity differences, and calculating the minimum value of the effective values of the three-phase current phase quantity differences; and calculating the ratio K of the maximum value to the minimum value, judging that the fault occurs on a section between the adjacent terminals when the K is greater than a setting value, and performing differential protection, otherwise, performing no differential protection. The invention uses zero sequence current as braking quantity, and the adjacent terminals use phase current information to realize differential protection, thereby reducing the influence of load fluctuation and line load switching, and having simple setting and higher sensitivity and reliability of protection action in case of high-resistance fault.
Description
Technical Field
The invention belongs to the technical field of relay protection of power distribution networks, and particularly relates to a fault differential protection method, a fault differential protection system, a fault differential protection medium and fault differential protection equipment for a low-resistance grounding system.
Background
The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Along with the enlargement of the scale of the power distribution network and the deepening of the transformation of the power distribution network, the system capacitance current is greatly increased, and the advantages of low overvoltage level, capability of eliminating resonance overvoltage, convenience in operation and maintenance and the like are considered, so that a small-resistance grounding system is widely adopted in a medium-voltage power distribution network in a part of large cities. When a single-phase grounding fault occurs in a small-resistance grounding system, the zero sequence protection action is not in time or refuses, the grounding point and the nearby insulation are damaged more, so that when the current of the grounding point is larger and the zero sequence protection action is not in time or refuses, the grounding point and the nearby insulation are damaged more, and the interphase fault occurs. Whether the earth fault is permanent or transient, the earth fault acts on tripping, so that the tripping times of the line are greatly increased, the normal power supply of a user is influenced to a certain extent, and the reliability of the power supply is reduced.
The small-resistance grounding system mostly adopts timing-limited zero-sequence (III-section) overcurrent protection, and realizes the coordination with the protection of a downstream branch circuit and a distribution transformer through action time limit. The current constant value (3 times zero sequence current constant value) of the zero sequence overcurrent protection of the 10kV small-resistance grounding power distribution network is generally 40-60A, and only grounding resistance of about 90-140 omega can be detected to the maximum. Therefore, the high-resistance grounding will be refused to operate, and the long-time fault operation of the system can cause the grounding transformer protection action to cut off the bus power supply or the interphase short circuit fault, thereby enlarging the fault range and the damage degree.
At present, for single-phase earth fault protection of a small-resistance earth system, a document, namely 'high-resistance earth fault longitudinal differential protection of a small-resistance earth system', proposes an earth fault differential protection scheme with zero-sequence voltage amplitude correction by utilizing a proportional relation between zero-sequence voltage and zero-sequence current, but the protection method needs zero-sequence voltage information and is relatively complex in setting. The document "method for judging high-resistance grounding fault of small-resistance grounding system based on projected quantity differential of neutral point current and zero sequence current" proposes a method for judging high-resistance grounding fault based on projected quantity differential of neutral point current and zero sequence current of line, but the method needs to measure neutral point current at the same time and cannot locate fault sections.
Disclosure of Invention
In order to solve at least one technical problem existing in the background technology, the invention provides a fault differential protection method, a fault differential protection system, a medium and a fault differential protection device for a small-resistance grounding system.
In order to achieve the purpose, the invention adopts the following technical scheme:
a fault differential protection method of a low-resistance grounding system is applied to a line terminal and comprises the following steps:
detecting the effective value of the zero-sequence current mutation quantity according to a set interval;
obtaining three-phase current according to a preset period;
calculating three-phase current phase quantity differences between the current terminal and the adjacent terminal, calculating the maximum value of effective values of the three-phase current phase quantity differences by using the three-phase current phase quantity differences, and calculating the minimum value of the effective values of the three-phase current phase quantity differences;
and calculating the ratio K of the maximum value to the minimum value, judging that the fault occurs on a section between the adjacent terminals when the K is greater than a setting value, and performing differential protection, otherwise, performing no differential protection.
As an alternative embodiment, the step of acquiring the three-phase current in real time according to the preset period further includes: setting a current setting value, regularly collecting a zero-sequence current mutation effective value according to a preset period, judging that the grounding system has a grounding fault if the zero-sequence current effective value exceeds the current setting value, continuing to execute subsequent steps if the zero-sequence current effective value exceeds the current setting value, and otherwise, re-judging until the subsequent steps are executed after the zero-sequence current effective value is met.
In a more limited embodiment, the current setting value is 0.5-1.5A.
As an alternative embodiment, the setting value is set to be greater than 1.2.
As an alternative embodiment, three-phase current information is exchanged between neighboring terminals before calculating a three-phase current phase amount difference with the neighboring terminals.
A low resistance grounding system fault differential protection system comprising:
the first data acquisition module is used for detecting the effective value of the zero-sequence current mutation quantity according to a set interval;
the second data acquisition module is used for acquiring three-phase current according to a preset period;
the first calculation module is used for calculating three-phase current phasor difference with an adjacent terminal, calculating the maximum value of effective values of the three-phase current phasor difference and calculating the minimum value of the effective values of the three-phase current phasor difference by using the three-phase current phasor difference;
and the second calculation module is used for calculating the ratio K between the maximum value and the minimum value, judging that the fault occurs on the section between the adjacent terminals when the K is larger than a set value, and performing differential protection, otherwise, performing no differential protection.
As an optional implementation manner, the system further comprises a line ground fault determination module, which is used for determining that the ground fault occurs in the ground system when the effective value of the zero-sequence current exceeds the set current value, if so, continuing to execute the subsequent steps, otherwise, resuming the determination until the requirement is met, and then executing the subsequent steps.
In a more limited embodiment, the current setting value is 0.5-1.5A.
As an alternative embodiment, the setting value is set to be greater than 1.2.
As an alternative embodiment, the system further comprises a data exchange module for exchanging three-phase current information between adjacent terminals.
A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method as set forth above.
A terminal device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the method as described above when executing the program.
Compared with the prior art, the invention has the beneficial effects that:
the invention can overcome the influence of load fluctuation or line switching when the system is in normal operation, has high sensitivity of protection action when in high-resistance fault, and is not influenced by CT polarity reversal connection and three-phase parameter unbalance.
Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and together with the description, serve to explain the invention and not to limit the invention.
Fig. 1 is a schematic flowchart of a fault differential protection method for a low-resistance grounded system based on zero-sequence current braking according to an embodiment of the present invention;
fig. 2 is a structural block diagram of a fault differential protection system of a low-resistance grounding system based on zero-sequence current braking according to an embodiment of the present invention;
fig. 3 is a typical simulation model of the small-resistance grounding system Matlab/Simulink according to the embodiment of the present invention;
FIG. 4 is a simulated waveform of a fault point of a typical small resistance grounding system grounded through a 100 Ω/1500 Ω resistor.
Detailed Description
The invention is further described with reference to the following figures and examples.
It is to be understood that the following detailed description is exemplary and is intended to provide further explanation of the invention as claimed. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.
It is noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of exemplary embodiments according to the invention. As used herein, the singular is intended to include the plural unless the context clearly dictates otherwise, and it should be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of features, steps, operations, elements, components, and/or combinations thereof.
Example one
The invention provides a fault differential protection method of a small-resistance grounding system based on zero-sequence current braking, which comprises the following steps of:
s1, detecting the effective value delta I of the inner zero sequence current mutation quantity in real time according to the preset period by the line terminal0；
S2, the line terminal obtains the three-phase current in real time according to the preset period
It should be noted that, the three-phase current is obtained in real time at the line terminal according to the preset period
Before, whether the line has the ground fault or not needs to be judged, and only when the line has the ground fault, the zero sequence current effective value 3I needs to be further obtained according to the preset period at the detection point of the line in the fault steady-state process02And three-phase current sudden change effective value delta IA、ΔIB、ΔIC；
The method for judging the line ground fault comprises the steps of setting a setting value IsetThe method comprises the steps that a line terminal regularly collects zero sequence current mutation effective value delta I according to a preset period, wherein the zero sequence current mutation effective value delta I is 0.5-2A0If the zero sequence current effective value is delta I0Over-setting value IsetAnd if so, judging that the grounding system has a grounding fault.
S3, exchanging three-phase current information by the adjacent line terminals;
s4, calculating the phase quantity difference of the three-phase current
Calculating effective value delta I of three-phase current phase quantity difference by using three-phase current phase quantity differenceA、ΔIB、ΔICMaximum value Δ I inminCalculating effective value delta I of phase quantity difference of three-phase currentA、ΔIB、ΔICMinimum value of Δ Imin；
S5, calculating effective value delta I of phase quantity difference of three-phase currentA、ΔIB、ΔICMaximum value Δ I inmaxEffective value delta I of phasor difference with three-phase currentA、ΔIB、ΔICMinimum value of Δ IminThe ratio K is larger than the setting value K when K is satisfiedsetIf the fault occurs in the section between the adjacent terminals, differential protection is carried out, otherwise, the section is judged to be a healthy section, and protection is returned;
it should be noted that the setting value K is setset＞1.2；
With the popularization of a distributed control concept based on the peer-to-peer real-time data exchange among terminals, the intelligent power distribution terminal is widely installed and applied in an urban power distribution network, differential protection can be realized by using the power distribution terminal, the influence of load fluctuation or line switching during the normal operation of a system can be overcome, and the protection action sensitivity is high during high-resistance faults and is not influenced by CT polarity reversal and three-phase parameter unbalance.
Referring to fig. 3, fig. 4 and table 1, a fault differential protection method of the low-resistance grounding system based on zero-sequence current braking according to the present embodiment will be described in further detail below with reference to the low-resistance grounding system.
As shown in FIG. 3, a simulation model of a 10kV neutral point grounded system through a small resistor is established in Matlab/Simulink, wherein a neutral point grounding resistor RnThe system comprises 4 outgoing lines which are all cable lines, intelligent distribution terminals (circuit breakers) BK 1-BK 9 are installed in the network, the line length between the terminals is shown in the figure, and fault points are arranged at the middle positions of BK1 and BK 2.
The zero sequence resistance of the cable line is 2.7 omega/km, the zero sequence inductance is 1.109mH/km, the zero sequence capacitance is 0.276uF/km, the positive sequence resistance is 0.27 omega/km, the positive sequence inductance is 0.255mH/km, and the positive sequence capacitance is 0.376 uF/km.
Taking this as an example, the validity of the method of the present invention is verified by using the above system, and the specific implementation steps are as follows:
step (ii) ofFirstly, the method comprises the following steps: line terminal real-time detection presets cycle (this embodiment takes 1 cycle) in zero sequence current abrupt change variable effective value delta I0If the zero sequence current effective value is delta I0Over-setting value Iset(setting value I is set in the present embodimentset2A), determining that the ground fault occurs in the ground system, if so, continuing to execute subsequent steps, otherwise, re-determining until the subsequent steps are satisfied, and if not, executing the subsequent steps again, wherein as shown in the following table, only BK1 zero-sequence current mutation quantity at the terminal BK 1-BK 9 satisfies Δ I when the transition resistance is 100 Ω/1000 Ω/1500 Ω0> 2A, and therefore BK1 and BK2 perform the subsequent steps, the remaining terminals are inactive.
Step two: the line terminals BK1 and BK2 obtain three-phase current in real time according to preset periods (5 cycles are obtained in the embodiment)
Performing the subsequent steps;
step three: the line terminals BK1, BK2 exchange three-phase current information, and subsequent steps are executed;
step four: calculating the phasor difference between the three-phase currents of the BK1 and the BK2 at the line terminal
Calculating effective value delta I of three-phase current phase quantity difference by using three-phase current phase quantity differenceA、ΔIB、ΔICMaximum value of Δ ImaxCalculating effective value delta I of phase quantity difference of three-phase currentA、ΔIB、ΔICMinimum value of Δ Imin. The difference between the three-phase currents and the phase amounts of the three-phase currents at the line terminals BK1 and BK2 with the transition resistances of 100 Ω/1000 Ω/1500 Ω is calculated as shown in Table 1 and FIG. 4, and Δ I is obtainedmaxAnd Δ IminExecuting the subsequent steps;
step five: calculating effective value delta I of phase quantity difference of three-phase currentA、ΔIB、ΔICMaximum value Δ I inmaxEffective value delta I of phase difference with three-phase currentA、ΔIB、ΔICMinimum value of Δ IminThe ratio K is larger than the setting value K when K is satisfiedset(in this embodiment, 1.5 is taken), it is determined that a fault occurs in a section between the adjacent terminals, and differential protection is performed, otherwise, it is determined that the section is a sound section, and protection returns.
As shown in table 1 and fig. 4, the operating values K of the line terminals BK1 and BK2 at the transition resistances of 100 Ω/1000 Ω/1500 Ω satisfy the requirements, and the line between BK1 and BK2 is determined as the faulty section.
TABLE 1 line terminals BK1 and BK2 simulation data
TABLE 2 simulation data for line terminals BK2 and BK3
TABLE 3 simulation data for line terminals BK4 and BK5
TABLE 4 simulation data for line terminals BK6 and BK7
TABLE 5 line terminals BK8 and BK9 simulation data
Example two
A low resistance grounding system fault differential protection system comprising:
the first data acquisition module is used for detecting the effective value of the zero-sequence current mutation quantity according to a set interval;
the second data acquisition module is used for acquiring three-phase current according to a preset period;
the first calculation module is used for calculating three-phase current phasor difference with an adjacent terminal, calculating the maximum value of effective values of the three-phase current phasor difference and calculating the minimum value of the effective values of the three-phase current phasor difference by using the three-phase current phasor difference;
and the second calculation module is used for calculating the ratio K between the maximum value and the minimum value, judging that the fault occurs on the section between the adjacent terminals when the K is larger than a set value, and performing differential protection, otherwise, performing no differential protection.
In some embodiments, the system further includes a line ground fault determination module, configured to determine that a ground fault occurs in the ground system when it is determined that the zero-sequence current effective value exceeds the set current setting value, continue to execute subsequent steps if the zero-sequence current effective value exceeds the set current setting value, and otherwise, execute the subsequent steps again until the zero-sequence current effective value meets the set current setting value.
In some embodiments, the system further comprises a data exchange module, configured to exchange three-phase current information between adjacent terminals.
EXAMPLE III
The present embodiment provides a computer-readable storage medium, on which a computer program is stored, which when executed by a processor implements the steps in the method as provided in the first embodiment.
Example four
The present embodiment provides an electronic device, which includes a memory, a processor, and a computer program stored in the memory and executable on the processor, and the processor executes the computer program to implement the steps in the method according to the first embodiment.
The present invention has been 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 flow diagrams and/or block diagrams, and combinations of flows and/or blocks in the flow diagrams 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.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made to the present invention by 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 (10)
1. A fault differential protection method for a small-resistance grounding system is characterized by comprising the following steps: the method comprises the following steps:
detecting the effective value of the zero-sequence current mutation quantity according to a set interval;
acquiring three-phase current according to a preset period;
calculating three-phase current phase quantity differences between the current terminal and the adjacent terminal, calculating the maximum value of effective values of the three-phase current phase quantity differences by using the three-phase current phase quantity differences, and calculating the minimum value of the effective values of the three-phase current phase quantity differences;
and calculating the ratio K of the maximum value to the minimum value, judging that the fault occurs on the section between the adjacent terminals when K is greater than a setting value, and performing differential protection, otherwise, performing no differential protection.
2. The fault differential protection method for the small-resistance grounding system as claimed in claim 1, wherein: the method comprises the following steps of obtaining three-phase current in real time according to a preset period: setting a current setting value, regularly collecting a zero-sequence current mutation effective value according to a preset period, judging that the grounding system has a grounding fault if the zero-sequence current effective value exceeds the current setting value, continuing to execute subsequent steps if the zero-sequence current effective value exceeds the current setting value, and otherwise, re-judging until the subsequent steps are executed after the zero-sequence current effective value exceeds the current setting value.
3. The fault differential protection method for the small-resistance grounding system as claimed in claim 2, wherein: the current setting value is 0.5-1.5A.
4. The fault differential protection method for the small-resistance grounding system as claimed in claim 1, wherein: the setting value is set to be larger than 1.2.
5. The fault differential protection method for the small-resistance grounding system as claimed in claim 1, wherein: before calculating the phase difference of the three-phase current with the adjacent terminal, exchanging the three-phase current information between the adjacent terminals.
6. A fault differential protection system of a small-resistance grounding system is characterized in that: the method comprises the following steps:
the first data acquisition module is used for detecting the effective value of the zero-sequence current mutation quantity according to a set interval;
the second data acquisition module is used for acquiring three-phase current according to a preset period;
the first calculation module is used for calculating three-phase current phase quantity differences between the first calculation module and the adjacent terminal, calculating the maximum value of effective values of the three-phase current phase quantity differences by using the three-phase current phase quantity differences, and calculating the minimum value of the effective values of the three-phase current phase quantity differences;
and the second calculation module is used for calculating the ratio K of the maximum value to the minimum value, judging that the fault occurs on a section between the adjacent terminals when the K is greater than a setting value, and performing differential protection, otherwise, performing no differential protection.
7. The differential fault protection system for a low resistance grounding system as claimed in claim 6, wherein: the system also comprises a line ground fault judging module which is used for judging that the ground fault occurs in the grounding system when the zero sequence current effective value exceeds the set current value, if so, continuing to execute the subsequent steps, and otherwise, re-judging until the zero sequence current effective value meets the set current value and then executing the subsequent steps.
8. A differential fault protection system for a low resistance earth system as claimed in claim 6 or 7 wherein: the system also comprises a data exchange module used for exchanging three-phase current information between adjacent terminals.
9. A computer-readable storage medium characterized by: stored thereon a computer program which, when being executed by a processor, carries out the steps of the method as claimed in any one of claims 1-5.
10. A terminal device comprising a memory, a processor and a computer program stored on the memory and executable on the processor, the processor implementing the steps of the method according to any of claims 1-5 when executing the program.
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116826677A (en) * | 2023-07-18 | 2023-09-29 | 国网湖北省电力有限公司超高压公司 | Adaptive current differential protection method for power transmission line |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN116826677A (en) * | 2023-07-18 | 2023-09-29 | 国网湖北省电力有限公司超高压公司 | Adaptive current differential protection method for power transmission line |
| CN116826677B (en) * | 2023-07-18 | 2024-01-30 | 国网湖北省电力有限公司超高压公司 | Adaptive current differential protection method for power transmission line |
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