267:B Article ID: 1007―1881 The dynamic characteristics of the turbine governing system are the basic guarantee for the safe operation of the unit. The new unit should be subjected to dynamic load rejection test to fully understand the dynamic characteristics of the turbine governing system and ensure the turbine generator set. Safe to run. The load rejection test is a comprehensive test involving all aspects of machine, electricity and furnace. In addition to the characteristics of the adjustment system, the adjustment and test of other systems of the unit will also affect the success or failure of the load rejection test. Therefore, the load rejection test must be carried out with elaborate technical preparations to eliminate all kinds of known defects including design, which will adversely affect the dynamic characteristics of the unit, and ensure that the adjustment security system is perfect, the accident is expected to be sufficient, and the anti-accident measures are perfected. Under the premise, the load rejection test can be carried out.
This paper combines the characteristics of the 3 1 unit speed control system of the second phase of Beilun Power Plant. The turbine of the second phase of Beilun Power Plant is TC 4-42, single-axis, four-cylinder four-row steam, sub-critical, one-time intermediate reheat, impulse, double back. The condensing steam type is designed to have a rated output of 6 MW and is manufactured by Toshiba Corporation of Japan. The steam turbine control system uses a digital electro-hydraulic control system (DEH), which is supplied by Toshiba and the turbine. The system is based on programmable controller, with high control precision, dual structure of hardware configuration, layered control function, good reliability, actuators are single-side oil-injected oil, and high-pressure fuel-resistant as a regulating system. Hydraulic working medium. The bypass system is produced by the Swiss company Sulzer and is equipped with the AV6 control system. The high-pressure bypass is one way, and the capacity is the flow that can pass 50% BMCR under the rated parameters. The low-pressure bypass is two-way, and the capacity can be increased by the amount of steam bypassed by the high-pressure bypass. The former mainly considers the flow capacity of mass flow, while the latter mainly considers the flow capacity of volume flow.
11 unit start-up mode The typical design of TOSHIBA company unit is without bypass, and the high-pressure cylinder is started by high-pressure control. After the bypass system is equipped, the steam turbine control system is combined with the high and medium pressure cylinder combined start mode with bypass to improve the flexibility of the unit operation. Therefore, the start-up and operation of the unit are divided into two modes: input and exit of the bypass.
The difference between the bypass system input and the exit in the unit startup or normal operation is whether the high and low pressure bypass control valves are open. If any of the high and low pressure bypass control valves are not fully closed, the unit is bypassed. The system input mode, and vice versa, the bypass system exit mode.
1.2DEH load shedding protection function The DEH control system adopted by the unit has a steam turbine load shedding prediction function to prevent the unit from overspeed accidents under severe conditions such as load shedding.
This is a protection function for the turbine when the generator is suddenly overloaded, and is realized by the power-load imbalance detection circuit (POWER-IOADUNBALENCE). The PLU detection circuit measures the generator current representative power, and the pressure represents the load after the first stage of the turbine is measured; when the generator power is instantaneously reduced (the rate of change is greater than 4C% Ne / 1ms) or the deviation between the generator power and the turbine load is greater than 4 At %Ne, the PLU acts to quickly shut down the CV and ICV through the high-pressure control (CV) and medium-voltage control (ICV) quick-acting solenoid valve (FASV) to prevent the turbine from overspeeding. At this time, the governor set value (GOV) .SET) automatically returns to the empty load position. After the unbalanced signal disappears, the door is opened to maintain the turbine 30/nin operation. The system additionally has a *PLUTEST* button to check if the loop is working properly.
2 Technical points of the load test The load test process includes: the formulation of the test plan, the adjustment of the security system and the static test, the preparation of the test test system and the operating system, the interlock protection test of the unit and the implementation of the load rejection test.
21 甩 load test program formulation (1 main equipment interlock protection mainly considers whether the design of the unit's machine, electricity and furnace interlock can meet the requirements of the load rejection test; whether the bypass system can ensure the load rejection test smoothly .
The load rejection test must consider the adaptability of each main auxiliary machine and system of the unit to different test plans, and select a test plan that can ensure the safety of the unit and the power grid. The general considerations are: the operation mode of the bypass system, the switching of the plant power, the operation mode of the electrical equipment after the load rejection of the unit, the combustion adjustment method of the boiler, the control steam pressure mode and the load dump test on the safety production of the power grid.
22 Adjustment of the security system and static test In the various tasks of the load rejection test, the adjustment and static test of the adjustment security system should be completed and carefully recorded according to the design requirements of the manufacturer. Do a good job of inspection and testing before starting.
After the unit is started, the tests include: emergency shutdown test, emergency breaker operation test, overspeed test, main valve tightness test, and speed control valve tightness test. When performing the valve tightness test, the reheating system should maintain a certain pressure and check the tightness of the medium pressure valve.
The large capacity unit is designed with load shedding prediction function to improve the dynamic characteristics of these units and prevent overspeed. This is an integral part of the regulation system. Therefore, this type of unit should be loaded with the load shedding prediction function when performing the load rejection test.
23 The method of occurrence of the load rejection test should be safe, simple, fast and reliable for the operation of the load rejection during the test. The generator outlet switch can be manually opened or the test button can be incorporated into the protection of the disengaged generator through the knife gate. After operating the test button connected, the unit should be unpacked, but the turbine should not be interlocked to trip. At the same time, it should be ensured that the load shedding prediction function can operate correctly.
24 Inspection of load rejection test conditions The following inspection tests shall be carried out before the load rejection test: valve activity test, oil pump self-start test, non-deceleration oil injection test, diesel generator start test, light plate alarm test light test; The conditional unit should conduct a steam exhaust check valve activity test.
3 Load rejection test results The three units of the second phase of Beilun Power Plant carried out the load rejection test of Unit 4 on June 27, 2000. On August 9 and September 2, the units of Unit 5 and Unit 3 were carried out respectively. Load test.
The basic situation of the unit operation after load rejection is shown in Table 1. Among them, Unit 45 stopped two coal mills at the same time, and Unit 3 stopped three coal mills at the same time.
The basic parameters of the unit after the load rejection test and the test results of the dynamic parameters of the adjustment system are shown in Table 2. In the No. 4 unit, after the load shedding, the low-pressure bypass A is low due to the desuperheating water pressure; the reason for the long-term stability of Unit 3 is that the control parameters of the medium-voltage control are unreasonable, resulting in the load rejection test of the three units of the medium-pressure swinging The dynamic characteristic curve of the adjustment system is completely measured, and various dynamic parameters of the adjustment system can be obtained through calculation. It is not difficult to see from the table that the dynamic response of the unit regulation system is good, and the speed can be stabilized in a short time after the load rejection; the dynamic characteristics of the adjustment system meet the design requirements and can meet the needs of the unit operation.
4 Experiences of the load rejection test 41 The use of the bypass must be carefully bypassed. The operation mode should be determined according to the design of the bypass and the specific conditions of the unit. It is confirmed that the bypass system itself is completely protected, the pressure and temperature are adjusted, and the pipe is adjusted. The road design can be put into the bypass quick opening function under the premise of the load rejection condition; for the bypass system with weak links, poor automatic adjustment performance and insufficient supply of desuperheated water, preventive measures should be taken during the test. For example, using two condensate pumps in parallel operation mode, manual smoothing adjustment, etc. Whether it is manual adjustment or automatic adjustment, it must be fully warmed and hydrophobic before the test.
Considering the limitation of the exhaust steam temperature of the high pressure cylinder, in order to make the high pressure cylinder require about 0%~6C%) and to minimize the sufficient steam flow of the high pressure bypass to cool the high pressure cylinder, it is necessary to reduce the medium pressure opening degree; Units that do not participate in the regulation of medium voltage regulation should maintain high cylinder work, that is, reduce the reheat steam pressure.
Therefore, do the rolling bypass in the closed position.
During the load test, it is required to open the low-pressure bypass to a certain opening degree. (Generally, the basic conditions after the load rejection test of the 3 units. The project name unit unit load-breaking operation situation No. 3 unit No. 4 unit No. 5 unit remarks number of coal mills The number of oil guns, the condensate pump, the electric pump, the rotating water, the hot steam, the water pump, the water level, the water level, the high temperature, the cylinder, the ventilation valve, the forced high pressure cylinder, the exhaust valve, the automatic high pressure bypass, the automatic low pressure bypass. Operation mode Automatic drum water level control Automatic deaerator water level control Automatic condenser water level control Automatic DEH operation mode Factory electricity operation mode Start/Ready change table 23 Unit load rejection test result Item name Unit unit after load rejection related parameters Remarks No. 3 Unit No. 4 Unit No. 5 Unit High Pressure Bypass Opening Low Pressure Bypass A Opening Low Pressure Bypass B Opening Main Steam Pressure After Load Maximum Value Main Steam Temperature Reheat Steam Pressure Maximum Value After Load Maximum value of steam flow after load rejection Maximum value of water flow after load rejection High pressure cylinder exhaust steam temperature Maximum load after condensate pressure Minimum value after 甩 load Speed ​​minimum speed Maximum speed stable speed After the valve is closed, the flying speed reaches the maximum speed Time stability time Dynamic overshoot The rotor initial acceleration Rotor time constant Rotor moment of inertia 42 High row check valve and high exhaust valve At present, large units are designed A high-pressure cylinder ventilation valve ensures that the high-pressure cylinder has sufficient cooling steam flow at low load. When the unit is under load, the high-discharge check valve is closed, and the high-pressure cylinder ventilation valve can only be used to maintain the high-pressure cylinder cooling steam flow. The test shows that if the high pressure cylinder ventilation valve is forcibly opened after the unit is under load, it is effective to reduce the steam flow rate of the high pressure cylinder.
At the same time, after the load rejection test is over, the unit speed should be connected to the grid as soon as possible after it stabilizes. If the grid connection is not timely, it is not enough to maintain the high-pressure cylinder cooling steam flow only by the high-pressure cylinder ventilation valve. At this time, the side-opening degree should be lowered to reduce the reheat steam pressure as much as possible, which is beneficial to open the high-row check valve in advance. To increase the steam flow rate of the high pressure cylinder.
43 Pressure Relief Modes and Means After the load shedding, due to the heat storage effect, the boiler steam pressure will rise, and the reheat system will also store a large amount of steam. The steam in the reheating system has some adverse effects on the operation of the unit after the load rejection, and the proportion of the medium and low pressure cylinders is large, causing the blast of the high pressure cylinder or even the operation of the cylinder. Generally, the adjustment performance of the medium pressure regulating door is poor, and the reheat steam pressure which is too high at the time of empty load will further deteriorate the adjustment quality, and the rotation speed of the unit will be difficult to stabilize, which brings difficulties to the grid connection again. Therefore, for reheat units, try to reduce the pressure of the reheat system as soon as possible after load rejection.
The superheated steam system relief can be accomplished through the safety door and the open exhaust valve as well as the unit bypass system. The reheat steam system can be relieved by a low pressure bypass, a safety door, a reheater air venting valve, and a reheater drain system. In addition to the reheating unit with medium-pressure cylinder start-up load, other reheat units should consider how to prevent over-pressure of the overheating system and reduce the pressure of the reheating system to ensure that the unit enters stable operation as soon as possible.
44 Adjustment and control of important parameters (1调整 load heat load adjustment and pressure control general load rejection test, from the unit to the grid disconnection to the unit reconnected for 5~1min time, the unit transition process 20 More than s can be ended and the unit enters an empty load operation state.
The key to smooth operation of the unit within 10 minutes is to maintain the balance of steam generation and consumption, that is, the balance of heat load. The key issue is how to adjust the fuel before and after the load rejection.
Before the load shedding test, the boiler can be stabilized by stopping the oil gun, stopping the coal mill to reduce the boiler fuel quantity, and minimizing the impact of the boiler heat storage on the test; after the load rejection, the boiler fuel should be quickly lowered to At the level of empty load, this is the balance point between the generation and consumption of steam between the furnaces of this type. At the beginning of the load rejection, the increase of the boiler main steam pressure may cause the boiler safety door to operate. Under the pressure relief of the safety door, the main steam pressure will quickly return to the normal value. After the safety door is returned to the seat, the fuel is adjusted by the boiler to maintain the main The steam pressure is stable. If too much fuel is invested, the safety door will jump or fail to return to the seat, or it will be forced to open the high-pressure bypass, which will affect the stability of the turbine speed and the unit will be connected to the grid again.
(2) In the water level control thermal system of each water container in the thermal system, the volume of the steam drum is the smallest, the deaerator is the largest, and the condenser is centered in the three water containers of steam drum, deaerator and condenser. The condensate pump is responsible for providing cooling water, sealing water and desuperheating water to some important equipment and systems. When dumping, the water level of the steam drum and the condenser should be controlled first. After the load is generated, the condenser condensate It will be greatly reduced, because the heat load will decrease, the water volume of the thermal system will also decrease. Therefore, after the load is removed, the water supply amount of the demineralized water must be increased, and the water volume of the deaerator is reduced, so that the water level of the condenser can always be It satisfies the need of normal operation of the condensate pump. The task of buffering the volume change of the heat system is mainly done by the deaerator, but the water level of the deaerator should also be controlled within the range that can satisfy the normal operation of the feed pump.
5 Conclusions and recommendations The 600 MW unit load rejection test successfully measured the dynamic characteristics of the regulation system, and the test was successful.
(2) The load test is a comprehensive test involving the machine, electricity, furnace, etc., and must be fully and closely coordinated during the test.
(3) With the large capacity of the unit, the rich flow of the condensate pump sometimes cannot meet the requirements of the severe working conditions such as the load shedding of the unit. The stable operation of the condensate system plays an important role in the success of the unit's load rejection test. It is recommended to use two condensate pumps in parallel operation during the full load test.
(4 The use of the bypass system must be cautious. After the unit is unloaded, it is required to open the low-pressure bypass to a certain opening degree (generally required to be around 5%~60%) and minimize the opening of the high-pressure bypass; for bypass manual The unit controlled shall follow the principle of “opening the front side first and then opening the high sideâ€.
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