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Francis turbine simulation

Hi all,

We are new to this software and want to simulate the transients occuring in a Francsi turbine. We have gone through the turbine example given with the software and have tried to understand the various inputs provided in order to specify the problem. We are facing a few problems :

1) We have not been able to understand the use of the "turbine curve" that is required to be provided in the turbine parameters. Once we have proivided the complete 4-quadrant characterisistics, what is needed to be given in this turbine curve.

2) Where do we specify the initial operating conditions of head, power and discharge in the turbine parameters ?

3) The 4-quadrant characteriscs are given in terms of percentages of rated head, discharge and power. But we do not need to specify the actual rated values in the case of "Instant load rejection". How does the software then interprete the actual values ?

Any help would be deeply appreciated.

Thanks in advance

Parents
  • Hello,

    In answer to the first two questions, the Turbine Curve is used only in the initial conditions calculation. This is the relationship between head and flow at the start of the simulation. It is needed in order to get an accurate starting point for use in the transient calculation. The flow and head relationship defined in the Turbine Curve is not used in the transient analysis. The transient analysis will use a four-quadrant curve derived from the rated flow and head, as well as the moment of inertia, rotational speed, and specific speed. The points on the constructed quadrant curve are relative to the initial conditions operating point (head/flow) where are derived from the turbine curve.

    So in answer to your second question, the Turbine Curve defines the initial head and flow for the turbine.

    For the third question, the four-quadrant curve uses the calculated flow and head results derived from the inital conditions calculation and the Turbine Curve. After you calculate the initial conditions, flow and head results will be available. These results are used in the transient analysis for four-quadrant curve you selected. The exception to this is the Load Acceptance case, where you would enter the rated flow and rated head.

    Please let us know if you have additional questions on this or need some additional clarification. Note that this information and more can also be found in the following TechNote:

    communities.bentley.com/.../7139.using-turbines-in-bentley-hammer.aspx

    Regards,

    Scott Kampa

    Bentley Technical Support

Reply
  • Hello,

    In answer to the first two questions, the Turbine Curve is used only in the initial conditions calculation. This is the relationship between head and flow at the start of the simulation. It is needed in order to get an accurate starting point for use in the transient calculation. The flow and head relationship defined in the Turbine Curve is not used in the transient analysis. The transient analysis will use a four-quadrant curve derived from the rated flow and head, as well as the moment of inertia, rotational speed, and specific speed. The points on the constructed quadrant curve are relative to the initial conditions operating point (head/flow) where are derived from the turbine curve.

    So in answer to your second question, the Turbine Curve defines the initial head and flow for the turbine.

    For the third question, the four-quadrant curve uses the calculated flow and head results derived from the inital conditions calculation and the Turbine Curve. After you calculate the initial conditions, flow and head results will be available. These results are used in the transient analysis for four-quadrant curve you selected. The exception to this is the Load Acceptance case, where you would enter the rated flow and rated head.

    Please let us know if you have additional questions on this or need some additional clarification. Note that this information and more can also be found in the following TechNote:

    communities.bentley.com/.../7139.using-turbines-in-bentley-hammer.aspx

    Regards,

    Scott Kampa

    Bentley Technical Support

Children
  • Hello Scott

    Thanks for your response.

    I, however still have some doubts regarding the turbine curve.

    1)You have mentioned that the turbine curve is needed only to calculate the inital operating conditions. Does this mean that if I know my initial operating conditions, I can put a single head and flow value instead of a curve to specify my initial operating condition.

    2) Secondly, if I need to specify a curve comprising of mulitiple values, then what is the curve that I should input considering that a turbine operates at different guide vane openings, different heads & discharges, what exactly needs to be specifed in the turbine curve. (Unlike a pump, there is no fixed head-flow characteristics of a turbine which could be described by a single curve. The turbine operating conditions are characterised by the 4-quadrant curve that is anyways being given as input).

    3) Thirdly, how would the software estimate my desired operating condition based upon such a curve. In other words, how do I ensure that the software has estimated the initial operating conditions in line with my requirement.

    4) The moment of inertia of the turbine that is to be entered should be inclusive of the entire rotating mass including the generator as well as the turbine (since both are mounted on the same shaft).

    Thanks

  • 1) The program does not inhibit you from doing this, but it is not typical. The turbine curve represents the relationship between the head and flow at the specific speed you select when the wicket gate is fully open. A single head and flow value is not typically used for a couple of reasons. First, turbine curve gives the user the ability to model different setups for the initial conditions without needing to create a new turbine curve. For instance, if you change the demands or downstream tank level, the turbine head and flow will adjust to a different value other than the rated value you have.

    Second, if the model is not well-calibrated, you may end up with a discrepancy in HGL/pressure results downstream. A turbine curve gives the user a bit of leeway and can help in calibration of the system. Note that you may be able to get the turbine curve data from the manufacturer.

    2) The turbine curve is specific to the initial conditions and represents the head/flow relationship at the specific speed you are using when the wicket gate is fully open. Other conditions, such as a difference in wicket gate position, do not come into play for the turbine curve. That will be handled by the four-quadrant curve selected for the transient analysis.

    3) HAMMER works best with a well-calibrated model. If the data is inputted correctly and the model is well-calibrated, you should find that the flow and head at the turbine matches your measured results, even if you are using an actual curve. If it doesn't, you will want to calibrate your model to get it as close as possible to the field results. Manual calibration (adjusting demands, tank levels, pipe roughness, etc.) can be done. If you have access to Bentley WaterGEMS, there is a module called Darwin Calibrator that can run an automated calibration study. More information on Darwin Calibrator can be found here: communities.bentley.com/.../5910.using-darwin-calibrator.aspx

    4) How HAMMER handles moment of inertia can be found in the turbine TechNote, found here: communities.bentley.com/.../7139.using-turbines-in-bentley-hammer.aspx

    This TechNote may be useful for other aspects of modeling turbines as well.

    Regards,

    Scott

    Answer Verified By: Sushma Choure 

  • I'll add some additional thoughts regarding question #3

    HAMMER's initial conditions solver essentially treats the turbine curve as a GPV headloss curve. Depending on the network conditions (boundary hydraulic grades, physical properties, etc), it will iterate to find a solution (and point on the turbine curve) that balances energy across the model. So, if something else in the model is changed, such as an adjustment to the pipe roughness, increase in a boundary tank/reservoir hydraulic grade, etc, the model will shift position on the turbine curve to balance energy again.

    If your "requirement" is to operate at a specific head and flow, and all other parameters of the model are configured accurately and correctly, there is one other method of specifying the initial head and flow that may be worth considering. You can use a rarely used, legacy feature that allows you to manually specify the initial conditions, instead of allowing the initial conditions steady state solver to calculate them for you. For most models this is not a feasible approach, but if your turbine model is relatively small, it may be worth considering. To do this, open your calculation options under Analysis > Calculation Options > Transient Solver. At the bottom of the list you will see an option called "Specify Initial Conditions". Set this to true to expose various "initial" fields in the properties of your elements. For example for your pipes, you will see a "Flow (Initial)", "Hydraulic Grade (Initial Start)" and "Hydraulic Grade (Initial Stop)". By way of the initial flow and hydraulic grade in the pipes adjacent to the turbine, HAMMER will know what the initial operating point is and will use that for the transient simulation (along with the other parameters like the specific speed). Extra care needs to be taken with this approach, but you won't need to enter an accurate "turbine curve" (though you may need to enter some values in the turbine curve to avoid a validation message, even though the curve won't be used with the calculation option set to True). As discussed already, you could as an alternative, attempt to force a specific initial/nominal flow and head by entering a minimum amount of points on the turbine curve, all close to the desired operating point.

    I've added some of the above information to the "Using Turbines" technote that Scott had mentioned.


    Regards,

    Jesse Dringoli
    Technical Support Manager, OpenFlows
    Bentley Communities Site Administrator
    Bentley Systems, Inc.

    Answer Verified By: Sushma Choure