CN106300302A - A kind of distribution protection method - Google Patents
A kind of distribution protection method Download PDFInfo
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- CN106300302A CN106300302A CN201510296725.4A CN201510296725A CN106300302A CN 106300302 A CN106300302 A CN 106300302A CN 201510296725 A CN201510296725 A CN 201510296725A CN 106300302 A CN106300302 A CN 106300302A
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Abstract
The invention discloses a kind of distribution protection method, it is characterised in that comprise the steps: when current protection circuit breaks down, calculate the initial setting current value at current protection circuit head end；Calculate the maximum rear end motor feedback currents value at current protection circuit head end；Calculate the fault curre under the minimum operational mode at current protection circuit head end；Take in the fault curre under initial setting current value described at current protection circuit head end, maximum rear end motor feedback currents value, minimum operational mode maximum as the setting current setting value of current protection circuit.The present invention reduces the motor feedback currents impact on non-fault line protection device; can also be identical value by the protection seting of block switch same under different running method; the setting method that not only simplify protection also substantially increases reliability and the selectivity of protection, and the method is applicable to have automation function, the power distribution network of many block switches.
Description
Technical Field
The invention relates to a power distribution network protection method, and belongs to the technical field of power system control.
Background
The main purpose of distribution network automation is to realize the functions of state detection, data measurement and operation optimization under the normal operation condition of a power grid, fault diagnosis, fault isolation, power supply recovery and the like under the fault condition, and the main control object is a medium-voltage distribution network. Through years of development, the automation level of the distribution network in China is improved to a great extent, and necessary segmentation, communication automation and ring network power supply are realized on important distribution lines by means of an automatic distribution terminal (FTU) and a modern communication technology.
When a power grid or electrical equipment breaks down or abnormal conditions affecting safe operation occur, the automatic power distribution network can automatically remove the fault equipment and eliminate the abnormal conditions, and the protection of the section switch is required to meet the requirements of reliability, selectivity, speed and sensitivity. The protection action of the sectional switch of the fault section is required to be quick and accurate and not to be mistakenly operated.
Usually, the motor load in the line is calculated to be equivalent to the inductive impedance simply, and the influence of the feedback current on the protection is not considered, so that the protection of the distribution line with more motor load on the line and large feedback current in the short circuit is very unfavorable, the selectivity of the protection is difficult to ensure, the protection malfunction is possibly caused, and the accident range is enlarged.
As shown in fig. 1, the distribution network has an automation function, overcurrent protection is provided for each of the section switches a to H, H is a normally open interconnection switch, and in a normal case, when a short-circuit fault occurs at a position K1 on a L1-section line, due to the setting of a protection fixed value and an action time limit, the switch B trips, H is closed, and other switches do not act, so that it is ensured that the L2 and L3-section lines can be supplied with power by another power supply or line, the fault range is reduced as much as possible, and the selectivity of the protection device is ensured; similarly, when the short-circuit fault occurs in the line K2 of the line L4, the fault is removed by the E protection action, H is closed, other switches do not act, and the lines of the line L5 and the line L6 are powered by other power sources or lines.
However, when there is a large amount of motor loads in the line, due to the influence of the motor feedback current during the fault, the coordination of the protection is very complex, especially for the distribution line with the ring network operation mode as shown in fig. 1, after the fault of a certain line is removed, the protection may be in different operation modes, resulting in completely different fault current and motor feedback current, and the setting of the protection and the coordination between the protection are very difficult.
Taking fig. 1 as an example, when a short-circuit fault occurs in K1, due to the existence of a large number of motor loads on lines L2 and L3, a large amount of feedback current flows to a short-circuit point, and meanwhile, a short-circuit effect also occurs on a line adjacent to the line, and a large amount of motor feedback current also flows to the short-circuit point, so that switch C, D, E, F, G and even bus switch a may be subjected to the impact of the motor feedback current to cause malfunction, thereby enlarging the accident range, failing to meet the selectivity requirement of protection, and being difficult to implement the automation function of the power distribution network.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: the problem of switch malfunction caused by impact of motor feedback current on a non-fault section switch in a power distribution network is solved, and the reliability and the selectivity of protection are improved.
In order to achieve the above object, the present invention provides a method for protecting a power distribution network, comprising the following steps:
when the current protection line is in fault,
calculating an initial setting current value at the head end of the current protection circuit;
calculating the maximum rear-end motor feedback current value at the head end of the current protection circuit;
calculating the fault current value under the minimum operation mode at the head end of the current protection line;
and taking the maximum value of the initial setting current value at the head end of the current protection circuit, the maximum rear end motor feedback current value and the fault current value in the minimum operation mode as the setting current set value of the current protection circuit.
Preferably, the initial setting current value at the head end of the current protection line is calculated by:
and when the current protection line has a fault, the quotient of the fault current value and the reliability coefficient of the head end of the current protection line is obtained.
Preferably, the fault current value of the head end of the current protection line is calculated by the following method:
wherein, Ip (2)For current values of fault current protecting the head end of the line, ishIs the three-phase fault inrush current peak.
Preferably, the motor feedback current is determined by a factory value of the motor or obtained by modeling and simulating the motor.
Preferably, the fault current value at the current protection in the minimum operation mode is calculated by the following method:
wherein, IkFor the value of the fault current at the present protection in the minimum operation mode,is the phase potential of the system equivalent power supply, ZsTo protect the impedance between the installation site and the system equivalent supply, ZkIs the impedance between the short circuit point and the protection installation.
Preferably, the method further comprises the step of determining the setting current set value of the same protection device in the power distribution network in different operation modes:
and selecting the minimum setting current setting value of the same protection device obtained in different operation modes as the setting current setting value of the same protection device in different operation modes.
The method for protecting the power distribution network reduces the influence of the feedback current of the motor on a non-fault line protection device, can also set the protection of the same section switch in different operation modes to be the same value, not only simplifies the setting method of the protection, but also greatly improves the reliability and the selectivity of the protection, is suitable for the power distribution network with an automatic function and a plurality of section switches, and has important significance for safe and reliable operation, automation and intelligent development of the power distribution network.
Drawings
FIG. 1 is a diagram of a distribution line in a prior art looped network operation;
FIG. 2 is a schematic diagram of a single power radial distribution network of the present invention;
FIG. 3 is a schematic diagram of a power distribution network of the dual-power hand-pulled looped network.
Detailed Description
The following detailed description of embodiments of the present invention is provided in connection with the accompanying drawings and examples. The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.
At present, the selectivity of the section switch protection is mainly ensured by the cooperation of the protection action value and the time limit. The protection action setting is generally calculated according to a method of avoiding the maximum short-circuit current at the tail end of the protection circuit, and the short-circuit current is calculated according to the following formula:
wherein,Ikfor the value of the fault current at the present protection in the minimum operation mode,is the phase potential of the system equivalent power supply, ZsTo protect the impedance between the installation site and the system equivalent supply, ZkIs the impedance between the short circuit point and the protection installation.
Usually, the motor load in the line is calculated to be equivalent to the inductive impedance simply, and the influence of the feedback current on the protection is not considered, so that the protection of the distribution line with more motor load on the line and large feedback current in the short circuit is very unfavorable, the selectivity of the protection is difficult to ensure, the protection malfunction is possibly caused, and the accident range is enlarged.
Therefore, the invention provides a power distribution network protection method, which comprises the following steps: when the current protection circuit has a fault, calculating an initial setting current value at the head end of the current protection circuit; calculating the maximum rear-end motor feedback current value at the head end of the current protection circuit; calculating the fault current value under the minimum operation mode at the head end of the current protection line; and taking the maximum value of the initial setting current value at the head end of the current protection circuit, the maximum rear end motor feedback current value and the fault current value in the minimum operation mode as the setting current value of the current protection circuit. The following examples will explain the protection method for the power distribution network provided by the present invention in detail.
In an embodiment of the present invention, in a power distribution network with a large number of motor loads, when a line is divided into multiple segments by a section switch (or called an intelligent power distribution terminal FTU), if a line protected by one of the section switches fails (generally, a two-phase fault), a set current value of the current section switch needs to be adjusted according to a load in the currently protected line.
First, a step of calculating an initial setting current value at the head end of the present protection line is described.
Setting initial setting current values of all protections in a distribution network, and dividing fault current at the head end of the section of the line by a reliability coefficient to obtain the initial setting current value at the head end of the current protection line when two-phase fault occurs at the tail end of the section of the line in a minimum operation mode. Wherein the reliability factor is set by a professional according to daily experience. The fault current of the head end of the line of the section is calculated in the following mode:
wherein, Ip (2)For current values of fault current protecting the head end of the line, ishIs the three-phase fault inrush current peak.
This is illustrated below with reference to a specific circuit failure example.
As shown in fig. 2, the distribution line is powered by a single power supply S1, and the section switches A, B, C each have a relay protection device and the line carries a motor load. When a two-phase short circuit fault occurs at line terminal K1, the fault current at protection C is less than the terminal fault current due to the effect of the motor feedback current. Therefore, when the setting current value of the protection C is the tail end fault of the line, the fault current at the head end of the line, namely the position C is obtained by dividing the fault current by the reliability coefficient.
Secondly, calculating the maximum rear-end motor feedback current value at the head end of the current protection circuit;
the maximum back-end motor feedback current at the front end of the current protection circuit can be determined according to a factory value of the motor or obtained by modeling and simulating the motor.
As shown in fig. 2, the distribution line is powered by a single power supply S1, and the section switches A, B, C each have a relay protection device and the line carries a motor load. When a two-phase short-circuit fault occurs at the end K1 of the line, the maximum back-end feedback current at the fault of the protection C (i.e. the head end of the line) is obtained by modeling simulation. And the feedback current generated by the rear-end motor can not cause the false operation of C protection when the head end is in fault.
Thirdly, calculating the fault current value under the minimum operation mode at the head end of the current protection line;
in the minimum operation mode, when a two-phase short-circuit fault occurs at the tail end of the line, fault current flows through the protection position. The fault current value at the current protection in the minimum operation mode is calculated by the following method:
wherein, IkFor the value of the fault current at the present protection in the minimum operation mode,is the phase potential of the system equivalent power supply, ZsTo protect the impedance between the installation site and the system equivalent supply, ZkIs the impedance between the short circuit point and the protection installation.
As shown in fig. 2, the fault current at protection C when a two-phase short-circuit fault occurs at the end of the line in the minimum operation mode is calculated in the above manner.
And verifying whether the protection C generates actions or not, and ensuring that the protection C does not refuse to move when the tail end of the line generates a two-phase short circuit in a minimum operation mode. In particular, whether or not the corresponding action occurs when two short circuits occur at the end in the minimum operating mode without motor load C.
And finally, introducing the step of selecting the setting current set value of the current protection circuit.
In order to ensure the reliability and selectivity of the protection device for the current protection circuit, the setting current set value of the current protection device needs to be selected correspondingly. When a setting current set value of the current protection circuit is selected, it must be ensured that when the current protection circuit fails, the feedback current generated by the rear-end motor when the head end of the current protection circuit fails is calculated, so that the protection device of the current protection circuit cannot be operated by mistake. It should also be ensured that the protection device of the current protection line does not fail when a two-phase short circuit occurs at the end of the current protection line in the minimum operation mode. Therefore, the setting current set value of the current protection circuit should be larger than the maximum rear end motor feedback current of the current protection circuit and larger than the fault current of the protection when two-phase short circuit occurs at the tail end of the circuit in the minimum operation mode of the current protection circuit. This is illustrated below with reference to a specific circuit failure example.
As shown in fig. 2, the distribution line is supplied with power by a single power supply S1, the section switch a, the section switch B, and the section switch C all have relay protection devices, and the line has a motor load. When a two-phase short circuit fault occurs at the tail end K1 of the circuit, the feedback current generated by the rear-end motor is ensured not to cause the malfunction of the protection of the section switch C. And the protection section switch C is ensured not to be refused when the tail end of the line is in a two-phase short circuit in the minimum operation mode.
Similarly, the setting method of the section switch a and the section switch B is the same as the setting method of the section switch C, and is obtained by dividing the fault current at the head end of the section of line, namely the section switch a and the section switch B, by the reliability coefficient when the line tail end K1 is short-circuited. And comparing the current with the maximum rear end motor feedback current and the short-circuit current when the two-phase short circuit occurs at the tail end in the minimum operation mode, and taking the values more than or equal to the three values as setting current setting values of the section switch A and the section switch B, wherein the specific process refers to the setting current setting value of the section switch C, and the detailed description is omitted here.
In another embodiment of the present invention, when different operation modes may occur in the same protection in the ring distribution network, the setting method of the setting current of the protection device in different operation modes is substantially the same as that in the above embodiment, and the difference is that the smallest setting current setting value of the same protection device obtained in different operation modes is selected as the setting current setting fixed value of the same protection device in different operation modes. This is illustrated below with reference to a specific circuit failure example.
As shown in fig. 3, for the distribution line of the hand-pulled ring network, the section switch a, the section switch B, the section switch D and the section switch E are normally closed switches, and the interconnection switch C is a normally open switch. Lines AC, EC are powered by power supplies S1 and S2, respectively. Different setting current set values I of the same protection device obtained by the section switch B in different operation modesB1、IB2、IB2Selection of IB1、IB2、IB2The minimum of the two is explained as an example of setting the current setting constant value of the same protection device in different operation modes.
Setting the section switch B according to the method when the line normally runs, wherein the setting current value is IB1(ii) a When the AB section line has a fault, the section switch A is disconnected, the C is closed, the BC line is powered by the power supply S2 at the other side, the section switch B changes the operation mode of the original power supply from S1 into the power supply from S2, the line load condition changes, the section switch B is set again according to the method, and the setting value is IB2(ii) a When the DE section line has a fault, the section switch E is switched off, the interconnection switch C is switched on, the line CD is supplied with power by the power supply S1 on the other side, the section switch B is in the third operation mode, the line load condition is changed, the section switch B is re-set, and the setting value is IB3. In order to ensure that the section switch B can accurately act in different operation modes, I is selectedB1、IB2、IB3The minimum value is the final setting value of the section switch B.
Similarly, the setting method of the section switch A, the section switch D and the section switch E is the same as that of the section switch B, and when the tail end of the line K1 is in short circuit, the fault current at the head end of the line, namely the section switch A, the section switch D and the section switch E is divided by the reliability coefficient to obtain the fault current. And comparing the current with the maximum rear end motor feedback current and the short-circuit current when two-phase short circuit occurs at the tail end in the minimum operation mode, and taking the values which are more than or equal to the three values as setting current setting values of the section switch A, the section switch D and the section switch E.
In summary, the method for protecting the power distribution network provided by the invention reduces the influence of the feedback current of the motor on the non-fault line protection device, can also set the protection of the same section switch in different operation modes to the same value, not only simplifies the setting method of the protection, but also greatly improves the reliability and selectivity of the protection.
The above embodiments are only for illustrating the invention and are not to be construed as limiting the invention, and those skilled in the art can make various changes and modifications without departing from the spirit and scope of the invention, therefore, all equivalent technical solutions also belong to the scope of the invention, and the scope of the invention is defined by the claims.
Claims (6)
1. A power distribution network protection method is characterized by comprising the following steps:
when the current protection line is in fault,
calculating an initial setting current value at the head end of the current protection circuit;
calculating the maximum rear-end motor feedback current value at the head end of the current protection circuit;
calculating the fault current value under the minimum operation mode at the head end of the current protection line;
and taking the maximum value of the initial setting current value at the head end of the current protection circuit, the maximum rear end motor feedback current value and the fault current value in the minimum operation mode as the setting current set value of the current protection circuit.
2. The power distribution network protection method of claim 1, wherein the initial setting current value at the head end of the current protection line is calculated by:
and when the current protection line has a fault, the quotient of the fault current value and the reliability coefficient of the head end of the current protection line is obtained.
3. The method for power distribution network protection of claim 2, wherein the current fault current value at the head end of the protection line is calculated by:
wherein, Ip (2)For current values of fault current protecting the head end of the line, ishIs the three-phase fault inrush current peak.
4. The method for protecting a power distribution network of claim 1, wherein the motor feedback current is determined by a motor factory value or is obtained by modeling and simulating a motor.
5. The method for protecting a power distribution network according to claim 1, wherein the value of the fault current at the present protection in the minimum operation mode is calculated by:
wherein, IkFor the value of the fault current at the present protection in the minimum operation mode,is the phase potential of the system equivalent power supply, ZsTo protect the impedance between the installation site and the system equivalent supply, ZkIs the impedance between the short circuit point and the protection installation.
6. The power distribution network protection method according to any one of claims 1 to 5, further comprising a determination step of setting current set values in different operation modes of the same protection device in the power distribution network:
and selecting the minimum setting current setting value of the same protection device obtained in different operation modes as the setting current setting value of the same protection device in different operation modes.
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109298289A (en) * | 2018-11-29 | 2019-02-01 | 广东电网有限责任公司 | Method, system and electronic device for locating fault point in distribution network |
| CN109670654A (en) * | 2019-01-09 | 2019-04-23 | 国网江西省电力有限公司电力科学研究院 | A kind of automatic identification distribution line protection rational method of definite value |
| CN111371075A (en) * | 2019-12-26 | 2020-07-03 | 国网北京市电力公司 | Feeder protection processing method, storage medium and processor |
| CN114725941A (en) * | 2022-06-09 | 2022-07-08 | 沈阳易鑫泰电力科技有限公司 | Rural overhead power distribution network frame reconstruction system and automatic reconstruction method |
Family Cites Families (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN100418281C (en) * | 2006-10-16 | 2008-09-10 | 黑龙江大学 | Realization method of self-adaptive current quick-break protection for power supply and distribution lines |
| CN103474949B (en) * | 2013-08-07 | 2016-12-28 | 南京因泰莱配电自动化设备有限公司 | The setting method of a kind of self adaptation three section protection and device |
| CN104319738B (en) * | 2014-10-17 | 2017-05-17 | 国家电网公司 | Protection setting calculation model for high-voltage variable-frequency motor |
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2015
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Cited By (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN109298289A (en) * | 2018-11-29 | 2019-02-01 | 广东电网有限责任公司 | Method, system and electronic device for locating fault point in distribution network |
| CN109670654A (en) * | 2019-01-09 | 2019-04-23 | 国网江西省电力有限公司电力科学研究院 | A kind of automatic identification distribution line protection rational method of definite value |
| CN109670654B (en) * | 2019-01-09 | 2022-08-16 | 国网江西省电力有限公司电力科学研究院 | Method for automatically identifying rationality of protection setting value of distribution network line |
| CN111371075A (en) * | 2019-12-26 | 2020-07-03 | 国网北京市电力公司 | Feeder protection processing method, storage medium and processor |
| CN114725941A (en) * | 2022-06-09 | 2022-07-08 | 沈阳易鑫泰电力科技有限公司 | Rural overhead power distribution network frame reconstruction system and automatic reconstruction method |
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