Shaft Orbit Plots (II)

Not- 1X Compensation of an Orbit

•          At Left orbit is the uncompensated orbit

•          At right is the same orbit with the 1X component removed

•          The remaining vibration is primarily 1/2X from a rub

Measurement of peak-to-peak amplitude of an Orbit

X transducer measurement axis is drawn together with perpendicular lines that are tangent to maximum and minimum points on the orbit

Direction of Precession in Orbits

•          In the orbit plot shaft moves from the blank towards the dot. In the plot on left the inside loop is forward precession

•          In the right orbit the shaft has reverse precession for a short time at the outside loop at bottom

Effect of Radial Load on Orbit Shape

•          Orbits are from two different steam turbines with opposite rotation. Both machines are experiencing high radial loads

•           Red arrows indicate the approximate direction of the applied radial load.

•           Red arcs represent the probable orientation of the bearing wall

Deflection Shape of Rotor Shaft

•          When keyphasor dots of simultaneous orbits at various bearings along the length of the rotor are joined an estimate of the three dimensional deflection shape of the rotor shaft can be obtained

 *   This is a rigidly coupled rotor system