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Analysis of the force applied when the servomotors

The description is relatively simple and is only for the reference of relevant technical personnel. It is mainly used to deal with the problem of jumping or lifting of the speed control ring when the double servomotor of the push-pull arrangement operates the turbine.

The speed governor needs to adjust the switching speed of the servomotor according to relevant design requirements during debugging. The adjustment of the speed of the servomotor is realized by limiting the amount of oil passing through the servomotor through a throttle valve. There are usually two methods, one is to limit the speed of the oil return of the servomotor, which is called oil return throttling, and the other It is to limit the speed of the oil intake of the servomotor. This is called oil intake throttling. Both methods have their own advantages and disadvantages. This article only briefly describes the different forces that the push-pull arrangement of the double servomotor uses different throttling methods to produce on the speed control ring.

1. Push-pull servomotor structure

The force analysis when using different throttle modes to operate the speed regulating ring

Since one end of the servomotor needs to be fixed on the base, only one end of the servomotor has an extension rod, which results in different force areas (area in contact with oil) at the left and right ends of the piston, and there is an extension rod (piston rod) The force area is small at one end, and the force area at the end without extension rod is large (see the figure below).

The force analysis when using different throttle modes to operate the speed regulating ring

2. Force analysis (only analyze the thrust of the servomotor to the speed regulating ring, without considering the torque)

The force analysis when using different throttle modes to operate the speed regulating ring

       When the servomotor is pushed and pulled, the two chambers of the two servomotors are to be cross-connected respectively, that is, the F1 side is connected to the F4 side, and the F2 side is connected to the F3 side. The communication means that the oil pressure is the same. Let S1 represent the force-bearing area of one end without extension rods, and S2 represent the force-receiving area of one end with extension rods, P1 represents the oil pressure on the F1 and F4 sides, and P2 represents the oil pressure on the F2 and F3 sides.

The force on the upper side servomotor is F1-F2=P1*S1-P2*S2

The force of the lower side servomotor is F3-F4=P2*S1-P1*S2

The resultant force is: (F1-F2)+(F3-F4)=(P1*S1-P2*S2)+ (P2*S1-P1*S2)

The simplified formula is: (P1+P2)X(S1-S2)

       The difference between P1 and P2 depends on the resistance of the governor ring. The greater the resistance, the greater the difference (pressure difference produces thrust), the smaller the resistance, the smaller the difference. In the case of ignoring the pipeline pressure loss, when the return throttle is used, the maximum pressure of the two is close to the rated pressure, and when the intake throttle is used, the maximum pressure of the two is the difference in pressure difference. The value of S1-S2 is the area of the protruding rod (piston rod). It can be seen that the larger the piston rod, the greater the resultant force. A deeper understanding is that the greater the resultant force of the piston rod diameter relative to the piston diameter under the same operating work. The bigger.

       Now focus on the analysis of a special situation-that is, when the resistance of the water guiding mechanism is particularly small, the different forces on the speed regulating ring when the servomotor adopts the oil inlet throttling and the oil return throttling.

       If the resistance of the water guiding mechanism is relatively small (when there is no load or when the servomotor type is relatively large), then the difference between P1 and P2 is very small. According to the above analysis, it can be seen that if the oil return throttling is used, both Both are close to the rated pressure. If the fuel inlet throttle is used, both are close to zero pressure. It can be seen that the pressure difference in the two cases is very large.

For example:

The parameters of the forward power station servomotor: piston diameter 130mm, rod diameter 80mm, rated pressure 16MPa.

Calculated S1-S2=50.3 CM2

The pressure value of P1 and P2 can be seen through the pressure gauge

When the resistance of the speed control ring is small, the thrust of the oil return throttle is: (16MPa+14.5MPa) *50.3 CM2=153000N=15300kg=15.3 tons. This force is quite large, causing the turbine governor ring to lift on site.

 

The thrust of the fuel inlet throttle is (1.5MPa+0MPa) *50.3 CM2=7545N=754.5 kg=0.7545 tons. This force is much smaller than the use of oil return throttling, so after the servomotor is changed to the oil intake throttling, the turbine governor ring will not lift.

 
 
 
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