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Thread: VFD Problems

  1. #1

    Join Date
    May 2018

    VFD Problems

    Issue resolved
    Last edited by SMH; May 3, 2019 at 09:53 AM.

  2. #2
    Forum Moderator

    Innovyze Employee

    Innovyze Employee

    Join Date
    May 2015
    Although your issues got resolved, I am going to post a few hints on how to best use VSP pumps in InfoWater:

    Key considerations To keep in Mind when using Implicit VSP Pump Control that may help you:

    1. Max Speed – Limit to 1 not 2. Most pumps are not designed to run at greater than 100 percent speed. Use values that are consistent with what the actual pump can do. A pump allowed to run up to 200% speed would be much more than a real pump limited to 100% can do. See image below for the impact of 200% speed has on the pump curve (click if need a larger image)
      1. Pump curve Speed.png

    2. Additional parallel pumps – these are additional pumps of the same size that the controller can use to maintain control. Total pumps = additional pumps +1. So a 4 pump station would use 3 additional parallel pumps
    3. Make sure all other pumps at the facility are off when using Additional Parallel pumps – They would interfere with operation if allowed to run and are accounted for by the VSP controller. Additional Parallel pumps should be total number of pumps the same size minus 1.
    4. All pumps run at the same speed setting when on. While this is slightly different than what typically happens in the real world, the flow and pressure results for the entire station should be identical to the real world system. This is done due to the mathematical challenges of using VSP pumps and simplifies the calculations.
    5. In InfoWater the downstream junction is the hidden junction for the pump (pumps are lines in EPANET, the hidden junctions allow it to run as a point element in the model.) The VSP control will use the elevation of the pump for the hidden node so that the “pressure” at this junction will be calculated using the elevation of the pump itself. Make sure the pressure setting used is consistent with this elevation.
    6. If using remote junction control don’t use the same junction to control multiple VSP pumps
    7. Make sure the Pressure setting specified is higher than the downstream pressure or the Solver will generally be unable to find a workable solution that would allow the pump to operate (as water flows from high head to low head). This can generate an error that says “ unable to maintain head at control node at time X” .Depending on the number of trials this can also result in model non convergence and reaching max trials and a warning like “WARNING: Maximum trials exceeded at X hrs. System may be unstable” to be seen in the Full Status report.
      1. To see the full status report use these settings in the report options on the standard tab: and then after a run open it using the Hydraulic Status report.pngicon in the run manager.
      2. It should look like this: (click if need a larger image)
      3. Full Report with Warning Messages & Summary.png

    8. It is often helpful to think of Pressure based VSP control as a fixed head at the location being controlled as this is what you are asking the system to do. Since the HGL or head is based on the pressure and the elevation (HGL = pressure (with unit conversion as necessary) + Elevation ) knowing the elevation and the pressure setpoint you can calculate the HGL you are asking the system to maintain. The model will adjust the pump speed within the Min and max speeds specified to try and maintain the pressure or flow value specified. An error message will be generated if it is not feasible to maintain the requested pressure with the speed ranges specified.
    9. Controls: If the pump is turned off by a control or has an initial status of closed the VSP control will be off. When the pump is running the VSP control will be active. Controls can be simple or rule based.
    10. One issue that can periodically occur at lower speed settings is that the pump cannot operate if the pump shutoff is less than the static lift of the pump. This can occur with a VSP because the shutoff head of the pump is reduced as the pump speed reduces and so there is generally a physical lower limit speed that can be used for pump at which they cannot run. If you get errors at lower pump speeds this can sometimes be the cause. Most real world pumps often have minimum speeds in the range of 50-70% due to this.

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