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Failure And Treatment Of Water Turbine

Author: source: date: 2020-03-07 12:01:30
First, the unit is overspeed

During sudden load shedding during load operation of the unit, the speed of the turbine may increase by 20% to 40%, or even higher, because the guide vanes cannot be closed instantaneously. When the unit's speed rises to a certain value (its setting value is determined by the unit's moment of inertia, it is generally set to 140% of the rated speed), the unit has an overspeed accident. Due to the increase of the speed, the centrifugal force of the rotating part of the unit sharply increases, causing the unit's swing and vibration to increase significantly, and even causing collision between the rotating part and the fixed part. Therefore, the unit should be prevented from overspeeding.

In order to prevent overspeed accidents, most power stations are currently equipped with overspeed limiters, accident solenoid valves or accident oil pumps, and are equipped with hydraulic turbine main valves or quick gates. These devices are automatically controlled by the unit's accident protection circuit.

①②③The phenomenon when the unit overspeed occurs

Unit noise increased significantly.

The load meter indication of the generator is zero and the voltmeter indication rises (overvoltage protection may be activated).

"Hydraulic Machinery Accident" light sign is on, over-speed protection is activated, and accident shutdown occurs.

The overspeed limiter is activated, and the red light of the full open position of the main valve (or fast gate) of the turbine goes out (that is, the process of closing). If an accident oil pump is used for overspeed protection, the accident oil pump starts the pump oil and closes the guide vane.

 

② Handling when the unit is overspeed

When it is determined through the phenomenon that the unit is overspeed, the overspeed protection device should be monitored for normal operation. If the overspeed protection is refused or the operation is abnormal, the emergency shutdown should be performed manually, and the turbine main valve (or quick gate) should be closed at the same time.

If during the emergency stop, the unit is overspeed due to the shear pin shearing or the main pressure valve being stuck, etc., even if the speed has not reached the setting value of the overspeed protection action, the overspeed protection device should be manually operated to guide the water. The leaf and main valve close quickly. For units without a turbine main valve, the water inlet gate in front of the unit should be closed as soon as possible.

Second, the bearing accident of the unit

① Temperature rise of Babbitt alloy bearings

Generally, the thrust, upper guide, lower guide and other bearings of the unit and the turbine guide bearing are all made of Babbitt alloy bearings, so the thin oil is used for lubrication and cooling. When the temperature of any of these bearings rises to the accident temperature, the bearing temperature is too high and the accident protection action is performed, and an emergency stop is performed to avoid burning the bearing bush.

When the bearing temperature is higher than the set value, the light plate of the "hydraulic machinery accident" on the side plate lights up, 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. Prior to this, there may have been fault signals of increased bearing temperature; or there may have been signals such as interrupted supercooled water, reduced cooling water pressure, and reduced bearing oil levels.

When the above phenomenon occurs, first check and analyze the instructions of the measuring instrument. For example, check the readings of both the expansion thermometer and the resistance thermometer, and compare and identify the bearing temperature and the bearing oil temperature. And check the bearing oil level and cooling water. If it proves that the bearing temperature has not risen, it is a protection malfunction, then the accident shutdown circuit can be reset and the unit idling can be started. After further inspection and implementation, there is no problem, and then it can be connected to the grid for power generation. When it is confirmed that the bearing temperature is too high, the actual cause must be found out and handled properly.

There are many factors that can cause the temperature of Babbitt bearings to rise. The common causes and solutions are as follows:

Reduced lubricating oil: due to poor sealing of the bearing oil groove or improper closing of the drain valve, resulting in a large amount of oil leakage or oil dumping, due to the decrease in lubricating oil, a good oil film cannot be formed, which causes the bearing temperature to rise. Deal with the bad seal and refill the bearing with lubricating oil.

Deterioration of oil: Because the lubricant in the bearing is used for a long time, or there is water or other acidic impurities in the oil, the quality of the oil is deteriorated and the lubrication performance is affected. At this time, the new oil should be replaced. Especially when there is a large amount of water in the bearing (such as water leak from the cooler, etc.), the lubrication and cooling medium will be changed, which will directly affect the lubrication condition of the bearing and will cause the bearing to burn out quickly. Replace the oil in the bearing oil sump.

Cooling water interruption or cooling water pressure reduction: blocked cooling water pipes, damaged valve flaps, and air in the pipeline will affect the overflow of the cooler, causing the cooler to not function properly and causing the bearing oil temperature to rise. Immediately put the unit in standby cooling water, or exhaust the pipe. 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.

Increasing the main bearing swing: When the main shaft swing increases, the friction between the shaft and the bearing pads increases, the heat generation increases, resulting in poor lubrication conditions and the formation of a good oil film. At this time, efforts should be made to reduce the unit swing . For example, change the active and reactive load of the unit, make the unit run in a 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.
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② Lubrication water of water guide bearing is interrupted

Rubber tile water guide bearings are lubricated with water. These bearings are commonly known as water bearings. When water bearing lubrication water is interrupted, the phenomenon is similar to the above oil bearing, except that an additional "bearing lubrication water interruption" signal is displayed.

(1) Causes and consequences of the interruption of the lubricating water: due to the dirty water or debris, the water intake filter or filter is blocked, causing the water pressure to decrease; or the automatic water supply valve is closed by some reason by mistake; when the water pump supplies water The pump water supply was interrupted due to mechanical or electrical reasons. These will cause the accident of lubricating water interruption. When the lubricating water is interrupted or the amount of water is reduced, the lubrication and cooling conditions between the collar and the bearing pads will be deteriorated, and even dry friction will occur, which will cause the bearing to burn out. At this time, the hydraulic turbine loses its radial support, resulting in a sharp increase in vibration and swing. Water channeling sometimes occurs, which affects the normal operation of the unit.

(2) Treatment method: Generally adopt the following measures

When the lubricating water is interrupted or the water pressure is reduced, you should first put in a backup water source, then clean the water filter and filter, or find the cause of the accidental closing of the automatic water supply valve of the lubricating water. After the treatment is completed, the normal water supply of the original water supply system is restored.

If the bearing uses a pump to supply water, when the pump stops supplying water or the outlet water pressure drops, which causes interruption of lubrication water, the backup water pump should be started first, and then the cause of the pump stopping water supply or the drop in outlet water pressure should be identified, and corresponding actions should be taken. deal with;

When the water supply cannot be restored immediately, in order not to cause the accident to expand, the machine should be stopped immediately.


Inspection of hydraulic turbines

(1) Inspection standard: The water turbine and its parts and components in export power generation equipment are legally inspected on the basis of passing the factory inspection. The main standards for inspection are: JB626 "Basic Technical Conditions for Hydraulic Turbines"; JB3161-82 "Rules for Model Tests of Hydraulic Turbines" and related standards for materials, material tests, and major components. The parameters and economic and technical indicators specified in the contract's foreign inspection standards or technical agreements are also the basis for export inspections.

(2) Inspection items: The inspection items for hydraulic turbines are determined based on contracts, technical agreements, product standards and export requirements. The inspection contents mainly include: review of information (design and manufacturing), general appearance inspection; performance and economic and technical indicators inspection and packaging quality inspection.

Data review: mainly review the design and manufacturing basis, drawings, product specifications, qualification reports and material reports of related 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 turbine main body, auxiliary equipment and parts is performed. The main contents are: whether the product specifications, models, dimensions, nameplates, etc. are consistent with the goods certificate. Whether there is any damage or rust leakage in the appearance quality; whether the color and quality of the paint meet the export requirements; whether the transmission parts are flexible and balanced; the control part is sensitive, reliable and accurate; the quality of the welded parts and the quality of the welds;

Performance test: Check whether the technical parameters, performance indicators and economic indicators of the product meet the standards or contract requirements through tests.

a. Material properties, processing dimensions, accuracy, assembly quality and performance of main components;

b. Pressure test of hydraulic turbine and auxiliary pipelines;

c. runner seal test;

d. No-load operation test;

e. The first load test of the turbine;

f. Load rejection test;

g. 72 hours continuous test with load;

h. The test of the speed control system and the 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 a model or a 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 procedure. When the machine is used for acceptance, it can be carried out after one year of operation.

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