Short-circuit fault judgment method and device applicable to load side of mother protection system

Abstract

The present invention discloses a short-circuit fault judgment method and device applicable to the load side of the busbar protection system. By collecting the current, busbar voltage and busbar system action signal on the load side of the busbar protection system, judging by the change of current before and after the action of the busbar protection system, judging by the protection start and protection action respectively, and assisting the judgment with the busbar protection system action signal and the re-pressure lock opening condition, the protection function of quickly judging the short-circuit fault is realized. This technical solution can accurately identify the fault after the busbar voltage maintenance system is actuated, and complete the judgment within 40ms, solving the problem of protection refusal to operate due to the reduction of short-circuit current on the load side protection after the busbar voltage maintenance system is actuated, and is suitable for various operating environments where busbar voltage maintenance systems are installed, such as industrial enterprises.

Description

Technical Field

[0001] The present invention belongs to the technical field of power system protection and control, and in particular relates to a short-circuit fault judgment method and device suitable for the load side of a main protection system. Background Art

[0002] "Power sway" is a phenomenon of short-term voltage fluctuation or short-term power outage in the power grid caused by lightning strikes, short circuits or other disturbances. It is also a common power quality problem in industrial enterprises. In order to ensure the power supply reliability of important loads, the bus voltage maintenance system (hereinafter referred to as the bus voltage maintenance system) is an important anti-power sway method and is becoming more and more widely used.

[0003] After the bus protection system is activated, the current limiting reactor will be put into use, which will quickly support the bus voltage at more than 95%, and at the same time significantly reduce the short-circuit current. However, the reduction of short-circuit current will have an adverse effect on the lower-level protection that uses current as a criterion. There are two main existing solutions. The first is to abandon the rapidity of protection and use long-delay protection, that is, overcurrent II stage to cut off the fault. This method increases the damage of short-circuit faults to the primary system. The second is to ensure that the protection can still operate after the current limiting reactor is put into use by reducing the set value, but this method sacrifices the reliability and selectivity of the protection, resulting in problems such as false operation or over-tripping.

[0004] Therefore, in a power system using a main protection system, when a short circuit fault occurs on the load side of the main protection system, it is very important to be able to accurately identify the fault while taking into account the reliability, selectivity and sensitivity of the protection device for the safe power supply of large industrial enterprises. Summary of the invention

[0005] The purpose of the present invention is to provide a short-circuit fault judgment method and device suitable for the load side of the main protection system, which can overcome the shortcomings of the existing short-circuit fault judgment solution on the load side of the main protection system that cannot take into account the rapidity, selectivity and reliability of protection.

[0006] In order to achieve the above object, the solution of the present invention is:

[0007] A short-circuit fault judgment method applicable to the load side of a main protection system comprises the following steps:

[0008] Step 1, collecting the bus voltage and current on the load side of the main protection system and the action signal of the main protection system;

[0009] Step 2: When the following criteria are met, the switch is tripped to cut off the fault: the protection function is activated, the protection is started, the protection is operated, and all the lockout opening conditions are met at the same time.

[0010] In the above step 2, the conditions for the protection function to be activated are met, including the hard pressure plate, soft pressure plate and control word are all activated.

[0011] In the above step 2, the conditions for protection startup are met, including that the maximum current on the load side of the main protection system is greater than the set starting current constant.

[0012] The above conditions for protection start-up also include delayed start-up and delayed return; when the maximum current on the load side of the main protection system is greater than the starting current setting, the protection delay starts after the time set by the starting time setting; after the protection is started, when the current on the load side of the main protection system is less than the starting current setting, the protection delay returns after the time set by the widening time setting.

[0013] In the above step 2, the protection action conditions are met, including that the maximum current on the load side of the main protection system is greater than the set action current constant.

[0014] The above-mentioned protection action conditions also include action delay; when the maximum current on the load side of the main protection system is greater than the set action current setting and maintains the time set by the action time setting, it is judged as a protection action; after the protection action, when the maximum current on the load side of the main protection system is less than the action current setting, the protection action returns immediately.

[0015] In the above step 2, all the interlocking opening conditions are met, including the operation of the bus protection system and the input of the current limiting reactor; the negative sequence voltage value of the bus voltage is higher than the set negative sequence voltage setting, or any bus voltage line voltage is lower than the set low voltage setting, and the composite voltage interlocking element is opened.

[0016] A short-circuit fault judgment device suitable for the load side of a main protection system, comprising:

[0017] The acquisition unit is installed on the incoming switch of the busbar on the load side of the busbar protection system, and is used to collect the busbar voltage and current at the installation location and the action signal of the busbar protection system;

[0018] A processing unit, used for processing the signal collected by the collection unit;

[0019] A judging unit, used for judging that a short circuit fault exists in the protected part according to the signal processed by the processing unit when the following criteria are met: the protection function is put into operation, the protection is started, the protection is operated, and all the blocking and opening conditions are met at the same time; and,

[0020] The indicating unit is used to send an indicating signal to the power supply side switch of the protected part to eliminate the fault when the judging unit judges that a short circuit fault exists.

[0021] The above-mentioned acquisition unit includes a CT, which is used to collect the current on the load side of the mother protection system and send it to the processing unit;

[0022] The processing unit is used to calculate the maximum value of the three-phase current according to the current signal collected by the collection unit, and send it to the judgment unit;

[0023] The judgment unit is used to compare the maximum value of the three-phase current calculated by the processing unit with the starting current constant value, and when the maximum value of the three-phase current is greater than the starting current constant value, it is judged that the protection is started.

[0024] When the above-mentioned judgment unit judges whether the protection action is satisfied, it compares the maximum current value collected on the load side of the main protection system with the set action current constant value and judges it as a protection action.

[0025] The above-mentioned acquisition unit includes a PT, which is used to collect bus voltage signals and send them to the processing unit;

[0026] The processing unit is used to calculate the minimum value of the line voltage effective value and the negative sequence voltage effective value according to the voltage signal collected by the collection unit, and send them to the judgment unit;

[0027] The judgment unit is used to judge that when the negative sequence voltage value of the bus voltage is higher than the set negative sequence voltage setting value, or any bus voltage line voltage is lower than the set low voltage setting value, it is judged that the composite voltage locking element is open and the locking opening condition is met.

[0028] The acquisition unit includes a communication module for acquiring an action signal of a bus voltage maintenance system;

[0029] The judgment unit is used to judge that the locking release condition is met when the bus voltage holding system is actuated according to the action signal of the bus voltage holding system.

[0030] The communication module is connected to the bus voltage holding system for communication, and the communication mode includes a serial port, an Ethernet communication mode, or a hard contact input mode.

[0031] After adopting the above scheme, the present invention collects the current on the load side of the mother protection system, the bus voltage and the action signal of the mother protection system, and makes judgments by respectively judging the protection start and the protection action according to the change of the current before and after the action of the mother protection system, and assists the judgment with the action signal of the mother protection system and the opening condition of the re-pressure lock, thereby realizing the protection function of quickly judging the short-circuit fault. The present invention has the following beneficial effects:

[0032] (1) The present invention can quickly identify short-circuit faults and improve the rapidity of protection. It can quickly identify short-circuit faults and take protective action within 40ms after the short-circuit occurs. Considering the coordination with an external switch, the fault can be cleared within 100ms. Compared with the traditional method of clearing the fault in seconds of overcurrent II stage, it can greatly reduce the time of short-circuit fault occurrence and avoid equipment damage and casualties of people and animals as much as possible.

[0033] (2) The present invention can accurately identify faults after the mother protection system is activated, thereby improving the reliability of protection and preventing false protection operations. Compared with the method of simply reducing the overcurrent I stage setting value, it can effectively prevent false protection operations caused by factors such as large load input and out-of-zone faults;

[0034] (3) The present invention can accurately identify faults, improve the sensitivity of protection, and prevent protection failure. After the upper-level busbar protection system is activated, traditional overcurrent protection often fails to operate due to a significant reduction in short-circuit current. The method and device of the present invention can reliably prevent failure to operate, and is suitable for various operating environments such as industrial enterprises where busbar voltage maintenance systems are installed. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is the protection principle diagram of the present invention;

[0036] Figure 2 It is the protection logic block diagram of the present invention;

[0037] In the figure, I max is the maximum value of the three-phase current collected; I set1 I is the starting setting of the protection device; set2 is the action setting value of the protection device; T set1 is the starting time setting of the protection device; T set2 It is the extended time setting value after the protection device is started; T set3 It is the setting value of the action time of the protection device. DETAILED DESCRIPTION

[0038] The technical solutions and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0039] The present invention provides a short-circuit fault judgment method applicable to the load side of the mother protection system, such as Figure 1 As shown, it can be seen that a busbar protection system has been installed in a certain interval of busbar 1, and the busbar protection system includes a common switch DL1, a fast switch DL2 and a current limiting reactor, wherein the common switch DL1 and the fast switch DL2 are connected in series and connected between busbar 1 and busbar 2; the current limiting reactor is connected in parallel to both ends of the fast switch DL2; the method of the present invention is used to realize the rapid judgment and protection of the short-circuit fault on the load side of the busbar protection system, and specifically includes the following steps:

[0040] Step 1, collecting the bus voltage and current on the load side of the main protection system and the action signal of the main protection system;

[0041] Step 2: Determine whether to trip the power supply side switch of the protected part to remove the fault according to the following criteria: the protection function is enabled, the protection is started, the protection is in action, and all the lock-opening conditions are met at the same time. Figure 2 As shown;

[0042] The protection function is activated, which means that the hard pressure plate, soft pressure plate and control word are all activated;

[0043] The protection start refers to comparing the maximum current value collected on the load side of the mother protection system with the set starting current constant value to determine whether the protection is started; when determining the protection start, delayed start and delayed return are also added; the maximum current value can be the maximum effective value, the maximum transient value, the maximum change value, etc.;

[0044] Specifically, set the starting current constant I set1 , Start time setting value T set1 And the expansion time setting value T after startup set2 , when the maximum value of the three-phase current I max Greater than the starting current setting I set1 When the delay start time is set to T set1 After the protection is started; after the protection is started, when the maximum value of the collected three-phase current I max Less than the starting current setting I set1 When the delay widening time is set to T set2 After that, the protection returns. Among them, the starting current constant value I set1 It is set to no more than 1.5 times the minimum two-phase metallic short-circuit current within the protection range under the minimum operating mode to ensure sufficient sensitivity and verify I set1 Should be greater than the next level fast protection current setting to ensure selectivity; the starting time setting T set1 is the confirmation time of protection start, which can be 10ms; the extension time after start is set to T set2 It is the extension time of protection startup after the mother protection system is put into current limiting reactor after the protection is started, which can be 40ms.

[0045] The protection action refers to comparing the maximum current value collected on the load side of the main protection system with the set action current constant value to determine whether the protection action is to be taken; when determining the protection action, an action delay is also added;

[0046] Specifically, set the action current constant I set2 And action time constant T set3 When the maximum current value collected is greater than the action current setting value I set2 And maintain the set action time constant T set3 , it is judged that there is a short circuit fault and the protection is activated; after the protection is activated, when the maximum current collected is less than the action current setting value I set2 When the protection action returns immediately, the action current constant I set2It is set to be no greater than the current flowing through the load side current collection position after the mother protection system is put into operation and the current limiting reactor is put into operation. Since the action current should be greater than the residual current flowing through the load side current collection position after the mother protection system is put into operation and the current limiting reactor is put into operation, the action current constant I set2 The value is 0.9 times the residual current flowing through the current collection position on the load side after the current limiting reactor is put into operation, so as to ensure that after the mother protection system is actuated, it is determined that the short-circuit fault still exists and needs to be removed; the action time constant T set3 is the protection action confirmation time, its value must be greater than T set1 , 30ms is acceptable.

[0047] Among them, the said satisfying all the locking and opening conditions includes two locking and opening conditions in this embodiment, condition 1 is the action of the mother protection system, that is, the mother protection system on the upper power supply side is actuated, and the current limiting reactor is put into operation; condition 2 is the opening of the composite voltage locking element, that is, when the negative sequence voltage value of the bus voltage is higher than the set negative sequence voltage constant, or any bus voltage line voltage is lower than the set low voltage constant, at this time, the composite voltage locking element is opened, and it is considered that condition 2 is satisfied.

[0048] The present invention also provides a short-circuit fault judgment device suitable for the load side of the mother protection system, comprising:

[0049] The acquisition unit is installed on the incoming switch of the bus 2 on the load side of the mother protection system, and is used to collect the bus voltage and current at the installation location and the action signal of the mother protection system; the action signal collected by the acquisition unit is a Boolean value, which is used for the judgment unit to judge the action condition of the mother protection system;

[0050] The processing unit is used to process the signal collected by the collection unit; specifically, for the three-phase current signal collected by the collection unit, firstly obtain the maximum value of the three-phase current for the judgment unit and the current constant (for example, I set2 ) for comparison; for the bus voltage signal collected by the collection unit, first obtain the minimum value of the line voltage effective value and the negative sequence voltage effective value, which are used for the judgment unit to judge the opening condition of the composite voltage blocking element;

[0051] A judgment unit is used to judge whether a short circuit fault occurs within the protected range according to the collected signal; and

[0052] The indication unit is used to send an indication signal to the switch to clear the fault when the judgment result of the judgment unit is a protection action.

[0053] In this embodiment, the acquisition unit includes a CT, a PT and a communication module, wherein the CT is used to acquire the current of the bus 2, the PT is used to acquire the voltage of the bus 2, and the communication module is used to communicate with the mother protection system by means of optical fiber or the like, and receive an action signal from the mother protection system; the transmission method of the mother protection system sending the mother protection system action signal to the communication module includes a serial port and an Ethernet communication method, and a hard contact input method may also be used.

[0054] In this embodiment, the judgment unit judges whether a short circuit fault occurs within the protected range according to the following criteria: the protection function is put into operation, the protection is started, the protection is in action, and all the locking and opening conditions are met at the same time;

[0055] Among them, when the judgment unit judges whether the protection is started, it compares the collected current on the load side of the mother protection system with the set starting current constant value, and can also add delayed start and delayed return;

[0056] Specifically, the starting current constant I is set in advance. set1 , Start time setting value T set1 And the expansion time setting value T after startup set2 , when the maximum value of the three-phase current I max Greater than the starting current setting I set1 When the delay start time is set to T set1 After the protection is started; after the protection is started, when the maximum value of the collected three-phase current I max Less than the starting current setting I set1 When the delay widening time is set to T set2 After that, the protection returns. Among them, the starting current constant value I set1 It is set to no more than 1.5 times the minimum two-phase metallic short-circuit current within the protection range under the minimum operating mode to ensure sufficient sensitivity and verify I set1 Should be greater than the next level fast protection current setting to ensure selectivity; the starting time setting T set1 is the confirmation time of protection start, which can be 10ms; the extension time after start is set to T set2 It is the extension time of protection startup after the mother protection system puts the reactor into operation after the protection is started, which can be 40ms.

[0057] Among them, when the judgment unit judges whether the protection action is to be taken, the maximum current value of the load side of the main protection system collected is compared with the set action current constant value to judge whether the protection action is to be taken; when judging the protection action, the action delay is also added;

[0058] Specifically, set the action current constant I set2 And action time constant T set3 When the maximum current value collected is greater than the action current setting value Iset2 And maintain the set action time constant T set3 , it is judged that there is a short circuit fault and the protection is activated; after the protection is activated, when the maximum current collected is less than the action current setting value I set2 When the protection action returns immediately, the action current constant I set2 It is set to be no greater than the current flowing through the installation position of the load side acquisition unit after the mother protection system is activated and the current limiting reactor is put into operation. It can be set to 0.9 times the residual current flowing through the installation position of the load side acquisition unit after the current limiting reactor is put into operation, so as to ensure that after the mother protection system is activated, it is judged that the short-circuit fault still exists and needs to be removed; the action time constant T set3 is the protection action confirmation time, its value must be greater than T set1 , 30ms is acceptable.

[0059] Among them, when the judgment unit judges whether all the locking and opening conditions are met, it includes judging whether the two conditions of the mother protection system action and the composite voltage locking element opening are met. Among them, the mother protection system action means that the mother protection system on the upper power supply side is actioned and the current limiting reactor is put into operation; the composite voltage locking element is opened, that is, when the negative sequence voltage value of the bus voltage is higher than the set negative sequence voltage setting, or any bus voltage line voltage is lower than the set low voltage setting, the composite voltage locking element is opened at this time.

[0060] As a specific embodiment of the application of the present invention, Figure 1 As shown in the figure, when a short circuit fault occurs at point K1 in bus zone 2, the short circuit current is greater than the starting current setting value I set1 , protection starts after the time setting T set1 Start; at the same time, the mother protection system operates, controls the ordinary switch DL1 to remain closed, and controls the fast switch DL2 to open, thereby inputting the current limiting reactor; after the mother protection system operates to input the current limiting reactor, the current at the installation point of the protection device drops below I set1 But it is still at the action current setting I set2 Above, protect the T set3 Action, but the protection start is still in the extended time setting T set2 has not returned yet; at this time, the fault phase line voltage of bus 2 is lower than the low voltage setting value, or (in the case of asymmetric phase-to-phase fault) the negative sequence voltage is greater than the negative sequence voltage setting value, resulting in the opening of the composite voltage locking element; at the same time, the protection device receives the action signal of the mother protection system through the communication method (optical fiber in this embodiment), so the protection is activated and all the locking opening conditions are met, and the protection device trips the switch DL3 to cut off the fault.

[0061] The above embodiments are only for illustrating the technical idea of ​​the present invention, and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A short-circuit fault judgment method applicable to the load side of a main protection system, characterized in that The steps include: Step 1, collecting the bus voltage and current on the load side of the main protection system and the action signal of the main protection system; Step 2: When the following criteria are met, the switch is tripped to clear the fault: the protection function is enabled, the protection is started, the protection is activated, and all the blocking and opening conditions are met at the same time; In step 2, the conditions for the protection function to be put into use are met, including that the hard pressure plate, the soft pressure plate and the control word are all put into use; In step 2, the conditions for protection startup are met, including that the maximum current on the load side of the main protection system is greater than the set starting current constant value; In step 2, the protection action condition is met, including that the maximum current on the load side of the main protection system is greater than the set action current constant value; In step 2, all the interlocking opening conditions are met, including the operation of the bus protection system and the input of the current limiting reactor; and also when the negative sequence voltage value of the bus voltage is higher than the set negative sequence voltage setting, or when any bus line voltage is lower than the set low voltage setting, the composite voltage interlocking element is opened.

2. The method according to claim 1, characterized in that: The conditions for satisfying the protection start also include delayed start and delayed return; when the maximum current on the load side of the main protection system is greater than the starting current setting, the protection delay starts after the starting time setting time; after the protection is started, when the current on the load side of the main protection system is less than the starting current setting value, the protection delay returns after the widening time setting time.

3. The method according to claim 1, characterized in that: The conditions for satisfying the protection action also include an action delay; when the maximum current on the load side of the main protection system is greater than the set action current constant and maintains the time set by the action time constant, it is judged as a protection action; after the protection action, when the maximum current on the load side of the main protection system is less than the action current constant, the protection action returns immediately.

4. A short-circuit fault judgment device suitable for the load side of a mother protection system, characterized in that: include, The acquisition unit is installed on the incoming switch of the busbar on the load side of the busbar protection system, and is used to collect the busbar voltage and current at the installation location and the action signal of the busbar protection system; A processing unit, used for processing the signal collected by the collection unit; A judging unit is used to judge that a short circuit fault exists in the protected part according to the signal processed by the processing unit when the following criteria are met: the protection function is put into operation, the protection is started, the protection is in action, and all the locking and opening conditions are met at the same time; as well as, The indicating unit is used to send an indicating signal to the power supply side switch of the protected part to remove the fault when the judging unit judges that a short circuit fault exists; The conditions for the protection function to be activated are met, including the hard pressure plate, soft pressure plate and control word are all activated; The conditions for protection start-up are met, including that the maximum current on the load side of the main protection system is greater than the set starting current value; When the judgment unit judges whether the protection action is satisfied, it compares the maximum current value collected on the load side of the main protection system with the set action current value, and judges it as a protection action; All interlocking and opening conditions are met, including the operation of the mother protection system and the input of the current limiting reactor; The acquisition unit includes a PT, which is used to collect bus voltage signals and send them to the processing unit; The processing unit is used to calculate the minimum value of the line voltage effective value and the negative sequence voltage effective value according to the voltage signal collected by the collection unit, and send them to the judgment unit; The judgment unit is used to judge that when the negative sequence voltage value of the bus voltage is higher than the set negative sequence voltage setting value, or any bus line voltage is lower than the set low voltage setting value, it is judged that the composite voltage locking element is open and the locking opening condition is met.

5. The device according to claim 4, characterized in that: The acquisition unit includes a CT, which is used to collect the current on the load side of the mother protection system and send it to the processing unit; The processing unit is used to calculate the maximum value of the three-phase current according to the current signal collected by the collection unit, and send it to the judgment unit; The judgment unit is used to compare the maximum value of the three-phase current calculated by the processing unit with the starting current constant value, and when the maximum value of the three-phase current is greater than the starting current constant value, it is judged that the protection is started.

6. The device according to claim 4, characterized in that: The acquisition unit includes a communication module, which is used to acquire the action signal of the bus voltage maintenance system.

7. The device according to claim 6, characterized in that: The communication module is connected to the bus voltage maintenance system for communication, and the communication mode includes a serial port, an Ethernet communication mode, or a hard contact input mode.

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