Source: Centralized Control Circle
As a high-speed rotating equipment, the centrifugal force of the rotating parts is proportional to the square of the speed; When the speed of the steam turbine exceeds 20% of the rated speed, the centrifugal stress is close to 1.5 times of the stress at the rated speed, and the rotating parts will loosen, and the centrifugal force will exceed the allowable strength limit of the material and damage the parts. Therefore, the steam turbine is equipped with an overspeed protection device, which can act when the steam turbine speed exceeds 9-11% of the rated speed, and quickly cut off the steam intake and shutdown of the steam turbine.
Steam turbine overspeed protection is divided into three layers
1) OPC overspeed: 105% of the rated speed (OPC solenoid valve action);
2) AST overspeed: 110% of the rated speed (AST solenoid valve action); TSI overspeed: 110% of the rated speed (AST solenoid valve action);
3) Mechanical overspeed: 110±1% of the rated speed of the operating speed (3270-3330rpm)
When the action value reaches the speed of the flying hammer, the centrifugal force increases, the flying hammer flies out, strikes the lever of the critical safety device, removes the lower part of the safety oil of the spool valve of the critical safety device, moves the slide valve down, opens the oil drain channel of the diaphragm valve, removes the oil pressure of the upper part of the diaphragm valve, opens the diaphragm valve, discharges the oil pressure of the AST mother pipe, closes the main valves, and at the same time removes the OPC oil pressure through the check valve on the AST oil pressure mother pipe, closes the adjustment door, cuts off the steam intake of the steam turbine, and realizes the shutdown, as shown in Figure 1.
Figure 1
Steam turbine mechanical overspeed protection critical blocking and steam turbine hanging, braking are inseparable from the critical disconnector spool valve, so let's focus on how to achieve steam turbine mechanical overspeed protection critical shutting and steam turbine hanging, braking, as shown in Figure 2.
Figure 2
1. The structure of the spool valve of the critical interrupter
The main components of the emergency shut-off spool valve group are large spool valve, small spool valve, low-pressure shut-off solenoid valve, hanging gate solenoid valve, manual shut-off solenoid valve, etc., and its specific composition is shown in Figure 3. The turbine oil of 1.96MPa enters the upper, middle and lower chambers of the spool valve through three throttle holes, and realizes the operation of the steam turbine by changing the state of the hanging gate solenoid valve, the low-pressure blocking solenoid valve, the manual blocking solenoid valve and the relative position of the small spool valve.
Figure 3
2. Critical Interrupter Spool Valve Hanging Gate Operation
Before hanging the gate, the upper and lower chambers are filled with 1.96MPa pressure oil (yellow area), because the action area F1 of the upper chamber is greater than the action area of the lower cavity F2, so the slide valve falls at the bottom dead center (as shown in Figure 4); At this time, the gate solenoid valve is powered off, and the oil pressure of the gate in the upper cavity of the slide valve is established; The slide valve rises, so that the pipeline from the security oil to the unloading port of the security oil is closed, and the oil pressure from the security oil to the upper part of the diaphragm valve is established, so that the diaphragm valve moves down, and the AST oil drain pipeline is closed, and the AST pipeline oil is established (as shown in Figure 5), and the hanging gate operation is completed.
Figure 4
Figure 5
3. Critical Interrupter Spool Valve Gate Operation
There are two ways to realize the operation of the gate:
1) The electrical shutdown signal makes the low-voltage blocking solenoid valve (2YV) live, and the lower part of the spool valve is removed from the security oil (as shown in Fig. 6, 7, 8) to make the spool valve fall.
Figure 6
Figure 7
FIGURE 8
2) Press the manual shut-off valve (as shown in Figure 9, 10, 11) on the spot, and the spool valve falls.
Figure 9
FIGURE 10
FIGURE 11
At this time, the spring force of the lower part of the diaphragm valve is greater than the pressure of the upper part of the security oil, so that the diaphragm valve is opened, and the high-pressure security oil (AST oil) is discharged, so as to quickly close the valves and main valves, and block the steam inlet of the unit.
4. When the mechanical overspeed protection action is critical, the spool valve is activated
When the speed of the unit reaches the mechanical overspeed protection action condition, the impactor set in the eccentricity flies out, and moves downward through the lever to hit the small spool valve, so that the stress area of the upper part of the spool valve is greater than the lower part of the spool valve (as shown in Fig. 12, 13), so that the spool valve falls, and the steam intake of the steam turbine is blocked.
FIGURE 12
FIGURE 13