Hydropower Bearing Arrangments 1

[QCE]

Hello,

I have a hydropower question. Which bearing arrangement is more common in hydropower machines the combined thrust/ guide bearing under or over the rotor. I believe it is called umbrella and suspended bearing arrangements. Is one much more common then the other. I'm talking about for larger units above 15MW.

Is there an advantage to one over the other? What are the advantages?

I have been told by mechanics that the above arrangement is easier to do work on.

Is the choice just due to manufacturer or is there really specific reasons for picking a certain type?

Thank you in advance!

 

[Romefu12]

QCE
Your questions are a little vague, What type of Hydro Turbine are you speaking (by the over and under statement I would assume a Vertical Kaplan type Turbine?

Another question about the arrangement I would assume you are asking about the Combined Guide and Thrust Bearing being under the Generator Rotor?

Romefu12

 

[QCE]

I'm talking about a vertical unit. It can be a kaplan or a francis turbine.

I can not understand your second question.

I am trying to get some opinions about the thrust bearing being located above or below the rotor in these type of units.

 

[Romefu12]

QCE
Which Rotor are you speaking of?

I would assume that you are speaking of the thrust bearing being located below the generator rotor, with the turbine shaft and turbine runner hanging below?

If this is the case then in my opinion the theory of "gravity works" can be a blessing and a nightmare. I have worked on big and small hyro units. In the small units there really isn't any real problems however the Thrust Bearings in large units can be a back breaking task to remove and service because you can not reach anything with a crane.

I don't really see any real advantage to either configuration other than routine maintenance. In hydro units, the bigger they are the easier to work on.

Kine Regards
Romefu12

 

[21121956]

Hello everybody:

Hi QCE. Among the elements of hydraulic turbomachinery called "ancilliaries", maybe, the more relevants are the bearings; which support (thrust bearings) or guide (guide or radial bearings) the rotating parts of the generating group (turbine + shafts + generator).

In a vertical arrangement, the thrust bearing supports axially the weight of all rotating parts and the pulsating hydraulic thrust, provoked by the mass of water leaving the turbine runner.

In the vertical hydraulic groups, the thrust bearing can be placed at:

1. At the top of the generator, transmitting the axial resulting force via girders to the frame of the stator of the generator, that rests on the generator floor of the power house.

Applications: for small groups in geometry and mass. I have personnally worked in maintenance in power plants with groups of 15 MW and 25 MW with this type of array.

2. Intermediate. This is, immediately under the rotor of the generator. In this case, the outer part of the rotor (rotor spider girder) is inclined downward; for this reason this bearing is called "umbrella array".

The axial thrust is transmitted to the foundations of the power house via strong radial girders.
I have personnally worked in maintenance in power plants with groups of up to 75 MW with this arrangement.

3. At the top of the turbine head cover, over a very strong structure like a truncated cone. The axial thrust is transmitted to the foundations of the turbine floor of the power house (it is, to the spiral case concrete block mainly).

I have visited power plants with groups that have this arrangement, i.e. 225 MW, 250 MW and 350 MW each group.

In the intermediate and in the over the head cover array, all the stresses are transmitted to the foundations of the power house (merely, to the spiral case structure) via the intermediate guide vanes; wich in turn, must be calculated carefully to bear these important loads.

In my opinion, the location of the combined thrust and guide bearings, obey to the design itself of the generating group, and no matter what it is, the easy access to them for maintenance purposes is really guaranted.

 

[QCE]

Thank you #21121956!

I have been to many stations with the thrust bearing above the rotor and below the rotor. I am just trying to figure out why one is selected over the other. Now for my real question.

I was reading a tender for a 110MW hydropower station and it was stated that the thrust bearing must be placed above the rotor. I was trying to figure out why this customer wants it above. Would it not be better to let the manufacturer select the location on the design that they commonly use? It is a new power station so the foundation for the lower bracket or the generator soleplates could be designed to take the load. So why would you say that the company wants it above? I assume they think there is some advantage to this setup. I just could not think of any good reasons why they are try to restrict other arrangements in the tender.