A method for analyzing the leading-phase operation capability of generating units considering the reactive power loss limitation of the main transformer

Abstract

This invention relates to a method for analyzing the leading-phase operation capability of a generating unit considering the reactive power loss limit of the main transformer, belonging to the field of power system technology. Before the unit's leading-phase test begins, the method calculates the maximum current on the high-voltage side of the main transformer at the leading-phase depth based on a preset value, and determines whether the current will exceed the limit at this leading-phase depth. If it does, a smaller preset value for the leading-phase depth is determined. If it does not exceed the limit, the leading-phase test is conducted on-site according to the "Guidelines for Leading-Phase Tests of Synchronous Generators," and the state quantity of the high-voltage side current of the main transformer is monitored and recorded. If it exceeds the limit, further leading-phase operation should be stopped. Based on the measured data, the conclusion of the unit's leading-phase operation capability is analyzed, and a test report is issued. This invention effectively avoids the risk of main transformer overload tripping when conducting leading-phase tests according to the guidelines, and the unit's leading-phase operation capability obtained under this method is safer and more reliable for guiding dispatching operations.

Description

Technical Field

[0001] This invention belongs to the field of power system technology, specifically relating to a method for analyzing the leading-phase operation capability of generating units considering the reactive power loss limitation of the main transformer. Background Technology

[0002] my country's power grid system is continuously developing towards higher voltage, larger capacity, and longer distances. This leads to problems such as excess reactive power and high voltage, even approaching or exceeding the system's operating voltage limit, when the system load is low. This seriously affects the power quality of the system and may even jeopardize its stable operation. Furthermore, the penetration rate of new energy sources has increased significantly in recent years, while the operation of traditional thermal power units has decreased. This is changing the power grid's operating mechanism and increasing the difficulty of voltage control. Therefore, the power grid system needs more reactive power reserves to participate in voltage regulation. Existing synchronous generator units do not require additional auxiliary equipment or consume extra energy. They can generate and absorb reactive power relatively economically and conveniently, participating in the coordinated control of reactive power and voltage in the power grid. This improves the reactive power reserve level of the power grid system and is of great significance for the safe and stable operation of the power grid. To confirm the actual reactive power reserve capacity of different units, especially their reactive power absorption capacity (i.e., their leading-phase operation capacity), on-site leading-phase tests are needed for testing and verification to ensure the safe and stable operation of the units during leading-phase operation.

[0003] Currently, the industry mainly conducts on-site leading phase tests based on DL / T1523-2016 "Guidelines for Leading Phase Tests of Synchronous Generators." The leading phase capability of the generator during on-site testing is primarily determined by its limiting conditions. The guidelines specify that the limiting conditions for the leading phase depth of grid-connected synchronous generators should include: a) generator power angle, terminal voltage, and terminal current; b) high / low voltage station service bus voltage and high-voltage side bus voltage of the main transformer; c) end core and metal structural component temperature, generator inlet and outlet water temperature difference, and hot and cold air temperature difference. Related literature also proposes several limiting factors for the leading phase capability of synchronous generators, which can be summarized as generator stator and rotor voltage and current limitations, generator power angle limitations, generator end heating limitations, and station service power and system voltage limitations, which are consistent with the limiting conditions specified in the guidelines.

[0004] While there is considerable research on the limiting factors of generator unit leading-phase operation capability, none of these studies have considered the limiting effect of the main transformer's reactive power loss on generator leading-phase operation. The synchronous generator leading-phase test guidelines also do not mention this issue. Practice has shown that neglecting this problem during leading-phase testing could potentially lead to main transformer overload tripping and shutdown. Therefore, overcoming the shortcomings of existing technologies is a pressing issue that needs to be addressed in the field of power system technology. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for analyzing the leading phase operation capability of a unit considering the reactive power loss limitation of the main transformer.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for analyzing the leading-phase operation capability of a generating unit considering the reactive power loss limitation of the main transformer includes the following steps:

[0008] Step 1: Before the unit's phase advance test begins, calculate the maximum current on the high-voltage side of the main transformer at the time of phase advance based on the preset value of the phase advance depth, and determine whether the current on the high-voltage side of the main transformer will exceed the limit at this phase advance depth.

[0009] Step 2: If the high-voltage side current of the main transformer will exceed the limit at this advance depth, then a smaller preset value for the advance depth is determined, and the process proceeds to Step 1; if the high-voltage side current of the main transformer will not exceed the limit at this advance depth, the process proceeds to Step 3.

[0010] Step 3: Conduct the phase advance test on site in accordance with the provisions of DL / T1523-2016 "Guidelines for Phase Advance Test of Synchronous Generator", and monitor and record the state quantity of the high voltage side current of the main transformer. If it is found to exceed the limit, further phase advance should be stopped.

[0011] Step four: Obtain the actual phase-advancing operation data of the unit through on-site phase-advancing tests;

[0012] Step 5: Based on the obtained operating data, analyze the unit's leading-phase operation capability and issue a test report; in addition to the state quantities required by DL / T1523-2016 "Guidelines for Leading-Phase Tests of Synchronous Generators", the measured data in the report should also include the current on the high-voltage side of the main transformer.

[0013] Furthermore, preferably, in step one, the calculation method for the maximum current on the high-voltage side of the main transformer during the leading phase is as follows:

[0014] (1) Analyze and calculate the reactive power loss of the main transformer:

[0015] Calculate the winding leakage reactance and reactive power loss ΔQ XT and the reactive power loss ΔQ of the excitation branch BT ;

[0016] Among them, the winding leakage reactance reactive power loss ΔQ XT for:

[0017]

[0018] In equation (1), U k % is the short-circuit impedance of the main transformer, S N Main transformer rated capacity, I e The actual current on the high-voltage side of the main transformer, I N The rated current of the high-voltage side of the main transformer;

[0019] Reactive power loss ΔQ in the excitation branch BT for:

[0020]

[0021] In equation (2), I0% is the no-load current of the main transformer;

[0022] The total reactive power loss ΔQ during main transformer operation T for:

[0023]

[0024] (2) Calculate the maximum current on the high-voltage side of the main transformer during the leading phase, taking into account the reactive power loss of the main transformer:

[0025] The reactive power output from the high-voltage side of the main transformer is the reactive power output from the generator minus the reactive power losses of the main transformer itself, that is:

[0026] Q2 = Q G -ΔQ T (4)

[0027] In equation (4), Q2 is the reactive power output from the high-voltage side of the main transformer; Q G The reactive power output of the generator; the apparent power on the high-voltage side of the main transformer is related to its voltage and current by the following formula:

[0028] S2 2 =P G 2 +Q2 2 =3U2 2 I e 2 (5)

[0029] In equation (5), S2 is the apparent power on the high-voltage side of the main transformer, and P G U2 is the active power output of the generator, U2 is the voltage on the high-voltage side of the main transformer, and I is the active power output of the generator. e The actual current on the high-voltage side of the main transformer;

[0030] Based on equations (3), (4), and (5) above, the actual current I on the high-voltage side of the main transformer under different operating conditions when the unit is running in the leading phase is calculated. e When the reactive power output of the generator reaches the preset value of the leading phase depth, I e This is the maximum current on the high-voltage side of the main transformer when the phase advances.

[0031] Compared with the prior art, the beneficial effects of this invention are as follows:

[0032] This invention comprehensively considers the constraints limiting unit operation in a leading-phase manner, resulting in a more reliable and realistic leading-phase capability. It effectively avoids the risk of main transformer overload tripping during leading-phase tests conducted according to guidelines. Furthermore, the leading-phase operation capability obtained using this method is safer and more reliable for guiding dispatching operations. This invention reduces the risk of main transformer overload tripping during testing, a problem that traditional methods completely ignore.

[0033] This invention studies the limitations of main transformer reactive power loss on generator leading phase operation, anticipates whether the current on the high-voltage side of the main transformer will exceed the limit during the leading phase operation of the unit, and adjusts the leading phase test depth in a timely manner. The actual leading phase capability of the unit is obtained through field test verification, providing suggestions for unit leading phase test and scheduling scheme formulation, and has positive significance for reactive power adjustment after asynchronous networking. Attached Figure Description

[0034] Figure 1 This is a flowchart illustrating the method for analyzing the unit's leading-phase operation capability considering the reactive power loss limitation of the main transformer, as described in this invention.

[0035] Figure 2 This refers to the reactive power output of the generator on the high-voltage side of the main transformer under the PQ extreme operating conditions, and the extreme output range of the reactive power on the high-voltage side of the main transformer. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the embodiments.

[0037] Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the field or according to the product instructions. Materials or equipment whose manufacturers are not specified are all conventional products that can be obtained by purchase.

[0038] Example 1

[0039] A method for analyzing the leading-phase operation capability of a generating unit considering the reactive power loss limitation of the main transformer, characterized by comprising the following steps:

[0040] Step 1: Before the unit's phase advance test begins, calculate the maximum current on the high-voltage side of the main transformer at the time of phase advance based on the preset value of the phase advance depth, and determine whether the current on the high-voltage side of the main transformer will exceed the limit at this phase advance depth.

[0041] Step 2: If the high-voltage side current of the main transformer will exceed the limit at this advance depth, then a smaller preset value for the advance depth is determined, and the process proceeds to Step 1; if the high-voltage side current of the main transformer will not exceed the limit at this advance depth, the process proceeds to Step 3.

[0042] Step 3: Conduct the phase advance test on site in accordance with the provisions of DL / T1523-2016 "Guidelines for Phase Advance Test of Synchronous Generator", and monitor and record the state quantity of the high voltage side current of the main transformer. If it is found to exceed the limit, further phase advance should be stopped.

[0043] Step four: Obtain the actual phase-advancing operation data of the unit through on-site phase-advancing tests;

[0044] Step 5: Based on the obtained operating data, analyze the unit's leading-phase operation capability and issue a test report; in addition to the state quantities required by DL / T1523-2016 "Guidelines for Leading-Phase Tests of Synchronous Generators", the measured data in the report should also include the current on the high-voltage side of the main transformer.

[0045] Example 2

[0046] like Figure 1 As shown, a method for analyzing the leading-phase operation capability of a generating unit considering the reactive power loss limitation of the main transformer is characterized by the following steps:

[0047] Step 1: Before the unit's phase advance test begins, calculate the maximum current on the high-voltage side of the main transformer at the time of phase advance based on the preset value of the phase advance depth, and determine whether the current on the high-voltage side of the main transformer will exceed the limit at this phase advance depth.

[0048] Step 2: If the high-voltage side current of the main transformer will exceed the limit at this advance depth, then a smaller preset value for the advance depth is determined, and the process proceeds to Step 1; if the high-voltage side current of the main transformer will not exceed the limit at this advance depth, the process proceeds to Step 3.

[0049] Step 3: Conduct the phase advance test on site in accordance with the provisions of DL / T1523-2016 "Guidelines for Phase Advance Test of Synchronous Generator", and monitor and record the state quantity of the high voltage side current of the main transformer. If it is found to exceed the limit, further phase advance should be stopped.

[0050] Step four: Obtain the actual phase-advancing operation data of the unit through on-site phase-advancing tests;

[0051] Step 5: Based on the obtained operating data, analyze the unit's leading-phase operation capability and issue a test report; in addition to the state quantities required by DL / T1523-2016 "Guidelines for Leading-Phase Tests of Synchronous Generators", the measured data in the report should also include the current on the high-voltage side of the main transformer.

[0052] In step one, the calculation method for the maximum current on the high-voltage side of the main transformer during the leading phase is as follows:

[0053] (1) Analyze and calculate the reactive power loss of the main transformer:

[0054] Calculate the winding leakage reactance and reactive power loss ΔQ XT and the reactive power loss ΔQ of the excitation branch BT ;

[0055] Among them, the winding leakage reactance reactive power loss ΔQ XT for:

[0056]

[0057] In equation (1), U k % is the short-circuit impedance of the main transformer, S N Main transformer rated capacity, I e The actual current on the high-voltage side of the main transformer, I N The rated current of the high-voltage side of the main transformer;

[0058] Reactive power loss ΔQ in the excitation branch BT for:

[0059]

[0060] In equation (2), I0% is the no-load current of the main transformer;

[0061] The total reactive power loss ΔQ during main transformer operation T for:

[0062]

[0063] (2) Calculate the maximum current on the high-voltage side of the main transformer during the leading phase, taking into account the reactive power loss of the main transformer:

[0064] The reactive power output from the high-voltage side of the main transformer is the reactive power output from the generator minus the reactive power loss of the main transformer itself, that is:

[0065] Q2 = Q G -ΔQ T (4)

[0066] In equation (4), Q2 is the reactive power output from the high-voltage side of the main transformer; Q G The reactive power output of the generator; the apparent power on the high-voltage side of the main transformer is related to its voltage and current by the following formula:

[0067] S2 2 =P G 2 +Q2 2 =3U2 2 I e 2 (5)

[0068] In equation (5), S2 is the apparent power on the high-voltage side of the main transformer, and P G U2 is the active power output of the generator, U2 is the voltage on the high-voltage side of the main transformer, and I is the active power output of the generator. e The actual current on the high-voltage side of the main transformer;

[0069] Based on equations (3), (4), and (5) above, the actual current I on the high-voltage side of the main transformer under different operating conditions when the unit is running in the leading phase is calculated. e When the reactive power output of the generator reaches the preset value of the leading phase depth, I e This is the maximum current on the high-voltage side of the main transformer when the phase advances.

[0070] Example 3

[0071] like Figure 1 As shown, the method for analyzing the leading-phase operation capability of a unit considering the reactive power loss limitation of the main transformer includes the following steps:

[0072] Step 1: Before the unit's phase advance test begins, calculate the maximum current on the high-voltage side of the main transformer at the phase advance depth based on the preset value, and determine whether the current on the high-voltage side of the main transformer will exceed the limit at this phase advance depth. Due to the influence of transformer reactive power loss, the reactive power on the high-voltage side of the main transformer will be greater than that on the generator side when the unit is in phase advance. Since the capacity of the generator and the main transformer is generally equal, there may be a situation where the current on the generator side has not yet reached the limit but the current on the high-voltage side of the main transformer has already exceeded the limit when the unit is in phase advance.

[0073] Step 2: If the high-voltage side current of the main transformer will exceed the limit at this phase advance depth, then a smaller preset value for the phase advance depth is determined, and the process proceeds to Step 1. The determination of the preset value for the phase advance depth needs to comprehensively consider the unit's design capacity, operating status, and relevant grid dispatch requirements. If the high-voltage side current of the main transformer will not exceed the limit at this phase advance depth, the process proceeds to Step 3. When determining a smaller preset value for the phase advance depth, it is necessary to ensure that the preset value for the phase advance depth is as large as possible without causing the high-voltage side current of the main transformer to exceed the limit.

[0074] Step 3: Based on the existing limit conditions for the leading depth in DL / T1523-2016 "Guidelines for Leading Phase Test of Synchronous Generators", add the limit condition of "current on the high-voltage side of the main transformer", and then carry out the leading phase test on site. During the test, in addition to recording the state quantities required in DL / T1523-2016 "Guidelines for Leading Phase Test of Synchronous Generators", the state quantity of the high-voltage side current of the main transformer should also be monitored and recorded. Once it is found to exceed the limit, further leading phase should be stopped to ensure the safe and stable operation of the unit.

[0075] Step four: Obtain the actual phase-advancing operation data of the unit through on-site phase-advancing tests;

[0076] Step 5: Based on the obtained operating data, analyze the unit's leading-phase operation capability and issue a test report; in addition to the state quantities required by DL / T1523-2016 "Guidelines for Leading-Phase Tests of Synchronous Generators", the measured data in the report should also include the current on the high-voltage side of the main transformer.

[0077] The test report may include whether the relevant scheduling requirements are met, which limitations are likely to be exceeded under the deepest phase advance condition, and what precautions should be taken during subsequent phase advance operation, but is not limited to these. The test report may also be issued according to existing requirements.

[0078] Furthermore, in step one, the maximum current on the high-voltage side of the main transformer during phase advance is calculated through the following steps:

[0079] 1) First, analyze and calculate the reactive power loss of the main transformer:

[0080] When the main transformer is running, its reactive power loss is mainly manifested in the transformer winding leakage reactance and the excitation branch susceptance, which are respectively the reactive power loss ΔQ of the winding leakage reactance. XT and the reactive power loss ΔQ of the excitation branch BT .

[0081] Among them, the winding leakage reactance reactive loss ΔQ XT for:

[0082]

[0083] In equation (1), U k % is the short-circuit impedance of the main transformer, S N Main transformer rated capacity, I e The actual current on the high-voltage side of the main transformer, I N The rated current of the high-voltage side of the main transformer.

[0084] The reactive power loss ΔQ in the excitation branch BT for:

[0085]

[0086] In equation (2), I0% is the no-load current of the main transformer.

[0087] In summary, the total reactive power loss ΔQ during main transformer operation is... T for:

[0088]

[0089] 2) Calculate the maximum current on the high-voltage side of the main transformer during the leading phase, taking into account the reactive power loss of the main transformer:

[0090] The reactive power output from the high-voltage side of the main transformer is the reactive power output from the generator minus the reactive power loss of the main transformer itself, that is:

[0091] Q2 = Q G -ΔQ T (4)

[0092] In equation (4), Q2 is the reactive power output from the high-voltage side of the main transformer; Q G This refers to the reactive power output of the generator.

[0093] Since the active power output of the main transformer is almost equal to the active power output of the generator (ignoring the active power loss of the main transformer here, because the current change caused by the reactive power loss of the main transformer is much greater than the active power loss), the relationship between the apparent power on the high-voltage side of the main transformer and its voltage and current is as follows:

[0094] S2 2 =P G 2 +Q2 2 =3U2 2 I e 2 (5)

[0095] In equation (5), S2 is the apparent power on the high-voltage side of the main transformer; P G U2 is the active power output of the generator, U2 is the voltage on the high-voltage side of the main transformer, and I is the active power output of the generator. e This refers to the actual current on the high-voltage side of the main transformer.

[0096] Based on equations (3), (4), and (5) above, the actual current I on the high-voltage side of the main transformer can be calculated under different operating conditions (refer to the "Guidelines for Synchronous Generator Phase-Leading Tests") when the unit is operating in phase-leading mode. e When the reactive power output of the generator reaches the preset value of the leading phase depth, I e This is the maximum current on the high-voltage side of the main transformer when the phase advances.

[0097] Application Example 1

[0098] To further illustrate this, let's take a hydropower plant in Yunnan Province as a real-time example. One of its 850MW units uses a unit connection configuration. The method of this invention was applied to conduct a phase-leading test on it. Before the test began, a preset operating condition of the generator was: P G =850MW, Q G = -308MVar.

[0099] The method for analyzing the leading-phase operation capability of a generating unit considering the reactive power loss limitation of the main transformer includes the following steps:

[0100] Step 1: Before starting the advance test, determine the advance depth based on the preset value (i.e., P). G 850MW, Q G :

[0101] -308MVar) Calculate the maximum current on the high-voltage side of the main transformer of the unit, and determine whether the current on the high-voltage side of the main transformer will exceed the limit at this leading phase depth? By using equations (3), (4), (5) and relevant parameters of the unit (as shown in Table 1), it can be calculated that the maximum current on the high-voltage side of the main transformer is 1050A under this leading phase condition (at this time, the reactive power on the high-voltage side of the main transformer reaches -473.2MVar).

[0102] Table 1. Nameplate parameters of a certain generator unit

[0103]

[0104] Step 2: Through the calculation and analysis in Step 1, it was found that if the test is carried out at this advance depth, the high-voltage side current of the main transformer will exceed the limit, which may cause the main transformer to overload alarm or even trip during the test. Therefore, it is necessary to redetermine a smaller advance depth preset value and go back to Step 1 for recalculation and analysis. Through the recalculation and analysis in Step 1, it was found that when the advance depth preset value is adjusted to -203MVar, the high-voltage side current of the main transformer will not exceed the limit. The state quantities of the advance preset operating conditions before and after the adjustment are shown in Table 2.

[0105] Table 2 Preset Operating Conditions Before and After Adjustment

[0106] <![CDATA[P G / MW]]> <![CDATA[Q G / MVar]]> cosθ <![CDATA[Q2 / MVar]]> <![CDATA[I e / A]]> Pre-adjustment preset working conditions 850 -308 0.94 -473.2 1050 Pre-adjustment preset working conditions 850 -203 0.973 -350.6 992

[0107] Step 3: Based on the existing limit conditions for leading phase depth in DL / T1523-2016 "Guidelines for Leading Phase Test of Synchronous Generator", add the limit condition of "high voltage side current of main transformer". Then, conduct the leading phase test on site according to the preset operating conditions calculated and analyzed before the test. During the test, in addition to recording the state quantities required in DL / T1523-2016 "Guidelines for Leading Phase Test of Synchronous Generator", the state quantity of high voltage side current of main transformer should also be monitored and recorded. Once it is found to exceed the limit, further leading phase should be stopped to ensure the safe and stable operation of the unit.

[0108] Step four: Obtain actual phase-advancing operation data of the unit through on-site tests;

[0109] Step 5: Based on the measured data, analyze the conclusions of the unit's leading-phase operation capability and issue a test report; the measured data in the report should include not only the state quantities required in DL / T1523-2016 "Guidelines for Leading-Phase Tests of Synchronous Generators" but also the current on the high-voltage side of the main transformer.

[0110] Furthermore, the necessity of the method of the present invention is further illustrated by constructing a mathematical model using equations (3), (4), and (5) and conducting simulations. A 400MW unit in Power Plant B adopts a unit connection method, and the simulation parameters are shown in Table 3.

[0111] Table 3 Parameters of a Main Transformer in Power Plant B

[0112] parameter numerical values <![CDATA[S N ]]> 450MVA <![CDATA[U k %]]> 14.58 <![CDATA[I N ]]> 472.38A

[0113] The generator at Power Plant B has a rated capacity of 444.4 MVA. Based on a mathematical model, the PQ limit of this generator at Power Plant B, as well as the corresponding reactive power output on the high-voltage side of the main transformer under this extreme operating condition and the limit range of reactive power output on the high-voltage side of the main transformer, can be calculated. The generator's active power P... G Plot the relationship curves between the generator-side reactive power, the main transformer high-voltage side reactive power, and the main transformer high-voltage side reactive power limit, with the x-axis as the x-axis and reactive power as the y-axis, as shown below. Figure 2 As shown, it can be seen that under the same active power, the reactive power output of the generator and the reactive power output of the transformer high-voltage side always differ by a certain amount. This difference is mainly the reactive power loss of the transformer, and its magnitude depends primarily on the current flowing through the transformer.

[0114] Figure 2 As can be seen, if the generator absorbs inductive reactive power to its limit during the leading-phase operation, the inductive reactive power absorbed by the high-voltage side of the main transformer will far exceed the reactive power limit of the main transformer under this active operating condition (limited by its capacity). This will lead to a serious over-limit current on the high-voltage side of the main transformer, and the lower the voltage level on the high-voltage side of the main transformer, the more obvious the over-limit current will be. In severe cases, it will cause the main transformer to overload and trip during the leading-phase operation. Therefore, when the generator is operating in the leading-phase mode, attention should be paid to the magnitude of the current on the high-voltage side of the main transformer to prevent it from operating beyond its limit. It is evident that if the method of this invention is not adopted and the impact of the leading-phase process on the main transformer is directly ignored, there is a risk that the leading-phase process will cause the main transformer to overload or even trip. This analysis and calculation also proves the benefits of this invention.

[0115] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for analyzing the leading-phase operation capability of a generating unit considering the reactive power loss limitation of the main transformer, characterized in that, Includes the following steps: Step 1: Before the unit's phase advance test begins, calculate the maximum current on the high-voltage side of the main transformer at the phase advance depth based on the preset value, and determine whether the current on the high-voltage side of the main transformer will exceed the limit at this phase advance depth. The calculation method for the maximum current on the high-voltage side of the main transformer at the phase advance depth is as follows: first calculate the reactive power loss of the winding leakage reactance and the reactive power loss of the excitation branch to obtain the total reactive power loss of the main transformer during operation; then calculate the maximum current on the high-voltage side of the main transformer at the phase advance depth based on the reactive power loss of the main transformer. Step 2: If the high-voltage side current of the main transformer will exceed the limit at this advance depth, then a smaller preset value for the advance depth is determined, and the process proceeds to Step 1; if the high-voltage side current of the main transformer will not exceed the limit at this advance depth, the process proceeds to Step 3. Step 3: Conduct the phase advance test on site in accordance with the provisions of DL / T1523-2016 "Guidelines for Phase Advance Test of Synchronous Generator", and monitor and record the state quantity of the high voltage side current of the main transformer. If it is found to exceed the limit, further phase advance should be stopped. Step four: Obtain the actual phase-advancing operation data of the unit through on-site phase-advancing tests; Step 5: Based on the obtained operating data, analyze the unit's leading-phase operation capability and issue a test report; in addition to the state quantities required by DL / T1523-2016 "Guidelines for Leading-Phase Tests of Synchronous Generators", the measured data in the report should also include the current on the high-voltage side of the main transformer.

2. The method for analyzing the unit's leading-phase operation capability considering the reactive power loss limitation of the main transformer according to claim 1, characterized in that, In step one, the calculation method for the maximum current on the high-voltage side of the main transformer during the leading phase is as follows: (1) Analyze and calculate the reactive power loss of the main transformer: Calculate the winding leakage reactance reactive loss ΔQXT and the excitation branch reactive loss ΔQBT; Among them, the reactive power loss ΔQXT of the winding leakage reactance is: （1） In equation (1), Uk% is the short-circuit impedance of the main transformer, SN is the rated capacity of the main transformer, Ie is the actual current on the high-voltage side of the main transformer, and IN is the rated current on the high-voltage side of the main transformer. The reactive power loss ΔQBT of the excitation branch is: （2） In equation (2), I0% is the no-load current of the main transformer; The total reactive power loss ΔQT during main transformer operation is: （3） (2) Calculate the maximum current on the high-voltage side of the main transformer during the leading phase, taking into account the reactive power loss of the main transformer: The reactive power output from the high-voltage side of the main transformer is the reactive power output from the generator minus the reactive power loss of the main transformer itself, that is: （4） In equation (4), Q2 is the reactive power output from the high-voltage side of the main transformer; QG is the reactive power output from the generator; the relationship between the apparent power on the high-voltage side of the main transformer and its voltage and current is: （5） In equation (5), S2 is the apparent power on the high-voltage side of the main transformer, PG is the active power output by the generator, U2 is the voltage on the high-voltage side of the main transformer, and Ie is the actual current on the high-voltage side of the main transformer. Based on the above formulas (3), (4), and (5), the actual current Ie on the high-voltage side of the main transformer under different operating conditions when the unit is in the leading phase operation is calculated. When the reactive power output by the generator reaches the preset value of the leading phase depth, Ie is the maximum current on the high-voltage side of the main transformer when the leading phase occurs.

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