Line protection PT disconnection identification method and system based on voltage change trend and continuous current change characteristics

Abstract

The present application discloses a line protection PT disconnection identification method and system based on voltage change trend and continuous current change characteristics, the method comprising: determining the parameters of zero-sequence voltage and current without pressure judgment criteria, constructing voltage change trend and continuous current change judgment criteria; judging whether the line is operating normally and whether the starting element is started, if the line is operating normally and the starting element is not started, then starting the PT disconnection detection; analyzing the PT distribution, collecting the voltage and current data of the normal operation of the line; and making PT disconnection judgment based on zero-sequence voltage, current without pressure, voltage change trend and continuous current change judgment criteria. The present invention adds voltage change trend judgment criteria and continuous current change judgment criteria on the basis of the judgment logic composed of zero-sequence voltage and current without pressure judgment criteria, which can effectively reduce the probability of misjudgment in specific scenarios, thereby improving the safety and reliability of the line protection device.

Description

Technical Field

[0001] The invention belongs to the technical field of line relay protection, and relates to a line protection PT disconnection identification method and system based on voltage variation trend and continuous current variation characteristics. Background Art

[0002] Line protection devices are generally equipped with PT line break judgment logic. Correct identification of PT line break can effectively prevent the false operation of distance protection and directional zero-sequence protection caused by PT line break.

[0003] The existing PT disconnection judgment logic uses two criteria: zero-sequence voltage and current-no-voltage judgment:

[0004] The zero-sequence voltage criterion is: the sum of the three-phase voltages is not zero: Voltage threshold value, judged as PT disconnection. This criterion can be used to detect single-phase or two-phase disconnection.

[0005] The criterion for flow without pressure is: when PT is on the bus, if and If any phase voltage is less than the voltage threshold value, it is judged as PT disconnection; when PT is in the line, if any phase current is greater than 0.04 times the rated current or the circuit breaker is in the closed position (tripping position is opened), and If any phase voltage is lower than the voltage threshold, it is judged as a PT disconnection alarm.

[0006] The above two criteria are both delayed and are only put into operation when the line is operating normally and the starting element is not started. Once the starting element is started, the PT line break detection stops immediately and will not resume until the entire group is restored.

[0007] However, under adverse conditions such as voltage increase, long oscillation period, high resistance slow burning, etc., the PT line may be misjudged as disconnected based solely on zero-sequence voltage and current-without-pressure judgment criteria, which will lock distance protection and directional zero-sequence protection, causing the line protection device to refuse to operate. The specific analysis is as follows:

[0008] When a single-phase line on one side is tripped and fails to reclose, and the single-phase voltage on the other side increases, the zero-sequence voltage criterion may be met, resulting in a misjudgment of a PT line break; when the oscillation period is long, the current change is not obvious, and both the sudden change quantity starting and the static instability starting do not work, the current but no voltage criterion may be met, resulting in a misjudgment of a PT line break; when a single-phase grounding fault occurs through a transition resistor and a high-resistance slow burn occurs, the voltage and current change slowly, resulting in the failure of both the sudden change quantity starting and the zero-sequence auxiliary starting to work, the zero-sequence voltage criterion may be met, resulting in a misjudgment of a PT line break. Summary of the invention

[0009] In order to solve the deficiencies in the prior art, the present application provides a line protection PT disconnection identification method and system based on voltage change trends and continuous current change characteristics.

[0010] In order to achieve the above object, the present invention adopts the following technical solution:

[0011] A line protection PT disconnection identification method based on voltage change trend and continuous current change characteristics adds voltage change trend judgment and continuous current change judgment on the basis of the judgment logic composed of zero-sequence voltage and current-no-voltage judgment criteria, so as to prevent the line protection device from misjudging the PT disconnection due to voltage increase, long oscillation period, and high-resistance slow burning.

[0012] The present invention further includes the following preferred embodiments:

[0013] Preferably, the voltage change trend criterion is:

[0014] The voltage change from the start time to the end time of the PT disconnection judgment delay is a decreasing trend;

[0015] The continuous current change criterion is:

[0016] The current change at the start and end times of the PT disconnection detection delay is less than the allowable threshold value.

[0017] Preferably, the method comprises the following steps:

[0018] Step 1: Analyze the PT disconnection situation, determine the parameters of the zero-sequence voltage criterion and the current-no-voltage criterion, and construct the voltage change trend and continuous current change criterion;

[0019] Step 2: Determine whether the line is operating normally and whether the starting element is started. If the line is operating normally and the starting element is not started, go to step 3 to start the PT disconnection detection. Otherwise, the PT disconnection detection will be stopped immediately and will not be resumed until the whole group is restored.

[0020] Step 4: Analyze the PT distribution and collect voltage and current data of normal operation of the line;

[0021] Step 5: Determine PT disconnection based on zero-sequence voltage, current without voltage, voltage change trend, and continuous current change criteria:

[0022] When the zero-sequence voltage, voltage change trend and continuous current change criteria are met at the same time, or,

[0023] When the criteria of current but no pressure, voltage change trend and continuous current change are met at the same time, the PT is judged to be broken.

[0024] Preferably, the zero-sequence voltage criterion in step 1 is: Voltage threshold value;

[0025] The flow without pressure criterion is:

[0026] When PT is on the busbar, if and Any phase voltage is less than the voltage threshold;

[0027] When the PT is in the circuit, when the current in any phase is greater than 0.04 times the rated current or the circuit breaker is in the closed position, and Any phase voltage is less than the voltage threshold.

[0028] Preferably, the voltage threshold value is an effective value, 7V is used in the zero-sequence voltage criterion, and 8V is used in the current-no-voltage criterion.

[0029] Preferably, in step 1, time T1 is recorded as the starting time of the PT disconnection determination delay, and time T2 is recorded as the ending time of the PT disconnection determination delay, and the voltage change trend criterion is constructed as follows:

[0030] U 1A -U 2A >KU N

[0031] U 1B -U 2B >KU N

[0032] U 1C -U 2C >KU N

[0033] Among them, U 1A , U 1B , U 1C It is the effective value of the voltage of phases A, B and C at the time T1 of the protection installation;

[0034] U 2A , U 2B , U 2C It is the effective value of the voltage at the protection installation location at time T2;

[0035] U N is the secondary rated voltage of the protection device;

[0036] K is the reliability coefficient.

[0037] When any of the above three formulas is satisfied, the voltage change trend criterion is satisfied.

[0038] Preferably, in step 1, the continuous current change characteristic criterion is constructed as follows:

[0039] |I 1A -I 2A | <KIN

[0040] |I 1B -I 2B | <KI N

[0041] |I 1C -I 2C | <KI N

[0042] |I 10 -I 20 | <KI N

[0043] Among them, I 1A ,I 1B ,I 1C ,I 10 It is the effective value of phase A, B, C and zero-sequence current at the protection installation location at time T1;

[0044] I 2A ,I 2B ,I 2C ,I 20 It is the effective value of phase A, B, C and zero-sequence current at the protection installation location at time T2;

[0045] I N is the secondary rated current of the protective device;

[0046] K is the reliability coefficient.

[0047] When all the above four formulas are satisfied, the continuous current change characteristic criterion is met.

[0048] Preferably, U N It is the secondary rated voltage of the protection device, and the phase voltage is 57.7V and the line voltage is 100V;

[0049] I N Take 1A or 5A;

[0050] K is the reliability coefficient, which is between 0.1 and 0.2.

[0051] Preferably, in step 4, after determining that the PT is disconnected, a PT disconnection alarm is output after 1 second of confirmation.

[0052] The present invention also provides a line protection PT disconnection identification system based on voltage change trend and continuous current change characteristics, which is used to implement the line protection PT disconnection identification method based on voltage change trend and continuous current change characteristics.

[0053] Beneficial effects achieved by this application:

[0054] The present invention adds voltage change trend criteria and continuous current change criteria on the basis of the discrimination logic composed of zero-sequence voltage and current-no-pressure criteria, so as to prevent the line protection device from misjudging the PT line break due to adverse conditions such as voltage rise, long oscillation cycle, high-resistance slow burning, etc., and effectively avoids the distance protection and directional zero-sequence protection from being mistakenly locked. It can accurately identify the PT line break under normal conditions, and can accurately identify the PT line break even under adverse conditions such as voltage rise, long oscillation cycle, high-resistance slow burning, etc., which can effectively reduce the probability of misjudgment in specific scenarios, thereby improving the safety and reliability of the line protection device. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of a line protection PT disconnection identification method based on voltage variation trend and continuous current variation characteristics of the present invention. DETAILED DESCRIPTION

[0056] The present application is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present application.

[0057] See also Figure 1 The line protection PT disconnection identification method based on the voltage change trend and continuous current change characteristics of the present invention adds voltage change trend judgment and continuous current change judgment on the basis of the judgment logic composed of zero-sequence voltage and current-no-voltage judgment criteria, so as to prevent the line protection device from misjudging the PT disconnection due to voltage increase, long oscillation period, and high-resistance slow burning.

[0058] The voltage change trend criterion is:

[0059] The voltage change from the start time to the end time of the PT disconnection judgment delay is a decreasing trend;

[0060] The continuous current change criterion is:

[0061] The current change at the start and end times of the PT disconnection detection delay is less than the allowable threshold value.

[0062] In specific implementation, the line protection PT disconnection identification method based on the voltage change trend and the continuous current change characteristics of the present invention includes the following steps:

[0063] Step 1: Analyze the PT disconnection situation, determine the parameters of the zero-sequence voltage criterion and the current-no-voltage criterion, and construct the voltage change trend and continuous current change criterion;

[0064] The zero-sequence voltage criterion is: the sum of the three-phase voltages is not zero, and Voltage threshold value;

[0065] The flow without pressure criterion is:

[0066] When PT is on the busbar, if and Any phase voltage is less than the voltage threshold;

[0067] When the PT is in the circuit, when the current in any phase is greater than 0.04 times the rated current or the circuit breaker is in the closed position (tripping position is opened), and Any phase voltage is less than the voltage threshold.

[0068] Preferably, the voltage threshold value is an effective value, 7V is used in the zero-sequence voltage criterion, and 8V is used in the current-no-voltage criterion.

[0069] Furthermore, let T1 be the starting time of the PT disconnection judgment delay, and T2 be the ending time of the PT disconnection judgment delay, then the voltage change trend judgment criterion is constructed as:

[0070] U 1A -U 2A >KU N

[0071] U 1B -U 2B >KU N

[0072] U 1C -U 2C >KU N

[0073] Among them, U 1A , U 1B , U 1C It is the effective value of the voltage of phases A, B and C at the time T1 of the protection installation;

[0074] U 2A , U 2B , U 2C It is the effective value of the voltage at the protection installation location at time T2;

[0075] U N It is the secondary rated voltage of the protection device (the phase voltage is 57.7V and the line voltage is 100V);

[0076] K is the reliability coefficient, which can be 0.1 to 0.2, which is greater than the 5% variation range of the normal voltage.

[0077] When any of the above three formulas is satisfied, the voltage change trend criterion is satisfied.

[0078] Preferably, in step 1, the continuous current change characteristic criterion is constructed as follows:

[0079] |I 1A -I 2A | <KIN

[0080] |I 1B -I 2B | <KI N

[0081] |I 1C -I 2C | <KI N

[0082] |I 10 -I 20 | <KI N

[0083] Among them, I 1A ,I 1B ,I 1C ,I 10 It is the effective value of phase A, B, C and zero-sequence current at the protection installation location at time T1;

[0084] I 2A ,I 2B ,I 2C ,I 20 It is the effective value of phase A, B, C and zero-sequence current at the protection installation location at time T2;

[0085] I N is the secondary rated current of the protection device (1A or 5A);

[0086] K is the reliability coefficient, which can be taken as 0.1~0.2.

[0087] When all the above four formulas are satisfied, the continuous current change characteristic criterion is met.

[0088] Step 2: Determine whether the line is operating normally and whether the starting element is started. If the line is operating normally and the starting element is not started, go to step 3 to start the PT disconnection detection. Otherwise, the PT disconnection detection will be stopped immediately and will not be resumed until the whole group is restored.

[0089] That is, when the line is operating normally and the starting element is not started, the PT line break detection is started.

[0090] In actual operation, after the protection is started, the protection device enters the fault judgment logic, and the fault characteristics are sometimes similar to PT line break. Therefore, in order to prevent misjudgment, the PT line break judgment is not performed after the protection is started, and the PT line break detection is activated when the starting element is not started.

[0091] The whole group restoration means that the protection recognizes that the fault state has disappeared and the protection returns to the normal operating state.

[0092] Step 4: Analyze the PT distribution and collect voltage and current data of normal operation of the line;

[0093] Step 5: Determine PT disconnection based on zero-sequence voltage, current without voltage, voltage change trend, and continuous current change criteria:

[0094] When the zero-sequence voltage, voltage change trend and continuous current change criteria are met at the same time, or,

[0095] When the criteria of current but no pressure, voltage change trend and continuous current change are met at the same time, the PT is judged to be broken.

[0096] After determining that the PT is disconnected, the PT disconnection alarm is output with a delay of 1s.

[0097] The present invention discloses a line protection PT disconnection identification system based on voltage variation trend and continuous current variation characteristics, and the system is used to implement the line protection PT disconnection identification method based on voltage variation trend and continuous current variation characteristics.

[0098] The present invention adds voltage change trend criteria and continuous current change criteria on the basis of the discrimination logic composed of zero-sequence voltage and current-no-pressure criteria, so as to prevent the line protection device from misjudging the PT line break due to adverse conditions such as voltage rise, long oscillation cycle, high-resistance slow burning, etc., and effectively avoids the distance protection and directional zero-sequence protection from being mistakenly locked. It can accurately identify the PT line break under normal conditions, and can accurately identify the PT line break even under adverse conditions such as voltage rise, long oscillation cycle, high-resistance slow burning, etc., which can effectively reduce the probability of misjudgment in specific scenarios, thereby improving the safety and reliability of the line protection device.

[0099] The applicant of the present invention has made a detailed explanation and description of the implementation examples of the present invention in conjunction with the drawings in the specification. However, those skilled in the art should understand that the above implementation examples are only preferred implementation schemes of the present invention, and the detailed description is only to help readers better understand the spirit of the present invention, but not to limit the scope of protection of the present invention. On the contrary, any improvements or modifications based on the inventive spirit of the present invention should fall within the scope of protection of the present invention.

Claims

1. A line protection PT disconnection identification method based on voltage change trend and continuous current change characteristics, characterized by: On the basis of the judgment logic composed of zero-sequence voltage and current-no-voltage judgment, the voltage change trend judgment and continuous current change judgment are added to prevent the line protection device from misjudging the PT disconnection due to voltage increase, long oscillation cycle, and high-resistance slow burning; The voltage change trend criterion is: the voltage change from the start time to the end time of the PT disconnection judgment delay is a decreasing trend; The continuous current change criterion is: the current change between the start time and the end time of the PT disconnection judgment delay is less than the allowed threshold value; The method comprises the following steps: Step 1: Analyze the PT disconnection situation, determine the parameters of the zero-sequence voltage criterion and the current-no-voltage criterion, and construct the voltage change trend and continuous current change criterion; Step 2: Determine whether the line is running normally and whether the starting element is started. If the line is running normally and the starting element is not started, go to step 3 to start PT disconnection detection; Step 3: Analyze the PT distribution and collect voltage and current data of normal operation of the line; Step 4: Determine PT disconnection based on zero-sequence voltage, current without voltage, voltage change trend, and continuous current change criteria: When the zero-sequence voltage, voltage change trend and continuous current change criteria are met at the same time, or, When the criteria of current but no pressure, voltage change trend and continuous current change are met at the same time, the PT is judged to be broken.

2. The line protection PT disconnection identification method based on voltage change trend and continuous current change characteristics according to claim 1 is characterized in that: The zero-sequence voltage criterion in step 1 is: the three-phase zero-sequence voltage at the protection installation The flow without pressure criterion is: When PT is on the busbar, if and Any phase voltage is less than the voltage threshold; When the PT is in the circuit, when the current in any phase is greater than 0.04 times the rated current or the circuit breaker is in the closed position, and Any phase voltage is less than the voltage threshold.

3. The line protection PT disconnection identification method based on voltage variation trend and continuous current variation characteristics according to claim 2 is characterized in that: The voltage threshold value is an effective value, 7V is used in the zero-sequence voltage criterion, and 8V is used in the current-no-voltage criterion.

4. The line protection PT disconnection identification method based on voltage variation trend and continuous current variation characteristics according to claim 1 is characterized in that: In step 1, let T1 be the starting time of the PT disconnection judgment delay, and T2 be the ending time of the PT disconnection judgment delay. Then the voltage change trend judgment criterion is constructed as follows: U 1A -U 2A >STOP N U 1B -U 2B >STOP N U 1C -U 2C >STOP N Among them, U 1A , U 1B , U 1C It is the effective value of the voltage of phases A, B and C at the time T1 of the protection installation; U 2A , U 2B , U 2C It is the effective value of the voltage at the protection installation location at time T2; U N is the secondary rated voltage of the protection device; K is the reliability coefficient; When any of the above three formulas is satisfied, the voltage change trend criterion is satisfied.

5. The line protection PT disconnection identification method based on voltage variation trend and continuous current variation characteristics according to claim 4 is characterized in that: In step 1, the continuous current change characteristic criterion is constructed as: |I 1A -I 2A |<KI N |I 1B -I 2B |<KI N |I 1C -I 2C |<KI N |I 10 -I 20 |<KI N Among them, I 1A ,I 1B ,I 1C ,I 10 It is the effective value of phase A, B, C and zero-sequence current at the protection installation location at time T1; I 2A ,I 2B ,I 2C ,I 20 It is the effective value of phase A, B, C and zero-sequence current at the protection installation location at time T2; I N is the secondary rated current of the protective device; K is the reliability coefficient; When all the above four formulas are satisfied, the continuous current change characteristic criterion is met.

6. The line protection PT disconnection identification method based on voltage variation trend and continuous current variation characteristics according to claim 5 is characterized in that: U N It is the secondary rated voltage of the protection device, and the phase voltage is 57.7V and the line voltage is 100V; I N Take 1A or 5A; K is the reliability coefficient, which is between 0.1 and 0.

2.

7. The line protection PT disconnection identification method based on voltage variation trend and continuous current variation characteristics according to claim 1 is characterized in that: In step 4, after determining that the PT is disconnected, a PT disconnection alarm is output after 1 second of confirmation.

8. A line protection PT disconnection identification system based on voltage change trend and continuous current change characteristics, characterized by: The system is used to implement the line protection PT disconnection identification method based on voltage change trend and continuous current change characteristics as described in any one of claims 1-7.

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