Effects of Jacking Oil Pump on Stability

At low speed the oil wedge cannot form thus there is the risk in a hydrodynamic bearing of metal to metal contact and surface destruction. In order to avoid it the jacking oil pump is started at the start and closed when the speed is high enough for the film to support the rotor weight.

When the rotor stops the pump has to be started before the film looses its portance capacity and can only be stopped at full stop of the rotor. I do not know where the "jacking" oil flow is introduced in the bearing so that I cannot say if it will disturb or not the oil wedge but I think that at higher speeds the oil wedge is "stronger" and will not suffer from the added flow. However this depends on the bearing configuration and cannot be considered as more than an assumption.

Leaving the jacking oil on up to speeds of 2000 or so absoultly can have a negative impact on rotor stability and should not be done.

The vibration pattern to expect will be either a high vibration at 1X, or a high vibration at something less that 1/2 X.

I agree with Steve. It is because of this reason that in the running units test and trials of JOP is not done.

But in some posts it is mentioned that the JOP trials are done even in running units. This practice is not correct. Can Hari Ram Narvariya share some operating parameters to substantiate this statement.

Thanks

Himanshu

As the speed increase the rotor attains the required lift. Cut in of jacking oil pump at higher RPM will result only addition of extra oil to bearings in very small quantity and it will not effects the oil film. In 210 MW unit trial of JOP is taken at normal running of the set, no abnormality i.e. high vibrations, rise of bearing metal temperature or any metallic sound observed with JOP in running condition at 3000 rpm.

I fully agree with Mr. Hariram, we use to check the JO Pumps during normal operation of the machine, it is a standard check to ensure its availability during a trip out, and It is regularly done. we also check the jacking pressure available at each bearing, but so far we have not noticed anything abnormal or any change in any parameter of the turbine due to this.

My Question was about the effect of running of Jacking oil pump after hydrodynamic lub film layer is developed at higher RPM. What will be the impact if Jacking oil pump is allowed to run at higher RPM also,Will it disturb the stability of Lub oil film

Again yes it can. That does not mean it absoultly will, it depends on your machine design, but it can, especially if the bearings are plain journals rather than tilt pads.

Stability is a function of the rotor position in the bearing clearance, when it is close to the center then the rotor is less stable, when the rotor is closer to the bearing surface it is more stable.

Turning on the jacking oil at speed has the effect of moving the rotor close to the center of the bearing clearance, and again this is a much less stable operating position.

So I again recommend that you not do it.

nothing will happen at high speed of turbine if jacking oil pump run.small quantity of oil flow extra added to bearing this may be helped to cool the journal bearing.it cant detoriate the oil wedge of hydrodynamics.as shaft lift at higher speed that force is much higher than the jacking oil force.as u can see during rolling of turbineas speed increases oil pressure dropped because shaft lifted that time gradualy

Dev is right.

The pressure created by the hydrodynamic film is much higher than the one created by the hydrostatic (jacking oil pump). Infact due to this usually an orifice is put in the jacking oil line to prevent back flow.

In addition to this the quantity (flow) supplied by the jacking oil pump is much lower than the Main Oil Pump.

UD15