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April 13, 2020
Common faults and treatment in the operation of water hydraulic turbine
1. hydro turbine overspeed
When the load is suddenly dumped during the operation of the hydro turbine, the speed of the turbine may increase by 20% to 40% or even higher during the closing of the guide vane because the guide vane cannot be shut down instantaneously. When the speed of the hydro turbine increases to a certain value (the setting value is determined by the rotational inertia of the hydro turbine, the general setting is 140% of the rated speed), the hydro turbine has an overspeed accident. Due to the increase in speed, the centrifugal force of the rotating part of the hydro turbine increases sharply, causing the hydro turbine swing and vibration to increase significantly, even causing the collision of the rotating part and the fixed part. Therefore, the hydro turbine should be prevented from overspeed.
In order to prevent overspeed accidents of the hydro turbine, most power stations are currently equipped with overspeed limiters, accident solenoid valves or accident oil pumps, and are equipped with main valves or quick gates for water hydraulic turbines. These devices are automatically controlled by the hydro turbine's accident protection circuit.
①②③The phenomenon when the hydro turbine overspeed occurs
The noise of the hydro turbine increased significantly.
The load meter of the generator indicates zero, and the voltmeter indicates an increase (overvoltage protection may be activated).
The "hydraulic machinery accident" light is on, the overspeed protection action occurs, and an accidental shutdown occurs.
The overspeed limiter acts, and the red light of the full-open position of the main valve (or quick gate) of the turbine turns off (that is, it is closing). If the accidental oil pump is used for overspeed protection, the accidental oil pump starts the pump oil and closes the water guide vane.
②Handling when the hydro turbine is over speed
When it is determined by the phenomenon that the hydro turbine has been overspeeded, it should be monitored whether the overspeed protection device is operating normally. If the overspeed protection refuses to operate or does not operate normally, it should be manually stopped and the main valve (or quick gate) of the turbine should be closed.
If during the emergency shutdown, the hydro turbine is overspeeded due to the shear pin shearing or the main pressure valve stuck, etc., even if the speed has not reached the set value of the overspeed protection action, the overspeed protection device should be operated manually to make the water guide. The leaf and main valve close quickly. For the hydro turbine without the main valve of the turbine, the water inlet gate in front of the hydro turbine should be closed as soon as possible.
2. Bearing accident of the hydro turbine
①The temperature of babbitt bearing rises
The thrust, upper guide, lower guide and other bearings of the general hydro turbine and the guide bearing of the turbine are all made of babbitt alloy bearings, so the thin oil is used for lubrication and cooling. When the temperature of any one of the bearings rises to the accident temperature, the bearing temperature is too high and the accident protection action is carried out, and an emergency stop is performed to avoid burning the bearing bush.
When the bearing temperature is higher than the setting value, the light plate of the “hydraulic machinery accident” on the machine side plate is bright, the signal relay of the bearing temperature is too high, and the black needle of the expansion thermometer of the accident bearing coincides with or exceeds the red needle. Before this, there may have been a fault signal that the bearing temperature has risen; or there may have been signals such as an interruption of the cooling water, a reduction in the pressure of the cooling water, and a decrease in the bearing oil level.
When the above phenomenon occurs, the instructions of the measuring instruments should be checked and analyzed first. For example, the readings of the expansion thermometer and the resistance thermometer are checked, and the bearing temperature and the bearing oil temperature are compared and identified. And check the bearing oil level and cooling water. If it proves that the bearing temperature has not risen, and it is indeed a protection malfunction, the accident shutdown circuit can be reset and the hydro turbine can be started to run idly. After further inspection and implementation, if there is no problem, it can be connected to the grid for power generation. When it is confirmed that the bearing temperature is too high, it is necessary to find out the actual cause and handle it correctly.
There are many factors that can cause the temperature of the babbitt bearing to rise. The common reasons and treatment methods are as follows:
Reduced lubricating oil: due to poor sealing of the bearing oil groove or inadequate closing of the oil discharge valve, a large amount of oil leakage or oil rejection is caused. Due to the reduction of lubricating oil, a good oil film cannot be formed, which causes the bearing temperature to rise. At this time, depending on the specific situation, Treat the defective seals and replenish the bearings with lubricant.
Oil deterioration: The lubricating oil in the bearing is used for a long time, or there is moisture or other acidic impurities in the oil, which deteriorates the oil quality and affects the lubricating performance. At this time, new oil should be replaced. Especially when there is a lot of water in the bearing (such as water leakage from the cooler, etc.), the lubrication and cooling medium will be changed, which will directly affect the lubrication condition of the bearing, which will soon cause the bearing to burn out. At this time, the machine should be stopped immediately to deal with the water seepage or leakage. Replace the oil in the bearing oil groove.
Interrupted cooling water or reduced cooling water pressure: blocked cooling water pipes, damaged valve flaps, and air in the pipes will affect the overflow of the cooler, make the cooler not function properly, and cause the bearing oil temperature to rise. Immediately put the hydro turbine into standby cooling water, or exhaust the pipeline. If the cooling water pressure is too low, try to increase the amount of cooling water to reduce the bearing temperature to a normal value.
The main bearing swing increases: when the main shaft swing increases, the friction between the shaft and the bush increases, and the amount of heat increases, resulting in deterioration of the lubrication conditions and the formation of a good oil film. At this time, try to reduce the hydro turbine swing . For example, change the active and reactive load of the hydro turbine, make the hydro turbine run in the load area with less vibration, or stop to check whether there is a large change in the clearance of each guide bearing, and check whether the thrust bolts of each guide bush are loose.
②The lubricating water of the water guide bearing is interrupted
Rubber tile water guide bearings are lubricated with water. These bearings are commonly known as water bearings. When the lubricating water of the water bearing is interrupted, the phenomenon is similar to the above oil bearing, except that an "bearing lubricating water interruption" signal is displayed.
(1) Reasons and consequences of interruption of lubricating water: due to unclean water or debris, the intake water filter or filter is blocked, resulting in reduced water pressure; or the automatic water supply valve is mistakenly closed for some reason; , Due to mechanical or electrical reasons, the water supply of the pump is interrupted. These will cause the lubrication water interruption accident. When the lubricating water is interrupted or the amount of water is reduced, the lubrication and cooling conditions between the shaft collar and the bush will be deteriorated, and even dry friction will occur, resulting in the burning of the bearing. At this time, the turbine loses its radial support, resulting in a sharp increase in vibration and swing. Sometimes the phenomenon of water channeling occurs, which affects the normal operation of the hydro turbine.
(2) Treatment method: generally take the following measures
When the lubricating water is interrupted or the water pressure is reduced, first put in a backup water source, then clean the water filter and filter, or find the reason for the automatic closing of the lubricating water automatic supply valve, and restore the normal water supply of the original water supply system after the treatment.
If the bearing is supplied by a water pump, when the pump stops water supply or the outlet water pressure drops and the lubricating water is interrupted, first start the standby water pump to supply water, and then find out the reason why the water pump stops water supply or the outlet water pressure drops, and do the corresponding deal with;
When the water supply cannot be restored immediately, in order not to cause the accident to expand, the machine should be shut down immediately.
(1) Inspection standard: The turbine and its components in the export power generation equipment are subject to legal inspection on the basis of factory inspection. The standards for inspection are mainly: JB626 "Basic Technical Conditions of Turbine"; JB3161-82 "Turbine Model Test Regulations" and related materials, material tests, main parts and other standards. The parameters and economic and technical indicators specified in the contract ’s foreign inspection standards or technical agreements are also the basis for export inspection.
(2) Inspection items: The inspection items of the turbine are determined according to the contract, technical agreement, product standards and export requirements. The inspection content mainly includes: the review of data (design and manufacturing), general appearance inspection; performance and economic and technical indicators inspection and packaging quality inspection, etc.
Data review: mainly review the basis of design and manufacturing, drawings, product specifications, certificate and material reports of relevant materials, performance test reports and necessary test and test data;
General Appearance Quality Inspection: According to the relevant standards, a comprehensive inspection of the appearance quality of the main body, attachments and parts of the turbine will be conducted. The main contents are: whether the product specifications, models, external dimensions, nameplates, etc. are consistent with the cargo certificate. Whether the appearance quality is damaged, rusted and leaked; whether the color and quality of the paint meet the export requirements; whether the transmission parts are flexible and balanced; whether the control parts are sensitive, reliable, and accurate; the quality of the welded parts and the quality of the weld seam;
Performance test: Check whether the technical parameters, performance indicators and economic indicators of the product meet the standards or contract requirements through the test.
a. Material performance, processing size, precision, assembly quality and performance of main parts
b. Pressure test of water hydraulic turbine and auxiliary pipeline;
c. Runner seal test
d. No-load operation test;
e. The first load test of the turbine;
f. Load rejection test;
g. 72-hour continuous test with load;
h. The test of speed control system and automatic device system should meet its special technical conditions;
i. Other items specified in the contract or technical agreement;
j. Cavitation damage test;
k. The efficiency acceptance test of the turbine can be accepted by the model or real machine according to the contract or technical agreement. The method of model test is carried out on the energy test bench and cavitation test bench according to the model test regulations. When the real machine is used for acceptance, it can be carried out after one year of operation of the hydro turbine.