CN111366878A - System and method for verifying differential protection polarity of startup and standby variable branch - Google Patents

Abstract

The invention discloses a system and a method for verifying the polarity of the differential protection of the starting-standby variable branch. It is proposed to use the generator as a current source to conduct short-circuit tests on the high-voltage side and low-voltage side of the startup and standby transformers respectively, and use the short-circuit current to verify the polarity of the newly connected busbar differential protection branch and the differential protection poles of the startup and backup transformers. resistance, eliminate defects, and ensure that the differential protection operates properly. The method solves the problem that the starting and standby variable load current cannot verify the bus differential protection, does not need to organize a large number of loads, does not need to rent dummy loads, and has strong operability. It can ensure the correct polarity of the bus differential protection and the differential protection of the starting-standby variable, and prevent the differential protection from malfunctioning.

Description

A system and method for verifying the polarity of differential protection of starting and standby variable branches

technical field

The invention relates to the technical field of electric power testing, in particular to a system and method for verifying the polarity of a differential protection of a start-up-standby variable branch.

Background technique

The differential protection is the main protection of the power system, and the operation of the differential protection is related to whether the fault can be removed correctly in the event of an accident. In the differential protection system, due to inaccurate wiring, inaccurate calibration, and multi-point grounding of the secondary circuit, protection misoperations occur from time to time. Therefore, the polarity check should be carried out before the differential protection is put into operation. On the one hand, it is to eliminate defects such as wiring errors; Differential protection polarity verification is generally completed through a load test.

The power plant expansion project usually sets the starting and standby transformers as the starting and standby power sources. The starting and standby transformers are usually connected to 220kV or 500kV busbars. Therefore, after the bus differential protection is connected to the starting and standby transformer branches and before the starting and standby transformer differential protection is put into operation, it needs to be calibrated. Check differential protection. There are two difficulties for the load verification of the differential protection of the start-to-standby transformer branch: 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. The cost is relatively high; second, the capacity of the startup and standby transformer is limited, usually 30MVA or 50MVA. During normal operation, the load current on the high-voltage side is very small, which is lower than the unbalanced current of the bus differential protection, and the pure load current cannot complete the calibration of the bus differential protection. test.

Therefore, it is necessary to find a convenient, accurate and reliable system and method for the polarity verification of the differential protection of the starting and standby variable branches.

SUMMARY OF THE INVENTION

In order to overcome the above-mentioned deficiencies of the prior art, the purpose of the present invention is to provide a system and method for verifying the polarity of the differential protection of the starting and standby transformer branches. Conduct short-circuit tests on both sides respectively, and use short-circuit current to verify the polarity of the newly connected start-standby transformer branch and the polarity of the start-standby differential protection of the bus differential protection to eliminate defects and ensure the bus differential protection and the start-standby differential protection. Operating normally. The method does not need to organize a large number of loads, and does not need to rent dummy loads. The method is reliable and has strong operability.

In order to achieve the above object, the technical scheme adopted in the present invention is:

A system for verifying the polarity of differential protection of starting and standby transformer branches, comprising a high-voltage bus 3, the high-voltage bus 3 is connected to a generator transformer unit 2 and a starting and standby transformer unit 4, and the generator transformer unit 2 is connected to a generator excitation unit 1 , the startup-standby-transformation unit 4 is connected to the startup-standby-transformation branch unit 5 and the startup-standby-transformation two branch unit 6; Motion protection 8.

The generator excitation unit 1 includes an excitation transformer 9 , and the excitation transformer 9 is connected with an excitation switch 11 through an excitation regulator 10 .

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

The start-up transformer unit 4 includes a start-up transformer high-voltage side circuit breaker 17 connected to the high-voltage bus 3, and the start-up transformer high-voltage side circuit breaker 17 is sequentially connected to the start-up transformer high-voltage side current transformer 1 18, and the activation and backup transformer high-voltage side current. The transformer 2 19 and the grounding switch 27 on the high voltage side of the start-up transformer;

The start-up change-one branch unit 5 includes a start-up change-one branch short-circuit device 22, and the start-up change-one branch short-circuit device 22 is connected to the start-up change-one branch current transformer 21 and the start-up change-one branch busbar 23 at one time; The unit 6 includes a two-branch short-circuit device 25 of the start-up transformer and two-branch short-circuit device 25, which is connected to the current transformer 24 and the bus-bar 26 of the start-up transformer and the transformer in sequence.

The secondary current of the current transformer 15 on the high voltage side of the main transformer and the secondary current of the current transformer 1 18 on the high voltage side of the start-up transformer are sent to the busbar differential protection 7 to form the busbar differential protection;

The secondary current of the current transformer 2 19 on the high-voltage side of the startup and backup, the secondary current of the current transformer 21 of the first branch of the startup and backup and the secondary current of the current transformer 24 of the second branch of the startup and backup are sent to the differential transformer of the startup and backup. The protection 8 constitutes the differential protection of the start-up variable.

A verification method for verifying the polarity of the differential protection of the starting and standby variable branches, comprising the following steps;

1) Carry out the preparatory work for the polarity check of the busbar differential protection 7-start standby variable branch;

2) Adjust the output of the generator 12 to ensure that the secondary current on the high-voltage side of the high-voltage side of the start-up transformer is 1A;

3) Measure and record the current on the high-voltage side of the main transformer of the high-voltage side current transformer 15 of the main transformer and the current on the high-voltage side of the transformer on the high-voltage side of the backup transformer 18;

4) Check whether the differential current of bus differential protection 7 is zero, if the differential current of bus differential protection 7 is zero, go to step 6), when the differential current of bus differential protection 7 is not zero, go to step 5);

5) Drop the current of the high voltage side of the standby transformer to zero, check and eliminate CT defects;

6) Prepare for the start-up variable differential protection 8 verification;

7) Adjust the output of the generator 12 to ensure that the secondary current on the high-voltage side of the high-voltage side of the start-up changer is rated current;

8) Measure and record the high-voltage side current of the high-voltage side current transformer 219 of the high-voltage side, the current of the high-voltage side current transformer 21 of the high-voltage side current transformer 21 and the current of the two-branch current transformer 24 of the two-branch current transformer 24. Start-up transformer two-branch current;

9) Check whether the differential current of the differential protection 8 is zero, if the differential current of the differential protection 8 is zero, then go to step 11), when the differential current of the differential protection 8 is not zero , then go to step 10);

11) The polarity verification test of the differential protection of the start-up transformer branch is completed.

The concrete operation process of described step 1) is:

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 starting and standby transformers are correctly wired, the selection ratio of the current transformer is consistent with the fixed value list, and the secondary circuit has no open circuit phenomenon ;

102) Check to confirm that the main transformer high-voltage side circuit breaker 16 and the start-up transformer high-voltage side circuit breaker 17 are in the closed state, and the control power supply has been withdrawn;

103) Check and confirm that the grounding switch 27 on the high-voltage side of the start-up transformer as a short-circuit device is in the closed state, the grounding switch is in good contact, and the three-phase A, B, and C phases form a short-circuit device through the grounding grid;

104) Check to confirm that the excitation transformer is charged, close the de-excitation switch 11, adjust the working mode of the excitation regulator 10 to the manual state, and the start-standby sub-branch meets the current-passing condition.

Described step 4) comprises the following steps:

401) Check whether the current on the high-voltage side of the main transformer of the high-voltage side current transformer 15 of the main transformer and the current on the high-voltage side of the transformer on the high-voltage side of the backup transformer 18 are consistent with the calculated value;

402) Read the high-voltage side current of the main transformer of the current transformer 15 on the high-voltage side of the main transformer and the current transformer of the high-voltage side of the backup transformer 18 in the bus differential protection 7, and check whether it is consistent with the measured value. ;

403) Check whether the differential current of bus differential protection 7 is zero, and if it is zero, then it is considered that the current polarity of the starting and standby transformer branch current transformer-18 of the newly connected bus differential protection 7 is correct; If it is not zero, it is considered that the polarity of the secondary current connected to the start-up-standby-transformer unit 4 is incorrect.

Described step 5) comprises the following steps:

501) Drop the current transformer on the high-voltage side of the high-voltage side current transformer-18 to zero, divide the generator de-excitation switch 11, exit the de-excitation switch 11 to control the power supply, and disconnect the excitation transformer 9 power supply;

502) Check whether the current transformer on the high-voltage side of the high-voltage side of the high-voltage side of the high-voltage side of the high-voltage side of the high-voltage side of the standby-to-standby transformer-18 connected to the differential protection 7 of the busbar differential protection 7 is sufficient to have a shunt phenomenon, and whether the transformation ratio of the selected current transformer and the design value are If it is consistent, check whether the polarity of the connected current is correct. After confirmation, eliminate the defect.

Described step 6) comprises the following steps:

601) Drop the current transformer on the high-voltage side of the high-voltage side of the start-up and standby-change to zero, divide the generator de-excitation switch 11, exit the control power supply of the de-excitation switch 11, and disconnect the power supply of the excitation transformer 9;

602) Separately open the grounding switch 27 on the high voltage side of the standby transformer, and exit its control and power supply;

603) Check that the current loop of the current transformer 21, the current loop of the current transformer 21, the current loop of the current transformer 24, and the current loop of the current transformer 24 are accurate, and the current transformer transformation ratio selection and setting value Single consistent, no open circuit phenomenon in the secondary circuit;

604) Check and confirm that the short-circuit device 22 of the first branch of the start-up changer has been installed, and the contact is good, and the three-phase A, B, and C of the start-up changer branch are short-circuited through the short-circuit device; Check to confirm that the installation of the start-up changer two-branch short-circuit device 25 has been completed. , the contact is good, and the two branches A, B, and C of the start-up transformer are short-circuited through the short-circuit device;

605) The excitation transformer 9 is powered on, the de-excitation 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 startup and standby transformers has the current condition.

Described step 9) comprises the following steps:

901) Check the high-voltage side current of the main transformer of the high-voltage side current transformer 219, the current of the first-branch current of the current transformer 21 of the backup transformer 21, and the current of the second branch of the current transformer 24 of the backup transformer 24 Whether it is consistent with the calculated value;

902) In the differential protection of the start-up change, read the start-up change high-voltage side current of the high-voltage side current transformer 2 19 of the start-up change, the start-up change of a branch current transformer 21 and the start-up change of the first branch current and the start-up change of the second branch The current transformer 24 is turned on to change the two-branch current, and check whether it is consistent with the measured value;

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 start-up transformer-first-branch current transformer 21 and the start-up transformer-two-branch current transformers connected to the transformer 21 The polarity of the two-branch current of 24 is correct; if it is not zero, it is considered that the polarity of the secondary current connected to the first branch unit 5 and the second branch unit 6 of the start-up transformer is incorrect.

Described step 10) comprises the following steps:

1001) drop the current transformer on the high-voltage side of the high-voltage side current transformer two 19 to zero, divide the generator de-excitation switch 11, exit the control power supply of the de-excitation switch 11, and disconnect the excitation transformer 9 power supply;

1002) Check the differential protection of the start-up transformer 8, the first-branch unit 5 of the start-up transformer, and the low-voltage side current of the start-up transformer connected to the second-branch unit 6 of the start-up transformer is enough to have a shunting phenomenon, and the selected current transformer transformation ratio and design If the value is consistent, check whether the polarity of the connected current is correct. After confirmation, eliminate the defect.

Beneficial effects of the present invention:

The system and method of the present invention for verifying the polarity of the differential protection of the starting-standby sub-branch, in the specific operation, adopts the generator as the current source, and uses the short-circuit current to verify the differential protection of the busbar newly connected to the active-standby sub-branch. Polarity and start-up variable differential protection polarity to eliminate defects and ensure normal operation of differential protection. The size of the short-circuit current is not limited by the magnitude of the load current of the start-up/standby variable load. This method solves the problem that the start-up/standby variable load current cannot verify the differential protection of the busbar. There is no need to organize a large number of loads, and there is no need to rent dummy loads. It is economical and operable. Strong sex. This method is suitable for high-voltage busbars with different main wiring methods, and is suitable for starting and standby transformers with different wiring modes, which is convenient for popularization and application on site, ensures accurate and reliable differential protection of busbars and starting-standby transformers, and prevents misoperation of differential protection.

Description of drawings

1 is a circuit diagram of the present invention;

Figure 2 is a flow chart of the present invention.

Among them, 1 is the generator excitation unit, 2 is the generator transformer unit, 3 is the high-voltage bus, 4 is the starting and standby transformer unit, 5 is the starting and standby transformer branch unit, 6 is the starting and standby transformer two-branch unit, and 7 is the bus differential Protection device, 8 is the start-up variable differential protection, 9 is the excitation transformer, 10 is the rectifier cabinet and excitation regulator, 11 is the de-excitation switch, 12 is the generator, 13 is the generator closed bus, 14 is the main transformer, 15 Main transformer high-voltage side current transformer, 16 main transformer high-voltage side circuit breaker, 17 is the high-voltage side circuit breaker of the starting and standby transformers, 18, the starting and standby transformer high-voltage side current transformers 1, 19, the starting and standby transformer high-voltage side current transformers 2. 20 is the start-up transformer, 21 is the current transformer of the start-up change, 22 is the start-up change-a branch short circuit device, 23 is the start-up change-a branch bus, 24 is the start-up change two-branch current transformer, 25 It is the short-circuit device of the two branches of the starting and standby transformers, 26 is the busbar of the starting and standby transformers, and 27 is the grounding switch on the high-voltage side of the starting and standby transformers.

Detailed ways

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

Referring to FIG. 1, a system of the present invention for verifying the polarity of the differential protection of the starting and standby transformer branches includes a generator excitation unit 1, a generator transformer unit 2, a high-voltage bus 3, a starting and standby transformer unit 4, and a starting and standby transformer branch unit. 5. The second branch unit 6 of the startup and standby transformer, the busbar differential protection device 7, and the differential protection 8 of the startup and backup transformer. 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; side.

The generator excitation unit 1 includes: an excitation transformer 9, a rectifier device, an excitation regulator 10 and a de-excitation switch 11; the generator transformer unit 2 includes: a generator 12, a generator outlet closed bus 13, a main transformer 14, a main transformer The high-voltage side current transformer 15 and the main transformer high-voltage side circuit breaker 16; the activation and standby transformer unit 4 includes: activation and backup transformer high-voltage side circuit breaker 17, activation and backup transformer high-voltage side current transformer 1 18, activation and backup transformer high-voltage side current transformer 219. The grounding switch 27 on the high voltage side of the start-up transformer; the start-up transformer-a branch unit 5 includes: a start-up transformer-a branch short-circuit device 22, a start-up transformer-a branch current transformer 21, and a start-up transformer-a branch bus 23; The two-branch unit 6 of the standby-transformer includes: a short-circuit device 25 for the two-branch of the standby-transformation, a current transformer 24 for the two-branch of the standby-transformation, and a bus 26 for the two-branch of the standby-transformation.

The secondary current of the current transformer 15 on the high-voltage side of the main transformer and the secondary current of the current transformer 18 on the high-voltage side of the standby transformer are sent to the busbar differential protection device 7 to form the differential protection of the busbar; The secondary current of 19, the secondary current of the first-branch current transformer 21 and the secondary current of the second-branch current transformer 24 of the starting-standby are sent to the differential protection 8 of the starting-standby to constitute the starting-standby differential protection.

Referring to Figure 2,

A verification method for verifying the polarity of the differential protection of the starting and standby variable branches, comprising the following steps;

1) Carry out the preparatory work for the polarity check of the busbar differential protection 7-start standby variable branch;

2) Adjust the output of the generator 12 to ensure that the secondary current on the high-voltage side of the high-voltage side of the start-up transformer is 1A;

3) Measure and record the current on the high-voltage side of the main transformer of the high-voltage side current transformer 15 of the main transformer and the current on the high-voltage side of the transformer on the high-voltage side of the backup transformer 18;

4) Check whether the differential current of bus differential protection 7 is zero, if the differential current of bus differential protection 7 is zero, go to step 6), when the differential current of bus differential protection 7 is not zero, go to step 5);

5) Drop the current of the high voltage side of the standby transformer to zero, check and eliminate CT defects;

6) Prepare for the start-up variable differential protection 8 verification;

7) Adjust the output of the generator 12 to ensure that the secondary current on the high-voltage side of the high-voltage side of the start-up changer is rated current;

8) Measure and record the high-voltage side current of the high-voltage side current transformer 219 of the high-voltage side, the current of the high-voltage side current transformer 21 of the high-voltage side current transformer 21 and the current of the two-branch current transformer 24 of the two-branch current transformer 24. Start-up transformer two-branch current;

9) Check whether the differential current of the differential protection 8 is zero, if the differential current of the differential protection 8 is zero, then go to step 11), when the differential current of the differential protection 8 is not zero , then go to step 10);

11) The polarity verification test of the differential protection of the start-up transformer branch is completed.

The concrete operation process of described step 1) is:

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 starting and standby transformers are correctly wired, the selection ratio of the current transformer is consistent with the fixed value list, and the secondary circuit has no open circuit phenomenon ;

102) Check to confirm that the main transformer high-voltage side circuit breaker 16 and the start-up transformer high-voltage side circuit breaker 17 are in the closed state, and the control power supply has been withdrawn;

103) Check and confirm that the grounding switch 27 on the high-voltage side of the start-up transformer as a short-circuit device is in the closed state, the grounding switch is in good contact, and the three-phase A, B, and C phases form a short-circuit device through the grounding grid;

104) Check to confirm that the excitation transformer is charged, close the de-excitation switch 11, adjust the working mode of the excitation regulator 10 to the manual state, and the start-standby sub-branch meets the current-passing condition.

Described step 4) comprises the following steps:

401) Check whether the current on the high-voltage side of the main transformer of the high-voltage side current transformer 15 of the main transformer and the current on the high-voltage side of the transformer on the high-voltage side of the backup transformer 18 are consistent with the calculated value;

402) Read the high-voltage side current of the main transformer of the current transformer 15 on the high-voltage side of the main transformer and the current transformer of the high-voltage side of the backup transformer 18 in the bus differential protection 7, and check whether it is consistent with the measured value. ;

403) Check whether the differential current of bus differential protection 7 is zero, and if it is zero, then it is considered that the current polarity of the starting and standby transformer branch current transformer-18 of the newly connected bus differential protection 7 is correct; If it is not zero, it is considered that the polarity of the secondary current connected to the start-up-standby-transformer unit 4 is incorrect.

Described step 5) comprises the following steps:

501) Drop the current transformer on the high-voltage side of the high-voltage side current transformer-18 to zero, divide the generator de-excitation switch 11, exit the de-excitation switch 11 to control the power supply, and disconnect the excitation transformer 9 power supply;

502) Check whether the current transformer on the high-voltage side of the high-voltage side of the high-voltage side of the high-voltage side of the high-voltage side of the high-voltage side of the standby-to-standby transformer-18 connected to the differential protection 7 of the busbar differential protection 7 is sufficient to have a shunt phenomenon, and whether the transformation ratio of the selected current transformer and the design value are If it is consistent, check whether the polarity of the connected current is correct. After confirmation, eliminate the defect.

Described step 6) comprises the following steps:

601) Drop the current transformer on the high-voltage side of the high-voltage side of the start-up and standby-change to zero, divide the generator de-excitation switch 11, exit the control power supply of the de-excitation switch 11, and disconnect the power supply of the excitation transformer 9;

602) Separately open the grounding switch 27 on the high voltage side of the standby transformer, and exit its control and power supply;

603) Check that the current loop of the current transformer 21, the current loop of the current transformer 21, the current loop of the current transformer 24, and the current loop of the current transformer 24 are accurate, and the current transformer transformation ratio selection and setting value Single consistent, no open circuit phenomenon in the secondary circuit;

604) Check and confirm that the short-circuit device 22 of the first branch of the start-up changer has been installed, and the contact is good, and the three-phase A, B, and C of the start-up changer branch are short-circuited through the short-circuit device; Check to confirm that the installation of the start-up changer two-branch short-circuit device 25 has been completed. , the contact is good, and the two branches A, B, and C of the start-up transformer are short-circuited through the short-circuit device;

605) The excitation transformer 9 is powered on, the de-excitation 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 startup and standby transformers has the current condition.

Described step 9) comprises the following steps:

901) Check the high-voltage side current of the main transformer of the high-voltage side current transformer 219, the current of the first-branch current of the current transformer 21 of the backup transformer 21, and the current of the second branch of the current transformer 24 of the backup transformer 24 Whether it is consistent with the calculated value;

902) In the differential protection of the start-up change, read the start-up change high-voltage side current of the high-voltage side current transformer 2 19 of the start-up change, the start-up change of a branch current transformer 21 and the start-up change of the first branch current and the start-up change of the second branch The current transformer 24 is turned on to change the two-branch current, and check whether it is consistent with the measured value;

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 start-up transformer-first-branch current transformer 21 and the start-up transformer-two-branch current transformers connected to the transformer 21 The polarity of the two-branch current of 24 is correct; if it is not zero, it is considered that the polarity of the secondary current connected to the first branch unit 5 and the second branch unit 6 of the start-up transformer is incorrect.

Described step 10) comprises the following steps:

1001) drop the current transformer on the high-voltage side of the high-voltage side current transformer two 19 to zero, divide the generator de-excitation switch 11, exit the control power supply of the de-excitation switch 11, and disconnect the excitation transformer 9 power supply;

1002) Check the differential protection of the start-up transformer 8, the first-branch unit 5 of the start-up transformer, and the low-voltage side current of the start-up transformer connected to the second-branch unit 6 of the start-up transformer is enough to have a shunting phenomenon, and the selected current transformer transformation ratio and design If the value is consistent, check whether the polarity of the connected current is correct. After confirmation, eliminate the defect.

This method uses the generator as a current source to conduct short-circuit tests on the high-voltage side and low-voltage side of the startup and standby transformers respectively, and uses the short-circuit current to verify the polarity of the newly connected busbar differential protection branch and the differential protection poles of the startup and backup transformers. resistance, eliminate defects, and ensure that the differential protection operates properly. The size of the short-circuit current is not limited by the magnitude of the load current of the start-up/standby variable load. This method solves the problem that the start-up/standby variable load current cannot verify the differential protection of the busbar. There is no need to organize a large number of loads, and there is no need to rent dummy loads. It is economical and operable. Strong sex. This method is suitable for high-voltage busbars with different main wiring methods, and is suitable for starting and standby transformers with different wiring modes, which is convenient for popularization and application on site, ensures accurate and reliable differential protection of busbars and starting-standby transformers, and prevents misoperation of differential protection.

The above are only preferred embodiments of the present invention and do not limit the present invention. Any simple modifications, changes and equivalent structural changes made to the above embodiments according to the technical essence of the present invention still belong to the technology of the present invention. within the scope of the program.

Claims (10)

1. The system for verifying the startup and standby variable branch differential protection polarity is characterized by comprising a high-voltage bus (3), wherein the high-voltage bus (3) is connected with a generator transformer unit (2) and a startup and standby variable unit (4), a generator excitation unit (1) is connected to the generator transformer unit (2), a startup and standby variable branch unit (5) and a startup and standby variable branch unit (6) are connected to the startup and standby variable unit (4), and the startup and standby variable unit (4), the startup and standby variable branch unit (5) and the startup and standby variable branch unit (6) are connected with a startup and standby variable differential protection unit (8).

2. A system for verifying the polarity of a backup variable differential protection according to claim 1, wherein the generator excitation unit (1) comprises an excitation transformer (9), the excitation transformer (9) is connected to the field switch (11) through an excitation regulator (10);

the generator transformer unit (2) comprises a generator (12), the generator (12) is connected with a main transformer (14) through a generator outlet closed bus (13), the main transformer (14) is connected with a main transformer high-voltage side circuit breaker (16) through a main transformer high-voltage side current transformer (15), and the main transformer high-voltage side circuit breaker (16) is connected with a high-voltage bus (3);

the starting and standby transformer unit (4) comprises a starting and standby transformer high-voltage side circuit breaker (17) connected with the high-voltage bus (3), and the starting and standby transformer high-voltage side circuit breaker (17) is sequentially connected with a starting and standby high-voltage side current transformer I (18), a starting and standby high-voltage side current transformer II (19) and a starting and standby high-voltage side grounding disconnecting link (27).

3. The system for verifying the differential protection polarity of the starting-standby transformer branch according to claim 1, wherein the starting-standby transformer branch unit (5) comprises a starting-standby transformer branch short-circuit device (22), and the starting-standby transformer branch short-circuit device (22) is connected with the starting-standby transformer branch current transformer (21) and the starting-standby transformer branch bus (23) at a time; the starting-standby transformer secondary branch unit (6) comprises a starting-standby transformer secondary branch short-circuit device (25), and the starting-standby transformer secondary branch short-circuit device (25) is sequentially connected with a starting-standby transformer secondary branch current transformer (24) and a starting-standby transformer secondary branch bus (26);

the secondary current of the main transformer high-voltage side current transformer (15) and the secondary current of the standby high-voltage side current transformer I18 are transmitted to the bus differential protection device (7) to form bus differential protection;

and the secondary current of the second starting-standby high-voltage side current transformer (19), the secondary current of the first starting-standby transformer branch current transformer (21) and the secondary current of the first starting-standby transformer branch current transformer (24) are transmitted to the differential protection (8) to form the differential protection.

4. A method for verifying a system for verifying the polarity of a backup variable differential protection according to claim 1, comprising the steps of;

1) carrying out preparation work of starting up the polarity check of the branch of the bus differential protection (7);

2) adjusting the output of the generator (12) to ensure that the secondary current of the starting and standby high-voltage side of the first starting and standby high-voltage side current transformer (18) is 1A;

3) measuring and recording main transformer high-voltage side current of a main transformer high-voltage side current transformer (15) and standby high-voltage side current of a standby high-voltage side current transformer I (18);

4) checking whether the differential flow of the bus differential protection (7) is zero, if the differential flow of the bus differential protection (7) is zero, turning to the step 6), and if the differential flow of the bus differential protection (7) is not zero, turning to the step 5);

5) reducing the standby high-voltage side current to zero, and checking and eliminating CT defects;

6) carrying out check preparation of the starting-up and standby variable differential protection (8);

7) the output of the generator (12) is regulated, and the secondary current of the starting-standby transformer high-voltage side current transformer II (19) is ensured to be rated current;

8) measuring and recording a starting-up transformer high-voltage side current of a starting-up transformer high-voltage side current transformer II (19), a starting-up transformer branch current of a starting-up transformer branch current transformer (21) and a starting-up transformer branch current of a starting-up transformer branch current transformer 24;

9) checking whether the differential flow of the starting-up variable differential protection (8) is zero, if the differential flow of the starting-up variable differential protection (8) is zero, turning to the step 11), and if the differential flow of the starting-up variable differential protection (8) is not zero, turning to the step 10);

11) and (5) starting the variable branch differential protection polarity verification test and ending the test.

5. The method for verifying the differential protection polarity of the startup variable branch according to claim 4, wherein the specific operation process of the step 1) is as follows:

101) checking and confirming that a secondary circuit of a main transformer high-voltage side current transformer (15) and a secondary circuit of a standby high-voltage side current transformer I (18) are accurately wired, the ratio selection of the current transformers is consistent with a fixed value, and the secondary circuit has no open circuit phenomenon;

102) checking and confirming that a main transformer high-voltage side circuit breaker (16) and a standby transformer high-voltage side circuit breaker (17) are in a closing state and a control power supply is withdrawn;

103) checking and confirming that a starting high-voltage side grounding knife switch 27 serving as a short-circuit device is in a closing state, the grounding knife switch is in good contact, and A, B, C three phases pass through a grounding grid to form the short-circuit device;

104) and checking to confirm that the excitation transformer is electrified, closing a de-excitation switch (11), adjusting the working mode of the excitation regulator (10) to be a manual state, and starting the variable branch to have a through-flow condition.

6. A verification method for verifying the polarity of the differential protection of the startup variable branch according to claim 4, wherein said step 4) comprises the steps of:

401) checking whether main transformer high-voltage side current of a main transformer high-voltage side current transformer (15) and standby high-voltage side current of a standby high-voltage side current transformer I18 are consistent with the calculated value;

402) reading main transformer high-voltage side current of a main transformer high-voltage side current transformer (15) and standby high-voltage side current of a standby high-voltage side current transformer I (18) in a bus differential protection (7), and checking whether the current is consistent with a measured value;

403) checking whether the differential current of the bus differential protection (7) is zero, and if the differential current is zero, determining that the polarity of the standby branch current of the standby high-voltage side current transformer I (18) of the newly-accessed bus differential protection (7) is correct; if the polarity of the secondary current switched in by the starting transformer unit (4) is not correct, the polarity of the secondary current is not zero.

7. A verification method for verifying the polarity of the differential protection of the startup variable branch according to claim 4, wherein said step 5) comprises the steps of:

501) the standby high-voltage side current of the standby high-voltage side current transformer I (18) is reduced to zero, the motor field-suppression switch (11) is distributed, the field-suppression switch (11) is withdrawn to control the power supply, and the power supply of the excitation transformer (9) is disconnected;

502) the method comprises the steps of checking whether the current on the starting and standby high-voltage side of a first starting and standby high-voltage side current transformer (18) accessed by a starting and standby transformer unit (4) of the bus differential protection (7) is enough to have a shunting phenomenon, checking whether the transformation ratio of the selected current transformer is consistent with a design value, checking whether the polarity of the accessed current is correct, and eliminating defects after confirmation.

8. A method for verifying the polarity of differential protection of a startup variable branch according to claim 4, wherein said step 6) comprises the steps of:

601) the standby high-voltage side current of the standby high-voltage side current transformer I (18) is reduced to zero, the motor field-suppression switch (11) is distributed, the field-suppression switch (11) is withdrawn to control the power supply, and the power supply of the excitation transformer (9) is disconnected;

602) separately opening a standby high-voltage side grounding disconnecting link (27) and quitting the control and power supply thereof;

603) checking that a starting-standby one-branch current loop of a starting-standby one-branch current transformer (21) and a starting-standby two-branch current loop of a starting-standby two-branch current transformer (24) are accurately connected, the ratio selection of the current transformers is consistent with the fixed value list, and a secondary loop has no open circuit phenomenon;

604) checking and confirming that the starting-standby branch A, B, C three-phase short circuit is completed by the short circuit device, the contact is good, and the starting-standby branch A, B, C three-phase short circuit is completed; checking and confirming that the starting-up and standby transformer two-branch short-circuit device 25 is installed and well contacted, and the three phases of the starting-up and standby transformer two-branch A, B, C are short-circuited through the short-circuit device;

605) the excitation transformer (9) is powered on, the de-excitation switch (11) is closed, the working mode of the excitation regulator (10) is adjusted to be in a manual state, and the low-voltage side branch of the start-up device has a through-flow condition.

9. A method for verifying the polarity of differential protection of a startup variable branch according to claim 4, wherein said step 9) comprises the steps of:

901) checking whether main transformer high-voltage side current of a starting-standby transformer high-voltage side current transformer II (19), starting-standby transformer branch current of a starting-standby transformer branch current transformer (21) and branch current of a starting-standby transformer branch current transformer (24) are consistent with a calculated value;

902) reading a starting-up transformer high-voltage side current of a starting-up transformer high-voltage side current transformer II (19), a starting-up transformer branch current transformer (21) and a starting-up transformer branch current of a starting-up transformer branch current transformer 24 in the starting-up transformer differential protection, and checking whether the starting-up transformer high-voltage side current and the starting-up transformer branch current are consistent with a measured value;

903) checking whether the differential current of the starting-standby transformer differential protection (8) is zero, and if the differential current is zero, considering that the polarity of the starting-standby transformer branch current of the connected starting-standby transformer branch current transformer (21) and the polarity of the two branch current of the starting-standby transformer branch current transformer (24) are correct; if the polarity is not zero, the polarity of the secondary current switched in by the starting-up branch unit (5) and the starting-up branch unit (6) is not correct.

10. A method for verifying the polarity of differential protection of a startup variable branch according to claim 4, wherein said step 10) comprises the steps of:

1001) reducing the current of the starting-standby transformer high-voltage side of a second current transformer (19) of the starting-standby transformer high-voltage side to zero, distributing a de-excitation switch (11) of the motor, withdrawing the control power supply of the de-excitation switch (11), and disconnecting the power supply of the excitation transformer 9;

1002) and checking whether the current on the low-voltage side of the start-up and standby transformer accessed by the start-up and standby transformer differential protection (8), the start-up and standby transformer one-branch unit (5) and the start-up and standby transformer two-branch unit (6) is enough to have a shunting phenomenon, checking whether the transformation ratio of the selected current transformer is consistent with a design value, checking whether the polarity of the accessed current is correct, and eliminating defects after confirmation.

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