Loop closing operation safety control method and system for power grid with angular difference and storage medium

Abstract

The invention discloses a loop closing operation safety control method and system for a power grid with angular difference and a storage medium, and the method comprises the steps: building an equivalent circuit model containing a 30-degree angular difference looped network, calculating a per-unit value and a named value of loop closing current, and determining the voltage phase difference of each node of the looped network; checking a line protection constant value in the looped network and overload capacities of a transformer and a line, and obtaining an allowable current threshold value and a short-time overload multiple of equipment; configuring a temporary protection constant value area in an unlinking switch, adjusting an over-current protection constant value to a preset value for avoiding the maximum load current, and setting the action time limit to be 0 second; when the loop closing operation is executed, the current of a loop opening switch is monitored in real time, and when it is detected that the loop closing current exceeds a temporary constant value, 0-second delay tripping loop opening is started; calculating an allowable loop closing time window based on a transformer winding hot-spot temperature model and a line temperature rise curve, and controlling the loop closing operation to be completed within 25 seconds; and after loop closing, automatically switching a loop opening switch to an original constant value area, and recording loop closing current data for constant value optimization.

Description

Technical Field

[0001] The present invention relates to the technical field of closed-loop operation safety control, and more particularly to a closed-loop operation safety control method, system and storage medium for a power grid with an angle difference. Background Art

[0002] In the existing distribution network, since the main transformer of the upper substation adopts the Y / △ connection method, there is a 30-degree phase difference between some interconnection lines. According to the current dispatching regulations, such lines are not allowed to directly close the loop to adjust the power, and the load must be transferred by the "first open and then close" method, which will inevitably cause a short power outage for users. In order to reduce the impact of power outages on users, operations are usually scheduled at night or in the early morning. However, under extreme weather conditions, such as severe winter or hot summer, this operation poses a severe challenge to the health of line operation and maintenance personnel.

[0003] In recent years, some power supply companies have begun to implement the "one-button power transfer" operation on a regular basis with the help of the advanced functions of the new generation of distribution automation systems, shortening the power outage time to about 10 seconds, and basically achieving "zero perception" of power outages for users. However, this method still cannot solve the problem of power outages in substations with low-voltage tripping functions. In particular, the 30-degree phase angle difference closing and looping problem caused by the wiring method of the upper main transformer has always been a major problem in the operation of the distribution network. How to safely and efficiently solve this type of closing and opening operations without affecting the power supply to users is still a challenge that needs to be broken through in the field of distribution network technology.

[0004] The phase of the 35kV outgoing line of the 220kV substation is 30° ahead of that of the 35kV outgoing line of the 110kV substation. Therefore, for the 35kV substation, there is a 30° angle difference between the double incoming lines. Generally, the cold load reversal method is adopted, which will cause the power supply line to be shut down for a long time and increase the risk of complaints.

[0005] The publication number is CN106444589A, and the name is a 30-degree phase difference distribution line closing and unclosing operation system, which includes a distribution network closing and unclosing operation calculation and management module, a substation remote operation ticket management module, a substation remote operation ticket execution module, a remote operation front-end and a substation closing and unclosing device.

[0006] The publication number is CN118137449A, and the name is a 30-degree phase difference line closing and power regulation system, which includes: a 220kv main transformer, a 35kV power supply loop and a 110kV power supply loop; the first output end of the 220kv main transformer is connected to the 35kV power supply loop; the second output end of the 220kv main transformer is connected to the 110kV power supply loop; five 35kV impedances are arranged on the 35kV power supply loop, and each 35kV impedance is provided with a control switch. A 110kv main transformer is arranged between the 35kV power supply loop and the 110kV power supply loop; a 110kV side impedance is arranged on the 110kV power supply loop; a 110kV side switch is arranged at the 110kV side impedance position; according to the prepared power regulation plan, the 30° phase difference line closing operation is performed one by one, the calculation deviation is corrected in time, and the closing experience is accumulated.

[0007] Therefore, how to provide a method, system and storage medium for safe control of closed-loop operation of a power grid with an angle difference is an urgent problem to be solved by those skilled in the art. Summary of the invention

[0008] In view of this, the present invention provides a method, system and storage medium for safe control of closed-loop operation of a power grid with an angle difference, aiming to solve the technical problem that the use of cold load reversal will cause a long power supply line shutdown time.

[0009] In order to achieve the above object, the present invention adopts the following technical solution:

[0010] A method for safely controlling loop closing operation of a power grid with an angle difference comprises the following steps:

[0011] S1. Establish an equivalent circuit model including a 30° angle difference ring network, calculate the per unit value and nominal value of the closed loop current, and determine the voltage phase difference of each node in the ring network;

[0012] S2. Check the line protection setting value, transformer and line overload capacity in the ring network, and obtain the allowable current threshold and short-time overload multiple of the equipment;

[0013] S3. Configure the temporary protection setting area in the unblocking switch, adjust the overcurrent protection setting to the preset value that avoids the maximum load current, and set the action time limit to 0 seconds;

[0014] S4: When executing the closing operation, the opening switch current is monitored in real time. When it is detected that the closing current exceeds the temporary set value, the 0-second delay tripping is started to open the loop;

[0015] S5. Based on the transformer winding hot spot temperature model and the line temperature rise curve, the allowable closing time window is calculated and the closing operation is controlled to be completed within 25 seconds. After closing the loop, the unclosing switch is automatically switched to the original set value area, and the closing current data is recorded for set value optimization.

[0016] Furthermore, the closed-loop current calculation in S1 includes:

[0017] The total loop impedance is calculated based on the per-unit value method, the potential difference circulating current caused by the angle difference is calculated using the voltage source superposition method, and the nominal values ​​of the circulating current on the 35kV side and the 110kV side are obtained through reference parameter conversion.

[0018] Furthermore, the setting of the temporary protection setting value in S3 satisfies:

[0019] The overcurrent protection setting of the ring-breaking switch is 1.2 to 1.5 times the maximum value of the circulating current and higher than 150% of the current load current. The action time limit is 0 seconds.

[0020] Furthermore, the low voltage locking function of the loop-opening switch is released, and the sampling frequency of the D5000 system is synchronously adjusted to 1 second level to record the instantaneous current waveform data of the loop-closing in real time.

[0021] Furthermore, based on the transformer winding hot spot temperature limit of 98°C and the line temperature rise limit of 70°C, the allowable closing duration is calculated in combination with the short-circuit thermal stability equation, and the protection action time is set to ≤0.5 seconds.

[0022] Furthermore, before closing the loop, the bus voltage at the power supply end is adjusted to 95% to 98% of the nominal voltage, and a loop path with a larger impedance is preferentially selected to reduce the amplitude of the circulating current.

[0023] A closed-loop operation safety control system for an angle-difference power grid, comprising:

[0024] A circulation calculation module is used to construct an equivalent circuit and output a circulation prediction value;

[0025] The fixed value management module configures the multi-section protection fixed value library and the temporary fixed value issuing interface;

[0026] Thermal effect analysis module, which calculates the temperature rise of equipment based on real-time current data and generates time window alarms;

[0027] The automatic loop-breaking execution module triggers the switch to trip and synchronously switches the set value area according to the temporary set value.

[0028] Furthermore, the set value management module is integrated into the protection device, supporting online switching of set value areas without manual on-site modification.

[0029] Furthermore, the automatic de-looping execution module communicates with the SCADA system to obtain load current data in real time and dynamically adjust the temporary set value threshold.

[0030] A computer-readable storage medium stores a computer program. When the program is executed by a processor, a method for safely controlling the closed-loop operation of a power grid with an angle difference is implemented.

[0031] The present invention discloses a method, system and storage medium for safely controlling the closing operation of a power grid with an angle difference. Compared with the prior art, the present invention aims at the situation where there is an angle difference of 30° between the double incoming lines of a 35kV substation. Under the condition that the characteristics of the loop during thermal reverse load are fully considered, a detailed closing operation scheme and a protection setting value adjustment strategy are formulated through in-depth analysis and research on the closing of the loop with an angle difference of 30°. When the operation mode of the power grid is adjusted, the closing operation can be performed more flexibly, and the risk of equipment overload and protection malfunction caused by improper closing operation is reduced, thereby improving the reliability of power grid operation and the stability of power supply.

[0032] The overload capacity of the main transformer, line and other equipment in the loop was checked in detail to ensure that the relevant equipment would not be damaged due to overload during the loop closing operation, effectively protecting the safe operation of the equipment and extending the service life of the equipment;

[0033] Based on the calculation results of the closing current, a reasonable protection setting adjustment plan was formulated to avoid false tripping caused by inappropriate protection settings during the closing process, improve the action accuracy of the protection device, and further ensure the safe operation of the power grid. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0035] Figure 1 This is a schematic diagram of a 35kV system connection structure with a 30° angle difference according to the present invention.

[0036] Figure 2 The figure is a schematic diagram of the structure of a system equivalent circuit of the present invention.

[0037] Figure 3 This is a schematic diagram of loop setting in a power grid with a 30° angle difference according to the present invention.

[0038] Figure 4 The present invention is a schematic diagram of the closing loop protection startup and shutdown and fixed value adjustment.

[0039] Figure 5 This is a vector diagram of a Yd11 wiring group according to the present invention. DETAILED DESCRIPTION

[0040] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] The embodiment of the present invention discloses a method, system and storage medium for safely controlling the closed-loop operation of a power grid with an angle difference; Figure 1 The figure shows the connection diagram of the 35kV system with a 30° angle difference. The specific loop equipment is: 220kVA station 35kV busbar--369AC line--35kVC station--334BC line--110kVB station--110kVAB line--220kVA station 110 / 35kV. In normal operation, the BC line 390 switch of the C station is in operation, the AC line 389 switch is in hot standby, and the section 301 switch is in operation;

[0042] Yd11 wiring group vector diagram Figure 2 As shown, the #3 main transformer at Station A is a 220kV main transformer, adopting the YYd11 connection group, with rated voltages of 220kV, 115.5kV and 36.75kV respectively.

[0043] The B#2 main transformer is a 110kV main transformer, adopting the YYd11 connection group, with rated voltages of 110kV, 38.5kV and 10.5kV respectively.

[0044] Station C is a 35kV substation.

[0045] Since the 369 line is the outgoing line on the low voltage side of the #2 main transformer of Station A, and its connection method is a triangle connection method, its phase is 30° ahead of the phase on the high voltage side of the #2 main transformer of Station A, so the phase of the 369 line is 30° ahead of the phase on the high voltage side of the #2 main transformer of Station A; and the high and medium voltage sides of Station A and the high and medium voltage sides of the substation of Station B are both star connection methods, so the phase of the 346 line is the same as that of the high voltage side of the #2 main transformer of Station A. Therefore, the phase of the 369 line is 30° ahead of the phase of the 346 line, that is, there is a 30° angle difference between the two lines.

[0046] The circulating current caused by the 30° angle difference of the ring network is set with a reference capacity SB of 100MVA. At the same time, the average voltage of each voltage level is taken as the reference voltage to obtain the reference value, as shown in Table 1.

[0047] Table 1: Benchmark values ​​to be calculated

[0048] Benchmark parameters 220kV 110kV 35kV <![CDATA[I B (A)]]> 251 502 1560.4 <![CDATA[U B (kV)]]> 230 115 37 <![CDATA[Z B ]]> 529 132.25 13.69

[0049] Table 2: Per-unit value of transformer in ring network

[0050]

[0051] Table 3: Line standard value in ring network

[0052] name model Rated current (A station) Impedance per unit value 369AC Line-C LGJ-150 403 0.0465+j0.0922 169AB Line LGJ-240 570 0.0044+j0.0136 344BC Line LGJ-150 403 0.0686+j0.1359

[0053] In view of the fact that the "per-unit value" form is widely used in power system calculations, this scheme adopts the "per-unit value" form to calculate the closed-loop current.

[0054] When the switch 346 of station B is switched from hot standby to operation, the system is in a closed loop state. Because there is a 30° angle difference between line 369 and line 346, there will be a large closed loop current when the loop is closed.

[0055] In Hebei's "Relay Protection Fault Analysis, Setting Management and Simulation System": the "capacity reference value" is calibrated to 100MVA station, and the "voltage reference value" is calibrated to 230kV, 115kV, and 37kV.

[0056] The required "current reference value" and "impedance reference value" are calculated using the reference values ​​of capacity and voltage, as shown in Table 4.

[0057] Table 4: Benchmark values ​​involved in calculation

[0058]

[0059] The parameters and impedance per unit value of the equipment are queried in the "Relay Protection Fault Analysis, Setting Management and Simulation System", as shown in Table 5 and Table 6.

[0060] Table 5: Main transformer parameters

[0061]

[0062] Table 6: Line parameters

[0063] name model Rated current (A station) Impedance per unit value Route 369 LGJ-150 403 0.1677+j0.332 170 lines LGJ-240 570 0.0123+j0.03696 346 lines LGJ-150 403 0.0719+j0.1427

[0064] To simplify the calculation, the influence of system load and nonlinear components on the loop current is ignored.

[0065] At the 369 switch of the 35kV busbar outgoing line of the #3 transformer in station A, the voltage per unit value of the 35kV busbar of the #3 transformer in station A is set to 1. The voltage per unit value of the 110kV busbar of the #3 transformer in station A is 1∠-30°, and the voltage per unit value of the 35kV busbar of the #2 transformer in station B is 1∠-30°; the reference transformation ratio of the low-middle side of the #3 transformer in station A and the high-middle side of the #2 transformer in station B is:

[0066] (115.5 / 115):(36.75 / 37):(110 / 115):(38.5 / 37)=1.00:0.99:0.96:1.04. To simplify the calculation, the transformation ratio is taken as 1:1:1:1.

[0067] After converting the impedance per unit value, the total loop impedance per unit value is:

[0068] Z∑*=0.2519+j0.7866

[0069] Assuming the positive direction of the loop current is from the low-voltage side of station A through the loop to the medium-voltage side of station B, the normalized value of the loop current is:

[0070]

[0071] After converting the vector into a complex number, it becomes:

[0072]

[0073] Convert the loop current nominal value into the nominal value of the current of each voltage level line. The nominal value of the current flowing through the 35 kV line is:

[0074] I 环35 =I M *×I B35 =I M *×1560.4=977.9A

[0075] The nominal value of the current flowing through the 110kV line is:

[0076] I 环110 =I M *×I B110 =I M *×502=314.6A

[0077] Solution

[0078] Since the incoming switch of station C has no protection setting and no protection verification is performed, this solution uses switch 352 of station C as the closing switch of the loop, selects switch 346 of station B as the main opening switch of the loop, and selects switch 369 of station A as the backup opening switch of the loop. In order to ensure that the loop is opened as soon as possible after closing the loop and reduce the impact of the loop current on the system equipment, a protection device is used to realize automatic opening of the loop. The opening solution is to adjust the protection setting and protection time limit of the main opening switch and the backup opening switch so that their action setting is less than the closing current and greater than the load current, so as to ensure that the opening switch can operate reliably after the system is closed.

[0079] The set value is adjusted as follows: the set value of the protection section III of the switch 346 at station B is adjusted to 300A, and the protection time limit is adjusted to 0.1s; the set value of the protection section III of the switch 369 at station A is adjusted to 300A, and the protection time limit is adjusted to 0.3s. Other protection set values ​​and protection time limits remain unchanged.

[0080] The system equivalent circuit diagram is as follows Figure 2 As shown, the total loop impedance per unit is:

[0081] Z∑*=0.1195+j0.5186

[0082] The per unit value of the circulating current is:

[0083]

[0084] The nominal value of 35kV circulating current is:

[0085] I 环35 =I M *×I B35 =I M *×1560.4=1517.75A

[0086] The nominal value of 110kV circulating current is:

[0087] I 环110 =I M *×I B110 =I M *×502=488.28A

[0088] Analyze the loop device current:

[0089] Table 7: Closed loop current unit A under normal mode

[0090]

[0091] It can be seen from the above table that the loop current is too large under normal conditions, so the 35kV Peili Village Station needs to be transferred to the Xidongmen Station for power supply.

[0092] Table 8: Loop current after reverse supply mode Unit A

[0093]

[0094]

[0095] Loop equipment setting statistics:

[0096] The loop setting diagram of the power grid with a 30° angle difference is shown in the figure below: Figure 3 As shown;

[0097] Table 9: Loop equipment current protection settings (primary values)

[0098] Substation Loop switch I-stage setting Period I Section II fixed value Ⅱ Period Section III fixed value Period III Station A AC Line 369 3600A 0S 1320A 0.3S 720A 1.5S Chengxi Station AB line 169 none none none none none none Chengxi Station BC Line 334 4800A .0S 1320A 0.3S 806.4A 1.5S Station C ACT Wiring 389 none none none none none none Station C BC Line 390 none none none none none none

[0099] According to the circulation calculation results, after comprehensive analysis of the relevant protection actions, a closing protection shutdown and fixed value adjustment diagram is formulated (such as Figure 4 Note: The adjustment of the protection setting value can only take into account the maximum load current allowed by the entire loop.

[0100] In order to avoid the workload of maintenance personnel to modify temporary set values ​​on site during the loop opening and closing process, a set value set in other set value areas (it is recommended to be set to area 1) is re-issued for the switches (configured with protection) that need to be opened in the loop, which is specifically used for the operation personnel to start and stop the system when the loop is opened.

[0101] During on-site operation, the 334 switch of the BC line of station B was set as the de-looping switch, and the set values ​​of the first, second and third sections were all set to 200A, with a time limit of 0s (according to statistical values, the load current of the 334BC line at 14 o'clock is not greater than 100A. In order to quickly trip the 334 switch to de-loop the loop when the closing loop instantaneous protection device reliably senses the closing loop current, the set value of the 334 switch is set to 200A according to the load current). The 369 switch of the AC line is a backup tripping switch. The set value of the 369 switch of the AC line cannot be changed online, so the set value of the 369 switch is not modified.

[0102] Note that after the loop is released, the setting area of ​​the loop release switch needs to be adjusted back to the setting area during normal operation to prevent false tripping. Each time the loop is closed, the closing switch current value can be recorded through the D5000 system and the protection device action sampling value (note that before closing the loop, the sampling definition of the D5000 system A station 369 switch and B station 334 switch should be set to 1 second in advance) to provide data support for the next adjustment of the closing setting value.

[0103] In order to make the unblocking switch protection device act quickly, the unblocking setting value is considered according to the load current of the 35kV operating switch of the C station. The scheme is shown in Table 10 (primary value):

[0104] Table 10: Temporary settings of loop equipment

[0105] Substation Loop switch I-stage setting Period I Section II fixed value Ⅱ Period Section III fixed value Period III Station B BC Line 334 200A 0S 200A 0S 200A 0S

[0106] Closing loop transient process analysis:

[0107] For the closing operation with a 30° angle difference, in addition to fully considering the size of the closing current, the thermal effect of the electrical equipment in the loop (mainly transformers and lines) and the existence time of the circulating current are all factors that need to be considered in the closing operation.

[0108] 1. Transformer thermal effect and time window calculation:

[0109] The following is a brief description of the thermal effect and time window of transformers based on the current domestic research results.

[0110] When the low-voltage power grid loop current of the power system flows through the transformer, the copper windings and iron core inside the transformer will produce a certain thermal effect, causing the system temperature to rise. In the short-circuit bearing capacity of the power transformer, for the oil-immersed transformer winding coil, the temperature rise should not exceed 250°C within 2S during the short-circuit period. Assuming that the transformer inter-turn insulation does not absorb heat, the winding temperature is calculated by considering the resistance change. The initial rated operating state of the transformer (ambient temperature is 40°C, average temperature rise is 65°C) is 105°C. According to the short-circuit current density and current duration of 10S when the transformer is running under extreme conditions, and according to the formula for the average temperature rise of the winding, the 10S average temperature rise of the transformer winding can be calculated to be 77.86°C. It can be seen that the winding temperature reaches 182.86°C, which is still less than the limit temperature of 250°C of the oil-immersed transformer winding. Therefore, from the analysis of the thermal effect principle of short-circuit current, the transformer allows the short-circuit current to last longer than 10S. The commutation duration is analyzed based on the transient characteristics of the thermal effect of the transformer. The "Oil-immersed Power Transformer Load Guide Standard" stipulates that the maximum allowable value for the transformer to operate beyond the rated limit is 1.5 times the rated value, the maximum allowable temperature of the winding coil is 120°C, the maximum allowable temperature of other metal parts is 140°C, and the top oil temperature is 105°C. The temperature rise process of the transformer is a process of heating and transitioning to a stable state. The load loss of the main transformer is heating for the winding, and the total loss is heating for the oil. The absorbed heat energy value is partly due to the temperature rise, and the other part is dissipated to the surrounding low-temperature medium through heat transfer. Taking into account the temperature limit, life, aging rate, etc. of the transformer, the maximum allowable value of the hot spot temperature of the transformer is 98°C. The analysis shows that during the closing period, the temperature rise rate of the transformer winding is much greater than the temperature rise rate of the transformer oil. Therefore, the thermal effect of the transformer mainly considers the hot spot temperature limit of the winding coil. Through a large amount of data analysis, it is concluded that the time for the hot spot temperature of the main transformer winding to reach the transformer winding life aging benchmark temperature value (98°C) is more than 25S. Therefore, this time window is the tolerable range of the thermal effect and thermal life of the transformer in the loop.

[0111] 2. Line thermal effect and time window calculation:

[0112] Assuming the transmission line is a uniform conductor, the conductor will increase in temperature due to the current passing through it. Excessive line temperature will affect the transmission efficiency and life of the line to a certain extent. my country stipulates that under normal circumstances, the maximum tolerable transmission temperature of steel-core aluminum stranded wire is 70°C. According to the formula for the allowable time from the conductor temperature during normal operation to the temperature limit, the temperature rise curve of the transmission line can be drawn. From the temperature rise curve, it can be seen that the time for the transmission line to reach the limit temperature from normal operation is more than 7S. Therefore, this time window is the tolerable range of the thermal effect and thermal life of the line in the ring.

[0113] Through the analysis of the thermal effects of the transformer and the line, we can see that we set the protection action time to 0-0.5S, which is much shorter than the time it takes for the transformer and the line to reach the limit temperature. Therefore, the transient characteristics of the closing process meet the grid stability requirements.

[0114] 3. Notes

[0115] Since the 35kV line is overloaded when closing the loop, the closing time should be controlled as short as possible. The calculated circulating current value and closing time should be within the allowable overload range of the line and main transformer in the loop.

[0116] To ensure that the loop can be released as soon as possible when the loop is closed, an automatic release point can be set in the line protection: the overcurrent protection current setting value of the line is less than the circulating current value. When the loop is closed, the voltage value changes little, so the low voltage lock must also be released.

[0117] In order to reduce the loop current when closing the loop, the power supply voltage can be appropriately lowered while ensuring that the voltage is qualified to reduce the circulating current.

[0118] The loop of the loop should be as large as possible to increase the impedance and reduce the circulating current. For a smaller loop, if the circulating current value is calculated to exceed the line stability limit and the allowable overload value of the main transformer, the closing operation is not allowed under normal circumstances. If the automatic release point of the relay protection is set, since its current is less than the fault current, even if the closing current is greater than the equipment limit, if the automatic release time of the relay protection and the current value are less than the thermal stability and dynamic stability limits of the equipment, the closing operation can be performed.

[0119] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0120] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for safe control of closed-loop operation of a power grid with an angle difference, characterized in that: include: S1. Establish an equivalent circuit model including a 30° angle difference ring network, calculate the per unit value and nominal value of the closed loop current, and determine the voltage phase difference of each node in the ring network; S2. Check the line protection setting value, transformer and line overload capacity in the ring network, and obtain the allowable current threshold and short-time overload multiple of the equipment; S3. Configure the temporary protection setting area in the unblocking switch, adjust the overcurrent protection setting to the preset value that avoids the maximum load current, and set the action time limit to 0 seconds; S4: When executing the closing operation, the opening switch current is monitored in real time. When it is detected that the closing current exceeds the temporary set value, the 0-second delay tripping is started to open the loop; S5. Based on the transformer winding hot spot temperature model and the line temperature rise curve, the allowable closing time window is calculated and the closing operation is controlled to be completed within 25 seconds. After closing the loop, the unclosing switch is automatically switched to the original set value area, and the closing current data is recorded for set value optimization.

2. A method for controlling the closed-loop operation safety of a power grid with an angle difference according to claim 1, characterized in that: The closed-loop current calculation in S1 includes: The total loop impedance is calculated based on the per-unit value method, the potential difference circulating current caused by the angle difference is calculated using the voltage source superposition method, and the nominal values ​​of the circulating current on the 35kV side and the 110kV side are obtained through reference parameter conversion.

3. The method for controlling the closed-loop operation safety of a power grid with an angle difference according to claim 1, characterized in that: The setting of the temporary protection setting value in S3 satisfies: The overcurrent protection setting of the ring-breaking switch is 1.2 to 1.5 times the maximum value of the circulating current and higher than 150% of the current load current. The action time limit is 0 seconds.

4. The method for controlling the closed-loop operation safety of a power grid with an angle difference according to claim 1, characterized in that: Release the low voltage locking function of the open loop switch, and synchronously adjust the D5000 system sampling frequency to 1 second level to record the instantaneous current waveform data of the closed loop in real time.

5. The method for controlling the closed-loop operation safety of a power grid with an angle difference according to claim 1, characterized in that: Based on the transformer winding hot spot temperature limit of 98°C and the line temperature rise limit of 70°C, the allowable closing duration is calculated using the short-circuit thermal stability equation, and the protection action time is set to ≤0.5 seconds.

6. The method for controlling the closed-loop operation safety of a power grid with an angle difference according to claim 1, characterized in that: Before closing the loop, adjust the bus voltage at the power supply end to 95% to 98% of the nominal voltage, and give priority to loop paths with larger impedance to reduce the circulating current amplitude.

7. A loop-closed operation safety control system for a power grid with an angle difference, used to implement any loop-closed operation safety control method for a power grid with an angle difference according to any one of claims 1 to 6, characterized in that: include: A circulation calculation module is used to construct an equivalent circuit and output a circulation prediction value; The fixed value management module configures the multi-section protection fixed value library and the temporary fixed value issuing interface; Thermal effect analysis module, which calculates the temperature rise of equipment based on real-time current data and generates time window alarms; The automatic loop-breaking execution module triggers the switch to trip and synchronously switches the set value area according to the temporary set value.

8. A loop-closed operation safety control system for an angle-difference power grid according to claim 7, characterized in that: The set value management module is integrated into the protection device, supports online switching of set value areas and does not require manual on-site modification.

9. A loop-closed operation safety control system for an angle-difference power grid according to claim 7, characterized in that: The automatic loop release execution module communicates with the SCADA system to obtain load current data in real time and dynamically adjust the temporary set value threshold.

10. A computer-readable storage medium storing a computer program, characterized in that: When the program is executed by a processor, any one of the methods for controlling the closed-loop operation of a power grid with an angle difference described in claims 1-6 is implemented.

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