A black start system and method for 110kV system assisting 500kV system thermal power unit

Abstract

The present invention discloses a 110kV system assisted 500kV system thermal power unit black start system and method, comprising a 110kV system bus, a 500kV system and a thermal power generator, wherein the 110kV system bus and the 500kV system are connected via a first three-winding transformer and a second three-winding transformer. By simulating a power outage in the 500kV system, the safety diesel generator of the thermal power generator is put into hot standby mode. The thermal power unit realizes the electric trip function by tripping the reverse power, further switching the plant power supply to ensure the safety of the plant auxiliary equipment of the thermal power unit. The thermal power unit relies on the 110kV system bus to provide power, implements the ignition, rushing, constant speed and voltage building of the thermal power unit, and simultaneously connects the thermal power unit to the 110kV system through the 6kV low-voltage system, and then disconnects the 110kV system power switch to achieve stable operation of the thermal power with its own plant power supply, further closes the 500kV circuit breaker, and restores the power supply of the 500kV system; when the 110kV system loses power, the 500kV system restores the power supply of the 110kV system through the second three-winding transformer and the first three-winding transformer.

Description

Technical Field

[0001] The invention belongs to the technical field of black start of thermal power plants, and in particular relates to a black start system and method for a 110kV system assisting a 500kV system thermal power unit. Background Art

[0002] Hydropower and gas turbines have become the first-tier black start power supply points for my country's power system due to their unique natural advantages. However, it is well known that the limited hydropower and gas turbines in the first echelon are not enough to support the load supply of the huge power grid. The main purpose of the first echelon black start power supply of the power system is to quickly restore power supply to the entire network and important loads, and the other purpose is to ignite the second echelon units that consume primary energy. Among the primary energy units, the largest proportion is the thermal power unit. Generally speaking, thermal power units do not have the ability to black start. After some thermal power units are transformed through FCB island operation, that is, after the power grid loses power, the thermal power units quickly switch to generators with their own factory power operation, waiting for the order to send out power. The main problem with this black start method is that the control of thermal power units is extremely complex, and the conditions for achieving long-term reliable operation of FCB islands are extremely harsh. According to actual data statistics, the long-term stable operation of thermal power FCB islands has the risk of failure due to its complex process, and some experiments have proved this problem. All thermal power units in my country are equipped with backup power supplies, which are connected to the same network as the power supply sent from the machine end. Therefore, when the power grid loses power, the backup power supply and the power supply line will lose power at the same time. The startup process of the thermal power unit must rely on the backup power supply to provide energy. After the power grid loses power, the power supply of the first echelon mainly supplies power to the backup power supply of the second echelon, and assists its normal operation before it can be successfully ignited, rushed, and built up. my country has two major power grid systems, the 110kV system and the 500kV system. Due to different geographical environments, the power supply types of the two major power grids are different. The probability of simultaneous power failure of the two major power grids is very low. There has been no accident of simultaneous power failure in decades of operation. The advantages of the two major power grids are used to help the thermal power units to smoothly implement black start and realize the rapid reconstruction of the power grid that has lost power. That is, in the case of black start, the one that has not lost power helps the other to restore power supply. The following problems exist in the currently known thermal power black start technologies: (1) Currently, most thermal power black starts are implemented through the FCB self-powered island operation mode, which is difficult to control and has limitations such as how to ensure long-term stable operation of the island. (2) Currently, when thermal power units are black started and operated in FCB island mode, most of them are achieved through boiler bypass load shedding, that is, the thermal power units instantly switch from a high load state to a low load operation with their own power supply after losing power. There have been no cases of switching from low load to high load in a black start situation. (3) Currently, there is no relevant literature on the participation of thermal power units in the black start of two major power grids in mutual start-up. Summary of the invention

[0003] In view of the problems existing in the prior art, the present invention provides a black start system and method for a 110kV system to assist a 500kV system thermal power unit, so as to achieve black start coordination when two major power grids lose power, stabilize the constructed power grid, and reduce the impact of power outages.

[0004] The present invention is achieved through the following technical solutions:

[0005] A 110kV system assisting a 500kV system thermal power unit black start system, comprising a 110kV system bus, a first three-winding transformer, a first 6kV bus, a second three-winding transformer, a thermal power generator and a 500kV system;

[0006] One end of the 110kV system bus is connected to the 110kV system, and the other end is connected to the high-voltage side of the first three-winding transformer via the first 110kV switch, the 100kV circuit breaker, and the second 110kV switch in sequence; the low-voltage side A branch of the first three-winding transformer is connected to the first 6kV bus via the first 6kV switch; the low-voltage side B branch of the first three-winding transformer is connected to the second 6kV bus via the second 6kV switch;

[0007] The first 6kV bus is connected to the low-voltage side A branch of the second three-winding transformer via the third 6kV switch, the second 6kV bus is connected to the low-voltage side B branch of the second three-winding transformer via the fourth 6kV switch, and the high-voltage side of the second three-winding transformer is connected to the 500kV system via the main transformer, the 500kV circuit breaker, and the 500kV knife switch in sequence;

[0008] The output end of the thermal power generator is connected to the high voltage side of the second three-winding transformer.

[0009] Preferably, it also includes a first grounding switch and a second grounding switch;

[0010] One end of the first grounding switch is connected to the neutral point of the thermal generator, and the other end is connected to the ground via a grounding resistor;

[0011] One end of the second grounding switch is connected to the neutral point on the high-voltage side of the first three-winding transformer, and the other end is connected to the ground. The neutral point on the high-voltage side of the main transformer is directly connected to the ground.

[0012] 3. According to claim 2, a 110kV system assisted 500kV system thermal power unit black start system, the 110kV system bus operates normally, and when the 500kV system loses power, the first 110kV knife switch, 100kV circuit breaker, second 110kV knife switch, fourth 6kV switch, third 6kV switch, second grounding knife switch, first grounding knife switch, 500kV circuit breaker, and 500kV knife switch are all in a closed state; the thermal generator is shut down, the 500kV circuit breaker, fourth 6kV switch and third 6kV switch are disconnected, and the second 6kV switch and first 6kV switch are closed.

[0013] Furthermore, when the thermal generator performs a black start, the thermal generator is connected to the 110kV system bus, the fourth 6kV switch is closed, the second 6kV switch and the first 6kV switch are disconnected, the thermal generator realizes island operation with its own factory power supply, the 500kV circuit breaker is closed, and the 500kV system is powered by the thermal generator.

[0014] Furthermore, when the 110kV system bus loses power, the 500kV system operates normally, the first 110kV switch, 100kV circuit breaker, the second 110kV switch, the fourth 6kV switch, the third 6kV switch, the first grounding switch, the 500kV circuit breaker, the 500kV switch and the second grounding switch are all in a closed state, the second 6kV switch and the first 6kV switch are closed, and the 110kV system bus is restored to power supply by the 500kV system.

[0015] A black start method for a 110 kV system assisting a 500 kV system thermal power unit comprises the following steps:

[0016] 1) Put the fire-powered generator into operation as a security diesel generator and put it in hot standby mode, and proceed to step 2);

[0017] 2) stopping the thermal power generator by using a trip reverse power mode, and proceeding to step 3);

[0018] 3) The 500kV circuit breaker is opened, and the process goes to step 4);

[0019] 4) The demagnetization switch of the thermal power generator is opened, and the process proceeds to step 5);

[0020] 5) The third 6kV switch is opened, and the process goes to step 6);

[0021] 6) The fourth 6kV switch is opened, and the process goes to step 7);

[0022] 7) The first 6kV switch is closed, and the process goes to step 8);

[0023] 8) The second 6kV switch is closed, and the process goes to step 9);

[0024] 9) Confirm that the thermal power generator and the main transformer are in a no-pressure state, and proceed to step 10);

[0025] 10) Confirm that the 110kV system busbar is operating normally, and proceed to step 11);

[0026] 11) The speed of the thermal power generator is increased to 3000 r / min, and the process proceeds to step 12);

[0027] 12) The voltage at the thermal power generator end is built up to 20 kV, and the process goes to step 13);

[0028] 13) Using the synchronization device to close the third 6kV switch, and proceed to step 14);

[0029] 14) Manually close the fourth 6kV switch and proceed to step 15);

[0030] 15) Manually disconnect the first 6kV switch and proceed to step 16);

[0031] 16) Manually disconnect the second 6kV switch and proceed to step 17);

[0032] 17) The thermal power generator carries the second three-winding transformer load to maintain island operation, and the process goes to step 18);

[0033] 18) Close the 500kV circuit breaker and restore the thermal power generator to supply power to the 500kV system.

[0034] Furthermore, in the step 1), the security diesel generator is started to no-load mode, the voltage is built up to the rated 400V, and adjusted to hot standby state.

[0035] Furthermore, in the step 2), the thermal generator is stopped by using a program-trip reverse power mode, and the thermal generator protection device automatically starts a quick-cut device to switch between the working power supply and the standby power supply.

[0036] Furthermore, in step 13), the synchronization device adjusts and captures the time when the secondary side signals of the third 6kV switch and the first 6kV switch voltage transformer are of the same frequency, voltage and phase, and closes the third 6kV switch.

[0037] Compared with the prior art, the present invention has the following beneficial technical effects:

[0038] The present invention simulates a power failure of a 500kV system, puts a safety diesel generator of a thermal power generator into a hot standby state, realizes an electric trip function of the thermal power unit by tripping reverse power, further switches to factory power, and ensures the safety of factory auxiliary machines of the thermal power unit. The thermal power unit relies on a 110kV system busbar to provide power, implements ignition, rushing, constant speed, and voltage building of the thermal power unit, and simultaneously realizes that the thermal power unit is connected to the 110kV system through a 6kV low-voltage system, then disconnects the 110kV system power switch, realizes stable operation of the thermal power unit with factory power, further closes the 500kV circuit breaker, and restores the power supply of the 500kV system; when the 110kV system loses power, the 500kV system restores the power supply of the 110kV system through the second three-winding transformer and the first three-winding transformer; the present invention provides a novel thermal power black start system and method, which, in extreme cases, helps the power grid to quickly get rid of unfavorable conditions, restores the normal operation of the power grid, and reduces the impact on human production and life.

[0039] Furthermore, the present invention starts the security diesel generator set during black start to prevent the failure of the factory power supply switching, causing the auxiliary machine of the thermal power generator to lose power and damage the main body of the equipment.

[0040] Furthermore, the present invention simulates a power failure in a 500kV system and safely shuts down the thermal power unit by tripping the reverse power, thereby preventing the turbine from overspeeding due to the main steam valve not being tightly closed during shutdown, and quickly switching the thermal power unit to factory power, thereby ensuring the safety of the main equipment of the thermal power unit.

[0041] Furthermore, the present invention utilizes a 110kV system to provide black start power for the thermal power unit. After the thermal power unit is successfully black started, the 110kV system and the 500kV system are interconnected in a synchronous manner, and the 110kV system is exited, so that the thermal power unit can operate stably from low load to high load with its own factory power, and the thermal power unit is further sent to the 500kV system to restore power supply to the 500kV system.

[0042] Furthermore, in the present invention, when the 110kV system loses power, the 500kV system supplies power to the 110kV system through the second three-winding transformer and the first three-winding transformer, thereby enabling the 500kV system to assist the 110kV system in a black start. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic diagram of the principle of the present invention.

[0044] Figure 2 This is a schematic diagram of the principle of simulating power failure of a 500kV system according to the present invention.

[0045] Figure 3 This is a schematic diagram of the principle of black starting a 500kV system from a 110kV system of the present invention.

[0046] Figure 4 This is a schematic diagram of the principle of a 110kV system black start of a 500kV system according to the present invention.

[0047] Figure 5 This is the terminal voltage waveform during the black start of the thermal power generator of the present invention.

[0048] In the figure: 1-110kV system bus; 2-first 110kV knife switch; 3-100kV circuit breaker; 4-second 110kV knife switch; 5-first three-winding transformer; 6-second 6kV switch; 7-first 6kV switch; 8-second 6kV bus; 9-first 6kV bus; 10-fourth 6kV switch; 11-third 6kV switch; 12-second three-winding transformer; 13-grounding resistor; 14-first grounding knife switch; 15-thermal generator; 16-main transformer; 17-500kV circuit breaker; 18-500kV knife switch; 19-500kV system; 20-second grounding knife switch. DETAILED DESCRIPTION

[0049] The present invention is further described in detail below in conjunction with specific embodiments, which are intended to explain the present invention rather than to limit it.

[0050] The present invention can solve the technical problem of thermal power black start. After the 500kV system loses power, the 110kV system is used to start the thermal generator to further restore the power supply of the 500kV system; at the same time, after the 110kV system loses power, the 500kV system can be used to assist the 110kV system in restoring power. It can be realized that when the 500kV system loses power, the 110kV system is used to start the thermal power unit and restore the power supply of the 500kV system; when the 110kV system loses power, the 500kV system is used to assist the 110kV system in restoring power. The present invention provides a new thermal power black start technology, which realizes the black start coordination when the two major power grids lose power, thereby building a strong power grid and reducing the impact and losses caused by power grid outages on the entire society.

[0051] The present invention provides a 110kV system assisting a 500kV system thermal power unit black start system, such as Figure 1 As shown, it includes a 110kV system bus 1, a first three-winding transformer 5, a first 6kV bus 9, a second three-winding transformer 12, a thermal power generator 15 and a 500kV system 19;

[0052] One end of the 110kV system bus 1 is connected to the 110kV system, and the other end is connected to the high-voltage side of the first three-winding transformer 5 via the first 110kV switch 2, the 100kV circuit breaker 3, and the second 110kV switch 4 in sequence; the low-voltage side A branch of the first three-winding transformer 5 is connected to the first 6kV bus 9 via the first 6kV switch 7; the low-voltage side B branch of the first three-winding transformer 5 is connected to the second 6kV bus 8 via the second 6kV switch 6;

[0053] The first 6kV bus 9 is connected to the low-voltage side A branch of the second three-winding transformer 12 via the third 6kV switch 11, the second 6kV bus 8 is connected to the low-voltage side B branch of the second three-winding transformer 12 via the fourth 6kV switch 10, and the high-voltage side of the second three-winding transformer 12 is connected to the 500kV system 19 via the main transformer 16, the 500kV circuit breaker 17, and the 500kV knife switch 18 in sequence;

[0054] The output end of the thermal generator 15 is connected to the high-voltage side of the second three-winding transformer 12; the rated capacity of the thermal generator 15 is 300MW, the 110kV system bus 1 is connected to the 110kV level power grid, the 500kV system 19 is connected to the 500kV level voltage, and the 110kV system bus 1 is used to start the thermal generator 15 and restore the 500kV system 19 after the 500kV system 19 loses power.

[0055] In this embodiment, it also includes a first grounding switch 14 and a second grounding switch 20;

[0056] One end of the first grounding switch 14 is connected to the neutral point of the thermal generator 15, and the other end is connected to the ground via the grounding resistor 13;

[0057] One end of the second grounding switch 20 is connected to the neutral point of the high-voltage side of the first three-winding transformer 5, and the other end is connected to the ground. The neutral point of the high-voltage side of the main transformer 16 is directly connected to the ground; the transformation ratio of the first three-winding transformer 5 is 110kV / 6.3kV / 6.3kV, the transformation ratio of the second three-winding transformer 12 is 20kV / 6.3kV / 6.3kV, the rated output voltage of the thermal generator 15 is 20kV, and the transformation ratio of the main transformer 16 is 525kV / 20kV; the grounding resistor 13 is used to ground the neutral point of the thermal generator.

[0058] like Figure 2As shown, the 110kV system bus 1 operates normally. When the 500kV system 19 loses power, the 500kV circuit breaker 17 protection cabinet reclosing is exited. The first 110kV switch 2, 100kV circuit breaker 3, second 110kV switch 4, fourth 6kV switch 10, third 6kV switch 11, second grounding switch 20, first grounding switch 14, 500kV circuit breaker 17, 500kV switch 18 are all in a closed state. The thermal generator 15 uses the reverse power trip to open the reverse power. The 500kV circuit breaker 17 is disconnected, the fast-cut device of the thermal generator 15 disconnects the fourth 6kV switch 10 and the third 6kV switch 11, the second 6kV switch 6 and the first 6kV switch 7 are closed, and the load of the second three-winding transformer 12 is switched to the 110kV system bus 1 for power supply; the thermal generator 15 and the main transformer 16 are in a no-pressure state; the reverse power large gate shutdown method is adopted to prevent the thermal generator 15 from overspeeding due to the failure of all turbine blades to be closed.

[0059] like Figure 3 As shown, when the thermal generator 15 performs black start, the thermal generator 15 has a fixed speed of 3000r / min, the terminal voltage is 20kV, the third 6kV switch 11 is closed by the synchronization device, the thermal generator 15 is connected to the 110kV system bus 1, the fourth 6kV switch 10 is manually closed, the load of the second 6kV bus 8 and the first 6kV bus 9 is transferred to the thermal generator 15, the active power of the first three-winding transformer 5 is reduced to zero, the second 6kV switch 6 and the first 6kV switch 7 are disconnected, the thermal generator 15 realizes self-contained plant power island operation, the 500kV circuit breaker 17 is closed, and the 500kV system 19 is restored to be powered by the thermal generator 15, the excitation voltage of the thermal generator 15 is 103V, the active power is 16MW, the reactive power is 15Mvar, and the high-voltage side voltage of the main transformer 16 is 530kV and the current is 24A.

[0060] like Figure 4 As shown, when the 110kV system bus 1 loses power, the 500kV system 19 operates normally, the first 110kV switch 2, 100kV circuit breaker 3, second 110kV switch 4, fourth 6kV switch 10, third 6kV switch 11, first earthing switch 14, 500kV circuit breaker 17, 500kV switch 18 and second earthing switch 20 are all in a closed state, the second 6kV switch 6 and the first 6kV switch 7 are closed, and the 110kV system bus 1 is restored to be powered by the 500kV system 19. A method for black starting of a 110kV system-assisted 500kV system thermal power unit comprises the following steps:

[0061] 1) Put the thermal power generator 15 into the security diesel generator and put it in hot standby state, and enter step 2);

[0062] 2) Stop the thermal generator 15 by using the reverse power mode of tripping, and proceed to step 3);

[0063] 3) The 500kV circuit breaker 17 is opened, and the process goes to step 4);

[0064] 4) The demagnetization switch of the thermal generator 15 is opened, and the process proceeds to step 5);

[0065] 5) The third 6kV switch 11 is opened, and the process goes to step 6);

[0066] 6) The fourth 6kV switch 10 is opened, and the process goes to step 7);

[0067] 7) The first 6kV switch 7 is closed, and the process goes to step 8);

[0068] 8) The second 6kV switch 6 is closed, and the process goes to step 9);

[0069] 9) Confirm that the thermal power generator 15 and the main transformer 16 are in a no-pressure state, and proceed to step 10);

[0070] 10) Confirm that the 110kV system bus 1 operates normally, and proceed to step 11);

[0071] 11) The speed of the thermal generator 15 is increased to 3000 r / min, and the process proceeds to step 12);

[0072] 12) The voltage at the end of the thermal generator 15 is built up to 20 kV, and the process goes to step 13);

[0073] 13) Using the synchronization device to close the third 6kV switch 11, and proceed to step 14);

[0074] 14) Manually close the fourth 6kV switch 10 and proceed to step 15);

[0075] 15) Manually disconnect the first 6kV switch 7 and proceed to step 16);

[0076] 16) Manually disconnect the second 6kV switch 6 and proceed to step 17);

[0077] 17) The thermal power generator 15 carries the second three-winding transformer 12) load to maintain island operation, and enters step 18);

[0078] 18) Close the 500kV circuit breaker 17 and restore the thermal generator 15 to supply power to the 500kV system 19. In this embodiment, the security diesel generator is adjusted to the hot standby state to prevent the load switching failure between the second 6kV bus 8 and the first 6kV bus 9 from causing the thermal generator 15 to lose power. After the power failure, the security diesel generator is immediately switched off to ensure the safety of the unit.

[0079] In this embodiment, in the step 1), the security diesel generator is started to the no-load mode, the voltage is built up to the rated 400V, and adjusted to the hot standby state; in the step 2), the thermal generator 15 is stopped by the program jump reverse power mode, and the thermal generator 15 protection device automatically starts the quick-cut device to switch the working power supply and the standby power supply; in the step 13), the synchronization device adjusts and captures the time when the secondary side signals of the third 6kV switch 11 and the first 6kV switch 7 voltage transformer are at the same frequency, voltage and phase, and closes the third 6kV switch 11.

[0080] like Figure 5 As shown, the voltage parameters of the thermal generator 15 of the present invention run smoothly, the voltage indication is correct, and the voltage is built up to the rated value and maintained at 20kV.

[0081] The present invention discloses a 110kV system assisted 500kV system thermal power unit black start system and method, which mainly comprises a 110kV system bus, a 500kV system and a thermal power generator, wherein the 110kV system bus and the 500kV system are connected through a first three-winding transformer and a second three-winding transformer. The present invention simulates a power failure of a 500kV system, puts a safety diesel generator of a thermal power generator into a hot standby state, realizes an electric trip function of the thermal power unit by tripping reverse power, further switches to factory power, and ensures the safety of factory auxiliary machines of the thermal power unit. The thermal power unit relies on a 110kV system busbar to provide power, implements ignition, rushing, constant speed, and voltage building of the thermal power unit, and simultaneously realizes that the thermal power unit is connected to the 110kV system through a 6kV low-voltage system, then disconnects the 110kV system power switch, realizes stable operation of the thermal power unit with factory power, further closes the 500kV circuit breaker, and restores power supply to the 500kV system; when the 110kV system loses power, the 500kV system restores power supply to the 110kV system through the second three-winding transformer and the first three-winding transformer; the present invention provides a novel thermal power black start technology, realizes black start coordination when two power grids lose power, thereby building a strong power grid and reducing the impact and loss caused by power outages on the entire society.

[0082] The above is only a preferred embodiment of the patent of the present invention, and does not impose any limitation on the patent of the present invention. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A 110kV system assisting a 500kV system thermal power unit black start system, characterized in that: It includes a 110kV system busbar (1), a first three-winding transformer (5), a first 6kV busbar (9), a second 6kV busbar (8), a second three-winding transformer (12), a thermal power generator (15) and a 500kV system (19); One end of the 110kV system busbar (1) is connected to the 110kV system, and the other end is connected to the high-voltage side of the first three-winding transformer (5) via a first 110kV knife switch (2), a 100kV circuit breaker (3), and a second 110kV knife switch (4) in sequence; the low-voltage side A branch of the first three-winding transformer (5) is connected to the first 6kV busbar (9) via a first 6kV switch (7); the low-voltage side B branch of the first three-winding transformer (5) is connected to the second 6kV busbar (8) via a second 6kV switch (6); The first 6kV busbar (9) is connected to the low-voltage side A branch of the second three-winding transformer (12) via a third 6kV switch (11); the second 6kV busbar (8) is connected to the low-voltage side B branch of the second three-winding transformer (12) via a fourth 6kV switch (10); the high-voltage side of the second three-winding transformer (12) is connected to the 500kV system (19) via a main transformer (16), a 500kV circuit breaker (17), and a 500kV knife switch (18) in sequence; The output end of the thermal generator (15) is connected to the high voltage side of the second three-winding transformer (12).

2. A 110kV system assisting a 500kV system thermal power unit black start system according to claim 1, characterized in that: It also includes a first grounding switch (14) and a second grounding switch (20); One end of the first grounding switch (14) is connected to the neutral point of the thermal generator (15), and the other end is connected to the ground via a grounding resistor (13); One end of the second grounding switch (20) is connected to the neutral point on the high-voltage side of the first three-winding transformer (5), and the other end is connected to the ground. The neutral point on the high-voltage side of the main transformer (16) is directly connected to the ground.

3. A 110kV system assisting a 500kV system thermal power unit black start system according to claim 2, characterized in that: The 110kV system busbar (1) operates normally. When the 500kV system (19) loses power, the first 110kV knife switch (2), the 100kV circuit breaker (3), the second 110kV knife switch (4), the fourth 6kV switch (10), the third 6kV switch (11), the second grounding knife switch (20), the first grounding knife switch (14), the 500kV circuit breaker (17), and the 500kV knife switch (18) are all in a closed state; the thermal power generator (15) is shut down, the 500kV circuit breaker (17), the fourth 6kV switch (10), and the third 6kV switch (11) are disconnected, and the second 6kV switch (6) and the first 6kV switch (7) are closed.

4. A 110kV system assisting a 500kV system thermal power unit black start system according to claim 3, characterized in that: When the thermal power generator (15) performs a black start, the thermal power generator (15) is connected to the 110kV system bus (1), the fourth 6kV switch (10) is closed, the second 6kV switch (6) and the first 6kV switch (7) are disconnected, the thermal power generator (15) realizes island operation with its own factory power supply, the 500kV circuit breaker (17) is closed, and the 500kV system (19) is powered by the thermal power generator (15).

5. A 110kV system assisting a 500kV system thermal power unit black start system according to claim 4, characterized in that: When the 110kV system busbar (1) loses power, the 500kV system (19) operates normally, the first 110kV knife switch (2), the 100kV circuit breaker (3), the second 110kV knife switch (4), the fourth 6kV switch (10), the third 6kV switch (11), the first earthing knife switch (14), the 500kV circuit breaker (17), the 500kV knife switch (18) and the second earthing knife switch (20) are all in a closed state, the second 6kV switch (6) and the first 6kV switch (7) are closed, and the 110kV system busbar (1) is restored to be powered by the 500kV system (19).

6. A method for black starting of a 500kV thermal power unit assisted by a 110kV system, characterized in that: The system according to any one of claims 1 to 5 comprises the following steps: 1) Put the thermal power generator (15) into the safety diesel generator and put it in hot standby state, and enter step 2); 2) stopping the thermal generator (15) by using a trip reverse power mode, and proceeding to step 3); 3) The 500kV circuit breaker (17) is opened, and the process proceeds to step 4); 4) The demagnetization switch of the thermal generator (15) is opened, and the process proceeds to step 5); 5) The third 6kV switch (11) is opened, and the process proceeds to step 6); 6) The fourth 6kV switch (10) is opened, and the process proceeds to step 7); 7) The first 6kV switch (7) is closed, and the process proceeds to step 8); 8) The second 6kV switch (6) is closed, and the process goes to step 9); 9) Confirm that the thermal power generator (15) and the main transformer (16) are in a no-voltage state, and proceed to step 10); 10) Confirming that the 110 kV system busbar (1) is operating normally, proceeding to step 11); 11) The thermal generator (15) is accelerated to 3000 r / min, and the process proceeds to step 12); 12) The voltage at the end of the thermal generator (15) is built up to 20 kV, and the process proceeds to step 13); 13) Using the synchronization device to close the third 6kV switch (11), and proceeding to step 14); 14) Manually close the fourth 6kV switch (10) and proceed to step 15); 15) Manually disconnect the first 6kV switch (7) and proceed to step 16); 16) Manually disconnect the second 6kV switch (6) and proceed to step 17); 17) The thermal power generator (15) carries the second three-winding transformer (12) with its own load to maintain island operation, and the process goes to step 18); 18) The 500 kV circuit breaker (17) is closed, and the thermal generator (15) is restored to supply power to the 500 kV system (19).

7. The method for black starting a 500kV thermal power unit using a 110kV system as an auxiliary device according to claim 6, characterized in that: In the step 1), the security diesel generator is started to the no-load mode, the voltage is built up to the rated 400V, and adjusted to the hot standby state.

8. The method for black starting a 500kV thermal power unit using a 110kV system as an auxiliary device according to claim 6, characterized in that: In the step 2), the thermal generator (15) is stopped by using a trip reverse power mode, and the thermal generator (15) protection device automatically starts a quick-cut device to switch between the working power supply and the standby power supply.

9. The method for black starting a 500kV thermal power unit using a 110kV system as an auxiliary device according to claim 6, characterized in that: In step 13), the synchronization device adjusts and captures the time when the secondary side signals of the voltage transformers of the third 6kV switch (11) and the first 6kV switch (7) are of the same frequency, voltage and phase, and closes the third 6kV switch (11).

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