A generator-transformer group differential protection polarity test system and method

Abstract

The invention discloses a generator-transformer group differential protection polarity test system and method, comprising a primary current meter, a generator protection device, a transformer protection device, a high-resistance grounding unit, a generator unit, a main transformer unit, a booster station main transformer interval unit and a booster station bus; the booster station bus is connected to the high-resistance grounding unit via the booster station main transformer interval unit, the main transformer unit and the generator unit, the transformer protection device is connected to the booster station main transformer interval unit and the generator unit, the generator protection device is connected to the generator unit, and the primary current meter is connected to the high-resistance grounding unit. The system and method can realize the generator-transformer group differential protection polarity test, and have strong versatility, high safety, small prerequisite workload, and do not increase the electrical whole set starting test time.

Description

Technical Field

[0001] The invention belongs to the technical field of power commissioning and power testing, and relates to a generator-transformer group differential protection polarity testing system and method. Background Art

[0002] With the rapid economic development, people's living standards are improving day by day, electricity demand is increasing day by day, and the capacity of newly built generator sets is increasing. Before the newly built unit is connected to the grid for the first time, a vector test is required to test whether the polarity of the generator-transformer differential protection is correct. The conventional method for testing the polarity of the generator-transformer differential protection is to set a short-circuit point at the generator end at the rated speed of the generator rotor, conduct a generator end short-circuit test, test the polarity of the generator differential protection, and judge whether the polarity of the generator differential protection is correct. After the generator end short-circuit test is completed, a short-circuit point is set on the high-voltage side of the main transformer, and a short-circuit test is conducted on the high-voltage side of the main transformer to test the polarity of the main transformer differential protection and judge whether the polarity of the main transformer differential protection is correct. This method can effectively test the polarity of the generator-transformer differential protection, but it needs to be carried out at the rated speed of the generator rotor, and two short-circuit points need to be set at the generator end and the high-voltage side of the main transformer. The initial workload is large, which increases the time of the entire electrical startup test. Therefore, it is of great significance to find a generator-transformer differential protection polarity test system and method. Summary of the invention

[0003] The purpose of the present invention is to overcome the shortcomings of the above-mentioned prior art and provide a generator-transformer group differential protection polarity test system and method, which can realize the generator-transformer group differential protection polarity test, and has strong versatility, high safety, small workload, and does not increase the electrical whole set startup test time.

[0004] To achieve the above-mentioned object, the generator-transformer group differential protection polarity test system of the present invention comprises a primary current meter, a generator protection device, a transformer protection device, a high-resistance grounding unit, a generator unit, a main transformer unit, a booster station main transformer bay unit and a booster station bus;

[0005] The busbar of the booster station is connected to the high-resistance grounding unit through the main transformer bay unit, main transformer unit and generator unit of the booster station, the transformer protection device is connected to the main transformer bay unit and generator unit of the booster station, the generator protection device is connected to the generator unit, and the primary current meter is connected to the high-resistance grounding unit.

[0006] The main transformer bay unit of the booster station includes a main transformer high-voltage side circuit breaker, a main transformer high-voltage side current transformer, a main transformer high-voltage side grounding switch and a main transformer high-voltage side isolation switch;

[0007] The busbar of the booster station is connected to one end of the isolating switch on the high-voltage side of the main transformer. The other end of the isolating switch on the high-voltage side of the main transformer is divided into two paths, one of which is grounded after passing through the grounding switch on the high-voltage side of the main transformer, and the other is connected to the main transformer unit through the circuit breaker on the high-voltage side of the main transformer. The current transformer on the high-voltage side of the main transformer is arranged on the line between the circuit breaker on the high-voltage side of the main transformer and the isolating switch on the high-voltage side of the main transformer, and the current transformer on the high-voltage side of the main transformer is connected to the transformer protection device.

[0008] The main transformer unit includes the main transformer low-voltage side break, the main transformer, the main transformer high-voltage side break, the main transformer high-voltage side closed bus and the second set of test lines. The main transformer bay unit of the booster station is connected to one end of the main transformer high-voltage side closed bus. The other end of the main transformer high-voltage side closed bus is divided into two paths, one of which is connected to the generator unit via the main transformer high-voltage side break, the main transformer and the main transformer low-voltage side break, and the other is connected to the generator unit via the second set of test lines.

[0009] The generator unit includes a generator neutral point closed busbar, a generator neutral point current transformer, a generator neutral point break, a generator, a generator end break, a generator end closed busbar, a generator end first set of current transformers, a generator end second set of current transformers and a first set of test lines;

[0010] One end of the generator end closed bus is connected to the main transformer unit, and the other end of the generator end closed bus is divided into two paths, one of which is connected to the generator neutral point closed bus through the generator end break, the generator and the generator neutral point break, and the other is connected to the generator neutral point closed bus through the first group of test lines. The generator neutral point closed bus is connected to the high-resistance grounding unit;

[0011] The first set of current transformers at the generator end and the second set of current transformers at the generator end are installed on the closed bus at the generator end, the generator neutral point current transformer is installed on the generator neutral point closed bus, the first set of current transformers at the generator end are connected to the transformer protection device, and the generator neutral point current transformer and the second set of current transformers at the generator end are connected to the generator protection device.

[0012] The high-resistance grounding unit includes a grounding transformer, a grounding transformer auxiliary resistor and a grounding switch;

[0013] The generator unit is connected to one end of the grounding switch and the current output terminal of the primary current meter. The other end of the grounding switch is grounded through the primary winding of the grounding transformer. The grounding transformer-subsidiary resistor is connected in series to the secondary winding of the grounding transformer. The grounding terminal of the primary current meter is grounded.

[0014] The method for testing polarity of differential protection of a generator-transformer group of the present invention comprises the following steps:

[0015] 1) Carry out preliminary preparations for the generator-transformer group differential protection polarity test;

[0016] 2) Perform a phase A polarity test and connect the current output terminal of the primary current meter to phase A of the generator neutral point closed busbar;

[0017] 3) Adjust the primary current meter to output 50A primary current;

[0018] 4) Measure and record the secondary current amplitudes of the generator neutral point current transformer, the first set of current transformers at the generator end, the second set of current transformers at the generator end, and the current transformer at the high voltage side of the main transformer when the primary current meter outputs a primary current of 50A;

[0019] 5) Determine whether the secondary current amplitude of the generator neutral point current transformer, the first group of current transformers at the generator end, the second group of current transformers at the generator end, and the current transformer at the high-voltage side of the main transformer is consistent with its theoretical value and whether the polarity is correct. When the secondary current amplitude of the generator neutral point current transformer, the first group of current transformers at the generator end, the second group of current transformers at the generator end, and the current transformer at the high-voltage side of the main transformer is consistent with its theoretical value and the polarity is correct, go to step 6); otherwise, go to step 7);

[0020] 6) Adjust the primary current meter output to 100A primary current, and then go to step 8);

[0021] 7) Adjust the primary current meter output to 0A primary current, turn off the primary current meter, find and eliminate the defect, and then go to step 3);

[0022] 8) Measure and record the secondary current amplitudes of the generator neutral point current transformer, the first set of current transformers at the generator end, the second set of current transformers at the generator end, and the current transformer at the high voltage side of the main transformer when the primary current meter outputs a primary current of 100A;

[0023] 9) Determine whether the secondary current amplitude of the generator neutral point current transformer, the first group of current transformers at the generator end, the second group of current transformers at the generator end, and the current transformer at the high-voltage side of the main transformer is consistent with its theoretical value and whether the polarity is correct. When the secondary current amplitude of the generator neutral point current transformer, the first group of current transformers at the generator end, the second group of current transformers at the generator end, and the current transformer at the high-voltage side of the main transformer is consistent with its theoretical value and the polarity is correct, go to step 10); otherwise, go to step 11);

[0024] 10) The polarity test of phase A of the generator-transformer differential protection is completed, and the process goes to step 12);

[0025] 11) Adjust the primary current meter output to 0A primary current, turn off the primary current meter, find and eliminate the defect, and then go to step 6);

[0026] 12) Perform polarity tests of phase B and phase C of the generator-transformer differential protection in sequence according to steps 2) to 11), and then go to step 13);

[0027] 13) The polarity test of the generator-transformer group differential protection is completed.

[0028] The specific operations of step 1) are:

[0029] 101) The generator neutral point current transformer, the first set of current transformers at the generator end, the second set of current transformers at the generator end and the current transformers at the high voltage side of the main transformer within the scope of the generator-transformer group differential protection polarity test have been installed in place and the individual tests have been completed according to the regulations;

[0030] 102) Complete the installation and commissioning of the secondary secondary circuits of the neutral point current transformers of each generator, the first set of current transformers at the generator end, the second set of current transformers at the generator end, and the current transformers at the high-voltage side of the main transformer, ensuring that the secondary secondary circuits of the neutral point current transformers of the generator, the first set of current transformers at the generator end, the second set of current transformers at the generator end, and the current transformers at the high-voltage side of the main transformer are correctly wired, and the secondary load is balanced in three phases without open circuit;

[0031] 103) The generator protection device and transformer protection device have been installed and the static debugging work has been completed.

[0032] In the process of judging whether the secondary current amplitude of the generator neutral point current transformer, the first set of generator end current transformer, the second set of generator end current transformer and the main transformer high voltage side current transformer is consistent with its theoretical value and whether the polarity is correct, the secondary current theoretical value of the generator neutral point current transformer, the first set of generator end current transformer, the second set of generator end current transformer and the main transformer high voltage side current transformer is equal to the primary current value output by the primary current meter divided by its transformation ratio;

[0033] Use a clamp phase meter to check whether the secondary current values ​​of the generator neutral point current transformer, the first set of current transformers at the generator end, the second set of current transformers at the generator end, and the current transformer at the high voltage side of the main transformer are consistent with their theoretical values;

[0034] Check whether the current sampling values ​​of the generator protection device and transformer protection device are equal to the theoretical values;

[0035] Check whether the differential current of the differential protection of the generator protection device and the transformer protection device is zero.

[0036] The present invention has the following beneficial effects:

[0037] During specific operation, the generator-transformer group differential protection polarity test system and method described in the present invention completes the generator-transformer group differential protection polarity test through a primary current meter before the electrical whole set starting test, and there is no need to perform the generator-transformer group differential protection polarity test again during the electrical whole set starting test. The workload is small and the starting time of the electrical whole set is greatly shortened. At the same time, during the detection process, the generator-transformer group differential protection polarity test is performed to check the secondary side current of the generator neutral point current transformer, the generator end current transformer and the main transformer high-voltage side current transformer, and verify the integrity and accuracy of the current transformer secondary circuit. The system has strong versatility and high safety, is suitable for generator-transformer group differential protection polarity tests of different types of units, and is convenient for on-site promotion and use. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a structural schematic diagram of the present invention;

[0039] Figure 2 It is a flow chart of the present invention.

[0040] Among them, 1 is a primary current meter, 1-1 is a grounding terminal, 1-2 is a current output terminal, 2 is a generator protection device, 3 is a transformer protection device, 4 is a high-resistance grounding unit, 4-1 is a grounding transformer, 4-2 is a grounding transformer auxiliary resistor, 4-3 is a grounding knife switch, 5 is a generator unit, 5-1 is a generator neutral point closed bus, 5-2 is a generator neutral point current transformer, 5-3 is a generator neutral point break, 5-4 is a generator, 5-5 is a generator end break, 5-6 is a generator end closed bus, 5-7 is a generator The first set of current transformers at the machine end, 5-8 is the second set of current transformers at the generator end, 5-9 is the first set of test lines, 6 is the main transformer unit, 6-1 is the main transformer low-voltage side break, 6-2 is the main transformer, 6-3 is the main transformer high-voltage side break, 6-4 is the main transformer high-voltage side closed bus, 6-5 is the second set of test lines, 7 is the main transformer bay unit of the substation, 7-1 is the main transformer high-voltage side circuit breaker, 7-2 is the main transformer high-voltage side current transformer, 7-3 is the main transformer high-voltage side grounding switch, 7-4 is the main transformer high-voltage side isolation switch, and 8 is the substation bus. DETAILED DESCRIPTION

[0041] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0042] refer to Figure 1The generator-transformer group differential protection polarity test system of the present invention comprises a primary current meter 1, a generator protection device 2, a transformer protection device 3, a high-resistance grounding unit 4, a generator unit 5, a main transformer unit 6, a booster station main transformer bay unit 7 and a booster station bus 8; the booster station bus 8 is connected to the high-resistance grounding unit 4 via the booster station main transformer bay unit 7, the main transformer unit 6 and the generator unit 5, the transformer protection device 3 is connected to the booster station main transformer bay unit 7 and the generator unit 5, the generator protection device 2 is connected to the generator unit 5, and the primary current meter 1 is connected to the high-resistance grounding unit 4.

[0043] The main transformer bay unit 7 of the booster station includes a main transformer high-voltage side circuit breaker 7-1, a main transformer high-voltage side current transformer 7-2, a main transformer high-voltage side grounding switch 7-3 and a main transformer high-voltage side isolating switch 7-4; the booster station bus 8 is connected to one end of the main transformer high-voltage side isolating switch 7-4, and the other end of the main transformer high-voltage side isolating switch 7-4 is divided into two paths, one of which is grounded after passing through the main transformer high-voltage side grounding switch 7-3, and the other is connected to the main transformer unit 6 through the main transformer high-voltage side circuit breaker 7-1, the main transformer high-voltage side current transformer 7-2 is arranged on the line between the main transformer high-voltage side circuit breaker 7-1 and the main transformer high-voltage side isolating switch 7-4, and the main transformer high-voltage side current transformer 7-2 is connected to the transformer protection device 3.

[0044] The main transformer unit 6 includes a main transformer low-voltage side break 6-1, a main transformer 6-2, a main transformer high-voltage side break 6-3, a main transformer high-voltage side closed bus 6-4 and a second group of test lines 6-5. The booster station main transformer bay unit 7 is connected to one end of the main transformer high-voltage side closed bus 6-4. The other end of the main transformer high-voltage side closed bus 6-4 is divided into two paths, one of which is connected to the generator unit 5 via the main transformer high-voltage side break 6-3, the main transformer 6-2 and the main transformer low-voltage side break 6-1, and the other is connected to the generator unit 5 via the second group of test lines 6-5.

[0045] The generator unit 5 includes a generator neutral point closed bus 5-1, a generator neutral point current transformer 5-2, a generator neutral point break 5-3, a generator 5-4, a generator end break 5-5, a generator end closed bus 5-6, a first group of generator end current transformers 5-7, a second group of generator end current transformers 5-8 and a first group of test lines 5-9; one end of the generator end closed bus 5-6 is connected to the main transformer unit 6, and the other end of the generator end closed bus 5-6 is divided into two paths, one of which is connected to the generator neutral point closed bus through the generator end break 5-5, the generator 5-4 and the generator neutral point break 5-3. 5-1, and the other is connected to the generator neutral point closed bus 5-1 through the first group of test lines 5-9, and the generator neutral point closed bus 5-1 is connected to the high-resistance grounding unit 4; the first group of current transformers 5-7 at the generator end and the second group of current transformers 5-8 at the generator end are installed on the generator end closed bus 5-6, the generator neutral point current transformer 5-2 is installed on the generator neutral point closed bus 5-1, the first group of current transformers 5-7 at the generator end are connected to the transformer protection device 3, and the generator neutral point current transformer 5-2 and the second group of current transformers 5-8 at the generator end are connected to the generator protection device 2.

[0046] The high-resistance grounding unit 4 includes a grounding transformer 4-1, a grounding transformer auxiliary resistor 4-2 and a grounding switch 4-3; the generator unit 5 is connected to one end of the grounding switch 4-3 and the current output terminal 1-2 of the primary current meter 1, the other end of the grounding switch 4-3 is grounded after passing through the primary winding of the grounding transformer 4-1, the grounding transformer auxiliary resistor 4-2 is connected in series to the secondary winding of the grounding transformer 4-1, and the grounding terminal 1-1 of the primary current meter 1 is grounded.

[0047] refer to Figure 2 The method for testing polarity of differential protection of a generator-transformer group of the present invention comprises the following steps:

[0048] 1) Carry out preliminary preparations for the generator-transformer group differential protection polarity test;

[0049] 2) Perform a phase A polarity test by connecting the current output terminal 1-2 of the primary current meter 1 to the phase A of the generator neutral point closed bus 5-1;

[0050] 3) Adjust the primary current meter 1 to output 50A primary current;

[0051] 4) Measure and record the secondary current amplitudes of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the current transformer 7-2 at the high voltage side of the main transformer when the primary current meter 1 outputs a primary current of 50A;

[0052] 5) Determine whether the secondary current amplitude of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the current transformer 7-2 on the high-voltage side of the main transformer is consistent with its theoretical value and whether the polarity is correct. When the secondary current amplitude of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the current transformer 7-2 on the high-voltage side of the main transformer is consistent with its theoretical value and the polarity is correct, go to step 6); otherwise, go to step 7);

[0053] 6) Adjust the output of the primary current meter 1 to 100A primary current, and then go to step 8);

[0054] 7) Adjust the output of the primary current meter 1 to 0A primary current, turn off the primary current meter 1, find and eliminate the defect, and then go to step 3);

[0055] 8) Measure and record the secondary current amplitudes of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the current transformer 7-2 at the high voltage side of the main transformer when the primary current meter 1 outputs a primary current of 100A;

[0056] 9) Determine whether the secondary current amplitude of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the current transformer 7-2 on the high-voltage side of the main transformer is consistent with its theoretical value and whether the polarity is correct. When the secondary current amplitude of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the current transformer 7-2 on the high-voltage side of the main transformer is consistent with its theoretical value and the polarity is correct, go to step 10); otherwise, go to step 11);

[0057] 10) The polarity test of phase A of the generator-transformer differential protection is completed, and the process goes to step 12);

[0058] 11) Adjust the output of the primary current meter 1 to 0A primary current, turn off the primary current meter 1, find and eliminate the defect, and then go to step 6);

[0059] 12) Perform polarity tests of phase B and phase C of the generator-transformer differential protection in sequence according to steps 2) to 11), and then go to step 13);

[0060] 13) The polarity test of the generator-transformer group differential protection is completed.

[0061] The specific operations of step 1) are:

[0062] 101) The generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end and the main transformer high voltage side current transformer 7-2 within the scope of this generator-transformer group differential protection polarity test have been installed in place and have completed individual tests in accordance with the regulations;

[0063] 102) Complete the installation and commissioning of the secondary secondary circuits of the neutral point current transformer 5-2 of each generator, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the current transformer 7-2 at the high voltage side of the main transformer, ensuring that the secondary secondary circuits of the neutral point current transformer 5-2 of the generator, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end, and the secondary secondary circuits of the current transformer 7-2 at the high voltage side of the main transformer are correctly wired, the secondary load is balanced in three phases, and there is no open circuit;

[0064] 103) The generator protection device 2 and the transformer protection device 3 have been installed and the static debugging work has been completed.

[0065] In the process of judging whether the secondary current amplitude of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end and the current transformer 7-2 on the high-voltage side of the main transformer is consistent with its theoretical value and whether the polarity is correct, the theoretical value of the secondary current of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end and the current transformer 7-2 on the high-voltage side of the main transformer is equal to the primary current value output by the primary current meter 1 divided by its transformation ratio; check whether the secondary current value of the generator neutral point current transformer 5-2, the first group of current transformers 5-7 at the generator end, the second group of current transformers 5-8 at the generator end and the current transformer 7-2 on the high-voltage side of the main transformer is consistent with its theoretical value through a clamp phase meter; check whether the current sampling values ​​of the generator protection device 2 and the transformer protection device 3 are equal to the theoretical value; check whether the differential protection differential current of the generator protection device 2 and the transformer protection device 3 is zero.

Claims

1. A generator-transformer group differential protection polarity test system, characterized in that: It comprises a primary current meter (1), a generator protection device (2), a transformer protection device (3), a high-resistance grounding unit (4), a generator unit (5), a main transformer unit (6), a booster station main transformer bay unit (7) and a booster station busbar (8); The booster station busbar (8) is connected to the high-resistance grounding unit (4) via the booster station main transformer bay unit (7), the main transformer unit (6) and the generator unit (5); the transformer protection device (3) is connected to the booster station main transformer bay unit (7) and the generator unit (5); the generator protection device (2) is connected to the generator unit (5); and the primary current meter (1) is connected to the high-resistance grounding unit (4); The main transformer bay unit (7) of the booster station comprises a main transformer high-voltage side circuit breaker (7-1), a main transformer high-voltage side current transformer (7-2), a main transformer high-voltage side grounding switch (7-3) and a main transformer high-voltage side isolating switch (7-4); The booster station busbar (8) is connected to one end of the main transformer high-voltage side isolating knife switch (7-4); the other end of the main transformer high-voltage side isolating knife switch (7-4) is divided into two paths, one of which is grounded after passing through the main transformer high-voltage side grounding knife switch (7-3); the other is connected to the main transformer unit (6) through the main transformer high-voltage side circuit breaker (7-1); the main transformer high-voltage side current transformer (7-2) is arranged on the line between the main transformer high-voltage side circuit breaker (7-1) and the main transformer high-voltage side isolating knife switch (7-4); the main transformer high-voltage side current transformer (7-2) is connected to the transformer protection device (3); The main transformer unit (6) comprises a main transformer low-voltage side break (6-1), a main transformer (6-2), a main transformer high-voltage side break (6-3), a main transformer high-voltage side closed busbar (6-4) and a second group of test lines (6-5); the booster station main transformer bay unit (7) is connected to one end of the main transformer high-voltage side closed busbar (6-4); the other end of the main transformer high-voltage side closed busbar (6-4) is divided into two paths, one of which is connected to the generator unit (5) via the main transformer high-voltage side break (6-3), the main transformer (6-2) and the main transformer low-voltage side break (6-1); and the other is connected to the generator unit (5) via the second group of test lines (6-5); The generator unit (5) comprises a generator neutral point closed busbar (5-1), a generator neutral point current transformer (5-2), a generator neutral point break (5-3), a generator (5-4), a generator end break (5-5), a generator end closed busbar (5-6), a first set of generator end current transformers (5-7), a second set of generator end current transformers (5-8) and a first set of test wires (5-9); One end of the generator end closed busbar (5-6) is connected to the main transformer unit (6), and the other end of the generator end closed busbar (5-6) is divided into two paths, one of which is connected to the generator neutral point closed busbar (5-1) via the generator end break (5-5), the generator (5-4) and the generator neutral point break (5-3), and the other is connected to the generator neutral point closed busbar (5-1) via the first group of test lines (5-9), and the generator neutral point closed busbar (5-1) is connected to the high resistance grounding unit (4); The first set of current transformers (5-7) at the generator end and the second set of current transformers (5-8) at the generator end are installed on the generator end closed busbar (5-6), the generator neutral point current transformer (5-2) is installed on the generator neutral point closed busbar (5-1), the first set of current transformers (5-7) at the generator end are connected to the transformer protection device (3), and the generator neutral point current transformer (5-2) and the second set of current transformers (5-8) at the generator end are connected to the generator protection device (2); The high-resistance grounding unit (4) comprises a grounding transformer (4-1), a grounding transformer auxiliary resistor (4-2) and a grounding switch (4-3); The generator unit (5) is connected to one end of the grounding switch (4-3) and the current output terminal (1-2) of the primary current meter (1); the other end of the grounding switch (4-3) is grounded via the primary winding of the grounding transformer (4-1); the grounding transformer secondary resistor (4-2) is connected in series to the secondary winding of the grounding transformer (4-1); and the grounding terminal (1-1) of the primary current meter (1) is grounded.

2. A method for testing polarity of differential protection of a generator-transformer group, characterized in that: The generator-transformer group differential protection polarity test system according to claim 1 comprises the following steps: 1) Carry out preliminary preparations for the generator-transformer group differential protection polarity test; 2) Perform a phase A polarity test by connecting the current output terminal (1-2) of the primary current meter (1) to phase A of the generator neutral point closed busbar (5-1); 3) Adjust the primary current meter (1) to output 50A primary current; 4) Measure and record the secondary current amplitudes of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) when the primary current meter (1) outputs a primary current of 50A; 5) Determine whether the secondary current amplitudes of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) are consistent with their theoretical values ​​and whether the polarities are correct. If the secondary current amplitudes of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) are consistent with their theoretical values ​​and the polarities are correct, go to step 6); otherwise, go to step 7); 6) Adjust the output of the primary current meter (1) to 100A primary current, then go to step 8); 7) Adjust the output of the primary current meter (1) to 0A primary current, turn off the primary current meter (1), find and eliminate the defect, and then go to step 3); 8) Measure and record the secondary current amplitudes of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) when the primary current meter (1) outputs a primary current of 100A; 9) Determine whether the secondary current amplitudes of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) are consistent with their theoretical values ​​and whether the polarities are correct. If the secondary current amplitudes of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) are consistent with their theoretical values ​​and the polarities are correct, go to step 10); otherwise, go to step 11); 10) The polarity test of phase A of the generator-transformer differential protection is completed, and the process goes to step 12); 11) Adjust the output of the primary current meter (1) to 0A primary current, turn off the primary current meter (1), find and eliminate the defect, and then go to step 6); 12) Perform polarity tests of phase B and phase C of the generator-transformer differential protection in sequence according to steps 2) to 11), and then go to step 13); 13) The polarity test of the generator-transformer group differential protection is completed.

3. The method for testing polarity of differential protection of a generator-transformer group according to claim 2, characterized in that: The specific operations of step 1) are: 101) The generator neutral point current transformer (5-2), the first set of current transformers at the generator end (5-7), the second set of current transformers at the generator end (5-8) and the main transformer high voltage side current transformer (7-2) within the scope of this generator-transformer differential protection polarity test have been installed and completed the individual tests in accordance with the regulations; 102) Complete the installation and commissioning of the secondary circuits of the neutral point current transformer (5-2) of each generator, the first set of current transformers (5-7) at the generator end, the second set of current transformers (5-8) at the generator end, and the current transformer (7-2) at the high voltage side of the main transformer. Ensure that the secondary circuits of the neutral point current transformer (5-2) of the generator, the first set of current transformers (5-7) at the generator end, the second set of current transformers (5-8) at the generator end, and the current transformer (7-2) at the high voltage side of the main transformer are correctly wired, and the secondary load is balanced in three phases without open circuit. 103) The generator protection device (2) and transformer protection device (3) have been installed and static commissioning has been completed.

4. The method for testing polarity of differential protection of a generator-transformer group according to claim 2, characterized in that: In the process of judging whether the secondary current amplitudes of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) are consistent with their theoretical values ​​and whether the polarities are correct, the theoretical values ​​of the secondary currents of the generator neutral point current transformer (5-2), the first set of generator end current transformers (5-7), the second set of generator end current transformers (5-8) and the main transformer high voltage side current transformer (7-2) are equal to the primary current value output by the primary current meter (1) divided by its transformation ratio; Check whether the secondary current values ​​of the generator neutral point current transformer (5-2), the first set of generator end current transformer (5-7), the second set of generator end current transformer (5-8) and the main transformer high voltage side current transformer (7-2) are consistent with their theoretical values ​​by using a clamp phase meter; Check whether the current sampling values ​​of the generator protection device (2) and the transformer protection device (3) are equal to the theoretical values; Check whether the differential protection current of the generator protection device (2) and the transformer protection device (3) is zero.

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