Shenyang Getai Hydropower Equipment Co., Ltd.

Installation Gap And Error Caused By Large Shaft Swing

Apr. 18, 2019

Here is Casting Guide Vane Manufacturer talking about Installation gap and error caused by large shaft swing.

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It has been suggested that the installation clearance of a brand mechanical over speed protection device is larger than that of the ALSTOM mechanical over speed protection device, so the impact on the large axis oscillation is correspondingly smaller, and even claims to be the only product that is not affected by the large axis oscillation.

Casting Guide Vane Manufacturer

The actual situation is not the case. In the process of the centrifugal flying pendulum moving outward, it actually follows a Hooke's law that we are familiar with in middle school physics, that is, the variation of centrifugal force is equal to the deformation of the spring multiplied by the elastic coefficient, ie ΔFC= KΔ, for a fixed-size wobble Δ, simply increasing the mounting clearance to 3 mm has no effect on reducing the deviation of the operating speed unless the K value is reduced.

So, is it possible to choose the spring K by using a larger installation clearance? In fact, both ALSTOM and other imported over speed protector designs use spring pre-compression, which means that the spring has a relatively large pre-compression to ensure that only when the spring is nearing over speed, The centrifugal force is greater than the pre-tightening force, and the centrifugal block of the flying pendulum is instantaneously pulled out to improve the life of the spring and avoid the influence of the linearity of the spring and the fatigue factor on the accuracy. The choice of K is mainly determined by the maximum centrifugal force and the installation size of the flying pendulum spring and does not depend on the installation clearance.

Therefore, the value of K is certain. It is easy to see from ΔFC=K.Δ that as long as the large-axis oscillation does not reach the installation clearance, the installation clearance has no relationship with the error caused by the large-axis oscillation, regardless of the installation clearance design of 1.5. Mm is still bigger 3mm, it is the same.

In order to verify this conclusion, we carried out simulation tests in the laboratory according to the 1.5mm gap and the 3.0mm gap. It turns out that the error caused by the 3.0mm gap for the swing is no smaller than the 1.5mm gap.

There is no scientific basis for the so-called large shaft swing due to the large installation clearance.

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