CN110416981B - Electric automobile access distribution network area current protection method and system - Google Patents
Electric automobile access distribution network area current protection method and system Download PDFInfo
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- CN110416981B CN110416981B CN201910700662.2A CN201910700662A CN110416981B CN 110416981 B CN110416981 B CN 110416981B CN 201910700662 A CN201910700662 A CN 201910700662A CN 110416981 B CN110416981 B CN 110416981B
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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
- H02H7/261—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 involving signal transmission between at least two stations
- H02H7/262—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 involving signal transmission between at least two stations involving transmissions of switching or blocking orders
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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
- H02H7/261—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 involving signal transmission between at least two stations
- H02H7/263—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 involving signal transmission between at least two stations involving transmissions of measured values
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Abstract
The invention relates to a method and a system for protecting current in a power distribution network area accessed by an electric automobile, belongs to the technical field of relay protection of a power system, and solves the problem of mismatch between current protection backup sections caused by large-scale penetration of the power distribution network of the existing electric automobile. The method comprises the following steps: when the power distribution network fails, collecting current values on all the feeder lines; comparing the current value on each feeder line with the current setting value, and judging whether the current protection II section and the current protection III section of each feeder line are started or not; and according to the current protection starting information of each feeder line, performing criterion calculation on the current protection on each feeder line by using a protection criterion, and sending an action instruction to the circuit breaker on the feeder line according to a criterion calculation result so as to be executed by the circuit breaker. The problem of mismatch of upper and lower protection in traditional current protection of the power distribution network is effectively solved, the problem is not limited by factors such as the charging capacity of electric vehicles, the number and positions of charging facilities and the like, and the fault section can still be correctly identified under the condition that information is partially lost or wrong.
Description
Technical Field
The invention relates to the technical field of relay protection of power systems, in particular to a method and a system for protecting regional current of an electric vehicle connected to a power distribution network.
Background
The large amount of accesses of the electric automobile not only deeply influence the operation mode of the power distribution network and the change of the network structure, but also play a decisive role in the distortion characteristic of the electric quantity when the distribution line breaks down. With the higher and higher permeability of electric vehicles in distribution networks, the traditional relay protection scheme faces a serious challenge. Therefore, a new power distribution network protection method suitable for large-scale electric automobile access is urgently needed to be researched and proposed.
Existing protection schemes mainly focus on admission capacity limiting schemes, adaptive protection schemes, and fault location schemes based on communication technologies. The scheme for limiting the access capacity considers factors such as harmonic wave constraint, voltage constraint and protection adaptability, and passively obtains the access capacity of the electric automobile to be accessed to the power distribution network. The self-adaptive protection scheme is based on the original protection configuration, and the protection fixed value is adjusted on line by calculating parameters such as system potential, equivalent impedance, branch coefficient and the like, so that faults are identified and removed. According to the fault positioning scheme based on the communication technology, the fault positioning is realized by acquiring, transmitting and processing information such as amplitude phase of local or global electrical quantity of the power distribution network, action condition of protection and the like. However, under the condition of large-scale access of the electric automobile, the distribution network structure and the operation mode change frequently, the protection is difficult to consider both selectivity and sensitivity, and the protection is difficult to match and even has serious mismatch problem.
Disclosure of Invention
In view of the above analysis, the present invention aims to provide a method and a system for protecting current in a power distribution network area accessed by an electric vehicle, so as to solve the problem of mismatch between current protection backup sections caused by a large-scale permeable power distribution network of the existing electric vehicle.
The purpose of the invention is mainly realized by the following technical scheme:
a method for protecting the current of an electric automobile connected to a power distribution network area comprises the following steps:
when the power distribution network fails, collecting current values on all the feeder lines;
comparing the current value on each feeder line with the current setting value, and judging whether the current protection II section and the current protection III section of each feeder line are started or not;
performing criterion calculation on the current protection on each feeder line by using a protection criterion according to the starting information of the current protection II section and the current protection III section of each feeder line;
and sending an action instruction to the circuit breaker on the feeder line according to the criterion calculation result so as to be executed by the circuit breaker.
On the basis of the scheme, the invention is further improved as follows:
further, the protection criterion is:
wherein I with superscripts II, III denotes current element activation information for current protection segments II and III, respectively, subscript S denotes the present feeder current protection, subscript L denotes the downstream feeder current protection, I denotes the current protection number, 1 denotes current element activation, 0 denotes current element deactivation, "action" denotes a trip command to a circuit breaker on the present feeder, "not action" denotes no command, and "latch" denotes a latch signal to a circuit breaker on the present feeder.
Further, if the current value of a certain feeder line cannot be acquired, the starting information of the current protection II section and the starting information of the current protection III section of the feeder line are both set to be 1; and continuing to use the protection criterion to calculate the criterion, if the fault still exists after the breaker on the feeder line executes the action command, setting the starting information of the current protection II section and the starting information of the current protection III section of the feeder line to be 0 by 1, and re-calculating the criterion.
Further, if the feeder line where the fault is located has the fault still existing after the action command is sent out for a certain time delay, setting the starting information of the current protection section II and the starting information of the section III of the feeder line where the fault is located to be 0, and carrying out criterion calculation again.
Further, setting values of a current protection section II and a current protection section III of the ith feeder line are calculated according to the following formula:
wherein the content of the first and second substances,
represents the minimum short-circuit current amplitude when the two-phase fault occurs at the tail end of the ith feeder line,
the minimum short-circuit current amplitude value when the two-phase interphase fault occurs at the tail end of the next-stage feeder line of the ith feeder line is represented;
the sensitivity coefficients of current protection stage II and stage III are shown separately.
Further, it is calculated according to the following formula
Wherein, KdIs a fault type coefficient;
representing a protective back side equivalent potential, Zg1Representing a protective backside positive sequence equivalent impedance;
representing the line impedance of the ith feeder;
and the line impedance from the beginning of the ith feeder line to the end of the next feeder line is shown.
Further, the comparing the current value on each feeder line with the current setting value to judge whether the current protection section II and the current protection section III of each feeder line are started includes:
for protection on each feeder line, if the current value is greater than the setting value of the current protection II section, starting the current protection II section; and if the current value is greater than the setting value of the current protection III section, starting the current protection III section.
The invention also discloses a regional current protection system for the electric automobile to be connected to the power distribution network, which comprises the following components: the system comprises a data acquisition module, a starting information acquisition module, a regional host discrimination module and a circuit breaker, wherein the circuit breaker is arranged on each feeder line and is close to the starting bus position of the feeder line;
the data acquisition module is used for acquiring current values on all the feeder lines when the power distribution network fails;
the starting information acquisition module is used for receiving the current values on the feeder lines sent by the data acquisition module, comparing the current values on the feeder lines with current setting values, and judging whether the current protection II sections and the current protection III sections of the feeder lines are started or not;
the regional host machine distinguishing module is used for receiving the starting information of the current protection II section and the current protection III section of each feeder line sent by the starting information obtaining module, and performing criterion calculation on the current protection on each feeder line by using a protection criterion according to the starting information of the current protection II section and the current protection III section of each feeder line; and the action command is sent to the circuit breaker on the feeder line according to the criterion calculation result so as to be executed by the circuit breaker.
On the basis of the scheme, the invention is further improved as follows:
further, the protection criterion stored in the area host determination module is:
wherein I with superscripts II, III denotes current element activation information for current protection segments II and III, respectively, subscript S denotes the present feeder current protection, subscript L denotes the downstream feeder current protection, I denotes the current protection number, 1 denotes current element activation, 0 denotes current element deactivation, "action" denotes a trip command to a circuit breaker on the present feeder, "not action" denotes no command, and "latch" denotes a latch signal to a circuit breaker on the present feeder.
Further, the data acquisition module and the starting information acquisition module are arranged at the protective installation positions on the feeder lines; the regional host distinguishing module is arranged in a power distribution substation connected with a regional power distribution network.
The invention has the following beneficial effects: the invention provides a method and a system for protecting regional current of an electric vehicle accessed to a power distribution network, aiming at the problem that the selectivity and the sensitivity of the current protection of the power distribution network are difficult to harmonize due to the large-scale access of the electric vehicle. The method can effectively solve the problem of mismatch of upper and lower-level protection in the traditional current protection of the power distribution network, is not limited by factors such as the charging capacity of the electric automobile, the number and the positions of charging facilities and the like, can still correctly identify the fault section under the condition of partial missing or error information, and has higher redundancy and stronger fault-tolerant capability. Because the system and the method are realized based on the same principle, the system also has the corresponding technical effect of the method
In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
Fig. 1 is a flowchart of a method for protecting a current of an electric vehicle connected to a distribution network area in embodiment 1 of the present invention;
FIG. 2 is a schematic diagram of a protection range based on sensitivity requirement tuning in embodiment 1 of the present invention;
FIG. 3 is a positive sequence network Thevenin equivalent circuit in embodiment 1 of the present invention;
fig. 4 is a diagram of an IEEE 33 node power distribution system according to embodiment 2 of the present invention;
fig. 5 is a schematic structural diagram of a regional current protection system for an electric vehicle connected to a power distribution network in embodiment 3 of the present invention.
Detailed Description
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.
Example 1
The invention discloses a specific embodiment of a method for protecting regional current of an electric vehicle connected to a power distribution network, and a flow chart is shown in figure 1 and comprises the following steps:
step S1: when the power distribution network fails, collecting current values on all the feeder lines; specifically, if it is detected that the current value flowing through a certain point in the power distribution network is much larger than the current value in normal operation, the power distribution network has a fault.
Step S2: comparing the current value on each feeder line with the current setting value, and judging whether the current protection II section and the current protection III section of each feeder line are started or not; specifically, for protection on each feeder line, if the current value is greater than the setting value of the current protection II section, the current protection II section is started; if the current value is greater than the setting value of the current protection III section, starting the current protection III section;
step S3: performing criterion calculation on the current protection on each feeder line by using a protection criterion according to the starting information of the current protection II section and the current protection III section of each feeder line;
step S4: and sending an action instruction to the circuit breaker on the feeder line according to the criterion calculation result so as to be executed by the circuit breaker.
Preferably, before using the above method, the setting values of the current protection sections II and III in step S2 need to be determined, and the present invention provides a preferred way of determining the setting values: and carrying out current protection setting according to the principle of preferentially ensuring the sensitivity. 1) The current II section ensures that the tail end of the line has enough sensitivity when in fault; 2) the current III section ensures that the fault at the tail end of the next stage of line has enough sensitivity. FIG. 2 is a schematic diagram of a protection range based on sensitivity requirement tuning. In fig. 2, the end of the present line of protection 1 is B, and the end of the next-stage line is C; the end of the current line of the protection 2 is C, the end of the next-stage line is D, and so on …
Setting values of a current protection II section and a current protection III section of the ith feeder line are calculated according to the following formula:
wherein the content of the first and second substances,
respectively representing the sensitivity coefficients of the current protection II section and the current protection III section, and generally taking the values to be 1.2; the method of the invention needs to ensure the sensitivity and the whole length of the protection circuit, so the short-circuit current needs to be the two-phase short-circuit current at the tail end of the feeder line, and the short-circuit current is the minimum when the two-phase short-circuit fault occurs to the feeder line, so the obtained setting value can meet the sensitivity requirement, and the protection of the whole length of the circuit is realized. Therefore, the temperature of the molten metal is controlled,
represents the minimum short-circuit current amplitude when the two-phase fault occurs at the tail end of the ith feeder line,
the minimum short-circuit current amplitude value when the two-phase interphase fault occurs at the tail end of the next-stage feeder line of the ith feeder line is represented; can be calculated by the following formula
Wherein, KdAnd represents a fault type coefficient, and when used for calculating the minimum short-circuit current amplitude when a two-phase-to-phase fault occurs,
representing a protective back side equivalent potential, Zg1Representing a protective backside positive sequence equivalent impedance;
representing the line impedance of the ith feeder;
and the line impedance from the beginning of the ith feeder line to the end of the next feeder line is shown. Z is obtained byg1: during normal operation, the measured current at the protective installation is detected
Measuring voltage
When asymmetric fault occurs on the line, the positive sequence equivalent impedance Z of the system is assumedg1Equal to negative sequence equivalent impedance Zg2Then the back side positive sequence equivalent impedance Z is protectedg1It can be calculated in the negative sequence network of asymmetric faults:
in the formula (I), the compound is shown in the specification,
and the negative sequence components of the measured voltage and current at the protection installation position are represented and obtained by acquiring the phase components of the voltage and the current at the protection installation position and passing through a transformation matrix of a symmetric component method. Taking the protection at a in figure 3 as an example,
can be expressed as:
Zg1to protect the positive sequence equivalent impedance of the backside,
in order to protect the backside system current,
can be obtained by the above method.
Preferably, considering that the current I section cannot protect the full length of the line, and the current II section and the current III section can protect the full length of the line according to the sensitivity setting, the protection criterion in this embodiment is mainly implemented by the start information of the current II section and the current III section, and can be represented as:
wherein, I with superscripts II and III respectively represents the current element start information of current protection II and III, subscript S represents the current protection of the feeder, subscript L represents the current protection of the downstream feeder, I represents the number of the current protection, 1 represents the current element start, 0 represents the current element not start, action represents the trip command to the breaker on the feeder, non-action represents the fault not on the feeder, when no command is sent, blocking represents the fault occurring in the action range of the protection but not on the feeder, when no action is needed, to avoid the protection from tripping beyond the level, to ensure the selectivity, when the blocking signal is sent to the breaker on the feeder, in formula (8), E represents the blocking signal of the current element start information of the current protection II and III, the subscript S represents the current protection II, the subscript L represents the1And the method is used for judging whether the feeder line has a fault. When at least one of the current protection II section and the current protection III section on the feeder line is started and the current protection II section and the current protection III section at any feeder line position at the downstream are not started, E1Judging that the fault occurs in the protection range of the line as 1, otherwise E1＝0；E2And the fault detection circuit is used for judging whether the next-stage feeder line has a fault or not. When at least one of the current protection II section and the current protection III section of the feeder line is started, and the current protection II section and the current protection III section of a certain level exist at the downstream, E2Judging that a fault occurs in the crossing region of the protection range of the feeder line and the protection range of the downstream feeder line as-1, otherwise, E20. The meaning of the protection criteria is shown in table 1:
TABLE 1 content and meanings of protection criteria
When the distribution network protection system has the problems of failure of a protection device, disconnection of a measuring device, failure of a protection communication module and the like, the regional host cannot acquire current protection starting information of the protection device, and certain protection information is lost. If the current value on a certain feeder line cannot be acquired, the starting information of the current protection II section and the starting information of the current protection III section of the feeder line are both set to be 1; and continuing to use the protection criterion to calculate the criterion, if the fault still exists after the breaker on the feeder line executes the action command, setting the starting information of the current protection II section and the starting information of the current protection III section of the feeder line to be 0 by 1, and re-calculating the criterion.
When the distribution network protection system has communication reasons, the current protection starting information may be changed from 0 to 1 or 1 to 0, and the regional host computer acquires wrong current protection starting information. Common starting information transmission errors are divided into three types, namely fault line, fault point upstream and fault point downstream protection starting information transmission errors and the like. When the starting information of the current II section or the current III section at the upstream of the fault line or the fault point is changed from 1 to 0, the starting information of the current II section or the current III section is mutually supplemented, and the whole judgment result of the criterion is not influenced by a certain information transmission error. When the current protection starting information of a downstream line of a fault point is changed from 0 to 1, the regional host judges that the fault occurs in the line and sends an action signal, after a certain time delay, the regional host detects that the fault still exists, the starting information of the current protection II section and the starting information of the current protection III section of the feeder line where the fault exists are both set to be 0, and criterion calculation is carried out again to correctly remove the fault without influencing selectivity.
Example 2
In embodiment 2 of the present invention, a specific process for implementing current protection by using the above method is given, and an IEEE 33 node standard power distribution system is built on an RTDS platform, as shown in fig. 4. 5 charging stations are accessed at different locations in the system, each station having a maximum charging capacity of 1.8 MW. The regional host is arranged on the power node 1, and starting information of all protected current II sections and III sections of the power distribution system is uploaded to the regional host.
(1) Zone current protection scheme verification
At line L8-9Upper distance protection 70% F1Three-phase short circuit occurs at points, and the starting condition of each protection and the area current protection criterion result can be obtained according to the formula (8) and are shown in the table 2. From the table, the regional master is protected to the protection R8-9Sending a tripping command; regional master to protection R6-7And R7-8Sending a lock command to effectively avoid protection R6-7And R7-8A skip action; no other protections are enabled and no command is sent to it by the zone master. Therefore, the regional protection can realize accurate fault positioning.
TABLE 2F1Calculation result of protection criterion when fault occurs
At line L27-28Upper distance protection 70% F2After the two-phase interphase short circuit fault occurs, the protection starting conditions and the regional current protection criterion result can be obtained according to the formula (8) and are shown in table 3. As can be seen from the table, protection R27-28Receiving a tripping command sent by a regional host; protection of R6-26And R26-27The locking command sent by the regional host is received, and the protection R is effectively avoided6-26And R26-27The problem of false operation; no other protections are enabled and no command is sent to it by the zone master. Therefore, regional protection can effectively solve the contradiction between protection sensitivity and selectivity, and reliably identify faults.
(2) Regional protection scheme fault tolerance verification
① protection startup information missing
When three-phase fault occurs in line R27-28F of (A)2Point if upstream protection R26-27Or the line protection R27-28If the information is missing, the missing start information will be defaulted to 1 by the regional host. The area protection criterion result is consistent with the case where the startup information is not lost, as shown in table 3. If downstream protection R28-29If the information in (2) is missing, the local master sets the start information of the current segments II and III to 1, and as can be seen from table 4, the local master locates the fault on the line L28-29However, the fault has not yet been cut off, for which purpose R will be protected28-29The section II and section III starting information are reset to 0, and the criterion calculation is carried out again, so that the obtained area protection criterion result is consistent with that when the starting information is not lost, as shown in table 3, the fault is protected by protection R27-28And (4) cutting off correctly.
TABLE 4F2Protection criterion calculation result when fault is detected and starting information is lost
② protection against start-up information transmission errors
If upstream protection R26-27Or the line protection R27-28The area protection criterion result is consistent with the start information transmission error without error, as shown in table 3. If downstream protection R28-29If the transmission of the start information is wrong, the start information of the current II section or the current III section is 1. Protection R is obtained from regional protection criterion27-28E1+ E2 ═ 1, blocking the protection. And protect R28-29E1+ E2 equals 1, and the protection action cuts off the line L28-29After that, the fault is still present, in which case R will be protected28-29The start information is reset to 0 and the criterion calculation is performed again, the obtained area protection criterion result is consistent with the start information transmission error-free, as shown in table 3, the fault is finally protected by protection R27-28And (6) accurately cutting.
Therefore, the regional current protection scheme solves the problem of mismatch between current protection backup sections caused by large-scale infiltration of the electric automobile distribution network, and has high redundancy and high fault-tolerant capability.
Example 3
In embodiment 3 of the present invention, there is also disclosed a system for protecting a local current of an electric vehicle connected to a power distribution network, as shown in fig. 5, including: the system comprises a data acquisition module, a starting information acquisition module, a regional host discrimination module and a circuit breaker, wherein the circuit breaker is arranged on each feeder line and is close to the starting bus position of the feeder line; the data acquisition module is used for acquiring current values on all the feeder lines when the power distribution network fails; the starting information acquisition module is used for receiving the current values on the feeder lines sent by the data acquisition module, comparing the current values on the feeder lines with current setting values, and judging whether the current protection II sections and the current protection III sections of the feeder lines are started or not; the regional host machine distinguishing module is used for receiving the starting information of the current protection II section and the current protection III section of each feeder line sent by the starting information obtaining module, and performing criterion calculation on the current protection on each feeder line by using a protection criterion according to the starting information of the current protection II section and the current protection III section of each feeder line; and the action command is sent to the circuit breaker on the feeder line according to the criterion calculation result so as to be executed by the circuit breaker. The data acquisition module and the starting information acquisition module are arranged at the protective installation positions on the feeder lines; the regional host distinguishing module is arranged in a power distribution substation connected with a regional power distribution network. Preferably, the protection criteria stored in the area host determination module are:
wherein I with superscripts II, III denotes current element activation information for current protection segments II and III, respectively, subscript S denotes the present feeder current protection, subscript L denotes the downstream feeder current protection, I denotes the current protection number, 1 denotes current element activation, 0 denotes current element deactivation, "action" denotes a trip command to a circuit breaker on the present feeder, "not action" denotes no command, and "latch" denotes a latch signal to a circuit breaker on the present feeder.
The specific implementation process of the embodiment of the system may be as follows with reference to the embodiment of the method, and the embodiment is not described herein again. Since the principle of the present embodiment is the same as that of the above method embodiment, the present system also has the corresponding technical effects of the above method embodiment.
Those skilled in the art will appreciate that all or part of the flow of the method implementing the above embodiments may be implemented by a computer program, which is stored in a computer readable storage medium, to instruct related hardware. The computer readable storage medium is a magnetic disk, an optical disk, a read-only memory or a random access memory.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (8)
1. A protection method for electric automobile access distribution network area current is characterized by comprising the following steps:
when the power distribution network fails, collecting current values on all the feeder lines;
comparing the current value on each feeder line with the current setting value, and judging whether the current protection II section and the current protection III section of each feeder line are started or not;
performing criterion calculation on the current protection on each feeder line by using a protection criterion according to the starting information of the current protection II section and the current protection III section of each feeder line;
sending an action instruction to the circuit breaker on the feeder line according to the criterion calculation result so as to be executed by the circuit breaker;
the protection criterion is as follows:
wherein I with superscripts II and III respectively represents the current element starting information of the current protection II section and III section, subscript S represents the current protection of the feeder line, subscript L represents the current protection of the downstream feeder line, I represents the number of the current protection, 1 represents the current element starting, 0 represents the current element not starting, action represents the tripping command to the breaker on the feeder line, non-action represents no command, locking represents the locking signal to the breaker on the feeder line;
E1for judging whether the feeder line has fault, when at least one of the current protection sections II and III on the feeder line is started and the current protection sections II and III at any downstream feeder line position are not started, E1Judging that the fault occurs in the protection range of the line as 1, otherwise E1＝0；
E2The feeder line fault judging device is used for judging whether the next-stage feeder line has a fault or not; when at least one of the current protection II section and the current protection III section of the feeder line is started, and the current protection II section and the current protection III section of a certain level exist at the downstream, E2Judging that a fault occurs in the crossing region of the protection range of the feeder line and the protection range of the downstream feeder line as-1, otherwise, E2＝0。
2. The method for protecting the current of the electric automobile accessed to the power distribution network area according to claim 1, wherein if the current value of a certain feeder line cannot be acquired, the starting information of the current protection II section and the starting information of the current protection III section of the certain feeder line are both set to be 1; and continuing to use the protection criterion to calculate the criterion, if the fault still exists after the breaker on the feeder line executes the action command, setting the starting information of the current protection II section and the starting information of the current protection III section of the feeder line to be 0 by 1, and re-calculating the criterion.
3. The method for protecting the current of the electric automobile accessed to the distribution network area according to claim 1, wherein if the feeder line where the fault is located has the fault on the feeder line after a certain delay of an action command, setting the starting information of the current protection II section and the starting information of the current protection III section of the feeder line where the fault is located to be 0, and performing criterion calculation again.
4. The method for protecting the current of the electric automobile connected to the power distribution network area according to claim 1, wherein the setting values of the current protection II section and the current protection III section of the ith feeder line are calculated according to the following formula:
wherein the content of the first and second substances,
represents the minimum short-circuit current amplitude when the two-phase fault occurs at the tail end of the ith feeder line,
the minimum short-circuit current amplitude value when the two-phase interphase fault occurs at the tail end of the next-stage feeder line of the ith feeder line is represented;
the sensitivity coefficients of current protection stage II and stage III are shown separately.
5. The method for protecting the current of the electric automobile connected to the distribution network area according to claim 4, characterized in that the method is calculated according to the following formula
Wherein, KdIs a fault type coefficient;
representing a protective back side equivalent potential, Zg1Representing a protective backside positive sequence equivalent impedance;
representing the line impedance of the ith feeder;
and the line impedance from the beginning of the ith feeder line to the end of the next feeder line is shown.
6. The method for protecting the current of the electric automobile accessed to the distribution network area according to any one of claims 1 to 5, wherein the step of comparing the current value on each feeder line with the current setting value and judging whether the current protection II section and the current protection III section of each feeder line are started comprises the following steps:
for protection on each feeder line, if the current value is greater than the setting value of the current protection II section, starting the current protection II section; and if the current value is greater than the setting value of the current protection III section, starting the current protection III section.
7. The utility model provides an electric automobile inserts regional current protection system of distribution network which characterized in that includes: the system comprises a data acquisition module, a starting information acquisition module, a regional host discrimination module and a circuit breaker, wherein the circuit breaker is arranged on each feeder line and is close to the starting bus position of the feeder line;
the data acquisition module is used for acquiring current values on all the feeder lines when the power distribution network fails;
the starting information acquisition module is used for receiving the current values on the feeder lines sent by the data acquisition module, comparing the current values on the feeder lines with current setting values, and judging whether the current protection II sections and the current protection III sections of the feeder lines are started or not;
the regional host machine distinguishing module is used for receiving the starting information of the current protection II section and the current protection III section of each feeder line sent by the starting information obtaining module, and performing criterion calculation on the current protection on each feeder line by using a protection criterion according to the starting information of the current protection II section and the current protection III section of each feeder line; the circuit breaker is also used for sending an action instruction to the circuit breaker on the feeder line according to the criterion calculation result so as to be executed by the circuit breaker;
the protection criteria stored in the area host distinguishing module are:
wherein I with superscripts II and III respectively represents the current element starting information of the current protection II section and III section, subscript S represents the current protection of the feeder line, subscript L represents the current protection of the downstream feeder line, I represents the number of the current protection, 1 represents the current element starting, 0 represents the current element not starting, action represents the tripping command to the breaker on the feeder line, non-action represents no command, locking represents the locking signal to the breaker on the feeder line;
E1for judging whether the feeder line has fault, when at least one of the current protection sections II and III on the feeder line is started and the current protection sections II and III at any downstream feeder line position are not started, E1Judging that the fault occurs in the protection range of the line as 1, otherwise E1＝0；
E2The feeder line fault judging device is used for judging whether the next-stage feeder line has a fault or not; when at least one of the current protection II section and the current protection III section of the feeder line is started, and the current protection II section and the current protection III section of a certain level exist at the downstream, E2Judging that a fault occurs in the crossing region of the protection range of the feeder line and the protection range of the downstream feeder line as-1, otherwise, E2＝0。
8. The system for protecting the regional current of the electric vehicle accessed to the power distribution network according to claim 7, wherein the data acquisition module and the starting information acquisition module are arranged at protective installation positions on each feeder line; the regional host distinguishing module is arranged in a power distribution substation connected with a regional power distribution network.
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