Kaplan Hydro Turbine

[wbd]

Hello,

I'm hoping someone who is experienced in hydro power can answer this question.

On a Kaplan hydro turbine, the proper manual sequence is to open the blades partially and then the wicket gates.

My question is if the sequence is reversed (wicket gates opened, then blades, would the turbine spin in the wrong direction briefly?

 

[WaterMan22]

No, the unit should rotate in the normal direction. Although, it may run a bit rough.

 

[wbd]

Okay, what would cause the unit to run briefly in one direction and then change directions? The unit was being started from a stop and had not been sync'd to the grid yet.

 

[TurbineGen]

Are you using only water to start the unit? If so, what is the water level at the turbine? Is it possible your turbine is seeing water come up through the bottom before you open your high head valve? How much reverse rotation do you get?

Is this a pumped storage facility?

------------------------------------------------------------------------
If it is broken, fix it. If it isn't broken, I'll soon fix that.

 

[wbd]

This is a low head hydro (40 ft) that had been watered up. There is a head gate and tailrace gate and both had been opened to allow penstock to water up.
We got about 1 full revolution in the wrong direction prior to the unit then spinning in the correct direction.

 

[tmoritz]

Is this a new unit? If not, then what did you change just prior to this problem? Did you unstack down to the turbine by chance?

Is this a conventional design with scroll case, stay vanes, and wicket gates or is it an open radial entry with just wicket gates? How big is this unit?

Inquiring minds would like to know.

Tom Moritz
Mechanical Engineer
US Bureau of Reclamation

 

[wbd]

This is not a new unit, has been in service for ~15 years. There is no scroll case. The penstock feeds into the turbine thru wicket gates to the moveable blades of the turbine. The unit is 4MW.
The unit had been taken down for annual maintenance which consists of:
Blade to case clearance checks
Wicket gate alignments
Hub oil check
Clean out debris
Wicket gate timing check
Blade timing checks
Generator megger
Cooling water strainer cleaning
Lube oil cooler cleaning
among some other tasks.

 

[tmoritz]

Hmm...I can think of only two ways you could get a unit to spin backwards: 1) if the swirl direction (angular momentum) of the flow entering the unit was opposite from the unit's normal rotation, or 2) the reaction force on the blades was counter to the unit's normal rotation.

The tainter gates should be imparting signifcant swirl at small gate openings. I assume you have stay vanes too. They will contribute to swirl too. Had you unstacked down to the turbine level it is possible to reverse the direction of the wicket gates, very low probability. This would impart alot of swirl in the reverse direction that could eventually be overcome by the reaction force at the runner. I could see something like this happening if you had two units side-by-side but designed to run in opposite directions, you unstack one then reassemble using the adjacent unit as a reference. If this were the case you would see a significant reduction in unit efficiency and it would run very rough.

Generation of a reaction force counter to normal unit rotation would require an extreme blade angle, well beyond vertical. This is also a very low probability probably to the point of impossible but at this point you are probably considering all suggestions/ideas. I could see a scenario where the hub seals had to be replace and this required removing the blades. When the blades are reinstalled the bolt pattern is indexed one bolt hole clockwise or counter-clockwise.

I'm not questioning the capabilities of your tradesmen here, I am just brainstorming possible causes.

Regards,

Tom Moritz

Tom Moritz
Mechanical Engineer
US Bureau of Reclamation

 

[niallnz]

Is this a verticle machine? with high pressure jacking oil in the thrust bearing? I'm thinking that as part of your start sequence, you turn on the jacking oil before opening the wicket gates, and maybe with a bit of gate leakage, high tail water or even alignment, the machine will naturally roll in one direction or the other. I have seen other larger hydro machines roll backwards when the jacking oil is turned on, opening the wicket gates fixes that problem

Cheers
Niallnz