Method and system for fault reopening protection during transformer magnetizing inrush current blocking period

Abstract

The present invention discloses a method and system for fault reopening protection during transformer excitation inrush current lockout, wherein the method comprises: performing a first judgment based on a first round of judgment conditions after the protection judgment criterion is started; when the result of the first judgment is that the current differential protection lockout condition is satisfied, a lock current differential protection signal is issued, and the final lockout result is outputted together with the existing lockout judgment criterion and gate of the protection device; or when the result of the first judgment is that the current differential protection lockout condition is not satisfied, an open current differential protection signal is issued, and the final open result is outputted together with the existing open judgment criterion or gate of the protection device; performing a second judgment based on a second round of judgment conditions during the current differential protection lockout period; when the result of the second judgment is that the current differential protection openness condition is satisfied, the current current differential protection lockout is interrupted.

Description

Technical Field

[0001] The present invention relates to the technical field of power system relay protection, and more particularly to a method and system for fault reopening protection during transformer excitation inrush current blocking. Background Art

[0002] Transformers are critical components in power systems. Transformer failures can degrade the quality of their output power and pose a serious threat to the safety of power equipment. Accurately identifying and disconnecting faulty transformers is crucial. Current differential protection is commonly used for transformer primary protection. Furthermore, due to the large, irregular currents present when the transformer is switched on at no-load, a second harmonic blocking strategy is typically implemented to prevent false tripping of the current differential protection. When switching on at no-load, the second harmonic of the current is high, exceeding the blocking threshold, which blocks the current differential protection. However, if a transformer fault, such as a weak interturn fault, occurs after the second harmonic blocks the current differential protection, the second harmonic will not be released in time, resulting in slow fault clearance by the current differential protection, threatening the safe and stable operation of the power system. Summary of the Invention

[0003] The technical solution of the present invention provides a protection method and system for fault reopening during transformer excitation inrush current blocking, so as to solve the problem of how to reopen fault protection during transformer excitation inrush current blocking.

[0004] In order to solve the above problems, the present invention provides a method for fault reopening protection during transformer excitation inrush current blocking, the method comprising:

[0005] After locking the current differential protection, a first judgment is performed based on the first round of judgment conditions. When the result of the first judgment is that the current differential protection locking condition is met, a locking current differential protection signal is issued, and the final locking result is outputted according to the existing locking judgment criteria and the gate of the protection device; or when the result of the first judgment is that the current differential protection locking condition is not met, an opening current differential protection signal is issued, and the final opening result is outputted according to the existing opening judgment criteria or the gate of the protection device;

[0006] During the current differential protection blocking period, a second discrimination is performed based on the second round of discrimination conditions. When the result of the second discrimination is that the current differential protection opening condition is met, the current current differential protection blocking is interrupted.

[0007] Preferably, the protection start value in the first round of discrimination conditions is a low start value:

[0008] If the absolute value of two consecutive phase current sampling values ​​is greater than 0.05 times the rated current value, the current differential protection is activated.

[0009] Preferably, the protection start value in the second round of discrimination conditions is a high start value:

[0010] If the absolute value of two consecutive phase current sampling values ​​is greater than 1 times the rated current value, the current differential protection is activated.

[0011] Preferably, the protection blocking criteria of the first round of discrimination conditions and the second round of discrimination conditions are:

[0012] (|i φ (t)|<i φmax ||i φ (t+1)|<i φmax )∪(|i φ (t+2)|<i φmax )∪(|i φ (t+3)|<i φmax ) Formula 1

[0013] |i φ (t)|+|i φ (t+2)|+|i φ (t+3)|+|i φ (t+4)|<0.2i φmax Formula 2

[0014] Among them, i φ is the sampling value of the phase current, i φmax It is called the relative large point, and t is the current sampling time;

[0015] When the sampling value of the phase current satisfies at least one criterion in formula 1 or formula 2, the current differential protection is locked;

[0016] When the sampling value of the phase current within 18ms after the current differential protection is started does not satisfy Formula 1 and does not satisfy Formula 2 at the same time, the current differential protection is released.

[0017] Preferably, the protection lockout criterion for determining that the magnetizing inrush current is not established is in an OR gate relationship with the transformer's original magnetizing inrush current release criterion;

[0018] The protection lockout criterion determines that the magnetizing inrush current is established in an AND gate relationship with the transformer's original magnetizing inrush current lockout.

[0019] Preferably, the method further includes a start criterion:

[0020] Calculate the sudden change Δi of the current of each phase sampling value on each side of the transformer φ (t) = i φ (t)-i φ (tT), where φ represents the phase, which can be A, B or C, T is 20ms; t is the current sampling time;

[0021] When there are two consecutive sampling values ​​of current on one side of the transformer that satisfy |Δi φ(t)≥0.05I e , where I e For the rated current, start the transformer on this side for determination.

[0022] Preferably, it also includes determining the phase used for protection calculation on each side:

[0023] Calculate the current mutation Δi of phase a, b, and c sampling values ​​on the transformer startup judgment side respectively a , Δi b , Δi c The integral D a 、D b 、D c , D a =∑|Δi a |、D b =∑|Δi b |、D c =∑|Δi c |, D a 、D b 、D c The largest phase among the three phases is used as the phase for judgment.

[0024] According to another aspect of the present invention, a system for fault reopening protection during a transformer magnetizing inrush current blocking period is provided, the system comprising:

[0025] The first discrimination unit is configured to perform a first discrimination based on the first round of discrimination conditions after locking the current differential protection, and when the result of the first discrimination is that the current differential protection locking condition is met, issue a current differential protection locking signal, and output a final locking result based on the existing locking criteria of the protection device and the gate; or when the result of the first discrimination is that the current differential protection locking condition is not met, issue an open current differential protection signal, and output a final opening result based on the existing opening criteria or the gate of the protection device;

[0026] The second discrimination unit is used to perform a second discrimination based on the second round discrimination condition during the current differential protection locking period, and interrupt the current current differential protection locking when the result of the second discrimination is that the current differential protection opening condition is met.

[0027] Preferably, the protection start value in the first round of discrimination conditions is a low start value:

[0028] If the absolute value of two consecutive phase current sampling values ​​is greater than 0.05 times the rated current value, the current differential protection is activated.

[0029] Preferably, the protection start value in the second round of discrimination conditions is a high start value:

[0030] If the absolute value of two consecutive phase current sampling values ​​is greater than 1 times the rated current value, the current differential protection is activated.

[0031] Preferably, the protection blocking criteria of the first round of discrimination conditions and the second round of discrimination conditions are:

[0032] (|i φ (t)|<i φmax )∪(|i φ (t+1)|<i φmax )∪(|i φ (t+2)|<i φmax )∪(|i φ (t+3)|<i φmax ) Formula 1

[0033] |i φ (t)|+|i φ (t+2)|+|i φ (t+3)|+|i φ (t+4)|<0.2i φmax Formula 2

[0034] Among them, i φ is the sampling value of the phase current, i φmax It is called the relative large point, and t is the current sampling time;

[0035] When the sampling value of the phase current satisfies at least one criterion in formula 1 or formula 2, the current differential protection is locked;

[0036] When the sampling value of the phase current within 18ms after the current differential protection is started does not satisfy Formula 1 and does not satisfy Formula 2 at the same time, the current differential protection is released.

[0037] Preferably, the protection lockout criterion for determining that the magnetizing inrush current is not established is in an OR gate relationship with the transformer's original magnetizing inrush current release criterion;

[0038] The protection lockout criterion determines that the magnetizing inrush current is established in an AND gate relationship with the transformer's original magnetizing inrush current lockout.

[0039] Preferably, it further comprises an initial unit for starting the criterion:

[0040] Calculate the sudden change Δi of the current of each phase sampling value on each side of the transformer φ (t) = i φ (t)-i φ (tT), where φ represents the phase, which can be A, B or C, T is 20ms; t is the current sampling time;

[0041] When there are two consecutive sampling values ​​of current on one side of the transformer that satisfy |Δi φ (t)|≥0.05I e , where I eFor the rated current, start the transformer on this side for determination.

[0042] Preferably, the initial unit is further used to determine the phase used for protection calculation on each side:

[0043] Calculate the current mutation Δi of phase a, b, and c sampling values ​​on the transformer startup judgment side respectively a , Δi b , Δi c The integral D a 、D b 、D c , D a =∑|Δi a |、D b =∑|Δi b |、D c =∑|Δi c |, D a 、D b 、D c The largest phase among the three phases is used as the phase for judgment.

[0044] The technical solution of the present invention provides a method and system for fault reopening protection during transformer excitation inrush current lockout, wherein the method comprises: performing a first judgment based on a first round of judgment conditions after locking the current differential protection; when the result of the first judgment is that the current differential protection lockout condition is met, issuing a lock current differential protection signal, and combining the protection device's existing lockout judgment criteria and gate to output a final lockout result; or when the result of the first judgment is that the current differential protection lockout condition is not met, issuing an open current differential protection signal, and combining the protection device's existing open judgment criteria or gate to output a final open result; performing a second judgment based on a second round of judgment conditions during the current differential protection lockout period; when the result of the second judgment is that the current differential protection open condition is met, interrupting the current differential protection lockout. The method and system for fault reopening protection during transformer excitation inrush current lockout proposed by the technical solution of the present invention can achieve reliable reopening of the current differential protection in the event of a transformer fault during transformer inrush current lockout, while ensuring reliable locking of a single excitation inrush current fault and reliable opening of a single transformer fault. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] A more complete understanding of exemplary embodiments of the present invention may be obtained by referring to the following drawings:

[0046] Figure 1 Flowchart of a method for fault reopening protection during transformer magnetizing inrush current blocking according to a preferred embodiment of the present invention;

[0047] Figure 2 Schematic diagram of comprehensive output results under the condition of magnetizing inrush current according to a preferred embodiment of the present invention;

[0048] Figure 3 Schematic diagram of comprehensive output results in the case of transformer failure according to a preferred embodiment of the present invention;

[0049] Figure 4 Schematic diagram of comprehensive output results when a transformer fault occurs during magnetizing inrush current blocking according to a preferred embodiment of the present invention;

[0050] Figure 5 Schematic diagram of the action result of the proposed protection criterion under the condition of magnetizing inrush current according to a preferred embodiment of the present invention;

[0051] Figure 6 A schematic diagram of opening protection criteria when a transformer fault occurs during magnetizing inrush current blocking according to a preferred embodiment of the present invention;

[0052] Figure 7 is a schematic diagram of the action results of the proposed protection criterion when a transformer fault occurs during the magnetizing inrush current blocking period according to a preferred embodiment of the present invention; and

[0053] Figure 8 The figure is a system structure diagram of a fault reopening protection during transformer excitation inrush current blocking according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0054] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0055] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0056] Figure 1The present invention is a flowchart of a method for re-opening fault protection during transformer magnetizing inrush current lockout according to a preferred embodiment of the present invention. To address the issue of transformer faults occurring during second harmonic lockout, where the second harmonic lockout strategy fails to open in a timely manner, resulting in slow fault clearing of current differential protection, the present invention adds a criterion for rapid transformer fault opening based on existing protection configurations. This criterion utilizes single-side phase current sampling information to distinguish between magnetizing inrush current and transformer faults, opening current differential protection in the event of a fault and blocking it in the event of a magnetizing inrush current. Current information is continuously identified during the lockout period, allowing current differential protection to be immediately opened in the event of a transformer fault.

[0057] The present invention proposes a protection method for fault reopening during transformer excitation inrush current lockout. The method can realize reliable reopening of current differential protection in the event of a transformer fault during transformer inrush current lockout, while ensuring reliable lockout of a single excitation inrush current fault and reliable reopening of a single transformer fault.

[0058] like Figure 1 As shown, the present invention provides a method for fault reopening protection during transformer excitation inrush current blocking, the method comprising:

[0059] Step 101: After locking the current differential protection, a first discrimination is performed based on the first round of discrimination conditions. When the result of the first discrimination is that the current differential protection locking condition is met, a current differential protection locking signal is issued, and the final locking result is outputted based on the existing locking criteria of the protection device and the gate. Alternatively, when the result of the first discrimination is that the current differential protection locking condition is not met, an open current differential protection signal is issued, and the final opening result is outputted based on the existing opening criteria or the gate of the protection device.

[0060] Step 102: During the current differential protection blocking period, a second discrimination is performed based on the second round discrimination conditions. When the result of the second discrimination is that the current differential protection opening condition is met, the current current differential protection blocking is interrupted.

[0061] The protection scheme of the present invention is as follows: after protection is initiated, a first lock / release judgment is performed. If the current differential protection lock conditions are met, the protection is locked; otherwise, the protection is released. During the lock period, a second lock / release judgment is performed on the phase currents. If the release conditions are met, the current lock command is interrupted and the protection is released. The first lock / release judgment is called the first round of judgment, and the second lock / release judgment is called the second round of judgment.

[0062] Preferably, the protection start value in the first round of discrimination conditions is a low start value:

[0063] If the absolute value of two consecutive phase current sampling values ​​is greater than 0.05 times the rated current value, the current differential protection is activated.

[0064] Preferably, the protection start value in the second round of discrimination conditions is a high start value:

[0065] If the absolute value of two consecutive phase current sampling values ​​is greater than 1 times the rated current value, the current differential protection is activated.

[0066] The present invention uses different protection triggering values ​​for the first and second rounds of discrimination. To ensure protection sensitivity, the first round uses a low triggering value: protection is activated when the absolute value of two consecutive phase current sampling values ​​is greater than 0.05 times the rated current value. To ensure protection reliability, the second round uses a high triggering value: protection is activated when the absolute value of two consecutive phase current sampling values ​​is greater than 1 times the rated current value.

[0067] Preferably, the protection blocking criteria of the first round of discrimination conditions and the second round of discrimination conditions are:

[0068] (|i φ (t)|<i φmax )∪(|i φ (t+1)|<i φmax )∪(|i φ (t+2)|<i φmax )∪(|i φ (t+3)|<i φmax ) Formula 1

[0069] |i φ (t)|+|i φ (t+2)|+|i φ (t+3)|+|i φ t+4)|<0.2i φmax Formula 2

[0070] Among them, i φ is the sampling value of the phase current, i φmax It is called the relative large point, and t is the current sampling time;

[0071] When the sampling value of the phase current satisfies at least one criterion in formula 1 or formula 2, the current differential protection is locked;

[0072] When the sampling value of the phase current within 18ms after the current differential protection is started does not satisfy Formula 1 and does not satisfy Formula 2 at the same time, the current differential protection is released.

[0073] The first-round and second-round discrimination of the present invention use the same protection blocking criterion, as shown in formulas (1) and (2). When at least one of the criteria is met, the protection is blocked; when formula (1) and formula (2) are not met within 18 ms after the protection is started, the protection is opened.

[0074] (|i φ (t)|<iφmax )∪(|i φ (t+1)|<i φmax )∪(|i φ (t+2)|<i φmax )∪(|i φ (t+3)|<i φmax ) (1)

[0075] |i φ (t)|+|i φ (t+2)|+|i φ (t+3)|+|i φ (t+4)|<0.2i φmax (2)

[0076] where i φ is the sampling value of the phase current, i φmax is called the relatively large point, i φmax The specific algorithm is: start calculating from the first point of startup, and continue calculating for 18ms. If the value of the calculation point is greater than the calculation value of the previous point, such as |i φ (t|>|i φ (t-1)|, then retain the relative maximum point i φmax =|i φ (t)|.

[0077] Preferably, the protection lockout criterion for determining that the magnetizing inrush current is not established is in an OR gate relationship with the transformer's original magnetizing inrush current release criterion;

[0078] The protection lockout criterion determines whether the excitation inrush current is established and has a gate relationship with the transformer's original excitation inrush current lockout.

[0079] The criterion of the present invention works together with the original excitation inrush current locking criterion of the existing transformer to output the protection action result: the criterion for determining that the excitation inrush current is not established has an OR gate relationship with the original excitation inrush current opening criterion of the transformer; the criterion for determining that the excitation inrush current is established has an AND gate relationship with the original excitation inrush current locking criterion of the transformer.

[0080] Preferably, the method further includes a start criterion:

[0081] Calculate the sudden change Δi of the current of each phase sampling value on each side of the transformer φ (t) = i φ (t)-i φ (tT), where φ represents the phase, which can be A, B or C, T is 20ms; t is the current sampling time;

[0082] When there are two consecutive sampling values ​​of current on one side of the transformer that satisfy ||i φ (t)|≥0.05I e , where Ie For the rated current, start the transformer on this side for determination.

[0083] Preferably, it also includes determining the phase used for protection calculation on each side:

[0084] Calculate the current mutation Δi of phase a, b, and c sampling values ​​on the transformer startup judgment side respectively a , Δi b , Δi c The integral D a 、D b 、D c , D a =∑|Δi a |、D b =∑|Δi b |、D c =∑|Δi c |, D a 、D b 、D c The largest phase among the three phases is used as the phase for judgment.

[0085] (1) Excitation inrush current

[0086] The criterion of the present invention can reliably identify the excitation inrush current. When the criterion determines that the excitation inrush current is established, a blocking signal is output. At this time, the blocking relationship with the original excitation inrush current of the transformer is an AND gate relationship. The two are combined to output a blocking signal, and the current differential protection is locked. Figure 2 shown.

[0087] (2) Transformer failure

[0088] This criterion can reliably identify transformer faults. When this criterion determines that the magnetizing inrush current is not established, an open signal is output. At this time, the relationship with the original magnetizing inrush current blocking of the transformer is an OR gate relationship. The two are combined to output an open signal, and the current differential protection is open. Figure 3 shown.

[0089] (3) Transformer failure during magnetizing inrush current blocking

[0090] After the magnetizing inrush current occurs, this criterion sends out a blocking signal, which has an AND gate relationship with the original magnetizing inrush current criterion of the transformer, and outputs a blocking signal. If a transformer fault occurs during the blocking period, this criterion can reliably send out an opening signal, which has an OR gate relationship with the original magnetizing inrush current blocking of the transformer. The two combine to output an opening signal, and the current differential protection is blocked. Figure 4 shown.

[0091] Attachment Figure 5 :Protection criterion lockout under magnetizing inrush current condition

[0092] When the transformer is switched on without load and magnetizing inrush current is generated, the action result of the proposed protection criterion is as follows: Figure 5 As shown in the figure, the vertical axis 1 indicates protection action and 0 indicates no action. It can be seen that under the condition of magnetizing inrush current, the action result of the proposed protection criterion is blocking for 100ms.

[0093] Attachment Figure 6 :Protection judgment criteria open in case of transformer fault

[0094] When a transformer (turn-to-turn) fault occurs, the action result of the proposed protection criterion is as follows: Figure 6 As shown in the figure, the vertical axis 1 indicates protection action and 0 indicates no action. It can be seen that in the case of transformer fault, the action result of the proposed protection criterion is open for 100ms.

[0095] Attachment Figure 7 :When a transformer fault occurs during the magnetizing inrush current blocking period, the protection criteria is opened

[0096] After the transformer is closed under no-load conditions, an excitation inrush current is generated and the protection is locked. If a (turn-to-turn) fault occurs during the lockout period, the proposed protection criterion will operate as follows: Figure 7 As shown in Figure 1, where the vertical axis 1 indicates protection action and 0 indicates no action. It can be seen that when a transformer fault occurs during the magnetizing inrush current blocking period, the proposed protection criterion will be open for 100ms.

[0097] 1. Start criterion: Calculate the sudden change Δi of the current of each phase sampling value on each side of the transformer φ (t) = i φ (t)-i φ (tT), where φ represents the phase, which can be A, B or C, and T is 20ms. When two consecutive sampling points meet |Δi φ (t)|≥0.05I e , where I e For the rated current, the transformer starts on that side. The side that has started continues to calculate the next step, and the side that has not started stops calculating.

[0098] 2. Determine the phase used for protection calculation on each side: Calculate the integral of the current mutation of each phase sampling value on each side of the transformer. Take any side as an example, and set Δi a , Δi b , Δi c Perform 10ms integration (integration includes the two points where calculation starts), D a =∑|Δi a |、D b =∑|Δi b |、D c =∑|Δi c |, D a 、Db 、D c The phase with the largest value among the three phases is used for the subsequent determination.

[0099] 3. Identification of magnetizing inrush current: Calculate the maximum and minimum values ​​of the phase obtained in step 2. The calculation method is: start from the first point of startup, calculate continuously for 18ms, find the maximum point and the minimum point, if the value of the calculated point is greater than the calculated value of the previous point, such as |i φ (t)|>|i φ (t-1)|, then retain the relative maximum point i φmax =|i φ (t)|, if the absolute value of the calculated point is less than 0.1 times the calculated value of the previous maximum point, such as |i φ (t)|<0.1i φmax , then this point is a relatively small point i φmin =|i φ If four small dots appear consecutively, or the sum of the absolute values ​​of the four dots is less than 0.2 times the maximum dot, regardless of whether the duration is longer than 18ms, the inrush current is considered to be present. If four small dots do not appear consecutively within 18ms, and the integral value of four consecutive dots is greater than 0.2 times the maximum dot, the inrush current is considered to be absent.

[0100] 4. Processing of comprehensive judgment results on each side:

[0101] (1) If only one side is started, the calculation results of the starting side are directly output;

[0102] (2) When both sides are started, if the calculation results of both sides are the same, the same result will be given; if the calculation results of both sides are different, one is open and the other is locked, the result will be given according to the following principle: in the calculation process of both sides, if the locked signal is given first, the maximum value of the locked signal side that has been found will be compared with the maximum value of the other side. If the maximum value of the locked signal side is greater than 1 / 2 times the maximum value of the other open side, the comprehensive result should be judged as locked, otherwise it should be open.

[0103] (3) When starting on three sides, if the calculation results of the three sides are the same, the same result will be given; if the calculation results of the three sides are different, the result will be given according to the following principle: the maximum value of the locked signal side that has been found will be compared with the maximum value of other open sides. If the maximum value of the locked signal side is greater than 1 / 2 times the maximum value of other open sides, the comprehensive result should be judged as locked, otherwise it should be open.

[0104] 5. Fault opening criteria during locking period:

[0105] If the comprehensive result in step 4 is open, the following steps will not be performed. After opening for 100ms, the system will be reset and wait for the next startup.

[0106] If the comprehensive result in step 4 is locked: temporarily not reset, whether the high value starting condition is met continuously is calculated by judging whether there are two consecutive points in any phase of the three single-phase currents on each side of the transformer that meet |Δi φ (t)|≥I e If the condition is met, the transformer restarts. After starting, repeat steps 3 and 4. If the new calculation result is open, it will be reset after 100ms. If the new calculation result is blocked, it will be reset after 100ms. If it is not met, |Δi φ (t)|≥I e If the condition is met, the lock state will be maintained for 1.5 seconds before being reset.

[0107] 6. The relationship between the proposed criteria and the existing protection configuration:

[0108] (1) When this criterion determines that the magnetizing inrush current is not established, it has an OR gate relationship with the transformer's original magnetizing inrush current opening criterion;

[0109] (2) When this criterion determines that the excitation inrush current is established, the relationship between it and the original excitation inrush current blocking of the transformer is an AND gate relationship.

[0110] Figure 8 The figure is a system structure diagram of a fault reopening protection during transformer excitation inrush current blocking according to a preferred embodiment of the present invention.

[0111] like Figure 8 As shown, the present invention provides a system for fault reopening protection during transformer excitation inrush current blocking, the system comprising:

[0112] The first determination unit 801 is configured to perform a first determination based on the first round of determination conditions after locking the current differential protection. When the result of the first determination is that the current differential protection locking condition is met, the first determination unit 801 issues a signal to lock the current differential protection, and outputs a final locking result based on the existing locking criteria and gate of the protection device. Alternatively, when the result of the first determination is that the current differential protection locking condition is not met, the first determination unit 801 issues a signal to open the current differential protection, and outputs a final opening result based on the existing opening criteria or gate of the protection device.

[0113] The second judging unit 802 is configured to perform a second judgment based on the second round judgment condition during the current differential protection locking period, and interrupt the current current differential protection locking when the result of the second judgment satisfies the current differential protection opening condition.

[0114] Preferably, the protection start value in the first round of discrimination conditions is a low start value:

[0115] If the absolute value of two consecutive phase current sampling values ​​is greater than 0.05 times the rated current value, the current differential protection is activated.

[0116] Preferably, the protection start value in the second round of discrimination conditions is a high start value:

[0117] If the absolute value of two consecutive phase current sampling values ​​is greater than 1 times the rated current value, the current differential protection is activated.

[0118] Preferably, the protection blocking criteria of the first round of discrimination conditions and the second round of discrimination conditions are:

[0119] (|i φ (t)|<i φmax )∪(|i φ (t+1)|<i φmax )∪(|i φ (t+2)|<i φmax )∪(|i φ (t+3)|<i φmax ) Formula 1

[0120] |i φ (t)|+|i φ (t+2)|+|i φ (t+3)|+|i φ (t+4)|<0.2i φmax Formula 2

[0121] Among them, i φ is the sampling value of the phase current, i φmax It is called the relative large point, and t is the current sampling time;

[0122] When the sampling value of the phase current satisfies at least one criterion in formula 1 or formula 2, the current differential protection is locked;

[0123] When the sampling value of the phase current within 18ms after the current differential protection is started does not satisfy Formula 1 and does not satisfy Formula 2 at the same time, the current differential protection is released.

[0124] Preferably, the protection lockout criterion for determining that the magnetizing inrush current is not established is in an OR gate relationship with the transformer's original magnetizing inrush current release criterion;

[0125] The protection lockout criterion determines whether the excitation inrush current is established and has a gate relationship with the transformer's original excitation inrush current lockout.

[0126] Preferably, the system further comprises an initialization unit for starting the criterion:

[0127] Calculate the sudden change Δi of the current of each phase sampling value on each side of the transformer φ (t) = i φ (t)-i φ (tT), where φ represents the phase, which can be A, B or C, T is 20ms; t is the current sampling time;

[0128] When there are two consecutive sampling values ​​of current on one side of the transformer that satisfy |Δi φ (t)|≥0.05I e , where I e For the rated current, start the transformer on this side for determination.

[0129] Preferably, the system further comprises an initial unit for determining the phases used for protection calculation on each side:

[0130] Calculate the current mutation Δi of phase a, b, and c sampling values ​​on the transformer startup judgment side respectively a , Δi b , Δi c The integral D a 、D b 、D c , D a =∑|Δi a |、D b =∑|Δi b |、D c =∑|Δi c |, D a 、D b 、D c The largest phase among the three phases is used as the phase for judgment.

[0131] The system 800 for fault reopening protection during magnetizing inrush current blocking of a transformer in a preferred embodiment of the present invention corresponds to the method 100 for fault reopening protection during magnetizing inrush current blocking of a transformer in a preferred embodiment of the present invention, and will not be described in detail here.

[0132] It will be understood by those skilled in the art that the embodiments of the present invention may be provided as methods, systems, or computer program products. Therefore, the present invention may take the form of a complete hardware embodiment, a complete software embodiment, or an embodiment combining software and hardware. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The solutions in the embodiments of the present invention may be implemented in various computer languages, for example, the object-oriented programming language Java and the interpreted scripting language JavaScript.

[0133] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems), and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0134] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0135] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0136] Although the preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0137] Obviously, those skilled in the art may make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if such changes and modifications fall within the scope of the claims and their equivalents, the present invention is intended to include such changes and modifications.

[0138] The invention has been described above with reference to a few embodiments. However, it is readily apparent to a person skilled in the art that other embodiments than the ones disclosed above are equally within the scope of the invention, as defined by the appended patent claims.

[0139] Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a / the [means, component, etc.]" are to be interpreted openly as referring to at least one instance of the means, component, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not necessarily need to be performed in the exact order disclosed, unless explicitly stated otherwise.

Claims

1. A method for fault reopening protection during a transformer magnetizing inrush current lockout period, the method comprising: After the protection judgment is started, the first judgment is performed based on the first round of judgment conditions. When the result of the first judgment is that the current differential protection locking condition is met, a locking current differential protection signal is issued, and the final locking result is output by the gate together with the existing locking judgment of the protection device; Or when the first judgment result is that the current differential protection locking condition is not met, an opening current differential protection signal is issued, and the protection device outputs the final opening result according to the existing opening judgment criterion or gate; During the current differential protection blocking period, a second discrimination is performed based on the second round of discrimination conditions. When the result of the second discrimination is that the current differential protection opening condition is met, the current current differential protection blocking is interrupted. The protection blocking criteria of the first round of discrimination conditions and the second round of discrimination conditions are: (|i φ (t)| < i φmax ) ∪ (|i φ (t + 1)| < i φmax ) ∪ (|i φ (t + 2)| < i φmax ) ∪ (|i φ (t + 3)| < i φmax ) Equation 1 |i φ (t)| + |i φ (t + 2)| + |i φ (t + 3)| + |i φ (t + 4)| < 0.2i φmax Equation 2 Among them, i φ is the sampling value of the phase current, i φmax It is called the relative large point, and t is the current sampling time; i φmax The algorithm is: start calculating from the first point of startup, and continue calculating for 18ms. If the value of the calculated point is greater than the calculated value of the previous point, such as |i φ (t)|>|i φ (t-1)|, then keep i φmax =|i φ (t)|; When the sampling value of the phase current satisfies at least one criterion in formula 1 or formula 2, the current differential protection is locked; When the sampling value of the phase current within 18ms after the current differential protection is started does not satisfy Formula 1 and does not satisfy Formula 2 at the same time, the current differential protection is released.

2. The method according to claim 1, wherein the protection start value in the first round of discrimination conditions is a low start value: If the absolute value of two consecutive phase current sampling values ​​is greater than 0.05 times the rated current value, the current differential protection is activated.

3. The method according to claim 1, wherein the protection start value in the second round of discrimination conditions is a high start value: If the absolute value of two consecutive phase current sampling values ​​is greater than 1 times the rated current value, the current differential protection is activated.

4. The method according to claim 1, wherein the protection lockout criterion for determining that the magnetizing inrush current is not established is in an OR gate relationship with the transformer's original magnetizing inrush current release criterion; The protection lockout criterion determines that the magnetizing inrush current is established in an AND gate relationship with the transformer's original magnetizing inrush current lockout.

5. The method according to claim 1, further comprising a starting criterion: Calculate the sudden change Δi of the current of each phase sampling value on each side of the transformer φ (t) = i φ (t)-i φ (tT), where φ represents the phase, which can be A, B or C, T is 20ms; t is the current sampling time; When there are two consecutive sampling values ​​of current on one side of the transformer that satisfy |Δi φ (t)|≥0.05I e , where I e For the rated current, start the transformer on this side for determination.

6. The method according to claim 5, further comprising determining the phases used for protection calculation on each side: Calculate the current mutation Δi of phase a, b, and c sampling values ​​on the transformer startup judgment side respectively a , Δi b , Δi c The integral D a 、D b 、D c , D a =∑|Δi a |、D b =∑|Δi b |、D c =∑|Δi c |, D a 、D b 、D c The largest phase among the three phases is used as the phase for judgment.

7. A system for fault reopening protection during transformer magnetizing inrush current blocking, the system comprising: A first discrimination unit is configured to perform a first discrimination based on the first round of discrimination conditions after the current differential protection is locked. When the result of the first discrimination is that the current differential protection locking condition is met, a locking current differential protection signal is issued, and the locking result is output by an AND gate with the existing locking criteria of the protection device; Or when the first judgment result is that the current differential protection locking condition is not met, an opening current differential protection signal is issued, and the protection device outputs the final opening result according to the existing opening judgment criterion or gate; a second discrimination unit, configured to perform a second discrimination based on a second round of discrimination conditions during the current differential protection blocking period, and interrupt the current current differential protection blocking when the result of the second discrimination is that the current differential protection opening condition is satisfied; The protection blocking criteria of the first round of discrimination conditions and the second round of discrimination conditions are: (|i φ (t)|<i φmax ) ∪ (|i φ (t + 1)|<i φmax ) ∪ (|i φ (t + 2)| < i φmax ) ∪ (|i φ (t + 3)| < i φmax ) Equation 1 |i φ (t)|+|i φ (t + 2)|+|i φ (t + 3)|+|i φ (t + 4)|<0.2i φmax Equation 2 Among them, i φ is the sampling value of the phase current, i φmax It is called the relative large point, and t is the current sampling time; i φmax The algorithm is: start calculating from the first point of startup, and continue calculating for 18ms. If the value of the calculated point is greater than the calculated value of the previous point, such as |i φ (t)|>|i φ (t-1)|, then keep i φmax =|i φ (t)|; When the sampling value of the phase current satisfies at least one criterion in formula 1 or formula 2, the current differential protection is locked; When the sampling value of the phase current within 18ms after the current differential protection is started does not satisfy Formula 1 and does not satisfy Formula 2 at the same time, the current differential protection is released.

8. The system according to claim 7, wherein the protection start value in the first round of discrimination conditions is a low start value: If the absolute value of two consecutive phase current sampling values ​​is greater than 0.05 times the rated current value, the current differential protection is activated.

9. The system according to claim 7, wherein the protection start value in the second round of discrimination conditions is a high start value: If the absolute value of two consecutive phase current sampling values ​​is greater than 1 times the rated current value, the current differential protection is activated.

10. The system according to claim 7, wherein the protection lockout criterion for determining that the magnetizing inrush current is not established is in an OR gate relationship with the transformer's original magnetizing inrush current release criterion; The protection lockout criterion determines that the magnetizing inrush current is established in an AND gate relationship with the transformer's original magnetizing inrush current lockout.

11. The system according to claim 7, further comprising an initialization unit for initiating the criterion: Calculate the sudden change Δi of the current of each phase sampling value on each side of the transformer φ (t) = i φ (t)-i φ (tT), where φ represents the phase, which can be A, B or C, T is 20ms; t is the current sampling time; When there are two consecutive sampling values ​​of current on one side of the transformer that satisfy |Δi φ (t)|≥0.05I e , where I e For the rated current, start the transformer on this side for determination.

12. The system according to claim 11, wherein the initial unit is further configured to determine the phases used for protection calculation on each side: Calculate the current mutation Δi of phase a, b, and c sampling values ​​on the transformer startup judgment side respectively a , Δi b , Δi c The integral D a 、D b 、D c , D a =∑|Δi a |、D b =∑|Δi b |、D c =∑|Δi c |, D a 、D b 、D c The largest phase among the three phases is used as the phase for judgment.

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