PLC is the most effective way to eradicate the loa

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Radical cure of hydraulic unit load rejection and lifting with PLC

hydraulic generator load rejection and lifting has serious harm, which must be completely cured. As long as we have a correct understanding of the root cause of the lifting and the sudden action of fracture, we can eradicate the lifting by using the programmable logic controller (PLC, which organically combines computer technology with relay control technology) to implement PID control so that there is no water hammer in the runner room draft tube section

1. the necessity of radical cure of hydraulic unit lifting

in the production practice of hydraulic power generation, after the accidental load shedding of hydraulic generator unit, the guide vane is required to close quickly to prevent the runaway speed, resulting in a sharp decline in the overflow flow, resulting in a sharp increase in the vacuum of the runner chamber, and a hydraulic shock wave (also known as water hammer, with a propagation speed of about 1000m/s) is generated in the runner chamber draft tube section. Lifting occurs when the sum of water hammer recoil force and reverse water thrust is greater than the weight of the rotating part of the unit, that is, PM HS ρ> KZ (where PM refers to the maximum positive pressure under the head cover after water hammer, expressed in kg/cm2; HS refers to the suction height of the turbine (generally negative); ρ---- The gravity of water; KZ ---- relative weight of rotating part of the unit, kg/cm2) [1]. In the past, Soviet experts and domestic experts paid enough attention to the water hammer in the penstock, but did not pay enough attention to the harm caused by the water hammer in the runner chamber draft tube section

it seems that a small number of machine lifts will not cause damage to the unit structure. People are also used to dealing with machine lifts from the aspects of improving material strength and roughly reducing the degree of machine lifts. Undoubtedly, these measures were of great positive significance in the past. However, in fact, as long as the lifting machine exists, the cumulative result will damage the equipment and cause major accidents. In August 1965, the 4 # machine of Shuifumiao hydropower station, the 2 # machine of Anren Dashi hydropower station in October 1985, and a unit of majingao hydropower station in Mayang in September 1987 all broke the main shaft snap ring recess due to machine lifting, and the rotor fell on the brake; In March, 1988, Huaihua Hongyan hydropower station 4# machine broke one side of the main shaft snap ring recess when it was lifted and dropped, but it was not found in time. After the unit was restarted, the rotating part rotated eccentrically, the generator stator was scraped with fan blades around the rotor for cooling, the stator bar (winding) insulation layer was scraped off, and the strong internal short-circuit current caused the generator to catch fire, which was shocking

now set the lifting height as H (m), and the speed before the thrust pad collides with the mirror plate after lifting and falling is approximately v = √ 2GH. If h = 0.01M (slight lifting), then V ≈ 0.443m/s. Although this value is small, it should be noted that the thrust pad collides with the mirror plate Δ After t (very small) time, V becomes zero; If the average force and reaction force when the thrust pad collides with the mirror plate is f (Newton), and the mass of the rotating part of the unit is m (Dongjiang M = 532000kg; Gezhouba small machine M = kg; Gezhouba large machine M = kg; Three Gorges M = kg), then there is F Δ t=MV,∴F=MV/ Δ t. So we can find that f is amazing and makes α= F/Mg。

Table 1 average force between thrust pad and mirror plate f (n) and α The value of

is visible Δ T Yu small, f Yu large, impact stress and strain and material fatigue problems make the material strength difficult to bear, especially when f is transmitted to the snap ring recess, it is easy to cause damage to the main shaft, and the material strength is large, but it only bears more collisions, so it is very necessary to eradicate the lifting of hydraulic units

2. The correct idea of radical cure of hydraulic unit lifting

literature [1] analyzes the traditional anti lifting measures and their theoretical defects: that is, the forced vacuum breaking valve acts by the rapid pressure of the inclined block under the speed regulating ring, the outlet position of the valve is in the high pressure area around the runner chamber under the top cover, and the air intake in the runner chamber is very small; When the self-priming vacuum breaking valve acts, a large vacuum has been formed, and the water hammer wave is at t = (2 × 25~2 × 50)/1000 = return after 0.05 ~ 0.1 seconds. Although the air inlet position is good, there is little air inlet; The two-stage closing guide vane method can only slightly reduce the water hammer in the runner chamber draft tube section, and it is almost ineffective in solving the unit lifting of large KZ value. For example, the 14 # unit of Gezhouba Dajiang power plant lost load and lifted 25mm on July 4, 1987. We have noticed that the water hammer in the runner room draft tube section is the root cause and crux of the lifting machine, so the correct idea to eradicate the load rejection and lifting of the hydraulic unit is: after the load rejection of the unit, in order to prevent the runaway speed, the guide vane is required to be closed quickly, resulting in a sharp decline in the water flow in the runner room draft tube section, in order to prevent the water hammer in the runner room draft tube section, The compressed air flow (converted to the pressure state of the runner chamber) equal to the reduced value of the overflow flow shall be automatically added to the central area of the runner chamber (the area with low pressure) without delay, so as to maintain the pressure of the runner chamber in the stable flow state before load rejection at all times. 226 it is easy to realize this goal by using high and new technology for the inner door of unplasticized polyvinyl chloride (PVC). We can use the programmable controller (PLC) with PID loop command to carry out PID (proportional integral differential) operation according to its CPU, and then use the output of PID operation to control the electric regulating valve to adjust the air intake. It is reiterated that the control goal is to maintain the pressure in the runner chamber at all times consistent with the pressure in the steady flow state before load rejection

3. Hydraulic unit lifting and radical cure PL is a very serious C control system hardware and control program

34 After conditioning 1. In order to monitor the pressure in the runner chamber, four pressure sensors 1, 2, 3 and 4 are respectively arranged along the + X, + y, ― X and ― Y directions on the distribution circumference (D1 is the nominal diameter of the runner; DZ is the diameter of the main shaft) with a diameter of (D1 + DZ)/2 of the overflow surface on the top cover of the water turbine

3.2 in order to add an appropriate amount of gas to the runner chamber, an electric regulating valve is connected in series on the air supply branch between the compressed air supply main pipe and the air inlet near the center area of the top cover of the water turbine (the branch pipe is also opened for gas transmission, which can be combined with phase regulation and pressure water) to regulate the air intake. If the maximum gas transmission speed in the branch pipe is set to be 24m/s, the diameter of the gas supply branch pipe D ≈ 33 √ QSM (mm; QSM is the maximum discharge of the turbine m3/s)

3.3 a SIMATIC S-type PLC (8 inputs/6 outputs, a total of 14 digital I/O points) and an EM235 type (4 analog inputs/1 analog output) analog expansion module are set in the microcomputer PLC PLC control system

3.4 first give the input and output signals

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