A system and method for checking the polarity of branch differential protection of standby transformer

Abstract

The present invention discloses a system and method for verifying the polarity of the start-up transformer branch differential protection. It proposes to use a generator as a current source, perform short-circuit tests on the high-voltage side and the low-voltage side of the start-up transformer respectively, and use the short-circuit current to verify the polarity of the bus differential protection newly connected to the start-up transformer branch and the polarity of the start-up transformer differential protection, eliminate defects, and ensure the normal operation of differential protection. This method solves the problem that the start-up transformer load current cannot verify the bus differential protection, does not need to organize a large amount of load, does not need to rent a dummy load, and has strong operability. It can ensure that the polarity of the bus differential protection and the start-up transformer differential protection is correct, and prevent the differential protection from malfunctioning.

Description

Technical Field

[0001] The present invention relates to the technical field of electric power testing, and in particular to a system and method for verifying the polarity of a start-up standby transformer branch differential protection. Background Art

[0002] Differential protection is the main protection of the power system. The operation of differential protection is related to whether the fault can be correctly removed in the event of an accident. Differential protection systems often experience misoperation due to careless wiring, inaccurate calibration, and multiple grounding of the secondary circuit. Therefore, polarity verification should be performed before differential protection is put into use. On the one hand, it is to eliminate defects such as wiring errors; on the other hand, it is to check whether the differential protection will misoperate when the load current flows normally through the equipment. Differential protection polarity verification is generally completed through load testing.

[0003] The expansion project of a power plant usually requires the installation of a starter transformer as a starting and backup power source. The starter transformer is usually connected to a 220kV or 500kV busbar. Therefore, the differential protection needs to be verified after the busbar differential protection is connected to the starter transformer branch and before the starter transformer differential protection is put into use. There are two difficulties in the load verification of the starter transformer branch differential protection: First, the load equipment of the power plant is mainly fans and water pumps. It is difficult to organize a large load in the early stage of construction, and it is necessary to rent a dummy load as a load, which is costly; second, the capacity of the starter transformer is limited, usually 30MVA or 50MVA. During normal operation, the load current on the high-voltage side is very small, lower than the unbalanced current of the busbar differential protection, and the pure load current cannot complete the verification of the busbar differential protection.

[0004] Therefore, it is necessary to find a system and method for checking the polarity of the start-up transformer branch differential protection that is easy to operate, accurate and reliable. Summary of the invention

[0005] In order to overcome the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide a system and method for verifying the polarity of the start-up transformer branch differential protection. The method uses a generator as a current source to perform short-circuit tests on the high-voltage side and the low-voltage side of the start-up transformer, respectively, and uses the short-circuit current to verify the polarity of the bus differential protection newly connected to the start-up transformer branch and the start-up transformer differential protection polarity, eliminate defects, and ensure that the bus differential protection and the start-up transformer differential protection operate normally. The method does not need to organize a large amount of load, does not need to rent a dummy load, and is reliable and highly operable.

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

[0007] A system for checking the polarity of a standby transformer branch differential protection includes a high-voltage bus 3, the high-voltage bus 3 is connected to a generator transformer unit 2 and a standby transformer unit 4, the generator transformer unit 2 is connected to a generator excitation unit 1, the standby transformer unit 4 is connected to a standby transformer first branch unit 5 and a standby transformer second branch unit 6, and the standby transformer unit 4, the standby transformer first branch unit 5 and the standby transformer second branch unit 6 are connected to a standby transformer differential protection 8.

[0008] The generator excitation unit 1 comprises an excitation transformer 9 , which is connected to a demagnetization switch 11 via an excitation regulator 10 .

[0009] The generator transformer unit 2 includes a generator 12, which is connected to a main transformer 14 via a generator outlet closed bus 13. The main transformer 14 is connected to a main transformer high-voltage side circuit breaker 16 via a main transformer high-voltage side current transformer 15, and the main transformer high-voltage side circuit breaker 16 is connected to the high-voltage bus 3.

[0010] The standby transformer unit 4 includes a standby transformer high-voltage side circuit breaker 17 connected to the high-voltage bus 3, and the standby transformer high-voltage side circuit breaker 17 is sequentially connected to a standby transformer high-voltage side current transformer 1 18, a standby transformer high-voltage side current transformer 2 19 and a standby transformer high-voltage side grounding switch 27;

[0011] The standby transformer branch unit 5 includes a standby transformer branch short-circuit device 22, which is connected to the standby transformer branch current transformer 21 and the standby transformer branch bus 23 at one time; the standby transformer branch unit 6 includes a standby transformer branch short-circuit device 25, which is connected to the standby transformer branch current transformer 24 and the standby transformer branch bus 26 in sequence.

[0012] The secondary current of the main transformer high-voltage side current transformer 15 and the secondary current of the standby transformer high-voltage side current transformer 18 are sent to the bus differential protection 7 to form the bus differential protection;

[0013] The secondary current of the second current transformer 19 on the high-voltage side of the standby transformer, the secondary current of the first branch current transformer 21 of the standby transformer and the secondary current of the second branch current transformer 24 of the standby transformer are sent to the standby transformer differential protection 8 to form the standby transformer differential protection.

[0014] A method for verifying the polarity of a start-up standby transformer branch differential protection comprises the following steps:

[0015] 1) Carry out preparation work for the polarity check of the standby transformer branch of bus differential protection 7;

[0016] 2) Adjust the output of the generator 12 to ensure that the secondary current of the high-voltage side current transformer 18 of the standby transformer is 1A;

[0017] 3) measuring and recording the main transformer high-voltage side current of the main transformer high-voltage side current transformer 15 and the standby transformer high-voltage side current transformer 18;

[0018] 4) Check whether the differential current of the bus differential protection 7 is zero. If the differential current of the bus differential protection 7 is zero, go to step 6); if the differential current of the bus differential protection 7 is not zero, go to step 5);

[0019] 5) Reduce the current on the high-voltage side of the standby transformer to zero, and check and eliminate CT defects;

[0020] 6) Prepare for the start-up transformer differential protection 8 calibration;

[0021] 7) Adjust the output of the generator 12 to ensure that the secondary current of the high-voltage side current transformer 19 of the standby transformer is the rated current;

[0022] 8) Measure and record the standby transformer high voltage side current of the standby transformer high voltage side current transformer 2 19, the standby transformer first branch current of the standby transformer first branch current transformer 21, and the standby transformer second branch current of the standby transformer second branch current transformer 24;

[0023] 9) Check whether the differential current of the standby transformer differential protection 8 is zero. If the differential current of the standby transformer differential protection 8 is zero, go to step 11); if the differential current of the standby transformer differential protection 8 is not zero, go to step 10);

[0024] 10) lowering the high-voltage side current of the standby transformer high-voltage side current transformer 2 19 to zero, disconnecting the generator demagnetization switch 11, exiting the demagnetization switch 11 control power supply, and disconnecting the power supply of the excitation transformer 9;

[0025] Check whether there is shunting phenomenon in the low-voltage side current of the standby transformer connected to the starter transformer differential protection 8, the first branch unit 5 and the second branch unit 6, whether the selected current transformer ratio is consistent with the design value, and whether the connected current polarity is correct. After confirmation, eliminate the defects.

[0026] 11) The polarity verification test of the standby transformer branch differential protection is completed.

[0027] The specific operation process of step 1) is as follows:

[0028] 101) Check and confirm that the secondary circuit of the current transformer 15 on the high-voltage side of the main transformer and the secondary circuit of the current transformer 18 on the high-voltage side of the standby transformer are correctly wired, the current transformer ratio selection is consistent with the setting list, and there is no open circuit in the secondary circuit;

[0029] 102) Check and confirm that the main transformer high-voltage side circuit breaker 16 and the standby transformer high-voltage side circuit breaker 17 are in the closed state, and the control power supply has been disconnected;

[0030] 103) Check and confirm that the grounding switch 27 on the high-voltage side of the standby transformer, which serves as a short-circuit device, is in a closed state, the grounding switch has good contact, and the three phases A, B, and C form a short-circuit device through the grounding grid;

[0031] 104) Check and confirm that the excitation transformer is energized, close the demagnetization switch 11, adjust the working mode of the excitation regulator 10 to manual state, and start the standby transformer branch to meet the current flow conditions.

[0032] The step 4) comprises the following steps:

[0033] 401) Check whether the main transformer high voltage side current of the main transformer high voltage side current transformer 15 and the standby transformer high voltage side current transformer 18 are consistent with the calculated value;

[0034] 402) reading the main transformer high voltage side current of the main transformer high voltage side current transformer 15 and the standby transformer high voltage side current transformer 18 at the bus differential protection 7, and checking whether they are consistent with the measured values;

[0035] 403) Check whether the differential current of the bus differential protection 7 is zero. If it is zero, it is considered that the starting standby transformer branch current polarity of the starting standby transformer high-voltage side current transformer 18 of the newly connected bus differential protection 7 is correct; if it is not zero, it is considered that the secondary current polarity connected to the starting standby transformer unit 4 is incorrect.

[0036] The step 5) comprises the following steps:

[0037] 501) lowering the high-voltage side current of the standby transformer high-voltage side current transformer 18 to zero, disconnecting the generator demagnetization switch 11, exiting the demagnetization switch 11 control power supply, and disconnecting the power supply of the excitation transformer 9;

[0038] 502) Check whether the current on the high-voltage side of the standby transformer connected to the bus differential protection 7 standby transformer unit 4 is shunted, whether the selected current transformer ratio is consistent with the design value, and whether the connected current polarity is correct. After confirmation, eliminate the defect.

[0039] The step 6) comprises the following steps:

[0040] 601) lowering the high-voltage side current of the standby transformer 18 to zero, disconnecting the generator demagnetization switch 11, exiting the demagnetization switch 11 control power supply, and disconnecting the power supply of the excitation transformer 9;

[0041] 602) Open the standby transformer high voltage side grounding switch 27 separately, and exit its control and power supply;

[0042] 603) Check that the wiring of the first branch current loop of the first branch current transformer 21 and the second branch current loop of the second branch current transformer 24 is correct, the current transformer ratio selection is consistent with the setting list, and there is no open circuit in the secondary circuit;

[0043] 604) Check and confirm that the short-circuit device 22 of the first branch of the standby transformer has been installed and the contact is good. The three phases A, B and C of the first branch of the standby transformer are short-circuited through the short-circuit device; check and confirm that the short-circuit device 25 of the second branch of the standby transformer has been installed and the contact is good. The three phases A, B and C of the second branch of the standby transformer are short-circuited through the short-circuit device;

[0044] 605) The excitation transformer 9 supplies power, closes the demagnetization switch 11, adjusts the working mode of the excitation regulator 10 to the manual state, and starts the low-voltage side branch of the standby transformer to meet the flow conditions.

[0045] The step 9) comprises the following steps:

[0046] 901) Check whether the main transformer high voltage side current of the standby transformer high voltage side current transformer 2 19, the standby transformer first branch current of the standby transformer first branch current transformer 21, and the second branch current of the standby transformer second branch current transformer 24 are consistent with the calculated value;

[0047] 902) reading the standby transformer high voltage side current of the standby transformer high voltage side current transformer 2 19, the standby transformer first branch current transformer 21 and the standby transformer second branch current transformer 24 in the standby transformer differential protection, and checking whether they are consistent with the measured values;

[0048] 903) Check whether the differential current of the standby transformer differential protection 8 is zero. If it is zero, it is considered that the polarity of the standby transformer first branch current of the connected standby transformer first branch current transformer 21 and the second branch current of the standby transformer second branch current transformer 24 are correct; if it is not zero, it is considered that the polarity of the secondary current connected to the standby transformer first branch unit 5 and the standby transformer second branch unit 6 is incorrect.

[0049] Beneficial effects of the present invention:

[0050] The system and method for verifying the polarity of the starting standby transformer branch differential protection described in the present invention adopts a generator as a current source during specific operation, and uses the short-circuit current to verify the polarity of the starting standby transformer branch newly connected to the bus differential protection and the polarity of the starting standby transformer differential protection, thereby eliminating defects and ensuring the normal operation of the differential protection. The magnitude of the short-circuit current is not limited by the magnitude of the starting standby transformer load current. This method solves the problem that the starting standby transformer load current cannot verify the bus differential protection. There is no need to organize a large amount of loads or rent dummy loads, and it is economical and highly operable. This method is applicable to high-voltage busbars with different main wiring methods and to starting standby transformers with different wiring methods. It is easy to promote and use on site, ensuring that the bus differential protection and the starting standby transformer differential protection are accurate and reliable, and preventing misoperation of the differential protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 A circuit diagram of the present invention;

[0052] Figure 2 It is a flow chart of the present invention.

[0053] Among them, 1 is the generator excitation unit, 2 is the generator transformer unit, 3 is the high-voltage bus, 4 is the standby transformer unit, 5 is the standby transformer branch unit 1, 6 is the standby transformer branch unit 2, 7 is the bus differential protection device, 8 is the standby transformer differential protection, 9 is the excitation transformer, 10 is the rectifier cabinet and excitation regulator, 11 is the demagnetization switch, 12 is the generator, 13 is the generator closed bus, 14 is the main transformer, 15 is the high-voltage side current transformer of the main transformer, 16 is the main transformer 1 is the high-voltage side circuit breaker of the standby transformer, 17 is the high-voltage side circuit breaker of the standby transformer, 18 is the current transformer one on the high-voltage side of the standby transformer, 19 is the current transformer two on the high-voltage side of the standby transformer, 20 is the standby transformer, 21 is the first branch current transformer of the standby transformer, 22 is the first branch short-circuit device of the standby transformer, 23 is the first branch busbar of the standby transformer, 24 is the second branch current transformer of the standby transformer, 25 is the second branch short-circuit device of the standby transformer, 26 is the second branch busbar of the standby transformer, and 27 is the grounding switch on the high-voltage side of the standby transformer. DETAILED DESCRIPTION

[0054] The present invention will be further described in detail below in conjunction with the accompanying drawings.

[0055] refer to Figure 1 The system for checking the polarity of the start-up transformer branch differential protection of the present invention comprises a generator excitation unit 1, a generator transformer unit 2, a high-voltage bus 3, a start-up transformer unit 4, a start-up transformer first branch unit 5, a start-up transformer second branch unit 6, a bus differential protection device 7, and a start-up transformer differential protection 8. The generator transformer unit 2 and the start-up transformer unit 4 are connected to the high-voltage bus 3; the generator excitation unit 1 provides excitation current to the generator; the start-up transformer first branch unit 5 and the start-up transformer second branch unit 6 are connected to the low-voltage side of the start-up transformer.

[0056] The generator excitation unit 1 includes: an excitation transformer 9, a rectifier and an excitation regulator 10 and a demagnetization switch 11; the generator transformer unit 2 includes: a generator 12, a generator outlet closed bus 13, a main transformer 14, a main transformer high-voltage side current transformer 15 and a main transformer high-voltage side circuit breaker 16; the standby transformer unit 4 includes: a standby transformer high-voltage side circuit breaker 17, a standby transformer high-voltage side current transformer 1 18, a standby transformer high-voltage side current transformer 2 19, and a standby transformer high-voltage side grounding switch 27; the standby transformer first branch unit 5 includes: a standby transformer first branch short-circuit device 22, a standby transformer first branch current transformer 21, and a standby transformer first branch bus 23; the standby transformer second branch unit 6 includes: a standby transformer second branch short-circuit device 25, a standby transformer second branch current transformer 24, and a standby transformer second branch bus 26.

[0057] The secondary current of the main transformer high-voltage side current transformer 15 and the secondary current of the standby transformer high-voltage side current transformer 18 are sent to the bus differential protection device 7 to form bus differential protection; the secondary current of the standby transformer high-voltage side current transformer 2 19, the secondary current of the standby transformer branch 1 current transformer 21 and the secondary current of the standby transformer branch 2 current transformer 24 are sent to the standby transformer differential protection 8 to form the standby transformer differential protection.

[0058] refer to Figure 2 ,

[0059] A method for verifying the polarity of a start-up standby transformer branch differential protection comprises the following steps:

[0060] 1) Carry out preparation work for the polarity check of the standby transformer branch of bus differential protection 7;

[0061] 2) Adjust the output of the generator 12 to ensure that the secondary current of the high-voltage side current transformer 18 of the standby transformer is 1A;

[0062] 3) measuring and recording the main transformer high-voltage side current of the main transformer high-voltage side current transformer 15 and the standby transformer high-voltage side current transformer 18;

[0063] 4) Check whether the differential current of the bus differential protection 7 is zero. If the differential current of the bus differential protection 7 is zero, go to step 6); if the differential current of the bus differential protection 7 is not zero, go to step 5);

[0064] 5) Reduce the current on the high-voltage side of the standby transformer to zero, and check and eliminate CT defects;

[0065] 6) Prepare for the start-up transformer differential protection 8 calibration;

[0066] 7) Adjust the output of the generator 12 to ensure that the secondary current of the high-voltage side current transformer 19 of the standby transformer is the rated current;

[0067] 8) Measure and record the standby transformer high voltage side current of the standby transformer high voltage side current transformer 2 19, the standby transformer first branch current of the standby transformer first branch current transformer 21, and the standby transformer second branch current of the standby transformer second branch current transformer 24;

[0068] 9) Check whether the differential current of the standby transformer differential protection 8 is zero. If the differential current of the standby transformer differential protection 8 is zero, go to step 11); if the differential current of the standby transformer differential protection 8 is not zero, go to step 10);

[0069] 10) lowering the high-voltage side current of the standby transformer high-voltage side current transformer 2 19 to zero, disconnecting the generator demagnetization switch 11, exiting the demagnetization switch 11 control power supply, and disconnecting the power supply of the excitation transformer 9;

[0070] Check whether there is shunting phenomenon in the low-voltage side current of the standby transformer connected to the starter transformer differential protection 8, the first branch unit 5 and the second branch unit 6, whether the selected current transformer ratio is consistent with the design value, and whether the connected current polarity is correct. After confirmation, eliminate the defects.

[0071] 11) The polarity verification test of the standby transformer branch differential protection is completed.

[0072] The specific operation process of step 1) is as follows:

[0073] 101) Check and confirm that the secondary circuit of the current transformer 15 on the high-voltage side of the main transformer and the secondary circuit of the current transformer 18 on the high-voltage side of the standby transformer are correctly wired, the current transformer ratio selection is consistent with the setting list, and there is no open circuit in the secondary circuit;

[0074] 102) Check and confirm that the main transformer high-voltage side circuit breaker 16 and the standby transformer high-voltage side circuit breaker 17 are in the closed state, and the control power supply has been disconnected;

[0075] 103) Check and confirm that the grounding switch 27 on the high-voltage side of the standby transformer, which serves as a short-circuit device, is in a closed state, the grounding switch has good contact, and the three phases A, B, and C form a short-circuit device through the grounding grid;

[0076] 104) Check and confirm that the excitation transformer is energized, close the demagnetization switch 11, adjust the working mode of the excitation regulator 10 to manual state, and start the standby transformer branch to meet the current flow conditions.

[0077] The step 4) comprises the following steps:

[0078] 401) Check whether the main transformer high voltage side current of the main transformer high voltage side current transformer 15 and the standby transformer high voltage side current transformer 18 are consistent with the calculated value;

[0079] 402) reading the main transformer high voltage side current of the main transformer high voltage side current transformer 15 and the standby transformer high voltage side current transformer 18 at the bus differential protection 7, and checking whether they are consistent with the measured values;

[0080] 403) Check whether the differential current of the bus differential protection 7 is zero. If it is zero, it is considered that the starting standby transformer branch current polarity of the starting standby transformer high-voltage side current transformer 18 of the newly connected bus differential protection 7 is correct; if it is not zero, it is considered that the secondary current polarity connected to the starting standby transformer unit 4 is incorrect.

[0081] The step 5) comprises the following steps:

[0082] 501) lowering the high-voltage side current of the standby transformer high-voltage side current transformer 18 to zero, disconnecting the generator demagnetization switch 11, exiting the demagnetization switch 11 control power supply, and disconnecting the power supply of the excitation transformer 9;

[0083] 502) Check whether the current on the high-voltage side of the standby transformer connected to the bus differential protection 7 standby transformer unit 4 is shunted, whether the selected current transformer ratio is consistent with the design value, and whether the connected current polarity is correct. After confirmation, eliminate the defect.

[0084] The step 6) comprises the following steps:

[0085] 601) lowering the high-voltage side current of the standby transformer 18 to zero, disconnecting the generator demagnetization switch 11, exiting the demagnetization switch 11 control power supply, and disconnecting the power supply of the excitation transformer 9;

[0086] 602) Open the standby transformer high voltage side grounding switch 27 separately, and exit its control and power supply;

[0087] 603) Check that the wiring of the first branch current loop of the first branch current transformer 21 and the second branch current loop of the second branch current transformer 24 is correct, the current transformer ratio selection is consistent with the setting list, and there is no open circuit in the secondary circuit;

[0088] 604) Check and confirm that the short-circuit device 22 of the first branch of the standby transformer has been installed and the contact is good. The three phases A, B and C of the first branch of the standby transformer are short-circuited through the short-circuit device; check and confirm that the short-circuit device 25 of the second branch of the standby transformer has been installed and the contact is good. The three phases A, B and C of the second branch of the standby transformer are short-circuited through the short-circuit device;

[0089] 605) The excitation transformer 9 supplies power, closes the demagnetization switch 11, adjusts the working mode of the excitation regulator 10 to the manual state, and starts the low-voltage side branch of the standby transformer to meet the flow conditions.

[0090] The step 9) comprises the following steps:

[0091] 901) Check whether the main transformer high voltage side current of the standby transformer high voltage side current transformer 2 19, the standby transformer first branch current of the standby transformer first branch current transformer 21, and the second branch current of the standby transformer second branch current transformer 24 are consistent with the calculated value;

[0092] 902) reading the standby transformer high voltage side current of the standby transformer high voltage side current transformer 2 19, the standby transformer first branch current transformer 21 and the standby transformer second branch current transformer 24 in the standby transformer differential protection, and checking whether they are consistent with the measured values;

[0093] 903) Check whether the differential current of the standby transformer differential protection 8 is zero. If it is zero, it is considered that the polarity of the standby transformer first branch current of the connected standby transformer first branch current transformer 21 and the second branch current of the standby transformer second branch current transformer 24 are correct; if it is not zero, it is considered that the polarity of the secondary current connected to the standby transformer first branch unit 5 and the standby transformer second branch unit 6 is incorrect.

[0094] This method uses a generator as a current source to perform short-circuit tests on the high-voltage side and the low-voltage side of the standby transformer, respectively. The short-circuit current is used to verify the polarity of the newly connected standby transformer branch and the polarity of the standby transformer differential protection, thereby eliminating defects and ensuring the normal operation of the differential protection. The magnitude of the short-circuit current is not limited by the magnitude of the standby transformer load current. This method solves the problem that the standby transformer load current cannot verify the bus differential protection. There is no need to organize a large amount of load or rent a dummy load. It is economical and highly operable. This method is applicable to high-voltage buses with different main connection methods and to standby transformers with different connection methods. It is easy to promote and use on site, ensuring that the bus differential protection and the standby transformer differential protection are accurate and reliable, and preventing misoperation of the differential protection.

[0095] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for verifying the polarity of a branch differential protection of a standby transformer, characterized in that: The steps include: 1) Carry out preparation work for polarity verification of the standby transformer branch of the bus differential protection device (7); 2) adjusting the output of the generator (12) to ensure that the secondary current of the high-voltage side current transformer 1 (18) of the high-voltage side of the standby transformer is 1A; 3) measuring and recording the main transformer high-voltage side current of the main transformer high-voltage side current transformer (15) and the standby transformer high-voltage side current transformer 1 (18); 4) Check whether the differential current of the bus differential protection device (7) is zero. If the differential current of the bus differential protection device (7) is zero, go to step 6); if the differential current of the bus differential protection device (7) is not zero, go to step 5); 5) Reduce the high-voltage side current of the standby transformer to zero, check and eliminate CT defects; 6) Prepare for the start-up transformer differential protection (8) verification; 7) adjusting the output of the generator (12) to ensure that the secondary current of the high-voltage side of the standby transformer of the second current transformer (19) is the rated current; 8) measuring and recording the standby transformer high voltage side current of the standby transformer high voltage side current transformer 2 (19), the standby transformer first branch current of the standby transformer first branch current transformer (21), and the standby transformer second branch current of the standby transformer second branch current transformer 24; 9) Check whether the differential current of the standby transformer differential protection (8) is zero. If the differential current of the standby transformer differential protection (8) is zero, go to step 11). If the differential current of the standby transformer differential protection (8) is not zero, go to step 10); 10) reducing the high-voltage side current of the second current transformer (19) on the high-voltage side of the standby transformer to zero, turning off the generator demagnetization switch (11), exiting the demagnetization switch (11) control power supply, and disconnecting the power supply of the excitation transformer (9); Check whether the current on the low-voltage side of the standby transformer connected to the starter transformer differential protection (8), the first branch unit of the standby transformer (5), and the second branch unit of the standby transformer (6) is shunted, whether the selected current transformer ratio is consistent with the design value, and whether the connected current polarity is correct. After confirmation, eliminate the defects; 11) The polarity verification test of the start-up and standby transformer branch differential protection is completed; The step 6) comprises the following steps: 601) reducing the high-voltage side current of the standby transformer high-voltage side current transformer 1 (18) to zero, turning off the generator demagnetization switch (11), exiting the demagnetization switch (11) control power supply, and disconnecting the power supply of the excitation transformer (9); 602) Open the standby transformer high voltage side grounding switch (27) separately, and shut down its control and power supply; 603) Check that the wiring of the first branch current loop of the first branch current transformer (21) and the second branch current loop of the second branch current transformer (24) are correct, the current transformer ratio selection is consistent with the setting list, and there is no open circuit in the secondary circuit; 604) Check and confirm that the short-circuit device (22) of the first branch of the standby transformer has been installed and the contact is good. The three phases A, B and C of the first branch of the standby transformer are short-circuited through the short-circuit device; check and confirm that the short-circuit device 25 of the second branch of the standby transformer has been installed and the contact is good. The three phases A, B and C of the second branch of the standby transformer are short-circuited through the short-circuit device; 605) the excitation transformer (9) supplies power, the demagnetization switch (11) is closed, the working mode of the excitation regulator (10) is adjusted to the manual state, and the low-voltage side branch of the standby transformer is ready for current flow; The step 9) comprises the following steps: 901) Check whether the main transformer high voltage side current of the second standby transformer high voltage side current transformer (19), the standby transformer first branch current of the standby transformer first branch current transformer (21), and the second branch current of the standby transformer second branch current transformer (24) are consistent with the calculated value; 902) reading the standby transformer high voltage side current of the standby transformer high voltage side current transformer 2 (19), the standby transformer first branch current of the standby transformer first branch current transformer (21) and the standby transformer second branch current of the standby transformer second branch current transformer 24 in the standby transformer differential protection, and checking whether they are consistent with the measured values; 903) Check whether the differential current of the start-up transformer differential protection (8) is zero. If it is zero, it is considered that the polarity of the start-up transformer first branch current of the connected start-up transformer first branch current transformer (21) and the second branch current of the start-up transformer second branch current transformer (24) is correct; if it is not zero, it is considered that the polarity of the secondary current connected to the start-up transformer first branch unit (5) and the start-up transformer second branch unit (6) is incorrect; The method is implemented by the following system, which comprises a high-voltage busbar (3), the high-voltage busbar (3) is connected to a generator transformer unit (2) and a start-up standby transformer unit (4), the generator transformer unit (2) is connected to a generator excitation unit (1), the start-up standby transformer unit (4) is connected to a start-up standby transformer first branch unit (5) and a start-up standby transformer second branch unit (6), and the start-up standby transformer unit (4), the start-up standby transformer first branch unit (5) and the start-up standby transformer second branch unit (6) are connected to a start-up standby transformer differential protection (8); The generator excitation unit (1) comprises an excitation transformer (9), and the excitation transformer (9) is connected to a demagnetization switch (11) via an excitation regulator (10); The generator transformer unit (2) comprises a generator (12), the generator (12) is connected to a main transformer (14) via a generator outlet closed bus (13), the main transformer (14) is connected to a main transformer high-voltage side circuit breaker (16) via a main transformer high-voltage side current transformer (15), and the main transformer high-voltage side circuit breaker (16) is connected to a high-voltage bus 3; The standby transformer unit (4) comprises a standby transformer high-voltage side circuit breaker (17) connected to the high-voltage busbar (3); the standby transformer high-voltage side circuit breaker (17) is sequentially connected to a standby transformer high-voltage side current transformer 1 (18), a standby transformer high-voltage side current transformer 2 (19) and a standby transformer high-voltage side grounding switch (27); The standby transformer first branch unit (5) comprises a standby transformer first branch short-circuit device (22), which is connected to the standby transformer first branch current transformer (21) and the standby transformer first branch bus (23) at one time; the standby transformer second branch unit (6) comprises a standby transformer second branch short-circuit device (25), which is connected to the standby transformer second branch current transformer (24) and the standby transformer second branch bus (26) in sequence; The secondary current of the main transformer high-voltage side current transformer (15) and the secondary current of the standby transformer high-voltage side current transformer (18) are sent to the bus differential protection device (7) to form bus differential protection; The secondary current of the second current transformer (19) on the high-voltage side of the standby transformer, the secondary current of the first branch current transformer (21) of the standby transformer and the secondary current of the second branch current transformer (24) of the standby transformer are sent to the standby transformer differential protection (8) to form the standby transformer differential protection.

2. A verification method for a system for verifying the polarity of a standby transformer branch differential protection according to claim 1, characterized in that: The specific operation process of step 1) is as follows: 101) Check and confirm that the secondary circuit of the current transformer (15) on the high-voltage side of the main transformer and the secondary circuit of the current transformer (18) on the high-voltage side of the standby transformer are correctly wired, the current transformer ratio selection is consistent with the setting list, and there is no open circuit in the secondary circuit; 102) Check and confirm that the main transformer high-voltage side circuit breaker (16) and the standby transformer high-voltage side circuit breaker (17) are in the closed state, and the control power supply has been disconnected; 103) Check and confirm that the grounding switch (27) on the high-voltage side of the standby transformer, which serves as a short-circuit device, is in a closed state, the grounding switch has good contact, and the three phases A, B, and C form a short-circuit device through the grounding grid; 104) Check and confirm that the excitation transformer is energized, close the demagnetization switch (11), adjust the working mode of the excitation regulator (10) to the manual state, and start the standby transformer branch to meet the current flow conditions.

3. A verification method for a system for verifying the polarity of a standby transformer branch differential protection according to claim 1, characterized in that: The step 4) comprises the following steps: 401) Check whether the main transformer high voltage side current of the main transformer high voltage side current transformer (15), the standby transformer high voltage side current of the standby transformer high voltage side current transformer 1 (18) are consistent with the calculated value; 402) reading the main transformer high-voltage side current of the main transformer high-voltage side current transformer (15) and the standby transformer high-voltage side current transformer 1 (18) at the bus differential protection device (7), and checking whether they are consistent with the measured values; 403) Check whether the differential current of the bus differential protection device (7) is zero. If it is zero, it is considered that the starting standby transformer branch current polarity of the starting standby transformer high voltage side current transformer 1 (18) of the newly connected bus differential protection device (7) is correct; if it is not zero, it is considered that the secondary current polarity connected to the starting standby transformer unit (4) is incorrect.

4. A verification method for a system for verifying the polarity of a standby transformer branch differential protection according to claim 1, characterized in that: The step 5) comprises the following steps: 501) reducing the high-voltage side current of the standby transformer high-voltage side current transformer 1 (18) to zero, turning off the generator demagnetization switch (11), exiting the demagnetization switch (11) control power supply, and disconnecting the power supply of the excitation transformer (9); 502) Check whether the current on the high-voltage side of the standby transformer connected to the standby transformer unit (4) of the bus differential protection device (7) is shunted, whether the selected current transformer ratio is consistent with the design value, and whether the connected current polarity is correct. After confirmation, eliminate the defect.

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