Switching method for steam source of water feed pump turbine

Abstract

The invention relates to a switching method for a steam source of a water feed pump turbine, which belongs to the technical field of water supply of thermal power generating units and comprises the following steps of: a, judging whether the running steam source pressure of the water feed pump turbine is lower than 1MPa or not, and if so, switching the steam source of the water feed pump turbine in time; b, judging whether the unit load is stable or not and whether the auxiliary steam pressure is stable or not, and if yes, switching a steam source of a water feeding pump turbine; c, judging whether the boiler feed water flow is more than 800t / h and has no fluctuation or not, and if yes, switching a steam source of a steam turbine of a feed pump; and d, judging whether two feed pump turbines operate at the same time or one feed pump turbine and the electric pump operate at the same time. The method has the advantages that the operation efficiency of a thermal power plant is improved, unplanned shutdown accidents are reduced, and the service life of equipment is prolonged, so that the stability and the economical efficiency of a whole power system are enhanced; rapid and safe switching of the steam source of the water feeding pump turbine is achieved, equipment damage and unit non-stop are avoided, and the safety and economic benefits of unit operation are enhanced.

Description

Technical Field

[0001] The invention relates to a method for switching a steam source of a water feed pump steam turbine, and belongs to the technical field of water feed for thermal power units. Background Art

[0002] During the operation of a thermal power plant, the stable operation of the feedwater pump steam turbine is crucial to the efficiency and safety of the entire power plant. The main function of the feedwater pump is to provide the required high-pressure feedwater to the boiler to maintain a normal steam cycle. In modern thermal power plants, the feedwater pump is usually driven by a steam turbine, and the steam source of the steam turbine usually comes from the power plant's own steam system, mainly including four-stage extraction steam (abbreviated as four-stage extraction) and auxiliary steam (abbreviated as auxiliary steam).

[0003] In the existing technology, steam source switching is a key operation in the operation of thermal power plants, especially when the load of the main steam turbine changes, it is necessary to switch from the four-extraction steam source to the auxiliary steam source, or vice versa. This switching operation requires extremely high accuracy and timeliness of the operation, because improper switching may cause drastic fluctuations in the boiler feed water flow, thereby affecting the stable operation of the boiler and even causing unplanned shutdown (non-stop) accidents. These accidents will not only lead to interruptions in power production, but may also cause damage to equipment, increase maintenance costs, and affect the economy and reliability of the power plant. Summary of the invention

[0004] In order to overcome the defects of the prior art, the present invention provides a method for switching the steam source of a feedwater pump turbine. The technical solution of the present invention is:

[0005] A method for switching a steam source of a feedwater pump steam turbine comprises the following steps:

[0006] a. Determine whether the steam source pressure of the feedwater pump steam turbine is lower than 1MPa. If so, switch the steam source of the feedwater pump steam turbine in time;

[0007] b. Determine whether the unit load is stable and the auxiliary steam pressure is stable. If so, switch the steam source of the feedwater pump turbine;

[0008] c. Determine whether the boiler feed water flow is above 800t / h and has no fluctuations. If so, switch the steam source of the feed water pump turbine;

[0009] d. Determine whether two feedwater pump steam turbines are running at the same time or one feedwater pump steam turbine and electric pump are running at the same time. If so, switch the steam source of the feedwater pump steam turbine;

[0010] e. Determine whether there is an alarm signal for the feed pump steam turbine, and whether the bearing vibration and casing temperature of the feed pump steam turbine are within the normal range. If so, switch the steam source of the feed pump steam turbine; f. Switch the steam source of the feed pump steam turbine. During the switching process of the feed pump steam turbine steam source, monitor and adjust the feed pump steam turbine parameters and boiler feed water flow.

[0011] In the step b, specifically:

[0012] Unit load stability judgment criteria:

[0013] Load change rate: Within 10 minutes, the load change rate of the unit shall not exceed ±1%;

[0014] Load fluctuation range: Within 10 minutes, the unit load fluctuation range does not exceed ±5MW; auxiliary steam pressure stability judgment standard:

[0015] Pressure change rate: within 10 minutes, the auxiliary steam pressure change rate shall not exceed ±0.5%;

[0016] Pressure fluctuation range: within 10 minutes, the fluctuation range of auxiliary steam pressure shall not exceed ±0.01MPa;

[0017] When the above stability standards of unit load and auxiliary steam pressure are met at the same time, it is judged to be in a stable state.

[0018] In the step f, when the steam source of the pump turbine is switched from the four-extraction steam source to the auxiliary steam source, the auxiliary steam source pressure of the unit is higher than the four-extraction pressure by more than 0.1 MPa; when the steam source of the pump turbine is switched from the auxiliary steam source to the four-extraction steam source, the four-extraction steam source pressure of the unit is higher than the auxiliary steam pressure by more than 0.1 MPa.

[0019] In the step f, when the steam source of the feedwater pump turbine is switched from the four-extraction steam source to the auxiliary steam source, the unit load is between 300MW and 400MW, specifically:

[0020] (1) Open the auxiliary steam source drain valve 6 hours in advance, open the manual and electric doors of the auxiliary steam source to the feedwater pump turbine, and fully warm the steam source pipeline;

[0021] (2) Before switching the steam source, fully open the manual steam gate from the auxiliary steam source to the feedwater pump turbine. The auxiliary steam source pressure of the unit is higher than the four-stage extraction pressure by more than 0.1 MPa. The electric steam gate from the cold section to the feedwater pump turbine is fully opened normally. Record the boiler feedwater flow, pump turbine speed, steam pressure before the shut-off valve of the pump turbine, and the opening of the low-pressure steam inlet regulating valve.

[0022] (3) Close the electric door of the steam source from the four pumping pumps to the feedwater pump turbine. When closing from 100% to 40%, close 10% each time; when closing from 40% to 20%, close 5% each time; when closing from 20% to 0%, close 3% each time. The interval between each closing operation is 1 minute. After each operation, check the boiler feedwater flow, pump turbine speed, steam pressure before the shut-off valve of the pump turbine, and the opening of the low-pressure steam inlet regulating valve. If there is no change, proceed to the next step;

[0023] (4) When the electric gates from the four-extraction steam source to the feedwater pump turbine steam source are fully closed, switch the electric gate mode to the remote position.

[0024] In the step f, when the steam source of the feedwater pump turbine is switched from the auxiliary steam source to the auxiliary steam source, the unit load is above 400MW, specifically:

[0025] (1) Open the drain valve of the four-stage steam source 2 hours in advance, open the electric door of the four-stage steam source to the water pump turbine, and fully warm up the steam source pipeline. Before switching the steam source, fully open the manual door of the four-stage steam source to the water pump turbine;

[0026] (2) When the steam source of the water pump turbine is switched from the auxiliary steam source to the four-extraction steam source, the four-extraction steam source pressure of the unit is higher than the auxiliary steam pressure by more than 0.1MPa, and the electric door from the cold section to the water pump turbine steam source is fully opened normally. Record the boiler feed water flow, water pump turbine speed, steam pressure before the water pump turbine shut-off valve, and the opening of the low-pressure steam inlet regulating valve;

[0027] (3) Close the electric door of the steam source from auxiliary steam to the water pump turbine. When closing from 100% to 40%, close 10% each time; when closing from 40% to 20%, close 5% each time; when closing from 20% to 0%, close 3% each time; each closing operation is performed at an interval of 1 minute. After each operation, check the boiler feed water flow, water pump turbine speed, water pump turbine shut-off valve front steam pressure and low pressure steam inlet regulating valve opening. If there is no change, proceed to the next step;

[0028] (4) After the electric door from the auxiliary steam to the water pump turbine is fully closed, switch the electric door mode to the remote position.

[0029] In the step f, when the steam source of the feedwater pump turbine is switched from the auxiliary steam source to the auxiliary steam source, the unit load is above 400MW, specifically:

[0030] When the auxiliary steam source pressure is lower than the four-extraction steam source pressure, the feed water pump turbine steam source will not be switched from the four-extraction steam source to the auxiliary steam source; when the four-extraction steam source pressure is lower than the auxiliary steam source pressure, the water pump turbine steam source will not be switched from the auxiliary steam source to the four-extraction steam source; when it must be operated, the operation should be slow, and the pressure deviation between the four-extraction steam source and the auxiliary steam source should be less than 0.2MPa.

[0031] When the auxiliary steam pressure is lower than the four-extraction pressure, and the steam source of the feedwater pump turbine is switched from the four-extraction steam source to the auxiliary steam source, check that the electric doors of the auxiliary steam source and the cold section to the steam source are fully open and normal, record the boiler feedwater flow rate and the opening of the low-pressure steam inlet regulating valve, and slowly close the electric door of the four-extraction to the water pump turbine steam source on site, from 100% to 40%, close 5% each time; from 40% to 20%, close 3% each time; from 20% to 0%, close 2% each time; each closing operation is 1 minute apart, and after each operation is completed, adjust the boiler feedwater flow rate to normal in time, and check that the boiler feedwater flow rate has returned to stability before proceeding to the next step;

[0032] During the switching process, if it is found that the opening of the low-pressure steam inlet regulating valve of the steam source is greater than 80%, stop the switching operation immediately, open the electric door from the four-extraction steam source to the feedwater pump turbine steam source, and restart the operation after the auxiliary steam source pressure is increased; after the electric door from the four-extraction steam source to the feedwater pump turbine steam source is fully closed, switch the electric door mode to the remote position.

[0033] When the pressure of the four-extraction steam source is lower than the pressure of the auxiliary steam source, and the steam source of the water pump turbine is switched from the auxiliary steam source to the four-extraction steam source, check that the electric doors from the four-extraction steam source and the cold section to the water pump turbine steam source are fully open and normal, record the boiler feed water flow rate and the opening of the low-pressure steam inlet regulating valve, and close the electric door from the auxiliary steam to the water pump turbine steam source. In the process of closing from 100% to 40%, close 5% each time; in the process of closing from 40% to 20%, close 3% each time; in the process of closing from 20% to 0%, close 2% each time; each closing operation The operation interval is 1 minute. After each operation, adjust the boiler feed water flow to normal in time. After each operation, check that there is no obvious change in the boiler feed water flow before proceeding to the next step. If it is found that the opening of the low-pressure steam inlet regulating valve of the pump turbine is greater than 80% during the switching process, stop the switching operation immediately, open the electric door from the auxiliary steam source to the pump turbine steam source, and operate again after the pressure of the four-extraction steam source increases. After the electric door from the auxiliary steam source to the pump turbine steam source is fully closed, cut the electric door mode to the remote position.

[0034] When switching the steam sources of the two feedwater pump turbines of the same unit, the operation should be carried out at an interval of more than 30 minutes to avoid causing disturbances in the boiler feedwater flow.

[0035] The advantages of the present invention are: through accurate pressure judgment, stability assessment, real-time monitoring, detailed operating steps, load-dependent switching strategy, safe pressure difference control and emergency response measures, a safer, more stable and efficient feedwater pump turbine steam source switching method is provided.

[0036] The above advantages help to improve the operating efficiency of thermal power plants, reduce unplanned shutdown accidents, and extend the service life of equipment, thereby enhancing the stability and economy of the entire power system, realizing the rapid and safe switching of the steam source of the feed pump turbine, avoiding equipment damage and unit unplanned shutdown, and enhancing the safety and economic benefits of unit operation. DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with specific embodiments, and the advantages and features of the present invention will become clearer as the description proceeds. However, these embodiments are exemplary only and do not constitute any limitation to the scope of the present invention. It should be understood by those skilled in the art that the details and forms of the technical solution of the present invention may be modified or replaced without departing from the spirit and scope of the present invention, but these modifications and replacements all fall within the scope of protection of the present invention.

[0038] The present invention relates to a method for switching a steam source of a feedwater pump steam turbine, comprising the following steps: a. judging whether the operating steam source pressure of the feedwater pump steam turbine is lower than 1MPa, and if so, switching the steam source of the feedwater pump steam turbine in time;

[0039] b. Determine whether the unit load is stable and the auxiliary steam pressure is stable. If so, switch the steam source of the feedwater pump turbine;

[0040] c. Determine whether the boiler feed water flow is above 800t / h and has no fluctuations. If so, switch the steam source of the feed water pump turbine;

[0041] d. Determine whether two feedwater pump steam turbines are running at the same time or one feedwater pump steam turbine and electric pump are running at the same time. If so, switch the steam source of the feedwater pump steam turbine;

[0042] e. Determine whether there is an alarm signal for the feed pump steam turbine, and whether the bearing vibration and casing temperature of the feed pump steam turbine are within the normal range. If so, switch the steam source of the feed pump steam turbine; f. Switch the steam source of the feed pump steam turbine. During the switching process of the feed pump steam turbine steam source, monitor and adjust the feed pump steam turbine parameters and boiler feed water flow.

[0043] In the step b, specifically:

[0044] Unit load stability judgment criteria:

[0045] Load change rate: Within 10 minutes, the load change rate of the unit shall not exceed ±1%;

[0046] Load fluctuation range: Within 10 minutes, the unit load fluctuation range does not exceed ±5MW; auxiliary steam pressure stability judgment standard:

[0047] Pressure change rate: within 10 minutes, the auxiliary steam pressure change rate shall not exceed ±0.5%;

[0048] Pressure fluctuation range: within 10 minutes, the fluctuation range of auxiliary steam pressure shall not exceed ±0.01MPa;

[0049] When the above stability standards of unit load and auxiliary steam pressure are met at the same time, it is judged to be in a stable state.

[0050] In the step f, when the steam source of the pump turbine is switched from the four-extraction steam source to the auxiliary steam source, the auxiliary steam source pressure of the unit is higher than the four-extraction pressure by more than 0.1 MPa; when the steam source of the pump turbine is switched from the auxiliary steam source to the four-extraction steam source, the four-extraction steam source pressure of the unit is higher than the auxiliary steam pressure by more than 0.1 MPa.

[0051] In the step f, when the steam source of the feedwater pump turbine is switched from the four-extraction steam source to the auxiliary steam source, the unit load is between 300MW and 400MW, specifically:

[0052] (1) Open the auxiliary steam source drain valve 6 hours in advance, open the manual and electric doors of the auxiliary steam source to the feedwater pump turbine, and fully warm the steam source pipeline;

[0053] (2) Before switching the steam source, fully open the manual steam gate from the auxiliary steam source to the feedwater pump turbine. The auxiliary steam source pressure of the unit is higher than the four-stage extraction pressure by more than 0.1 MPa. The electric steam gate from the cold section to the feedwater pump turbine is fully opened normally. Record the boiler feedwater flow, pump turbine speed, steam pressure before the shut-off valve of the pump turbine, and the opening of the low-pressure steam inlet regulating valve.

[0054] (3) Close the electric door of the steam source from the four pumping pumps to the feedwater pump turbine. When closing from 100% to 40%, close 10% each time; when closing from 40% to 20%, close 5% each time; when closing from 20% to 0%, close 3% each time. The interval between each closing operation is 1 minute. After each operation, check the boiler feedwater flow, pump turbine speed, steam pressure before the shut-off valve of the pump turbine, and the opening of the low-pressure steam inlet regulating valve. If there is no change, proceed to the next step;

[0055] (4) When the electric gates from the four-extraction steam source to the feedwater pump turbine steam source are fully closed, switch the electric gate mode to the remote position.

[0056] In the step f, when the steam source of the feedwater pump turbine is switched from the auxiliary steam source to the auxiliary steam source, the unit load is above 400MW, specifically:

[0057] (1) Open the drain valve of the four-stage steam source 2 hours in advance, open the electric door of the four-stage steam source to the water pump turbine, and fully warm up the steam source pipeline. Before switching the steam source, fully open the manual door of the four-stage steam source to the water pump turbine;

[0058] (2) When the steam source of the water pump turbine is switched from the auxiliary steam source to the four-extraction steam source, the four-extraction steam source pressure of the unit is higher than the auxiliary steam pressure by more than 0.1MPa, and the electric door from the cold section to the water pump turbine steam source is fully opened normally. Record the boiler feed water flow, water pump turbine speed, steam pressure before the water pump turbine shut-off valve, and the opening of the low-pressure steam inlet regulating valve;

[0059] (3) Close the electric door of the steam source from auxiliary steam to the water pump turbine. When closing from 100% to 40%, close 10% each time; when closing from 40% to 20%, close 5% each time; when closing from 20% to 0%, close 3% each time; each closing operation is performed at an interval of 1 minute. After each operation, check the boiler feed water flow, water pump turbine speed, water pump turbine shut-off valve front steam pressure and low pressure steam inlet regulating valve opening. If there is no change, proceed to the next step;

[0060] (4) After the electric door from the auxiliary steam to the water pump turbine is fully closed, switch the electric door mode to the remote position.

[0061] In the step f, when the steam source of the feedwater pump turbine is switched from the auxiliary steam source to the auxiliary steam source, the unit load is above 400MW, specifically:

[0062] When the auxiliary steam source pressure is lower than the four-extraction steam source pressure, the feed water pump turbine steam source will not be switched from the four-extraction steam source to the auxiliary steam source; when the four-extraction steam source pressure is lower than the auxiliary steam source pressure, the water pump turbine steam source will not be switched from the auxiliary steam source to the four-extraction steam source; when it must be operated, the operation should be slow, and the pressure deviation between the four-extraction steam source and the auxiliary steam source should be less than 0.2MPa.

[0063] When the auxiliary steam pressure is lower than the four-extraction pressure, and the steam source of the feedwater pump turbine is switched from the four-extraction steam source to the auxiliary steam source, check that the electric doors of the auxiliary steam source and the cold section to the steam source are fully open and normal, record the boiler feedwater flow rate and the opening of the low-pressure steam inlet regulating valve, and slowly close the electric door of the four-extraction to the water pump turbine steam source on site, from 100% to 40%, close 5% each time; from 40% to 20%, close 3% each time; from 20% to 0%, close 2% each time; each closing operation is 1 minute apart, and after each operation is completed, adjust the boiler feedwater flow rate to normal in time, and check that the boiler feedwater flow rate has returned to stability before proceeding to the next step;

[0064] During the switching process, if it is found that the opening of the low-pressure steam inlet regulating valve of the steam source is greater than 80%, stop the switching operation immediately, open the electric door from the four-extraction steam source to the feedwater pump turbine steam source, and restart the operation after the auxiliary steam source pressure is increased; after the electric door from the four-extraction steam source to the feedwater pump turbine steam source is fully closed, switch the electric door mode to the remote position.

[0065] When the pressure of the four-extraction steam source is lower than the pressure of the auxiliary steam source, and the steam source of the water pump turbine is switched from the auxiliary steam source to the four-extraction steam source, check that the electric doors from the four-extraction steam source and the cold section to the water pump turbine steam source are fully open and normal, record the boiler feed water flow rate and the opening of the low-pressure steam inlet regulating valve, and close the electric door from the auxiliary steam to the water pump turbine steam source. In the process of closing from 100% to 40%, close 5% each time; in the process of closing from 40% to 20%, close 3% each time; in the process of closing from 20% to 0%, close 2% each time; each closing operation The operation interval is 1 minute. After each operation, adjust the boiler feed water flow to normal in time. After each operation, check that there is no obvious change in the boiler feed water flow before proceeding to the next step. If it is found that the opening of the low-pressure steam inlet regulating valve of the pump turbine is greater than 80% during the switching process, stop the switching operation immediately, open the electric door from the auxiliary steam source to the pump turbine steam source, and operate again after the pressure of the four-extraction steam source increases. After the electric door from the auxiliary steam source to the pump turbine steam source is fully closed, cut the electric door mode to the remote position.

[0066] When switching the steam sources of the two feedwater pump turbines of the same unit, the operation should be carried out at an interval of more than 30 minutes to avoid causing disturbances in the boiler feedwater flow.

[0067] The working principle of the present invention is:

[0068] During startup, the electric gate of the steam source from the cold section to the water pump turbine is put into operation when the unit load is 100MW. During shutdown, the electric gate of the steam source from the cold section to the water pump turbine is closed when the cold section pressure is lower than the auxiliary steam pressure. Before closing, confirm that the high-pressure steam inlet regulating valve of the water pump turbine is in the closed state. It is generally closed when the unit load is reduced to 50MW.

[0069] The present invention achieves the purpose of the present invention by setting the following steps:

[0070] Accurate pressure judgment standard: By setting a specific steam source pressure threshold (such as 1MPa), the present invention can more accurately determine when the steam source needs to be switched, thereby avoiding unstable operation or failure of equipment caused by too low pressure.

[0071] Multi-parameter comprehensive evaluation of stability: The present invention not only takes into account the stability of unit load and auxiliary steam pressure, but also sets specific stability standards, such as load change rate and pressure fluctuation range, to ensure that steam source switching is carried out under the most suitable conditions and reduce the impact on boiler feed water flow.

[0072] Real-time monitoring of flow and equipment status: By real-time monitoring of boiler feed water flow and key operating parameters of the feed water pump turbine (such as bearing vibration and casing temperature), the present invention can ensure that switching is performed when the equipment is in the best condition, reducing operational risks.

[0073] Detailed switching steps and operating conditions: The present invention specifies in detail the specific steps for steam source switching, including pre-warming the pipes, slowly adjusting the electric door opening, recording and checking key parameters, etc. These steps contribute to a smooth transition and reduce the impact on the system.

[0074] Load-dependent switching strategy: According to the different unit loads, the present invention adopts different switching strategies, such as switching to the auxiliary steam source between 300MW and 400MW, and switching back to the four-extraction steam source above 400MW. This strategy can better adapt to different operating conditions and improve the flexibility and responsiveness of the system.

[0075] Safe pressure difference control: During the steam source switching process, the present invention strictly controls the pressure difference between the four-extraction steam source and the auxiliary steam source to ensure that the switching is performed within a safe pressure range and avoid equipment damage caused by sudden pressure changes.

[0076] Countermeasures in emergency situations: When an abnormal opening of the low-pressure steam inlet regulating valve is detected, the present invention provides guidance for immediately stopping the switching operation and taking remedial measures. This preventive measure helps to prevent accidents.

[0077] Provision of interval time: For the switching of steam sources of two feedwater pump turbines of the same unit, the present invention stipulates an interval time of at least 30 minutes to avoid disturbance to the boiler feedwater flow caused by frequent switching in a short period of time.

[0078] For example, the normal working steam source of a 1000MW feedwater pump steam turbine comes from the four-stage extraction steam of the main steam turbine, and the standby steam source comes from the exhaust steam of the high-pressure cylinder of the main steam turbine. When the load of the main steam turbine drops to the normal working steam source pressure and cannot meet the requirements of the steam turbine to drive the boiler feedwater pump, the regulator automatically switches the steam source from the working steam source to the standby steam source (cold section) without disturbance, and operates under this condition. When the main engine load rises again, the regulator can automatically switch the steam source to the working steam source. There is another auxiliary steam source as the starting and debugging steam source of the small steam turbine, which can meet the requirements of the unit to start with a steam pump. The exhaust steam of the small steam turbine enters the condenser. When the unit is operating normally, two steam-driven feedwater pumps operate in parallel, and a single feedwater pump can supply 55% BMCR of feedwater to the boiler.

[0079] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for switching the steam source of a feedwater pump turbine, characterized in that: The following steps are involved: a. Determine whether the steam source pressure of the feedwater pump steam turbine is lower than 1MPa. If so, switch the steam source of the feedwater pump steam turbine in time; b. Determine whether the unit load is stable and the auxiliary steam pressure is stable. If so, switch the steam source of the feedwater pump turbine; c. Determine whether the boiler feed water flow is above 800t / h and has no fluctuations. If so, switch the steam source of the feed water pump turbine; d. Determine whether two feedwater pump steam turbines are running at the same time or one feedwater pump steam turbine and electric pump are running at the same time. If so, switch the steam source of the feedwater pump steam turbine; e. Determine whether there is an alarm signal from the feedwater pump steam turbine, and whether the bearing vibration and casing temperature of the feedwater pump steam turbine are within the normal range. If so, switch the steam source of the feedwater pump steam turbine; f. Switch the steam source of the feedwater pump turbine. During the switching process, monitor and adjust the feedwater pump turbine parameters and boiler feedwater flow.

2. The method for switching the steam source of a feedwater pump turbine according to claim 1, characterized in that: In the step b, specifically: Unit load stability judgment criteria: Load change rate: Within 10 minutes, the load change rate of the unit shall not exceed ±1%; Load fluctuation range: Within 10 minutes, the unit load fluctuation range does not exceed ±5MW; Auxiliary steam pressure stability judgment standard: Pressure change rate: within 10 minutes, the change rate of auxiliary steam pressure shall not exceed ±0.5%; Pressure fluctuation range: within 10 minutes, the fluctuation range of auxiliary steam pressure shall not exceed ±0.01MPa; When the above stability standards of unit load and auxiliary steam pressure are met at the same time, it is judged to be in a stable state.

3. The method for switching the steam source of a feedwater pump turbine according to claim 1 or 2, characterized in that: In the step f, when the steam source of the pump turbine is switched from the four-extraction steam source to the auxiliary steam source, the auxiliary steam source pressure of the unit is higher than the four-extraction pressure by more than 0.1 MPa; when the steam source of the pump turbine is switched from the auxiliary steam source to the four-extraction steam source, the four-extraction steam source pressure of the unit is higher than the auxiliary steam pressure by more than 0.1 MPa.

4. The method for switching the steam source of a feedwater pump turbine according to claim 3, characterized in that: In the step f, when the steam source of the feedwater pump turbine is switched from the four-extraction steam source to the auxiliary steam source, the unit load is between 300MW and 400MW, specifically: (1) Open the auxiliary steam source drain valve 6 hours in advance, open the manual and electric doors of the auxiliary steam source to the feedwater pump turbine, and fully warm the steam source pipeline; (2) Before switching the steam source, fully open the manual steam gate from the auxiliary steam source to the feedwater pump turbine. The auxiliary steam source pressure of the unit is higher than the four-stage extraction pressure by more than 0.1 MPa. The electric steam gate from the cold section to the feedwater pump turbine is fully opened normally. Record the boiler feedwater flow, pump turbine speed, steam pressure before the pump turbine shut-off valve, and the opening of the low-pressure steam inlet regulating valve. (3) Close the electric door of the steam source from the four-stage pump to the feedwater pump turbine. When closing from 100% to 40%, close 10% each time; when closing from 40% to 20%, close 5% each time; when closing from 20% to 0%, close 3% each time. The interval between each closing operation is 1 minute. After each operation, check the boiler feedwater flow, pump turbine speed, steam pressure before the shut-off valve of the pump turbine, and the opening of the low-pressure steam inlet regulating valve. If there is no change, proceed to the next step; (4) When the electric gates from the four-extraction steam source to the feedwater pump turbine steam source are fully closed, switch the electric gate mode to the remote position.

5. The method for switching the steam source of a feedwater pump turbine according to claim 3, characterized in that: In the step f, when the steam source of the feedwater pump turbine is switched from the auxiliary steam source to the auxiliary steam source, the unit load is above 400MW, specifically: (1) Open the drain valve of the four-stage steam source 2 hours in advance, open the electric door of the four-stage steam source to the water pump turbine, and fully warm up the steam source pipeline. Before switching the steam source, fully open the manual door of the four-stage steam source to the water pump turbine; (2) When the steam source of the water pump turbine is switched from the auxiliary steam source to the four-extraction steam source, the four-extraction steam source pressure of the unit is higher than the auxiliary steam pressure by more than 0.1 MPa, and the electric door from the cold section to the water pump turbine steam source is fully opened normally. Record the boiler feed water flow, water pump turbine speed, steam pressure before the water pump turbine shut-off valve, and the opening of the low-pressure steam inlet regulating valve; (3) Close the electric door of the steam source from auxiliary steam to the water pump turbine. When closing from 100% to 40%, close 10% each time; when closing from 40% to 20%, close 5% each time; when closing from 20% to 0%, close 3% each time; each closing operation is performed at an interval of 1 minute. After each operation, check the boiler feed water flow, water pump turbine speed, water pump turbine shut-off valve front steam pressure and low pressure steam inlet regulating valve opening. If there is no change, proceed to the next step; (4) After the electric door from the auxiliary steam to the water pump turbine is fully closed, switch the electric door mode to the remote position.

6. The method for switching the steam source of a feedwater pump turbine according to claim 5, characterized in that: When the auxiliary steam source pressure is lower than the four-extraction steam source pressure, the feed water pump steam turbine steam source will not be switched from the four-extraction steam source to the auxiliary steam source; when the four-extraction steam source pressure is lower than the auxiliary steam source pressure, the water pump steam turbine steam source will not be switched from the auxiliary steam source to the four-extraction steam source.

7. The method for switching the steam source of a feedwater pump turbine according to claim 6, characterized in that: When the auxiliary steam pressure is lower than the four-extraction pressure, and the steam source of the feedwater pump turbine is switched from the four-extraction steam source to the auxiliary steam source, check that the electric doors of the auxiliary steam source and the cold section to the steam source are fully open and normal, record the boiler feedwater flow rate and the opening of the low-pressure steam inlet regulating valve, and slowly close the electric door of the four-extraction to the water pump turbine steam source on site, from 100% to 40%, close 5% each time; from 40% to 20%, close 3% each time; from 20% to 0%, close 2% each time; each closing operation is 1 minute apart, and the boiler feedwater flow is adjusted to normal in time after each operation. When the boiler feedwater flow is checked to be stable, proceed to the next step; If it is found during the switching process that the opening of the low-pressure steam inlet regulating valve of the steam source is greater than 80%, stop the switching operation immediately, open the electric door from the four-extraction steam source to the feedwater pump turbine steam source, and restart the operation after the auxiliary steam source pressure is increased; after the electric door from the four-extraction steam source to the feedwater pump turbine steam source is fully closed, switch the electric door mode to the remote position.

8. The method for switching the steam source of a feedwater pump turbine according to claim 6, characterized in that: When the pressure of the four-extraction steam source is lower than the pressure of the auxiliary steam source, and the steam source of the water pump turbine is switched from the auxiliary steam source to the four-extraction steam source, check that the electric doors from the four-extraction steam source and the cold section to the water pump turbine steam source are fully open and normal, record the boiler feed water flow rate and the opening of the low-pressure steam inlet regulating valve, and close the electric door from the auxiliary steam to the water pump turbine steam source. In the process of closing from 100% to 40%, close 5% each time; in the process of closing from 40% to 20%, close 3% each time; in the process of closing from 20% to 0%, close 2% each time; each closing operation is 1 minute apart, and the boiler feed water flow rate is adjusted to normal in time after each operation is completed. After each operation is completed, check that there is no obvious change in the boiler feed water flow rate before proceeding to the next step; If it is found during the switching process that the opening of the low-pressure steam inlet regulating valve of the water pump turbine is greater than 80%, stop the switching operation immediately, open the electric door from the auxiliary steam source to the water pump turbine steam source, and restart the operation after the pressure of the four-extraction steam source increases; after the electric door from the auxiliary steam source to the water pump turbine steam source is fully closed, switch the electric door mode to the remote position.

9. The method for switching the steam source of a feedwater pump turbine according to claim 7, characterized in that: When switching the steam sources of the two feedwater pump turbines of the same unit, the operation should be carried out at an interval of more than 30 minutes to avoid causing disturbances in the boiler feedwater flow.