Transformer differential protection stability test method

Abstract

The present invention discloses a method for testing the stability of transformer differential protection, including: testing that the differential protection does not malfunction during external transformer faults; testing that the differential protection reliably operates during internal transformer faults; testing that the restricted grounding does not malfunction during external faults; testing that the restricted grounding operates reliably during internal transformer faults; checking and verifying that the transformer's current transformers are correctly wired and polarized; and testing that the transformer's backup protection reliably operates during external transformer faults. The method primarily verifies the stability and sensitivity of the differential protection for medium and high voltage transformers, checking the correctness of the wiring during installation, the correctness of the current transformer's ratio, the polarity of the current transformer, and the configuration and setting of the relay protection, ultimately verifying successful power supply the first time.

Description

Technical Field

[0001] The present invention belongs to the field of safe power transformation, and in particular relates to a test verification method, specifically a transformer differential protection stability test method. Background Art

[0002] Because transformers are fundamental to power conversion and utilization, their use and testing have become a key focus of current power industry work. Transformer stability testing is essential for successful transformer commissioning and a valuable method for verifying transformer protection. For large power transformers with high capacity and voltage levels, the low secondary current during primary current flow can prevent conventional protection devices from recognizing the current, or volt-ampere phase meters from accurately reading the current. Summary of the Invention

[0003] This invention addresses the problems inherent in the prior art by proposing a method for increasing the secondary current during stability testing. This method primarily verifies the stability and sensitivity of the differential protection for medium and high voltage transformers. It checks the correctness of the wiring during installation, the correctness of the current transformer's ratio, the polarity of the current transformer, and the configuration and setting of the relay protection, ultimately verifying successful power delivery.

[0004] Technical solution:

[0005] A transformer differential protection stability test method, comprising:

[0006] When testing the external fault of the transformer, the differential protection does not malfunction.

[0007] Test the reliable operation of transformer internal fault differential protection;

[0008] Test that the restricted earthing does not malfunction in the event of an external fault;

[0009] Test that the restricted earth fault detector can operate reliably when there is a fault inside the transformer;

[0010] Check and verify that the transformer current transformer wiring is correct and the polarity is correct;

[0011] When testing external faults of the transformer, the transformer backup protection device will operate reliably.

[0012] Preferably, testing that the differential protection does not malfunction during an external fault of the transformer specifically includes:

[0013] (1) Check that the wiring of the high and low voltage side current transformers is correct and secure, and that the primary current flow test has been completed; check that only one point of the secondary circuit of the current transformer is grounded; and ensure that the current transformer will not malfunction;

[0014] (2) The final setting of the relay protection device has been set and the unit test has been completed; it is judged that the protection device will not malfunction;

[0015] (3) Check that the excitation curves of the current transformers on the high and low voltage sides have similar inflection points to ensure that the high impedance protection is reliable;

[0016] (4) Use a short-circuit wire to short-circuit the neutral grounding resistance box to increase the measured current value;

[0017] (5) The current transformer coil with high impedance protection function has been short-circuited to ground to prevent false operation;

[0018] (6) The secondary measuring coils in the secondary side coils of the current transformer that are not related to the transformer protection function should be short-circuited and grounded to obtain the accuracy of the test;

[0019] (7) Check that the phase line on the low-voltage side of the transformer has been short-circuited to ground, and the short-circuit point is after the low-voltage side current transformer to obtain reliable test data;

[0020] (8) Isolate the differential protection connection; ensure that the differential protection trip output does not operate when the circuit breaker trips, ensure the continuity and reliability of the test circuit power supply, and read the differential current and braking current values;

[0021] (9) Before the stability test, check that the voltage and phase sequence of the test power supply are correct to ensure that the simulated real power receiving operation state and phase angle are correct;

[0022] (10) Stability test: The bus outside the current transformer area on the low-voltage side of the transformer has been short-circuited and grounded; first, the transformer backup protection and the transformer neutral point restricted ground fault protection are withdrawn, and a 400VAC three-phase test power supply is connected to the high-voltage side of the transformer. The current value of the lead wire of the secondary side protection coil of the current transformer of each phase on the high and low voltage sides is measured. The measurement result is compared with the calculation result. It should be within the allowable error range. At this time, the transformer differential protection does not operate.

[0023] Preferably, testing the reliable operation of the transformer internal fault differential protection specifically includes:

[0024] Sensitivity test: After power failure, first short-circuit and ground the bus outside the current transformer area on the low-voltage side of the transformer; swap the polarity of one phase of the lead-out line of the secondary side of the current transformer on either the high-voltage or low-voltage side; connect the test power again and measure the current on the high- and low-voltage sides. If the differential current is greater than the set value, the trip indicator LED of the relay protection device should light up and indicate a tripping action; after the test is completed, restore the current transformer polarity wiring; this step verifies that the current transformer polarity error causes the transformer fault to be within the area and the differential protection to operate reliably.

[0025] Preferably, testing the reliable operation of the transformer internal fault differential protection specifically includes:

[0026] Sensitivity test: Create a fault point inside the current transformer area on the low-voltage side of the transformer: a phase on the low-voltage side of the transformer is grounded; reconnect the test power supply and measure the current on the high- and low-voltage sides. If the differential current is greater than the set value, the relay protection device should have a trip indicator LED on and a trip action indication; at this time, there is an obvious fault point inside the transformer differential protection area. This step verifies the transformer differential protection sensitivity and reliable operation.

[0027] Preferably, testing that the restrictive grounding does not malfunction during an external fault specifically includes:

[0028] Stability test of the neutral point restricted grounding protection: Exit the transformer differential protection. Short-circuit and ground each phase outside the current transformer area on the low-voltage side of the transformer according to the wiring schematic diagram. Apply a single-phase test power supply to the high-voltage side of the transformer. Measure the secondary current of the transformer's low-voltage side current transformer and the secondary current of the neutral point current transformer. At this point, the differential current is 0, and the restricted grounding differential protection does not operate. Perform the same test on the other two phases.

[0029] If the above test protection operates and the current transformer is not saturated, the current transformer polarity, ratio, and wiring are correct. This step tests the stability of the transformer neutral point restricted ground fault protection when the fault is outside the fault zone, the differential current of the transformer current transformer and the neutral point ground current transformer is zero, the polarity is correct, and the protection will not malfunction. At this time, the backup protection device should indicate ground overcurrent protection operation instead of restricted ground differential protection operation.

[0030] Preferably, testing whether the restricted grounding can reliably operate when there is an internal fault in the transformer specifically includes:

[0031] Neutral point differential protection sensitivity test: Short-circuit and ground each phase outside the current transformer on the low-voltage side of the transformer; first, exit the transformer differential protection and activate the neutral point restricted grounding differential protection. Since this protection is a high-impedance protection, tripping and non-tripping tests should be performed to prevent burning of the protection device. The current transformer secondary lead-out line current should be measured quickly after the test power is closed; isolate the restricted grounding protection tripping outlet and repeat the above steps to cross-short-circuit the two secondary lines of the current transformer on the low-voltage side, and the neutral point current transformer secondary wiring remains unchanged; measure the current transformer secondary side current. If the differential current is greater than the protection setting, the protection device displays the restricted grounding differential protection action, restore the isolation connection, and the circuit breaker trips. Similarly, test the other two phases; this verifies the correct polarity of the current transformer and the sensitivity of the neutral point restricted grounding protection differential action, ensuring that the protection can operate reliably when a fault occurs during operation.

[0032] Preferably, testing whether the restricted grounding can reliably operate when there is an internal fault in the transformer specifically includes:

[0033] Neutral point differential protection sensitivity test: With the transformer differential protection turned off, the restricted earth fault protection is turned on, and the fault point is created inside the current transformer area on the secondary side of the transformer; at this time, the test power is turned on again, and the current on the high and low voltage sides is measured. If the differential current is greater than the set value, the trip indicator LED of the relay protection device should light up, and there should be an indication of circuit breaker tripping; at this time, there is an obvious fault point inside the transformer differential protection area. This step verifies the reliable operation of the sensitivity of the transformer restricted earth differential protection.

[0034] Preferably, when testing the external fault of the transformer, the reliable action of the transformer backup protection specifically includes:

[0035] Perform transformer neutral point overcurrent protection test, and ground the secondary side of the current transformer of a phase on the low-voltage side in the test wiring; when the fault point is outside the differential protection area, the transformer differential protection and restricted ground differential protection will not operate, and the ground overcurrent protection of the transformer rear protection device will operate; this is used to judge the stability of the transformer differential protection. When the fault is outside the differential protection area, other transformer protection devices will operate reliably.

[0036] Beneficial effects of the present invention

[0037] The present invention verifies the stability of the transformer differential protection to ensure successful power supply at one time. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 The wiring diagram of the transformer body stability test in the embodiment

[0039] Figure 2 This is the wiring diagram for transformer body sensitivity test in the embodiment

[0040] Figure 3 This is the stability test wiring diagram of the neutral point grounding differential protection test in the embodiment.

[0041] Figure 4 This is the wiring diagram for the neutral point differential protection sensitivity test in the embodiment.

[0042] Figure 5 This is the transformer neutral point overcurrent protection test in the embodiment DETAILED DESCRIPTION

[0043] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto:

[0044] Before using this method, make sure that:

[0045] 1 Anyone in the test area must comply with HSSE management regulations.

[0046] 2 Before starting the transformer stability test and sensitivity test, all electrical equipment unit tests should have been completed and passed the acceptance test.

[0047] Based on the above, the transformer stability test mainly verifies the following issues:

[0048] 1. The differential protection of each transformer has been reliably configured and wired correctly.

[0049] 2. The polarity of each current transformer is correct, the secondary transformation ratio of the current transformer is correct, and the final setting of the protection is set correctly.

[0050] 3. The differential protection device of each transformer is configured correctly.

[0051] 4. The differential protection devices of all transformers can be put into operation safely.

[0052] 5. The transformer's differential protection logic functions correctly and operates stably in normal conditions without any faults or malfunctions.

[0053] The following examples illustrate this application method:

[0054] 1. Check that the wiring of the current transformers on the high and low voltage sides is correct and firm, and that the primary current flow test of the current transformer has been completed.

[0055] 2. Check and confirm that only one point of the current transformer secondary circuit is grounded. Figure 1 shown.

[0056] 3. The final setting of the relay protection device has been set and the unit test has been completed.

[0057] 4. Check that the excitation curves of the high and low voltage current transformers have similar inflection points to ensure the high impedance protection function is reliable. Use a short-circuit wire to short-circuit the resistor of the neutral grounding resistor cabinet to increase the measured current value.

[0058] 5. Before the transformer primary side power-on test, the current transformer coil with high impedance protection function has been short-circuited to ground (such as the current transformer with restricted ground fault protection) to prevent false operation.

[0059] 6. Other secondary sides of the current transformer that are not related to the transformer protection function should be short-circuited and grounded.

[0060] 7. Check that the phase line on the low-voltage side of the transformer has been short-circuited to ground, and the short-circuit point is after the low-voltage side current transformer.

[0061] 8. Isolate the differential protection outlet pressure plate.

[0062] 9. Before testing, check that the voltage and phase sequence of the test power supply are correct.

[0063] 10. Connect the test power supply to the high voltage side of the transformer and measure the high and low voltage current values. Compare the measured results with the calculated results and they should be within the allowable error range. The phase angles of the currents on the high and low voltage sides should be the same as the phase angles of the transformer groups.

[0064] 11. Stability Test: Before the test, disable the transformer restricted ground fault differential protection and enable the transformer differential protection. Measure the secondary currents of the high and low voltage current transformers and read the differential current and restraining current from the differential protection device. If the differential protection does not operate and the differential current is zero, the operating fault point is outside the protection zone.

[0065] Test wiring as Figure 1 :

[0066] 12. Sensitivity test: Exit the transformer neutral point grounding differential protection at this time.

[0067] (1) After power is turned off, swap the polarity of the secondary side of the current transformer on either side of the high and low voltage. Repeat step 11 and test again, measuring the high and low voltage currents. If the differential current is greater than the set value, the relay protection should trip and the differential protection should operate.

[0068] (2) Method 2 can create a ground fault point within the differential protection area, which can also prove the sensitivity of the differential protection.

[0069] Test wiring as Figure 2 :

[0070] 13. Restore the secondary polarity of the current transformer or change the grounding point and continue testing other phases.

[0071] 14. Stability test of the neutral ground differential protection. Before testing, disable the transformer differential protection and activate the restricted ground fault differential protection device. Remove the ground shorting wire on the secondary side of the high-impedance current transformer in step 5. Apply a single-phase power supply to the high-voltage side of the transformer, measure the phase current on the secondary side of the transformer's low-voltage side current transformer, and the current on the secondary side of the neutral point current transformer. Read the differential current and braking current from the restricted ground fault protection device. At this point, the differential current is 0, and the differential protection does not operate. Perform the same test on the other two phases. If the protection operates in the above test, check that the current transformer is not saturated and that the current transformer polarity, ratio, and wiring are correct.

[0072] Stability test wiring Figure 3 :

[0073] 15. Neutral point differential protection sensitivity test. Neutral point restricted ground differential protection is a high-impedance protection and should be tested for both tripping and non-tripping. Repeat step 14 to cross-circuit the two secondary wires of the low-voltage current transformer, leaving the neutral point current transformer secondary wiring unchanged. Measure the current transformer secondary current. If the differential current is greater than the protection setting (the differential current value at this point is the sum of the measured currents), the differential protection is activated. Repeat the same test for the other two phases.

[0074] Test wiring diagram as follows Figure 4 :

[0075] 16. Alternatively, the fault point in the low-voltage side current transformer area can be directly grounded to measure the differential current.

[0076] The test wiring can also be used as follows Figure 2 As shown:

[0077] 17. After the test, restore the differential trip connection and the secondary connections of other current transformers.

[0078] 18. At the same time, the transformer neutral point overcurrent protection test can be carried out. If the fault point is outside the differential protection area, the differential protection will not operate, but the neutral point overcurrent protection will operate.

[0079] Test wiring as Figure 5 As shown:

[0080] 19. Test Calculation Example (1. When the actual results measured in the experiment are the same as the calculated results, or are within the allowable error range, the current transformer ratio and polarity configuration of the transformer differential protection are correct. Verify that the current transformer can operate stably and reliably in actual operation to prevent malfunction of the differential protection. 2. By calculating the current value, prove that the selection of the test power supply is reasonable, safe and reliable):

[0081] During the test, the current transformer secondary lead current meter was Fluke 80i-110s AC and DC current clamp and Fluke multimeter.

[0082] Jiangsu Huapeng Transformer Co., Ltd.

[0083]

[0084] Primary side test voltage: 400V

[0085] 35.0KV differential current transformer ratio: 600:1

[0086] 10.5KV differential current transformer ratio: 4000:1

[0087] 10.5KV zero-sequence current transformer ratio: 150:1

[0088] Rated capacity: 16MVA High voltage side voltage: 35.0KV

[0089] High voltage side rated current: 256.6A Low voltage side voltage: 10.5KV

[0090] Low voltage side rated current: 879.8A Transformer impedance: 8%

[0091] High-voltage side test gear voltage: 35.0KV High-voltage side test gear current: 256.6A

[0092] Test voltage x current value of the high-voltage side gear

[0093] Calculate the primary current on the high-voltage side = transformer impedance x voltage value of the high-voltage side gear

[0094] 400V x 256.6A

[0095] =8% x 35000V

[0096] =36.66A

[0097] 36.66x1

[0098] Calculated high voltage side secondary current = 600

[0099] =0.0611A

[0100] The high-voltage side current value calculated by the voltage value x of the high-voltage side gear

[0101] Calculate the primary current on the low-voltage side = the voltage value of the low-voltage gear position

[0102] 35000V x 36.66A

[0103] =10500V

[0104] =122.2A

[0105] 122.2x1

[0106] Calculate the secondary current on the low voltage side = 4000

[0107] =0.03055A

[0108] The calculation example shows that when the actual results measured in the experiment are the same as the calculated results, or are within the allowable error range, the current transformer ratio and polarity configuration of the transformer differential protection are correct. The current transformer can be verified to work stably and reliably in actual operation to prevent malfunction of the differential protection.

[0109] The specific embodiments described herein are merely illustrative of the spirit of the present invention. Persons skilled in the art may make various modifications, additions, or substitutions to the described specific embodiments without departing from the spirit of the present invention or exceeding the scope of the appended claims.

Claims

1. A transformer differential protection stability test method, comprising: Testing the transformer external fault differential protection does not malfunction. Testing the transformer external fault differential protection does not malfunction specifically includes: (1) Check that the wiring of the high and low voltage side current transformers is correct and secure, and that the primary current flow test has been completed; check that only one point of the secondary circuit of the current transformer is grounded; and ensure that the current transformer will not malfunction; (2) The final setting of the relay protection device has been set and the unit test has been completed; it is judged that the protection device will not malfunction; (3) Check that the excitation curves of the current transformers on the high and low voltage sides have similar inflection points to ensure that the high impedance protection is reliable; (4) Use a short-circuit wire to short-circuit the neutral grounding resistance box to increase the measured current value; (5) The current transformer coil with high impedance protection function has been short-circuited to ground to prevent false operation; (6) The secondary measuring coils in the secondary side coils of the current transformer that are not related to the transformer protection function should be short-circuited and grounded to obtain the accuracy of the test; (7) Check that the phase line on the low-voltage side of the transformer has been short-circuited to ground, and the short-circuit point is after the low-voltage side current transformer to obtain reliable test data; (8) Isolate the differential protection connection; ensure that the differential protection trip output does not operate when the circuit breaker trips, ensure the continuity and reliability of the test circuit power supply, and read the differential current and braking current values; (9) Before the stability test, check that the voltage and phase sequence of the test power supply are correct to ensure that the simulated real power receiving operation state and phase angle are correct; (10) Stability test: The busbar outside the current transformer area on the low-voltage side of the transformer has been short-circuited and grounded; first, the transformer backup protection and the transformer neutral point restricted ground fault protection are disabled, and a 400VAC three-phase test power supply is connected to the high-voltage side of the transformer. The current value of the lead wire of the secondary side protection coil of the current transformer of each phase on the high and low voltage sides is measured. The measurement result is compared with the calculated result. It should be within the allowable error range. At this time, the transformer differential protection does not operate; Test the reliable operation of differential protection during internal fault of transformer; Test that the restricted earth fault detector does not malfunction when there is a transformer external fault; Test that the restricted earth fault detector can operate reliably when there is a fault inside the transformer; Check and verify that the transformer current transformer wiring is correct and the polarity is correct; When testing external faults of the transformer, the transformer backup protection device will operate reliably.

2. The method according to claim 1, characterized in that Testing the reliable operation of transformer internal fault differential protection specifically includes: Sensitivity test: After power failure, first short-circuit and ground the bus outside the current transformer area on the low-voltage side of the transformer; swap the polarity of one phase of the lead-out line of the secondary side of the current transformer on either the high-voltage or low-voltage side; connect the test power again and measure the current on the high- and low-voltage sides. If the differential current is greater than the set value, the trip indicator LED of the relay protection device should light up and indicate a tripping action; after the test is completed, restore the current transformer polarity wiring; this step verifies that the current transformer polarity error causes the transformer fault to be within the area and the differential protection to operate reliably.

3. The method according to claim 1, characterized in that Testing the reliable operation of transformer internal fault differential protection specifically includes: Sensitivity test: Create a fault point inside the current transformer area on the low-voltage side of the transformer: a phase on the low-voltage side of the transformer is grounded; reconnect the test power supply and measure the current on the high- and low-voltage sides. If the differential current is greater than the set value, the relay protection device should have a trip indicator LED on and a trip action indication; at this time, there is an obvious fault point inside the transformer differential protection area. This step verifies the transformer differential protection sensitivity and reliable operation.

4. The method according to claim 1, characterized in that Testing that the restricted earthing does not malfunction in the event of an external fault specifically includes: Stability test of the neutral point restricted grounding protection: Exit the transformer differential protection. Short-circuit and ground each phase outside the current transformer area on the low-voltage side of the transformer according to the wiring schematic diagram. Apply a single-phase test power supply to the high-voltage side of the transformer. Measure the secondary current of the transformer's low-voltage side current transformer and the secondary current of the neutral point current transformer. At this point, the differential current is 0, and the restricted grounding differential protection does not operate. Perform the same test on the other two phases. If the above test protection is activated and the current transformer is not saturated, the polarity, transformation ratio and wiring of the current transformer are correct; this step tests that when the fault is outside the area, the differential current of the transformer current transformer and the neutral point grounding current transformer is 0, the polarity is correct, the stability of the transformer neutral point restricted grounding protection, and the protection will not malfunction. At this time, the backup protection device should display the grounding overcurrent protection action instead of the restricted grounding differential protection action.

5. The method according to claim 1, characterized in that Testing the reliable operation of restricted earthing in the event of internal transformer faults specifically includes: Neutral point differential protection sensitivity test: Short-circuit and ground each phase outside the current transformer on the low-voltage side of the transformer; first, exit the transformer differential protection and activate the neutral point restricted grounding differential protection. Since this protection is a high-impedance protection, tripping and non-tripping tests should be performed to prevent burning of the protection device. The current transformer secondary lead-out line current should be measured quickly after the test power is closed; isolate the restricted grounding protection tripping outlet and repeat the above steps to cross-short-circuit the two secondary lines of the current transformer on the low-voltage side, and the neutral point current transformer secondary wiring remains unchanged; measure the current transformer secondary side current. If the differential current is greater than the protection setting, the protection device displays the restricted grounding differential protection action, restore the isolation connection, and the circuit breaker trips. Similarly, test the other two phases; this verifies the correct polarity of the current transformer and the sensitivity of the neutral point restricted grounding protection differential action, ensuring that the protection can operate reliably when a fault occurs during operation.

6. The method according to claim 1, characterized in that Testing the reliable operation of restricted earthing in the event of internal transformer faults specifically includes: Neutral point differential protection sensitivity test: With the transformer differential protection turned off, the restricted earth fault protection is turned on, and the fault point is created inside the current transformer area on the secondary side of the transformer; at this time, the test power is turned on again, and the current on the high and low voltage sides is measured. If the differential current is greater than the set value, the trip indicator LED of the relay protection device should light up, and there should be an indication of circuit breaker tripping; at this time, there is an obvious fault point inside the transformer differential protection area. This step verifies the reliable operation of the sensitivity of the transformer restricted earth differential protection.

7. The method according to claim 1, characterized in that When testing transformer external faults, the reliable actions of the transformer backup protection include: Conduct transformer neutral point overcurrent protection test, test wiring to ground the secondary side of the current transformer of a phase on the low-voltage side; when the fault point is outside the differential protection area, the transformer differential protection and restricted ground differential protection do not operate, and the ground overcurrent protection of the transformer rear protection device operates; this is used to judge the stability of the transformer differential protection. When the fault is outside the differential protection area, other transformer protection devices can operate reliably.

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