As the accident valve and maintenance valve, the inlet valve usually only has two working states: full opening or full closing, which cannot be used to regulate the flow. The main valve is not allowed to open in the case of moving water, its role is:
(1) As the backup protection of the unit overspeed When the unit load rejection coincides with the failure of the governor, the main valve can be quickly closed under the condition of moving water, and the water flow is cut off to prevent the unit from running out of speed for more than the allowable value. To avoid an accident.
(2) Reduce the leakage of the unit during shutdown, shorten the time required for starting the machine when starting up. The water guiding mechanism of the turbine is often closed, and there is a large amount of water leakage after the shutdown. This not only wastes water energy, but also leaks in the gap. Causes cavitation damage. According to statistics, the leakage of the general guide vane is 2% to 3% of the maximum flow of the turbine, and the serious one can reach 5%. Some small units with high heads cannot stop because of excessive water leakage. When the unit is long and the machine is shut down, closing its inlet valve can greatly reduce the amount of water leakage.
The unit will stop for a short time and generally does not close the inlet valve. Because this will release the water in the pressure steel pipe, it needs to be refilled before the next start, which not only prolongs the start-up time of the unit, but also keeps the unit in standby state at any time, and loses the flexibility and quickness of the operation of the hydropower station. . At this time, the water inlet valve is opened to keep the pressure steel pipe in a water-filling state, which saves the booting time. For medium and high head power stations with long pressure pipes, this effect of the inlet valve is more pronounced.
(3) Providing safe working conditions for unit maintenance When the power station uses a pressure pipe to divert water for several units to generate electricity, each unit needs to be equipped with an inlet valve. When one unit is shut down during maintenance, it will not affect the normal operation of other units.
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