The load rejection test of turbine units is one of the important tests that must be completed in the infrastructure commissioning phase required by the Ministry of Power “Regulations for the start-up and completion acceptance of thermal power plant capital construction projectsâ€. Its main purpose is to evaluate the dynamic characteristics of steam turbine control systems. The steam turbine load rejection test is to directly disconnect the generator main oil switch, and the plant power is switched to the backup power supply. The unit and the power grid are decoupled and the entire electric load is removed. The steam turbine maintains a stable operation of 3 000 r/min. In order to meet the stability and safety requirements of power systems, FCB operating conditions (FCB, FASTCUT BACK) are designed in large steam turbine units. The main purpose is to disconnect the generator from the power grid after a load rejection of the power grid. Under automatic control, the operation of turbine islands is maintained (ie, the power consumption of the generator set is loaded with power from the factory), the boiler maintains the minimum combustion load, and the host bypass system automatically maintains the parameters of the normal operation of the generator. After the power grid is restored, the generator sets can be directly connected to the grid. With load operation. However, due to various reasons, the test success rate of the unit island operation mode is very low. After the completion of the 168h trial run and conventional load rejection test, the No. 1 and No. 2 units of the Hejin Power Plant succeeded in conducting the turbine island test. Overview Two 350MW coal-fired generating units of the first phase of the Hejin Power Plant are imported from Mitsubishi, which is equipped with 1205T/H-MB-FRR single-tube steam bags manufactured by Mitsubishi Heavy Industries, with radiation, reheating, tangent-cutting and forced-circulation open-air boilers. TC2F-35.4" Subcritical, once a thermal power expert at Middle Polytechnic University, engineer; Guo Jian (1963-), male, Taiyuan, Shanxi Province, graduated from Taiyuan University of Technology in 1986, majoring in thermal dynamics, senior engineer; Duan Chengqun This issue is on page 52.
Reheat, reaction-type single-axis double-cylinder double steam condensing steam turbine and Mitsubishi Electric MB-J horizontal full hydrogen internal cooling, hidden pole full-quiet thyristor excitation generator generator-transformer unit wiring, Access to system control system at 220kV voltage level is DCS manufactured by Mitsubishi Heavy Industries. The model number is DIASYS-JP/V. Functions include DAS, CCS, MT-3EH, BF-DEH, BMS, and GWC. The turbine bypass system adopts two series of high and low voltage series. The bypass device has a capacity of 40% of the total flow, and the bypass regulator valve is manufactured by CCI, the United States. The high and medium pressure turbines are composed of impulse and reaction type. Two chambers are symmetrically arranged on both sides of the high and medium pressure cylinders. Each chamber includes one main valve and two high pressure valves. The medium pressure main valve and the medium pressure control gate constitute Medium pressure joint valve.
Turbine regulation system uses digital electro-hydraulic control system (ie, DEH). The adjustment system of the turbine includes three parts of the speed-measuring element amplifying element and actuator. After the closed loop with the rotor, the negative feedback of the composition speed is automatically adjusted. The Mitsubishi unit uses 2.5MPa pressure turbine oil as the power pool for the control system. The DEH is equipped with multiple microcomputer systems. It is the subsystem of the multi-level distributed computer control system of the unit. DEH is calculated through the distributed control system communication network and the unit. The system transmits signals so that the operation of the DEH is integrated with the control of the entire unit. The output of the control signal is selected by 3 or 2* logic or median selection, and then the electro-hydraulic converter is driven to perform the regulation function. 2 Conventional load rejection test The requirements in the “Procedures for the start-up and completion acceptance of thermal power plant capital construction projects†of the Ministry of Electric Power, before the 168h trial run of No. 1 and No. 2 units of the Hejin Power Plant, conducted a 50%, 75%, and 100% conventional load rejection. Test, due to the conventional load rejection test is carried out in the capital construction commissioning unit, and the success of the rejection load Table 1 No. 1 and No. 2 rejection of the 100% rated load test record Item Load rejection parameter After-load rejection test Parameter peak load/ MW/1 No. 02 action once, action time action once, action time 0.032s1 No. high-pressure control door 1001000 closing time 290ms0 closing time 290ms No. 2 high pressure Adjust the door 1001000 Closing time 290ms0 Closing time 290ms No. 3 High-pressure modulation gate 27.522.50 Closing time 120ms0 Closing time 120ms No. 4 High-pressure regulating gate 1100 Left-side medium-pressure regulating gate 10010000 Closing time 191 Closing time 192 Right-side medium pressure regulating gate 10010000 Closing time 191 Closing time 192 rate Nearly 100%; so no more description is given here.Main parameters of the conventional load rejection test for 2 units Table 1 Tested, the dynamic characteristics of the control systems of the 2 units are fully in line with the acceptance requirements 3 Unit load rejection island operation (FCB test) The FCB test is a relatively large, complex and risky severe disturbance test. It involves all aspects of the steam turbine boiler, electrical, thermal and power plant specialties and the whole plant. The success or failure of the FCB test will have a direct impact. The operation mode of the island and the switching of the power supply for the factory and other factors are used, so the test is carried out after the trial scheme and safety measures have been repeatedly demonstrated and approved by the leading group and the personnel involved in the trial have performed a comprehensive technical presentation.
3.1 Preliminary tests and system checks The static valves of the main valve and the speed control valve are closed; the static test of the main valve and the regulating valve is qualified; the activity test of the exhaust check door is qualified; the ESC system can meet the start and stop of the system. And lifting load requirements; unit main valve and speed control valve tightness test qualified; complete RB test, all tests are qualified, auxiliary machine system is running well; addition and subtraction; boiler combustion system, factory electricity fast cutting system, power generation Excitation system generator protection system, spare branch power supply of thermal control system is operating normally, and turbine generator set vibration is qualified; island operation is performed on the main process of island operation test of No. 3.21 steam turbine unit after 168h trial run on January 14, 2001. After completing the preparatory tests and system inspections, the participants took part in the technical exchanges. After 15:37:27 in the afternoon, the commander conducted a countdown of 10 seconds, and manually pulled out the generator outlet main oil switch at 15:37:37. 52G, FCB operation, electric load rejection to 18.5 MW, the crew maintains small island operation. The main process of the manual operation of the unit by coordinating operation mode is as follows.
3MPa,2主汽汽安全门 The main grinding control cut into an automatic standby mode, maintaining the mill running at a minimum load of 20t / h, CD layer oil gun automatic injection, fuel flow 7. / h control protection OPC action; pressure before the machine 17. 3MPa, 2 main steam safety door PCV1 and PCV2 action.
Four high-profile gates GV Bu GV4 and two medium-voltage gates ICV1, ICV2 close two high-pressure gates and two medium-pressure gates start to open.
37 minutes and 55 seconds high and low side pressure control valve automatically release the full open command and restore the automatic adjustment mode 39 minutes and 46 seconds GOV manual grid-connected, 52G reclosed the unit after the furnace to follow the power adjustment mode: high-side adjustment of the main steam The pressure is controlled by GOV power control in ESC mode. But at this moment the electric load momentarily drops to 4. 9MW, this is because when the grid connection, the turbine speed only has 2990r/min, causes the reverse power protection movement of the generator, just because the machine main control command increases rapidly, the adjustment door opens greatly, has avoided 52G once again switch off the brake 40 minutes 38 seconds due to fluctuations in the water level of the drum, will be high bypass manual, forced to 20%. Coordination for the follow-up mode, electric load 40 minutes 42 seconds FCB automatic reset, boiler control, grinding Both the coal machine master and the fuel master are cut to manual. Trying to increase the load command of the boiler to increase the electric load, but because the load is controlled in the GOV circuit of the electric adjustment, it is invalid 1g) The unit can be set negative at various control parties. The load curve her shingjkU0%3* high side automatic vote, coordination and cut for the furnace to follow the power adjustment mode, the electric load 12. The owner controls cut to the electric control mode, manually increase the opening degree.
After the pressure relief valve is fully closed, after 6s, the high-side given pressure offset is put into the main control and automatic projection is performed. After the unit cuts and co-ordinates the control mode, the rated power suddenly dumps the load to the plant and re-establishes the grid and quickly loads the turbine rotor inside. The change in thermal stress is a particularly important factor to consider. From the data provided by Mitsubishi, the first time the initial test data sheet records the initial value of the data, the maximum value, the minimum value, the final value, the unit load/MW35835814. Table 3 The second test data The initial value of the recorded value of the maximum value of the minimum value of the final value of the unit load / MW/349. 3.32 island unit operation test on the basis of the successful test of Unit 1, we at 22:57 on March 23, 2001 in Unit 2 In the first FCB test, the high side was successfully opened, but due to the full hearth fire extinguishing MFT action, the test failed, and the fuel analysis by all parties considered that the primary fuel command fell too quickly (300t/min). In the FCB test, the rate was 25t/min. For this purpose, the 300t/min of the No. 2 machine was changed to 8t/min. After a great deal of preparation work, after the second test and system inspection, the test was conducted. Personnel Technology After reaching the bottom, when the general commander logged down for 10s, the generator outlet main oil switch 52G was manually pulled out at 9:10:10, FCB operation, and the electric load was thrown to 13.7MW, and the island was operated with electricity. The unit was cut into a machine by a coordinated operation mode and the furnace was manually operated in the same way as Unit 1. The test of Unit 2 was very successful.
The test data is shown in Table 3. 4 Conclusions Modern large-scale steam turbines use thermal stress in their control to control the life of the rotor. Therefore, the temperature of the rotor after the FCB becomes an important determinant of the load-bearing speed of the grid-connected units. Most turbine generators The equipment is designed to withstand complete separation from the system for a period of time and has no load or stable operation with its own power supply. When the temperature from the first stage of the ring is immediately reduced by approximately 120*C, and then within 15 minutes due to the super heater outlet temperature adjusted to the newly established steam parameter level, the first stage steam temperature is further reduced by 90°C. A peak stress is generated within 10 min to 15 min from the start of the transient. The stress gradually decays to zero in approximately 1 h. If the power is maintained for a long time, the rotor will be forcibly cooled to a new equilibrium state and then moderately moderated. The rate is completely reloaded to avoid large stresses in the opposite direction. For a typical 3000r/min rotor, the peak stress after the stress is fully converted from 100 to 400 cycles may cause initial cracks in the rotor and can therefore be calculated. A cycle of this magnitude is approximately Q of the total fatigue performance of the rotor. From this, it can be seen that achieving the FCB function of the unit is very important, but the long-term operation under this operating condition is very obvious to the unit's equipment. Although the load test can test the dynamic characteristics of the steam turbine governing system, but in normal operation, the chiller may abruptly remove the load at any time. Failure to use the power supply in time to cause downtime of the auxiliary machine If the operator improperly handles it, it may cause the operating parameter to exceed the limit, causing serious accidents such as large shaft bending and burning of the bearing shell. If the operation mode of the unit island is realized and promoted, not only can the similarity be avoided. The occurrence of the incident has greatly helped the safe operation of the power plant.
FCB island operation is a very effective operation mode for large-scale turbine units adapting to grid changes. In this mode, if the turbine units can be quickly connected to the grid in a short period of time, the safe and economic operation of the unit and the safety of the grid can be achieved. Stable operation is of great significance. It should be a necessary operating mode for modern units. The relative difference between the results should be smaller than the relative expansion uncertainty of the device, which is verified. The verification data of the two devices are shown in Table 2 and Table 2 The results of the comparison (applied voltage 5000) Table 4 Comparison results of the two sets of devices Beijing Electric Power Research Institute / G The relative difference of the device / Permissible value% 100M100.12100.102 Through the above argument, the combination of high pressure and high resistance box The verification device is practical and feasible in the actual verification work. It is stable and reliable, and the measurement range is that Kfn-10na can meet the verification of most high-voltage high-resistance boxes.
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