A transformer differential protection secondary circuit abnormality identification method

Abstract

The application discloses a transformer differential protection secondary circuit abnormality identification method, according to the situation that symmetrical differential current and asymmetrical differential current are generated when the transformer differential protection secondary circuit is abnormal, the type of transformer differential protection secondary circuit abnormality is accurately identified through the two kinds of differential current; the current operation state of the transformer is identified through judging the transformer differential current and the three-phase current of each CT participating in the differential protection, then the differential current is recalculated by adjusting the CT polarity, clock number and the like of the CT participating in the transformer differential protection one by one to match the current differential current, so that the formation type of the symmetrical differential current is identified; the formation type of the asymmetrical differential current is identified by calculating the number of asymmetrical CTs. The method can automatically, quickly and accurately identify the formation cause of the transformer differential protection secondary circuit abnormality, and is convenient for operation and maintenance personnel to quickly locate and eliminate the abnormality of the transformer differential protection secondary circuit.

Description

Technical Field

[0001] This invention belongs to the field of power system relay protection technology, specifically relating to a method for identifying anomalies in the secondary circuit of transformer differential protection. Background Technology

[0002] Long-term power system operation data shows that incorrect relay protection operation caused by wiring errors in the secondary circuit of transformer differential protection occurs frequently, posing a serious threat to the safe and stable operation of the power grid.

[0003] Chinese patent (publication number CN112379194A) discloses a method for identifying abnormalities in the secondary circuit of a transformer differential protection device. It can automatically detect the secondary circuit of the transformer protection device and give a normal or abnormal detection conclusion. Its shortcoming is that it cannot effectively identify the type of abnormality after detecting the abnormality. Summary of the Invention

[0004] The purpose of this invention is to provide a method for identifying abnormalities in the secondary circuit of transformer differential protection, which facilitates the rapid location and elimination of abnormalities in the secondary circuit of transformer differential protection.

[0005] To achieve the above objectives, the solution of the present invention is:

[0006] A method for identifying anomalies in the secondary circuit of a transformer differential protection system includes the following steps:

[0007] Step 1: Obtain the three-phase voltage and three-phase current on each side of the transformer;

[0008] Step 2: By calculating the differential current of the transformer differential protection and the changes in the three-phase current of each CT involved in the transformer differential protection, determine the operating status of the transformer. If the operating status of the transformer changes, wait; otherwise, proceed to step 3.

[0009] Step 3: Determine if the differential current is symmetrical in three phases; if symmetrical, proceed to step 4; otherwise, proceed to step 7.

[0010] Step 4: Replace the polarity of each CT involved in the transformer differential protection one by one, and recalculate the differential current. If the differential current disappears at this time, it is determined that the polarity of the CT is incorrect. If the differential current does not disappear, continue to replace the polarity of the remaining CTs and recalculate the differential current to determine whether the differential current disappears. If it does not disappear, proceed to step 5.

[0011] Step 5: Replace the clock count of each CT involved in the transformer differential protection one by one, and recalculate the differential current. If the differential current disappears at this time, it is determined that the clock count of that CT is incorrect. If the differential current does not disappear, continue to replace the clock count of the remaining CTs and recalculate the differential current to determine whether the differential current disappears. If it does not disappear, proceed to step 6.

[0012] Step 6: Calculate the active power flowing into each CT participating in the transformer differential protection and compare it with the set active power. If the two are different, it is determined that the secondary coil of the CT is selected incorrectly. If the two are the same, continue to compare the active power flowing into the other CTs with their set active power. If they are all the same, it is determined that there is another fault.

[0013] Step 7: Determine the asymmetry of the three-phase current of each CT involved in the transformer differential protection. If the number of asymmetrical CTs exceeds 1, it is determined to be another fault; if the number of asymmetrical CTs is 1, proceed to step 8.

[0014] Step 8: Determine whether the three-phase current amplitudes of the asymmetrical CT are equal; if the three-phase current amplitudes are equal, it is determined that the phase sequence of the CT is incorrect; if they are not equal, it is determined that the CT is disconnected.

[0015] In step 2 above, the specific method for determining the transformer's operating status by calculating the differential current of the transformer differential protection and the changes in the three-phase currents of each CT involved in the transformer differential protection is as follows:

[0016] Step 21: Record the differential current of the transformer differential protection and the characteristic values ​​of the three-phase current of each CT participating in the transformer differential protection for each calculation cycle; if the differential current is lower than the current setting value of the differential protection, continue to wait; otherwise, go to step 22.

[0017] Step 22: Compare the differential current characteristic value of the current calculation period t0 with the differential current characteristic value of the previous X calculation periods tx. If it exceeds the set threshold, it is determined that the transformer operating status has changed. Compare the three-phase current characteristic values ​​of each CT participating in the differential protection of the transformer in the current calculation period t0 with the current characteristic values ​​of the previous X calculation periods tx. If they exceed the set threshold, it is determined that the transformer operating status has changed. If none of them exceed the threshold and the duration reaches the set time, it is determined that the transformer operating status has not changed.

[0018] In step 21 above, the differential protection current setting value is set to 0.2 times the rated current of the transformer.

[0019] In step 22 above, the threshold for the change of differential current characteristic value is set to 0.04 times the rated current of the transformer.

[0020] In step 22 above, the threshold for the change of the characteristic value of the three-phase current of the CT is set to 0.04 times the rated value of the CT.

[0021] After adopting the above solution, the beneficial effects of this invention compared with the prior art are as follows: by collecting and calculating the three-phase voltage and three-phase current on each side of the transformer, the type of abnormality of the secondary circuit of the transformer differential protection in an abnormal operating state can be automatically identified, which facilitates operation and maintenance personnel to quickly locate and eliminate the abnormality of the secondary circuit of the transformer differential protection. Attached Figure Description

[0022] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0023] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0024] The secondary circuit of transformer differential protection includes current sampling circuits for each side of the transformer (each side refers to the high-voltage side, medium-voltage side, and low-voltage side of the transformer, the same below). For example... Figure 1 As shown, the transformer differential protection secondary circuit anomaly identification method of the present invention includes the following steps:

[0025] (1) Automatically collect and calculate the three-phase voltage and three-phase current on each side of the transformer;

[0026] (2) By calculating the differential current of the transformer differential protection (hereinafter referred to as differential current) and the changes in the three-phase current of each CT involved in the transformer differential protection, the operating status of the transformer is determined; if the operating status of the transformer changes, wait; otherwise, proceed to step (3).

[0027] (3) Determine whether the differential current is three-phase symmetrical; if it is symmetrical, proceed to step (4); otherwise, proceed to step (7).

[0028] (4) Replace the polarity of each CT involved in the transformer differential protection one by one and recalculate the differential current. If the differential current disappears at this time, it is determined that the polarity of the CT is wrong. If the differential current does not disappear, continue to replace the polarity of the other CTs and recalculate the differential current to determine whether the differential current disappears. If none of them disappear, proceed to step (5).

[0029] (5) Replace the clock count of each CT involved in the transformer differential protection one by one, and recalculate the differential current. If the differential current disappears at this time, it is determined that the clock count of the CT is wrong. If the differential current does not disappear, continue to replace the clock count of the remaining CTs and recalculate the differential current to determine whether the differential current disappears. If none of them disappear, proceed to step (6).

[0030] (6) Calculate the active power flowing into each CT participating in the transformer differential protection and compare it with the set active power. If the two are different, it is determined that the secondary coil of the CT is selected incorrectly. If the two are the same, continue to compare the active power flowing into the other CTs with their set active power. If they are all the same, it is determined that there is another fault.

[0031]

[0032] In the formula, Indicates separation, =A, B, C, three phases; U φThis indicates the effective voltage value on the transformer side where the CT is located; I φ This indicates that the CT scan Phase current RMS value; P setφ This indicates the set active power flowing into the transformer; Set g This indicates the set allowable deviation value, which is a constant.

[0033] (7) Determine the asymmetry of the three-phase current of each CT involved in the transformer differential protection. If the number of asymmetrical CTs exceeds 1, it is determined to be another fault. If the number of asymmetrical CTs is 1, proceed to step (8).

[0034] (8) Determine whether the three-phase current amplitudes of the asymmetrical CT are equal; if the three-phase current amplitudes are equal, it is determined that the phase sequence of the CT is incorrect; if they are not equal, it is determined that the CT is disconnected.

[0035] In step (2), the specific method for determining the transformer operating status by calculating the changes in the transformer differential current and the three-phase current of each CT participating in the transformer differential protection is as follows: record the characteristic values ​​of the transformer differential current and the three-phase current of each CT participating in the transformer differential protection for each current calculation cycle; if the differential current is lower than the current setting value of the differential protection, continue to wait; otherwise, continue to perform the following steps: compare the differential current characteristic value of the current calculation cycle t0 with the differential current characteristic value of the previous X calculation cycles tx, and if it exceeds the set threshold, determine that the transformer operating status has changed; compare the three-phase current characteristic value of each CT participating in the transformer differential protection for the current calculation cycle t0 with the current characteristic value of the previous X calculation cycles tx, and if it exceeds the set threshold, determine that the transformer operating status has changed; if neither exceeds the threshold and the duration reaches the set time, determine that the transformer operating status has not changed.

[0036]

[0037] In the formula, for Phase difference flow eigenvalues Three phases; The first CT to participate in the differential protection calculation Phase current, adjusted vector; The phase current characteristic value of the nth CT participating in the differential protection calculation, where n = 1, 2, 3, ..., N; N is the total number of CTs participating in the differential protection calculation, typically 2 to 6 in engineering practice; I th0 ,I th1 ,I th2 These are the differential protection current setting value, the differential current change setting threshold, and the CT phase current change setting threshold, respectively.

[0038] In engineering, differential protection has a current setpoint I. th0 0.2I can be taken.e I e A threshold I is set for the transformer's rated current and differential current variation. th1 0.04I can be taken. e ;CT phase current change setting threshold I th2 0.04I can be taken. n I n This is the CT rated value.

[0039] In summary, when the secondary circuit of transformer differential protection malfunctions, the resulting differential current (hereinafter referred to as differential current) is divided into two types: symmetrical differential current and asymmetrical differential current. This invention accurately identifies the type of malfunction in the secondary circuit of transformer differential protection using these two types of differential current. The current operating state of the transformer is identified by judging the transformer differential current and the three-phase current of each CT involved in the differential protection. Then, the differential current is recalculated by adjusting the polarity and clock position of each CT involved in the transformer differential protection to match the current differential current, thereby identifying the type of symmetrical differential current. The type of asymmetrical differential current is identified by calculating the number of CTs with asymmetrical three-phase currents. This invention can automatically, quickly, and accurately identify the causes of malfunctions in the secondary circuit of transformer differential protection, facilitating maintenance personnel to quickly locate and eliminate the malfunctions in the secondary circuit of transformer differential protection.

[0040] The above embodiments are merely illustrative of the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solutions based on the technical concept proposed in this invention shall fall within the scope of protection of this invention.

Claims

1. A method for identifying anomalies in the secondary circuit of a transformer differential protection system, characterized in that... Includes the following steps: Step 1: Obtain the three-phase voltage and three-phase current on each side of the transformer; Step 2: By calculating the differential current of the transformer differential protection and the changes in the three-phase current of each CT involved in the transformer differential protection, determine the operating status of the transformer. If the operating status of the transformer changes, wait; otherwise, proceed to step 3. Step 3: Determine if the differential current is symmetrical in three phases; if symmetrical, proceed to step 4. Conversely, proceed to step 7; Step 4: Replace the polarity of each CT involved in the transformer differential protection one by one, and recalculate the differential current. If the differential current disappears at this time, it is determined that the polarity of the CT is incorrect. If the differential current does not disappear, continue to change the polarity of the other CTs and recalculate the differential current to determine whether the differential current disappears; if it does not disappear, proceed to step 5. Step 5: Replace the clock count of each CT involved in the transformer differential protection one by one, and recalculate the differential current. If the differential current disappears at this time, it is determined that the clock count of the CT is incorrect. If the differential current does not disappear, continue to change the remaining CT hour numbers and recalculate the differential current to determine if the differential current has disappeared; if it does not disappear, proceed to step 6. Step 6: Calculate the active power flowing into each CT participating in the transformer differential protection and compare it with the set active power. If the two are different, it is determined that the secondary coil of the CT is selected incorrectly. If the two are the same, continue to compare the active power flowing into the other CTs with their set active power. If they are all the same, it is determined that there is another fault. Step 7: Determine the asymmetry of the three-phase current of each CT involved in the transformer differential protection. If the number of asymmetrical CTs exceeds 1, it is determined to be another fault; if the number of asymmetrical CTs is 1, proceed to step 8. Step 8: Determine whether the three-phase current amplitudes of the asymmetrical CT are equal; if the three-phase current amplitudes are equal, it is determined that the phase sequence of the CT is incorrect; if they are not equal, it is determined that the CT is disconnected.

2. The method as described in claim 1, characterized in that: In step 2, the specific method for determining the transformer's operating status by calculating the differential current of the transformer differential protection and the changes in the three-phase current of each CT involved in the transformer differential protection is as follows: Step 21: Record the characteristic values ​​of the differential current of the transformer differential protection and the three-phase current of each CT involved in the transformer differential protection for each calculation cycle; If the differential current is lower than the differential protection current setting value, continue to wait; Conversely, proceed to step 22; Step 22: Compare the differential current characteristic value of the current calculation period t0 with the differential current characteristic value of the previous X calculation periods tx. If it exceeds the set threshold, it is determined that the transformer operating status has changed. Compare the three-phase current characteristic values ​​of each CT participating in the differential protection of the transformer in the current calculation period t0 with the current characteristic values ​​of the previous X calculation periods tx. If they exceed the set threshold, it is determined that the transformer operating status has changed. If none of them exceed the threshold and the duration reaches the set time, it is determined that the transformer operating status has not changed.

3. The method as described in claim 2, characterized in that: In step 21, the differential protection current setting value is set to 0.2 times the rated current of the transformer.

4. The method as described in claim 2, characterized in that: In step 22, the threshold for the change of differential current characteristic value is set to 0.04 times the rated current of the transformer.

5. The method as described in claim 2, characterized in that: In step 22, the threshold for the change of the characteristic value of the three-phase current of the CT is set to 0.04 times the rated value of the CT.

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